STABLE CHLORINE ISOTOPE STUDY OF MARTIAN SHERGOTTITES AND NAKHLITES; WHOLE ROCK AND ACID LEACHATES AND RESIDUES

N. Nakamura<sup>1,6</sup>, L. E. Nyquist<sup>1</sup>, Y. Reese<sup>2</sup>, C.-Y. Shih<sup>3</sup>, T. Fujitani<sup>4</sup> and O. Okano<sup>5</sup>. <sup>1</sup>NASA Johnson Space Center, ARES Mail Code KR, 2101 NASA Pkwy, Houston, TX 77058, USA. E-mail: noboru.nakamura@nasa.gov. <sup>2</sup>Mail Code JE-23, ESCG/Muniz Engineering, Houston, TX 77058, USA. <sup>3</sup>ESCG Jacobs-Sverdrup, Houston, TX 77058, USA. <sup>4</sup>Marine Tech. College, Ashiya 659, Japan. <sup>5</sup>Okayama University, Okayama 700, Japan. <sup>6</sup>Kobe University, Nada, Kobe 657, Japan. E-mail: nakamuransjp@yahoo.co.jp.

**Introduction:** We have established a precise analytical technique for stable chlorine isotope measurements of tiny planetary materials by TIMS (thermal ionization mass spectrometry) [1], for which the results are basically consistent with the IRMS technique (gas source mass spectrometry) [2-4]. We present here results for Martian shergottites and nakhlites; whole rocks, HNO₃-leachates and residues, and discuss the chlorine isotope evolution of planetary Mars.

**Experimental:** Whole rocks of Zagami (shergottite, basalt), Nakhla (nakhlite, basalt) and MIL03346 (nakhlite, basalt) and 1N-HNO₃ leachates and residues of Zagami and MIL samples were examined for chlorine contents by ion chromatography and isotopic composition by TIMS in this work. The 1 N-HNO₃ leaching was carried out at room temperature for 15-20 h. Bulk and residue samples were analyzed for chlorine isotopes after treatment by HF leaching, AgCl precipitation and Cs-form resin. Isotopic analyses of leachates were also carried out by a similar method without HF-treatment.

**Results and Discussion:** *Leaching effect* - The second Zagami sample subjected to leaching experiments shows higher total Cl abundance (160 ppm) compared to the 1st sample (114 ppm) reported at 42th LPSC [1], but rather similar abundance to that of Dreibus et al. [5] (145 ppm). About 60% of total chlorine in the bulk sample was leached out in the 1N-HNO₃ fraction, indicating that major parts of chlorine exist in soluble phases (for example, chloroapatite) in Zagami. On the other hand, only 20% of bulk MIL chlorine (221 ppm) was leached out in the acid fraction.

**Chlorine Isotopic Composition:** Our Orgueil (CI) results show significantly smaller δ³⁷ClSMOC (-0.5‰) compared to that of Sharp et al. (δ³⁷ClSMOC = 1.2‰) [4] but still within the range of δ³⁷ClSMOC values reported by the New Mexico Univ. group [6]. Bulk Zagami, shergottite, shows δ³⁷ClSMOC almost the same as seawater. On the other hand, Zagami leachate and two bulk nakhlites (Nakhla and MIL03346) show relatively similar δ³⁷ClSMOC values (1.5 ± 0.5‰). In Marrtian meteorites, the acid leachates were considered to be derived from more leachable components such as fluids, suggesting that they might represent Martian crustal components [7].

**References:** [1] Nakamura N. et al. 2011. Abstract #2513. 42nd Lunar and Planetary Science Conference. [2] Bonifacie M. et al. 2007. *Chemical Geology* 242:187-201. [3] Musashi M. et al. 1998. *Analytical Chemistry* 363:261-269. [4] Sharp D. Z. et al. 2007. *Nature* 446:1062-1064. [5] Dreibus G. et al. 1979. *Origin and Distribution of the Elements*. pp. 33-38. [6] Mercer J. A. et al. 2011. Abstract #2463. 42nd Lunar and Planetary Science Conference. [7] Sautter V. et al. 2006. *Earth and Planetary Science Letters* 252:45-55.

NANO-SCALE ANATOMY OF Stardust COMETARY TRACKS CONTINUED: BULBOUS TRACKS 147 AND 168

K. Nakamura-Messenger<sup>1,2</sup>, L. P. Keller<sup>1</sup>, S. Messenger<sup>1</sup>, S. J. Clemett<sup>1,3</sup>, A. N. Nguyen<sup>1,2</sup> and D. Frank<sup>4</sup>. <sup>1</sup>Robert M Walker Laboratory for Space Science, ARES, NASA/JSC, Houston, TX, USA. <sup>2</sup>ESCG/Jacobs Technology, Houston, TX, USA. <sup>3</sup>ESCG/ERC Inc., Houston, TX, USA. <sup>4</sup>ESCG/Hamilton Sundstrand, Houston, TX, USA. E-mail: keiko.nakamura-1@nasa.gov.

**Introduction:** Comet Wild 2 dust grains captured by the Stardust spacecraft show a wide range of chemical compositions, both among and within individual particle tracks [1]. This sample diversity complicates answering basic questions such as the bulk composition of the comet and modal mineralogy. We have developed new sample preparation and analytical techniques tailored for analysis of entire Wild 2 aerogel tracks, and successfully ultramicrotomed a "carrot" type A track along its axis while preserving its original shape [2]. This innovation allowed us to examine the distribution of fragments along the entire track from the entrance hole all the way to the terminal particle. This report focuses on our systematic disassembly and coordinated analysis of two Stardust bulbous type tracks from the mm to nm-scale.

**Experimental:** The walls of tracks #147 (4600 µm long with 7 terminal particles, TPs) and #168 (2640 µm long, 3 TPs) were photodocumented using an extended depth-of-field image processing technique that generates a single infocus image from a series of photographs. The TPs were removed, embedded in epoxy, and ultramicrotomed separately. Scanning TEM was used for elemental and detailed mineralogy characterization. This approach also enabled spatially resolving the target sample from fine-scale mixtures of compressed aerogel and melt.

**Results and Discussion:** We obtained preliminary mineralogical analyses of 3 TPs and particles recovered from a crack near the entrance area (30 µm) from Track #147, and 2 TPs from T168. T147, TP2 (18 µm) entirely consists of Fe-Ni alloy (5 atom% Ni). T147, TP3 (19 µm) contains Fa 28 with partial olivine-pyroxene intergrowth and minor albite. T147, TP4 (12 µm) contains pentlandite, Fe-olivine, albite and high Ca pyroxene with Na and Cr (kosmochlor component). The Fe-olivine + albite + Ca-pyroxene assemblage is common in other Wild 2 samples as well [3]. No surviving crystalline cometary materials were observed from track walls yet, but only mixed and melted materials of aerogel and cometary constituents. T168, TP1 (10 µm) contains Fe-olivine, albite and pentlandite. T168, TP2 (8 µm) has concentric texture with a core of olivine grains (100 nm in size) with coexisting indigenous amorphous SiO₂ surrounded by a carbon mantle (800 nm thickness), which in turn is surrounded by a layer of compressed aerogel. A nebular origin as possible precursors to type II chondrules in ordinary chondrites has been proposed for the Fe-olivine + albite + Ca-pyroxene assemblages in Wild 2 [3]. However, in T147, this assemblage coexists with pentlandite which would not have been a stable phase in the nebula [4]. In future work, NanoSIMS will be used for isotopic analyses, and ultrafast two-step laser mass spectrometry (ultra L²MS) to investigate the nature and distribution of organic phases. The albite in T168, TP1 may be large enough to measure Mg/Al system using NanoSIMS. We also plan to measure H, N, C isotopes of the carbon shell of T168, TP2 and O isotopes of the silicates inside.

**References:** [1] Brownlee D. E. et al. 2006. *Science* 314:1711. [2] Nakamura-Messenger K. et al. 2011. *Meteoritics & Planetary Science*, in press. [3] Joswiak D. et al. 2009. *Meteoritics & Planetary Science* 44:1561. [4] Brearley A. J. 1999. *Science* 285:1380.
STUDY OF CHONDRULES IN CH CHONDRITES - III: OXYGEN ISOTOPE RATIOS OF SILICA-BEARING, METAL-BEARING, AND ¹⁶O-RICH CHONDRULES

D. Nakashima¹, M. Kimura², K. Yamada², T. Noguchi², T. Ushikubo¹ and N. T. Kita¹. ¹University of Wisconsin-Madison, USA. E-mail: naka@geology.wisc.edu. ²Ibaraki University, Japan.

**Introduction:** From a systematic survey of chondrule oxygen isotope ratios in Asuka-881020 (CH), we reported that magnesian and ferroan cryptocrystalline (CC) chondrules were derived from two distinct isotope reservoirs with $\Delta^{17}$O values of -2% and +1.5%, respectively [1]. CH chondrites also contain ferroan nonporphyritic chondrules such as silica-bearing (SB) and FeNi metal-bearing (MB) chondrules [2], which may be related to ferroan CC chondrules according to their similar sizes (<100 µm) and FeO-rich chemistry. Exceptionally $^{16}$O-rich oxygen isotope ratios were reported from a glassy chondrule with olivine rim by [3] in Acer 214 (CH). Here we report additional oxygen three-isotope analyses of several minor types of chondrules in Asuka-881020.

**Results:** IMS-1280 at UW-Madison was used to obtain oxygen isotope ratios using 2 × 4 µm spots, which yield analytical precisions of 1–2% (2 SD). All data plot along a slope 1 line on a three-isotope oxygen diagram ($\delta^{17}$O vs. $\delta^{18}$O). Isotope ratios of ferrous pyroxene and silica in SB chondrules are consistent within the analytical uncertainties. Nine SB chondrules with spherical shapes have nearly identical $\Delta^{17}$O values with the average +1.2 ± 1.4% (2 SD), while five SB chondrules with irregular shapes and fine-grained textures have variable $\Delta^{17}$O values from -6 to +5%. Three ferroan MB chondrules have $\Delta^{17}$O values from 0 to +2%. Two olivine-rimmed Al-rich chondrules show $\Delta^{17}$O values of -12% and -6%, respectively. We analyzed one magnesian MB chondrule that shows the $\Delta^{17}$O value (-21%) as low as CAIs, though it has no olivine rim.

**Discussion:** Nearly identical oxygen isotope ratios of ferrous pyroxene and silica in SB chondrules suggest formation from common isotope reservoirs. Spherical SB and ferroan MB chondrules have similar $\Delta^{17}$O values to ferroan CC chondrules, and are depleted in refractory and volatile elements like ferroan CC chondrules. Thus, these three types of ferroan chondrules might have formed via fractional condensation from an isotopically uniform gaseous reservoir. $\Delta^{17}$O range of irregular-shaped SB chondrules overlaps with that of type I porphyritic chondrules in Asuka-881020 [1], implying that the irregular-shaped SB chondrules formed in the solar nebula like the porphyritic chondrules [4].

Al-rich chondrules with olivine rim show intermediate $\Delta^{17}$O values between $^{16}$O-rich CAIs [5] and ferromagnesian chondrules [1] in CH chondrites, indicating mixing of CAI-like materials and ferromagnesian chondrules as their precursors. The lowest $\Delta^{17}$O value from this work was obtained from the magnesian MB chondrule, which is not enriched in refractory elements unlike CAIs. The origin of the magnesian MB chondrule would be related to that of olivine-rimmed glassy chondrule in [3]. They may have formed from a $^{16}$O-rich gaseous reservoir or preserved the $^{16}$O-rich composition after melting [3].

**References:** [1] Nakashima D. et al. 2010. *Meteoritics & Planetary Science* 45:A148. [2] Krot A. N. et al. 2000. *Meteoritics & Planetary Science* 35:1249–1258. [3] Kobayashi K. et al. 2003. *Geochemical Journal* 37:663–669. [4] Krot A. N. et al. 2010. *Geochimica et Cosmochimica Acta* 74:2190–2211. [5] Sahijpal S. et al. 1999. *Meteoritics & Planetary Science* 45:A101.

HIGH-PRECISION OXYGEN ISOTOPE ANALYSIS OF EQUILIBRATED ORDINARY CHONDRITES: FOR COMPARISON WITH THE ITOKAWA PARTICLES

D. Nakashima, T. Ushikubo and N. T. Kita. University of Wisconsin, WI, USA. E-mail: naka@geology.wisc.edu.

**Introduction:** X-ray fluorescence and near-infrared measurements by the Hayabusa spacecraft suggested that the surface materials of the asteroid Itokawa were similar to LL5 or LL6 chondrites [1, 2], which was confirmed by preliminary examination of particles recovered from the asteroid Itokawa [e.g., 3, 4]. Oxygen isotope ratios of equilibrated ordinary chondrites (EOCs) by ion microprobe are important for comparison with the Itokawa particles, but are scarce. Here we report oxygen isotope ratios of four phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in LL5 (Siena), LL6 (St. Séverin), and H6 (Guareña).

**Results:** IMS-1280 at UW-Madison was used to obtain oxygen isotope ratios using 10 × 15 µm spots, which yield analytical precisions of ~0.4‰ for $\delta^{18}$O, $\delta^{17}$O, and $\Delta^{17}$O (2 SD). Olivine, low-Ca and high-Ca pyroxene, and plagioclase in respective meteorites have indistinguishable $\Delta^{17}$O values and show averages of +1.2 ± 0.1‰ (n = 29; Siena), +1.3 ± 0.1‰ (n = 32; St. Séverin), and +0.9 ± 0.1‰ (n = 32; Guareña) (2SE). The $\delta^{18}$O values range from +4.7 to +6.3‰ (Siena), from +4.5 to +5.8‰ (St. Séverin), and from +3.7 to +5.2‰ (Guareña). The four mineral phases in all three meteorites show systematic changes in $\delta^{18}$O values, in the order of high-Ca pyroxene, olivine, low-Ca pyroxene, and plagioclase. Morphology of chondrules remains in Siena (LL5), and we analyzed several chondrules in Siena. The average $\Delta^{17}$O values are variable among chondrules (+0.4 to +1.5‰). One POP chondrule with the average $\Delta^{17}$O of ~ +1.5‰ contains an olivine grain with $\Delta^{17}$O of ~ -2.0‰, which may be a relict olivine.

**Discussion:** Siena and St. Séverin (LL) have higher $\Delta^{17}$O values than Guareña (H), which is consistent with bulk chondrite data [5]. The $\delta^{18}$O values of olivine in Siena are systematically higher than those in St. Séverin by 0.5‰, consistent with the negative correlation between $\delta^{18}$O values and petrologic types observed in bulk chondrites [5].

Oxygen isotope equilibrium temperatures were calculated from plagioclase and high-Ca pyroxene pairs in matrices. The differences in $\delta^{18}$O between two minerals were 1.6 ± 0.4‰ (Siena), 1.3 ± 0.2‰ (St. Séverin), and 1.6 ± 0.1‰ (Guareña), which correspond to temperatures of 720 ± 140 °C (Siena), 870 ± 120 °C (St. Séverin), and 750 ± 50 °C (Guareña). These temperatures are consistent with those for oxygen thermometry in EOCs by [6] as well as olivine-spinel thermometry [7].

The relict olivine grain with $\Delta^{17}$O of -2.0‰ in the POP chondrule has $Fa_{24.7}$, which is within the range in Siena ($Fa_{24.8}$ ± 0.2; n = 16). Our data suggests that oxygen isotope heterogeneity originally in primitive chondrules was survived even in type 5 EOCs. Such a heterogeneous grain could exist among Itokawa particles.

**References:** [1] Okada T. et al. 2006. *Science* 312:1338–1341. [2] Abe M. et al. 2006. *Science* 312:1334–1338. [3] Nakamura T. et al. 2011. *Abstract* #1766. 42nd Lunar and Planetary Science Conference. [4] Yurimoto H. et al. 2011. *Abstract* #1755. 42nd Lunar and Planetary Science Conference. [5] Clayton R. N. et al. 1991. *Geochimica et Cosmochimica Acta* 55:2317–2337. [6] Clayton R. N. 1993. *Annual Review of Earth and Planetary Sciences* 21:115–149. [7] Kessel R. et al. 2007. *Geochimica et Cosmochimica Acta* 71:1855–1881.
THE VARIETY OF THERMAL EVOLUTION OF PRIMITIVE
HYDROUS ASTEROIDS RECORDED IN DEHYDRATED
CARBONACEOUS CHONDRITES

A. Nakato¹, T. Nakamura¹, T. Noguchi², I. Ahn³ and J. I. Lee³.
¹Tohoku University, Miyagi 980-8578, Japan. E-mail: aiko@s.tohoku.ac.jp.
²Ibaraki University, Ibaraki 310-8512, Japan.
³Korean Polar Research Institute, Incheon 406-840, Korea.

Diversities of thermal evolution, starting from low-temperature
aqueous alteration and subsequent high-temperature thermal dehydration,
in primitive hydrous asteroids can be evaluated based on mineralogical
and chemical variation in dehydrated carbonaceous chondrites [e.g., 1].
Synchrotron XRD analysis indicates that matrix phyllosilicates in Belgica
(B-) 7904, Dhofar 735, PCA 91084, PCA 91008, Yamato-86695, EET
87522, WIS 91600, LAR 06318, ALH 84033, DOM 03183, and MIL
05152 are decomposed by heating [2]. Most of samples, excepting B-7904
and Dhofar 735, experienced weak thermal metamorphism. To know the
degree of heating based on evidence from organics, we analyzed matrices
by using micro-Raman spectroscopy. As expected, most of weak heated
samples, except for PCA 91008 that underwent heavy weathering at
Antarctica, showed a broad D1-band suggestive of low maturation grade
of organics. The results suggest that those samples suffered heating
weaker than Murchison samples that were experimentally heated at
600 °C for 1 h [3].

LAR 06318 and ALH 84033 show unique oxygen isotopic
compositions. Although most weakly heated samples that we analyzed are
plotted on CM-CO-Tagish Lake line, only LAR 06318 and ALH 84033
are plotted on or close to CCAM line. *Because* partially decomposed
phyllosilicates are most dominant phases in these two samples, their
oxygen compositions are close to those of the decomposed phases. Based
on low totals of FE-EPMA analysis, dehydration of phyllosilicates was
not so much progress. Therefore, oxygen composition of the two
meteorites were established during aqueous alteration and not severely
affected by heating. Phyllosilicates having various oxygen isotopic
compositions can be formed under following conditions during aqueous
alteration (1) original solution had various oxygen isotopic ratios. (2)
water/rock ratio varies considerably.

Our results suggest that B-7904 and Dhofar 735 suffered heating at
the highest temperatures among 11 samples. This interpretation is
consistent with previous studies [e.g., 4, 5]. Based on micro-Raman
analysis, their maturation grade of organics is higher than heated
Murchison at 900 °C. But narrow Fe-Mg zoning at outer edges of
chondrule olivines in B-7904 and Dhofar 735 implies that duration of the
heating is much shorter than those expected for internal heating by short-
lived radionuclide, like $^{26}$Al. As shown in [5], oxygen isotope
compositions of the two samples determined in our study also show
smaller $\overline{\text{A}\overline{\text{A}}}^{17}\text{O}$ than those of the other samples, and matrices have Si-rich
chemical composition, suggesting that the conditions of thermal evolution
are different from those in typical CM and dehydrated CM chondrite
parent bodies.

**References:** [1] Hiroi T. et al. 1993. *Science* 261:1016-1018. [2] Nakato A. et al. Abstract #1725. 42nd Lunar and Planetary Science Conference. [3] Nakato A. et al. 2008. *Earth, Planets and Space* 60:855-854. [4] Tomeoka K. 1990. *Proceedings of the NIPR Symposium on Antarctic Meteorites* 3:40-54. [5] Ivanova M. A. et al. 2010. *Meteoritics & Planetary Science* 45:1108-1123.

EXAMINATION OF ORGANIC COMPOUNDS IN THE HAYABUSA
SAMPLES FROM THE ASTEROID ITOKAWA

H. Naraoka¹, H. Mita², K. Hamase¹, M. Mita³, H. Yabuta⁴, K. Saito⁵,
K. Fukushima⁵, F. Kitajima¹, S. A. Sandford⁶, T. Nakamura⁷, T.
Noguchi⁸, R. Okazaki¹, K. Nagao⁹, M. Ebihara¹⁰, H. Yurimoto¹¹, A.
Tsuchiyama⁴, M. Abe¹², K. Shirai¹², M. Ueno¹², T. Yada¹², Y.
Ishibashi¹², T. Okada¹², A. Fujimura¹², T. Mukai¹², M. Yoshikawa¹² and
J. Kawaguchi¹². ¹Kyushu University, Kyushu, Japan. E-mail:
naraoka@geo.kyushu-u.ac.jp. ²Fukuoka Institute of Technology,
Fukuoka, Japan. ³Shiseido Co. Ltd. ⁴Osaka University, Osaka, Japan.
⁵Nagoya University, Nagoya, Japan. ⁶NASA/ARC ⁷Tohoku University,
Tohoku, Japan. ⁸Ibaraki University, Ibaraki, Japan. ⁹University of
Tokyo, Tokyo, Japan. ¹⁰Tokyo Metropolitan University, Tokyo, Japan.
¹¹Hokkaido University, Hokkaido, Japan. ¹²ISAS/JAXA.

**Introduction:** So far, two sample return missions have provided
samples for organic analyses; lunar soils by the Apollo Program [1] and
cometary dust particles by the Stardust mission [2]. The Hayabusa
mission has provided the first opportunity to examine the occurrence of
organic matter directly on the surface of an asteroid. Asteroid Itokawa is
an S-type asteroid, a parent body of LL5-6 ordinary chondrites [3].
Although it seems to be depleted in organic matter due to its high
formation temperature, the organic matter may be delivered from comets
or carbonaceous meteorites, and/or organic precursors may be implanted
by solar wind [4]. In this study, organic compound analyses were
performed for the solvent-extract of the Hayabusa particles.

**Materials and Methods:** Five particles (approximately 40–180 µm), which consist mainly of olivine and pyroxene in mineral composition, were rinsed with small amount of organic solvents in a diamond holder. After acid hydrolysis the amino acids with enantiomeric separation was analyzed by two-dimensional high performance liquid chromatography with highly sensitive fluorescence detection (detection limit; approximately sub femto mole). Other organic compound analysis including a search for PAHs was performed using ToF-SIMS. Carbonaceous grains (approximately 50 µm) of Y791191 (CM2) were also analyzed as a reference.

**Results and Discussion:** The glycine (Gly) and DL-alanine (Ala) were observed from the particle extracts only at a procedural blank level. L-Ala was more enriched relative to D-Ala, indicating a terrestrial signature rather than asteroidal signatures. On the other hand, Gly, Ala and α-aminoisobutyric acid (approximately 100 ppm) were detected in the HCl extract of Y791191, where Ala was present as a nearly racemic mixture. As to ToF-SIMS analysis, no substantial difference was observed in positive and negative ions between the Hayabusa sample and procedural blank. The concentration of indigenous organic compounds is less than approximately ppm, if present.

**References:** [1] Harada K. et al. 1971. *Science* 173:433-435. [2] Sandford S. et al. 2006. *Science* 314:1720-1724. [3] Abe M. et al. 2006. *Science* 312:1334-1338. [4] Fox S. W. et al. 1976. *Geochimica et Cosmochimica Acta* 40:1069-1071.
5130

## DAWN AT VESTA: FIRST RESULTS FROM THE FRAMING CAMERAS

Nathues¹, C. T. Russell², C. Raymond³, U. Christensen¹, H. Sierks¹, R. Jaumann⁴, H. U. Keller⁵, S. Mottola⁴, G. Neukum⁶, M. Hoffmann¹, L. Le Corre¹, V. Reddy¹, S. E. Schröder¹, J. -Y. Li⁷, B. J. Buratti³, P. Gutiérrez Marqués¹, I. Buettner¹, I. Hall¹, T. Maue¹, M. Richards¹ and the Dawn Science Team. ¹MPI for Solar System Research, Katlenburg-Lindau, Germany. E-mail: nathues@mps.mpg.de. ²UCLA. ³JPL. ⁴DLR. ⁵TUB. ⁶FUB. ⁷UMD.

**Introduction:** Vesta is the largest intact differentiated asteroid [1] that is considered to be a model for the initial stages of planetary differentiation [2]. NASA's Dawn mission is expected to rendezvous with Vesta in July 2011 for a yearlong global characterization mission. The Framing Cameras (FC) onboard the Dawn spacecraft will image the asteroid in clear and seven narrow band filters (0.4–1.0 µm) [3].

We plan to present the first results from the Dawn FC observations of Vesta obtained during approach. Our aim is to answer three basic questions by comparing Dawn FC data with our current understanding of Vesta from HST and ground-based studies. These questions are: (1) Is the hemispherical albedo dichotomy on Vesta confirmed? (2) Is there color variation on Vesta, if so how does the color variation correlate with HST color and ground-based spectral maps? (3) Is the large topographic feature on Vesta's South Pole confirmed?

**Scientific Question 1: Albedo dichotomy:** Low resolution resolved color data can be helpful in answering several key questions about the nature and origin of Vesta's surface. From HST observations [4] the hemispheric albedo dichotomy on Vesta is well known. The eastern hemisphere of Vesta has higher albedo than the western hemisphere; this is consistent with ground-based lightcurve observations [2]. Such global albedo variations can be detected and confirmed from observations in approach.

**Scientific Question 2: Color variegation:** Spectral [2] and color variations [4] on Vesta have been attributed to compositional heterogeneity of distinct surface units. Low-resolution global color ratio maps from FC data can identify and confirm these features reported by HST [4] and ground-based telescopes [5]. Average color spectra of progressive rotational phases from the rotational characterizations can be directly compared with similar spectra from HST and ground-based telescopes.

**Scientific Question 3: Global topographic feature:** The largest topographic feature on Vesta detected from HST images by [6] is the South Pole crater with an estimated diameter ~460 km and a depth of ~20 km [1]. Current shape models of Vesta indicate a large central peak within this crater. Images at resolution greater than HST (38 km pix⁻¹) should confirm the presence of this feature and help define its origin.

**References:** [1] Thomas et al. 1997. *Icarus* 128. [2] Gaffey. 1997. *Icarus* 127. [3] Sierks et al. 2011. *Space Science Reviews*, in press. [4] Binzel et al. 1997. *Icarus* 128. [5] Reddy et al. 2010. *Icarus* 210. [6] Thomas et al. 1997. *Science* 277.

5514

## ORIGIN AND COMPOSITION OF CARBONATES, SULFATES, AND HALITE ON MARS

A. W. Needham¹,², N. A. Starkey¹, D. Johnson¹, T. Tomkinson¹,³, C. Guillermier¹,⁴, R. L. Abel²,³, I. A. Franchi¹ and M. M. Grady¹,². ¹PSSRI, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK. E-mail: A.W.Needham@open.ac.uk. ²Department of Mineralogy, The Natural History Museum, London, SW7 5BD, UK. ³SUERC ⁴Harvard Medical School ⁵Imperial College, London.

**Introduction:** The nakhlite meteorites, widely accepted to originate on Mars, preserve complex mixtures of silicate alteration, carbonates, sulfates, halides, oxides, and iron oxy-hydroxides [1–3]. These phases may have formed at different times, under different fluid flow regimes (groundwater, hydrothermal, crater lake), experiencing a range of water-rock ratios, evaporative histories, and varying degrees of interaction with the atmosphere and bedrock [2, 3].

Using information gathered from our 3D investigations of Nakhla's fluid pathways [4] we have undertaken a range of in-situ geochemical and isotopic analyses of carbonate, sulphate and halite in the Nakhla meteorite.

**Samples and Methods:** The 3D mineralogy of a small section of Nakhla was analyzed by computed tomography (CT) [4]. Using a Metris X-Tek HMX ST 225 System a resolution of ~5 µm per voxel was acheived, producing several thousand CT “slices,” subsequently reconstructed to provide 3D representations of the sample. Several sites of interest were identified in the CT data and the section of Nakhla was physically cut to reveal these sites for in situ studies. High-resolution backscatter electron and false-color EDS images were obtained using a FEI Quanta 200 dual-beam system; the focused ion beam (FIB) capabilities of this instrument have been used to extract FIB sections ranging from electron-transparent (~100 nm) to ~5 µm thick sections for Raman spectroscopy, electron microprobe, and NanoSIMS analyses. We have previously demonstrated the capabilities of the NanoSIMS 50 L for analyzing the range of carbon and oxygen isotope compositions in the Martian meteorite ALH 84001 [5]. Continuing improvements in the precision of oxygen isotope analyses (presented by [6]), especially including ¹⁷O measurements, are essential for analyses of samples with smaller isotopic differences, such as for our analyses of Nakhla secondary minerals, e.g., carbonates with <10‰ δ¹⁸O variations [7, 8] in order to understand the nature of the fluids and formation conditions.

**Summary:** Combining 3D mineralogy with subsequent high-precision and high-spatial resolution 2D mineralogical, chemical, and isotopic analyses, provides detailed information on the formation and alteration of secondary minerals on Mars. Understanding all aspects of these minerals is essential to reconstructing the true history of water on Mars, and the inherent implications for past climate and potential habitability.

**References:** [1] Gooding J. L. et al. 1991. *Meteoritics* 26:135–143. [2] Bridges. J. C. and Grady. M. M. 2000. *Earth and Planetary Science Letters* 176: 267–279. [3] Grady M. M. et al. 2007. Abstract #1826. 38th Lunar and Planetary Science Conference. [4] Needham A. W. et al. 2011. Abstract #5440. 72nd Annual Meeting of the Meteoritical Society. [5] Tomkinson T. et al. 2010. Abstract #5368. 72nd Annual Meeting of the Meteoritical Society. [6] Starkey et al. 2011. 73rd Annual Meeting of the Meteoritical Society. [7] Vicenzi and Eiler 1998. *Meteoritics & Planetary Science* 33. [8] Saxton J. M. et al. 2000. *Geochemistry Geophysics Geosystems* 6:1299–1309.
MICROSTRUCTURES OF RARE SILICATE Stardust FROM NOVA AND SUPERNOVAE

A. N. Nguyen¹,², L. P. Keller¹, Z. Rahman¹,² and S. Messenger¹. ¹Robert M. Walker Laboratory for Space Science, ARES, NASA JSC, Houston TX, USA. ²ESCG/Jacobs Technology, Houston, TX, USA. E-mail: lan-anh.n.nguyen@nasa.gov.

**Introduction:** Most silicate stardust analyzed in the laboratory and observed around stellar environments derives from O-rich red giant and AGB stars [1, 2]. Supernova (SN) silicates and oxides are comparatively rare, and fewer than 10 grains from nova or binary star systems have been identified to date. Very little is known about dust formation in these stellar environments. Mineralogical studies of only three O-rich SN [3–5] and no nova grains have been performed. Here we report the microstructure and chemical makeup of two SN silicates and one nova grain.

**Experimental:** Silicate grains having exotic O isotopic compositions were identified amongst matrix grains of the Acfer 094 meteorite by NanoSIMS O and Si isotopic imaging. Grains having unusual isotopic signatures were then measured for Mg, and in some cases Fe, isotopes after removal of surrounding grains by focused ion beam milling [6]. Cross sections were then produced for three of these presolar silicates and their microstructures were determined by transmission electron microscopy (TEM).

**Results and Discussion:** Supernova silicates. Two silicates had O and Mg isotopic ratios consistent with condensation in 15M SNe. Grain 6–16 is enriched in ¹⁸O (1.5 × solar) and slightly depleted in ²⁵Mg. Si and Fe isotopic ratios are solar within error. This grain is amorphous and has a chemical composition consistent with Mg-rich olivine (Fo95). Grain 2–33b is anomalous in both O and Mg (δ¹⁷O = 355‰, δ¹⁸O = 700‰, δ²⁵Mg = −250‰, δ²⁶Mg = 130‰), but not Si. Little grain material remained after the NanoSIMS analyses, but TEM analysis indicated an amorphous Fe-rich silicate with minor Mg and Ca and nanophase FeNi metal inclusions. This structure is reminiscent of glass with embedded metal and sulfides (GEMS) [7], though beam damage cannot be excluded. While presolar GEMS have been identified in interplanetary dust particles [8], conclusive identification of these grains in meteorite samples has not been made.

The mineralogies of two other SN silicates have previously been determined: B10A is an aggregate of crystalline olivine (Fo83) [3] and 2–4 is amorphous MgSiO₃ [5]. The chemical compositions of B10A, 2–4 and 6–16 suggest equilibrium condensation. In contrast to other SN dust phases, the SN silicates have varied mineralogies and are mostly amorphous, though alteration from an initially crystalline state cannot be ruled out.

Nova silicate. Silicate 4_2 was found to be highly ¹⁷O-rich and also anomalous in ¹⁸O and Mg isotopes (δ¹⁷O = 32410‰, δ¹⁸O = −130‰, δ²⁵Mg = 1025‰, δ²⁶Mg = 90‰), suggestive of a nova source (see [6]). An extremely limited amount of material remained for TEM analysis, but the silicate contains Al (Al/Si = 0.3) and some Fe, likely contamination from an underlying Fe oxide grain. Nova grains are exceptionally rare and no other microstructural studies of O-rich nova dust exist to date. Identification of additional nova silicates is highly desirable.

**References:** [1] Nguyen A. N. et al. 2010. *The Astrophysical Journal* 719:166. [2] Waters L. B. F. M. et al. 1996. *Astronomy & Astrophysics* 315:L361. [3] Messenger S. et al. 2005. *Science* 309:737. [4] Stroud R. M. et al. 2008. Abstract #1778. 39th Lunar and Planetary Science Conference. [5] Nguyen A. N. et al. 2010. *Meteoritics & Planetary Science* 45:A5423. [6] Nguyen A. N. et al. 2011. Abstract #2711. 42nd Lunar and Planetary Science Conference. [7] Bradley J. P. and Dai Z. R. 2004. *The Astrophysical Journal* 617:650. [8] Keller L. P. and Messenger S. 2011. *Geochimica et Cosmochimica Acta*, in revision.

LOVINA: IS THIS A METEORITE?

K. Nishiizumi¹ and M. W. Caffee². ¹Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA. E-mail: kuni@ssl.berkeley.edu. ²Department of Physics, Purdue University, West Lafayette, IN 47907-1396, USA.

**Introduction:** Lovina (8.2 kg) was found on Lovina beach in Bali, Indonesia, on January 1981. It is a strikingly oblong, weathered iron with cm-scale pyramids projecting from its upper surface (orientation as found on beach) and cm-sized vugs in the lower surface [1]. Based on petrographic, mineralogical, and geochemical analysis [2], Lovina is classified as an ungrouped iron meteorite (ataxite). The bulk chemical composition, including trace elements, suggests Lovina is a high Ni iron meteorite, although its unusual appearance casts some doubt on this assertion. Since all recovered extraterrestrial materials contain cosmogenic nuclides produced in space we have measured the concentrations of cosmogenic nuclides ¹⁰Be, ²⁶Al, and ³⁶Cl to verify its extraterrestrial origin.

**Results and Discussion:** A piece of Lovina was cleaned by etching with 5% HNO₃/ethanol solution using an ultrasonic bath for ~30 min. 249 mg of the cleaned sample was then dissolved in 4 N HNO₃ along with the carrier solutions. The chemical composition of our sample is 57.8% Fe, 0.94% Co, and 36.4% Ni. After chemical separation and purification the cosmogenic radionuclides were measured by AMS at Purdue University. Lovina contains 0.0055 ± 0.0005 dpm ¹⁰Be kg⁻¹, 0.0029 ± 0.0021 dpm ²⁶Al kg⁻¹, and 0.0025 ± 0.0008 dpm ³⁶Cl kg⁻¹. These activities are 3 to 4 orders of magnitude lower than those of typical iron meteorites, and the lowest among all iron meteorites except interior pieces from the Nantan or Gibeon meteorites. If the cosmogenic nuclides in Lovina were produced in space, the recovered sample of Lovina was near the center of an object more than ~3 m in diameter, or it resided at ~1.5 m depth in a large object in space. In addition, the ¹⁰Be and ³⁶Cl concentrations require a ~1.4 Myr terrestrial age. Alternatively, this concentration of ³⁶Cl can be produced on the Earth if Lovina were exposed at the surface in Indonesia for ~0.1 Myr. Although the observed ¹⁰Be is slightly higher than would be expected with a 0.1 Myr terrestrial exposure, the ¹⁰Be could be elevated from exposure of Lovina to terrestrial contamination. Although we etched the sample, the concentration of ¹⁰Be, ~5 × 10⁵ atom g⁻¹, could be absorbed from rain or seawater. It is perhaps noteworthy that Lovina has many pits in its surface. Tektites from Southeast Asia contain more than 2 orders of magnitude higher ¹⁰Be than found in Lovina. Based on cosmogenic radionuclide concentrations, it is our opinion that Lovina is unlikely to be of extraterrestrial origin. We will remeasure the cosmogenic radionuclides, as well as noble gases in a larger piece to verify these conclusions.

**Acknowledgments:** We thank Daryl Pitt of Macovich Collection for providing sample.

**References:** [1] Meteoritical Bulletin, No. 93, 2008 March. [2] Flemming R. L. et al. 2008. Abstract #2412. 39th Lunar and Planetary Science Conference.
X-RAY ABSORPTION NEAR-EDGE SPECTROSCOPY OF
SUPERNOVA CARBONACEOUS GRAINS

L. R. Nittler¹, E. Groopman², T. J. Bernatowicz², T. K. Croat² and E. K. Zinner². ¹Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA. E-mail: Inittler@ciw.edu. ²Laboratory for Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130, USA.

**Introduction:** Transmission electron microscopy and Raman spectroscopy have been previously used with great success to characterize presolar carbonaceous grains and infer useful astrophysical information about their formation conditions [1–3]. Here, we report the first application of synchrotron transmission X-ray microscopic (STXM) techniques to meteoritic graphitic grains with isotopic compositions indicating a presolar formation in type II supernovae.

**Samples and Methods:** We analyzed ultramicrotome slices of two presolar graphites: KE3-e6, from Murchison [2], and OR1d5m-G15 (ORG15), from Orgueil. STXM measurements were performed at beamline 5.3.2.2 of the Advanced Light Source (Lawrence Berkeley National Lab). X-ray absorption near-edge spectroscopic (XANES) analyses were made in "image stack" mode, wherein the sample is moved in a raster pattern under the <50 nm X-ray beam and a complete absorption spectrum is acquired at each pixel. XANES stacks were acquired at the C, N, and O K-edges and the Ti L<sub>2,3</sub> edge.

**Results and Discussion:** Isotopic analyses of the two graphite grains indicate a SN origin, e.g., <sup>18</sup>O, <sup>15</sup>N, and <sup>28</sup>Si excesses. TEM analysis of the analyzed slice of KE3-e6 indicates a turbostratic graphite morphology and several Ti-rich subgrains. The C-edge XANES spectrum for this grain shows typical graphite features at 285.2 and approximately 291 eV, due to 1 s π* and σ* transitions, respectively, as well as a small feature at 288.6 eV. This is probably due to C=O bonding (also seen in the O K-edge spectrum), suggesting that the observed O is bonded to the graphene layers as a lactone. N-XANES spectra reveal significant N contents and an absorption feature at approximately 401 eV, possibly indicating amide-type bonding. Ti- and O-XANES spectra of five Ti-rich sub-grains indicate that one is most likely TiO<sub>2</sub>, and the rest TiC. However, the spectra suggest the presence of some O (and N) even in the TiC grains, as previously inferred from SIMS measurements of other supernova grains [4]. The STXM data for grain ORG15 indicate a "cauliflower-like" morphology and a C-XANES spectrum slightly different from that of KE3-e6. Rather than a single sharp 1 s π* feature at 285.2 eV, ORG15 shows features at 284.8, 285.4 and to a lesser extent at 287.5 eV. Most likely, this grain consists of a composite of graphitic C with some smaller, well-organized PAH-like material. In contrast, the N-edge spectrum for ORG15 is similar to that of KE3-e6. Our preliminary results demonstrate the utility of XANES analysis of graphitic presolar grains. In future studies, we will probe the chemistry of Fe-rich sub-grains and the C-edge structure of grains for which Raman spectra indicate a strongly disordered nature [3].

**Acknowledgments:** We thank David Kilcoyne for help with the STXM and George Cody for useful discussions.

**References:** [1] Bernatowicz T. J. et al. 1996. *The Astrophysical Journal* 472:760–782. [2] Croat T. K. et al. 2003. *Geochimica et Cosmochimica Acta* 67:4705–4725. [3] Zinner E. et al. 1995. *Meteoritics* 30:209–226. [4] Stadermann F. J. et al. 2005. *Geochimica et Cosmochimica Acta* 69:177–188.

FIRST DIRECT EVIDENCE OF ASTEROIDAL SPACE
WEATHERING FOUND ON THE SURFACE OF ITOKAWA
PARTICLES

T. Noguchi¹, T. Nakamura², M. Kimura¹, M. E. Zolensky³, M. Tanaka⁴, T. Hashimoto⁵, M. Konno⁵, A. Nakato², T. Ogami², A. Fujimura⁶, M. Abe⁶, T. Yada⁶, T. Mukai⁶, M. Ueno⁶, T. Okada⁶, K. Shirai⁶, Y. Ishibashi⁶ and R. Okazaki⁷. ¹Ibaraki University. E-mail: tngc@mx.ibaraki.ac.jp. ²Tohoku University. ³NASA/JSC. ⁴National Institute for Materials Science. ⁵Hitachi High-Technologies Corporation. ⁶ISAS/JAXA. ⁷Kyushu University.

**Introduction:** Surfaces of airless bodies exposed to interplanetary space gradually have their structures, optical properties, chemical compositions, and mineralogy changed by solar wind implantation and sputtering, irradiation of galactic and solar rays, and micrometeorite bombardment. These alteration processes and the resultant optical changes are called "space weathering" [1-3]. It has been already proved by transmission electron microscopy (TEM) that metallic iron nanoparticles deposited on the surfaces of lunar soils result from space weathering [4]. TEM observation suggested that both micrometeorite bombardment and solar wind implantation and sputtering played important roles in the formation of the nanoparticles. Asteroidal space weathering has been advocated based on ground-based and in situ observation of asteroids [5-7]. Initial investigation of fine-grained particles retrieved from the asteroid Itokawa by the Hayabusa spacecraft revealed that the S-type asteroid Itokawa is surfaced by space weathered LL chondrite-like materials [8]. Here we describe the surface modification of the Itokawa particles.

**Materials and Methods:** We analyzed 10 Itokawa particles. We prepared ultrathin sections of the particles. Four particles were prepared in a N<sub>2</sub> purged environment and six were in the earth's atmosphere. In both cases, we used dehydrated ethylene glycol instead of distilled water as the trough liquid to prevent contact with water. Ultrathin sections were observed by spherical aberration corrected scanning TEM.

**Results and Discussion:** Five out of 10 particles we examined have 30-60-nm-thick rims containing Fe-enriched nanoparticles often accompanied with minor sulfur. Sulfur-bearing Fe-rich nanoparticles exist on the top of the surface (~10-nm thick). Except for the very surface, materials that contain the nanoparticles considerably preserve the crystal structures of their substrate minerals. This fact shows a stark contrast to the amorphous nature of the host of the metallic Fe nanoparticle-bearing rims in lunar soils [4]. Lattice fringes of most nanoparticles were difficult to observe, with a few exceptions. Textures and chemical compositions of the nanoparticle-bearing rims are dependent on the substrate minerals. We think that the main agent of space weathering of Itokawa is sputtering by solar wind rather than micrometeorite bombardment.

**References:** [1] Hapke B. 2001. *Journal of Geophysical Research* 106:10039–10073. [2] Clark B. E. et al. 2002. *Asteroids III*. Tucson: University of Arizona Press. [3] Chapman C. R. 2004. *Annual Review of Earth and Planetary Science* 32:539–567. [4] Keller L. P. and McKay D. S. 1997. *Geochimica et Cosmochimica Acta* 61:2331–2341. [5] Binzel R. P. et al. 2002. *Asteroids III*. Tucson: The University of Arizona Press. [6] Clark et al. 2001. *Meteoritics & Planetary Science* 36:1617–1637. [7] Hiroi T. et al. 2007. *Nature* 443:56–58. [8] Kerr R. A. *Science* 332:302.
## HYDROTHERMAL ALTERATION EXPERIMENTS OF AMORPHOUS SILICATES: EFFECT OF ORGANIC-INORGANIC INTERACTION

R. Noguchi¹, A. Tsuchiyama¹, H. Yabuta¹ and S. Ichikawa². ¹Department of Earth Space Science, Osaka University, Osaka, Japan. E-mail: noguchi@astroboy.ess.sci.osaka-u.ac.jp. ²Institute for Nano Science Design, Osaka University, Osaka, Japan.

**Introduction:** Most carbonaceous chondrites with primitive chemical compositions have experienced aqueous alteration in their parent bodies. In order to understand the formation of minerals during the aqueous alteration process, we have previously carried out hydrothermal alteration experiments using Fe-free amorphous silicates with CI chondritic composition [1]. The previous study showed that saponite, serpentine, calcite, and a relatively small amount of aragonite are formed from amorphous silicates and deionized water. This study focuses on the organic-inorganic interaction upon the aqueous alteration process of chondrites, since carbonaceous chondrites contain large amounts of organic compounds (approximately 2%) [2] that could have been involved to formation of some minerals, such as carbonates.

**Experiments:** The glass of the system, SiO₂–MgO–Al₂O₃–CaO–Na₂O, with the CI chondrite chemical composition was used. The glass sample was ground to make micron-scale powders. Two kinds of amino acids, glycine and alanine, were used as the analog of whole organic matter in the carbonaceous chondrites. The ratio of alanine to glycine is 2.56:1.00, based on that in the GRA 95229 which is weakly altered CR chondrite [3]. Silicates (100 mg), amino acids (23 mg) and deionized water (0.1 or 0.5 mL) were placed in Teflon vessels so that water to rock mass ratios were 1.0 and 5.0, sealed with stainless jacket, and were heated in an electric furnace at 150 °C for 1, 2, 4, and 8 weeks under water saturated vapor pressures (approximately 3.0 bars). After heating experiments, vessels were rapidly cooled to room temperature in water. Solid products were recovered from solutions and dried in vacuum at room temperature. Parts (approximately 80 mg) of solid materials were extracted with hot Milli-Q water for 24 h. The water extracts were analyzed with high-performance liquid chromatography (HPLC) to quantify the concentrations of amino acids. Solid products were analyzed with powder X-ray diffractometer (XRD) and field emission scanning electron microscopy (FE-SEM) to identify the formed mineral pahse.

**Results and Discussion:** The XRD analysis and the FE-SEM observations of all the samples obtained from the hydrothermal experiments showed that serpentine and saponite, which are major phase in the chondrites, were formed. Aragonite, minor phase in CM chondrite, was also formed in all the experiments. However, calcite was not formed. The concentrations of alanine and glycine decreased with increasing time of heating, which is consistent with the trend of amino acid concentrations in aqueous-altered carbonaceous chondrites. On the other hand, the ratio of alanine to glycine decreased with increasing time of heating. This is a reverse trend to that of carbonaceous chondrites.

**References:** [1] Noguchi R. et al. 2011. Abstract #1789. 42nd Lunar and Planetary Science Conference. [2] Pizzarello S. et al. 2006. *Meteorites and the early solar system* II:625–651. [3] Martins Z. et al. 2007. *Meteoritics & Planetary Science* 42:2125–2136.

## OXYGEN ISOTOPIC ANALYSES OF WATER IN BJURBÖLE MATRIX AND CHONDRULES

M. Nunn and M. Thiemens. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla CA, USA. E-mail: mnunn@ucsd.edu.

**Introduction:** Past oxygen isotopic analyses of Bjurböle have been limited to whole rock and chondrule studies. We present here the first oxygen isotopic measurements of water contained in the matrix and chondrules of the L4 equilibrated ordinary chondrite Bjurböle.

**Method:** Water was extracted by vacuum pyrolysis from a 1 g sample of matrix and a 1.6 g sample of chondrules from the Bjurböle meteorite. A new, low volume, ultra low blank system was built specifically for these measurements. Each fraction was pumped overnight on a vacuum line to remove adsorbed terrestrial water before heating step-wise to 150, 350, 600, and 1000 °C. While heating, evaporated volatiles were collected in a liquid nitrogen cold trap. Water was quantitatively converted to molecular oxygen with bromine pentafluoride. Isotopic abundances were measured on a double-collecting isotope ratio mass spectrometer.

**Results and Discussion:** Direct fluorination of Bjurböle chondrules and whole rock and UV laser probe analyses of individual Bjurböle chondrules have shown the Δ¹⁷O value to cluster around 1 [1, 2]. Compared to these data, water extracted from the Bjurböle matrix and chondrules is isotopically light (Δ¹⁷O ≤ 0.8), presumably reflecting different equilibration histories of water and oxygen-bearing minerals. Additionally, the proximity of Δ¹⁷O values of water extracted at lower temperatures to that of terrestrial water indicates low-temperature heating is necessary to remove adsorbed terrestrial water and yield more accurate results.

**References:** [1] Clayton et al. 1991. *Geochimica et Cosmochimica Acta* 55:2317. [2] Ash et al. 1997. Abstract #5282. 60th Annual Meteoritical Society Meeting.
5385

A QUANTITATIVE, TIME-DEPENDENT MODEL OF OXYGEN ISOTOPES IN THE SOLAR NEBULA: STEP 1

J. A. Nuth¹, J. A. Paquette²,³, A. Farquhar²,⁴ and N. M. Johnson². ¹Solar System Exploration Division, Code 690, NASA's Goddard Space Flight Center, Greenbelt MD 20771, USA. E-mail: joseph. a.nuth@nasa.gov. ²Astrochemistry Laboratory, Code 691, NASA GSFC. ³NASA Postdoctoral Fellow. ⁴USRP Student Intern.

**Introduction:** The remarkable discovery that oxygen isotopes in primitive meteorites were fractionated along a line of slope 1 rather than along the typical slope 0.52 terrestrial fractionation line occurred almost 40 years ago [1]. However, a satisfactory, quantitative explanation for this observation has yet to be found, though many different explanations have been proposed. The first of these explanations proposed that the observed line represented the final product produced by mixing molecular cloud dust with a nucleosynthetic component, rich in ¹⁶O, possibly resulting from a nearby supernova explosion. Donald Clayton [2] suggested that galactic chemical evolution would gradually change the oxygen isotopic composition of the interstellar grain population by steadily producing ¹⁶O in supernovae, then producing the heavier isotopes as secondary products in lower mass stars. Thiemens and collaborators proposed a chemical mechanism that relied on the availability of additional active rotational and vibrational states in otherwise-symmetric molecules, such as CO₂, O₃ or SiO₂, containing two different oxygen isotopes [3, 4] and a second, photochemical process that suggested that differential photochemical dissociation processes could fractionate oxygen [5]. This second line of research has been pursued by several groups [6, 7], though none of the current models is quantitative.

**Lightning as the Processing Agent:** Based on experiments [8] done at GSFC that produced nonmass-dependently fractionated solid oxides from plasma, we have previously suggested [9] that dust processed via nebular lightning could explain the observed oxygen isotopic distribution in the solar system. Necessary conditions for nebular lightning have been previously discussed [10–12] and we will present preliminary work suggesting that lightning is a major component of protostellar nebulae.

We will also present preliminary results of the time dependent evolution of oxygen isotopes in nebular dust and the largest uncertainties that remain in the model.

**References:** [1] Clayton R., Grossman L., and Mayeda T. 1973. *Science* 182:485. [2] Clayton D. 1988. *The Astrophysical Journal* 334:191–195. [3] Thiemens M. H. and Jackson T. 1987. *Geophysical Research Letters* 6:624. [4] Thiemens M. H. 1996. In *Chondrules and the protoplanetary disk*, edited by Hewins R. H., Jones R. H., and Scott E. R. D. Boston: Cambridge University Press. pp. 107–118. [5] Thiemens M. H. and Heidenreich J. E. 1983. *Science* 219:1073. [6] Clayton R. N. 2002. *Nature* 415:860–861. [7] Lyons J. R. and Young E. D. 2005. *Nature* 435:317–320. [8] Kimura Y., Nuth J. A., Chakraborty S., and Thiemens M. H. 2007. *Meteoritics & Planetary Science* 42:1429–1439. [9] A Simple Mechanism for Fractionating Oxygen Isotopes in the Solar System Joseph A. Nuth III, Annual Meeting of the Meteoritical Society, Nancy France, July 2009. Abstract#.[10] Gibbard S. G., Levy E. H., and Morfill G. E. 1997. *Icarus* 130:517–533. [11] Love S. G., Keil K., and Scott E. R. D. 1995. *Icarus* 115:97–108. [12] Desch S. J., and Cuzzi J. N. 2000. *Icarus* 143:87–105.

5155

Rb-Sr AND Sm-Nd STUDY OF ASUKA-881394: EVIDENCE OF “LATE” METAMORPHISM

L. E. Nyquist¹, C.-Y. Shih², Y. Reese³ and H. Takeda⁴. ¹KR, NASA Johnson Space Center, Houston, TX 77058, USA. E-mail: laurence.e.nyquist@nasa.gov. ²ESCG Jacobs-Sverdrup, Houston, TX 77058, USA. ³Mail Code JE-23, ESCG/Muniz Engineering, Houston, TX, 77058, USA. ⁴Chiba Inst. of Tech., 2-17-1 Tsudanuma, Narashino City, Chiba 275-0016, Japan.

**Introduction:** The Asuka-881394 achondrite contains fossil ²⁶Al and ⁵³Mn [1–3] and has a ²⁰⁷Pb/²⁰⁶Pb age of 4566.5 ± 0.2 Ma [3], the oldest for an achondrite. Preliminary results showed initial ¹⁴⁶Sm/¹⁴⁴Sm = (7.4 ± 1.2) × 10⁻³, indicative of an ancient age, but ⁸⁷Rb-⁸⁷Sr and ¹⁴⁷Sm-¹⁴³Nd ages of 4370 ± 60 and 4490 ± 20 Ma, respectively [1], were younger than expected from the presence of short-lived nuclides. We revisit the Rb-Sr and Sm-Nd chronology of A-881394 in an attempt to establish whether “late” metamorphism led to inconsistency in its apparent ages.

**Min-Pet:** The granulitic texture of A-881394 led Wadhwa et al. [4] to suggest that it had experienced an extensive thermal event in which it lost Na and other volatiles, accounting for its very calcic An₉₈ plagioclase. Prior to discovery of its fossil short-lived nuclides, very calcic plagioclase and unusually magnesian pyroxene were considered to be its most important features [2, 4]. It was suggested that Na may have been lost via catastrophic bombardment into a magma ocean during late-stage accretion, resulting in increased anorthite, magnesian pyroxene, and silica at the expense of albite [2].

**Rb-Sr Data:** Combined data from investigations in 2001 [1] and 2010 give a “disturbed isochron” corresponding to 4.50 ± 0.18 Ga. Evidence for early crystallization is preserved in low ⁸⁷Sr/⁸⁶Sr of plagioclase separates. ⁸⁷Rb/⁸⁶Sr is lower than for cumulate eucrites Y-980318/433, and comparable to values for angrites. Initial ⁸⁷Sr/⁸⁶Sr = 0.698992 ± 19, within uncertainty of 0.698972 ± 8 for angrite LEW 86010 [5], but not clearly resolved from values for eucrites. Handpicked tridymite (2001) and a mineral separate leachate (2010) determine the isochron slope, and when combined with one pyroxene separate and its residue after leaching give an apparent secondary isochron age of 4.0 ± 0.8 Ga.

**Sm-Nd Data:** New data (2010) give an isochron age of 4.524 ± 0.063 Ga, and all thirteen data from both investigations give 4.511 ± 0.033 Ga. It is likely that the Sm-Nd system also has been disturbed. Handpicked tridymite (2001) plus combined leachates (2010) define an apparent age with pyroxenes of 4.4 ± 0.2 Ga. Removing these “outliers” (tridymite and two leachates) leads to a revised age of 4.516 ± 0.037 Ga. Combined data from both investigations give revised initial ¹⁴⁶Sm/¹⁴⁴Sm = (9.1 ± 1.4) × 10⁻³ and T$_{LEW}$ = 4.584 ± 0.023 Ga relative to 4558 Ma [6] and ¹⁴⁶Sm/¹⁴⁴Sm = 7.6 × 10⁻³ for LEW 86010 [5].

**Conclusion:** Disturbed and partially reset ⁸⁷Rb-⁸⁷Sr and ¹⁴⁷Sm-¹⁴³Nd ages appear to be consistent with disturbance of these isotopic systems by some catastrophic or metamorphic events on the A881394 parent asteroid. These events followed an earlier catastrophic bombardment as envisioned by the Na-loss model leading to An₉₈ plagioclase [2]. The occurrence of such events probably continued to times less than approximately 4.4 Ga ago.

**References:** [1] Nyquist L. E. et al. 2001. *Meteoritics & Planetary Science* 36:A151. [2] Nyquist L. E. et al. 2003. *Earth and Planetary Science Letters* 214:11–25. [3] Wadhwa M. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5189–5201. [4] Takeda H. et al. 1997. *Antarctic Meteorite Research* 10:401–413. [5] Nyquist L. E. et al. 1994. *Meteoritics* 29:872–885. [6] Lugmair G. W. and Galer S. J. G. 1992. *Geochimica et Cosmochimica Acta* 56:1673–1694.
## MEASUREMENTS OF <sup>26</sup>Al IN THE Stardust CHONDRULE FRAGMENT “IRIS”

R. C. Ogliore¹, A. L. Butterworth², Z. Gainsforth², G. R. Huss¹, K. Nagashima¹, J. Stodolna² and A. J. Westphal². ¹University of Hawai‘i at Mānoa, Honolulu, HI, USA. E-mail: ogliore@higp.hawaii.edu. ²University of California, Berkeley, CA, USA.

**Introduction:** The former presence of radioactive <sup>26</sup>Al ($t_{1/2}$ = 0.73 Myr) has been identified in chondrules that have experienced little metamorphism [e.g., 1]. The lack of radiogenic <sup>26</sup>Mg in other chondrules can be interpreted as a disturbance of the <sup>26</sup>Al-<sup>26</sup>Mg isotope system due to thermal or aqueous alteration, inhomogeneity of <sup>26</sup>Al in the solar nebula, or a few Myr time delay between the formation of these objects and the earliest solar system objects, CAIs (from which the canonical <sup>26</sup>Al/<sup>27</sup>Al ≈ 5 × 10<sup>-5</sup> is deduced) [1]. Jupiter-family comets appear to be made of a mixture of solar system materials with different histories [2], including chondrule fragments [3]. We report measurements of the <sup>26</sup>Al-<sup>26</sup>Mg system in a type II chondrule fragment from comet Wild-2, returned to Earth by NASA’s Stardust mission.

**Methods:** We extracted a 23 × 15 × 5 µm terminal particle from Stardust track C2052,2,74 (“Iris”) [4]. This particle has characteristics of a type II chondrule fragment [5]. We identified fragments of oligoclase (An~20) on four approximately 100 nm microtomed slices on a TEM grid. Since the Al-rich phases needed for useful measurements of the <sup>26</sup>Al-<sup>26</sup>Mg system were surrounded by Mg-rich phases, we covered the potentially interfering neighboring phases with a Pt shield deposited by FIB. We then glued the grid to a bullet, and measured <sup>24</sup>Mg, <sup>25</sup>Mg, <sup>26</sup>Mg, <sup>27</sup>Al using the UH Cameca ims-1280 (primary <sup>16</sup>O<sup>-</sup> beam at approximately 10 pA, approximately 2 µm spot size, simultaneous measurement of Mg isotopes followed by peak-jumping to <sup>27</sup>Al, approximately 4800 mass-resolving power). We acquired approximately 200 cycles at each spot with 15s for the Mg isotopes and 1s for <sup>27</sup>Al per cycle, until the sample was nearly consumed. On each slice we measured one or two spots in the Stardust oligoclase. We used Miyakejima anorthite, prepared and mounted similarly to the Stardust sample, as the standard.

**Analysis:** For each cycle, we assume the dead-time corrected counts of <sup>26</sup>Mg in the Stardust chondrule fragment follow a Poisson distribution, with expectation value equal to the sum of two sources: (1) the natural <sup>26</sup>Mg abundance (deduced from the plagioclase standard) proportional to the <sup>24</sup>Mg- (also, <sup>25</sup>Mg-) corrected counts for that cycle, and (2) a radiogenic contribution proportional to the corrected, time-interpolated <sup>27</sup>Al counts. The constant of proportionality of (2) is the initial <sup>26</sup>Al/<sup>27</sup>Al, and is easily derived by the maximum likelihood method. We determined a robust confidence interval for the initial <sup>26</sup>Al/<sup>27</sup>Al by using a Monte Carlo simulation that accounts for statistical uncertainty and instrumental mass fractionation.

**Results:** We found no evidence for extinct <sup>26</sup>Al in the Stardust chondrule fragment; the one-sided 2σ upper bound for initial <sup>26</sup>Al/<sup>27</sup>Al is approximately 3 × 10<sup>-6</sup>. The Stardust fragment either formed or was heated in an asteroidal parent body at least 3 Myr after CAIs formation. Incorporation into the comet must have occurred after that. Our result constrains the formation of cometary nuclei.

**References:** [1] Kita N. T. et al. 2005. In *Chondrites and the protoplanetary disk*, ASP 341:558-587. [2] Brownlee D. E. et al. 2006. *Science* 314:1711-1716. [3] Joswiak D. J. et al. 2010. Abstract #2119. 41st Lunar and Planetary Science Conference. [4] Butterworth A. L. et al. 2010. Abstract #2446. 41st Lunar and Planetary Science Conference. [5] Gainsforth Z. et al. 2011. *Meteoritics & Planetary Science*. This conference.

## THE STAC FADA “IMPACT EJECTA” LAYER: NOT WHAT IT SEEMS

G. R. Osinski¹, L. Preston¹, L. Ferrière¹,², T. Prave³, J. Parnell⁴, A. Singleton¹ and A. E. Pickersgill¹. ¹Department Earth Sciences, University of Western Ontario, London, ON, Canada. E-mail: gosinski@uwo.ca. ²Natural History Museum, Burgring 7, A-1010 Vienna, Austria. ³Department Earth Sciences, University of St. Andrews, St. Andrews, UK. ⁴Department Geology & Petroleum Geology, University of Aberdeen, Aberdeen, UK.

**Introduction:** The Stac Fada Member (SFM) forms part of the Stoer Group of the Torridonian of NW Scotland. The SFM is unique in the Torridonian, being characterized by the presence of greenish altered glass clasts. Its origin has been debated for decades with several hypotheses being proposed but all invoking some connection with volcanic activity in the region (e.g., [1]). More recently, Amor et al. [2] suggested that the SFM represents “a chord section through the continuous ejecta blanket surrounding an impact crater.” Here, we confirm the presence of shocked material within the SFM and then discuss its origin.

**Methods:** Fieldwork was carried out in August 2008 and June 2009. We performed optical microscopy on 26 polished thin sections using an optical microscope and a four-axis universal stage. Quantitative analyses and investigation of textures were carried out on a JEOL JXA-8900 L electron microprobe.

**Confirmation of Shocked Material within the SFM:** The investigated breccia samples display a large heterogeneity of shock effects in quartz grains; including grains with PFs and/or PDFs (mostly 1-2 sets; up to 4 sets per grain). It is notable that some samples contain no shocked quartz grains. The crystallographic orientations of 90 PF and PDF sets in 59 quartz grains were measured by U-stage. A large proportion of the measured PDFs show orientations parallel to ω{} and ~12% of the measured PDFs are parallel to the π{} orientation. Amor et al. [2] identified possible PDFs in 25 quartz grains from 9 thin sections. Our observations confirm the presence of PDFs in quartz in the SFM; although several discrepancies are notable.

**Impact Origin?** We have confirmed that the SFM contains shocked material. However, based on a review of all terrestrial impact ejecta deposits and considerations of impact ejecta emplacement [3] we find several observations and properties of the SFM that are *not* consistent with it being a “continuous ejecta blanket” as proposed by [2]. Most importantly, it contains an order of magnitude less shocked material than other proximal impact melt-bearing ejecta layers (e.g., “suevite” from the Ries impact structure Germany [4]); and it is very well sorted compared to other impact ejecta deposits. In this latter respect, it shares many similarities to the Onaping Formation of the Sudbury impact structure, Canada, which has been recently reinterpreted as hot impact melt that interacted with seawater [5]. As such, we propose that the SFM is not of primary impact origin but is more akin to volcaniclastic rocks, which represent volcanic materials that have been *transported* and *reworked* by wind or water. This has implications for the recognition of impact ejecta deposits and their emplacement in H₂O-rich environments.

**Acknowledgments:** This work was funded by the Canadian Space Agency CARN Program and NSERC.

**References:** [1] Young G. M. 2002. *Transactions Earth Sciences* 93:1-16. [2] Amor K. et al. 2008. *Geology* 36:303-306. [3] Osinski G. R. et al. 2011. *Earth and Planetary Science Letters*, in press. [4] Engelhardt W.v. 1997. *Meteoritics & Planetary Science* 32:545-554. [5] Grieve R. A. F. et al. 2010. *Meteoritics & Planetary Science* 45:759-782.
U-Pb and Pb-Pb DATINGS AND D/H RATIOS OF PHOSPHATES IN THE MARTIAN METEORITES

Y. Ota¹,², N. Takahata², Y. Sano² and N. Sugiura¹. ¹School of Science, University of Tokyo, Tokyo, Japan. E-mail: y_ohta@aori.u-tokyo.ac.jp. ²Atmosphere and Ocean Research Institute.

**Introduction:** There are many studies that reported U-Pb and Pb-Pb dating in phosphates in the Martian meteorites. The ages of Shergottites are reported about 4 billion years [1] and 200 Myr [2]. These Martian meteorite ages are not precisely determined and this age is very important for the discussion about variation of D/H ratio in Mars. Here we show the U-Pb and Pb-Pb ages and D/H ratio in Martian Meteorites at the same phosphate grains.

**Samples and Methods:** We use the ALH 84001, Zagami, DaG476 and some Martian meteorites. Phosphate minerals in a thin section were detected by SEM-EDS and it was coated with gold films before the NanoSIMS measurement. For U-Pb and Pb-Pb dating, primary O- ions with a beam intensity of 10 nA were used in a spot diameter of about 10–20 µm, and for D/H ratios, with a beam intensity of 1 nA in a spot diameter of about a few micrometers. The apatite derived from Prairie Lake called PRAP whose age was known [3] was used as a standard, and the apatite collected from Emilchil Errachidia in Morroco whose water abundance was measured was used as a standard of D/H ratio and water abundance.

**Result:** The phosphate mineral in ALH 84001 crystallized about 4 billion years ago according to the U-Pb, Pb-Pb system. The age obtained in this study is consistent with those of the previous studies [4] within the experimental error. D/H ratios in ALH 84001 are up to 3000 approximately 3500‰. There is a negative correlation between the δD and amount of water. The U-Pb ages of phosphate minerals in Zagami are almost zero, so it had reset because of some metamorphism. But the Pb-Pb isochron age at the same spot of U-Pb dating is about 4 Gyr. This age is defined by two grains. D/H ratios in Zagami and DaG476 are about 0 approximately 1000‰. Our data show Zagami crystallized at 4 Gyr ago by the Pb-Pb age, and it has experienced some metamorphism so U-Pb age is almost zero.

**Discussion:** The crystallization ages of phosphates in ALH 84001 and Zagami are probably about 4 Ga, but U-Pb ages of phosphates in Zagami had reset recently. It seems that D/H ratios of phosphates in ALH 84001 keep the value 4 billion years ago and this value is higher than previous studies [5]. However D/H ratios of phosphates in Zagami are almost terrestrial values or mixed values with terrestrial and Martian water because of resetting age. There are many data of phosphate in Shergottites that U-Pb ages are about 200 Myr and D/H ratios are over 4000‰ [6]. Our data support the scenario that these Martian meteorites crystallize about 4 Gyr ago, and metamorphose resetting U-Pb ages and replacing D/H ratio about 200 Myr ago.

**References:** [1] Bouvier A. et al. 2009. *Earth and Planetary Science Letters* 280:285–295. [2] Nyquist et al. 1998. *Journal of Geophysical Research* 103:31445–31455. [3] Sano Y. et al. 1999. *Chemical Geology* 153:171–179. [4] Terada K. et al. 2003. *Meteoritics & Planetary Science* 38:1697–1703. [5] Greenwood et al. 2008. *Geophysical Research Letter* 35:L05203. [6] Watson et al. 1994. *Science* 265:86–90.

COSMOGENIC NOBLE GASES OF THE GEBEL KAMIL IRON METEORITE

U. Ott¹, S. Merchel², L. Folco³ and M. D'Orazio⁴. ¹MPI für Chemie, Postfach 3060, D-55020 Mainz, Germany. E-mail: uli.ott@mpic.de. ²HZDR, D-01328 Dresden, Germany. ³MNA, Siena, Italy. ⁴DST Pisa, Italy.

**Introduction:** The Kamil Crater in southern Egypt was first identified during a Google Earth survey. A closer inspection during a geophysical expedition in February 2010 not only revealed details of its structure but also identified several thousand iron meteorite specimens with a total weight of ~1.7 tons [1,2]. The meteorite is classified as an ungrouped Ni-rich ataxite [3]. He, Ne and Ar measurements have been performed on samples from the only regmaglypted 83 kg individual as well as from a piece of the shrapnel produced during the impact [1,2].

**Experimental:** We measured two samples each from the individual and the shrapnel, separated by a distance of ~1 cm in each case. Material from in between is being used for accelerator mass spectrometry of long-lived cosmogenic radionuclides. Because of instabilities in the gain of the electron multiplier, the noble gas abundances were not determined by the (standard) peak height method, but rather by isotope dilution. For that, about 1/3 of the sample gas was “spiked” with a gas mixture ($^{3}$He/$^{4}$He/$^{22}$Ne/$^{36}$Ar ~ 1.2 x 10$^{-8}$/1.1 x 10$^{-6}$/1.0 x 10$^{-10}$/3.8 x 10$^{-9}$ cc, Ne and Ar isotopic compositions atmospheric).

**Results:** As normal for iron meteorites, noble gases are purely spallogenic. Relevant results are listed in Table 1 (concentrations in 10$^{-8}$ cc g$^{-1}$ units; uncertainties in the last digits in parentheses; I = individual, S = shrapnel).

**Discussion:** Using the model calculations of [4], we can derive bounds on the pre-atmospheric size of the object and can define a possible range of cosmic ray exposure ages. Most useful is the $^{4}$He/$^{38}$Ar ratio (cf. Fig. 13 in [4]). Based on the maximum ratio of ~90 (S-C), a minimum radius for the meteoroid is ~85 cm. This implies a preatmospheric mass of >20,000 kg, in excellent agreement with the estimate of [1]. Furthermore, the shrapnel samples must originate from further inside the meteoroid than the individual (35–45 cm vs 15–25 cm). To reach agreement between $^{4}$He/$^{38}$Ar and $^{4}$He/$^{21}$Ne, a sulfur/ phosphorus content in the range 0.4–0.8 wt % contributing to $^{21}$Ne production is required (4, 5; cf. Fig. 11 in [4]). Conflicting cosmic ray exposure ages, however, follow from the relation between $^{4}$He/$^{38}$Ar ratio and $^{38}$Ar production rate according to [4]. While for the individual an age on the order of 400–500 Ma is indicated, estimates for the shrapnel samples are lower in the 200–300 Ma range. The discrepancy may be solved by the radionuclide measurements, which are in progress.

**References:** [1] Folco L. et al. 2010. *Science* 329:804. [2] Folco L. et al. 2011. *Geology* 39:179–182. [3] Weisberg M. K. et al. 2010. *Meteoritics & Planetary Science* 45:1530–1551. [4] Ammon K. et al. 2009. *Meteoritics & Planetary Science* 44:485–503; in detail at: http://noblegas.unibe.ch/index.php?content=noblegas/data. [5] Ammon K. et al. 2008. *Meteoritics & Planetary Science* 43:685–699.

<table><thead><tr><th>Sample</th><th><sup>3</sup>He</th><th><sup>4</sup>He</th><th><sup>21</sup>Ne</th><th><sup>38</sup>Ar</th></tr></thead><tbody><tr><td>I-C</td><td>147 (10)</td><td>622 (18)</td><td>1.59 (4)</td><td>9.47 (29)</td></tr><tr><td>I-g</td><td>138 (9)</td><td>604 (20)</td><td>1.58 (4)</td><td>8.20 (34)</td></tr><tr><td>S-C</td><td>44 (5)</td><td>214 (16)</td><td>0.42 (1)</td><td>2.39 (10)</td></tr><tr><td>S-f</td><td>41 (5)</td><td>193 (18)</td><td>0.35 (1)</td><td>2.31 (11)</td></tr></tbody></table>
## EXTREME CADMIUM AND THALLIUM ISOTOPE FRACTIONATIONS IN ENSTATITE CHONDRITES

C. S. Palk¹,², M. Rehkämper¹,², R. Andreasen¹,² and A. Stunt¹. ¹IARC, Department of Earth Science & Engineering, Imperial College, London SW7 2AZ, UK. E-mail: c.palk09@imperial.ac.uk. ²Natural History Museum, London SW7 5BD, UK.

**Introduction:** The extinct ²⁰⁵Pb-²⁰⁵Tl decay system ($t_{1/2}$ = 15 Myr) features two volatile elements and may hence be useful for studying volatile loss in the early solar system. Analyses of the Pb-Tl system are best combined with measurements of Cd isotope compositions to monitor stable isotope fractionations from evaporation and condensation [1, 2]. In this study, we measure Pb, Tl and Cd abundances and isotopic compositions in bulk samples of enstatite chondrites. To date, results have been obtained for Indarch (EH4), Abee (EH4), St. Mark's (EH5), MAC 02839 (EL3), PCA 91020 (EL3), and Khairpur (EL6). Data for additional samples will be available at the meeting.

**Results:** The Pb, Tl and Cd abundances of the samples display considerable and systematic variability. In particular, the EL3 and EH4 enstatite chondrites have much higher volatile element contents (of about 40–100 ppb Tl, 300–900 ppb Cd) than the EH5 and EL6 samples, which record more intense thermal metamorphism and feature ~5 ppb Tl and ~10–20 ppb Cd. The Pb abundances also show a similar offset between samples of petrologic types 3 and 4 vs. 5 and 6, but two of the meteorites (Indarch, St. Mark's) have Pb isotope compositions, which are indicative of pervasive contamination by terrestrial Pb.

The most extreme stable isotope fractionations were found in two EL chondrites (PCA 91020, Khairpur), which are depleted in light Cd isotopes and display $\epsilon^{114/110}$Cd values of about +70 (relative to a bulk silicate Earth with $\epsilon^{114/110}$Cd ≈ 0). Moderate Cd stable isotope effects with $\epsilon^{114/110}$Cd values of about +8 were furthermore identified for MAC 02839 and St. Mark's. Only Indarch and Abee feature essentially unfractionated Cd, relative to carbonaceous chondrites, with $\epsilon^{114/110}$Cd ≈ +3. In contrast, only a single sample (PCA 91020) displays a clearly fractionated Tl isotope composition characterized by $\epsilon^{205}$Tl ≈ +22, whereas all other meteorites have $\epsilon^{205}$Tl of between -2.9 and +0.8, similar or identical to the bulk silicate Earth value of -2.0 ± 0.5.

**Discussion:** The data obtained so far indicate that stable isotope fractionations are commonplace for Cd in enstatite chondrites. This is in accord with the results of earlier work [3], which found that Cd isotopes are an excellent monitor of parent body processes that effect the abundances of volatile elements. The only meteorite to display both large Cd and Tl stable isotope effects is the highly shocked (S5) sample PCA 91020 [4], possibly suggesting that Tl may be readily mobilized during shock metamorphism. Due to the presence of stable isotope fractionation for Cd and, at least in some samples, Tl, together with the terrestrial Pb contamination of two meteorites, it will be challenging to construct a ²⁰⁵Pb-²⁰⁵Tl parent body isochron for enstatite chondrites.

**References:** [1] Baker R. G. A. et al. 2010. *Earth and Planetary Science Letters* 291:39–47. [2] Andreasen R. et al. 2009. Abstract #A43. *Geochimica et Cosmochimica Acta* 73:13. [3] Wombacher F. et al. 2008. *Geochimica et Cosmochimica Acta* 72:646–667. [4] Rubin A. E. et al. 1997. *Geochimica et Cosmochimica Acta* 61:847–858.

## FE/MG COMPLEMENTARITY IN CHONDRULES AND MATRIX OF CARBONACEOUS CHONDRITES

H. Palme¹ and D.C. Hezel². ¹Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany. E-mail: herbert.palme@uni-koeln.de. ²Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicherstrasse 49b, D-50674 Köln.

**Introduction:** We have recently shown that matrices of carbonaceous chondrites (CC) are consistently high in SiO₂ and low in MgO while chondrules have the opposite signature [1]. The bulk CI-ratio of CC requires the formation of both components from a single reservoir [1, 2]. The distribution of Mg and Si between chondrules and matrix must have been established in the solar nebula. We show here that the same reasoning applies to Fe.

We have complemented recent chemical data by INAA on Mokoia (CV3) chondrules [2] by a large number of new matrix analyses. Fig. 1 indicates high Fe and low Mg for matrix and low Fe and high Mg for chondrules. Metal is absent in Mokoia. CC bulk Fe and Mg contents [3] plot between chondrules and matrix, although Fe is slightly variable, which is attributed to bulk reservoir fractionation [4]. Overall there is a clear complementary relationship between chondrules and matrix. Both thermal metamorphism and aqueous alteration would transport Fe from matrix into chondrules and thus erase the differences. Despite significant aqueous alteration of the Mokoia matrix the chondrules were not or only slightly affected [3].

A compilation of CC matrix data by [5] shows the same spread in matrix Fe and Mg as in Fig. 1. Chondrules should thus have a similar compositional range in Fe and Mg as in Fig. 1.

This suggests forsteritic olivine as a major chondrule component in CC. Since Fe, Ni and Co occur in chondritic ratios in Mokoia and Allende chondrules [3, 6, 7] Fe must have entered chondrules as Fe Ni-metal and was then oxidized during chondrule melting.

**References:** [1] Hezel D. C. and Palme H. 2010. *Earth and Planetary Science Letters* 280:85–93. [2] Hezel D. C. and Palme H. 2008. *Earth and Planetary Science Letters* 265:716–725. [3] Jones R. H. and Schilk A. J. 2009. *Geochimica et Cosmochimica Acta* 73:5854–5883. [4] Wolf D. and Palme H. 2001. *Meteoritics & Planetary Science* 36: 559–571. [4] Palme H. and Lodders K. 2009. Abstract #5243. Annual Meteoritical Society Meeting. [5] Huss G. R. et al. 2005. In: *Chondrites and the protoplanetary disk* (ASP Conference series, vol. 341), pp. 701–731. [6] Rubin A. E. and Wasson J. T. 1982. *Geochimica et Cosmochimica Acta* 51:1923–1937. [7] Palme H. and Spettel B. Unpublished data.

<figure><img src="image_25.png" /><figcaption>Fig. 1. Fe vs. Mg in matrix and chondrules of Mokoia.</figcaption></figure>
DISK DISPERSAL AND THE FORMATION OF PLANETARY
SYSTEMS

I. Pascucci. Lunar and Planetary Laboratory, The University of Arizona, AZ, USA. E-mail: pascucci@lpl.arizona.edu.

Gas-rich dust disks around young stars (hereafter, protoplanetary
disks) provide the raw material to build up planets. Thus, the time scale
over which they disperse and the physical mechanisms contributing to
their dispersal are key in understanding what type of planets can form
and on what time scale. Significant progress has been made in the past
few years in measuring the dispersal time scale of protoplanetary disks.
Surveys of nearby star-forming regions and associations have established
that by age 10 Myr only a few percent of premain sequence sun-like stars
still retain a gas-rich dust disk [1-3]. Still much debate exists on the disk
dispersal mechanisms and on their efficiency.

In this talk, I will discuss the theoretical mechanisms proposed to
explain the dispersal of protoplanetary disks with special emphasis on
viscous accretion, planet formation, and star-driven photoevaporation. I
will seek constraints from observations of protoplanetary disks and from
the Solar System to evaluate the role of these mechanisms in dispersing
primordial gas and dust. I will also present newly discovered gas lines
that can be used to trace star-driven photoevaporative flows and discuss
how to measure the rate at which disks lose their mass via
photoevaporation [4-6]. Finally, I will show how these disk dispersal
mechanisms impact the final architecture of planetary systems.

**References:** [1] Pascucci I. et al. 2006. *The Astrophysical Journal* 651:1177. [2] Hernandez J. et al. 2008. *The Astrophysical Journal* 686:1195. [3] Pascucci I. and Tachibana S. 2010. In *Protoplanetary dust: Astrophysical and cosmochemical perspectives*, edited by Apai D. and Lauretta D. Cambridge University Press. pp. 263–298. [4] Pascucci I. and Sterzik M. 2009. *The Astrophysical Journal* 702:724. [5] Pascucci I. et al. 2011. *The Astrophysical Journal*, in press (arXiv:1105.0045). [6] Sacco G., Flaccomio E., and Pascucci I. et al. In preparation.

FIRST REPORT OF SUEVITE FROM DHALA IMPACT
STRUCTURE, INDIA

J. K. Pati. Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad-211 002, India. E-mail: jkpati@yahoo.co.in.

**Introduction:** The Dhala structure (N 25°17′59.7″; E 78°8′3.1″) [1] is a confirmed impact structure [2] of Paleoproterozoic age [3] in the western part of the Archean Bundelkhand craton, India. The target rocks (2.5 Ga Archean Bundelkhand granitoids [3]) are covered by a thick (5–150 m) melt breccia sheet. This is, in turn, overlain by postimpact sediments (Dhala Group [4]) of unknown age followed by the Vindhyan Supergroup of rocks of Proterozoic age. In addition to impact melt breccia, the two other breccia types observed earlier include monomict granitoid breccia and another type of apparently lithic breccia.

**Dhala Suevite:** This latter, dark greenish gray to greenish brown, apparently lithic breccia contains altered microscopic melt clasts in a matrix dominated by clastic material. It occurs above the impact melt breccia with a gradational contact to the footwall. The sediments belonging to the Dhala Group occur with a sharp unconformable/erosional (?) contact above lithic breccia. The thickness of the melt clast-bearing breccia unit is about 1.5 m in the central elevated area of the impact structure. This rock comprises lithic clasts (20–30 vol%), mineral clasts (20–40 vol%), and melt clasts (1–5 vol%), besides martix, with a general clast to matrix ratio of 40:60. Sizes of mineral and lithic clasts range from <1 to 60 mm. The mineral clasts are angular to subrounded, whereas the lithic clasts are angular to subangular. The mineral clasts include quartz, feldspar, biotite, apatite, zircon, and opaques. The dominant shock features observed in quartz and feldspar grains are planar deformation features (PDF): one to four sets of PDF in quartz clasts and one or two sets of PDF in feldspar grains. Zircon grains (up to 100 µm in size) show fractures cross-cutting the oscillatory zoning. A few zircon grains show granular texture. The melt clasts are pale to dark green, pale to dark brown, dark gray and reddish brown. They vary in size from <5 mm to >40 mm, and in shape from circular, elliptical, bomb-like, globular, spindle-shape, and fishing-hook to barrel shapes. They are only partially devitrified and remain largely isotropic. Some of the reddish brown melt clasts contain unmelted mineral and lithic clasts that are mostly rounded in shape and show reaction rims with the surrounding melt with microlites. These microclasts show deformation in the form of fractures, bent twin lamelle and shock deformation features (like PDFs). The pale brown colored melt clasts contain randomly distributed and oriented pale green microlites. Many melt clasts show fluidal texture.

**Conclusion:** This is the first report of a melt clast-bearing breccia containing diagnostic shock metamorphic evidence from the Dhala structure, India. The characteristics of this breccia define it as suevite. The oldest suevite (1.85 Ga) previously reported derives from the Sudbury structure, Canada [5]. Once the age of the Dhala impact event will be better constrained, the associated suevite could possibly become the oldest occurrence of this important type of impact breccia.

**Acknowledgments:** J. K. P. thanks Uwe Reimold, Germany, for his continued help and support. PLANEX is also thanked for their research support.

**References:** [1] Pati J. K. 2005. *Meteoritics & Planetary Science* 40:A121. [2] Pati J. K. et al. 2008. *Meteoritics & Planetary Science* 43:1383–1398. [3] Pati J. K. et al. 2010. Geological Society of America Special Paper 465. pp. 571–591. [4] Jain S. C. et al. 2001. *Geological Survey of India Special Publication* 64:289–297. [5] French B. M. 1998. Lunar and Planetary Institute, Houston, TX, Contribution CB-954. 120 p.
5476

IN SITU SYNCHROTRON X-RAY TRANSMISSION MICROSCOPY
OF CR CHONDRITES QUE 99177 AND GRA 95229

Z. Peeters¹, C. M. O'D. Alexander¹, H. Changela², L. R. Nittler¹, S. Price¹ and R. M. Stroud². ¹Carnegie Institution of Washington, Washington, DC 20015, USA. E-mail: zpeeters@dtm.ciw.edu. ²Naval Research Laboratory, Code 6s366, 4555 Overlook Ave. SW, Washington, DC 20375-532, USA.

**Introduction:** As part of a coordinated, multiple-analysis approach to understanding the structure and origin of the insoluble organic matter (IOM) in primitive meteorites, we have performed X-ray absorption near-edge spectroscopy (XANES) of matrix materials from two CR chondrites, QUE 99177 and GRA 95229. QUE 99177 is a very primitive CR3 chondrite with little evidence for parent-body alteration [1], whereas GRA 95229 is a more aqueous altered CR2. Previous nanoSIMS isotopic mapping of sections of QUE 99177 [2, 3] revealed carbon to be largely distributed throughout the matrix as sub-?m sized particles with a wide range of H, C and N isotopic compositions. However, during mapping, an unusually large (8.4 × 2.8 µm) carbon-rich vein was discovered. The vein was targeted for focussed ion-beam (FIB) lift-out with the Carnegie Zeiss Auriga FIB-SEM. For comparison, FIB lift-out sections were also extracted from a different (random) part of the QUE 99177 matrix and from a polished section of GRA95229. The FIB sections were taken to the scanning transmission X-ray microscope (STXM) on beamline 5.3.2.2 at the Advanced Light Source in Berkeley for XANES mapping.

**Results and Discussion:** The carbon-rich vein in QUE 99177, as measured by nanoSIMS from the top of the inclusion (i.e., before lift-out) was enriched in D (δD = +6000 ‰) and in ¹⁵N (δ¹⁵N = +500 ‰), significantly higher than the bulk IOM composition for this meteorite (δD = +3139 ‰, δ¹⁵N = +187 ‰ [4]). The FIB section showed that the carbon-rich vein extended 5.5 µm into the meteorite. C-edge XANES mapping of the carbon-rich vein revealed three bands (aromatic or vinylic carbon bonds, carbonyl bonds, and carboxyl bonds) commonly seen in chondritic IOM, plus carbonate. Compared to other carbon in the FIB sections of QUE 99177 and GRA 95229, the C-XANES spectrum of the C-rich vein appears slightly different, both in the positions and ratios of the observed absorption features. Similarly, the N-edge XANES spectra of the vein differs from the other studied materials in showing significantly more absorption due to imidyl and nitrile bonds. Planned TEM and nanoSIMS isotopic analysis of the FIB sections will allow detailed sub-?m correlation of chemical, mineralogical and isotopic data to better understand the nature of the organic matter and its relation to inorganic matrix materials.

**References:** [1] Abreu N. M. and Brearley A. J. 2010. *Geochimica et Cosmochimica Acta* 74:1146-1171. [2] Nguyen A. N. et al. 2008. *Meteoritics & Planetary Science* 43:A5277. [3] Floss C. and Stadermann F. J. 2009. *The Astrophysical Journal* 697:1242-1255. [4] Alexander C. M. O'D. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4380-4403.

5353

ABUNDANCES OF RADIOACTIVE ELEMENTS ON THE SURFACE
OF MERCURY: FIRST RESULTS FROM THE MESSENGER
GAMMA-RAY SPECTROMETER

P. N. Peplowski¹, D. K. Hamara², D. J. Lawrence¹, T. J. McCoy³, W. V. Boynton², L. G. Evans⁴, E. A. Rhodes¹, S. C. Solomon⁵, L. R. Nittler⁵ and A. L. Sprague². ¹Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA. ²University of Arizona, Tucson, AZ 85721, USA. ³Smithsonian Institution, Washington, DC 20560-0119, USA. ⁴Computer Sciences Corporation, Lanham-Seabrook, MD 20706, USA. ⁵Carnegie Institution of Washington, Washington, DC 20015, USA.

**Introduction:** On 18 March 2011, MESSENGER became the first spacecraft to enter orbit around Mercury, inaugurating a one-year campaign of orbital operations [1]. This investigation includes mapping the surface composition from orbit using the MESSENGER Gamma-Ray Spectrometer (GRS) [2]. Data from the GRS can be used to determine the surface composition to depths of tens of centimeters by measuring gamma rays originating from both radioactive elements (K, Th, and U) and excitation of stable elements (e.g., Si, Fe, Ti, O) by interactions with incident galactic cosmic rays. This work details the measurement of K and Th abundances on the surface, the results of which have important implications for our understanding of the formation and thermal history of Mercury [3].

**Preliminary Results:** GRS data acquired during the first month of orbital operations have been used to determine the average abundances of K (1078 ± 49 ppm) and Th (0.173 ± 0.088 ppm) in the northern hemisphere of Mercury. The K/Th ratio in this region is 6230 ± 3180, which is within the range of values for the other terrestrial planets but is significantly higher than the average lunar value of 360 [4].

**Discussion:** Ratios of the volatile incompatible K to the refractory incompatible Th provide insights into volatile element depletions in planetary bodies. The K/Th ratio for the surface of Mercury is similar to that for Mars (4000–7000 over 95% of the surface [5]). The K/Th ratio for Mercury is also similar to that for Martian meteorites. Absolute surface abundances for Mercury are a factor of three to four lower than for Mars, however, probably reflecting the enhancement of K and Th abundances at the Martian surface by aqueous processes. The K/Th ratio of Mercury, particularly when coupled with the high S abundance of Mercury [6], suggests that evaporation or refractory condensation models [3] for the formation of Mercury are not viable. These models should produce volatile-poor compositions, counter to the observations presented here. Other models are less constrained by these data, although chondritic melting models appear to predict higher Th abundances (approximately 1 ppm) [4] than observed. Future determination of U abundances from GRS observations should provide additional constraints on these models.

**References:** [1] Solomon S. C. et al. 2007. *Space Science Review* 131:3-39. [2] Goldsten J. O. et al. 2007. *Space Science Review* 131:339-391. [3] Taylor G. J. and Scott E. R. D. 2003. Treatise on Geochemistry, vol. 1, pp. 477-485. [4] Taylor G. J. et al. 2006. *Journal of Geophysical Research* 111, E03S06-E03S10. [5] Taylor G. J. et al. 2006. *Journal of Geophysical Research* 111, E03S06. [6] Weider S. Z. et al. This conference.
A COMPARATIVE STUDY OF TROILITE IN VARIOUS METEORITES USING MÖSSBAUER SPECTROSCOPY WITH A HIGH VELOCITY RESOLUTION

E. V. Petrova¹, V. I. Grokhovsky¹, M. I. Oshtrakh¹, R. N. Kolunin¹ and V. A. Semionkin¹,². ¹Faculty of Physical Techniques and Devices for Quality Control, Ural Federal University, Ekaterinburg, 620002, Russian Federation. E-mail: grokh47@mail.ru. ²Faculty of Experimental Physics, Ural Federal University, Ekaterinburg, 620002, Russian Federation.

**Introduction:** Troilite FeS is the main sulfur mineral in the extraterrestrial matter. FeS was found in various meteorites in various forms (inclusions in iron meteorites or component of ordinary chondrites). Therefore, troilite may vary in different meteorites. To study meteoritic troilite Mössbauer spectroscopy with a high velocity resolution was used. This technique is useful for analysis of iron hyperfine parameters with high accuracy.

**Experimental:** Samples of various ordinary chondrites (Farmington L5, Tsarev L5, Vengerovo H6, Richardton H5, Saratov L4, Zvonkov H6) and FeS extracted from iron meteorite Sikhote-Alin IIAB were prepared as powder. Mössbauer spectra of these samples were measured using automated precision Mössbauer spectrometric system with a high velocity resolution [1] at room temperature in 4096 channels.

**Results and Discussion:** Mössbauer spectra of ordinary chondrites demonstrated usual complicated pattern with three magnetic sextets related to Fe-Ni alloy and FeS and five quadrupole doublets related to olivine, pyroxene and iron oxide. Mössbauer spectrum of troilite extracted from Sikhote-Alin consists of one magnetic sextet. It was interesting to observe variation of the values of magnetic hyperfine field for troilite in studied meteorites. This variation was in the range of approximately 308–323 kOe. The values of magnetic hyperfine field for troilite in ordinary chondrites may be divided in two groups with small differences of the field outside the instrumental error. The largest value of magnetic hyperfine field for troilite in ordinary chondrites was approximately 314 kOe for Zvonkov H6 while the smallest one was of approximately 308 kOe for Farmington L5. In contrast, the value of magnetic hyperfine field for troilite from Sikhote-Alin meteorite was approximately 323 kOe. These differences may be a result of small structural variations and deviations in stoichiometry in troilite from different meteorites. It is possible that small structural and composition variations reflect differences in mineral formation in the studied meteorites. Therefore, accurate Mössbauer hyperfine parameters of troilite may provide additional information for analysis of meteorites formation and evolution.

**Acknowledgments:** This work was supported in part by the Federal Grant-in-Aid Program "Human Capital for Science and Education in Innovative Russia" (Governmental Contracts No. P1154 and No 14.740.11.1006).

**Reference:** [1] Semionkin V. A. et al. 2010. *Bulletin of the Russian Academy of Sciences: Physics* 74:416–420.

IN SITU NANOSIMS MEASUREMENT OF D/H RATIO AND H EMISSION IN MATRIX ANALOGUES

L. Piani¹, F. Robert¹ and L. Remusat¹. ¹LMCM, CNRS-MNHN, UMR7202, Case 52, 57 Rue Cuvier, 75005 Paris, France, E-mail: lpiani@mnhn.fr.

**Introduction:** The nature and consequences of the possible interactions between water/clay minerals and insoluble organic matter (IOM) on chondrites is still debated [1,2]. The *in situ* comparison of their respective D/H ratio should shed new light on the processes that occurred during the hydrothermal alteration on chondrites parent bodies. A decade ago, SIMS measurements using negative primary oxygen beam were performed to assess the H isotopic composition of ordinary chondrites (OC) matrices [3]. Under these analytical conditions, H emission for H-bearing silicates is higher than that for IOM: up to 92% of secondary H⁺ extracted from the matrix comes from hydroxylated minerals. Thus, the D/H ratios of the H-bearing silicates in matrix could be measured *in situ* with this method but the D/H ratio of the associated IOM has to be determined. An attempt has been tested by [4] with a Cs⁺ primary beam on the ims 1280 ion microprobe. However, such a measurement is challenging: in their analytical conditions (1) the H⁻ emission between IOM and phyllosilicates are not markedly different (higher for the phyllosilicates by only a factor 3 to 10) and (2) “matrix effects” modify the D/H ratio. In this context, we have investigated the H⁻ emission and the instrumental H isotopic fractionation on laboratory prepared mixtures of phyllosilicates and IOM with NanoSIMS.

**Experimental:** Terrestrial montmorillonite (hereafter referred to as Mtm) having D/H = 143 × 10⁻⁶, terrestrial type III kerogen (D/H = 141 × 10⁻⁶) and the IOM isolated from the OC GRO 95502 (D/H = 669 × 10⁻⁶ [2]) were mixed. The Mtm was mixed with either the kerogen or the IOM in variable proportions. Analyses were performed using Cs⁺ and O⁻ primary beams. The Hemission (and C⁻, OH⁻, OD⁻, Si⁻ for Cs⁺) and the D/H ratio for different laboratory prepared mixtures were determined.

**Results:** *I. O⁻ Primary Ion Beam.* The emission yields of H for the IOM and Mtm are similar: 46 and 45 cps/pA, respectively. Consequently, the D/H ratio of the mixings should only depend on the proportion of each end-member: the measured D/H ratios of the mixtures are consistent with mass balance predictions.

*II. Cs⁺ Primary Ion Beam.* H and OH emission yields for the IOM are respectively 20 and 2 times higher than those for the Mtm. Therefore, in mixtures (natural or not), the cross contributions of IOM and Mtm on both the D/H and the OD/OH ratios cannot be neglected. Furthermore, the H and OH emission yields for the 50/50 (wt%) IOM and Mtm mixture are enhanced by a factor of 1.6 and 4.0, respectively, compared with those measured for pure IOM. Measured D/H ratios in this IOM and Mtm mixture is lower than expected by calculation using the emission yields of the pure end-members: 404 ± 22 × 10⁻⁶ instead of 454 × 10⁻⁶. Since the mixture OH/H ratio is closer to Mtm than expected, this isotopic effect likely results from an enhanced contribution of the Mtm on H and OH due to the addition of the carbonaceous compound (IOM). Further experiments are in progress to better constrain this matrix effect.

**References:** [1] Remusat L. et al. 2010. *The Astrophysical Journal* 713:1048–1058. [2] Alexander C. M. O’D. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4380–4403. [3] Deloule E and Robert F. 1995. *Geochimica et Cosmochimica Acta* 59:4695–4706. [4] Bonal L. et al. 2010. *Geochimica et Cosmochimica Acta* 74:6590–6609.
APPLICATION OF LICHENOMETRY TO METEORITE STUDIES

J. M. Pillinger¹, C. T. Pillinger¹, M. Powell² and M. Butler³. ¹Planetary and Space Sciences Research Institute, The Open University, Milton Keynes MK7 6AA, UK. ²15, Rotten Row, Riseley MK44 1EJ, UK. ³96, Townfield Road, Flitwick MK45 1JG, UK. E-mail: j.m.pillinger@open.ac.uk.

**Introduction:** The lichen colonisation of a large, weathered, ordinary chondrite that had been surface exposed in Wiltshire, UK, for numerous decades, was studied. As the terrestrial provenance of the meteorite was unclear, it was proposed that an examination of the lichens present on the surface may offer confirmation of the geographical location at which it was reported, at least at the continent level. Additionally using the technique of lichenometry [1] information about the time of exposure at the location was sought. Lichen growths on meteorites exposed to the natural environment are not uncommon; they are considered by some to adversely affect the appearance of the specimen. A study of the lichens on the Ella Island (Greenland) meteorite demonstrated early colonisation of a fall [2]. Unfortunately, the meteorite studied in the work reported here remained in storage for 20 years after removal from the exposed location. Nevertheless the lichens were in sufficiently good state of preservation to allow identification. The community is described and discussed.

**Results:** Eight species of lichen have been named on the meteorite with some degree of certainty. These include the most conspicuous species and were determined by simple inspection as *Diploicia canescens* (rare), *Lecanora albescens* (rare), *L. campestris* (occassional), *L. dispersa* (occasional), *L. muralis* (occasional), *Phaeophyscia orbicularis* (occasional), *Physcia adscendens* (rare) and *Verrucaria fuscella* (rare). One small thallus was present that strongly resembles *Caloplaca arcis* (rare). Large colonies of a fertile *Caloplaca* species (frequent) was provisionally identified as *Caloplaca holocarpa* sens. str as was *Amandinea punctata* (occasional). Large areas of sterile crust, forming a background to the more distinctive lichens were present in some quantity on the meteorite and included *Lecania erysibe* (abundant) and possibly *Caloplaca chlorina* (abundant). A tentative identification was of *Verrucaria muralis* (rare). Two thalli of *Lecanora campestris* measured 6.0 × 3.2 cm and 4.3 × 3.5 cm respectively. Two thalli of *L. muralis* measured 3.6 × 2.0 cm and 2.2 × 1.5 cm. A single thallus of *Diploicia canescens* measured 1.7 cm in diameter.

**Discussion:** The meteorite had not acquired any of the specialist lichens associated with the sarsen stones of Wiltshire, nor specialized iron species. The meteorite flora is reminiscent of that of ironstones and iron-rich sandstones (gravestones) and some types of brick: no species associated with a non-UK origin were identified. The community is consistent with exposure at a poorly eutrophic site where nutrients from bird droppings is low. All species were considered pioneers of bare rock thus a time of decades of environmental exposure at the Wiltshire location is not inconsistent by comparison to similar colonies on dated gravestones. Study of further meteorite finds exhibiting lichen colonisation may produce a useful dataset allowing conclusions to be reached about exposure time on Earth, location and climatic conditions endured.

**References:** [1] Winchester V. 1998. *Botanical Journal of the Linnean Society* 96:57–68. [2] Hansen E. S. and Graff-Petersen P. 1986. *Lichenologist* 18:71–78.

EVALUATION OF VARIOUS HYPOTHESES RELATING TO THE LOCATION OF THE FALL AND THE SUBSEQUENT HISTORY OF A LARGE METEORITE LATELY RECOVERED IN WILTSHIRE, UK

C. T. Pillinger and J. M. Pillinger. Planetary and Space Sciences Research Institute, The Open University, Milton Keynes, MK7 67AA, UK. E-mail: c.t.pillinger@open.ac.uk.

**Introduction:** A large, 60 kg, weathered meteorite was reported to have been in the UK for at least 60 years when it was taken to the Natural History Museum, London, twenty years ago. Previous to 1991, eye witness and photographic evidence demonstrate that it rested for many years near to the front door of an imposing country house in Wiltshire. It was reputed to have been either brought to the UK or otherwise collected locally by Lt Col Frederick George Glyn Bailey in the early twentieth century. The descendants of FGG Bailey have made the specimen available and encouraged a study to ascertain more information about the meteorite before arranging for it to be on permanent local public display. The meteorite is described in an accompanying abstract.

The presence of a meteorite of unknown terrestrial provenance offers a considerable challenge. While a scientific examination [1] can offer some information, much depends on an exhaustive examination of contemporary documents. Some while ago we were able to piece together a detailed account of the circumstances surrounding the fall of the Wold Cottage meteorite to show it should not be considered as just any old ordinary chondrite [2].

**Results:** The life and times of Lt Col FGG Bailey have been researched thoroughly in order to highlight any possible links he may have had to a meteorite find either in the UK or the rest of the World. The meteorite is inextricably linked to the house where it was located for so many years: Lake House. Thus the history of the Lake House Estate, the house, its previous occupants and their associates, including their interests and scientific aptitude, have also been studied in an attempt to establish the earthly provenance of the specimen.

Several hypotheses have been considered to account for the presence of the meteorite in Wiltshire. Necessarily these hypotheses revolve round the people who could conceivably have had an involvement in the meteorite's history on Earth. Questions regarding whether they might have had the motivation, opportunity and capability to recognize a meteorite have been considered. Even if they did, they would have needed the resources to move such a large stone and have the desire to collect and display it.

A document trail has been initiated which provides new and verifiable information about the terrestrial provenance of the meteorite associated with Lake House. The latest findings will be presented together with an up-to-date probability/possibility assessment of the place of first collection and hence the site of the fall. The work reported here may offer some pointers to others searching archive material for reports connected to meteorite related events.

**References:** [1] Pillinger C. T. et al. This conference. [2] Pillinger C. T. and Pillinger J. M. 1996. *Meteoritics & Planetary Science* 31:589–605.
5321

THE DANEBURY IRON AGE METEORITE

C. T. Pillinger¹, J. M. Pillinger¹, R. C. Greenwood¹, D. Johnson¹, A. G. Tindle², A. J. T. Jull³ and D. W. H. Allen⁴. ¹PSSRI ²EES, Open University, Milton Keynes MK7 6AA, UK. ³University of Arizona, Tucson AZ85721, USA. ⁴Hampshire County Museums Service, Winchester UK. E-mail: c.t.pillinger@open.ac.uk.

**Introduction:** The Danebury meteorite's existence was first reported in the Meteoritical Bulletin in 1991 [1] following an effort to characterize metal containing artifacts recovered in 1974 from an archaeological dig conducted at the site of an Iron Age hillfort, Danebury Ring, in the county of Hampshire, England. After that initial report the object was "mislaid" and no further details appeared. In 2008 we initiated a search for the specimen and it has been recovered, sadly less a central slice removed to make a probe mount. We are now able to provide a better petrological description using a PTS of an interior cut of the 20 g surviving mass (H5, low weathering grade W1/2) and more information about the circumstances under which the meteorite was found.

**The Anatomy of a Hill Fort:** The Iron Age is a period of prehistory which in Britain extends from around 800 BC until the Roman occupation of the mid first century AD. Southern Britain abounds with sites affording evidence of a turbulent period when inhabited locations are identified by the emphasis placed on defence fortifications. Danebury Ring can be regarded as a classic Iron Age hill fort site. It has been studied throughout a major campaign of annual excavations undertaken between 1969 and 1988 [2]. Systematic study of the 5 ha enclosure revealed evidence for scores of buildings. Hundreds of thousands of pottery shards, bone fragments as well as numerous objects of stone and metal were located with 10 cm accuracy before being recovered from some 2500 pits.

**Iron Age Grain Pits:** The Iron Age populace of Britain were essentially farmers. The pits excavated on Danebury Hill were dug originally to store the summer's grain harvest over the winter while the crop to be consumed immediately was kept above ground in granaries. Some budding Iron Age scientist had discovered that whilst burying grain might sound counter-productive, grain placed in a chalk pit capped with clay begins to ferment at the margins creating an anaerobic environment where the rest of the material survives for later use. The thousands of grain pits excavated at Danebury attest the efficacy of the science.

**The Terrestrial Residence History of the Meteorite:** The Danebury meteorite was recovered was excavated from the back-filled grain pit #706. Its stratigraphic location revealed that the meteorite went into the hole during a second episode of the back-filling process. Pits no longer in use were initially refilled with the spoil from newly dug pits. After subsidence (2nd generation filling) "pot-holes" were flattened off with spoil from even later pits. The location of the meteorite in the 2nd level implies it could have been where it was found because that is the place it actually fell. We have measured ¹⁴C weathering age of the meteorite and obtained a value of 2350 ± 120 BP. This date coincides with a period identified when the fort was highly active i.e. concurrent with construction of its most sophisticated fortifications.

**References:** [1] Meteoritical Bulletin 70. 1991. *Meteoritics* 26:68–69. [2] Cunliffe B. et al. 1984. Council for British Archeology Research Report 52.

5326

THE METEORITE FROM LAKE HOUSE

C. T. Pillinger¹, J. M. Pillinger¹, R. C. Greenwood¹, D. Johnson¹, A. G. Tindle², A. J. T. Jull³ and M. Ashcroft⁴. ¹PSSRI. ²EES Open University, Milton Keynes MK7 6AA, UK. ³AMF, University of Arizona, Tucson AZ85721, USA. ⁴Magna Parva Ltd., Bardon Hill, LE67 1UB, UK. E-mail: c.t.pillinger@open.ac.uk.

**Introduction:** In 1991 a very big meteorite (>60 kg, dimensions: diameter 50 cm × height 40 cm) was brought to the Natural History Museum by the then occupier of Lake House, a country mansion in Wiltshire, UK, associated with a large estate of the same name. The circumstances concerning the likely origins of this "find" are dealt with in a companion abstract [1]. Our attention was attracted to it because of its proximity to Danebury Hill (20 km east), where the only British meteorite "find", collected under controlled circumstances, was located in 1974 [2]. If the large meteorite from Lake House turned out to be paired with the much smaller Danebury find, then the mystery surrounding its origin would be instantly solved.

The sample from Lake House was confirmed as a meteorite by Robert Hutchison [3] and subsequently returned to its owners. Our electron microprobe data from a PTS made from a chip taken at the OU suggest it should be classified as type H5 similar to our assignment for Danebury.

**Petrography:** The sample is a heavily weathered (W5) [4], moderately shocked (S4) [5], equilibrated ordinary chondrite (H5). Distinct chondrules are present, but these tend to have poorly defined boundaries. Porphyritic types predominate, but barred olivine and radial pyroxene textured chondrules are also common. Chondrule mesostasis is recrystallized, with grain sizes generally below 50 µm. The sample is cut by a network of veins, up to 2 mm thick, filled with secondary weathering products.

**Discussion:** In respect of weathering characteristics, the two specimens are entirely different—areas in our Danebury PTS are grade W1 and the whole specimen is no worse than W2, whereas the meteorite from Lake House is W5. The thin section of the latter was made from a near surface chip of the highly corroded sample; the Danebury analyses were performed using a fresh interior portion. Not wishing to have what appeared to be a very delicate specimen disintegrate, we attempted to extract an interior core from the larger meteorite using an experimental drill being developed for robotic space missions. Much to our surprise prolonged drilling was unable to penetrate more than a millimeter into a location where the crust appeared to be absent. In earlier performance tests the drill had no difficulty in obtaining 1.5 cm long cores from basalt and concrete. We conclude that the interior of the meteorite from Lake House may not be as weathered as it appears from the outside.

Because we had obtained a very precise terrestrial weathering age for Danebury, samples of the meteorite from Lake House were removed for Accelerator Mass Spectrometry terrestrial residence dating. The first sample studied has a ¹⁴C weathering age of 10,600 ± 1800 years BP. A second run with a better specimen gave 9500 ± 560 years. The large meteorite is clearly not related to the small one authenticated from the archeological site a few kilometers away. Given that it is a single stone, the meteorite represents an unusually large ordinary chondrite find.

**References:** [1] Pillinger C. T. and Pillinger J. M. This conference. [2] Pillinger C. T. et al. This conference. [3] Personal communication. [4] Wlotzka F. 1993. *Meteoritics* 28:460. [5] Stöffler D. et al. 1991. *Geochimica et Cosmochimica Acta* 55:3845–3867.
5080

MELT ON THE STRIATED SURFACE OF SHATTER CONES IN BASALT

L. Pittarello¹, C. Koeberl¹,² and A. P. Crósta³. ¹Department of Lithospheric Research, University of Vienna, A-1090 Vienna. E-mail: lidia.pittarello@univie.ac.at. ²Natural History Museum, A-1010 Vienna. ³Department of Geology & Natural Resources, Institute of Geosciences, Campinas, SP, Brazil.

**Introduction:** Shatter cones are one of the most reliable types of macroscopic evidence of shock metamorphism [1]. The local occurrence of melt on the striated surfaces of shatter cones, in the form of glassy siliceous spherules decorating the topographic lows of the striations, has been the described from large impact structures, such as Vredefort [e.g., 2, 3]. Different models [4-6] were proposed for melt formation on the surface of shatter cones, but none of them can explain all the observations [7]. Furthermore, a recent study on shock deformation distribution within shatter cones has demonstrated that the deformation in not localized exclusively on the surface and that the recorded shock peak is higher than how previously assumed [8]. Here we describe a homogeneous melt layer decorating the striated surface of shatter cones formed in fine-grained basalts, from the Vista Alegre impact structure, a 9.5 km diameter structure recently confirmed as being of impact origin, excavated in the basalts of the Paraná Basin, Brazil [9].

**Results:** A cross section of the cm-sized shatter cones from the Vista Alegre reveals several fractures parallel to the striated surface. Such fractures are generally filled by an ultracataclasite (grain size <1 µm), where some clasts of pyroxene are preserved. Along the striated surface a 50-µm-thick homogeneous film of melt is locally preserved. The melt is locally quenched, forming dendritic microlites 4-5 µm in size, with a mixed composition between plagioclase and augitic pyroxene. Raman micro-spectroscopy has confirmed the occurrence of amorphous material, but its exact nature still needs to be confirmed. No shatter cones have been reported from the other impact craters in basalts (Lonar, India and Logancha, Russia), and those from the Vargeão impact structure, Brazil, have not yet been studied in detail. One possible explanation for melt occurrence in basaltic shatter cones is the lower melting temperature of basalt compared to silica-rich rocks; another that the lack of evidence for friction could suggest a shock origin for the melt.

**References:** [1] French B. and Koeberl C. 2010. *Earth Science Reviews* 98:123-170. [2] Gay N. C. et al. 1978. *Earth and Planetary Science Letters* 41:372-380. [3] Nicolaysen L. O. and Reimold W. U. 1999. *Journal of Geophysical Research* 104:4911-4930. [4] Gibson H. M and Spray J. G. 1998. *Meteoritics & Planetary Science* 33:329-336. [5] Sagy A. et al. 2002. *Nature* 418:310-313. [6] Baratoux D. and Melosh H. J. 2003. *Earth and Planetary Science Letters* 216:43-54. [7] Wieland F. et al. 2006. *Meteoritics & Planeteray Science* 41:1737-1759. [8] Ferrière L. and Osinski G. R. 2010. Abstract #5273. *Meteoritics & Planetary Science* 45:A53. [9] Crósta A. P. et al. 2010. *Meteoritics & Planetary Science* 45:181-194.

Back-scattered FE-SEM image of a microlitic aggregate.

<figure><img src="image_26.png" /></figure>

5081

PETRO-CHEMICAL CHARACTERIZATION OF THE UNIQUE IMPACT CRATER ON EARTH IN SILICEOUS VOLCANIC ROCKS: THE EL'GYGYTGYN DRILL CORE

L. Pittarello¹, C. Koeberl¹,² and the El'gygytgyn Scientific Party. ¹Department of Lithospheric Research, University of Vienna, A-1090 Vienna. E-mail: lidia.pittarello@univie.ac.at. ²Natural History Museum, A-1010 Vienna.

**Introduction:** The El'gygytgyn impact structure, 3.6 Ma old and 18 km in diameter, was excavated in Late Cretaceous siliceous volcanic rocks of the central Chukotka, northeastern Russia [1]. It is the only known terrestrial impact structure formed in siliceous volcanic target and thus enables to investigate shock metamorphism in such lithologies. The impact structure, filled by a lake 12 km in diameter, was drilled in 2009 during an ICDP drilling project [2]. The drill core, penetrating through post-impact sediments, impactites and the fractured igneous basement, was sampled and studied through petrographic (optical and electron microscope, Raman micro-spectroscopy) and chemical analyses (XRF and INAA), from 316.08 m to 517.30 m in depth.

**Results:**

**Core Stratigraphy:** The main rock types of the crater basement are ignimbrite, tuff, and lava of rhyolitic composition; rarely from andesite and dacite [3]. The simplified stratigraphy of the core is: (1) 316-385 m impact lithic breccia including volcanic-like and melt clasts, locally with shocked minerals, in a fine-grained clastic matrix; (2) 385-427 m transition zone characterized by a reddish breccia alternating with dark veins of basalt-like melt; (3) 427-517 m greenish ignimbrite-like rock, with abundant melt particles, quartz-free and elongated parallel to flattening direction. This latter formation is crosscut by abundant fractures locally filled by carbonate, silicate and clay veins.

**Shock Features:** The abundance of shock features decreases rapidly from the top to the bottom of the studied core section, being almost absent in the brecciated layer (3). Specifically, in the layer (1) clasts of volcanic-like rocks include shocked phenocrysts. Locally, quite fresh PDFs occur in quartz grains, with up to 3 sets per grain. In the matrix, quartz grains are commonly either completely transformed into diaplectic glass or unshocked. Some µm-sized grains of coesite occur in quartz grains. Some feldpars contain PDFs and evidence of melting. The mafic minerals (biotite, amphibole) are rare and generally highly altered locally kinked or partially melted, maybe for volcanic or tectonic processes. In layer (3) no or very few shock features occur, with rare incipient basal PDFs in quartz.

**Geochemistry:** The bulk analyses of layers (1) and (3) are consistent with a trachy-rhyolite composition. Clasts in the breccia (1), separately analyzed, cover the full range of composition but are mainly rhyolites. On the other hand, the melt particles included in (3) show a mafic to intermediate composition. In (2) some basalt-like samples, with high loss of ignition, contains anomalous content of Co, Cr, and Ni, and will further investigated to relate such contamination to hydrothermal alteration or a possible meteoritic component.

**Acknowledgment:** This work was supported by the Austrian Science Foundation (FWF) project P21821-N19.

**References:** [1] Gurov E. P. et al. 1979. Abstract. 10th Lunar and Planetary Science Conference. pp. 479-481. [2] Melles M. et al. 2011 *Scientific Drilling* 11:29-40. [3] Gurov E. P. et al. 2005. *Geochimica et Cosmochimica Acta* Special Paper 384:391-412.
IMPACT MELT IN SMALL SIMPLE LUNAR HIGHLANDS CRATERS

J. B. Plescia¹ and M. J. Cintala². ¹Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723, USA. E-mail: jeffrey.plescia@jhuapl.edu. ²Code KR, NASA, Johnson Space Center, Houston, TX 77058, USA.

**Introduction:** Impact melt is a typical characteristic of large complex impact craters on all of the terrestrial planets; it also occurs in some larger simple craters. The melt forms pools on the crater floor, flows beyond the rim, and drapes the inner crater wall. Melt deposits have been assumed to only be associated with larger simple craters and complex craters [1-6] with the smallest recognized crater with melt being approximately 750 m in diameter. Theoretical models of impact melt generation suggested that only small volumes would be produced [7-8] and most of that would be ejected from the crater interior.

**Observations:** LRO LROC images show that impact-melt deposits are recognized associated with simple highlands craters down to diameters of approximately 200 m. The melt forms pools on the crater floor, veneer on the crater walls, flows on the crater and ejecta outside the crater. Melt also forms stringers of dark material extending over the rim and across the surface. Such melt deposits are relatively rare, and can be recognized only in some fresh craters. These observations indicate that identifiable quantities of impact melt can be produced in small impacts and the presence of such deposits shows that the material can be aggregated into recognizable deposits. Estimates of the amount of melt present in craters with melt pools on the floor [10⁻³–10⁻⁵ km³] are of the same order of magnitude as that estimated from the models of melt generation [8].

**Interpretations:** While target properties can influence the amount of melt produced during an impact, the physical properties of the highland megaregolith are more or less uniform in the context of impact crater formation. Similarly, variations in the properties of the projectile do not significantly change the amount of melt produced. Thus, some other aspect of the cratering process must be responsible. It is concluded that these craters represent vertical impacts rather than the more common oblique events. For a vertical impact, [10–11] the shock pressures can be larger and they are focused at the center of the crater. In such cases more melt is produced and less is ejected than in an oblique event.

**Conclusions:** Impact melt is observed in fresh simple lunar highlands craters as small as approximately 200 m diameter. Such deposits are rare. Small craters with recognizable impact melt are interpreted to represent vertical, rather than oblique, impacts.

**References:** [1] Dence M. 1971. *Journal of Geophysical Research* 76:5552–5565. [2] Moore H. 1972. Apollo 16 Preliminary Science Report, NASA SP315:29-45-29-51. [3] Howard K. and Wilshire H. 1975. *Journal Research U.S.G.S.* 3:237–251. [4] Hawke B. and Head J. 1977. 8th Lunar Prospector Spacecraft Conference, 415-417. [5] Hawke B. and Head J. 1977. *Impact and Explosion Cratering*, pp. 815-841. [6] Hawke B. and Head J. 1979. 10th Lunar Prospector Spacecraft Conference, pp. 510-512. [7] Schmidt R. and Housen K. 1987. *International Journal Impact Engineering* 5:543–560. [8] Cintala M. and Grieve R. 1998. *Meteoritics & Planetary Sciences* 33:889–912. [9] Robinson M. et al. 2010. *Space Science Review* 150:81–124. [10] Pierazzo E. et al. 1997. *Icarus* 127:408–423. [11] Pierazzo E. and Melosh H. 2000. *Icarus* 145:252–261.

FEATHER FEATURES IN QUARTZ: STRUCTURAL AND TEXTURAL INSIGHTS FROM FIRST TEM AND EBSD MEASUREMENTS

M. H. Poelchau¹, G. Trullenque¹ and T. Kenkmann¹. ¹Institut für Geowissenschaften, Universität Freiburg, Germany. E-mail: michael.poeichau@geologie.uni-freiburg.de.

**Introduction:** Feather features (FFs) are a recently discovered [1], deformational feature in quartz that has been found in 26 confirmed impact craters so far [2]. They are suggested to form under low shock pressures [2] and potentially can be added to the list of shock-induced microstructures in quartz, along with PDFs and planar fractures.

FFs consist of a main planar fracture (PF) that has been sheared during shock compression and from which short, parallel to subparallel lamellae emanate in one direction, typically at an angle of 50-60°. The orientation of these lamellae is always consistent with the sense of shear along the fracture. The crystallographic orientation of the fracture and lamellae show a degree of crystallographic control, with (0001), {10\bar{1}1} and {1\bar{1}2;2} as the most common rational low index crystallographic planes.

**Generation of FFs:** Analysis of multiple sets of FFs in natural samples shows that all FF lamellae within a sample trend in roughly the same direction, while the sheared PFs form conjugate sets at ~90° angles. The principal axis of stress of the shock wave is therefore assumed to lie at a 45° angle to the conjugate sets and parallel to the FF lamellae. Thus FFs can be used as indicators for the orientation of differential stress within the shock wave.

Although the generation of FFs as a shear-induced structure is clear in principle, details of their formation are not yet completely understood. Specifically, the quartz grain's lattice is commonly distorted near the shear fracture, visible as an undulatory extinction pattern under the microscope. In conventional structural geology, the orientation of this lattice distortion forms as the result of "dragging" of material along the shear plane. Surprisingly, FFs show the exact opposite orientation.

**Results and Implications:** EBSD (electron backscatter diffraction) measurements are currently being performed on FFs to analyze lattice deformation at a high resolution. Preliminary EBSD results confirm the lattice deformation determined by microscope analyses. Based on these initial results, we suggest that lattice deformation along the PF is caused by elastic lattice strain accumulated during shearing in the shock wave, which is then rapidly released during unloading, resulting in the opening of the FF lamellae as extensional fractures (mode I) while rotating the lattice between two individual lamellae, causing additional mode II in-plane shear along the lamellae and resulting in a distortion pattern visible in EBSD measurements. Preliminary TEM analyses show that the junctions of the FF lamellae with the PF are filled with vesicular amorphous material.

Further EBSD and TEM work is planned to give more detailed insights into the kinematics of dynamic fracturing and shearing. A deeper understanding of this process can potentially be used to constrain and differentiate fracturing mechanisms in shock waves (and their visible expressions in quartz grains) from fracturing in lower-dynamic, tectonic regimes.

**References:** [1] French B. M. et al. 2004. *GSA Bulletin* 116:200–218. [2] Poelchau M. H. and Kenkmann T. 2011. *Journal of Geophysical Research* 116:B02201.
IMPACTS INTO SANDSTONE: POROSITY EFFECTS IN THE STRENGTH REGIME

M. H. Poelchau, A. Dufresne, T. Kenkmann and the MEMIN Team. Institut für Geowissenschaften, Universität Freiburg, Germany. E-mail: michael-poelchau@geologie.uni-freiburg.de.

**Introduction:** The MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) is currently focused on experimental impact cratering into sandstone. One of the main goals of these experiments is determining the role porosity has on the impact process and on the resulting crater morphology. So far, four sets of impact experiments have been performed at the two-stage light gas gun facilities of the Ernst-Mach-Institut, Freiburg, Germany. Aluminum, steel and iron meteorite projectiles were accelerated to velocities between 2.5–7.8 km s⁻¹, resulting in impact energies ranging from 0.7–58.4 kJ. Targets were dry Seeberger sandstone blocks with a grain size of ~70 µm, a porosity of 20–25%, and a uniaxial compressive strength (UCS) of 35–40 MPa [1,2].

**Cratering Results and Discussion of Porosity Effects:** All crater dimensions were measured with a 3D laser scanner. Crater depth to diameter ratios range from 0.14 to 0.25. Craters formed by steel or meteoritic iron projectiles are slightly deeper (0.20) than the average craters formed in crystalline rocks with similar high-density projectiles (0.18) [3,4], indicating that the sandstone's porosity results in slightly increased penetration depth. The sandstone craters formed by aluminum projectiles, on the other hand, are much shallower (0.15), and thus reflect a stronger dependency of penetration depth on projectile density than on porosity, at least for porosity values of ~25%.

The effect of porosity becomes more apparent when crater volumes of the sandstone and non-porous crystalline rocks [3–5] are compared. For the same impact energy and roughly similar impact conditions (projectile mass, density and speed) the same crater volumes result, in spite of a difference of target crushing strength of nearly one order of magnitude (UCS of crystalline rocks is assumed at 300 MPa). This is in agreement with numerical modeling results [6] that show a dampening of the shock wave through porosity. Thus, the amount of energy available to work against the target's strength to form a crater is reduced by the work required to close pore space. Although density effects of the projectile on crater volume should be expected, no major differences were detected.

The cratering efficiency (the ratio of excavated target mass to projectile mass) in sandstone is also greatly reduced compared to strength scaled cratering efficiency values of crystalline rocks [3–5] by almost one order of magnitude. Based on the limited number of data, it is currently difficult to determine the exact effects of porosity on strength-scaled size parameters beyond a general reduction of cratering efficiency. Impact experiments into more highly porous target rocks are planned to better quantify the effects porosity has on cratering in strength dominated regimes.

**References:** [1] Kenkmann T. et al. 2011. *Meteoritics & Planetary Science*, in press. [2] Poelchau M. H. et al. 2011. Abstract #1824. 42nd Lunar and Planetary Science Conference. [3] Polanskey C. A. and Ahrens T. J. 1990. *Icarus* 84:140–155. [4] Burchell M. J. and Whitehorn L. 2003. *Monthly Notices of the Royal Astronomical Society* 341:192–198. [5] Smrekar S. et al. 1986. *Journal of Geophysical Research* 13:745–748. [6] Güldemeister N. et al. 2011. Abstract #1104. 42nd Lunar and Planetary Science Conference.

HIGH FIDELITY STUDIES OF INTERSTELLAR DUST ANALOG IMPACTS IN Stardust AEROGEL AND FOILS

F. Postberg, C. Allen, S. Bajt, H. A. Bechtel, J. Borg, F. E. Brenker, J. Bridges, D. E. Brownlee, M. Burchell, M. Burghammer, A. L. Butterworth, P. Cloetens, A. M. Davis, R. Doll, C. Floss, G. J. Flynn, D. Frank, Z. Gainsforth, E. Grün, P. R. Heck, J. K. Hillier, P. Hoppe, L. Howard, G. R. Huss, J. Huth, A. Kearsley, A. J. King, B. Lai, J. Leitner, L. Lemelle, A. Leonard, H. Leroux, L. R. Nittler, R. C. Ogliore, W. J. Ong, M. C. Price, S. A. Sandford, J. A. Sans Tresseras, S. Schmitz, T. Schoonjans, K. Schreiber, G. Silversmit, A. Simionovici, R. Srama, T. Stephan, J. Stodolna, R. M. Stroud, S. R. Sutton, R. Toucoulou, M. Trieloff, P. Tsou, A. Tsuchiyama, T. Tyliczszak, B. Vekemans, L. Vincze, A. J. Westphal, M. E. Zolensky and > 29,000 Stardust@home dusters. ISPE author affiliations are at http://www.ssl.berkeley.edu/~westphal/ISPE/.

In 2000 and 2002 the Stardust Mission exposed aerogel collector panels for a total of about 200 days to the stream of interstellar grains sweeping through the solar system. The material was brought back to Earth in 2006.

We present laboratory calibration of the collection process by shooting high speed [3–30 km s⁻¹] interstellar dust (ISD) analogs onto Stardust aerogel and foil flight spares. Particle impact speeds up to 50 km s⁻¹ can only be achieved by a Van de Graaff accelerator such as operated at the MPI für Kernphysik (Heidelberg) [1], and requires coating of nonconductive particles with thin films of either platinum [2] or polypyrrole [3].

Particle impact tracks in aerogel were identified by an optical microscope. Track diameters and depths were measured optically at high magnification using an encoded stage with 0.5 µm precision. Subsequently tracks in picokeystones were extracted and analyzed with Scanning Transmission X-ray Microscopy (STXM). This enabled an investigation into both the morphology of impact tracks as well as structural and chemical modification of projectile and collector material. Major campaigns were completed in spring 2011 with the goal to characterize tracks of interstellar grains with respect to the projectile speed, size, and density. Three different materials (orthopyroxene, iron, polystyrene) were therefore shot within several narrow speed and size windows (e.g., 14–16 km s⁻¹, 0.37–0.43 µm). For each set of parameters, about 50 particles were collected.

First results show a bulbous track shape at 15 km s⁻¹ similar to type A Stardust tracks with a terminal particle. For the first time it could be shown experimentally that cores of submicron minerals survive aerogel capture at speeds well above 10 km s⁻¹. The calibration is not only important for the systematic search and analyses of foils and aerogel [4, 5], but also allows recalculation of the ISD flux [6] for the Stardust collection period.

**References:** [1] Stübig M. et al. 2001. *Planetary and Space Science* 49:853. [2] Hillier J. K. et al. 2009. *Planetary and Space Science* 57:2081. [3] Armes S. et al. 1991. *Polymer* 32:2325. [4] Floss C. et al. 2011. This conference. [5] Stroud R. M. et al. 2011. This conference. [6] Landgraf M., Müller M., and Grün E. 1999. *Planetary and Space Science* 47:1029.
THE FIRST DOCUMENTED GEORGIA-AREA TEKTITE FOUND IN
BIBB COUNTY, GEORGIA

H. Povenmire. Florida Institute of Technology, 215 Osage Drive, Indian Harbour Beach, FL 32937, USA. E-mail: katiehall1@yahoo.com.

About 1999, a black glassy rock was found approximately in the
middle of Bibb County just south of Macon, GA. This was identified as a
Georgia tektite on May 19, 2011. This 18.42 g tektite is a flattened tear
drop shape and is 47 x 22 x 15 mm in size. It had been in running water
for a long time and the surface was smoothed. There are no bubbles or
inclusions. The find location was on the Fall Line and the Piedmont
Plateau. The two western adjoining counties, Crawford and Peach have
similar geology and will probably be confirmed with further field work.
The approximate find location was lat. 32d 42'N and long. 83d 44'W.

In 2010, a spectacular Georgia-area tektite was found in Aiken
County, South Carolina. In 2011, a second tektite was found in Allendale
County, South Carolina. This is a small disk- shaped tektite and was
found in an Indian midden overlooking the Savannah River. It was not
found in situ and further field work is in progress for more specimens.

About ten percent of Georgia tektites have shown indications of
being flaked by early Indians. However, complete artifacts are extremely
rare. In early 2011, a second Georgia tektite which had been flaked into a
projectile point was reported. This specimen was found in Dodge county
and artifact specialists have suggested that it was of archaic age and the
aborigines flaking it were likely of the Pickwick or Wacissa Cultures. This
7.1 g tektite was flaked, then damaged and then reworked several times.

In 2010, the third largest Georgia splash form tektite was re-ported
from Bleckley County. It has a weight of approximately 65 g. Precise data
on it is not available but it is of significant importance because it fills a
statistical gap in the size distribution of the large Georgia tektites.

In the last year, several museum quality tektites have been found.
These have come from Bleckley, Wilcox and Houston counties. Since
these specimens have come from previously con-firmed counties, they are
good scientific specimens but do not add to our knowledge of
distribution.

There have now been approximately 2700 Georgia-area tektites
found in 26 counties. The total area of the Georgia-area strewn field is
now approximately 10,000 square miles and this is larger than the Texas
bediasite strewn field.

Acknowledgments: I want to thank the help of Mike Stokes,
Thomas Thurman, Sharon Veal and Kalen Icard.

**References:** [1] Povenmire H. 2003. Tektites: A Cosmic Enigma Blue Note Publishing, Cocoa Beach, FL. [2] Povenmire H. and Lambert J. 2010. The First Georgia-Area Tektite found in Aiken County, South Carolina, *Meteoritics & Planetary Science*, 73rd Annual Meeting Abstract, New York.

FEASIBILITY OF IODINE AND BROMINE ANALYSIS IN GENESIS
SOLAR WIND COLLECTORS

O. Pravdivtseva¹, A. Meshik¹, C. M. Hohenberg¹ and D. S. Burnett². ¹McDonnell Center for the Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA. E-mail: olga@physics.wustl.edu. ²Geology 100-23, CalTech, Pasadena, CA, USA.

Comparison of elemental abundances in sun, meteorites and earth
provides understanding of the formation and evolution of the solar
system. Yet, the majority of the solar system abundances are based on
meteoritic values [1–6]. Here we report an attempt to estimate a feasibility
of direct measurements of iodine and bromine in the GENESIS solar
wind Aluminum on Sapphire collector (AloS) using neutron induced
conversions: ¹²⁷I(n,γβ)¹²⁸Xe, ⁷⁹Br(n,γβ)⁸⁰Kr and ⁸¹Br(n,γβ)⁸²Kr.

To estimate the extent of terrestrial halogen contamination in
GENESIS collectors, several flown fragments of AloS were submerged in
methanol (for 1 h and for 48 h), rinsed in methanol, dried, sealed under
vacuum in fused quartz ampoules and irradiated at the Missouri
University Research Reactor receiving fluence ~2 × 10¹⁹ thermal neutrons
cm⁻².

We analyzed two areas (0.07 and 0.7 cm²) of AloS the solar wind
collector washed for 48 h, and one area (0.13 cm²) of the collector washed
for 1 h. Xenon extracted from the largest area had a clear signature of
solar wind as indicated by ¹²⁹Xe/¹³²Xe = 1.045 ± 0.005 and other major
isotopes, while ¹²⁸Xe/¹³²Xe = 1.01 ± 0.03 had a 12-fold excess compared
to the solar value. Longer washing apparently reduces iodine
contamination 4 times, implying that it is surface correlated. Evidently, to
separate ¹²⁸Xe, derived from solar iodine, and the solar wind ¹²⁸Xe, the
iodine contamination should be reduced further, at least 10 times. It may
be achieved by combination of a longer and more aggressive cleaning
procedure (i.e., ozone cleaning followed by washing in non-polar solvents
at elevated temperatures) and depth-profiling laser extraction.

Krypton analyses of the irradiated AloS collectors demonstrates
solar wind signature with 17% excess in ⁸²Kr and 3-fold excess in ⁸⁰Kr.
Apparently, cleaning in methanol is much more efficient for Br that for I,
since a longer 48-hour washing reduced bromine contamination 50 times.

Our first "quick and dirty" experiment suggests that determination
of solar iodine and bromine is potentially feasible, especially considering
availability of cleaner Si-based Genesis collectors and the possibility of
analyzing larger collector areas irradiated with tripled neutron fluence.

**Acknowledgment:** This work is supported by NASA grant NNX07AM76G.

**References:** [1] Anders E. and Ebihara M. 1982. *Geochimica et Cosmochimica Acta* 46:2363–2380. [2] Anders E. and Grevesse N. 1989. *Geochimica et Cosmochimica Acta* 53:197–214. [3] Cameron A. G. W. 1968. In *Origin and distribution of the elements*, Ahrens L. H., ed. Pergamon, Oxford. pp. 125–143. [4] Cameron A. G. W. 1973. *Space Science Reviews* 15:121–146. [5] Suess H. E. and Urey H. C. 1956. *Reviews of Modern Physics* 28:53–74. [6] Lodders K. 2010. *Principles and Perspectives in Cosmochemistry* 379–417.
## HYDROCODE MODELING OF MICROMETER SCALE IMPACTS INTO AI FOIL: IMPLICATIONS FOR ANALYSES OF Stardust ISPE CRATERS

M. C. Price¹, A. T. Kearsley², M. J. Burchell¹, S. P. Armes³, M. J. Cole¹, J. K. Hillier⁴, F. Postberg⁵ and N. Starkey⁴. ¹School of Physical Sciences, University of Kent, Canterbury, CT2 7NH, UK. E-mail: mcp2@star.kent.ac.uk. ²Impacts & Astromaterials Research Centre, Natural History Museum, London SW7 5BD, UK. ³Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK. ⁴PSSRI, Open University, Milton Keynes, MK7 6AA, UK. ⁵Institute for Geosciences, Heidelberg University, Heidelberg, Germany.

**Introduction:** This work provides a validated hydrocode model to help interpret impact velocity and angle (and thus impactor origin) from nondestructive measurements of the dimensions of craters found on the Stardust interstellar collector foil. We have used a modified Cowper-Symonds [1] strength model for Al-1100 within AUTODYN, incorporating strain rate (and strain) hardening and pressure dependent melting [2] Our model has now been validated against experimental data for silica and sodalime glass (slg) projectiles fired onto Stardust flight spare foil at velocities of 6.1 km s⁻¹ [3, 4] and sub-micron iron particles accelerated in a Van de Graaff (VdG) accelerator [5, 6] at velocities up to 27 km s⁻¹. Results from recent experiments using the VdG accelerator in Heidelberg [7] are also being used to extend the validation.

**VdG Analog Foil Shots:** Two campaigns used Stardust flight spare foil as targets: March 2010: Platinum coated orthopyroxene (OPX) with particle diameter approximately 0.4 µm, accelerated in four runs to 6 (twice), 15 and 20 km s⁻¹. Data from these four foils are described in [2]. April-May 2011 (1) Polypyrrole coated olivine projectiles of approximately 0.25 µm diameter, accelerated to: 3, 6, 10, 15, 20, 70 km s⁻¹. (2) Polypyrrole coated polystyrene (approximately 0.4 µm diameter) accelerated to 3, 6, 10 km s⁻¹. (3) Pt coated OPX (approximately 0.25 and 0.4 µm diameter): accelerated to 3, 6, 10, 15 km s⁻¹.

**Results:** The hydrocode model reproduces the experimentally derived crater dimensions to within 10% for the majority of the data and, at worst, to within 25% for the highest speed and smallest projectile. This validation covers a range of projectile sizes from 150 nm to 4 µm, impact velocity 6–27 km s⁻¹ and projectile density from 2.4 to 7.8 g cm⁻³.

**Discussion:** Recent analyses [8, 9] of two sub-µm diameter craters on the Stardust interstellar collector foil show they were almost certainly made by secondary ejecta from the Zn- and Ce-bearing solar panel cover glass. Secondary glass particles are likely to have been ejected with a wide range of speeds, up to a few tens of km s⁻¹, to impact on the collector at oblique angles [10]. 3D numerical modeling of glass impactors is ongoing to determine the effect that solid impactor shape, impact angle and velocity may have on crater shape and if any measureable crater metric could be used to help determine an impactor's trajectory and velocity.

**References:** [1] Cowper G. R and Symonds P. S. 1957. *Technical Report #28*, Brown University. [2] Price M. C. et al. 2011. *Meteoritics & Planetary Science* (sub.). [3] Price M. C. et al. 2010. *Meteoritics & Planetary Science* 45:1409. [4] Kearsley A. T. et al. 2006. *Meteoritics & Planetary Science* 41:167. [5] Davidson R. F. and Walsh M. L. 1995. *Proceedings of the SCCM*. [6] Stradling G. L. et al. 1992. *Proceedings of the HVIS*. [7] Mocker A. et al. 2011. *Review of Science Instruments* (sub.). [8] Stroud et al. 2011. This issue. [9] Floss et al. 2011. This issue. [10] Westphal A. et al. 2008. Abstract #1855. 39th Lunar Prospector Spacecraft.

## NEW DATA ON GRAPHITE FROM THE ZAKŁODZIE ENSTATITE ACHONDRITE

T. A. Przylibski¹, T. Jakubowski², Ł. Karwowski³, R. Kryza⁴ and K. Uszczek¹. ¹Faculty of Geoengineering, Wrocław University of Technology, Mining and Geology, Wybrzeże S. Wyspiańskiego 27, 50-370 Wrocław, Poland. ²Balonowa 5/2, 54-129 Wrocław, Poland. ³Faculty of Earth Sciences, University of Silesia, ul. Będzińska 60, 41-200 Sosnowiec, Poland. ⁴University of Wrocław, Institute of Geological Sciences, ul. Cybulskiego 30, 50-205 Wrocław, Poland.

**Introduction:** Zakłodzie is one of the ungrouped enstatite achondrites. It was classified by some authors [1, 2] as an impact-melt rock, but others (T. A. Przylibski and research team) have suggested that a new meteorite group of primitive enstatite achondrites can be defined. They proposed to include into that group, apart from Zakłodzie, several other enstatite meteorites, e.g., Happy Canyon, Ilafegh 009, QUE 94204 and Yamato-8404 [3–5]. Zakłodzie has an extraordinary mineral composition, comprising e.g., keilite [5] and, in the innermost part, spherical nodules of graphite and metal, surrounded by enstatite crystals. Both, inclusions of graphite in metal grains and metal grains in graphite are found. These kinds of inclusions are important for establishing the temperatures of metamorphism leading to chondrule borders effaceing and recrystallization of plagioclase II [4]. Further constraints on the crystallization temperature can be inferred from determination of the graphite structure.

**Samples and Experiments:** Analyses were made on a fragment of the innermost part of Zakłodzie, a few cm² in size. Element mapping was done on SEM JEOL JSM-5500LV. Raman spectra were obtained on confocal microspectrometer T-64000 (Jobin-Yvon) equipped with microscope Olympus BX-40; the 514.5 nm Ar line was used for sample excitation. X-ray powder diffraction analyses were performed on X'Pert Philips PW 3710 diffractometer (Co Kα).

**Results:** Element mapping shows that carbon nodules are set in iron or, locally, enclosed in silicate minerals. The diameters of the nodules are between 0.1 and 4 mm (exceptionally, up to 9 mm). Graphite was observed in association with all other mineral components of the meteorite, i.e., sinoite, schreibersite, troilite, enstatite, and FeNi phases. The Raman spectra show graphite lines at 1580 cm⁻¹ for G band, and 1355 cm⁻¹ for D band; they also show broad peaks at 2700 cm⁻¹. According to Lespade method [6], the graphite from Zakłodzie is determined as semiordered to ordered. X-ray diffraction results confirm the hexagonal structure of alphagraphite. Further investigations are in progress to establish more detailed structural characteristics of the Zakłodzie graphite.

**References:** [1] Burbine T. H. et al. 2000. *Meteoritics & Planetary Science* 35:A36. [2] Keil K. and Bischoff A. 2008. *Meteoritics & Planetary Science* 43:1233–1240. [3] Piłski A. S. 2004. 3rd Meteorite Conference in Poznań. pp. 41–46. [4] Przylibski T. A. et al. 2005. *Meteoritics & Planetary Science* 40:A185–A200. [5] Karwowski Ł. et al. 2007. *American Mineralogist* 92:204–209. [6] Lespade P. et al. 1982. *Carbon* 20:427–430.
5219

CORRELATED NUCLEOSYNTHETIC ISOTOPE VARIABILITY IN
Cr, Sr, Ba, Sm, Nd, AND Hf IN MURCHISON AND QUE 97008

L. Qin¹,², R. W. Carlson¹, and C. M. O'D. Alexander¹. ¹DTM, Carnegie Institution of Washington, Washington, DC 20015, USA. ²Center for Isotope Geochemistry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. E-mail: lqin@lbl.gov.

**Introduction:** Step-wise acid digestion is a very useful means of increasing the magnitude of nucleosynthetic isotope anomalies and probing the nature of the carriers of isotope anomalies in chondrites. We performed step-wise dissolution of two primitive meteorites, the CM2 chondrite Murchison and the L3.05 chondrite QUE 97008. The isotopic compositions of Cr, Sr, Ba, Nd, Sm and Hf were characterized. We also examined the consequences of nucleosynthetically-induced isotope variations for the interpretation of the variations of radiogenic isotope abundances.

**Methods:** Approximately 5 g of each meteorite was crushed to <60 µm, and sequentially leached with (i) 8.5 N acetic acid (at room temperature for 24 h), (ii) 6 N HNO₃ (at room temperature for 5d), (iii) 6 N HCl (at 75 °C for 24 h), and the residue was dissolved with an HF-HNO₃ mixtureusing a Parr Bomb (at 170 °C for 1 w). From each leach and residue, Cr, Sr, Ba, Nd, Sm, and Hf were extracted and purified using conventional ion-exchange techniques. The isotopic compositions for all elements except Hf were measured on a Triton thermal ionization mass spectrometer. Hf isotopic compositions were determined on a Nu-plasma multi-collector ICP-MS.

**Results:** Isotopic anomalies of nucleosynthetic origin are observed in all elements in all leaches and the residue of Murchison. In general, where resolved, the nucleosynthetic isotopic anomalies are 2–5 fold smaller in QUE 97008 than in Murchison. The difference in the magnitude of anomalies is similar to the difference in their matrix abundances consistent with the suggestion that matrix is the main carrier of anomalous material. The anomalies in all but Cr are best explained by variable additions of pure s-process nuclides to a background nebular composition slightly enriched in r-process isotopes compared to average Solar System material. Leaching leaves a residue in Murchison that is strongly enriched in s-process nuclides with depletions of over 1 % in ¹³⁵Ba and 7 ε in ⁸⁴Sr. Combined with concentration data, this indicates that the isotopic compositions of Ba and Sr in the Murchison residue are strongly influenced by s-process-rich presolar SiC. Neodymium, Sm, and Hf display variable s-,r-process nuclide abundances as do Ba and Sr, but the anomalies are much smaller. Samarium shows variable relative abundances of the p-process isotope ¹⁴⁴Sm that do not correlate with ¹⁴²Nd, suggesting that the direct p-process contribution to ¹⁴²Nd is small. Correcting for nucleosynthetic variability in Nd explains the range in ¹⁴²Nd/¹⁴⁴Nd seen between C-, and O-, E-chondrites, but not the difference between chondrites and all modern Earth rocks, leaving decay of ¹⁴⁶Sm and a superchondritic Sm/Nd ratio as the likely explanation for Earth's high ¹⁴²Nd/¹⁴⁴Nd. The s-,r- variations observed in Hf caution relying on isotopically anomalous refractory inclusions for the initial abundance of the short-lived ¹⁸²Hf, a r-process nuclide, in the Solar System.

5129

ORIGIN OF THE CENTRAL MAGNETIC ANOMALY AT
HAUGHTON IMPACT STRUCTURE, CANADA

Y. Quesnel¹, J. Gattacceca¹, G. R. Osinski² and P. Rochette¹. ¹CEREGE, CNRS, Aix-Marseille University, Aix-en-Provence, France, E-mail: quesnel@cerege.fr. ²Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada.

**Context:** Located on Devon Island, Nunavut, Canada, the 23-km diameter Haughton impact structure is one of the best-preserved medium-size complex impact structures. The impact occurred ~39 Ma ago into a target formation composed of a 2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield [1]. Impact melt breccias filled the crater, while impact-related hydrothermal activity took place, but since then no significant geological event affected the area [2].

In the 1980s, ground magnetic and gravity measurements were carried out within the central part of the crater [3]. A significant anomaly was discovered and coarsely modeled by a source body of simple geometry. A recent airborne magnetic survey delivered additional data that covered the whole crater but no modeling was done [4].

**Method:** During Summer 2010, we performed a new ground magnetic survey to better characterize the central magnetic anomaly. A Geometries G858 caesium vapor magnetometer was used. After correct removal of the external and core magnetic fields, the resulting dataset allowed us to produce a local magnetic field map of high quality at ground level, whereas [3] only used profiles. We precisely modeled the anomaly to constrain the geometry and magnetization of its source, also using results from laboratory measurements of magnetic properties (remanent magnetization and magnetic susceptibility) of all target lithologies.

**Results:** The amplitude of the central magnetic anomaly reaches ~900 nT over a distance of 1.5 km. A local sharp transition of the gradient was identified, probably indicating a very shallow top of the magnetized source. Modeling indicates that a 0.7 km³ magnetized body with possible local superficial branches could be the source of this anomaly. Among the local lithologies, all Paleozoic sedimentary rocks are too weakly magnetic to account for the magnetic anomaly. Even the highest total (i.e. induced + remanent) magnetization intensities measured on basement samples are about 1 A m⁻¹, slightly weaker than those resulting from source modeling (1.5–2.5 A m⁻¹).

**Discussion:** The geometry of the modeled source body corresponds to the one expected with a central uplift. Magnetization property investigations exclude Paleozoic sedimentary rocks from comprising this inner part of the central uplift. Because the pre-impact magnetization intensities of basement formations cannot account for the magnetic anomaly too, an additional impact-related process is required. Post-impact hydrothermal alteration could have affected this uplifted basement, since evidence of such alteration is common at Haughton [2]. This geological process will enhance both remanent magnetization and magnetic susceptibility. In addition, the modeled magnetization directions correspond to the expected normal polarity regional directions of the main magnetic field when the impact occurred [5].

**References:** [1] Osinski G. R. et al. 2005. *Meteoritics & Planetary Science* 40:1759–1776. [2] Osinski G. R. et al. 2005. *Meteoritics & Planetary Science* 40:1859–1877. [3] Pohl J. et al. 1988. *Meteoritics* 23:235–238. [4] Glass B. J. et al. 2005. Abstract #2398. 36th Lunar and Planetary Science Conference. [5] Gattacceca J. et al. 2011. This meeting.
## A REAPPRAISAL OF THE METAMORPHIC HISTORY OF EH3 AND EL3 ENSTATITE CHONDRITES

E. Quirico¹, M. Bourot-Denise², C. Robin¹, G. Montagnac³ and P. Beck¹. ¹IPAG CNRS/University Grenoble 1 38041 Grenoble France. E-mail: eric.quirico@obs.ujf-grenoble.fr. ²LEME Museum National Histoire naturelle Paris France. ³Laboratoire de Géologie ENS Lyon France.

The thermal history of a series of EH3 and EL3 chondrites has been investigated by studying the degree of structural order of the organic matter (OM) located and characterized in matrix areas by Raman micro-spectroscopy [1]. By comparison with unequilibrated ordinary chondrites (UOCs) and CO and CV carbonaceous chondrites, the following petrologic types have been assigned to various E chondrites: Sahara 97096 and Alan Hills 84206: 3.1–3.4; Alan Hills 85170 and Parsa: 3.5; Alan Hills 85119: 3.7; Qingzhen, MacAlpine Hills 88136 and MacAlpine Hills 88184: 3.6–3.7. The petrologic type of Qingzhen is consistent with the abundance of the P3 noble gas component, a sensitive tracer of the grade of thermal metamorphism [2]. The petrologic types are qualitatively consistent with the abundance of fine-grained matrix for the whole series. No significant effects of shock processes on the structure of OM were observed. However such processes certainly compete with thermal metamorphism and the possibility of an effect cannot be fully discarded, in particular in the less metamorphosed objects. The OM precursors accreted by the EH3 and EL3 parent bodies appear to be fairly similar to those of UOCs and CO and CV carbonaceous chondrites. Raman data however show some slight structural differences that could be partly accounted for by shock processes. The metamorphic history of EH3 and EL3 chondrites has often been described as complex, in particular regarding the combined action of shock and thermal metamorphism [3,4]. Because OM maturity is mostly controlled by the temperature of peak metamorphism, it is possible to distinguish between the contributions of long duration thermal processes and that of shock processes. Comparison of the petrologic types with the closure temperatures previously derived from opaque mineral assemblages [5] has revealed that the thermal history of EH3 and EL3 chondrites is consistent with a simple asteroidal onion shell model. Thermal metamorphism in enstatite chondrites appears to be fairly similar to that which takes place in other chondrite classes. The complex features recorded by mineralogy and petrology and widely reported in the literature appear to be mostly controlled by shock processes.

**References:** [1] Quirico E. et al. 2011. *Geochimica et Cosmochimica Acta* 75:3088–3102. [2] Huss G. R. and Lewis R. S. 1994. *Meteoritics* 29:811–829. [3] Zhang Y. et al. 1995. *Journal of Geophysical Research* 100:9417–9438. [4] Kimura et al. 2005. *Meteoritics & Planetary Science* 40:855–868. [5] Zhang Y. and Sears D. W. G. 1996. *Meteoritics & Planetary Science* 31:647–655.

## NON-UNIFORM DISTRIBUTION OF THE MARTIAN REGOLITH COMPONENT IN SHERGOTTITES

M. N. Rao¹, L. E. Nyquist², D. K. Ross¹ and J. Park³. ¹Jacobs-ESCG, Johnson Space Center, Houston, TX. USA. E-mail: nageswara.rao@nasa.gov. ²ARES, NASA Johnson Space Center, Houston, TX. USA. ³Chemistry Department, Rutgers University, Piscataway, NJ, USA.

**Introduction:** Shergottite samples that show evidence for thermal neutron irradiated (n,γ) products such as ⁸⁰Kr excesses and ¹⁴⁹Sm isotopic deficits necessarily contain a Martian regolith component because the (n,γ) products are produced only in the top few meters of the Martian surface [1, 2]. The ⁸⁰Kr excesses from Br and the ¹⁴⁹Sm deficits determined in GRIM (gas-rich impact-melt) glasses, 27,8 and 104 from EET 79001 Lith A and B and in Shergotty-B yielded an integrated neutron fluence of ~10¹⁵ n/cm² to which the glass constituents were exposed near Mars surface [1,2]. Some of these glasses (8 and104) further show evidence for fast neutron (N, xp yn) products such ⁸³Kr and ⁸⁴Kr excesses from Sr and Rb yielding an integrated fast neutron (N) fluence of ~10¹⁶ N/cm² providing definitive evidence for a Martian regolith component in these glasses [2].

**Results:** We determined the ¹⁴⁹Sm isotopic deficit in the whole rock EET 79001, Lith B, amounting to a ε ¹⁴⁹Sm value of – 0.21 ± 0.16. This value corresponds to a thermal neutron fluence of (0.52 ± 0.39) × 10¹⁵ n/cm² to which this Lith B sample was exposed on Mars. This value is in agreement (within errors) with the fluence of (1.33 ± 0.75) × 10¹⁵ n/cm² determined using isotopic shifts in ¹⁴⁹Sm and ¹⁵⁷Gd isotopes by [3] in another Lith B (bulk) sample EET 79001,69. Because of this high fluence in bulk Lith B, we expected to find large pockets of secondary sulfides similar to those studied by us in, 104 (a GRIM) sample belonging also to Lth B [4]. We therefore studied a thin section EET 79001, 69 (Lith B) by EMPA/SEM techniques. However, we found very little immiscible sulfide melt blebs in this case.

In the case of EET 79001, Lith A bulk sample, we reported earlier [1] a thermal neutron fluence of (0.24 ± 0.31) × 10¹⁵ n/cm² which overlaps zero value. Further, this result is consistent with the observation that no ⁸⁰Kr excess was observed in the case of Lith A sample (EET 79001, 34) studied by [5] for Kr isotopic composition. However, in the case of GRIM glasses from Lith A, gypsum laths and S-rich aluminosiliactes were detected by [6] and positive elemental correlations between “SO₃⁻” and CaO and “SO₃⁻” and Al₂O₃ were found by [7].

In the lherzolite Y00027 (bulk), Kr isotopic composition was determined by [8] and no evidence for the neutron capture ⁸⁰Kr on Br was found. But, in a melt-vein glass (GRIM) from the same lherzolite, they found evidence for the occurrence of ⁸⁰Kr excess from Br indicative of a regolith component.

These results suggest that the S-rich Martian regolith component is not uniformly distributed in shergottite GRIM glasses and bulk samples.

**References:** [1] Rao M. N. et al. 2011. *Journal of Geophysical Research-Planets*, in press. [2] Rao M. N. et al. 2002. *Icarus* 156:352–372. [3] Hidaka H. et al. 2009. *Earth and Planetary Science Letters* 288:564–571. [4] Sutton S. et al. 2008. Abstract #1961. 39th Lunar and Planetary Science Conference. [5] Becker R. H. and Pepin R. O. 1984. *Earth and Planetary Science Letters* 69:225–242. [6] Gooding J. L. and Muenow D. W. 1986. *Geochimica et Cosmochimica Acta* 50:1049–1059. [7] Rao M. N. et al. 2004. Abstract #1501. 35th Lunar and Planetary Science Conference. [8] Nagao K. et al. 2008. *Polar Science* 2:195–214.
## TEMPERATURE AND SPECTRAL PHASE EFFECTS ON HED METEORITES: IMPLICATIONS FOR DAWN AT VESTA

V. Reddy¹,², E. A. Cloutis³, A. Nathues¹, J. P. Mann³, M. J. Gaffey² and U. Schade⁴. ¹Max-Planck Institute for Solar System Research, Germany. E-mail: reddy@mps.mpg.de. ²University of North Dakota, USA. ³University of Winnipeg, Canada. ⁴Helmholtz Zentrum Berlin, BESSY II, Germany.

**Introduction:** Asteroid 4 Vesta is the first target of NASA's Dawn mission, which is expected to begin its yearlong orbital mission in July 2011. The Framing Camera (FC), one of the three scientific instruments onboard the spacecraft [1], contains a set of seven filters ranging from 0.44 to 0.97 microns in addition to a clear filter. While the VIR spectrometer on Dawn has larger spectral coverage (0.25–5 microns) and spectral resolution (2–10 nm), Dawn FC has higher spatial resolution (up to ~20 m) than VIR (~50 m).

Spectral phase effects on Vesta have been already detected and approximately quantified by [2]. Gaffey [2] noted a change in the intensity of Vesta's 1-micron band with increasing phase angle. Hence we expect to see a wavelength dependent phase effect, which will alter the reflectance values of FC data depending on the band pass of the filter and viewing geometry (mainly phase angle). Beside the viewing geometry we expect also to observe spectral changes due to surface temperature, which will likely be present in the spectrometer data. Temperature uncertainties arise when spacecraft spectral data, obtained at much colder surface temperatures (80–300 K), is interpreted using laboratory calibrations developed at room temperatures (~300 K). In an effort to pre-quantify these phase angle-, and temperature-induced spectral effects, we conducted a series of laboratory studies of HED meteorites.

**Methodology:** Laboratory spectral measurements (0.3–25 microns) of Moama eucrite and orthopyroxene PYX032 (analog for a diogenite) at different phase angles (18–120°) were measured at the University of Winnipeg Planetary Spectrophotometer Facility. Data of temperature spectral series were obtained from two published sources [3,4], and reanalyzed after resampling to Dawn FC wavelength ranges. Spectral band parameters like Band I and II centers, Band Area Ratio (BAR) and band depths were measured using methods described in [5].

**Results:** Using laboratory spectral measurements of HED meteorites at different phase angles and temperatures we have developed a set of equations to correct Dawn FC color images and VIR cubes for temperature and phase angle effects. We noted a general increase in band depths and BAR at the shortest phase angle (13°) and a shallow decline between 30° and 90° and a dramatic drop between 90° and 120° for Moama eucrite. Eucrites and diogenites show maximum shift in Band II center with increase in temperature. The equations will correct the spectral parameters to standard geometry (0°) for phase angle data and room temperature (300 K).

**References:** [1] Sierks et al. 2011. *Space Science Reviews*. [2] Gaffey, 1997. *Icarus* 127. [3] Hinrichs et al. 2002. *Icarus* 155. [4] Schade and Wäsch, 1999. *Meteoritics & Planetary Science* 34. [5] Reddy, 2009. *PhD dissertation*, UND.

## PSEUDOTACHYLITIC BRECCIA AND IMPACT MELT ROCK FROM VREDEFORT: CHEMICAL AND ISOTOPIC SYSTEMATICS

W. U. Reimold¹, M. Thirlwall² and T. Mohr-Westheide¹. ¹Museum for Natural History, Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany E-mail: uwe.reimold@mfn-berlin.de; tanja.mohr@mfn-berlin.de. ²Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK. E-mail: m.thirlwall@gl.rhul.ac.uk.

Pseudotachylitic breccias (PTB) are frequently reported as characteristic melt breccia occurrences in impact structures. In contrast, notable occurrences are severely restricted, and massive ones occur only in the crater floors to the Vredefort Dome, South Africa, the Sudbury impact structure, Canada, and at Araguainha, Brazil. In recent years, particularly the Vredefort PTB have been studied extensively for structural, mineralogical and chemical evidence of the processes leading to the formation of these enigmatic rocks and for criteria that could be used to distinguish them from similar melt breccias. Extensive chemical analysis of PTB ranging from <1 mm veinlets to many meter sized, massive occurrences have made a strong case for either local generation through shock compression melting (thin veinlets—akin to shock veins known from chondritic meteorites) or decompression melting (cm to massive melt breccias) in the course of rapid formation of central uplifts [1]. The role of friction melting is, at best, limited—as evidenced by field and thin section observations. Nevertheless, these extensive chemical data are still challenged by a small group of workers who persist that massive PTB represent impact melt that intruded from the crater into the crater floor and thereby assimilated a lot of basement material. To further test this hypothesis—that, in any case, is not supported by the chemical data available to date, Rb-Sr, Sm-Nd and U-Pb isotopic analyses have been carried out by us on several Vredefort PTB samples from massive occurrences in granite and amphibolite, their respective host rocks, and—for comparison—several Vredefort Granophyre (impact melt rock) samples. The results demonstrate that PTB and their host rocks have significantly different isotopic systematics (recalculated to the impact age of 2.02 Ga) from that of the Granophyre. Furthermore, analyses of PTB/HR from different locations yielded locally different isotopic results. This further supports the chemical results that PTB melt was formed from local reservoirs (the respective host rocks), which are different from the reservoir of impact melt (mixture of the full crustal sequence affected by the impact). With respect to the εNd values calculated for an age of 3.15 Ga, the approximate age for the Archean granitoids that represent the host rock to PTB and the major precursor component of Granophyre, a significant variation between granitoid-hosted PTB and Granophyre is observed. In conclusion, not only the chemical data base but also these isotopic results do not support the “PTB=impact melt+assimilated” floor rock hypothesis—also in keeping with an isotopic study of Sudbury PTB and host rocks [2].

**References:** [1] Mohr-Westheide T. and Reimold W. U. 2010. GSA Special Paper 465. pp. 619–645. [2] Lafrance B. and Kamber B. 2010. *Precambrian Research* 180:237–250.
THE POSSIBLE ORIGIN OF THE NON MASS-DEPENDENT ISOTOPE FRACTIONATION IN OZONE AND ITS EXTENSION TO COSMICHEMISTRY

P. Reinhardt¹ and F. Robert². ¹Lab. Chimie Théorique. CNRS - UPMC UMR 7616 - 75252 Paris. E-mail: reinh@lct.jussieu.fr. ²LMCM, CNRS-MNHN, UMR7202, Case 52, 61 Rue Buffon, 75005 Paris, France. E-mail: robert@mnhn.fr.

**Introduction:** A non-mass-dependent oxygen isotopic compositions was reproduced through the synthesis of ozone [1]. Numerous theoretical models [2-3] have been proposed to account for the almost equal enrichment in ¹⁷O and ¹⁸O relative to ¹⁶O—referred in the literature to as “the non-mass dependent isotopic fractionation.” The generally accepted theory is based on a modification of the standard RRKM model of uni-molecular dissociation [2].

Here we follow a different approach. Ozone is formed via the stabilization of the complex O₃* (O₃* + M → O₃ + M) where O₃* results from O + O₂ → O₃*. We propose that the lifetime of O₃* is different if the isotopes involved in the reaction are dis- or indistinguishable; for example: ¹⁶O + ¹⁷O → ¹⁶O¹⁷OO* or ¹⁶O + ¹⁶OO → ¹⁶O¹⁶OO*, respectively (the isotopically non labeled O atom of the molecule has no role in this process). In our calculations, in order to emphasize this idea, the masses of the oxygen isotopes were numerically labeled but their mass differences were ignored (all calculations were actually performed for 16 amu).

**Principle:** In our numerical simulation, O₃* is produced via the collision between O and O₂ but the third body M is absent. Therefore O₃* always disintegrate. However, we assume (as in most chemical models) that for a lifetime τ longer than a critical value τ_Crit, the complex can be stabilized. Therefore, without an explicit model for ozone formation, we extrapolate our simulations to a real situation. We note τ the average lifetime of the complex in a range of τ values where O₃* can be stabilized as O₃ and P the probability to find it; the subscripts R and NR stand for isotope exchange (Reactive) and non-exchange (Non-Reactive) reactions, respectively. The effect arises from the fact that the partition w of the average lifetime is: w = τ_R P_R + τ_NR P_NR when isotopes are distinguishable but w = (τ_R + τ_NR) 1/2 [P_R + P_NR] when they are indistinguishable. Lifetimes can be derived from these partitions.

**Results:** The scattering is carried out within classical trajectory simulations, in an ab-initio potential of three oxygen atoms in a singlet ground state. This energy surface was calculated by the group of R. Schinke [4] with up-to-date quantum chemical means. The calculated isotopic fractionation factor α reproduces (1) the experimental results (for ¹⁶O¹⁷O¹⁸O the calculated α is 1.26 compared with 1.21 for the measured value) and (2) the observed variations with P and T [5, 6].

**Cosmochemical Consequences:** Since the present interpretation does not depend on the interaction potential involved in the formation of the complex, the M. Thiemens' proposal [7] according to which the ozone effect is relevant to Cosmochemistry is supported by the present treatment.

**References:** [1] Thiemens M. H. and Heidenreich III J. E. 1983. *Science* 219:1073. [2] Gao Y. Q. and Marcus R. M. 2001. *Science* 293:259. [3] Babikov D. et al. 2003. *The Journal of Chemical Physics* 119:2577. [4] Schinke R. and Fleurat-Lessart P. 2004. *The Journal of Chemical Physics* 121:5789. [5] Morton J. et al. 1990. *Journal of Geophysical Research* 95:901. [6] Janssen C. and Tuzson B. A. 2010. *The Journal of Chemical Physics* 114:9709. [7] Thiemens M. H. 2006. *Annual Review of Earth and Planetary Sciences* 34:217.

PARENT BODY INFLUENCE ON ORGANIC MATTER: THE MESSAGE FROM PARIS

L. Remusat¹, S. Bernard¹, C. Le Guillou² and A. Brearley². ¹LMCM, CNRS-MNHN, UMR7202, Paris, France. ²Department of Earth and Planetary Sciences, UNM, Albuquerque, USA. E-mail: remusat@mnhn.fr.

**Introduction:** Among the CM carbonaceous chondrites, Paris appears to be the less altered and has experienced mild thermal metamorphism [1]. Like other CM, Paris exhibits variations in alteration state within the same sample. This unique object among the CM class should shed new light on the parent body influence on the isotopic and molecular structure of the organic matter in carbonaceous chondrite. The effects of fluid circulation on chondritic organics remain unclear and have implications on the interpretations of the isotopic and molecular signatures of the insoluble organic matter (IOM) in chondrites [2, 3].

Recently, the analysis of organic matter in several pieces of Tagish Lake (ungrouped C2 chondrite intermediate between CI and CM) showing variable degrees of alteration has revealed chemical and isotopic heterogeneities for IOM and soluble compounds [4, 5]. These observations have lead to the conclusion that aqueous alteration has induced modifications of organic matter. It was also concluded that isotopic exchange has altered the D/H signature of the IOM in Tagish Lake. This conclusion is in contrast with the in situ NanoSIMS observation that the isotopic signature of organic particles is poorly affected by hydrothermal alteration [3]. The aim of this study is to compare the molecular properties and isotopic signature (measured in situ) of organic particles in the two lithologies found in Paris meteorite.

**Experimental:** A polished section of Paris meteorite was prepared without epoxy and was studied by NanoSIMS. Several areas on the least and most altered regions were rastered by a focused Cs⁺ beam to generate secondary ion images of H⁻, D⁻, ¹²C⁻, ¹⁶O⁻, ²⁶CN⁻, ²⁸Si⁻ and ³²S⁻. The spatial resolution is estimated to be 230 nm. Several FIB (focused ion beam) sections were prepared from the same areas for STXM (Scanning Transmission X-ray Microscopy) experiment to identify the functional groups and TEM (Transmission Electron Microscopy) study of the textural associations between organics and minerals.

**Results and Discussion:** Like in other CM, Paris exhibits micron size organic particles distributed randomly in the matrix. However, some areas showing a high signal in S and H lack organic particles. TEM should allow the characterization of these phases. Our NanoSIMS data indicate that the D/H ratio of organic particles in the heavily and poorly altered matrices is undistinguishable. Most of the organic particles exhibit 0 < δD < 2000‰; these data are consistent with other CM matrices [3]. A few D-rich hot spots are also observed, with a maximum at δD = 7950 ± 330‰. C/H and N/C are also similar in the two lithologies, though C/H in Paris appears significantly lower than their counterparts in other CM.

Our data thus indicate that aqueous alteration on CM parent body does not induce a significant modification of the composition of organic particles. Further STXM and TEM observations will be presented and will be used to check these interpretations based on NanoSIMS imaging.

**References:** [1] Zanda B. et al. 2010. Abstract #5312. 73rd MetSoc Meeting. [2] Alexander C. M. O'D. et al. 2007. *Geochimica et Cosmochimica Acta* 74:4417-4437. [3] Remusat L. et al. 2010. *The Astrophysical Journal* 713:1048-1058. [4] Glavin D. P. et al. 2010. Abstract #5131. 73rd MetSoc Meeting. [5] De Gregorio B. T. et al. 2010. Abstract #5398. 73rd MetSoc Meeting.
D/H RATIOS OF HIGHLY EVOLVED LUNAR ROCKS

K. L. Robinson¹, G. J. Taylor¹, E. Hellebrand¹ and K. Nagashima¹. ¹HIGP, UHNAI, University of Hawai'i at Mānoa. E-mail: krobinson@higp.hawaii.edu.

**Introduction:** The felsites are highly evolved lunar rocks, typically containing approximately 70 wt%SiO₂. Most have igneous textures that feature graphic intergrowths of K-feldspar and quartz [1]. Sampled felsites occur as clasts in breccias, sometimes coexisting with Fe-rich, low-Si clasts. This pairing of Fe-rich and Si-rich compositions suggests that the felsites could have formed through silicate liquid immiscibility from a magma with KREEP basalt composition in small intrusive bodies [1].

Recently, water has been detected in lunar pyroclastic glasses [2] and apatites [3, 4]. Apatite [Ca₅(PO₄)₃(F, Cl, OH)] incorporates water as OH into its crystal structure. At low abundances, water acts like an incompatible element and will become enriched in the melt. Thus, KREEP-rich magmas should be enriched in water when apatite begins to crystallize. Apatites in felsites could contain water sufficient to allow the D/H isotopic composition of the water to be determined, which is important for determining the source of the Moon's water and the extent of water loss during magmatic processing [e.g., 4, 5].

We identified four apatite grains large enough (> 20 µm) for SIMS analysis in two lunar rocks. Sample 14321,1047 is a quartz-K-feldspar felsite, while sample 77538,16 consists of felsite and associated Fe-rich phases; the apatite was within the Fe-rich phase.

**Methods:** Apatites were analyzed for P, Ca, Si, Na, Fe, Ce, F, Cl, Y, and La with the UH JXA-8500F electron microprobe. Hydrogen isotopic composition and water content were analyzed in situ with the UHims 1280 ion microprobe with a Cs⁺ primary beam. H₂O content of apatite samples was estimated from a calibration curve on H₂O (wt%) versus ¹H/¹⁸O determined using four apatite standards with different H₂O contents (provided by F. McCubbin). The detection limit for H₂O was approximately 100 ppm. Uncertainties on δD and water content are approximately 75‰ and 30% (2σ), respectively.

**Results:** We analyzed a total of five points among four apatite grains in two samples. The single large apatite in 14321,1047 had H₂O below our detection limit in both points analyzed. Two apatite grains were measured in 77538,16. They have H₂O contents of approximately 180 ppm. δD values for these points are +300–+400‰.

**Discussion:** We found very little water in the apatites measured. Apatites in both samples contain significant (wt% level) amounts of REEs, indicating that these highly-evolved, KREEP-rich magmas contained little water. In turn, this suggests that the lunar magma ocean (and the bulk Moon) had a low initial water content, as argued by [5]. The δD values in apatite in 77538 with detectable water are elevated, which agrees with findings in [4]. However, since the measured H₂O is barely above detection limit, we cannot say with absolute certainty that the δD of lunar water in this magmatically evolved lunar rock is elevated with respect to Earth.

**References:** [1] Robinson K. L. and Taylor G. J. 2011. Abstract #1257. 42nd Lunar and Planetary Science Conference. [2] Saal A. E. et al. 2008. *Nature* 454:192–195. [3] McCubbin F. M. et al. 2010. *PNAS* 107:11223–11228. [4] Greenwood J. P. et al. 2011. *Nature Geoscience* 4:79–82. [5] Elkins-Tanton L. et al. 2011. *Earth and Planetary Science Letters*, in press.

WESTON: THE RECOVERY AND DISPERSION OF A HISTORICALLY SIGNIFICANT METEORITE FALL

M. C. Robson. John J. McCarthy Observatory, New Milford, C 06776, USA. E-mail: Monty.Robson@mccarthyobservatory.org.

**Introduction:** Weston, the first scientifically documented meteorite fall in the New World, occurred in the decade in which most scientists finally agreed that stones do fall from the sky. It fell during morning astronomical twilight on 14 December 1807. Seven fragments were recovered from an elliptical strewn field in central Fairfield County, Connecticut, USA. This 12 km by 4 km ellipse is orientated north-south and centered on N 41° 16' and W 73° 16' [1].

The first fragments were recovered within about half an hour of the fall and the last of the seven within three weeks. The consensus of modern literature is that 150 kg of the meteorite was recovered. But meteoritic scholars from Wülfing [2] to Koblitz [3] only account for about 20 kg. In the first edition of the *Catalogue of meteorites*, G. T. Prior [4] added a note for Weston which has been included in all subsequent editions of the work: "Comparatively little has been preserved." Reasons for this apparent mass discrepancy will be discussed.

In an age when the fastest communication and transportation were limited to horse speed it seems remarkable how rapidly the mass of Weston was dispersed around the world. Unfortunately this took place without good record keeping so the history of only one Weston fragment is easily traced from recovery to today. Ongoing research now indicates two more fragments may have a completely known history.

**Discussion:** Two teams investigated the fall sites of Weston. Dr. Isaac Bronson and Rev. Dr. Horace Holley conducted the first investigation on December 19, 1807. The better-known on-site expedition to the area was performed by Yale College professors Benjamin Silliman and James Kingsley starting two days later. A careful reading of both the reports generated from these expeditions [5,6] is necessary to understand the recovery of Weston. Together these reports allow a recovery chronology to be developed that includes when, where, and by whom the fragments were recovered. The reports also describe the fall circumstances and give mass estimates for each fragment. This valuable information shows why so little of the meteorite can be accounted for today.

**Acknowledgments:** Sincere thanks go to these researchers for professional courtesy during visits to their collections: Dr. Timothy McCoy, National Meteorite Collection, Smithsonian Institution, Washington D.C.; Dr. Caroline Smith, Natural History Museum, London; Dr. Laurence Garvie, Center for Meteorite Studies, Tempe. Thanks also to Dr. Franz Brandstätter, of the Naturhistorisches Museum, Vienna, for his valuable correspondence.

**References:** [1] Robson M. and Pagliaro F. 2009. *Meteoritics & Planetary Science* 44:1343–1354. [2] Wülfing E. A. 1897. *Die meteoriten in sammlungen und ihre literature*. Tübingen: H. Laupp'schen. 460 p. [3] Koblitz, *Journal MetBase* 7.1. CD-ROM version 7.1. [4] Prior G. T. 1923. *Catalogue of meteorites* with special reference to those represented in the collection of the British Museum (Natural History). London: British Museum. ix+196 p. [5] Bronson I. 1807. Letter to the editor. *New-York Commercial Advertiser*. December 28, 1807. [6] Silliman B. and Kingsley J. 1807. Letter to the editor. New Haven, Connecticut, Herald December 29, 1807.
## COSMIC SPHERULE DENSITY IN SOIL AND SURFACE EXPOSURE AGE IN THE ATACAMA DESERT, CHILE

P. Rochette, A. Hutzler, A. Nyindong, S. Spitale, D. Bourles, R. Braucher, P. Chaurand and J. Gattacceca. CEREGE, CNRS/Université Aix-Marseille, Aix-en-Provence, France.

We have sampled various surfaces in the Atacama Desert during our meteorite search expeditions [1] and determined cosmic spherule (CS) density within these surfaces. Soil was sampled down to 10 cm depth on a surface varying from 0.1 to 1 m². Raw soil was sieved in the 200–800 µm fraction and subjected to magnetic extraction either on site (for larger samples) or back to the laboratory. CS larger than 200 µm were picked under the binocular and their extraterrestrial nature confirmed by SEM imaging and micro-chemical analysis using µXRF. CS > 200 µm density varies in the eight sites sampled from 100 to 2500 CS m⁻². Repeated sampling on the same surface for three sites (within a km distance) yield consistent CS densities. For the richest samples logarithmic cumulative size distribution slope around -5 indicates minor size distortion with respect to Antarctic collections, suggesting little horizontal (by wind or water) or vertical (by percolation below the sampled surface) transport. In those sites the proportion of Iron CS (ICS) is about 4%, again in agreement with Antarctic collections, taking into account the lack of glass CS due to magnetic extraction. However, in less rich samples, the size distribution slope (up to -3) and the ICS% (from 15 to 60%) indicate some density and size sorting. Assuming that ICS > 200 µm is the least mobile fraction of the CS flux, due to size, resistance to weathering and density, we propose that their density may be a proxy of surface age.

To test this hypothesis, surface exposure ages have been determined using in situ produced ¹⁰Be content in large quartz pebbles sampled on the same surfaces. Measurements were performed on ASTER, the 5MV AMS located at CEREGE [2]. Surface exposure ages calculated assuming no erosion vary from 0.15 to 6 Myr. Correlation between ICS density and exposure ages appears good in all sites except one, from a different climatic zone. Silicate CS density is much less well correlated with exposure age, comforting our hypothesis of higher reliability of ICS density. Drawback is that larger samples are needed to recover a significant ICS number.

**References:** [1] Gattacceca et al. 2009. Abstract #5083. Meteorical Society Meeting. [2] Arnold M. et al. 2010. *Nuclear Instruments and Methods in Physics Research B* 268:1954–1959. Doi:10.1016/j.nimb.2010.02.107.

## PETROGRAPHY AND MODAL ABUNDANCE OF METAL IN UREILITES: A COMBINED 2D AND 3D STUDY

A. J. Ross¹,², D. C. Hezel¹, L. E. Howard¹, C. L. Smith¹, H. Downes², J. S. Herrin, P. Jenniskens³ and M. Shaddad⁴. ¹Mineralogy Department, Natural History Museum, London, UK. E-mail: aidan.ross@ucl.ac.uk. ²Centre for Planetary Sciences at UCL/Birkbeck, London, UK. ³SETI Institute, Mountain View, CA, USA. ⁴Physics & Astronomy Department, University of Khartoum, Khartoum, Sudan.

**Introduction:** Most unrecciated ureilites are believed to represent intact samples of the ureilite parent body (UPB) mantle, consisting predominantly of olivine and pyroxenes with accessory carbon, metal and sulfide [1]. Although much of the original metal has been lost [2], what remains records partial melting and differentiation processes on the UPB. Knowing the modal abundances of metals within ureilite samples helps with the interpretation of bulk siderophile elements [2, 3] and of magnetic susceptibility [4]. X-ray computed tomography (CT) scanning allows nondestructive 3D imaging of samples, visualizing 3D spatial relationships which are not apparent in traditional petrographic studies of individual 2D thin sections.

We have analyzed a range of ureilite samples in 2D and 3D, including several samples of the anomalous ureilite Almahata Sitta (AS) [5]. As a quickly recovered fall, AS samples do not show oxidation of metal as seen in most other ureilites.

**Methods:** Samples were scanned using the Metris X-Tek HMX ST 225 CT system at the NHM and reconstructed using CT-PRO 2.0. Analysis of the scans was performed using VG Studio Max 2.0, using greyscale thresholding to separate phases. Thin sections or probe blocks were examined using the LEO 1455 VP SEM at the NHM. Whole section EDS X-ray chemical maps were acquired using Oxford Instruments INCA software and combined to differentiate minerals. These were processed by pixel counting in Photoshop to obtain modal mineralogies.

**Results and Discussion:** Metal in Almahata Sitta shows a large variation in modal percent and appearance between samples. For example, from SEM data AS#22 has approximately 1.8% metal with grain boundary metal not exceeding approximately 35 µm in width, whereas AS#44 shares many features with the anomalous ureilite LAR 04315 and is particularly metal-rich, with approximately 3.4% metal and some unusually large grains >250 µm in size. These percentages include siderophile-bearing metal in veins and primary inclusions as well as siderophile-free secondary reduction metal. All metal affects magnetic susceptibility, whereas bulk siderophile concentrations are not affected by reduction metal. Reduction metal makes up a greater percentage of the metal content of AS#22 than AS#44. Preliminary data analysis suggests that whilst it is easier to differentiate metal and sulfide using the SEM, carbon is harder to quantify in 2D as SEM samples are carbon-coated. The main sources of error in extrapolating the data are likely to be small sample size and sample heterogeneity.

**Acknowledgments:** We would like to thank R. Abel, A. T. Kearsley and A. Ball for equipment assistance. We thank ANSMET and the NHM for comparative ureilite samples.

**References:** [1] Mittlefehldt D. W. et al. 1998. In *Planetary materials*. Reviews in Mineralogy 36. [2] Rankenburg K. et al. 2008. *Geochimica et Cosmochimica Acta* 72:4642–4659. [3] Friedrich J. M. et al. 2010. *Meteoritics & Planetary Science* 45:1718–1727. [4] Kohout T. et al. 2010. *Meteoritics & Planetary Science* 45:1778–1788. [5] Jenniskens P. et al. 2009. *Nature* 458:485–488.
## ANALYSIS OF SECTIONED AEROGEL TRACKS OF COMET WILD 2 PARTICLES WITH C60-TOF-SIMS

D. Rost, T. Henkel and I. Lyon. The University of Manchester, Manchester M13 9PL, UK. E-mail: detlef.rost@manchester.ac.uk.

**Introduction:** The Stardust mission returned material from comet Wild 2 captured in aerogel. The analysis of these samples is a challenging task, especially for organic compounds. Driven by the impact explosion, some if not most of the surviving organics are found in the neighboring aerogel [1, 2]. There is intrinsic contamination in the aerogel [2, 3] and further terrestrial contamination should be avoided by analyzing samples as unaltered as possible, i.e., not pressed or embedded. Preferably, the spatial resolution should be on the scale of the (sub)micrometer sized surviving cometary particles. Finally, minimal sample consumption allows comprehensive examination with additional methods. Meeting all these needs is very challenging (e.g., two-step laser mass spectrometry is limited to spatial resolution > 10 µm [1, 2]).

**Method:** Recent developments in time-of-flight secondary ion mass spectrometry (ToF-SIMS) offer a viable new approach. Using cluster ions as the primary beam enables a gentle and efficient desorption of large molecules from the sample surface while a spatial resolution of down to 1 µm or less can be achieved. C₆₀ clusters have been shown to be most efficient for detecting organic compounds [e.g., 4], but also many major and some minor and trace elements can be measured at the same time with high accuracy [5]. For this study we use one of our ToF-SIMS instruments equipped with a 40 kV C₆₀ primary ion gun. We have previously demonstrated that some organics, including polycyclic aromatic hydrocarbons (PAHs), can be easily detected as intact molecules with only minor fragmentation [6]. We have also measured aerogel surface exposed to the cometary particle flux [7] and found indications for an enrichment in organics relative to unexposed blank flight aerogel.

**Results:** We analyzed a longitudinal section of track 15 (tile C2012) including adjacent aerogel. The untreated sample is held in place by a covering grid. We found organic compounds at constant background levels throughout the aerogel with no apparent enrichment toward the cometary track. This includes the characteristic PAHs naphthalene, phenanthrene and pyrene. Several micrometer sized enrichments of Na, Mg, Al, and K indicate inorganic cometary material stuck in the track walls.

**Discussion:** While organics dispersed into the surrounding aerogel have been identified in more than half of the tracks examined for this feature [1, 8], not all tracks show them [8]. Since bulbous tracks indicate a violent explosion upon particle entry their impacts are thought of being rich in volatile and organic components. Our analyzed track, however, is of carrot shape and at only 250 µm in length rather short. Therefore, it is reasonable that the impacting cometary particle contained only very few volatile and organic components, in accordance with our results.

Further optimizations to our instrument are planned to improve our detection threshold for organics. We plan to analyze more tracks, especially of the bulbous type.

**References:** [1] Sandford S. A. et al. 2006. *Science* 314:1720-1724. [2] Clemett S. J. et al. 2010. *Meteoritics & Planetary Science* 45:701-722. [3] Sandford S. A. et al. 2010. *Meteoritics & Planetary Science* 45:406-433. [4] Fletcher J. S. et al. 2006. *Applied Surface Science* 252:6513-6516. [5] Henkel T. et al. 2009. *Rapid Communications in Mass Spectrometry* 23:3355-3360. [6] Rost D. et al. 2010. Abstract #1973. 41st Lunar and Planetary Science Conference. [7] Rost D. et al. 2009. Abstract #2480. 40th Lunar and Planetary Science Conference. [8] Bajt S. et al. 2009. *Meteoritics & Planetary Science* 44:471-484.

## SOLAR SYSTEM INITIAL $^{176}$Hf/$^{177}$Hf INFERRED FROM THE EUCRITE NORTHWEST AFRICA 5073

J. Roszjar¹, E. E. Scherer², K. Mezger³ and A. Bischoff¹. ¹Institut für Planetologie, WWU Münster, Germany. E-mail: j_rosz01@uni-muenster.de.
²Institut für Mineralogie, WWU Münster, Germany. ³Institute of Geological Sciences, University of Bern, Switzerland.

**Introduction:** Northwest Africa (NWA) 5073 is a new Stannern-trend eucrite with the coarsest texture ever found among eucrite samples [1]. It is mainly composed of pyroxene and plagioclase and comprises abundant mesostasis. The mesostasis primarily consists of tridymite, Ni-poor metallic Fe, troilite, plagioclase, ilmenite, chromite, Ca-phosphate, zircon and baddeleyite. Zr-bearing phases are abundant and up to 25 µm in diameter [1]. Previous Lu-Hf analyses on this sample showed that the whole rock plotted on the external isochron for other basaltic eucrites, but that complex internal Lu-Hf systematics, yielded two ages, $4.68 \pm 0.14$ Ga and $4.31 \pm 0.14$ Ga, and two apparent initial values ($^{176}$Hf/$^{177}$Hf), $0.27976 \pm 13 (2\sigma)$ and $0.28020 \pm 8 (2\sigma)$ [2]. These results correlate with the petrographic observation that this sample had a complex thermal history [1]. To better define the internal isochron for this rock and to better constrain the Solar System initial $^{176}$Hf/$^{177}$Hf value, we separated unradiogenic ilmenite and zircon from the sample.

**Methods:** Zircon and ilmenite were separated from about 6.7 g of cleaned and crushed sample. These minerals were concentrated with a selective acid digestion procedure using HF-HNO₃-HCl. Via handpicking, a pure ilmenite and an ilmenite-zircon-mixture mineral fraction were separated. Chemical separation and isotope analysis procedures were those of [3] and [4]. Samples were analyzed for their Lu-Hf isotopic composition using an IsoProbeMC-ICP-MS. The accuracy and 2 s.d. external precision of Hf isotope analyses as a function of Hf concentration were evaluated by repeated measurement of standard solutions at different intensities [5]. Ages were calculated using a decay constant of $1.867 \times 10^{-11}$ year⁻¹ for $^{176}$Lu (e.g., [3, 6]).

**Results and Conclusion:** The ilmenite fraction lies above the older, $4.68$ Ga isochron at low Lu/Hf. The ilmenite+zircon fraction, together with the whole rock and three pyroxene fractions lie on a $4.61 \pm 0.11$ Ga trend. Although this is within error of the expected age of the sample, the initial $^{176}$Hf/$^{177}$Hf of $0.279832 (77)$ is higher than that of some other eucrite isochrons. This may suggest that ilmenite in the ilmenite+zircon fraction either partially re-equilibrated isotopically during a heating event or it lost some Lu during the selective digestion procedure. In either case, it seems that a pure zircon fraction, if recovered, might yield a somewhat lower initial $^{176}$Hf/$^{177}$Hf than the value reported here.

**References:** [1] Roszjar J., Metzler K., Bischoff A., Barrat J.-A., Geisler T., Greenwood R. C., Franchi I. A., and Klemme S. 2011. *Meteoritics & Planetary Science*, submitted. [2] Roszjar J. and Scherer. E. 2010. *Meteoritics & Planetary Science* 45:A175. [3] Scherer E. E., Münker C., Mezger K. 2001. *Science* 293:683-686. [4] Münker C., Weyer S., Scherer E., and Mezger K. 2001. *Geochemistry Geophysics Geosystems* 2:1064, doi: 10.1029/2001GC000183. [5] Bizzarro M., Baker J. A., Haack H., Ulfbeck D., and Rosing M. 2003. *Nature* 421:931-933. [6] Söderlund U., Patchett P. J., Vervoort J. D., and Isachsen C. E. 2004. *Earth and Planetary Science Letters* 219:311-324.
## A POSSIBLE PAIRED FALL OF NICOLÁS LEVALLE FROM ARGENTINA AND ITS P IN CHONDRULES

R. Rönick¹, T. Ntaflos¹ and H. Palme². ¹University of Vienna, Althanstrasse 14, A-1090, Vienna. (roman.roenick@univie.ac.at). ²Senckenberg Forschung, Senckenberganlage 25, D-60325, Frankfurt am Main.

**Introduction:** Recently a meteorite from Argentina was classified as L5 and named Nicolás Levalle (Meteoritical Bulletin Database, in press). We examined a meteorite which is presumably paired to this possible fall considering the date and location which was reported to us from locals (Mr. Blanco). We classified our sample as LL4. In addition, we studied this meteorite focusing on the abundance and distribution of P in chondrules.

**Petrology and Mineral Chemistry:** Modal abundances are 78 % chondrules (PO, BO, RP), 14% matrix, 5% troilite, 1 % taenite, 1% chromite and 1% minor phases (e.g., apatite). The Fa content of the olivines is 26.00 ± 0.33 mole%, n = 67 and the orthopyroxene composition is FS = 22.12 ± 0.52 mole%, En = 76.60 ± 0.44 mole%, n = 26. Still, the PO chondrules studied contain a clear to turbid glassy mesostasis. Therefore, we suggest to classify the sample as LL4. Undulatory extinctions of the olivines accompanied by rare planar fractures are indicative of a shock stage S3 [1]. The Meteoritical Bulletin lists a lower Fa content of 24.9 ± 0.20 mole% (n = 6) possibly indicating a brecciated meteorite.

**P-zoned Olivines in Particular Chondrules:** Some type IIA chondrules show P-zonation patterns within the olivines similar to those investigated in H-chondrites by [2], [3] and Semarkona LL3 by [4]. While divalent cations like Fe and Mg are completely equilibrated during thermal metamorphism, P retains the magmatic zonation patterns of the olivines. The incorporation of P during olivine crystallization is indicative of rapid crystallization and high P contents in the melt [5]. The content of P₂O₅ of the mesostasis of five investigated chondrules varies within a factor of about 5 (from 0.67 to 0.12 wt%) as P is locked up in phosphate whereas the content of SiO₂, MgO, FeO, CaO, Al₂O₃ and Cr₂O₃ remains relatively constant due to diffusion of the elements across the chondrule rims. At the interface between dendritic clinopyroxene and glass within the mesostasis of chondrules with high P₂O₅ contents tiny phases (<1 µm) rich in Ca and P occur which we consider as microcrystals of apatite formed during thermal metamorphism. The glass is free of P₂O₅. This may allow us to distinguish different types of chondrules whose original chemistry is erased during thermal metamorphism. Other type IIA PO chondrules have lower contents of P₂O₅ within the mesostasis. No P-zonation features of the olivines were found in the latter. [6] also found a positive correlation between P content in olivine and the mesostasis. Further studies of the zoning of P and other trace elements in UOCs and EOCs are planned.

**References:** [1] Stöffler D. et al. 1991. *Geochimica et Cosmochimica Acta* 55:3845–3867. [2] McCanta M. C. et al. 2008. Abstract #1807. 39th Lunar and Planetary Science Conference. [3] McCanta M. C. et al. 2009. Abstract #2048. 40th Lunar and Planetary Science Conference. [4] Hewins R. H. 2009. 40th Lunar and Planetary Science Conference. [5] Boesenberg J. S. et al. Abstract #1366. 35th Lunar and Planetary Science Conference. [6] Jones R. H. 1990 *Geochimica et Cosmochimica Acta* 54:1785–1802.

## ORIGIN AND ALTERATION OF AMOEBOID OLIVINE INCLUSIONS IN CK3 AND CV3 CHONDRITES

Alan E. Rubin. Institute of Geophysics, University of California, Los Angeles, CA 90095-1567, USA. E-mail: aerubin@ucla.edu.

Amoeboid olivine inclusions (AOIs) are composed of major olivine, minor Ca-pyx, anorthite, and in some cases, spinel ± low-Ca pyx ± melilite [1]. Some AOIs enclose small CAIs with Wark-Lovering rims [1, 2]. Although rare, melilite occurs in a few AOIs from minimally altered carbonaceous chondrites [1]. AOIs vary in size among chondrite groups: OC, 0.04–0.35 mm [3]; CO, 0.1–0.5 mm [4]; CR, <0.5 mm [5]; CV, 0.1–10 mm [6, 7]. I report here the occurrence of a 0.54 × 1.31 mm AOI in CK3 NWA 1559; I also studied 9 AOIs from CV3 Allende. CK and CV chondrites are closely related groups that likely formed in the same region of the nebula [8, 9]; their AOIs probably have similar histories.

The CK3 AOI interior contains irregular 3–15 µm-size Ca-pyx grains (Fs₁.₆Wo₄.₈) with 2.2 wt% Al₂O₃ (approximately 70 vol%), 2–20 µm-size pores (approximately 30 vol%) and accessory plagioclase. The 75–160 µm-thick rim of the AOI contains ferroan, 20–130 µm-size olivine grains (Fa34.3 ± 0.4) with faceted (120° triple junctures) and fragmental shapes. Coarse (25–50 µm-size) patches of plagioclase (Ab₆₁.₈ Or₁.₁) with 2–18 µm-thick Ca-pyx rinds occur in several places just beneath the olivine rim. (The CK3 AOI mineral compositions were all modified by parent-body processes.)

Nearly 80% of Allende AOIs have rims composed of 10–30 µm-size olivine grains, many with 120° triple junctures [10]. Rim olivine consists of low-FeO cores surrounded by ferroan overgrowths produced by parent-body processes. The rims are 10–80 µm thick and enclose porous patches of Ca-pyx, plagioclase ± spinel. They may be related to accretionary rims with 20–40 µm anhedral forsterite grains [10] that surround many CV CAIs [11].

On average, olivine constitutes (in vol%) approximately 50% of OC, CO, and CR AOIs [3–5], 50% of the CK3 AOI, and approximately 80% of AOIs in reduced CV chondrites [2]. CV AOIs may have acquired additional forsterite in the CV-CK region of the nebula (previously inferred to contain abundant olivine-rich dust [9]). This may account for the large sizes of CV AOIs. Although not particularly olivine-rich, the CK3 AOI probably formed in a similar manner.

Amoeboid olivine inclusions were sintered to partly melted in the nebula, plausibly by the same process that formed chondrules; many AOIs preserved some of their initial porosity. In more-extensively-melted AOIs, olivine crystallized first, followed by melilite, spinel, Ca-pyx and small amounts of anorthite. Much of the melilite and spinel was altered and replaced by Ca-pyx and anorthite [1]. Hydrothermal experiments show melilite to be very susceptible to parent-body alteration [12], consistent with its paucity in CM CAIs [13] and its corrosion in Allende CAIs [14]. Some of the pores in AOIs may have been formed by the corrosion of melilite.

**References:** [1] Krot A. et al. 2004. *Chemie der Erde* 64:185–239. [2] Komatsu M. 2003. Ph.D. thesis, University of Tokyo. [3] Itoh S. et al. 2007. *Meteoritics & Planetary Science* 42:1241–1247. [4] Chizmadia L. et al. 2002. *Meteoritics & Planetary Science* 37:1781–1796. [5] Aléon J. et al. 2002. *Meteoritics & Planetary Science* 37:1729–1755. [6] Grossman L. and Steele I. 1976. *Geochimica et Cosmochimica Acta* 40:149–155. [7] Komatsu M. et al. 2001. *Meteoritics & Planetary Science* 36:629–641. [8] Greenwood R. et al. 2010. *Geochimica et Cosmochimica Acta* 74:1684–1705. [9] Rubin A. 2010. *Geochimica et Cosmochimica Acta* 74:4807–4828. [10] Kornacki A. and Wood J. 1984. 14th Lunar and Planetary Science Conference. pp. B573–B587. [11] MacPherson G. et al. 1985. *Geochimica et Cosmochimica Acta* 49:2267–2279. [12] Nomura K. and Miyamoto M. 1998. *Geochimica et Cosmochimica Acta* 62:3575–3588. [13] Rubin A. 2007. *Meteoritics & Planetary Science* 42:1711–1726. [14] MacPherson G. and Grossman L. 1984. *Geochimica et Cosmochimica Acta* 48:29–46.