SELENIUM ISOTOPES IN SOME CHONDRITES

R. Jotter and U. Ott. Max-Planck-Institut für Chemie, Postfach 3060, D-55020 Mainz, Germany. E-mail: uli.ott@mpic.de.

**Introduction:** Among heavy elements, selenium is exceptional with respect to the extent of isotopic mass fractionation that may occur in nature (e.g., [1]). It has six stable isotopes ($^{74}$Se to $^{82}$Se), can occur in five difference valence states (−II to +VI) and is one of the most redox-sensitive elements. Equilibrium isotope fractionation (in terms of $^{82}$Se/$^{76}$Se) at low temperature may range up to several percent [2]. Chemically and in chondritic meteorites Se largely follows the ~2500× more abundant sulfur [3].

Selenium isotopes in meteorites have mostly been investigated with regard to nucleosynthetic anomalies, e.g., by stepwise dissolution [4, 5]. However, in this work due internal normalization, any information on mass dependent effects has been lost. To our knowledge, only [6] have reported useful isotopic data without internal normalization, but these are restricted to a few troilite samples from iron meteorites. Their Se isotopic composition turned out to be indistinguishable from that of the NIST SRM 3149 standard (±0.39 ‰ in $^{82}$Se/$^{76}$Se; [7]). We have set out to obtain a wider overview of Se isotopic composition in meteorites, beginning with bulk chondrites.

**Experimental:** Typically ~100–200 mg of meteorite are dissolved by HF/HNO₃ digestion. Selenium is separated using a microcolumn containing activated alumina [8] and purified using ascorbic acid as described in [9]. Mass spectrometric measurements are by N-TIMS using multiple collection on a Finnigan MAT 262 for isotopes $^{76}$Se to $^{80}$Se, with the extreme isotopes $^{74}$Se and $^{82}$Se measured on the central Faraday cup. Mass fractionation (δ $^{76}$Se/$^{80}$Se) is determined using a $^{74}$Se/$^{82}$Se (≈0.27:1) double spike.

**First Results:** At this time, data have been obtained for the carbonaceous chondrites Allende and Murchison as well as the L3.4 chondrite ALH 81032. Selenium abundances of Murchison and Allende agree well with literature values [3], while the abundance in ALH 81032 is close to the average concentration for L chondrites [10]. Isotopic data need to be considered preliminary, with an uncertainty in δ $^{76}$Se/$^{80}$Se close to 1 ‰. For a precise assessment (including analytical uncertainties) we will have to refine the composition of our double spike and assess the external reproducibility of standard measurements. Relative to the NRM 3149 standard both Allende and ALH 81032 may be somewhat light (δ $^{76}$Se/$^{80}$Se ~2 and ~1 ‰, resp.), while Se in Murchison is indistinguishable from the reference.

**References:** [1] Johnson T. M. 2004. *Chemical Geology* 204:201–214. [2] Li X. and Liu Y. 2011. *Earth and Planetary Science Letters* 304:113–120. [3] Dreibus G. et al. 1995. *Meteoritics* 30:439–445. [4] Plagge M. et al. 2003. Abstract #1217. 34th Lunar and Planetary Science Conference. [5] Dauphas N. et al. 2003. Abstract #1807. 34th Lunar and Planetary Science Conference. [6] Rouxel O. et al. 2002. *Geochimica et Cosmochimica Acta* 66:3191–3199. [7] Carignan J. and Wen H. 2007. *Chemical Geology* 242:347–350. [8] Pyrzynska K. et al. 1998. *Analytica Chimica Acta* 363:141–146. [9] Tanzer D. and Heumann K. G. 1991. *Analytical Chemistry* 63:1984–1989. [10] Wasson J. T. and Kallemeyn G. W. 1988. *Philosophical Transactions of the Royal Society London A* 325:535–544.

PETROGRAPHY OF LUNAR METEORITES DHOFAR 925 AND 961

K. H. Joy¹,²,³, D. A. Kring¹,² and M. E. Zolensky³. ¹CLSE, LPI/USRA, 3600 Bay Area Blvd., Houston, TX 77058, USA. E-mail: joy@lpi.usra.edu. ²NASA Lunar Science Institute. ³ARES, NASA Johnson Space Center, Houston, TX 77058, USA.

**Introduction:** Lunar meteorites Dhofar (Dho) 925 and 961 are brecciated lunar meteorites of intermediate Fe composition (7–17 FeO wt%) [1–3]. They are reputedly paired with each other, and are also grouped with the Dho 960 and Sayh al Uhaymir (SaU) 449 stones [1–3]. As Dho 961 is compositionally similar to regoliths in the South Pole-Aitkin (SPA) basin, it has been hypothesized that the group may have been launched from SPA on the farside of the Moon [3–5]. As such, they may contain chronological evidence to date the oldest lunar basin, helping to constrain the early impact history of the Moon.

**Methods:** One thick section from each meteorite was carbon coated and analyzed using the NASA JSC JEOL-7600F field-emission SEM and Cameca SX100 electron microprobe (EMP).

**Results:** Dho 925 and 961 are petrographically distinct [1, 5], but contain lithics with similar textures and mineral chemistries:

**Dho 925:** The sample (~7 × 6 mm) is composed of a clast-bearing dark-grey impact melt breccia. Clasts range from small (<10 µm) mineral and glass fragments up to 2 mm lithics (equilibrated magnesian anorthositic plutonics (plagioclase typically >60% by area, An₀.₄.₉₇; mafics typically <40%, Mg#68–80 [see also 1, 5]); very-low Ti (VLT) and low-Ti basalts (quenched variolitic and ophiitic texture); impact melts and melt breccias; fragmental breccias; and rare Si-K-feldspar assemblages).

**Dho 961:** The sample (~22 × 12 mm) is a fragmental breccia with a notable large (~4 × 2 mm) dark-grey, clast-bearing, impact melt breccia clast and a large (~5 × 3 mm) cream-coloured ophiitic basalt clast (similar to the KREEP igneous rocks described by [1]). Dho 961 contains a more diverse textural range of clasts than seen in Dho 925. For example, plutonic igneous fragments are typically more mafic (20–60% mafics), and VLT and low-Ti basalts are texturally diverse (variolitic, subophitic, ophiitic textures). A 300 µm thick melt vein in Dho 961 has a composition similar to the Dho 025 bulk rock [3].

**Impact Melts:** Impact melts and clast-bearing melt breccias (of size range 4 mm to 300 µm) in Dho 925 and 961 were analyzed using a 20 µm defocused EMP beam. Most are normative anorthositic gabbro, with compositions similar to the Dho 025 bulk rock [3]. A few clasts are normative anorthositic troctolite and troctolitic anorthosite. All are alkali poor (<0.6 Na₂O + K₂O wt%), similar to KREEP-poor feldspathic lunar meteorites, but are comparatively less aluminous: their Al-contents are more akin to Apollo VHA-impact melts (e.g., 20–25 Al₂O₃ [6]). We found no clasts in either stone of the olivine-bearing, ITE-rich, mafic impact melt breccia (Al₂O₃ ~15.4 wt%) reported to be a dominant component of Dho 961 [4–5] and used as supporting evidence for an SPA basin origin [4].

**References:** [1] Demidova S. I. et al. 2005. Abstract #1607. 36th Lunar and Planetary Science Conference. [2] Demidova S. I. et al. 2007. Petrology 15:386–407. [3] Korotev R. L. et al. 2010. Abstract #2126. 41st Lunar and Planetary Science Conference. [4] Jolliff B. A. et al. 2008. Abstract #2519. 39th Lunar and Planetary Science Conference. [5] Zeigler R. A. et al. 2010. Abstract #1985. 41st Lunar and Planetary Science Conference. [6] Spudis P. D. and Davis P. A. 1986. *Journal of Geophysical Research* 91:E84–E90.
5456

FIRST DESCRIPTIONS OF TWO NEW BOREHOLE PROFILES
FROM THE RIES IMPACT CRATER, GERMANY

D. Jung¹, S. Sturm², G. Arp³, J. Pohl⁴ and T. Kenkmann². ¹Bayerisches Landesamt für Umwelt LfU, ²Institut für Geowissenschaften, Albert-Ludwigs-Universität Freiburg, Germany. ³Universität Göttingen, ⁴LMU-München. E-mail: Sebastian.Sturm@geologie.uni-freiburg.de.

**Introduction:** The Ries impact crater with a diameter of ~25 km, located in southern Germany, is a complex crater structure that is famous for its largely preserved ejecta blanket inside and outside the crater [1,2]. The principal outline of the crater interior consists of (i) a central crater basin filled with suevite and lake deposits, (ii) an inner crystalline ring with a diameter of 12 km, that consists of uplifted brecciated basement units, (iii) the megablock zone displaying a hummocky relief and containing parautochthonous and allochthonous megablocks, and (iv) the tectonic crater rim [3,4]. Here we present borehole profiles of two new drilling sites at the Ries impact crater in southern Germany that were drilled by the Geological Survey of Bavaria (LfU). The first drilling location was selected to investigate a post-impact hydrothermal spring site and its basement, which is part of the crystalline ring. The second drilling location was aimed at constraining the occurrence and volume of impact melt rock in the Ries crater.

**Drilling Sites:** The first drilling site is located south of the city of Nördlingen and north of Reimlingen on the southern crystalline ring. (R4390848/H5411481). The 65 m deep borehole profile can be subdivided from base to top: (1) 65.0–63.9 m: altered, brecciated gneisses embedded in reddish clay material (bunte breccia?), (2) 63.9–56.2 m: altered mm to cm-sized gneiss and amphibolite fragments embedded in a grayish, fine-grained matrix, calcite veins and melt veins? present, (3) 56.2–36.7: grayish breccia, partly clast supported, with abundant biotite-rich gneiss and amphibolite fragments, (4) 36.7–23.0 m: intact gneisses with foliation dipping consistently 45°, (5) 23.0–22.5: grayish fine-grained matrix including cm-sized granitic clasts, (6) 22.5–0.4 m: Travertin limestone and Ries lake deposits, (7) 0.4–0.0 m: topsoil.

The second drilling site is located a few meters south of the outcrop Polsingen, in which impact melt rock is exposed (R4405236/H5420826). The 35 m deep borehole profile is subdivided from base to top: (1) 35.0–34.0: iron-rich, ocher sandstone (Dogger), (2) 34.0–27.5: brecciated limestone (Malmian) (3) 27.5–23.8: grayish marly limestone, quartzite at top, (4) 23.8–20.5 m: iron-rich, ocher sandstone (Dogger), (5) 20.5–5.8 m: heavily brecciated and sand-sized crystalline basement material (especially granitic fragments), (6) 5.8–3.0 m: mm to cm-sized crystalline clasts (especially granites) embebed in a dense reddish to grayish impact melt matrix. (7) 3.0–0.1 m: strongly brecciated reddish impact melt rock with mm to cm-size crystalline clasts (8) 0.1–0.0 m: topsoil.

**References:** [1] Pohl J. et al. 1977. *Impact and explosion cratering, Flagstaff, Arizona.* [2] Kenkmann T. and Ivanov B. 2006. *Earth and Planetary Science Letters* 252:15–29. [3] Stöffler D. et al. 2001. *Meteoritics & Planetary Science* 36(9). [4] Stöffler D. 1997. *Geologica Bavarica* 75:163–189.

5415

JOINT BELGIUM-JAPAN SEARCH FOR ANTARCTIC METEORITES IN THE 2010–2011 FIELD SEASON

H. Kaiden¹,², S. Goderis³, V. Debaille⁴, H. Kojima¹,² and Ph. Claeys³. ¹National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan. E-mail: kaiden@nipr.ac.jp. ²The Graduate University for Advanced Studies, Tachikawa, Tokyo 190-8518, Japan. ³Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium. ⁴Université Libre de Bruxelles, 50, Av. F.D. Roosevelt, CP 160/02, B-1050 Brussels, Belgium.

Since the 2009–2010 field season in Antarctica, Belgium and Japan have jointly conducted searches for meteorites in the Sør Rondane Mountains (SRM), East Antarctica [1]. A total of 635 meteorite specimens were found in the Mt. Balchen area (approximately 72.0° S, 27.5° E), which is located at the eastern end of the SRM, in the 2009–2010 field season [2]. Here we report the search for meteorites hosted by the Belgian Antarctic Research Expedition (BELARE) in the Nansen Ice field (approximately 72.7° S, 24.2° E) that is located on the south of the SRM in the 2010–2011 field season.

The 29th Japanese Antarctic Research Expedition (JARE) conducted systematic searches for meteorites on the Nansen Ice field and found about 1400 meteorite specimens in the 1988–1989 field season [3]. The meteorites were termed Asuka-88 meteorites, which include rare types such as the Asuka-881371 angritic achondrite and the Asuka-881757 gabbroic mare basalt. A meteorite search team consisting of three Belgians and two Japanese performed systematic meteorite searches in the Nansen Ice Field, where the meteorite search had not been carried out since 1989, from January 1 to 23, 2011, known as the SAMBA (Search for Antarctic Meteorites: Belgian Contribution) mission [4]. A total of 218 meteorites and meteorite fragments were collected during this period. Most of the collected meteorites are ordinary chondrites, but at least two achondrites were recognized in the field. The meteorites were individually put in clean polyethylene bags in the field and kept frozen until they were put in a freezer at the National Institute of Polar Research (NIPR), Japan. The position of each meteorite was recorded by GPS. The initial processing (weighing, measuring, photography, naming and brief description) and classification will be carried out at the NIPR. The meteorites collected by the joint Belgium-Japan team in the 2010–2011 field season will be termed Asuka 10 meteorites. Only a third of the Nansen Ice field was surveyed in 2010/2011, thus JARE and BELARE are planning to cover the rest of the area in 2012/2013.

The meteorite search was performed with the support of the Belgian Science Policy (BELSPO), the International Polar Foundation (IPF) and the Belgian Defense.

**References:** [1] Kaiden H. et al. 2010. *Meteoritics & Planetary Science* 45:A100. [2] Kaiden H. et al. 2010. 33rd Antarctic Meteorites:34–35. [3] Naraoka H. et al. 1990. *Antarctic Records* 34:216–224. [4] Claeys Ph. et al. 33rd Antarctic Meteorites:5–6.
5266

MICRO RAMAN SPECTROSCOPY AND CATHODOLUMINESCENCE INVESTGATIONS OF DIAMONDS IN UREILITES

A. Karczem ska¹ and T. Jakubowski². ¹Technical University of Łódź, Institute of Turbomachinery, Łódź, Poland. ²Balonowa 5/2 Wrocław, Poland.

**Introduction:** Raman mapping and scanning electron microscopy with cathodoluminescence are the powerful tools for investigations the diversity of carbon in meteorites [1-7]. They allow to show the distribution of diamonds in the samples. Diamonds in ureilites are of different sizes, from nanometers up to micrometers [4]. There are still questions about their origin. New results show wide diversity of diamonds types basis on Raman shifts and on cathodoluminescence spectra investigations.

**Samples and Experiments:** Study are based on several ureilites (DaG 868, Dhofar 1303, NWA 3140, JaH 054, Sahara 98505, Almahata Sitta). Raman mapping studies have been done with use of WITec alpha RA instrument equipped with an one grating (600 g mm⁻¹, BLZ = 500 nm) UHTS 300 spectrometer, Newton-CCD camera (1024 × 127 pixels) and Nikon 100× (NA = 0.95) objective. Frequency doubled NdYAG laser (532 nm line) was used for sample excitation. Scanning electron microscope LEO, type 1430 with microprobe EDS-ISIS 300 and cathodoluminescence device type VIS-View with spectrometer have been used for cathodoluminescence investigations.

**Results:** Monocrystalline cubic diamond has Raman peak at 1332 cm⁻¹. The Raman spectra in ureilites show the diamond peak shifts from 1297 to 1340 cm⁻¹ and the wide range of FWHM parameter. It is possibly because of the nanometer crystals sizes, or internal stresses in crystals, or because of different polytypes of diamond occurring in the sample. Even unshocked ureilites contain diamonds, it means that probably some of ureilitic diamonds have not shock origin.

**References:** [1] Karczem ska A. 2010. JAMME 45:114-119. [2] Le Guillou C. et al. 2010. *Geochimica et Cosmochimica Acta* 74:4167-4185. [3] Bischoff A. et al. 1999. Abstract #1100. Lunar and Planetary Science Conference. [4] Grund T. and Bischoff A. 1999. Abstract #5074. 62nd Annual Meteoritical Society Meeting. [5] Karczem ska A. et al. 2009. JAMME 37/2:292-297. [6] Jakubowski T. et al. 2009. Abstract #1382. 40th Lunar and Planetary Science Conference. [7] Karczem ska A. Jakubowski T., and Kozanecki M. 2009. Abstract #5382. 72nd Annual Meteoritical Society Meeting.

<figure><img src="image_17.png" /><figcaption>Fig.1. CL image of DaG 868 and Raman mapping of JaH 054, ureilite diamonds are bright spots.</figcaption></figure>

5336

A NEW METEORITE FALL AT SOTMANY, POLAND

Ł. Karwowski¹, A. S. Pilski², T. A. Przylibski³, J. Gattacceca⁴, P. Rochette⁴, K. Łuszczek³, R. Kryza⁵, B. Woźniak⁶, M. Woźniak⁶. ¹University of Silesia, Faculty of Earth Sciences, ul. Będzińska 60, 41-200 Sosnowiec, Poland. ²Niclaus Copernicus Museum, ul. Katedralna 8, 14-530 Frombork, Poland. ³Wrocław University of Technology, Faculty of Geoengineering, Mining and Geology, Wybrzeże S. Wyspiańskiego 27, 50-370 Wrocław, Poland. ⁴CEREGE, Aix-Marseille Université, Aix-en-Provence, France. ⁵Wrocław University, Institute of Geological Sciences, ul. Cybulskiego 30, 50-205 Wrocław, Poland. ⁶University of Warsaw, Department of Biology, ul. Miecznikowa 1, 02-096 Warsaw, Poland.

**Introduction:** On April 30, 2011, at 6:03 CEST, in a farm at the village of Sołtmany, NE Poland, a stone penetrated the edge of a roof and crushed onto a concrete step below. It was immediately found by the owners of the farm, alarmed by loud noise. Mr. Roman Rzepka from the nearby town of Gżycko, recognized the stone as meteoritic, and informed the authors. On May 2, fragments of the stone were purchased and distributed among laboratories for examination. Here are some preliminary results.

**Samples and Macroscopic Examination:** The meteorite was broken by impact into pieces: 813 g, 155 g and many smaller ones. TKW is at least 1066 g. Nearly all examined pieces have the fusion crust of about 1-1.5 mm thick. The crust is of the same thickness all around the meteorite, which suggests that the stone was a single fall. The hole in the roof and the trace of impact onto the step below proved that the fall was nearly vertical. Macroscopic examination showed that the stone was extremely fresh (Wo), nearly white in color, with clearly visible troilite and FeNi grains, up to 2-3 mm in size, dispersed uniformly through entire meteorite. Only few chondrules were distinguished macroscopically.

**Mineralogy and Petrology:** The mean compositions of olivine (Fa₂.₅.₅) and low-Ca pyroxene (Fs₂₂) indicate that the meteorite can be classified as an L chondrite [1]. This is confirmed by magnetic susceptibility logχ = 4.71 ± 0.04, typical of the lower range of L chondrites [2]. The texture examined both macroscopically and in thin section, the homogeneous compositions of olivines and pyroxenes, and the large grain-size of plagioclase, all indicate type 6 chondrite. There is no difference in composition of olivines and pyroxenes in chondrules and out of them. Low-Ca pyroxene is usually accompanied by Ca pyroxene (Wo: ~45%; Fs: ~46.5%). In larger grains of feldspar (An: ~10%; Or: ~5%), albitic twinning is visible. Sparse chondrules are well crystallized; no glass is visible. F-Cl apatite is an accessory. Opaque minerals are represented by troilite, kamacite, taenite and rare chromite. Taenite shows an unusual texture, with areas resembling plessite. In taenite grains, tiny inclusions of metallic copper are visible. The undulatory extinction in olivine and pyroxene indicates that the chondrite is weakly shocked (S2). This is confirmed by low anisotropy of magnetic susceptibility [3].

**Acknowledgments:** The authors are grateful to the finder of the meteorite, Mrs. Alfreda Lewandowska.

**References:** [1] Weisberg M. K. et al. 2006. In *Meteorites and the early solar system II* pp. 19-52. [2] Rochette P. et al. 2003. *Meteoritics & Planetary Science* 38:251-268. [3] Gattacceca J. et al. 2005. *Earth and Planetary Science Letters* 234:351-368.
5263

IMPACT DISRUPTION OF IRON METEORITE PARENT BODIES
UNDER WARM CONDITIONS

T. Katsura¹, A. M. Nakamura¹, S. Hasegawa², A. Takabe¹, M. Setoh¹,
and K. Sangen¹. ¹Earth and Planetary Science, Kobe University, 1-1
Rokkodai-cho, Nada-ku, Kobe, 657-8501 Japan. E-mail:
amnakamu@kobe-u.ac.jp. ²ISAS/JAXA, 3-1-1 Yoshinodai, Chuo-ku,
Sagamihara, Kanagawa 252-5210, Japan.

**Introduction:** Between the differentiation of the parent bodies of iron meteorites and the last collision events that thrust the population of iron meteorites into interplanetary space, the parent bodies, iron cores, and fragments must have experienced collisional events over a range of mass scales and impact velocities. The parent bodies of iron meteorites may have formed in the terrestrial planet region. Afterward, they or their fragments were scattered into the main belt [1]. As the ductile-brittle transition temperature of an iron meteorite on impact is around 200 K [2], the impact strength of iron samples [3] at room temperature is of interest.

**Impact Experiments:** We performed impact experiments on steel and iron meteorites at room temperature in two different velocity regimes. High-velocity impact experiments (velocities of 1.4–4.8 km s⁻¹) were performed using a two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS). The projectiles were disks of steel and Mundrabilla and Campo del Cielo iron meteorites a few millimeters in size. The targets were serpentinite and dunite blocks. Low-velocity impact experiments (velocities up to 1 km s⁻¹) were performed using a single-stage vertical powder gun at Kobe University. Copper cylinders 15 mm in diameter and 15 mm in height were used as projectiles on steel and Campo del Cielo cylinders as targets. After each impact experiment, we looked for fragments of steel and iron meteorites using a magnet. We measured the mass of the recovered fragments of iron material after impact.

**Results:** After the high-velocity impacts, all iron projectiles were thinned and deformed. Some projectiles were disrupted into several fragments with torn surfaces. The surface on the impact side lost metallic luster and was rough. The mass fraction of the largest fragments ranged from 0.07 to 0.99 of the originally projectile mass. After the low-velocity impacts, the mass fraction of the largest iron fragment ranged from 0.11 to 1.0. The iron targets were disrupted by a large crack penetrating parallel to the impact direction. Given larger-input kinetic-energy densities, radial disruption occurred. We estimated the initial peak pressure using a planer impact approximation. We found that the initial peak pressure required to disrupt catastrophically the smaller (millimeter size) specimens of iron materials was two to three times larger than the peak pressure required for the larger (centimeter size) specimens.

**Summary:** Impact disruption experiments of small (millimeter) and larger (centimeter) specimens of iron material indicated that the impact strength of iron meteorite parent bodies depends on the scale of the collision, even at temperatures above the ductile-brittle transition temperature.

**References:** [1] Bottke W. F., Nesvorný D., Grimm R. E., Morbidelli A. and O'Brien D. P. 2006. *Nature* 439:821–824. [2] Remo J. L. and Johnson A. A. 1975. *Journal of Geophysical Research* 80:3744–3748. [3] Ryan E. V. and Davis D. R. 1994. DPS Meeting #26, #31.10, BAAS, vol. 26, p. 1180.

5025

CATHODOLUMINESCENCE CHARACTERIZATION OF HIGH-
PRESSURE SILICA AND FELDSPAR MINERALS

M. Kayama¹, H. Nishido¹, T. Sekine² and K. Ninagawa³. ¹Research
Institute of Natural Sciences, Okayama University of Science, Japan.
E-mail: kayama@rins.ous.ac.jp. ²Department of Earth and Planetary
Systems Science, Graduate School of Science, Hiroshima University,
Japan. ³Department of Applied Physics, Okayama University of Science,
Japan.

**Introduction:** High-pressure minerals in various meteorites have been investigated in planetary sciences for a clarification of shock metamorphic processes. Although recent studies apply cathodoluminescence (CL) of stishovite and high-pressure glass to identify such high-pressure silica minerals, CL mechanisms of high-pressure silica minerals have not been clarified in detail. Furthermore, high-pressure feldspar minerals such as KAlSi₃O₈-hollandite and maskelynite have not been studied from the perspective of CL spectroscopy. In this study, natural and synthetic high-pressure silica and feldspar minerals have been characterized by CL spectroscopy to clarify their emission mechanisms.

**Samples and Methods:** Synthesized stishovite, coesite, KAlSi₃O₈-hollandite, and experimentally shock-induced sanidine and quartz at pressure of 40 GPa by a propellant gun were selected for CL measurements. A scanning electron microscopy-cathodoluminescence (SEM-CL) was used to obtain CL spectra of these samples.

**Results and Discussion:** CL spectrum of synthetic stishovite has a pronounced emission band at ~390 nm. CL intensity of the blue emission decreases with an increase in electron irradiation time. Similar blue emission was observed in CL spectra of silica minerals in Martian meteorites of NWA 2975 and Shergotty. On the other hand, synthetic coesite exhibits dull UV emission peaked below 300 nm and blue emission at ~380 nm. CL spectrum of experimentally shocked quartz at 40 GPa shows blue emissions at 460 nm, which have not been recognized in CL of natural quartz up to now. CL spectral patterns and features of these high-pressure silica minerals are quite different from other silica minerals such as quartz, tridymite and cristobalite.

CL spectrum of KAlSi₃O₈-hollandite consists of emission bands at 330 and 380 nm in UV-blue region. Similar UV-blue emission bands were detected in experimentally shocked sanidine at 40 GPa. Alkali feldspar glasses in NWA 2975 and Shergotty also exhibit UV-blue emissions at 330 and 380 nm, which might be assigned to defect centers in Al and Si octahedra produced under high pressure process. KAlSi₃O₈-hollandite has higher emission intensities than shocked samples at 40 GPa and the glasses in shergottite. It might be responsible for completely octahedral coordination of Si and Al in KAlSi₃O₈-hollandite and partially one in diaplectic glass. CL spectrum of KAlSi₃O₈-hollandite also shows emissions at 550, 580, 660, 710 and 730 nm, which were undetectable in shocked sanidine at 40 GPa and the glasses in shergottite. These emission bands are characteristics of CL signals derived from KAlSi₃O₈-hollandite.

These results indicate that CL signals can be applicable to identify high-pressure silica and feldspar minerals and to observe their distributions in meteorites with high spatial resolution (~1 µm). CL and infrared-CL (from 800 to 1800 nm) spectroscopy at room and liquid nitrogen temperature for these synthetic and experimentally shocked samples will be discussed here for further clarification of their CL mechanism.
COMETARY DUST RESIDUE IN LARGE STARDUST FOIL CRATERS: HOW MUCH SURVIVES, AND HOW TO SAFELY EXTRACT IT FOR ANALYSIS

A. T. Kearsley¹, M. J. Burchell², M. C Price², M. J. Cole², P. J. Wozniakiewicz³, H. A. Ishii³, N. Teslich³, J. P. Bradley³ and T. Salge⁴. ¹IARC, Department of Mineralogy, Natural History Museum, London SW7 5BD, UK. E-mail: antk@nhm.ac.uk. ²School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK. ³IGPP, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA. ⁴Bruker Nano GmbH, Schwarzschildstrasse 12, 12489 Berlin, Germany.

**Introduction:** Craters on Stardust foils show impacts by Wild 2 dust of a wide size range [1]. Sections from focussed ion beam (FIB) instruments reveal composition and structural preservation of dust in smaller craters [2]. There has been reluctance to attempt such preparations for larger craters (up to >200 µm), as their size and shape make widespread surface contamination by re-deposition of FIB-ablated material probable, and the extraction angle is too steep for an in-chamber micromanipulator. Before any preparation, it is important to know where residue is present. Auger mapping has been applied very successfully [3] but is slow to document large areas. Although energy-dispersive X-ray (EDX) mapping can find residue on walls and lips of craters [4], occasionally ideal targets for NanoSIMS [5], deeper parts are not seen by typical inclined EDX detectors. Here we explain methods to locate residue across the whole crater surface, quantify the amount, and change crater shapes for safe extraction of material.

**Methods:** Light gas gun shots were performed at Canterbury, using powders of lead sulfide, Bjurbole and Allende meteorites, and poly methylmethacrylate (PMMA), fired onto 100 µm thick Al1100 foil at approximately 6 km s⁻¹. A Zeiss EVO 15LS scanning electron microscope (SEM) was used for stereo imagery of PbS craters, to measure C/Al count ratios in PMMA craters for comparison to carbon thin-film calibration, and to map Bjurbole impact residue. Silicon drift detector (SDD) take-off angle was increased by long sample working distance, allowing examination of over 97% of the crater area, but this was relatively slow (16 h). An annular four-channel Bruker XFlash 5060F SDD, placed beneath the pole-piece of a Zeiss Supra 55 field emission SEM, gave hyperspectral X-ray maps of a whole Allende crater in <45 min. Digital elevation models (DEM) were created for the PbS craters, prior to and after deformation with a carefully controlled, shaped, steel needle.

**Results and Conclusions:** The mapped area and estimated thickness of Bjurbole residue suggest that approximately 55% of the impacting particle was preserved, but measurement of carbon film thickness revealed that <3% of each PMMA particle survived. The DEM showed that craters on Stardust foil can be made much broader and shallower, bringing all residue to locations for safe extraction by proven methods. It is now possible to locate, measure and extract residues from larger Stardust craters. This will release another important repository of cometary dust from Wild 2.

**References:** [1] Price M. C. et al. 2010. *Meteoritics & Planetary Science* 45:1409–1428. [2] Leroux H. et al. 2008. *Meteoritics & Planetary Science* 43:143–160. [3] Stadermann F. J. et al. 2009. Abstract #2120, 40th Lunar and Planetary Science Conference. [4] Kearsley A. T. et al. 2008. *Meteoritics & Planetary Science* 43:41–73. [5] Stadermann F. J. et al. 2008. *Meteoritics & Planetary Science* 43:299–313.

METEORITE POLISHED SECTIONS: X-RAY MAP IMAGERY FOR DOCUMENTATION, CURATION AND ‘VIRTUAL-LOAN’ OF IRREPLACEABLE MATERIALS

A. T. Kearsley¹, C. L. Smith¹, J. Spratt¹, G. K. Benedix¹, A. Hunt¹, S. S. Russell¹, K. H. Joy¹,²,³ and M. Gounelle⁴. ¹IARC, Department of Mineralogy, Natural History Museum, London, SW7 5BD, UK. E-mail: antk@nhm.ac.uk. ²CLSE, LPI-USRA, 3600 Bay Area. Blvd. Houston, Tx-77058, USA. ³NASA Lunar Science Institute. ⁴LMCM, CNRS & MNHN, UMR 7202, CP52, 57 rue Cuvier, 75 005 Paris, France.

**Introduction:** Polished meteorite surfaces are primary research materials and each may reveal unique textural relationships between phases of diagnostic composition and equilibration level. Many meteorites are represented by only a low total mass. They are challenging materials to prepare, with soft or reactive components that may alter in prolonged contact with water and air. Informed choice of abrasive compounds for lapping and polishing is important to avoid later confusion in searches for interesting grains (such as SiC, Al₂O₃ and diamond). Each section is therefore a substantial investment in precious sample and preparation time. As the significance of features may only be realized much later, with development of new analytical techniques, careful curation, storage and informed access is essential to use these resources responsibly. Fortunately, digital storage of diverse analytical data from a sample may now aid this process.

**Compositional Imagery:** Analytical scanning electron microscopy (SEM) is widely applied in meteorite research. Many textures are revealed by backscattered electron images (BEI), shown in almost all petrographic publications. Unfortunately, similarity of BE coefficients between diverse compositions often prevents distinction by gray tones in these images. Maps of element distribution may overcome this limitation, yielding such images as the three-color combined X-ray maps used to document calcium- and aluminum-rich inclusions so effectively [e.g., 1]. However, mapping by wavelength dispersive X-ray spectrometers [e.g., 2] requires long collection time, limiting the area examined in an acceptable length of instrument use. Recent improvements in energy dispersive (EDX) collection efficiency (especially large area silicon drift detectors (SDD), faster pulse processing, classifying many tens of thousands of X-rays per second), combined with sophisticated methods of automated beam and stage movement, now allow collection of a full EDX spectrum from each micrometer-scale pixel across areas of multiple square centimeters in instrument sessions of a few hours [e.g., 3]. A sample holder can be loaded at the end of a day of instrument use, map areas defined, and the instrument left to acquire data overnight, automatically saving results which are downloaded to a separate server the next morning, for processing and extraction of selected element X-ray maps. An entire collection of meteorite sections can be documented in this way, with copies of compositional image files then available as a ‘virtual-loan,’ allowing on-line selection of appropriate samples for research, without the need to transport precious samples whose suitability for a specific investigation would otherwise be unknown in advance.

**References:** [1] Krot A. N. and Keil K. 2002. *Meteoritics & Planetary Science* 37:91–111. [2] Ivanova M. A. et al. 2008. *Meteoritics & Planetary Science* 43:915–940. [3] Bland P. A. et al. 2007. *Meteoritics & Planetary Science* 42:1417–1427.
5109

ORGANIC ANALYSIS OF XENOLITHIC CLASTS IN METEORITES

Y. Kebukawa¹*, M. E. Zolensky², M. D. Fries³, A. Steele¹, A. L. D. Kilcoyne⁴ and G. D. Cody¹. ¹Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC, USA. ²NASA Johnson Space Center, Houston, TX, USA. ³Planetary Science Institute, San Diego, CA, USA. ⁴Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. *E-mail: ykebukawa@ciw.edu.

**Introduction:** Primitive xenolithic clasts have been found in regolith-
bearing meteorites [1]. They are most commonly similar to type 1-3
chondrites, but significant differences usually exist. Some of these clasts
should derive from Kuiper Belt Objects (KBOs) trapped in the inner
asteroid belt by scattering by giant planets in later period of planetary
formation, in the so-called Nice model [2, 3]. Here we present organic
analyses of several of these clasts by various spectroscopic methods, e.g.,
carbon X-ray absorption near edge structure (C-XANES), Fourier
transform infrared micro-spectroscopy (microFTIR), and Raman
spectroscopy.

**Results:** We have analyzed clasts from four meteorites: Kapaota (Howardite), Zag (H5), Sharps (H3.4) and Cold Bokkeveld (CM2). C-XANES and FTIR spectra show mostly aromatic nature with slightly aliphatics. The carbonyl features obtained by C-XANES might have been caused by focused ion beam (FIB) used in sample preparation. C-XANES spectra of all clasts did not show significant $1s-\sigma^*$ exiton features, suggesting that these clasts have not experienced high temperature, probably <200 °C [4], although some of their parent meteorites has subjected strong thermal processing. However, the Raman G-band center and full width at half maximum (FWHM) of the Zag clast show similarities to thermally metamorphosed CVs.

Most interestingly, the clasts from Sharps are significantly organic carbon rich and contain less silicates and carbonates, compare to the clasts from other three meteorites. G-band parameters obtained by Raman spectra of two distinct Sharps clasts both show similarity with CV and CO chondrites. However, these would be two different starting materials that have been metamorphosed to the type 3.4 petrographic class together. One clast contains what are probably vapor-grown graphite grains, some of which have been disrupted by shock. The other clast appears to have had a O, N-rich starting material. Both show signs of slight thermal metamorphism almost certainly while entrained in the Sharps H3.4 parent body. These Raman spectral features are consistent with FTIR spectra which show less aliphatics and carbonyls.

**Conclusions:** These primitive xenolithic clasts have organic features that are distinct from their parent meteorites and preserve their history from before accretion on single parent bodies. However, they may also have been affected by secondary process on their parent bodies, which results in very complex histories.

**References:** [1] Zolensky M. Z. et al. 2009. Abstract #2162. 40th Lunar and Planetary Science Conference. [2] Tsiganis K. et al. 2005. *Nature* 435:459–461. [3] Morbidelli A. et al. 2005. *Nature* 435:462–465. [4] Cody G. D. et al. 2008. *Earth and Planetary Science Letters* 272:446–455.

5455

IRRADIATION OF FeS: RELATIVE SPUTTERING RATES OF
TROILITE AND Mg SILICATES

L. P. Keller¹ and Z. Rahman². ¹Robert M. Walker Laboratory for Space Science, ARES, NASA/JSC, Houston, TX 77058, USA. E-mail: Lindsay.P.Keller@nasa.gov. ²ESCG/Jacobs Technology, TX 77058, USA.

**Introduction:** Astronomical measurements of S abundances in the diffuse interstellar medium (ISM) indicate ionized S is the dominant species with little (< 5%) S residing in grains [e.g., 1]. This is an enigmatic result, given that abundant Fe-sulfide grains are observed in dust around pre- and post-main sequence stars [2,3] and are major components of primitive meteoritic and cometary samples. These disparate observations suggest that the lifetime of Fe-sulfides in the ISM is short because of destruction processes. Our previous work has shown that FeS retains its crystallinity and does not amorphize during radiation processing, whereas enstatite and forsterite are readily amorphized [4,5]. Here, we have extended this study to measure the relative sputtering rates of FeS compared to silicates.

**Experimental:** We used a FEI Quanta 600 3D dual-beam focused ion beam (FIB) instrument to sputter sharp grain boundaries between troilite and enstatite or forsterite in chondrules within polished sections of the Vigarano CV3 chondrite. A 7 × 10 µm rastered region extending across the grain boundary was sputtered at normal incidence using either 30 kV, 7 nA $Ga^+$ for 1 min, or 5 kV, 1 nA, $Ga^+$ for 7 min. For the 30 kV experiments, we measured the depth of the sputtered pit directly in secondary electron images. For the 5 kV experiments, we extracted a FIB lift-out section from two of the pits and measured the pit depth and microstructure in the transmission electron microscope (TEM).

**Results and Discussion:** The 30 kV experiments produced pits in troilite that were ~4x deeper than the adjacent pits in enstatite or forsterite. More precise measurements were obtained from TEM examination of the 5 kV experiment FIB cross sections. The FeS/enstatite pit depth ratios for the two FIB sections were 4.2 and 3.9. The depth ratio variation is likely related to crystallographic orientation differences. Irradiation of FeS with 5 kV $Ga^+$ resulted in preferential sputtering of S and the formation of a 5–8 nm thick surface layer of nanophrase Fe metal. X-ray mapping shows that the zone of S sputtering extends to a depth of nearly 20 nm, but there is no evidence for FeS amorphization, consistent with our previous study [4].

The dominant grain destruction mechanism in the ISM is sputtering from passage of supernova-generated shock waves [6]. Our results indicate that FeS grains produced in evolved stars and injected into the ISM will be destroyed more rapidly than crystalline silicates. Despite their expected shorter interstellar lifetime, circumstellar Fe-sulfides should be preserved in meteoritic materials, but are as yet, undetected. Floss et al. [7] measured an abundance of presolar silicates in isotopically primitive interplanetary dust particles (IDPs) of 810 ppm. Given the S/Si ratio of ~0.5 in the diffuse ISM [1] and a destruction rate 4x faster than silicates, we estimate an abundance of presolar sulfides of ~100 ppm in isotopically primitive IDPs.

**References:** [1] Jenkins E. B. 2009. *The Astrophysical Journal* 700:1299. [2] Keller L. P. et al. 2002. *Nature* 417:148. [3] Hony S. et al. 2002. *Astronomy & Astrophysics* 393:L103. [4] Keller L. P. et al. 2010. Abstract #1172. 41st Lunar and Planetary Science Conference. [5] Christoffersen R. et al. 2011. *Meteoritics & Planetary Science*, in press. [6] Jones A. P. and Nuth J. A. 2011. *Astronomy & Astrophysics* 530:A44. [7] Floss, C. et al. 2006. *Geochimica et Cosmochimica Acta* 70:2371.
5458

A FIB-TEM STUDY OF Ca- AND Fe-RICH PYROXENES IN THE MATRICES OF OXIDIZED R AND CV3 CARBONACEOUS CHONDRITES

L. P. Keller¹ and Z. Rahman². ¹Robert M. Walker Laboratory for Space Science, ARES, NASA/JSC, Houston, TX 77058, USA. ²ESCG/Jacobs Technology, TX 77058, USA. E-mail: Lindsay.P.Keller@nasa.gov.

**Introduction:** Ca-Fe-rich pyroxenes are ubiquitous components in the matrices of the oxidized subgroup of the CV3 chondrites and are inferred to have formed during low grade, fluid-assisted metamorphism on their parent bodies [1,2]. Oxygen isotopic measurements of individual hedenbergite (Hd)-rich inclusions in Allende matrix are isotopically heavy, consistent with interaction with a ¹⁶O-depleted reservoir [2]. The precursors of the Hd-bearing assemblages are unknown, although [1] has suggested the precursors were similar to the anhydrous matrix materials present in the reduced CV3 chondrites. We are using electron microscopy to investigate the nm-scale mineralogy and petrography of the Hd-rich inclusions in the matrix of a type 3 clast in the PRE 95404 R chondrite and in ALH 85006 CV3 chondrite matrix.

**Experimental:** X-ray mapping and SEM imaging show that the Hd-rich inclusions are typically 10–50 µm rounded to amoeboid objects with a central void. We prepared a cross section of one of these objects from PRE 95404 using a FEI Quanta 600 3D dual-beam focused ion beam (FIB) instrument. Transmission electron microscopy (TEM) and quantitative x-ray mapping data were obtained from the FIB section using the JEOL 2500SE field-emission STEM equipped with a thin window, energy-dispersive x-ray (EDX) spectrometer.

**Results and Discussion:** The Hd-rich inclusion is highly porous and consists of µm-sized grains of Ca-rich pyroxene with minor pentlandite. EDX analyses show that the pyroxenes are either Hd100 or Di90Hd10 that share sharp compositional boundaries at the sub-µm scale. The crystal size coarsens toward the central void and many of the crystals show euhedral terminations into the void. The Hd grains typically contain nanophase inclusions of pentlandite, while the Di-rich grains only contain numerous sub-µm voids throughout their volume. X-ray mapping reveals that the Di-rich domains are elongate and lath-shaped with high aspect ratios. Some of the Hd domains are also lath-shaped, but most are larger, more rounded and equant.

The abundant voids within the Di-rich domains in these inclusions are consistent with volatile (H₂O) loss during their formation from a Mg-rich precursor, probably phyllosilicates. The Hd precursor may also have been phyllosilicates or more likely Fe-sulfides. In the latter case, the pentlandite inclusions in Hd are remnants of originally low-Ni Fe sulfides. The Ca source is less clear. Krot et al. [1] suggested that Ca was lost from chondrules and Ca- and Al-rich inclusions and re-precipitated in matrix during metasomatic alteration. Alternatively, CaCO₃ may have been part of the precursor assemblage in which case some of the porosity and void space in the inclusions resulted from decarbonation reactions.

The precursors to the Hd-rich inclusions in the oxidized CV3 and R chondrites were hydrated phases formed at low temperatures and subsequently metamorphosed on the parent body.

**References:** [1] Krot A. N. et al. 1998. *Meteoritics & Planetary Science* 33:623. [2] Cosarinsky M. et al. 2003. Abstract #1043. 31st Lunar and Planetary Science Conference.

5315

COLLAPSE OF A TRANSIENT CRATER CAVITY: FIRST RESULTS FROM ANALOG EXPERIMENTS

T. Kenkmann and P. Burgert. Institute of Geosciences—Geology, Albert-Ludwigs-University Freiburg, Germany. E-mail: thomas.kenkmann@geologie.uni-freiburg.de.

**Introduction:** Except for very small impact craters, the shape of almost all craters is modified by gravity driven mass movements. In simple craters the shape of the transient cavity that forms at the end of the excavation stage [1] is moderately modified, in complex craters the mass movements are substantial. To understand the kinematics of crater wall collapse in simple and complex craters we conducted analogue experiments with a variety of materials (sand, sand + flour mixtures, glass beads) and recorded the particle displacements by means of particle image strainometry (PIS) [2].

**Experiments:** The experimental setup consisted of a 50 cm box filled with the analogue material. A paraboloidal cavity mimicking a transient crater was created either with a replica that was removed after filling of analogue material was completed or by a partly buried balloon. The gravitational instability of the cavity was induced by a piston installed beneath the cavity moving downward at constant velocity [2]. In case of the balloon experiments, the cavity walls instantaneously collapsed when the balloon was punctured. Two cameras, installed at high angles to the target surface, recorded the collapse of the cavity. Pulsed LED flashes illuminated the setup. We used the Strain Master 3D software package by La Vision to record changes in the position of material points. PIS provides an accurate measure of the instantaneous displacement field of laboratory flow and is adapted for strain monitoring in analogue sandbox experiments [3]. Scaling of material cohesion and density between experiment and nature resulted in a scaling factor of approximately 10⁴, thus the 10 cm cavities formed in the experiments roughly correspond to 1 km cavities in nature.

**Results:** In the first set of experiments (using the replica), numerous slumps developed at the cavity rim and reached the cavity center. A slump often triggered the onset of subsequent adjacent flows. Slumps created lobate headscarps and superimposed onto each other at the bottom of the cavity, thereby filling the cavity. Additionally a system of circumferential tensile fractures formed outside the cavity. These concentric fissures allowed for slow creeping of the entire mass inside the concentric fissures into the cavity. Their occurrence resembles the concentric fissures around the 108 m Snowball crater [4].

The second set of experiments (exploding balloon, sand + flour) led to the simultaneous initiation of cohesive slumps along the steep rim. While moving inward these slumps subsequently disintegrated into granular flows due to oblique and frontal collision with other flows. The central portion of the crater floor is characterized by a rather turbulent and chaotic flow that resulted in a flattish morphology.

**References:** [1] Grieve R. A. F. 1991. *Meteoritics* 26:175–194. [2] Kenkmann T. and Burgert P. 2011. Abstract #1511. 42nd Lunar and Planetary Science Conference. [3] Adam J. et al. 2005. *Journal of Structural Geology* 27:283–301. [4] Jones G. H. S. 1977. In: Roddy D. J., ed. *Impact and Explosion cratering*, pp. 163–183.
## A TWO-STAGE APPROACH FOR PREDICTING COMPOSITION FROM MICROSCOPIC IMAGES: EXAMPLES FROM THE MARS EXPLORATION ROVERS SPIRIT AND OPPORTUNITY

K. Kiatpanichagij¹, J. G. Spray¹ and T. Trabucchi¹. ¹Planetary and Space Science Centre, University of New Brunswick, Fredericton, NB E3B 5A3, Canada. E-mail: kirkkiat@unb.ca.

**Introduction:** Rovers employed in planetary exploration missions are typically equipped with multiple measurement and observational instruments, e.g., an alpha particle X-ray spectrometer (APXS) for determining the chemical composition of target sites, and cameras for capturing target images at the geologist's hand-lens scale. Measurement via an APXS is a time-consuming process (the complete analysis of one sample has typically required at least three hours during MER operations). Conversely, cameras can capture images at much faster rates. Since there is a relationship between the area of chemical analysis and a complementary (coincident) image, a triage system can be designed that facilitates the use of images to limit the need to perform compositional analysis. Here we describe how such a system has been constructed and tested.

**Procedure:** The system consists of three building blocks: (1) an image segmentation block, (2) the first artificial neural network (ANN1), and (3) the second artificial neural network (ANN2). The image segmentation block groups similar pixels into meaningful regions. ANN1 mimics the ability of a geologist to classify the image regions into predefined rock or surface types, e.g., blueberries, basalts, dark soils, bright dusts. Finally, ANN2 predicts the chemical composition of the captured image from the areas of these surface types. ANN1 thus performs a classification task, and ANN2 performs a prediction task.

**Results:** Initially, our primary triage system employed pixel-based segmentation in the first building block. A low classification accuracy of the ANN1 was observed. However, with a low accuracy ANN1, the prediction error of ANN2, which is considered a system error, was bounded and the predicted values of chemical compositions were fairly close to the target values. To improve the system accuracy, a state-of-the-art multi-resolution segmentation approach was deployed in the first building block, derived from commercially available eCognition software (a technique usually used for analyzing remotely sensed images and medical images). It was in-house implemented and used in the developed triage system. Additionally, to comply with the increasing use of multi-core processors, a parallel version of the algorithm was developed and tested.

**Conclusions:** Approximately 30 compositional analyses and matching images are required to facilitate image-only compositional estimations given a common family of materials (e.g., blueberries set in sedimentary host). Ultimately, the goal is to enable the rover to perform autonomous decisions in real time. Currently, due to limitations in processor performance, the aim is to assist mission operations geologists in analyzing images of target sites, for which chemical compositions are not available.

## FINE-GRAINED REFRACTORY INCLUSIONS FROM THE REDUCED CV3 CHONDRITE THIEL MOUNTAINS 07007

H. Kim and B.-G. Choi. Earth Science Education, Seoul National University, Seoul, 151-748, Korea; E-mail: bchoi@snu.ac.kr.

The Thiel Mountains (TIL) 07007 was found by the 2nd Korea Expedition for Antarctic Meteorites; it has been classified as CV3 chondrite based on the bulk oxygen isotopic composition (Δ¹⁷O = -4.35‰) and petrological characteristics [1, 2].

A thin section of the meteorite (SNU-T068) having the area of ~266 mm² was studied for Petrological characteristics with optical microscope, scanning electron microscope and electron microprobe analyzer. Oxygen isotopic compositions of individual mineral phases are being measured using the NanoSIMS 50 at Korea Basic Science Institute and the data will be presented at the meeting.

TIL 07007 consists of relatively large chondrules, fine-grained refractory inclusions, amoeboid olivine inclusions and fine-grained matrix. Chondrules are mostly metal- and sulfide-rich type I porphyritic olivine or porphyritic olivine pyroxene chondrules: type II chondrules are relatively rare. Average area occupied by a single chondrule in the thin section is ~0.75 mm², which is somewhat larger than that of Allende we measured (~0.50 mm²). Possibly due to impact compaction, chondrules and inclusions are all elongated to the same direction. Numerous micro-faults also probably due to impact exist in chondrules, inclusions and matrix. Average major and minor axes of chondrules are 1.13 and 0.67 mm, respectively, giving the average eccentricity of ~0.75 (aspect ratio of ~1.7). TIL 07007 has no magnetite, its sulfide grains are nearly Ni-free and modal matrix/chondrule ratio is 0.50; these characteristics are similar with the other reduced CV3 chondrites, especially with Efremovka and Leoville [3, 4].

Nineteen refractory inclusions larger than 80 µm have been found in the thin section. Two of them are completely or partially surrounded by amoeboid olivine inclusions. Similar to chondrules, the inclusions are also elongated: one extreme is 2040 × 140 µm. All of them are fine-grained: no coarse-grained Ca-Al-rich inclusions of igneous texture are found. The mineral assemblage and texture of the fine-grained refractory inclusions are very similar to those in Leoville and Efremovka [4]. Mineralogy varies but typically is spinel, pyroxene (Al-diopside and Al-Ti diopside), anorthite and melilite as major minerals. Perovskite is also found in most of them. Three inclusions have minor or trace amount of forsterite. Hibonite is absent or rare. Some inclusions have a few Fe-Ni metal and sulfide grains. Secondary minerals are absent in most inclusions but found in two inclusions. Some inclusions show a zoned structure in mineralogy.

Seven inclusions are relatively spinel-rich and very similar to the fined-grained spinel-rich inclusions in Leoville and Efremovka [4]: two of the spinel-rich inclusions are melilite-free. Another seven inclusions are melilite-rich (AK₀-2₀): melilite occupies most area of the inclusions and has fine-grained irregular shaped spinel ± hibonite ± perovskite and anorthite ± diopside aggregates in it. The other three inclusions are rich in Al-diopside.

**References:** [1] Weisberg M. K. et al. 2010. *Meteoritics & Planetary Science* 45:1530–1551. [2] Choi B.-G. et al. 2009. *Journal of the Geological Society of Korea* 45:593–605. [3] Krot A. N. et al. 1995. *Meteoritics & Planetary Science* 30:748–775. [4] Krot A. N. et al. 2004. *Meteoritics & Planetary Science* 39:1517–1553.
OPAQUE MINERALS IN CH CHONDrites: INDICATORS OF FORMATION CONDITIONS

M. Kimura¹, T. Karube¹, M. K. Weisberg²,³, T. Mikouchi⁴ and T. Noguchi¹. ¹Ibaraki University, Japan. E-mail: makotoki@mx.ibaraki.ac.jp. ²Kingsborough College of the City University of New York, USA. ³American Museum of Natural History, USA. ⁴University of Tokyo, Japan.

**Introduction:** CH chondrites are characterized by remarkable features, such as Fe-Ni metal with solar Co/Ni ratio, small chondrule size distribution, and refractory inclusions with kushiroite and grossite [1,2]. Here we report our analytical results on opaque minerals in two CH chondrites, SaU 290 and Asuka 881020, in order to explore the formation conditions of CH chondrites. The opaque minerals are good indicators of formation conditions, especially the redox states.

**Petrology and Mineralogy:** We found Si-free and -enriched (<13 wt%) Fe-Ni metals, suessite, perryite, FeSi (fersilicite), barringerite, andreyivanovite, troilite, daubreelite, pyrrhotite, pentlandite, and magnetite in two CH chondrites. Some troilite contains Cr (<3 wt%). These minerals generally occur as isolated grains, among tiny chondrules, 80 µm in average diameter, and isolated silicates. Most of these minerals have not been previously found in CH chondrites, and we are using EBSD for phase indentification. Some of these opaques occur as intimate intergrowths; perryite, barringerite, and daubreelite are present in close association with Si-rich Fe-Ni metal, whereas pentlandite, pyrrhotite, and magnetite occur only in dark clasts.

**Discussion:** Some of the opaque minerals in CH chondrites, such as Si-bearing Fe-Ni metal, perryite, Cr-bearing troilite, and daubreelite, are typical in E chondrites. However, some Fe-Ni metals contain higher Si concentrations than those in any E chondrite. Some typical minerals in E chondrites, such as ninningerite and oldhamite, are not found in CH chondrites. On the other hand, the occurrences of Si-rich Fe-Ni metal and suessite are similar to some mineral assemblages in ureilites. These assemblages formed under more reducing conditions than opaque minerals in the E chondrites [3]. Magnetite, pentlandite and pyrrhotite, in close association with hydrous silicates, in dark clasts, formed under highly oxidizing conditions. Si-free Fe-Ni metal and Cr-free troilite are commonly encountered in ordinary chondrites and others.

We conclude that CH chondrites are highly unequilibrated mixtures of components that originated under highly reducing to highly oxidizing conditions. It is unlikely that these components formed from a single reservoir. This may be consistent with the highly heterogeneous oxygen isotopic compositions of CH chondrules which suggests that not all of the chondrules formed from the same reservoir [4].

**References:** [1] Weisberg M. K. et al. 1988. *Earth and Planetary Science Letters* 91:19-32. [2] Kimura M. et al. 2009. *American Mineralogist* 94:1479-1482. [3] Ikeda Y. 2007. *Polar Science* 1:45-53. [4] Nakashima D. et al. 2010. *Meteoritics & Planetary Science* 45:A148.

AGREEMENT OF EXPERIMENT AND THEORY IN HOMOGENEOUS NUCLEATION

Y. Kimura¹*, K. K. Tanaka², H. Miura¹ and K. Tsukamoto¹. ¹Tohoku University, Tohoku, Japan. E-mail: ykimura@m.tains.tohoku.ac.jp.
²Hokkaido University, Hokkaido, Japan.

**Introduction:** Classical nucleation theory has been widely used to describe dust formation in ejecta gas from evolved stars, supernovae and possibly in a plume after energetic shock in primitive solar nebula, whereas the classical theory always has large gaps with experiments. For example, homogeneous nucleation rates of droplets were measured as a function of temperature and supersaturation using ethanol and nonane [7, 8]. They calculated temperature and supersaturation ratio in the chamber from the initial temperature and pressure, and homogeneous nucleation rate was determined after the drops have grown to visible size to count the number after taken by camera. The nucleation rates were different in several orders of magnitude from the classical nucleation theory. Recently, it has been shown that semiphenomenological nucleation theory, which was proposed by Dillmann and Meier (1991) [3], can explain the result of molecular dynamic simulation of nucleation at relatively low temperature for liquid and solid [4, 5]. We made a new chamber with interferometer to measure the homogeneous nucleation environment and compared actual number of formed particles with that calculated by semiphenomenological nucleation theory.

**Experiments:** The newly constructed smoke chamber can produce nanometer sized particles via homogeneous nucleation after vaporization of a starting material. Mach-Zehnder type interferometer is also prepared together with the chamber and it can detect the changing of temperature and gas density as a difference of an optical path length. The interferometer is able to detect a small difference of refractive index as small as $10^{-6}$. Using the noncontact method, homogeneous condensation temperature and supersaturation of smoke particles are directly determined. The size and number of produced particles were observed by transmission electron microscope and compared with the calculated values.

**Results:** Preliminary experiment using manganese demonstrated that semiphenomenological nucleation model shows good agreement with the experiment for the nucleation temperature, size and number of formed particle, when we give initial temperature, pressure and time scale of supersaturation increase for nucleation from the experiment. Accordingly, we conclude the semi-phenomenological nucleation theory is useful for describe nucleation events even at such relatively higher temperature environments. Sticking coefficient and the surface free energy at the temperature of super cooling, i.e., lower than equilibrium temperature, can be obtained from the experiment and calculation. Those values are applicable to dust formation.

**References:** [1] Schmitt J. L., Adams G. W. and Zalabsky R. A. 1982. *The Journal of Chemical Physics* 77:2089-2097. [2] Adams G. W. Schmitt J. L. and Zalabsky R. A. 1984. *The Journal of Chemical Physics* 81:5074-5078. [3] Dillmann A. and Meier G. E. A. 1991. *The Journal of Chemical Physics* 94:3872. [4] Tanaka K. K. et al. 2005. *The Journal of Chemical Physics* 122:184514. [5] Tanaka K. K., Tanaka H., Yamamoto T., and Kawamura K. 2011. *The Journal of Chemical Physics* 134, in press.
DETERMINING TRACE ELEMENT ABUNDANCES IN SINGLE
PRESOLAR SiC GRAINS

A. J. King¹,², S. R. Sutton¹,³, M. Newville³, N. Liu¹,²,⁴, R. Trappitsch¹,²,⁴,
P. R. Heck²,⁵, A. M. Davis¹,²,⁵,⁶, M. J. Pellin¹,²,⁴,⁶ and T.
Stephan¹,²,⁴,⁵. ¹Department of the Geophysical Sciences. ²Chicago
Center for Cosmochemistry, University of Chicago, Chicago, IL, USA.
E-mail: ajking@uchicago.edu. ³Consortium for Advanced Radiation
Sources, Univ. of Chicago, Chicago, IL, USA. ⁴Materials Science
Division, Argonne National Laboratory, Argonne, IL, USA. ⁵Robert A.
Pritzker Center for Meteoritics and Polar Studies, The Field Museum,
Chicago, IL, USA. ⁶Enrico Fermi Institute, University of Chicago,
Chicago, IL, USA.

**Motivation:** Presolar SiC grains have been well characterized according to their isotopic compositions, providing details of the nucleosynthetic processes that take place in carbon-rich stars and supernovae. In addition, the abundances of trace elements in presolar SiC grains are also likely to be directly related to both nucleosynthesis and the condensation environment of the parent stars. Most studies of presolar SiC grains have been performed using secondary ion mass spectrometry (SIMS). However, this technique is destructive and suffers from matrix effects and a lack of suitable SiC standards, such that there have been few studies combining isotopic compositions and trace element abundances within individual presolar SiC grains [1].

Synchrotron X-ray fluorescence (SXRF), for which matrix effects are well understood and easily corrected for, has been successfully used to detect a wide range of trace elements in presolar SiC grains [2, 3]. Also, as SXRF is nondestructive, the same grains can then be investigated with other analytical techniques. However, in the earlier SXRF studies, the isotopic compositions of the grains were never measured due to technical difficulties in the design of the sample mount. We have now begun a combined trace element and isotopic study of individual presolar SiC grains.

**Experimental:** Presolar SiC grains from the KJG size fraction (1.5–3 µm) [4] will be deposited upon CVD diamond films. Previously, Kapton and SiN have been used as the mounting substrate but these were found to be fragile, made locating grains difficult, and in the latter case, prevented the use of Si as the reference element [2, 3]. The diamond films will initially be examined using a scanning electron microscope (SEM) in order to identify and map the SiC grains, with the same grains relocated at the Advanced Photon Source (APS) using a reflected light microscope. SXRF analyses will then be made using the GeoSoilEnviroCARS beamline 13-IDE. This beam-line can provide a spot size of ~2 µm, suitable for measurements of individual SiC grains. A beam energy of ~22.5 keV should be sufficient for fluorescence of many elements known to be present at ppm levels. Spectra will be calibrated using two NIST reference materials and background corrections made by measuring the substrate.

**Summary:** We will report trace element abundance data for ~15 presolar SiC grains. The sample mount is designed so that the isotopic compositions of the same grains can then be analyzed using SIMS and newly developed instruments such as CHILI [5].

**References:** [1] Amari S. et al. 1995. *Meteoritics* 30:679–693. [2] Kashiv Y. et al. 2010. *The Astrophysical Journal* 713:212–219. [3] Knight K. et al. 2008. Abstract #2135. 39th Lunar and Planetary Science Conference. [4] Amari S. et al. 1994. *Geochimica et Cosmochimica Acta* 58:459–470. [5] Stephan T. et al. 2011. *Meteoritics & Planetary Science*, this volume.

HIGH PRECISION OXYGEN ISOTOPE SYSTEMATICS OF A TYPE
B1 CAI FROM LEOVILLE (CV3)

N. T. Kita¹, T. Ushikubo¹, K. B. Knight²,³, R. A. Mendybaev², A. M. Davis², F. M. Richter², D. Nakashima¹, M. J. Spicuzza¹ and J. W. Valley¹. ¹WiscSIMS, University of Wisconsin, Madison, WI 53706, USA. E-mail: noriko@geology.wisc.edu. ²University of Chicago, Chicago, IL 60637, USA. ³Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.

**Introduction:** Oxygen three-isotope ratios of Ca-, Al-rich inclusions (CAIs) often show a large range of heterogeneity among different mineral phases in a single inclusion [e.g., 1, 2], which may reflect the complex history of CAIs in both the solar nebula and the parent asteroids. Here, we report new highly precise and accurate Secondary Ion Mass Spectrometer (SIMS) analyses of a type B1 CAI from Leoville (3535-1), which was previously studied for Mg and Si isotope fractionation and ²⁶Al-²⁶Mg chronology [3-5]. This is a large pristine CAI (6 × 8 mm) with a 0.5-mm-thick melilite mantle. Secondary minerals, such as nepheline, are absent in this CAI.

**SIMS Analysis:** An IMS-1280 at WiscSIMS was used for analysis, which yields analytical uncertainties of a single 15 µm spot of 0.3-0.4 ‰ (2SD) for δ¹⁸O and δ¹⁷O [6]. To obtain accurate δ¹⁸O and δ¹⁷O values from minerals in the CAI, we used natural and synthetic mineral standards for spinel, melilite and anorthite. For fassaite, synthetic glass standards with major element compositions similar to fassaite in the type B CAIs were synthesized. Homogeneity of oxygen isotope ratios and SIMS matrix correction factors were carefully evaluated for individual standards.

**Results:** Oxygen isotope ratios of spinel, fassaite and anorthite plot near the lower end of the CCAM line [1] with δ¹⁸O values of -44 ‰ to -40 ‰. The δ¹⁷O values of spinel, fassaite and anorthite are -23.6 ‰ from -23.8 ‰ to -21.5 ‰ and -22.9 ‰, respectively. The highest δ¹⁸O and δ¹⁷O values were obtained from fassaite within the melilite mantle. These data plot along the slope 1.0 line in δ¹⁸O vs. δ¹⁷O diagram, but are displaced to the right side of CCAM line. Melilite data plot at δ¹⁸O and δ¹⁷O of ~+11 ‰ and ~+4 ‰, respectively, correpoding to a δ¹⁷O value of -1.5 ‰. Melilite data are also significantly higher in δ¹⁸O relative to the CCAM.

**Discussion:** Slightly elevated δ¹⁷O values of anorthite and some fassaite compared to spinel could be caused by limited oxygen isotopic exchange with solar nebular gas when the CAI was reheated within 0.1 Ma of the earliest recorded events of the solar system [5]. Oxygen isotope ratios of melilite are not in equilibrium with other minerals and show high δ¹⁸O values, suggesting isotopic exchange at low temperature, possibly with parent body fluid or with nebular gas. However, simple diffusive isotopic exchange between CAI minerals and nebula gas or parent body fluid may not explain ¹⁶O-poor melilite in the entire CAI, while preserving the ¹⁶O-rich signature in anorthite [2, 7].

**References:** [1] Clayton R. N. et al. 1977. *Earth and Planetary Science Letters* 34:209–224. [2] Fagan T. J. et al. 2004. *Meteoritics & Planetary Science* 39:1257–1272. [3] Richter F. M. et al. 2007. Abstract #2303. 38th Lunar and Planetary Science Conference. [4] Knight K. B. et al. 2009. Abstract #2360. 40th Lunar and Planetary Science Conference. [5] Kita N. T. et al. 2010. Abstract #2154. 41st Lunar and Planetary Science Conference. [6] Kita N. T. et al. 2010. *Geochimica et Cosmochimica Acta* 74:6610–6635. [7] Nagashima K. et al. 2010. Abstract #2255. 41th Lunar and Planetary Science Conference.
5341

A PRELIMINARY MICRO-SPECTROSCOPIC ANALYSIS OF THE CARBONACEOUS MATTER IN THE PARTICLES RECOVERED BY THE HAYABUSA MISSION

F. Kitajima¹, M. Kotsugi², T. Ohkochi², H. Naraoka¹, Y. Ishibashi³, M. Abe³, A. Fujimura³, R. Okazaki¹, T. Yada³, T. Nakamura⁴, T. Noguchi⁵, K. Nagao⁶, A. Tsuchiyama⁷, H. Yurimoto⁸, M. Ebihara⁹, T. Mukai³, S. A. Sandford¹⁰, T. Okada³, K. Shirai³, M. Ueno³, M. Yoshikawa³ and J. Kawaguchi³. ¹Department of Earth & Planet Sciences, Kyushu University, E-mail: kitajima@geo.kyushu-u.ac.jp. ²Spring-8/JASRI ³ISAS/JAXA ⁴Department of Earth Planet & Material Sciences, Tohoku University. ⁵Coll. Sci., Ibaraki University. ⁶Geochem. Res. Center, Univ. Tokyo. ⁷Department of Earth Space Sciences, Osaka University. ⁸Natl Hist. Sci., Hokkaido University. ⁹Grad. School Sci. Engineer. Tokyo Metropol. University. ¹⁰NASA/ARC.

**Introduction:** Insoluble organic matter (IOM) is the major fraction of the chondritic carbonaceous matter [1]. Its disordered structure converts to ordered during thermal metamorphism, and it suggests to what extent thermal metamorphism has proceeded. [2]. Several spectroscopic techniques such as Raman [3, 4], infrared (IR) [5], solid-state ¹³C NMR and carbon X-ray absorption near edge structure (C-XANES) [4] are useful tools to evaluate the maturity level of IOM. The asteroid 25143 Itokawa belongs to S-type and its surface has been considered to have an olivine-rich mineral assemblage similar to that of LL5 or LL6 chondrites [6]. However, it is a rubble-pile object [7], suggesting possible carbonaceous fragments. Such fragments can be a clue to the thermal process involved in the formation history of Itokawa.

Samples and methods: Five particles (RA-QD02-0017, 0033, 0044, 0049, and 0064) were analyzed by non-destructive methods; micro-Raman and IR techniques. Because we hope to analyze the particles as intact as possible without using organic resin, newly developed a sample holder made from diamond [8]. Raman spectra were obtained using an excitation wavelength of 514.5 nm on an argon ion laser. The laser beam was focused by a microscope equipped with a 50× objective leading to a spot diameter of 2 micrometer. Mid-infrared measurements were performed using an aperture of which size was 50 micrometer × 50 micrometer.

**Results and Discussion:** All Raman spectra from the five particles show principal bands at around 821 and 851 cm⁻¹. These bands can be assigned to olivine, and it seems the major mineral. A few Raman spectra occasionally show Raman bands from the other minerals; pyroxene from the particle 0033, for example. However, all the particles show neither D- nor G-bands, which can be usually observed from chondritic IOM. All IR spectra show Si-O absorption at around 1000 cm⁻¹, and a broad absorption from about 2200 to 1650 cm⁻¹, which can also be assigned to olivine. However, the spectra lack in absorptions relating to carbonaceous matter. Although the particles may contain trace amount of low molecular weight organic compounds, there is no evidence for chondritic IOM.

**References:** [1] Sephton M. A. 2002. *Natural Product Reports* 19:292-311. [2] Kitajima F. et al. 2002. *Geochimica et Cosmochimica Acta* 66:163-172. [3] Sandford S. A. et al. 2006. *Science* 314:1720-1724. [4] Cody G. D. et al. 2008. *Earth and Planetary Science Letters* 272:446-455. [5] Kebukawa Y. et al. 2010. *Meteoritics & Planetary Science* 45:99-113. [6] Abe M. et al. 2006. *Science* 312:1334-1338. [7] Fujiwara A. et al. 2006. *Science* 312:1330-1334. [8] Kitajima F. et al. 2011. Abstract #1855. 42nd Lunar and Planetary Science Conference.

5090

LIMITS FOR ASTEROID 2008 TC₃ SIZE AND MASS BASED ON DENSITIES OF ALMAHATA SITTA METEORITES

R. Kiuru¹,², T. Kohout¹,³, M. Montonen¹, D. Britt⁴, R. Macke⁴, P. Scheirich⁵ and G. Consolmagno⁶. ¹Department of Physics, University of Helsinki, Helsinki, Finland. E-mail: risto.kiuru@helsinki.fi. ²Geological Survey of Finland, Espoo, Finland. ³Institute of Geology, Academy of Sciences of the Czech Republic, Prague, Czech Republic. ⁴Department of Physics, University of Central Florida, Orlando, USA. ⁵Astronomical Institute, Academy of Sciences of the Czech Republic, Ondřejov, Czech Republic. ⁶Vatican Observatory, Vatican City State.

**Introduction:** On October 6, 2008 a small asteroid designated 2008 TC₃ was discovered in space 20 h prior to impact on Earth [1]. So far over 600 fragments of the corresponding Almahata Sitta meteorites have been recovered at impact site in Nubian Desert, Sudan. We characterized these meteorites through measurement of their bulk and grain densities and porosities [2]. Most Almahata Sitta meteorite fragments were classified as ureilites [1], but recently a significant amount of various chondritic compositions has been found [3-6].

**Density of the Almahata Sitta Meteorite Fragments:** Our measurements on the Almahata Sitta ureilites reveal bulk densities between 2.9-3.3 g cm⁻³, the average being 3.1 g cm⁻³. These seem to be generally higher than those reported by [1], but closer to previous data from other ureilites by [7] and [8].

**Implications on Size and Mass of Asteroid 2008 TC₃:** Based on the densities of Almahata Sitta ureilites as the dominant lithological fraction of the asteroid, we can say that its bulk density should not exceed that of the meteorites, 3.1 g cm⁻³ (this includes the microporosity of the meteorite fragments). This value used together with albedo estimates of 0.09-0.2 by [9] and shape model by [10] was used to estimate the asteroid's mass. Since the asteroid broke down during atmospheric passage, we consider presence of significant macroporosity likely, and this will lower the mass estimate. For macroporosities of 20-50% we get mass estimates between 4 and 23 t. This is lower than those reported by [1] and [11].

**Acknowledgments:** We would like to thank the Grant Agency of the Czech Academy of Sciences of the Czech Republic (grant no. KJB300130903), Väisälän Foundation and University of Helsinki for research and travel funding, students and staff of University of Khartoum for their hospitality, help and support, and Peter Jenniskens and Muawia Shaddad for providing us with access to the Almahata Sitta meteorite material.

**References:** [1] Jenniskens P. et al. 2009. *Nature* 458:485-488. [2] Kohout T. et al. 2011. *Icarus* 212:697-700. [3] Bischoff A. et al. 2010. *Meteoritics & Planetary Science* 45:1638-1656. [4] Kohout T. et al. 2010. *Meteoritics & Planetary Science* 45:1778-1788. [5] Shaddad M. et al. 2010. *Meteoritics & Planetary Science* 45:1557-1589. [6] Zolensky et al. 2010. *Meteoritics & Planetary Science* 45:1618-1637. [7] Consolmagno G. et al. 2008. *Chemie der Erde* 68:1-29. [8] Macke R. et al. 2011. *Meteoritics & Planetary Science* 46:311-326. [9] Hiroi T. et al. 2010. Abstract #1148. 41st Lunar and Planetary Science Con reference. [10] Scheirich P. et al. 2010. *Meteoritics & Planetary Science* 45:1804-1811. [11] Borovička J. et al. 2009. *Astronomy & Astrophysics* 507:1015-1022.
THE MG ISOTOPE COMPOSITION OF PRESOLAR SILICATE GRAINS FROM AGB STARS: CONSTRAINTS ON THE Mg ISOTOPE INVENTORY OF THE LOCAL INTERSTELLAR MEDIUM AT SOLAR BIRTH

J. Kodolányi and P. Hoppe. Max Planck Institute for Chemistry, 55128 Mainz, Germany. E-mail: j.kodolanyi@mpic.de.

**Introduction:** The $^{25}$Mg/$^{24}$Mg and $^{26}$Mg/$^{24}$Mg ratios of the Sun (and the solar system) are at the lower end of ratios observed for stars with solar metallicity ($Z_{\text{solar}}$) and are substantially lower than those predicted by galactic chemical evolution (GCE) models for stars with $Z_{\text{solar}}$ in the solar neighbourhood [1,2]. An evaluation of the Mg isotope composition of the material from which the solar system formed could help understand this discrepancy. As more than half of the Mg in the interstellar medium (ISM) is hosted by oxide and silicate dust produced by evolved stars [3], the Mg isotope inventory of the local ISM at solar birth could be constrained partially by the Mg isotope composition of presolar silicate and oxide grains, which represent interstellar dust at the time of solar system formation. Magnesium isotope data on presolar silicate grains [4,5] reveal that silicate grains from asymptotic giant branch (AGB) stars, the most prolific sources of presolar silicate grains [e.g., 6], have $^{25,26}$Mg/$^{24}$Mg close to or slightly higher than solar [4, 5]. Here we provide additional Mg isotope data for presolar silicate grains from AGB stars.

**Experimental:** Presolar silicate grains were identified in the matrix of Acfer 094 (an unregulated carbonaceous chondrite), based on their O isotope compositions and Si-Al-O systematics. These were determined by the NanoSIMS, as were the grains' Mg isotope compositions (for analytical conditions see [4]).

**Results and Discussion:** Based on their O isotope composition (all grains belong to Group 1 of [7]), the identified 26 presolar silicate grains were produced in the winds of AGB stars with initial masses of 1.15–2.2 $M_{\text{solar}}$ and $Z \sim Z_{\text{solar}}$ [8]. The five grains analyzed successfully so far for Mg isotopes have $\delta^{25}$Mg between –10 (±17; 1 σ uncertainty) and 64 (±26) % and $\delta^{26}$Mg between –22 (±41) and 46 (±25) %, i.e., roughly comparable to the solar composition, but, on average, slightly higher than that. These compositions are similar to the composition of presolar oxide grains from low-mass AGB stars [e.g., 9] without grains with significant contribution to $^{26}$Mg from $^{26}$Al decay]. Our data probably reflect GCE, since stellar evolution models do not predict significant increase in $^{25,26}$Mg/$^{24}$Mg in the envelopes of low-mass AGB stars with $\sim Z_{\text{solar}}$, when compared to initial ratios [e.g., 10]. Furthermore, the measured $\delta^{25,26}$Mg values plot along a slope ~1 line (within error) in a $\delta^{25}$Mg vs. $\delta^{26}$Mg representation, which suggests only a small contribution (if any) to $^{26}$Mg from the decay of $^{26}$Al. Thus the silicate component of the local ISM probably had a slightly heavier Mg isotope composition on average than our Sun, at the time of solar system formation.

**References:** [1] Yong D. et al. 2003. *The Astrophysical Journal* 599:1357–1371. [2] Fenner Y. et al. 2003. Publications of the Astronomical Society of Australia 20:340–344. [3] Fitzpatrick E. L. 1997. *The Astrophysical Journal* 482:L199–L202. [4] Kodolányi J. and Hoppe P. 2011. *Proceeding Science (NIC XI)* 142. [5] Kodolányi J. and Hoppe P. 2011. Abstract #1094. 42nd Lunar and Planetary Science Conference. [6] Vollmer C. et al. 2009. *Geochimica et Cosmochimica Acta* 73:7127–7149. [7] Nittler L. R. et al. 1997. *The Astrophysical Journal* 483:475–495. [8] Nittler L. R. 2009. Publications of the Astronomical Society of Australia 26:271–277. [9] Zinner E. et al. 2005. *Geochimica et Cosmochimica Acta* 69:4149–4165. [10] Palmerini S. et al. 2011. *The Astrophysical Journal* 729.

BERYLLIUM-10 IN AUSTRALASIAN MICROTEKTITES

C. Koeberl¹, K. Nishiizumi², M. W. Caffee³ and B. P. Glass⁴. ¹University of Vienna, Althanstrasse 14, 1090 Vienna, Austria, and Natural History Museum, 1010 Vienna, Austria. E-mail: christian.koeberl@univie.ac.at. ²Space Science Laboratory, University of California, Berkeley, CA 94720, USA. ³Purdue University, West Lafayette, IN 47907, USA. ⁴University of Delaware, Newark, DE 19716, USA.

Previously, Australasian tektites have been measured for the concentrations of the cosmogenic radionuclide $^{10}$Be, which forms by interaction of cosmic rays with nitrogen and oxygen in the atmosphere and is concentrated in the top of any sediment column. These data help to constrain the location and characteristics of the source material. The $^{10}$Be half-life is 1.36 Myr; thus, it can only be studied in relatively young impact structures and glasses. The average value of $^{10}$Be in Australasian tektites is about $100 \times 10^6$ atoms g$^{-1}$ [1]. This is comparable to $^{10}$Be contents of near-surface source materials, e.g., soils or sediments (marine and land). Also, within the Australasian strewn field there is a correlation between the tektite type and the $^{10}$Be concentration [1]. Aerodynamically shaped tektites (Australites) found farther from the presumed impact site in southeast Asia have higher contents (on average about $136 \times 10^6$ atoms g$^{-1}$) compared to layered (Muong Nong-type) tektites, which have not been transported as far (on average about $59 \times 10^6$ atoms g$^{-1}$). This has obvious implications on the formation mechanism of tektites. The Ivory Coast tektites are regular (splash-form) tektites related to the Bosumtwi crater formed at 1.07 Ma, and if these tektites also formed from surficial materials as did the Australasian tektites, then they are expected to contain similar concentrations of $^{10}$Be. Measurements by [2] show that $^{10}$Be concentrations of Ivory Coast tektites are consistent with formation from mostly near-surface sediments or soils. Traces of $^{10}$Be were also found by [2] in a moldavite (Central European tektite). Thus all tektites in which $^{10}$Be can be measured show the presence of that nuclide, indicating that tektites in general are produced from near-surface target rocks.

One open question is if microtektites also contain Be-10, and how much? Due to the small sizes of microtektites, such measurements were difficult to impossible until now. As a first attempt, we selected three microtektites and a fragment from Site 1144A in the South China Sea, three microtektites from V29-39 and two from V29-40 from the Central Indian Ocean, and two from site V16-70 (which is father from the Indochina area). The compositions were measured by microprobe, and afterwards the microtektites were released from the epoxy, cleaned, and pooled, giving a total mass of 620.5 µg. Initially we hoped to measure the three main locations separately but the weight was insufficient. The content of Be-10 was measured by accelerator mass spectrometry at Purdue University. The microtektite composite contains $260 \pm 60 \times 10^6$ atoms $^{10}$Be/g. This concentration is notable for at least two reasons: first, this is about two times higher than that for the splash-form (ablated) australites, which otherwise have the highest $^{10}$Be content in the strewn field; second, as this is an average for microtektites recovered at various distances from the inferred source area, some microtektites could contain even higher contents of $^{10}$Be. The immediate conclusion is that microtektites are derived from the immediate surface of the target and that the form even before the “normal” tektites.

**References:** [1] Ma P. et al. 2004. *Geochimica et Cosmochimica Acta* 68:3883–3896. [2] Serefiddin F. et al. 2007. *Geochimica et Cosmochimica Acta* 71:1574–1582.
## MAGNETIC SUSCEPTIBILITY AS A TOOL FOR CHARACTERIZATION OF AN ASTEROID REGOLITH AND SAMPLE RETURN

T. Kohout¹,² and D. Britt³. ¹Department of Physics, University of Helsinki, Helsinki, Finland. E-mail: tomas.kohout@helsinki.fi. ²Institute of Geology, Academy of Sciences, Prague, Czech Republic. ³Department of Physics, University of Central Florida, Orlando, FL, USA.

**Introduction:** Magnetic susceptibility of a rock is dependent on concentration of ferromagnetic minerals. It proved to be reliable nondestructive tool in distinguishing various types of extraterrestrial materials [1, 2, 3], and in searching for compositional variations of meteorite falls [4, 5]. Magnetic susceptibility of an asteroid regolith can be compared to database of known meteorites in order to diagnose its mineralogy, homogeneity and maturity.

**In-situ Susceptibility Measurement of the Asteroid Regolith:** A simple susceptibility measurement coil can be incorporated into lander or surface drop probe. Its design can be similar to commercially available handheld susceptibility meters or to one described in [6] or [7]. The regolith homogeneity can be tested by spot measurements in various locations around asteroid.

Regolith on airless bodies is subject to space weathering often associated with production of iron nanoparticles. These particles are often in superparamagnetic state exhibiting high frequency dependence of magnetic susceptibility. Thus degree of susceptibility frequency dependence is quantitatively related to regolith maturity [8].

**Susceptibility Measurement of the Sample Return:** The magnetic susceptibility measurements of a sample return will provide similar information as in-situ measurements, but laboratory instrumentation provide higher precision. Additionally magnetic susceptibility results can be directly compared with mineralogical and chemical analysis. However, any sample return is likely to be a rather small, localized quantity.

**Conclusions:** Magnetic susceptibility can provide diagnostic parameters to determine regolith mineralogy and meteorite analog. Additionally regolith maturity can be estimated from frequency dependence of regolith susceptibility.

**References:** [1] Rochette P. et al. 2003. *Meteoritics & Planetary Science* 38:251-268. [2] Rochette P. et al. 2008. *Meteoritics & Planetary Science* 43:959-980. [3] Rochette P. et al. 2009. *Meteoritics & Planetary Science* 44:405-427. [4] Consolmagno G. J. et al. 2003. *Meteoritics & Planetary Science* 41:331-342. [5] Kohout et al. 2010. *Meteoritics & Planetary Science* 45:1778-1788. [6] Rochette P. et al. 2004. *Planetary and Space Science* 52:987-995. [7] Bentley M. S. 2009. *Planetary and Space Science* 57:1491-1499. [8] Bentley M. S. 2011 *Planetary & Space Science* 59:79-91.

## SHOCK ORIGIN INFERRED FOR UNUSUAL TEXTURES IN EH3 CHONDRITE PCA 82518

M. Komatsu¹, T. Fagan², T. Mikouchi³ and M. Miyamoto³. ¹Institute for Advanced Study, Waseda University, Tokyo, Japan. E-mail: komatsu@aoni.waseda.jp. ²Department of Earth Sciences, Waseda University. ³Department of Earth and Planetary Science, University of Tokyo.

**Introduction:** Enstatite chondrites are the most reduced group among chondrites. Like the other types of chondrites, the enstatite chondrites experienced various degrees of metamorphism and shock [e.g., 1]. We have examined the mineralogy and chemistry of EH3 chondrites in order to understand low temperature metamorphic reactions on the EH parent body. Here we describe the mineralogy, chemistry and matrix textures that distinguish EH3 chondrite PCA 82518, from several other EH3 chondrites (ALHA81189, Y-691, ALH 84170, and Sahara 97096).

**Results:** This meteorite is mainly composed of porphyritic to granular pyroxene chondrules, and irregularly shaped metal-sulfide clumps. Euhedral silica is commonly observed near chondrule rims and in pyroxene fragments. The presence of olivine and well-defined chondrules suggest that it belongs to type 3.

Many of the low-Ca pyroxene crystals in PCA contain numerous blebs of sub-micron sized Ni-poor Fe metal and troilite. These pyroxenes appear opaque in transmitted light and tend to be mantled by a thin layer of pure enstatite [2].

The matrix in PCA 82518 is different from that of other EH3s. The matrices of most EH3s are characterized by silicate sulfide and metal clasts ranging in size from one to several µm-across ("clastic matrix" of [3]). The fragmental, clastic textures of these grains can be seen easily in back-scattered electron images. In contrast, much of the PCA matrix is so fine that individual grains are not observed; this matrix may be glassy. The matrix contains kamacite crystals with bulbous shapes (convex crystal margins with matrix). In addition, elongate enstatite crystals extend from chondrules into matrix.

Pyroxene in PCA shows a wide range of Fs content similar to other EH3s; however, the Cr₂O₃ content in olivine is lower. In type 3 OC and CO chondrites, Cr₂O₃ apparently diffuses out of olivine during metamorphism [4].

**Discussion:** Well-defined chondrules and the presence of olivine indicate that PCA 82518 is a type 3 chondrite. However, the very fine, non-clastic matrix and bulbous metal crystals distinguish PCA from other EH3s. The bulbous metal texture indicates in situ crystallization or annealing, not clastic transport. This texture and elongate pyroxene extending into matrix may have resulted from a shock event, similar to that inferred for RKPA80259 [5]. The lower Cr₂O₃ of olivine compared to other EH3s is consistent with metamorphism at higher temperature [4].

PCA 82518 is classified by [1] as shock stage S3, based primarily on lamellar twinning and undulatory extinction in coarse enstatite. However, actual shock energy might have been higher than suggested by this classification if enstatite crystals were annealed. In any case, PCA 82518 experienced more extensive heating, probably due to shock, than the other EH3 chondrites in our study.

**References:** [1] Rubin A. et al. 1997. *Geochimica et Cosmochimica Acta* 60:847-858. [2] Lusby D. et al. 1987. *Geochimica et Cosmochimica Acta* 30:E679-E695. [3] Rubin A. et al. 2009. *Meteoritics & Planetary Science* 44:589-601. [4] Grossman J. N. and Blearley A. J. 2005. *Meteoritics & Planetary Science* 40:87-122. [5] Fagan T. J. et al. 2000. *Meteoritics & Planetary Science* 35:31-329.
FIRST <sup>40</sup>Ar-<sup>39</sup>Ar DATA OF THREE RECENTLY DISCOVERED ACHONDRITES: SAU 402, DH 312, AND DH 500

E. V. Korochantseva¹,², A. I. Buikin¹,², J. Hopp¹, A. V. Korochantsev² and M. Trieloff¹. ¹Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany. E-mail: Mario.Trieloff@geow.uni-heidelberg.de. ²Vernadsky Institute of Russian Academy of Sciences, Moscow, Russia.

**Introduction:** A relative scarcity of chronological data on primitive achondrites and current great interest in enstatite meteorites prompted us to undertake this high-resolution <sup>40</sup>Ar-<sup>39</sup>Ar study. Here we report first <sup>40</sup>Ar-<sup>39</sup>Ar data for three unrelated achondrites (1) SaU 402—ungrouped enstatite that could be an impact melt rock [1]; (2) Dh 312—a primitive achondrite, classified as an acapulcoite with low shock stage and weathering grade W3 [2]; (3) Dh 500—an unusual ungrouped brecciated primitive achondrite (S4, W4) possibly having some links to winonaites and silicate inclusions of the IAB/IIICD irons [3].

**Results and Discussion:** The age spectrum of SaU 402 yields an age plateau with an age of 4275 ± 17 Ma over approximately 50% of <sup>39</sup>Ar release (1σ error here and further). Most probably this age reflects the formation time of this impact melt rock. However, it may also date a later postformation event, similar to another enstatite impact melt rock Ilafegh 009 where the Ar-Ar age was significantly younger than the I-Xe age. The last total reset of both Dhofar meteorites occurred approximately 4.45 Ga ago. The age spectrum of Dh 312 shows a partial plateau with an age of 4450 ± 24 Ma (66–100% of <sup>39</sup>Ar release). Within uncertainty this age is the same as Ar-Ar ages of other acapulcoites and lodranites constraining the time of thermal metamorphism [5–7]. According to [3], the polymict breccia Dh 500 experienced intensive thermal and impact metamorphism which is consistent with the complex history inferred from this Ar-Ar study. The age spectrum of Dh 500 shows at least three events. It gives two partial plateaux with ages of 4307 ± 11 Ma (17–39% of <sup>39</sup>Ar) and 4454 ± 11 Ma (53–94% of <sup>39</sup>Ar). These ages are in the range of Ar-Ar ages of winonaites and silicate from IAB irons as well as unshocked ordinary chondrites [8–10]. Secondary events causing partial <sup>40</sup>Ar loss ≤ 3.2 Ga ago are indicated by age spectra of all samples. Primordial <sup>36</sup>Ar is detected in all samples and is released at temperatures > 1100 °C from primitive meteorites and in the temperature range of 800–1140 °C from SaU 402. Thus, all three meteorites carry valuable information on the processes in the early solar system.

**References:** [1] Connolly H. C., Jr. et al. 2006. *Meteoritics & Planetary Science* 41:1383–1418. [2] Grossman J. N. and Zipfel J. 2001. *Meteoritics & Planetary Science* 36:A293–A322. [3] Lorenz C. A. et al. 2003. Abstract #5045. *Meteoritics & Planetary Science* 38. [4] McCoy T. J. et al. 1995. *Geochimica et Cosmochimica Acta* 59:161–175. [5] Pellas P. et al. 1997. *Geochimica et Cosmochimica Acta* 61:3477–3501. [6] McCoy T. J. et al. 1997. *Geochimica et Cosmochimica Acta* 61:623–637. [7] Mittlefehldt D. W. et al. 1996. *Geochimica et Cosmochimica Acta* 60:867–882. [8] Benedix G. K. et al. 1998. *Geochimica et Cosmochimica Acta* 62:2535–2553. [9] Bogard D. D. et al. 2005. *Meteoritics & Planetary Science* 40:207–224. [10] Trieloff M. et al. 2003. *Nature* 422:502–506.

LUNAR METEORITES FROM ANTARCTICA AND OMAN

R. L. Korotev. Dept. of Earth & Planetary Sciences, Washington Univ., St. Louis, Missouri, U.S.A. E-mail: korotev@wustl.edu.

Thirty-three named lunar meteorite stones representing 19–21 meteorites have been found in Antarctica, all by government-sponsored expeditions (Japan and U.S.). (It has not yet been established whether the 4 MIL 0900XX lunar stones represent 1, 2, or 3 falls [1].) The total mass of lunar material recovered from Antarctica is 5.43 kg, and 0.12% (by stone name, excluding provisional names) of the meteorites from Antarctica currently listed in the Meteoritical Bulletin Database are from the Moon.

In comparison, 57 named lunar meteorites stones representing 16–22 meteorites have been found in Oman, all but one (SaU 169) by private collectors. Many of these are not well characterized, although we have analyzed samples at least one stone of all Omani lunaites by INAA (39 stones). The mass of lunar material from Oman, a country about the size of Poland, is 9.75 kg. In the area of the main concentration of meteorites (those with names Dhofar, Jiddat al Harasis, and Shiṣr), the concentration of lunar meteorite finds is a remarkable 0.9 g km⁻². This value is 3.8× that calculated by Nazarov et al. [2] because of 10 more years of new finds, including 5.5-kg Shiṣr 162. The fraction of lunar meteorites among named stones from Oman, 2.35% (by stone name), is 2000× that for Antarctica presumably because of collection bias, i.e., many ordinary chondrites from Oman never receive names.

Assuming 21 Antarctic lunaites, 13 are feldspathic breccias (3–9% FeO), four are mare basalts (21–23% FeO), and 4 are breccias containing both highlands and mare material (12–18% FeO). None has a large proportion of KREEP (MIL 090036 and Yamato 983885 have about 2 µg/g Th). Assuming 21 Omani lunaites (author's preference), 17 are feldspathic breccias, 1 (Dhofar 287) is a mare basalt, 1 (Dhofar 1180) is a mare-highlands breccia, and 2 are KREEP-rich breccias (SaU 169 with two lithologies having 9 and 30 µg/g Th and Dhofar 1442, a regolith breccia, having 14 µg/g Th). Thus, the distribution of lunar rock types differs considerably between the two regions.

Among the Antarctic lunaites, several cases of launch pairings are established or suspected, leading to 13–17 lunar craters represented. Because of lack of cosmic-ray exposure data for most Omani lunaites, launch pairings among the Omanian meteorites are not established. On the basis of similar composition and texture, SaU 449 is likely launch-paired with Dhofar 925/960/961 (340 km separation) [3] and JaH 348 may be launch paired with paired stones Dhofar 1436 and Dhofar 1443 (143 km separation). Although texturally different, Shiṣr 166 is compositionally identical to Dhofar 026 found 33 km away. These stones may represent yet another launch pairing.

On the basis of similar texture and compositions, possible Antarctic-Oman launch pairings include Dhofar 1428 and MAC 88104/5. Dhofar 1436/1443, an impact-melt breccia, is compositionally identical to MIL 07006, a regolith breccia.

Omani lunaites are contaminated, to varying degrees, with K, Sr, Cs, Ba, As, Se, Br, Sb, and U compared to their Antarctic counterparts and Apollo samples.

**References:** [1] Korotev R. L. et al. 2011. Abstract #1999. 42nd Lunar and Planetary Science Conference. [2] Nazarov M. A. et al. 2004. *Solar System Research* 38:49–58. [3] Korotev R. L. et al. 2009. *Meteoritics & Planetary Science* 44:1287–1322.
A PROTOPLANETESIMAL DUST COLLISION MODEL BASED ON
EXPERIMENTS

S. Kothe¹, C. Güttler¹, J. Blum¹, E.Beitz¹ and R. Weidling¹. ¹Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, E-mail: s.kothe@tu-bs.de.

**Introduction:** The formation of solid bodies in the early solar system, like e.g. planets, meteorites or asteroids started with the growth of small aggregates out of (sub-) micrometer sized dust grains. At distances of 1 AU from the young Sun, most of the particles are silicates. Collisions between those dust grains have initially low velocities and lead to sticking and hence to the growth of larger, at first fractal, aggregates. Further impacts are supposed to compact these agglomerates to non-fractal but still highly porous particles. Due to the interaction with the surrounding gas, these agglomerates collide at higher velocities. Therefore these collisions do not necessarily lead to sticking.

However, none of these processes is directly accessible by
observations so that we depend on theories, simulations and experiments
to develop a picture of these processes.

The collision behavior of two dust agglomerates has been studied in different experiments (e.g., reviewed in [1]) with typically micrometer sized dust particles and aggregates thereof. To reach low collision velocities, which are realistic in a protoplanetary disk, most of the experiments were performed under microgravity conditions on parabolic flights or in the drop tower in Bremen.

The experiments showed a variety of outcomes: while small particles at low collision velocities are still likely to stick, an increase in the impact energy leads to rebound of the particles, or, for even higher velocities of the order of 1 m s⁻¹, even to fragmentation. Both of these processes can restrain the growth of larger bodies.

**Collision Model:** To make the diversity of possible outcomes in these experiments accessible for theoretical approaches, we compiled them in a dust collision model (c.f. [2]). Depending on the particle masses, velocities, and porosities, the model predicts the outcome of collisions and distinguishes between different types of collisional outcomes, which are based on our experiments and extrapolations of these. For each type of collision, the model returns the particles porosities and size distribution after the collision.

**Improvements:** Since the original publication, several new experiments were conducted to improve the model. We found that there is a transition between the sticking and the bouncing regime and growth is still possible at velocities where we expect rebound [3]. Moreover, under certain circumstances fragmentation, which at first appears to constrain further growth, can actually lead to growth due to a small mass transfer [4,5].

This talk will give an introduction to our model and new
experiments which were used to improve it.

**References:** [1] Blum J. and Wurm G. 2008. *Annual Review of Astronomy and Astrophysics* 46:21–56. [2] Güttler C. et al. 2010. *Astronomy & Astrophysics* 513:A56. [3] Weidling et al. arXiv 1105:3909. [4] Beitz et al. 2011. arXiv: 1102:4441. [5] Kothe et al. 2010. *The Astrophysical Journal* 725:1242–1251.

CALCULATING IMPACT MELT VOLUMES PRODUCED BY NON-
VERTICAL IMPACTS ON THE EARTH, MOON, AND MARS

D. A. Kring¹, O. Abramov¹ and S. M. Wong². ¹Center for Lunar
Science and Exploration, USRA—Lunar and Planetary Institute, 3600
Bay Area Blvd., Houston Texas 77058, USA. E-mail: kring@lpi.usra.edu.
²Lunar and Planetary Laboratory, University of Arizona, Tucson,
Arizona 85721, USA.

**Introduction:** Previous studies have shown that the volume of impact melt generated and its volume relative to fragmented rock increases with crater diameter [1–3]. In a comparison of the parameters affecting impacts on different planetary surfaces, Grieve and Cintala [4] also suggested the melt volume associated with similar-sized transient craters is nearly six times greater on the Earth and Venus than on the Moon. Comparisons of this type were derived from analytical expressions that assume a vertical impact trajectory and, thus, are limited to only a small proportion of the impacts that occur on a planet. The most probable trajectories have impact angles of 45° [5] and impact events with even shallower inclinations are possible. Recently computer codes have been developed that allow three-dimensional simulations of impact events. One numerical study [6] used hydrocode modeling to determine the amount of melt produced by impacts at various impact angles on Earth and showed that it decreases with impact angle. We use that type of result to render an easy-to-use analytical expression for calculating impact melt volumes.

**Results:** Our analytical expression is derived for melt volumes produced by oblique impacts as a function of gravity, impact velocity, impact angle, and density of impact projectiles and target surfaces on the Earth, Moon, and Mars. The most probable oblique impact (45°) produces ~2 times less melt volume than a vertical impact, and ~2–7 times more melt than impacts with 30° and 15° trajectories, respectively. The melt volume for a particular crater diameter increases with gravity and impact velocity, so a crater on Earth will have more melt than similar-size craters on Mars and the Moon. For example, the formation of a transient crater with a particular diameter on Earth generates ~3 times more melt than on Mars and ~5 times more melt than on the Moon. However, the melt volume for a particular projectile diameter does not depend on gravity, but has a strong dependence on impact velocity, so the melt generated by a given projectile on the Moon is ~2 times greater than that on Mars. Collectively, these results imply thinner central melt sheets and smaller proportion of melt particles in impact breccias on the Moon and Mars than on Earth.

**References:** [1] Ahrens T. J. and O'Keefe J. D. 1977. In *Impact and explosion cratering*. pp. 639-656. [2] Grieve R. A. F. and Cintala M. J. 1992. *Meteoritics* 27:526-538. [3] Pierazzo E. et al. 1997. *Journal of Geophysical Research* 103:28,607-28,625. [4] Grieve R. A. F. and Cintala M. J. 1997. *Advances in Space Research* 20:1551-1560. [5] Shoemaker E. M. 1962. In *Physics and astronomy of the Moon*. 283-359. [6] Pierazzo E. and Melosh H. J. 2000. *Icarus* 145:252-261.
ORIGIN OF FERROAN OLIVINE IN MATRICES OF UNEQUILIBRATED CHONDRITES

A. Krot¹, I. Hutcheon², K. Nagashima¹, S. Crites¹, P. Gasda¹, L. Hallis¹, C. Jilly¹, M. Petaev³, K. Robertson¹, G. Taylor¹ and M. Telus¹.
¹University of Hawai'i at Mānoa, Honolulu, HI, USA.
²Lawrence Livermore National Laboratory, Livermore, CA, USA.
³Harvard University, Cambridge, MA, USA.

Ferroan olivine (fa, Fa₅₀–₁₀₀) is one of the major minerals in matrices of unequilibrated ordinary (UOCs) and carbonaceous (CV, CK, CO) chondrites. Two classes of models, nebular and asteroidal, have been proposed to explain its origin. According to the nebular models, matrix fa formed by gas-solid condensation under highly-oxidizing conditions resulted from evaporation of dust ± ice-enriched nebular regions during chondrule formation [1]. Recent thermodynamic calculations, however, do not support these models [2]. According to the asteroidal models, matrix fa formed during fluid-assisted thermal metamorphism on the chondrite parent asteroids [3, 4]. These models are consistent with the mineralogical observations and O- and ⁵³Mn-⁵³Cr isotope systematics of fa in CVs and MAC 88107 (ungr.) [3–7]. Here we report on the mineralogy and O-isotope compositions of fa in matrices of UOCs; ⁵³Mn-⁵³Cr measurements are in progress.

Ferroan olivine (Fa₆₀–₉₉) is found in several textural occurrences in Ngawi (1) 1–10 µm-sized grains in fine-grained rims around type I chondrules containing abundant opaque nodules composed of magnetite (mgt), Fe-Ni sulfide (sf), Ni-rich metal, and Fe-Ni carbides in their peripheries; (2) fa ± mgt ± sf veins crosscutting fine-grained rims around chondrules; (3) fa replacing opaque nodules in chondrule peripheries; (4) fa + phyllosilicates replacing chondrule mesostasis; and (5) isolated coarse (10–30 µm) grains and grains overgrowing opaque nodules in the matrix. Coarse fa grains commonly contain inclusions of sf and mgt and show the inverse chemical zoning: fayalite content decreases toward the edges of the grains, suggesting Fe-Mg interdiffusion during thermal metamorphism. The similar textural occurrences of fa are found in fine-grained rims and matrices of QUE 97008, EET 90161 (L3.05), MET 96503 (L3.1), and MET 00452 (H3.5). The Δ¹⁷O value of Ngawi fa, approximately 5‰, measured in situ by the UH Cameca ims-1280 is similar to those of coarse mgt grains in Ngawi and Semarkona [7].

These and previously published observations of the mineralogy and isotopic compositions of fa in matrices of metamorphosed ordinary and carbonaceous chondrites [3–7], and the nearly complete absence of fa in matrices of unmetamorphosed chondrites and cometary IDPs, support origin of matrix fa during fluid-assisted thermal metamorphism. ⁵³Mn-⁵³Cr and O-isotope studies of matrix fa in UOCs and CCs can be used to constrain time of aqueous alteration and, in combination with D/H measurements of organics and phyllosilicates, sources of water ice (inner versusouter disk) that accreted into their parent asteroids [8].

**References:** [1] Lauretta D. et al. 2003. *Geochimica et Cosmochimica Acta* 65:1337–1353. [2] Grossman L. 2010. *Meteoritics & Planetary Science* 45:7–20. [3] Krot A. et al. 2004. *Proceedings of the National Institute of Polar Research* 17:154–172. [4] Zolotov M. et al. 2006. *Meteoritics & Planetary Science* 41:1775–1796. [5] Dobrică E. and Brearley A. 2011. Abstract #2092. 42nd Lunar and Planetary Science Conference. [6] Choi B.-G. et al. 2000. *Meteoritics & Planetary Science* 35:1239–1249. [7] Choi B.-G. et al. 1998. *Nature* 35:1365–1387. [8] Alexander C. et al. 2010. *Geochimica et Cosmochimica Acta* 74:4417–4437.

VOLATILE ELEMENT DEPLETION AND NEUTRON CAPTURE EFFECTS IN IRON METEORITES: NEW CONSTRAINTS FROM CADMIUM

T. S. Kruijer¹, M. Zbinden¹, P. Sprung¹, T. Kleine², R. Wieler¹.
¹Institute of Geochemistry and Petrology, ETH Zurich.
Correspondence: thomas.kruijer@erdw.ethz.ch. ²Institut für Planetologie, Westfälische Wilhelms-Universität Münster.

**Introduction:** Cosmic-ray effects can hamper chronological applications to extraterrestrial materials [e.g., 1], e.g. obtaining accurate core formation ages for iron meteorites using the Hf-W system [e.g., 1, 2]. Some lunar rocks show cosmic-ray-induced ¹¹³Cd anomalies [3], but yet no study investigated Cd isotopes in iron meteorites. Cadmium, a chalcophile and volatile element, is expected to occur in very low, but measurable concentrations in iron meteorites. We here present new isotope dilution Cd data for metal and troilite samples from different groups of iron meteorites, and for the first time report a cosmic-ray induced Cd isotope anomaly in an iron meteorite.

**Methods:** Troilite and metal samples were dissolved in concentrated Hcl or Aqua Regia. A¹⁰⁶Cd-enriched spike was added to 200–700 mg aliquots for concentration determinations. Cadmium was separated from the matrix using a multi-stage ion exchange chromatography modified after [4]. Cadmium concentrations and isotope compositions were measured using a *Nu Plasma* MC-ICPMS at ETH Zurich. External uncertainties on concentration data for troilite are estimated to be 3% (2SD), while the uncertainties for metal samples are considerably higher due to significant blank corrections. Total procedural blanks varied between 4 and 12 pg Cd.

**Results and Discussion:** Cadmium abundances in troilite inclusions range from 0.4 to 5 ppb, while concentrations in the metal phase are all below 30 ppt. Cadmium abundances in the metal are 2–3 orders of magnitude lower than previously reported [5,6], but consistent with a more recent study [7]. Although average moderately volatile element (Ga and Ge) contents for different iron groups [8] generally correlate with the Cd contents presented here, Cd abundances vary between different troilite nodules from single meteorites. One troilite nodule separated from Toluca (IAB) has ε¹¹³¹¹¹Cd = -7.3 ± 3.3 and ε¹¹⁴¹¹¹Cd = 4.1 ± 4.7 (2SD) (i.e., 10⁴ deviation relative to the terrestrial value). The Cd isotope anomalies presented here are consistent with expected neutron capture effects for Cd isotopes, and in good agreement with correlated ε¹¹⁴Cd vs ε¹¹³Cd variations reported for irradiated lunar samples [4].

**Outlook:** The very low Cd concentrations and their systematic variation reflect the strong volatile element depleted nature of magmatic iron meteorites. Albeit analytically challenging, the first cosmic-ray induced Cd isotope anomaly reported here appears promising for the use of ¹¹³Cd as neutron capture dose monitor in iron meteorites.

**References:** [1] Leya I. et al. 2000. *Earth and Planetary Science Letters* 175:1–12. [2] Kleine T. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5150–5188. [3] Sands D. G. et al. 2001. *Earth and Planetary Science Letters* 186:335–346. [4] Wombacher F. 2003 *Geochimica et Cosmochimica Acta* 67:4639–4654. [5] Schmitt R. A. et al. 1963. *Geochimica et Cosmochimica Acta* 27:1077–1088. [6] Rosman K. J. R. and De Laeter J. R. 1974. *Geochimica et Cosmochimica Acta* 58:1665–1677. [7] Chen J. H. and Wasserburg G. J. 1983. 14th Lunar and Planetary Science Conference 1052. [8] Haack, H. and McCoy T. J. 2003. Treatise on Geochemistry.
5143

PSEUDOTACHYLITIC MELTING AND UNMIXING OF SILICATE, CARBONATE AND SULFIDE MELTS IN THE PULTUSK H-CHONDRITE

A. Krzesińska¹, A. Żelażniewicz¹ and R. Orlowski². ¹Institute of Geological Sciences, Pol. Acad. Sc., Res. Centre in Wrocław, Podwale 75, PL-50449 Wrocław, Poland. ²Res. Centre in Warsaw, Twarda 51/55, PL-00818, E-mail: agatakrz@twarda.pan.pl.

**Introduction:** The Pultusk meteorite is H4-5 S3 chondrite with silicates of typical, equilibrated composition [1–3]. It was significantly deformed due to shock-related shearing at high strain-rate (without high shock pressures) [3, 4]. In most of the specimens cataclastic, darkened zones occur. The conducted EDS measurements indicate that in such darkened zones, glassy blebs composed of iron-depleted silicate-, iron-nickel sulfide- and carbonate-domains are present.

Iron-pure silicates and iron-nickel sulfides in cataclased zones: In matrix of cataclased parts of chondrite, ~20–120 µm large, irregular blebs occur. They are generally composed of amorphous phases; however, some microcrystallites may also be detected. Such blebs never occur in the light, host part of the chondrite. Modal composition of blebs differs from the host rock's composition as blebs are either completely free of metal and sulfides or contain many laths of iron-nickel sulfides. Silicate glasses in blebs have generally composition of enstatite (En94.1 ± 2.6 Fs5.0 ± 2.9 Wo0.9 ± 0.3) and iron-pure diopside (En52.9 ± 7.4 Fs4.2 ± 2.5 Wo42.9 ± 8.0) and in some cases of forsterite (Fo98.6 ± 0.5 Fa1.4 ± 0.5).

The composition of the silicates in the vicinity of all of these objects is typical for H chondrite (En80.5 Fs17.5 ± 1.6 Wo2.0 ± 1.5 and Fo80.7 Fa19.3 ± 1.2). No transition zone is observed.

Carbonates inside of blebs: In one of blebs, CaO-rich microcrystallites occur. Their composition is: SiO₂–0.22; FeO–0.85; MgO–0.05 and CaO–54.79 wt%. They are most likely calcitic because of carbon contents.

**Discussion and Conclusion:** Blebs of such iron-pure silicate composition are hardly expected in a thermally equilibrated chondrite and must postdate nebular and accretional processes. The composition of blebs cannot be related to enstatite chondrite projectile as sulfides in blebs do not contain normally lithophile elements. The origin of calcite seems to be the most mysterious problem. Origin as weathering product [5] is excluded as specimens are fresh finds and blebs occur inside them

Since blebs occur only inside zones with the obvious evidence of cataclasis, they may be related to pseudotachylitic melting and unmixing due to high strain-rate impact event. It seems that three immiscible melts then unmixed: magnesium-silicate, iron sulfide and carbonate. The origin of carbon is however unknown. Moreover, pseudotachylitic melting is likely as such unmixing of silicate and sulfide/carbonate melts occur in terrestrial impact structures [6,7] and iron-depleted glasses have been formed in H chondrite deformed at high strain-rate [8].

**Acknowledgments:** This work was supported by MNiSW grant no. N N307 474838.

**References:** [1] Binns R. A. 1968 *Geochimica et Cosmochimica Acta* 32:299–317. [2] Stöffler D. et al. 1991. *Geochimica et Cosmochimica Acta* 55:3845–3867. [3] Krzesinska A. 2010. Abstract #1140. 41st Lunar and Planetary Science Conference. [4] Krzesińska A. 2010. vol. 5. *EPSC2010-499*. [5] Rubin A. E. 1997. *Meteoritics & Planetary Science* 32:231–247. [6] Osinski and Spray. 2010. *EPSL* 194:17–29. [7] Deutsch A. et al. 1998. Abstract # 1386. 29th Lunar and Planetary Science Conference. [8] Van der Bogert C. H. et al. 2003. *Meteoritics & Planetary Science* 38:1521–1531.

5257

YOUNG $^{26}$Al-$^{26}$Mg AGES OF CHONDRULES IN THE LL3.1 CHONDRITE BISHUNPUR: EVIDENCE FOR THERMAL PROCESSING ON ASTEROIDAL BODY?

E. Kurahashi¹,², K. Nagashima³, A. N. Krot³ and S. S. Russell². ¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany. E-mail: e.kurahashi@uni-muenster.de. ²Natural History Museum, London, UK. ³HIGP/SOEST, University of Hawai'i at Mānoa, USA.

**Introduction:** An increasing amount of data on protoplanetary solids using precise isotope measurements provides important constraints on the formation ages of solids in the early solar system [e.g., 1–5]. Here, we report new results of the Al-Mg isotope system of the Bishunpur (LL3.1) chondrules.

**Mineralogy and Petrology:** A type I chondrule (#25, ~450 µm in diameter) consists of elongated orthopyroxene (Fs₅Wo₁), high-Ca pyroxene (Fs₁₁Wo₃₇) and glassy mesostasis containing fine grains of metal and high-Ca pyroxene. A type II chondrule (#24, 520 × 260 µm) consists of olivine (Fo~81) and glassy mesostasis including high-Ca pyroxene crystallites (Fs₁₉Wo₄₁). There are no secondary minerals in either chondrule. $^{26}$Al-$^{26}$Mg isotope systematics: Mg-isotope measurements were performed with the UH Cameca ims-1280. Four points in glassy mesostasis (Al/Mg = 23–69) in #25 and 3 points in glassy mesostasis (Al/ Mg = 26–37) in #24 were measured with a ~5 µm beam spot. Both chondrules show no clear evidence of $^{26}$Mg-excesses and provide only upper limits of the initial $^{26}$Al/$^{27}$Al ratios of 9.9 × 10⁻⁷ and 4.2 × 10⁻⁶, respectively. Assuming a homogeneous distribution of $^{26}$Al in the early solar system with the inferred initial $^{26}$Al/$^{27}$Al ratio of 5 × 10⁻⁵ [6], these data imply relative chondrule formation ages of > 4.1 Ma for #25 and > 2.6 Ma for #24 after Ca, Al-rich inclusions (CAIs).

**Discussion:** Despite the pristine mineralogy of the chondrules studied, the inferred Al-Mg ages are clearly younger than the previously reported chondrule ages from Bishunpur, ranging from 0.8 to 2.5 Ma after CAIs [1, 2]. To evaluate a possibility of instrumental artefact, a chondrule from CR2 Elephant Moraine (EET) 92174, which has been previously measured for $^{26}$Al-$^{26}$Mg systematics [5], was analyzed under the same conditions. The results obtained are in excellent agreement with the data reported by Nagashima et al. [5]. Based on the petrological observations of metal-troilite-silicate inclusions in matrix and fine-grained rims around chondrules in Bishunpur, Kojima et al. [7] concluded that this meteorite is a breccia that experienced impact process(es) prior to the final accretion. Both chondrules studied here are partly surrounded by fine-grained rims and metal-sulfide-silicate inclusions occur next to the chondrules. We infer that there is a possibility of redistributions of radiogenic $^{26}$Mg in chondrules during re-accretion of Bishunpur parent body by impact event(s).

**References:** [1] Kita N. et al. 2005. In *Chondrites and the protoplanetary disk*, pp. 558–587. [2] Mostefaoui S. et al. 2002. *Meteoritics & Planetary Science* 37:421–438. [3] Kunihiro T. et al. 2004. *Geochimica et Cosmochimica Acta* 68:2947–2957. [4] Kurahashi E. et al. 2008. *Geochimica et Cosmochimica Acta* 72: 3865–3882. [5] Nagashima K. et al. 2007. Abstract #5291. *Meteoritics & Planetary Science* 42. [6] MacPherson G. J. et al. 1995. *Meteoritics* 30:365–386. [7] Kojima T. et al. 2003. *Geochimica et Cosmochimica Acta* 67:3065–3078.
5005

EVIDENCES OF A SHOCK METAMORPHISM IN THE
CHONDRITE GRUZ'KE (H4)

N. V. Kychan. Institute of environmental geochemistry NAS of Ukraine, 34a Palladin av., Kyiv, Ukraine. E-mail: Nkychan@i.ua.

The chondrite Gruz'ke was found on 2007 March next to the village Gruz'ke in the Kirovograd region, Kirovograd district, Ukraine (48°32'N, 32°03'E). According to previous study [2], meteorite Gruz'ke was classified as an H4 ordinary chondrite. Presence of the numerous evidences of a shock metamorphism allowed us to classify the chondrite as a shock stage S4, based on the scheme of Stöffler et al. [3]. On the basis of the weathering classification of Wlotzka [4], the Gruz'ke chondrite belongs to the stage W2.

Here we present the additional data on a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) study of inclusions in the metal and troilite particles [2] and shock effects in polished sections of the Gruz'ke chondrite. One of the polished sections was etched by 5-% nital during 10 s. The ordinary for chondrites shock effects are presented in minerals of the meteorite by the structures of deformation (planar structures in olivine, Neumann lines in kamacite and lamellas in troilite), shock heating (mosaicism of olivine, polycrystalline structure of kamacite and troilite, partial or complete transformation of martensite to coarse plessite within a zone taenite, secondary troilite) and melting (veins of troilite and pockets of silicates). Some shocked minerals have evidences of additional fragile and plastic deformations, such as shear structures of lamellas and monocrystals in troilite, distortion of the Neumann lines in kamacite and grains of zone taenite. At the same time, the presence within the chondrite of melted regions composed of maskelenite (Ab<sub>78.9</sub>An<sub>13.2</sub>Or<sub>6.89</sub>) with numerous regular or irregular microcrystals of chromite and amoeboid coarse grains of kamacite and troilite with a high content of large inclusions (a pallasite-like structure) are the main features of the chondrite. Due to the high content of inclusions, the structure of the kamacite is similar to that of the Galkiv chondrite (H4) [1]. EDS-data indicate to the following average composition of the studied inclusions in the metal and troilite (in wt%): olivine (Fa<sub>18.6</sub>), pyroxene (Fs<sub>16.7</sub>En<sub>82.2</sub>Wo<sub>1.41</sub>), plagioclase (Ab<sub>80.6</sub>An<sub>11.7</sub>Or<sub>7.78</sub>), chromite (Cr<sub>2</sub>O<sub>3</sub>—55.7; FeO—29.3; Al<sub>2</sub>O<sub>3</sub>—7.05; MgO—3.98; TiO<sub>2</sub>—2.22; MnO—0.80; V<sub>2</sub>O<sub>5</sub>—0.73), merrillite (P<sub>2</sub>O<sub>5</sub>—48.7; CaO—43.4; MgO—3.37; Na<sub>2</sub>O—2.63; FeO—1.87), native copper (Cu—94.1; Fe—3.93; Ni—2.01) and silica (SiO<sub>2</sub>—98.5; FeO—1.47).

The presence of a lot of structures of shock metamorphism and the
character of their distribution within the chondrite point to as minimum
two shocks in the cosmic history of the meteorite parent body. The first
one resulted in the main shock alteration of the chondrite due to a shock
pressure in the range of 30–35 GPa, which was accompanied by a local
increase of temperature up to 988 °C and post-shock one ≤500 °C. The
large sizes of inclusions, which were produced in result of solid-state
diffusion during shock metamorphism, testify to a relatively slow cooling
of the meteorite parent body from the post-shock temperature. The last
shock was no more than 8 GPa and produced of only fragile and plastic
deformation within the minerals.

References: [1] V. P. Semenenko and A. L. Girich. 1998. *Meteoritics* & *Planetary Science* 33:A193–A196. [2] Semenenko et al. 2010. *Mineralogical Review* 60:59–69 (in Ukrainian). [3] D. Stöffler et al. 1991. *Geochimica et Cosmochimica Acta* 55:3845–3867. [4] F. Wlotzka. 1993. *Meteoritics* 28:460.

5384

BASAL SUEVITE AND BASAL IMPACT MELT ROCKS, A SINGLE IMPACTITE UNIT MARKING THE BOTTOM OF ROCHECHOUART TRANSIENT CRATER

P. Lambert¹, G. R. Osinski², and H. M. Sapers². ¹Sciences & Applications, 218 Bd Albert 1 er, F33800 Bordeaux, France. E-mail: lambertbdx@numericable.fr. ²Department Earth Sciences, University of Western Ontario, London, ON, Canada.

Early studies suggested a continuum between impact melt-bearing breccia ("suevite") and impact melt rocks at Rochechouart, with an intermediate population where lithic matrix and melt matrix domains co-exists at the hand specimen scale (D-E population in [1]). More recently "upper" and "basal" suevite have been distinguished within the Rochechouart impact deposits [2]; and Montoume breccias have been interpreted as particulate impact melt rocks, transitional between a melt rock and a melt-rich impact breccia [3]. Notably, a large proportion of impact melt rocks currently exposed at Rochechouart bears a significant proportion of lithic clasts [1, 2]. All the impact melt rocks exposed stand in direct contact with bedrock [1, 2] and can be referred as to "basal impact melt rocks."

Field, petrographic and geochemical data indicate that basal suevite and basal impact melts rocks at Rochechouart are members of a single impactite unit (basal impact melt-bearing unit) where the proportion of melt is more significant than its setting (in the matrix or as clasts), the latter varying locally and depending on the scale of observation. The unit spreads over the SW portion of the preserved crater deposits. It is characterized by (1) systematic setting in direct contact with the autochtonous-paraautochtonous bedrock; (2) limited mixing and transportation deduced from petrographic and/or geochemical data indicating a local origin of a significant proportion of both melts and lithic fractions [2]; (3) complex textures including local diffuse contacts between lithic matrix and melt matrix fractions, "melts in melts," schlieren melt matrix breccia clasts, [2]; and (4) depletion or absence of homogeneous melts.

The Rochechouart basal impact melt-bearing unit is interpreted as the result of combined mechanisms associated with the collapse of the transient cavity. These mechanisms involve mechanical fragmentation of the shocked bedrock in the floor of the transient cavity related to uplift and pressure release, superimposed heating due to structural uplift known to cause elevated transient local geotherms at terrestrial impact craters above 20 km diameter [4], and further "intrusion" and mixing with the crater fill deposits. This hypothesis is consistent with the relative inefficiency in homogenizing and mixing of melt at Rochechouart noted by [2]. More generally it could explain the lack of coherent impact melt sheet at Rochechouart. Field and petrological data indicate that significant melting occurs beyond readjustment during the slow thermal re-equilibration process within the heterogeneous mixture of lithic debris and melts.

Beyond impactite nomenclature and related issues, recognition of
basal suevite and basal impact melt rocks bear important geological
applications. They may constrain the position of the center of the original
crater (and its size to a lesser extend) at deeply eroded and/or re-
processed impact structures.

References: [1] Lambert P. 1977. *Earth and Planetary Science Letters* 35:258–268. [2] Lambert P. 2010. Geological Society of America Special Paper 465:509–541. [3] Sapers H. M. et al. 2009. Abstract #1284. 40th Lunar Prospector Spacecraft. [4] Naumov M. V. 2005. *Geofluids* 5:165–184
MICROSTRUCTURAL CHARACTERISTICS OF SHOCKED RUTILE
FROM THE CAPE CHARLES DRILL HOLE, CHESAPEAKE BAY
IMPACT STRUCTURE, VIRGINIA, USA

F. Langenhorst¹, J. W. Horton Jr.², J. C. Jackson², H. E. Belkin² and L.-M. Chou². ¹Institute of Geoscience, Friedrich-Schiller University Jena, Burgweg 11, D-07749 Jena, Germany. E-mail: Falko.Langenhorst@uni-jena.de. ²U. S. Geological Survey, Reston, VA 20192, USA.

**Introduction:** The late Eocene Chesapeake Bay impact structure is buried at shallow to moderate depths beneath continental-margin sediments in southeastern Virginia, USA. In preparation for the international Chesapeake Bay Impact Structure Deep Drilling Project, the United States Geological Survey drilled an 823 m test hole into the central uplift of the crater near Cape Charles, Virginia [1]. A combined X-ray diffraction and Raman study on monomict gneissic impact breccias from this test hole revealed the existence of a high-pressure polymorph of TiO₂ with the α-PbO₂ structure (TiO₂ II) [2]. After the Ries impact structure, Chesapeake Bay is the second crater where this polymorph has been found. Here, we have undertaken a transmission electron microscopic study to understand the mechanism of the phase transformation, which was fast enough to operate under the very short time scale of shock compression.

**Methods:** Brecciated gneisses from the Cape Charles drill hole were prepared into thin sections [2] and then ion-milled using a conventional Gatan Duomill as well as a Quanta 3D DualBeam. Microstructural observations were made using a 200 kV LEO922 transmission electron microscope (TEM).

**Results and Discussion:** The TiO₂ grains studied so far are the mixtures of rutile and the α-PbO₂-structured high-pressure polymorph that were originally described in [2]. TEM inspection of these grains shows that the initial TiO₂ phase, rutile, is very defect-rich, containing numerous stacking faults and microtwins. These planar faults occur on multiple, symmetrically equivalent {011} planes, forming an interconnected network. The local symmetry of the faults corresponds to the α-PbO₂ structure, but larger areas of the defect-free high-pressure polymorph have not yet been detected.

This overall microstructure is compatible with a martensitic (shear) transformation from rutile to the α-PbO₂-structured high-pressure polymorph, which has been proposed by Hyde and Andersson [3]. According to Hyde and Andersson [3] the rutile structure can be regarded as hexagonal close packed oxygen atoms with titanium atoms occupying half the close packed rows of octahedral interstices. Shear on oxygen planes of the rutile structure pushes the titanium atoms into new positions and results in the formation of the α-PbO₂-structured high-pressure polymorph. Since the shock duration was very short, there was not enough time for a complete realignment of atoms, explaining the defect-rich nature of the TiO₂ grains.

**Acknowledgments:** We are grateful for financial support provided by the Deutsche Forschungsgemeinschaft (LA 830 13-1 and 14-1).

**References:** [1] Horton J. W. Jr., Gohn G. S., Powars D. S. and Edwards L. E. 2008. *Geological Society of America Special Paper* 437:73-97. [2] Jackson J. C., Horton J. W. Jr., Chou I.-M. and Belkin H. E. 2006. *American Mineralogist* 91:604-608. [3] B. G. Hyde and Andersson S. 1988. *Inorganic Crystal Structures*. pp. 67-72.

SILICA SPECIATION: COUPLING SEM RAMAN AND CATHODOLUMINESCENCE

A. Laroussi¹, A. Jambon², O. Boudouma² and H. Chennaoui Aoudjehane¹,². ¹Laboratoire GAIA, Département de Géologie, Faculté des Sciences, Université Hassan II, BP 5366 Maârif, Casablanca Maroc (E-mail: a.laroussi@fsac.ac.ma). ²UPMC -Paris6, ISTE, Case 110, 4 place Jussieu, 75252 Paris, France.

Seifertite, stishovite, cristobalite, tridymite, quartz and high and low pressure glass, are silica phases found in Martian meteorites, eucrites, enstatite chondrites and lunar meteorites. Crystalline state of silica in meteorites and terrestrial rocks essentially depend on the intensity of the shock on the parent body and the chemical composition of the original silica.

Identification of silica phase is important, it allow having information on (P-T) conditions of its formation, especially the intensity of the shock. Cathodoluminescence CL spectroscopy on SEM, allowed to identify most silica phases and to valid the technique, that is simple, rapid, efficient and non destructive. Reference spectra have been collected [1-4].

We perform a Raman spectrometer prototype coupling to SEM and to CL spectrometer. Collecting spectra from a same minerals permit by using both techniques to intercalibrate the system. The aim is to be able to identify minerals and phases by using one or the other technique or both of them in the same equipment. It is especially important to be able to do it for minerals that are instable and can be destroy by one or the other technique, under the laser or electrons beam.

Raman spectra have been recorded on previously identified phases by CL of silica, plagioclase, maskelynite and pyroxenes; in order to valid this approach by comparing results.

We present here analyses on the lunar meteorite NWA 4734 [5-6], exceptional because the presence of high an low pressure silica phases: stishovite, seifertite, tridymite and cristobalite, and plagioclase and maskelynite [5, 7].

We began by the location of interesting phases by SEM images, CL spectra have been collected and the same points have been used to collect Raman spectra on VP Laser 532 mode, 0.2 mV with different counting timing.

Comparing results shows that this new approach seems to be interesting, at least for some minerals, and it could be used for meteorites and terrestrial rocks.

**References:** [1] Chennaoui Aoudjehane H. et al. 2005. *Meteoritics & Planetary Science* 40:967-979. [2] Chennaoui Aoudjehane H. et al. 2006. Abstract #1036. 37th Lunar Prospector Spacecraft. [3] Chennaoui Aoudjehane H. et al. 2006. Abstract #1037. 37th Lunar Prospector Spacecraft. [4] Chennaoui Aoudjehane H. et al. 2007. Abstract #1714. 37th Lunar Prospector Spacecraft. [5] Jambon A. et al. (soumis). [6] Connolly H. C. et al. 2008. *Meteoritics & Planetary Science* 43:571-632. [7] Chennaoui Aoudjehane et al. 2008. *Meteoritics & Planetary Science*. Abstract 5058.
A COMPARATIVE STUDY OF TRACE-ELEMENT DISTRIBUTIONS IN R AND H CHONDRITIC SULFIDES: QUANTITATIVE ASSESSMENT OF ENHANCED SULFUR FUGACITY IN THE EARLY SOLAR SYSTEM

D. S. Lauretta¹, A. V. Andronikov¹, K. M. Jackson¹ and L. Ojha¹.
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ, USA. E-mail: lauretta@lpl.arizona.edu.

**Introduction:** The R chondrites are a well-established chondrite group that contains chondrules, mineral fragments, sulfides, CAIs, and fine-grained matrix [1-5]. R chondrites have high $\dot{\text{A}}\dot{\text{A}}^{17}\text{O}$ (+2.9) [1, 6, 7]. They are oxidized as indicated by their high Fe (Fa$_{37-40}$) and Ni (up to 0.25 wt%) contents in olivine and lack of metal [1, 6-8]. They are also highly sulfidized, containing abundant pyrrhotite (Fe$_{1-x}$S) and pentlandite [(Fe,Ni)$_{0.8}$S$_{8}$] as well as other rare phases including chalcopyrite (FeCuS$_{2}$) and reports of pyrite (FeS$_{2}$) [1, 2, 3, 7, 9, 10]. The R chondrites record one of the most sulfidizing environments in the early solar system.

Using pyrrhotite-magnetite equilibrium, [9] determined the sulfur fugacity of LAP 04840 (R6) to be iron-troilite (IT) + 2. We used Cu-Fe-chalcopyrite equilibrium and the presence of Ni in the pyrrhotite to constrain sulfur fugacity in three R chondrites to IT + 1.6 to 2.8 [10]. Here, we use trace-element abundances in sulfide minerals to constrain the conditions of their formation. Since the H-chondrites are buffered at IT, they serve as a baseline for comparing the elemental abundances in R chondrite sulfides.

**Analytical Techniques:** We analyzed nine assemblages from three R chondrites (LAP031135, LAP04840, and PRE95411). In addition, we analyzed sixteen troilite grains from four H chondrites (Djati-Pengilon, Zag, Oum Dreyga, and Djoumine). Chemical analyses of trace element abundances in situ of metals and sulfides are carried out using LA-ICP-MS. The LA system at LPL consists of CETAC LSX-213 Nd:YAG 213 nm laser coupled with the Element 2 ICP-MS. We use the Hoba IVB iron meteorite sample [11] and NIST SRM-1250 as standards for analyzing metals, and MASS-1 USGS sulfide standard for sulfides [12].

**Results:** Compared to H-chondrite troilite, pyrrhotite in R chondrites is enriched in platinum group elements by factors ranging from 100–1000×. Trace element abundances in R-chondrite pyrrhotites combined with thermodynamic analysis indicate formation at IT + 2.3(±0.8) and 1050 K. If these conditions are representative of the nebular environment in which the R chondrites formed, then the determined sulfur fugacity is consistent with an H$_2$S/H$_2$ ratio of this region that is enhanced by a factor of ~670× over solar. Detailed characterization of these phases will provide better constraints on their formation.

**Acknowledgments:** This work was funded by NASA Grant NNX10AH50G (DSL PI).

**References:** [1] Kalllemeyn et al. 1996. *Geochimica et Cosmochimica Acta* 60:2243-2256. [2] Rubin and Kalllemeyn. 1989. *Geochimica et Cosmochimica Acta* 53:3035-3044. [3] Weisberg et al. 1991. *Geochimica et Cosmochimica Acta* 55:2657-2669. [4] Bischoff and Srinivasa. 2003. *Meteoritics & Planetary Science* 38:5-12. [5] Rout and Bischoff. 2008. *Meteoritics & Planetary Science* 43:1439-1464. [6] Bischoff et al. 1994. *Meteoritics* 29:264-275. [7] Schulze et al. 1994. *Meteoritics* 29:275-286. [8] Righter and Neff. 2007. *Polar Science* 1:25-44. [9] MxCanta et al. 2008. *Geochimica et Cosmochimica Acta* 72:5757-5780. [10] Jackson and Lauretta. 2010. *Meteoritics & Planetary Science Supplement* #5164. [11] Walker et al. 2008. *Geochimica et Cosmochimica Acta* 72:2198-2216. [12] Danyushevsky et al. 2011. *Geochemistry: Exploration, Environment, Analysis* 11:51-60.

SPECTRAL INDICES FOR IDENTIFYING TERRAINS ON VESTA WITH DAWN FRAMING CAMERA FILTERS

L. Le Corre¹, V. Reddy¹,², and A. Nathues¹.
¹Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, E-mail: lecorre@mps.mpg.de.
²Department of Space Studies, University of North Dakota, Grand Forks, USA.

**Introduction:** Vesta is the 3rd largest asteroid in the main belt [1] and the first target of NASA's Dawn mission which will begin its mapping phase in survey orbit around Vesta in August 2011. The Framing Camera (FC), one of three scientific instruments onboard the spacecraft [2], contains a set of seven color filters ranging from 0.44 to 0.97 microns in addition to a clear filter. The latter will be used mainly for mapping the morphology of Vesta's surface whereas the color filters will provide hints about surface composition either through the creation of color composite images allowing identifying spectrally distinct units, or through the analysis of the color spectra in combination with laboratory spectra of well-known howardite-eucrite-diogenite (HEDs) and non-HEDs samples.

**Goals:** Our study aims to find out what filter ratios and spectral criteria are best to characterize terrains on Vesta using the data acquired with the FC filters in the visible-near infrared. Obviously, our limitation is that we do not have ground truth measurements from the surface of this asteroid therefore we are going to assume that HEDs [3] and potentially other related types such as mesosiderites, pallasites and minerals like olivine-orthopyroxene (OPX) mixtures are analogous to terrains that might be observed on Vesta [4].

**Spectral Criteria:** Several spectral criteria such as reflectance ratios, spectral slopes and pseudo Band I minimum were plotted as a function of ratios of FC color filters to look for the best color parameters that can be used to extract compositional information. Band I minimum is used as a proxy for band center as FC cannot measure the whole 1-micron absorption band that is essential to study the mineralogy of HED terrains. The slope between 0.75 and 0.92 microns is also used to characterize the left wing of the pyroxene Band I. Spectral parameters have been computed using publicly available laboratory spectra of HEDs, pallasites, mesosiderites and olivine-OPX mixtures after resampling to FC filters.

**Classification:** In order to be able to distinguish the putative meteorite analogs on the surface of Vesta we selected the most relevant plots showing clusters of data points in distinctive areas or linear trends for each type. For each of them, four or five plots were attributed and will be used to identify surface composition in FC data. According to our study, it is possible to distinguish between eucrites and diogenites by using specific FC filters. Other non-HEDs types are recognizable as well. If none of the spectral criteria are fulfilled, we may assume it corresponds to howardite-like terrains or alternatively to another type of mineralogy that one can add to our spectral library after identification. Further testing of our method will involve effects of calibration, phase angle, and temperature on the selection of plots and cross-calibration with laboratory samples.

**References:** [1] Thomas P. et al. 1997. *Science* 277:1492-1495. [2] Sierks H. et al. 2011. *Space Science Reviews* online. [3] McSween H. et al. 2010. *Space Science Reviews* online. [4] Gaffey M. 1997. *Icarus* 127:130-157.
## CHARACTERIZATION AND POSSIBLE ORIGIN OF A CARBONACEOUS COATING ON AN UNUSUAL NANOCRYSTALLINE SILICATE AGGREGATE IN THE MATRIX OF THE MET 00426 CR3 CHONDRITE

C. Le Guillou¹, A. J. Brearley¹ and S. Bernard². ¹Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, New Mexico, USA. E-mail: coretin.san@gmail.com. ²LMCM-MNHN, Paris, France.

**Introduction:** Pristine chondrites are the best samples to study the nebular dust from which asteroidal parent bodies accreted. MET 00426 (CR3.00) is known to have preserved one of the highest concentrations of presolar silicates [1], as well as potential nebular condensates, as a result of minimal parent body aqueous alteration and metamorphism. Its matrix contains amorphous hydrated silicate, phyllosilicates, sulfides and organic matter particles [2, 3]. During FIB-TEM studies of MET 00426 matrix, we encountered an unusual particle coated with organic material, embedded within the normal fine-grained matrix. Here we report the results of TEM and STXM studies of this particle and discuss the possible formation mechanism of the carbonaceous material.

**Results:** The aggregate (500 nm in size) is composed of nanocrystalline Mg-Fe-Ca silicates (20–40 nm, probably diopside or augite) associated with sulfides and organic matter. The silicates are more Mg-rich (Mg# > 80 atom%) than the surrounding matrix and some individual domains are richer in Ca. Energy filtered TEM shows a continuous coating (approximately 20 nm in thickness) of carbonaceous material on the aggregate. High resolution TEM indicates that the carbonaceous material is slightly ordered, with small (1–5 nm) graphene layers stacked together and oriented parallel to the surface of the silicates. This degree of structural ordering is different from the more disordered organics found elsewhere in the matrix [3]. STXM mapping confirms the dominant aromaticity of this carbon coating and the absence of oxidized functional groups usually present in CR organics [3].

**Discussion:** This intriguing aggregate shares several microstructural similarities with presolar grains, such as grain size, high-Mg and Ca content, chemical variation at the nanometer scale and nanocrystalline features [4]. However, an attempt to measure the O-isotopic composition by NanoSIMS was unsuccessful. Nevertheless, we interpret this particle as having a nebular or presolar origin. Therefore, the occurrence of the carbon-coating provides information about organic formation prior to parent body accretion. This kind of coating has also been described around silicates in CP-IDPs [5], but the silicate mineralogy is different. Two possible synthesis mechanisms for the formation of this coating were suggested by [5]; Fischer-Tropsch processes [6] and polymerization of simple organic molecules by UV irradiation within an icy mantle on silicate grains that can occur in the interstellar medium [7]. In both cases, these observations demonstrate that organic synthesis reactions on the surface of silicate grains did contribute to the structural and chemical diversity of carbonaceous material in chondrites.

**References:** [1] Floss C. and Stadermann F. 2009. *The Astrophysical Journal* 697:1242–1255. [2] Abreu N. M. and Brearley A. J. 2010. *Geochimica et Cosmochimica Acta* 74:1146–1171. [3] Le Guillou C. et al. 2011. Abstract #1296. 42nd Lunar and Planetary Science Conference. [4] Vollmer C. et al. 2009. *The Astrophysical Journal* 700:774–782. [5] Flynn G. J. et al. 2010. Abstract #1079. 40th Lunar and Planetary Science Conference. [6] Nuth J. A. et al. 2008. Organic Matter in Space, Proceedings of the International Astronomical Union, IAU Symposium, 251 pp. 403–408. [7] Bernstein M. P. et al. 1999. *Science* 283:1135–1138.

## MATRIX MINERAL CHEMISTRY OF TIL 08007 CM CHONDRITE: IMPLICATIONS FOR INTERMEDIATE ALTERATION

H. W. Lee¹,², S. T. Kwon¹, J. I. Lee², I. S. Ahn², T. Nakamura³, A. Nakato³. ¹Yonsei University. E-mail: lhw615@yonsei.ac.kr. ²Korea Polar Research Institute. ³Tohoku University, Tohoku, Japan.

**Introduction:** CM chondrites contain tochilinite, cronstedtite, serpentine, carbonate, and sulfide in their matrix. These secondary minerals in matrix are well known as sensitive indicators for aqueous alteration on their parent bodies [1]. Tochilinite and cronstedtite are generally observed in PCP (poorly characterized phase) and serpentine replaced olivine or pyroxene. Carbonate and sulfide are associated with PCP or occur in matrix. As alteration advances, chemistry of secondary minerals of matrix is changed from Fe-rich (cronstedtite-like) to Mg-rich (serpentine-like) composition [2]. In addition, Mg, Fe, Mn-bearing carbonates occur in heavily altered CM chondrites. Modal abundance of sulfide increases during progressive alteration. In this study, we report mineral chemistry of matrix in TIL 08007 recovered by the 3rd KOREAMET and classified as CM chondrite [3], and discuss its implications associated with aqueous alteration.

**Analytical Methods:** We examined a polished thin section (KOPRIT018) by scanning electron microscopy (SEM), and electron probe micro analyzer (EPMA). Through SEM observation, we qualitatively identified PCP-like phases, carbonates, and sulfides in matrix. In order to analyze quantitatively matrix components, we carried out EPMA analysis with both focused and broad beams. Four areas containing PCP-like phases of a separated slice from TIL 08007 were selected for synchrotron radiation X-ray diffraction (SR-XRD) analyses.

**Results and Discussions:** In SEM-BSE, tochilinite-like phase and phyllosilicates are primarily observed within PCP-like phase (8.5 vol%). Some of them include Ca-carbonate grains. Tochilinite-like minerals in TIL 08007 are characterized by lower S content (by 10 approximately 15 wt%) and slightly higher Mg/Fe ratio compared to other typical CM chondrites (Murchison and Murray) [4]. Modal abundance of sulfide is 10 vol% ranging between less altered CMs (Murchison and Murray) and extensive altered ones (LAP 02277 and MET 01070) [5]. Phyllosilicates appear to be Fe-bearing serpentine. Based on SR-XRD analysis, major components of PCP-like phase are serpentine (7.2 Å), and tochilinite and serpentine mixed-layer mineral (6.0 Å). Weak peak of 5.4 Å probably indicates minor presence of tochilinite. From these results, lower S content in tochilinte-like phase may indicate that S was consumed to make sulfides and brucite layer of tochilinite formed mixed-layer mineral. Also, it is apparent that Fe-bearing serpentine was converted from cronstedtite by uptake of Mg and Si released from olivine and pyroxene during aqueous alteration. Additionally, the co-occurrence of both tochilinite-like phase and serpentine in PCP-like phase means that they are presumably on the transitional pathway during progressive aqueous alteration. The simple occurrence of Ca-carbonate supports that TIL 08007 did not reach extensive alteration. Therefore, the mineral chemistry of matrix implies that TIL 08007 is an intermediately altered CM2.3 chondrite.

**References:** [1] Tomeoka and Buseck. 1985. *Geochimica et Cosmochimica Acta* 49:2149–2163. [2] McSween. 1979a. *Geochimica et Cosmochimica Acta* 43:1761–1770. [3] Choi et al. 2008. *Journal of the Geological Society of Korea* 45:593–605. [4] Palmer. 2009. Ph.D. thesis. The University of Arizona. [5] Rubin et al. 2007. *Geochimica et Cosmochimica Acta* 71:2361–2382.
## 5138 INVESTIGATING THE PRESOLAR GRAIN INVENTORY OF CH CHONDRITES: A NANOSIMS STUDY OF ACFER 182

J. Leitner¹, P. Hoppe¹ and J. Zipfel². ¹Max Planck Institute for Chemistry, 55128 Mainz, Germany. E-mail: jan.leitner@mpic.de. ²Forschungsinstitut und Naturmuseum Senckenberg, 60325 Frankfurt, Germany.

**Introduction:** Primitive solar system materials contain varying amounts of presolar dust grains that formed in the winds of evolved stars or in the ejecta of stellar explosions. Presolar silicates and oxides are among the most abundant types of these grains [e.g., 1, 2]. The CR chondrite clan, consisting of the CR, CH, and CB chondrite groups, contains some of the most primitive meteorites, sharing certain mineralogical and chemical similarities [3,4]. High abundances of presolar silicates and carbonaceous grains were recently reported in individual CR chondrites [5–7], and a first presolar silicate grain was observed in the CH/CB chondrite Isheyevo [8]. Noble gas data imply the presence of carbonaceous presolar grains also in CH chondrites [9], but no presolar O-anomalous grains have been detected so far. In this ongoing study, we conduct a search for O-anomalous presolar silicate and oxide grains in fine-grained material located in lithic clasts of the CH3 chondrite Acfer 182. Investigating the occurrence and content of presolar matter in CH chondrites can shed light on the formation history of their parent body.

**Samples and Experimental:** We performed ion imaging of 10 × 10 µm²-sized matrix areas in a thin section of the CH3 chondrite Acfer 182 (paired with Acfer 207 and Acfer 214 [10]) with the NanoSIMS 50 ion probe in Mainz. ¹⁶O⁻, ¹⁷O⁻, ¹⁸O⁻, ²⁸Si⁻, and ²⁷Al¹⁶O⁻ were measured in multi-collection to identify presolar silicate and oxide grains.

**Results and Discussion:** 4,700 µm² of fine-grained material in matrix clasts have been analyzed for their O-isotopic composition. No presolar grains have been identified so far; based on the average presolar silicate grain size of ~300 nm, we estimate an upper limit of ~15 ppm for Acfer 182. This is comparable to the presolar silicate abundance of ~10 ppm we found for Isheyevo. The formation scenario for the CH chondrites is still under debate. According to a popular model, CH chondrites may represent a mixture of material produced by a giant impact between planetary bodies and nebular components that formed by thermal processing of dust in the protoplanetary disk [11, and references therein]. Detection of presolar grains in these meteorites would proof that at least one of the components contained interstellar matter that survived the impact. This would give support to the idea that surviving molecular cloud material might be one of the carriers of the large ¹⁵N enrichments of CH chondrites.

**Acknowledgments:** We acknowledge support by DFG through SPP 1385.

**References:** [1] Nguyen A. et al. 2007. *The Astrophysical Journal* 656:1223–1240. [2] Hoppe P. 2008. *Space Science Reviews* 138:43–57. [3] Weisberg M. K. et al. 1995. *Proceedings of the NIPR Symposium on Antarctic Meteorites* 8:11–32. [4] Krot A. N. et al. 2002. *Meteoritics & Planetary Science* 37:1451–1490. [5] Floss C. and Stadermann F. J. 2009. *Geochimica et Cosmochimica Acta* 73:2415–2440. [6] Leitner J. et al. 2011. *The Astrophysical Journal*, submitted. [7] Nguyen A. N. et al. 2010. *The Astrophysical Journal* 719:166–189. [8] Leitner et al. 2010. *Meteoritics & Planetary Science* 45:A166. [9] Huss G. R. et al. 2003. *Geochimica et Cosmochimica Acta* 67:4823–4848. [10] Bischoff A. et al. 1993. *Geochimica et Cosmochimica Acta* 57:2631–2648. [11] Bonal L. et al. 2010. *Geochimica et Cosmochimica Acta* 74:6590–6609.

## PHOSPHATES IN ORDINARY CHONDRITES

L. Leschner¹, J. Roszjar¹, T. John², and A. Bischoff¹. ¹Institut fuer Planetologie. Wilhelm-Klemm-Str. 10, 48149 Muenster, Germany, E-mail: l_lesc01@uni-muenster.de. ²Institut fuer Mineralogie. Corrensstr. 24, 48149 Muenster, Germany.

**Introduction:** Ca-phosphates, including both, apatite and merrillite are common accessory phases in most ordinary chondrites and as major hosts for U, Pb, and REE [1, 2] important mineral phases. They typically occur in type 4-6 ordinary chondrites and are less abundant in unequilibrated rocks. We have studied the grain sizes, and mineral chemistry of apatites and merrillites found in six ordinary chondrites of different type.

**Analytical Techniques:** Quantitative analyses were obtained using a JEOL JXA 8900 Superprobe electron probe micro analyzer operated at an acceleration voltage and beam current of 15 kV and 15 nA for major and minor elements, and 15 kV and 4 nA for halogens, respectively, using a defocused beam of 10 µm. H₂O values for apatites were calculated based on stoichiometry.

**Chemical composition:** We found that both Ca-phosphates have very similar chemical compositions among the H, L, and LL chondrites. This is obvious for CaO and P₂O₅, but also valid for the more minor components Na₂O and MgO (Table 1). Slight variations exist for FeO-, SiO₂-, and Ce₂O₃-concentrations among the minerals from different meteorites. Merrillite represents an important additional REE host. In contrast to terrestrial apatite, which is dominantly F-rich, all analyzed apatites are Cl-rich, which clearly indicates formation under F and OH poor conditions, as the latter both do have the more favorable ionic size to be incorporated into the apatite structure. Barwell apatite has the highest F-, Adzhi-Bogdo apatite the highest Cl concentrations.

**Results:** Mineralogy: Both, apatite and merrillite are typically intergrown with pyroxene, plagioclase, chromite, and troilite. Their grain size is roughly increasing from type 4 (typical sizes: 40–120 µm) to type 6 ordinary chondrites (typical sizes: 200–300 µm). Merrillite is generally larger than apatite. Importantly, the relative abundances of both phases vary significantly, e.g., merrillite is strongly dominating in Allegan, whereas in Bruderheim and Barwell apatite is by far more abundant.

**References:** [1] Brearley A. J. and Jones R. H. 1998. *Planetary materials* (ed. Papike J.) Reviews in Mineralogy, vol. 36. pp. 3-1 – 3-396. [2] Crozaz G. et al. 1989. *Earth and Planetary Science Letters* 93:157–169. [3] Bischoff A. et al. 1993 *Meteoritics* 28:570–578. [4] Terada K. and Bischoff A. 2009. *The Astrophysical Journal* 699:L68–L71.

<table><caption>Table 1. Phosphates in ordinary chondrites. Results in wt.%.</caption><thead><tr><th rowspan="2"></th><th colspan="5">Apatite</th><th colspan="5">Merrillite</th></tr><tr><th>Y(3)</th><th>PV(4)</th><th>AB(3)</th><th>BH(9)</th><th>B(4)</th><th>Y(2)</th><th>A(9)</th><th>PV(10)</th><th>AB(2)</th><th>BH(4)</th></tr></thead><tbody><tr><td>CaO</td><td>52.2</td><td>53.1</td><td>53.1</td><td>53.3</td><td>53.0</td><td>45.5</td><td>46.7</td><td>46.7</td><td>45.1</td><td>45.2</td></tr><tr><td>P₂O₅</td><td>39.7</td><td>41.7</td><td>41.2</td><td>41.1</td><td>40.9</td><td>46.3</td><td>46.9</td><td>46.8</td><td>47.0</td><td>46.7</td></tr><tr><td>Na₂O</td><td>0.30</td><td>0.46</td><td>0.26</td><td>0.37</td><td>0.38</td><td>2.72</td><td>2.75</td><td>2.75</td><td>2.90</td><td>2.74</td></tr><tr><td>K₂O</td><td>0.02</td><td>n.d.</td><td>0.03</td><td>0.02</td><td>n.d.</td><td>0.07</td><td>0.05</td><td>0.06</td><td>0.06</td><td>0.05</td></tr><tr><td>MgO</td><td>0.07</td><td>0.03</td><td>0.09</td><td>0.04</td><td>n.d.</td><td>3.6</td><td>3.6</td><td>3.6</td><td>3.5</td><td>3.6</td></tr><tr><td>MnO</td><td>0.06</td><td>0.07</td><td>&lt;0.01</td><td>0.04</td><td>0.04</td><td>0.05</td><td>0.04</td><td>0.04</td><td>0.04</td><td>&lt;0.01</td></tr><tr><td>SiO₂</td><td>0.29</td><td>n.d.</td><td>0.24</td><td>0.13</td><td>0.06</td><td>0.23</td><td>0.02</td><td>n.d.</td><td>0.05</td><td>0.05</td></tr><tr><td>FeO</td><td>0.65</td><td>0.38</td><td>0.65</td><td>0.14</td><td>0.22</td><td>0.68</td><td>0.32</td><td>0.47</td><td>0.99</td><td>0.51</td></tr><tr><td>Al₂O₃</td><td>0.04</td><td>&lt;0.01</td><td>0.03</td><td>0.03</td><td>&lt;0.02</td><td>0.06</td><td>&lt;0.01</td><td>0.03</td><td>&lt;0.01</td><td>n.d.</td></tr><tr><td>Cl</td><td>5.0</td><td>5.6</td><td>5.7</td><td>5.5</td><td>5.0</td><td>n.a.</td><td>n.a.</td><td>n.a.</td><td>n.a.</td><td>n.a.</td></tr><tr><td>F</td><td>0.46</td><td>0.30</td><td>0.30</td><td>0.46</td><td>0.63</td><td>n.a.</td><td>n.a.</td><td>n.a.</td><td>n.a.</td><td>n.a.</td></tr><tr><td>H₂O</td><td>0.22</td><td>0.19</td><td>0.14</td><td>0.13</td><td>0.17</td><td>n.c.</td><td>n.c.</td><td>n.c.</td><td>n.c.</td><td>n.c.</td></tr><tr><td>Total</td><td>99.01</td><td>101.83</td><td>101.74</td><td>101.26</td><td>100.40</td><td>99.21</td><td>100.38</td><td>100.45</td><td>99.64</td><td>98.85</td></tr></tbody></table>

Y. Ybbsitz (H4); A. Allegan (H5); PV, Portales Valley (H6); AB, Adzhi Bogdo (LL3–6); BH, Bruderheim (L6); B, Barwell (L6); Sr, S and Ti always below the detection limit; Ce was always at or below detection limit; n.a., not analyzed; n.d., not detected; n.c., not calculated; <, below detection limit; no. of grains in brackets; Phosphates from Adzhi Bogdo include grains from granite-like clasts [3, 4].
5235

## SMALL PRESOLAR Si-RICH GRAINS FROM THE QINGZHEN (EH3) METEORITE

Y. Lin¹, P. Hoppe², J. Huth², J. Zhang¹ and X. Zhao¹. ¹Key Laboratory of the Earth's Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing, China. Email: LinYT@mail.iggcas.ac.cn. ²Max Planck Institute for Chemistry, Mainz, Germany.

**Introduction:** In a previous study, an acid residue of the Qingzhen (EH3) meteorite, consisting mainly of SiC, Si₃N₄ and spinel, was separated into eight size fractions, ranging from 0.05 µm up to >10 µm. Only two of them (QZR4: 0.4-0.8 µm, QZR5: 0.8-2.0 µm) had been studied previously [1, 2]. In this work, we analyzed grains from two other size fractions (QZR2: 0.1-0.2 µm, QZR3: 0.2-0.4 µm) with the NanoSIMS. We compared the results with those for the larger grain size fractions from the same meteorite and those from the Murchison carbonaceous chondrite [3], in order to explore the distribution of various types of presolar Si-rich grains among size fractions from different chemical groups of chondrites.

**Results and Discussion:** 1501 Si-rich grains from a mount of the 0.1-0.2 µm fraction (labeled as QZR2A) and 1490 Si-rich grains from a mount of the 0.2-0.4 µm fraction (labeled as QZR3A) were analyzed for ¹²C, ¹³C, ²⁸Si, ²⁹Si and ³⁰Si by automated ion imaging with the NanoSIMS at MPI for Chemistry [4]. Abundance ratios of SiC/Si₃N₄ are 4.71:1 for QZR2A and 1.35:1 for QZR3A, slightly different from the SEM observation (3.19:1 for QZR2A, 2.03:1 for QZR3A). Twenty supernova (SN) X grains from QZR2A and 19 X grains from QZR3A were identified, representing abundances of 2% and 1.6% of all SiC grains, respectively. Five grains from QZR2A with large ²⁹Si-enrichment, which have a SN origin as well [3], and another four from QZR3A were discovered, which gives total SN grain abundances of 2.5% and 2.0%, respectively. These abundances are similar to those inferred for small presolar SiC grains from Murchison [3], but approximately 8 times as high as for the larger grains from Qingzhen [1]. AB grains are more abundant in both QZR2A (6.1%) and QZR3A (6.7%) in comparison with those from Murchison (3.1-3.7%) [3]. Three Si₃N₄ grains with ¹²C/¹³C < 10 (AB type) and 10 Si₃N₄ grains with ¹²C/¹³C of 15-24 were identified from QZR3A by ion imaging, whereas only one Si₃N₄ grain with significant ¹³C excess (¹²C/¹³C of 17) from QZR2A was found. These Si₃N₄ grains were relocated in the SEM, and at least for two of them no adjacent SiC grains were evident. Re-analysis of two of the AB-Si₃N₄ grains with the NanoSIMS 50L at IGGCAS showed normal N isotopes, and only slight ¹³C excesses (¹²C/¹³C of 34 ± 14, 25 ± 3), suggesting that the first measurements were probably affected by adjacent SiC AB grains. For grains with X signature, the abundance ratio of Si₃N₄/SiC is between 1:9 in this work and 1:4 in the large size fractions [1]. In contrast, AGB Si₃N₄ grains are comparatively rare compared to SiC. This is consistent with a previous report of only one candidate AGB Si₃N₄ grain from Indarch (EH4) [5].

**Acknowledgment:** This study was supported by Natural Science Foundation of China (40830421).

**References:** [1] Lin Y. et al. 2002. *The Astrophysical Journal* 575:257-263. [2] Lin Y. et al. 2010. *The Astrophysical Journal* 709:1157-1173. [3] Hoppe P. et al. 2010. *The Astrophysical Journal* 719:1370-1384. [4] Gröner E. and Hoppe P. 2006. *Applied Surface Science* 252:7148-7151. [5] Zinner E. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4786-4813.

5237

## A PETROGRAPHY-SIMS COMBINED STUDY OF ⁶⁰Fe-⁶⁰Ni AND ⁵³Mn-⁵³Cr IN SULFIDES FROM EH3 CHONDRITES

Y. Lin, J. Guo, S. Hu, W. Shen and Y. Liu. Key Laboratory of the Earth's Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Science. Email: LinYT@mail.iggcas.ac.cn.

**Introduction:** Presence of ⁶⁰Fe was confirmed in troilite [1, 2] and FeO-rich chondrules [3] from primitive ordinary chondrites. Recent study of unequilibrated enstatite chondrites showed disturbance of ⁶⁰Fe-⁶⁰Ni and ⁵³Mn-⁵³Cr in sulfides [4]. Our previous study of Qingzhen revealed various formations and thermal histories of sulfides [5]. In this study, we conducted SIMS analyses on sulfides with detailed petrographic settings from the Qingzhen and Sahara 97159 (EH3) meteorites, in order to explore ⁶⁰Fe-⁶⁰Ni and ⁵³Mn-⁵³Cr systems.

**Results and Discussion:** Troilite and sphalerite grains with schreibersite spherules and/or isolated in silicates from Qingzhen and Sahara 97159 were analyzed for isotopes of Fe, Ni, Mn, Cr, and Zn with the CAMECA ims 1280 at IGGCAS. These sulfides are Ni-free for EPMA [5], confirmed by SIMS with Fe/Ni ratios up to 2.4 × 10⁵. ⁶⁰Ni excesses were detected in all 10 sulfide assemblages (five from each meteorite). Each of them defines an ⁶⁰Ni/⁶¹Ni - ⁵⁶Fe/⁶¹Ni "isochron" line, except for analyses with Fe/Ni ratios > 10⁵ observed only in sphalerite. The high Fe/Ni analyses plot on the right to the "isochron" line, indicative of Fe-Ni redistribution. This is consistent with a previous report of lower (⁶⁰Fe/⁵⁶Fe)₀ values for higher Fe/Ni grains [4]. Sphalerite in Qingzhen is usually normally zoned, with Fe decreasing towards troilite [5]. This would increase the Fe/Ni ratios because Ni diffusing faster than Fe [6]. This is confirmed by a negative relationship between the Fe/Ni and Fe/Zn ratios. Seven of the 10 sulfide assemblages (three from Sahara 97159, four from Qingzhen) have (⁶⁰Fe/⁵⁶Fe)₀ of (0.93-1.6) × 10⁻⁶, and three others from 0.76 × 10⁻⁶ to 0.5 × 10⁻⁶. The high (⁶⁰Fe/⁵⁶Fe)₀ ratios are consistent with the estimation of (0.5-1) × 10⁻⁶ from chondrules [3], in the view of fast condensation of the solar nebula [7]. In case of ⁵³Mn-⁵³Cr system, only a sphalerite from Qingzhen shows ⁵³Cr excess, with an inferred (⁵³Mn/⁵⁵Mn)₀ of 6.3 × 10⁻⁸. Absence of ⁵³Cr excesses is likely due to Cr diffusion during thermal metamorphism in the parent body, as indicated by exsolution of tiny daubreelite in all troilite grains coexisting with Cr-sulfides [5].

**Conclusions:** Ni-free of schreibersite-bearing sulfides is confirmed by the SIMS analysis, supplying with robust evidence for condensation. Most of the sulfide assemblages have (⁶⁰Fe/⁵⁶Fe)₀ of (0.93-1.6) × 10⁻⁶, probably representative of the solar value. The partial Fe-Ni redistribution can be explained by diffusion during cooling. In contrast, Mn-Cr system was more severely affected by secondary events, consistent with the petrographic observation [5].

**Acknowledgment:** This study was supported by the Natural Science Foundation of China (40830421).

**References:** [1] Tachibana S. and Huss G. R. 2003. Abstract #1737. Lunar and Planetary Science Conference. [2] Mostefaoui S. et al. 2005. *The Astrophysical Journal* 625:271-277. [3] Tachibana S. et al. 2006. *The Astrophysical Journal* 639:L87-L90. [4] Guan Y. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4082-4091. [5] Lin Y. and El Goresy A. 2002. *Meteoritics & Planetary Science* 37:577-599. [6] Lauretta D. S. 2005. *Oxidation of Metals* 64:1-22. [7] Wang G. et al. 2007. *Meteoritics & Planetary Science* 42:1281-1289.
## CHARACTERISTICS AND GEOMETRY OF IMPACT-INDUCED CALCITE TWINNING

P. Lindgren¹, M. R. Lee¹ and M. J. Burchell². ¹School of Geographical and Earth Sciences, University of Glasgow. ²School of Physical Sciences, University of Kent. E-mail: paula.lindgren@glasgow.ac.uk.

**Introduction:** Calcite twinning can be used to infer stress magnitude and stress orientation, and is therefore widely applied as a palaeopiezometer in various terrestrial geological settings [1]. Also, the calcite microstructure in carbonaceous chondrite meteorites has been proven to be a useful tool for reconstructing the parent body deformation history during and/or after aqueous alteration [2]. In carbonaceous chondrites, calcite twinning is thought to be a result of deformation via impact gardening on the parent body (ies). However, the characteristics and geometry of calcite twinning during impact are not well-known, as the methods for calcite twin stress analyses are generally applied to calcite that was deformed at lower strain rates during tectonism [1]. To better understand the characteristics and geometry of calcite twinning in response to impacts and to test the methods of stress analyses, we have here carried out two sets of physical impact experiments on calcite using a light-gas gun [4]. We are currently analyzing the results using SEM imaging (2D and 3D) and EBSD analyses. Calcite speleothems were chosen for the experiments, as these are composed of pure calcite and are tectonically undeformed.

**Results and Discussion:** The first set of experiments used 1.5 × 1.5 mm sized cubes of calcite as projectiles, which were fired into a target of water at a speed of 1.068 km s⁻¹. These conditions gave a maximum peak pressure of ca 1 GPa [5]. SEM and EBSD analyses of the recovered calcite fragments show that they are heavily ruptured along cleavage planes, and have developed twins. The twins occur on the {1018} planes, and hence are calcite e-twins. This set of experiments shows that calcite twins can form by impact at shock pressures of ca 1 GPa, which are more realistic of impact gardening on asteroids than previous impact experiments on calcite at 85 GPa [6]. The second set of experiments used 0.8 mm diameter stainless steel bullets which were fired into two calcite targets at 1.068 and 1.098 km s⁻¹. In the first target the projectile was fired normal to the calcite c-axes, and in the second target the projectile was fired parallel to the calcite c-axes. Craters formed in both targets with maximum diameters of 7.4 mm and 5.9 mm, and volumes of ca 11 mm³ and 8.5 mm³, respectively. Both craters had similar depths of about 1.6 mm. The first target produced a highly irregular circumference and internal topography, while the second target produced a more bowl shaped crater. Calcite in the interiors of the craters is highly fractured and twinned. Melting occur at the base of both craters. Preliminary EBSD analyses of the top surface of the target, immediately outside the craters, show that twinning is absent here. Future EBSD analyses will investigate the characteristics and geometry of the calcite twins in cross sections of the interiors of the craters.

**References:** [1] González-Casado J. M. et al. 2006. *Journal of Structural Geology* 28: 1084–1092. [2] Lindgren P. et al. 2011. *Earth and Planetary Science Letters*, in press. [3] Brearley A. et al. 1999. Abstract #1301. 30th Lunar and Planetary Science Conference. [4] Burchell M. J. et al. 1999. *Measurement Science and Technology* 10: 41–50. [5] Melosh H. J. 1989. *Impact Cratering: A Geologic Process*, Oxford University Press, Oxford. [6] Langenhorst F. et al. 2003. High Pressure Compression of Solids V: Shock chemistry with applications to meteorite impacts.

## 3D MICROSTRUCTURE AND CALCITE TWIN STRESS ANALYSES IN THE MURCHISON (CM2) METEORITE

P. Lindgren and M. R. Lee. School of Geographical and Earth Sciences, University of Glasgow. E-mail: paula.lindgren@glasgow.ac.uk.

**Introduction:** The internal microstructure of a meteorite can provide important insights into its regional deformation history and the parent body environment within which it has resided [1, 2]. The CM2 carbonaceous chondrites contain a few volume percent carbonates, mainly calcite, which formed by parent body aqueous alteration [3], and may also be used to explore the deformation. Calcite is widely used in terrestrial structural geology since it deforms to produce twins whose orientations are geometrically related to the c axes of the host calcite and to the principal axes of stress [4]. The samples used in terrestrial studies contain abundant calcite and the twins are formed by low strain rates during tectonism. However, only small samples of carbonaceous chondrites are available for analysis, the calcite is rare, and the twins are likely to be impact induced [1, 5]. To test the applicability of calcite twin stress analyses to carbonaceous chondrites we carried out a 3D microstructural investigation on a fragment of Murchison (CM2). The fragment was embedded in resin and polished in to a block 8 × 7 × 5 mm in size. The orientation of calcite twins and the principal axes of stress were determined via SEM imaging and electron backscatter diffraction (EBSD) analyses on three sides of the block oriented normal to each other.

**Results and Discussion:** SEM imaging of the three sides of the block shows that the internal microfabric, i.e. the alignment of deformed chondrules and the foliation of the matrix components, links up in 3D as expected. EBSD analyses show that aragonite found on one side is oriented with its c axis in the same plane as the microfabric, implying that the aragonite and the microfabric formed under the same uniaxial stress regime. The calcite grains on the three sides have a weak crystallographic preferred orientation, but here the data are limited with a broad scatter. These calcite grains also have {1018} e-twins and preliminary results from two sides are somewhat scattered, but still suggest that the calcite twin stress analyses are consistent, i.e. the principal axes of stress (compression and extension) are connected in 3D. Results also reveal that multiple phases of twinning are present in at least one of the calcite grains, where one set of twins is offset and cross-cut by a second set of twins, indicating at least two deformation events. Some of the calcite grains exhibit a post-twinning subgrain microstructure with low/high angle boundaries (all <20° misorientation). Other calcite grains are aggregates of individual calcite crystals with high-angle grain boundaries, which grew in different orientations prior to twinning. Twins in these aggregate grains yield clustered principal axes of stress, which confirms that calcite twin stress analyses are a robust method to analyze deformation of carbonaceous chondrites and other calcite-bearing meteorites. Further work on the microstructures is to be complimented with 3D X-ray tomography.

**References:** [1] Lindgren P. et al. 2011. *Earth and Planetary Science Letters*, in press. [2] Trigo-Rodriguez J. M. 2006. *Geochimica et Cosmochimica Acta* 70: 1271–1290. [3] Brearley A. J. 2006. *Meteoritics and the early solar system II*. The University of Arizona Press, Tucson. [4] Turner F. J. 1953. *American Journal of Science* 251: 276–298. [5] Brearley A. et al. 1999. Abstract #1301. 30th Lunar and Planetary Science Conference.
5186

**Cu AND Fe ISOTOPE ABUNDANCES IN LOW Ti LUNAR BASALTES**
F. N. Lindsay¹, G. F. Herzog¹ and F. Albarède². ¹Department of Chemistry & Biological Chemistry, Rutgers University, New Brunswick, NJ 08854, USA. E-mail: flindsay@rci.rutgers.edu ²Ecole Normale Supérieure (LST) 69364 Lyon cedex 7, France.

**Introduction:** Enrichment in heavy isotopes of the moderately volatile elements Cu and Zn has been reported in high Ti lunar basalts [1, 2] relative to terrestrial counterparts for reasons not yet clear. Isotope measurements of low Ti basalts [3] hinted at similar enrichments on average. Here, we report Cu and Fe isotope abundances for six low Ti basalts as well as elemental abundances.

**Experimental Methods:** Powdered samples were treated as in [3]. Recoveries of elemental Cu and Zn were measured by high-resolution ICP-MS) and of Fe with a Varian ICP-optical emission spectrometer (OES). Concentrations were calculated using a standard solution calibration. Isotopic analysis was done at ENS, Lyon using a Nu Plasma multicollector mass spectrometer (MC- ICP-MS) [1]. Isotope ratios are expressed as δ values relative to: ⁶³Cu and NIST 976 for Cu; ⁵⁴Fe and IRMM-14 for Fe.

**Results and Discussion:** Fe isotope abundances (Table 1) are compatible with those reported by [5]; (δ⁵⁶Fe 0.07 ± 0.03‰, δ⁵⁷Fe 0.11 ± 0.04‰)] and show less fractionation than samples with high Ti [5; (δ⁵⁶Fe 0.19 ± 0.03‰, δ⁵⁷Fe 0.22 ± 0.05‰)]. High Ti basalts also show more fractionation in Zn (δ⁶⁶Zn 1.2 ± 0.02‰) than low Ti basalts (δ⁶⁶Zn 0.27 ± 0.06‰) [2, 3]. In contrast, Cu isotopes of low Ti basalts are more fractionated than high Ti samples: (high Ti δ⁵⁶Cu 0.5 ± 0.1‰) [2], low Ti δ⁵⁶Cu 2.0 ± 0.2‰). This surprising observation and the fact that δ⁵⁶Cu versus Cu(ppm) does not show a trend compatible with Rayleigh distillation (Fig. 1) suggests that the isotopic fractionation neither is controlled by volatilization, nor occurs during evaporation; preliminary Zn results [1] show a similar trend. We think it more likely that the fractionation is regulated by mineral chemistry and/or diffusion.

**References:** [1] Moynier F. et al. 2006. *Geochimica et Cosmochimica Acta* 70:6103–6117. [2] Herzog G. F. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5884–5904. [3] Lindsay F. et al. 2011. Abstract #1907. 42nd Lunar and Planetary Science Conference. [4] Klemme S. et al. 2006. *Chemical Geology* 234:251–263. [5] Liu Y. et al. 2010. *Geochimica et Cosmochimica Acta* 74:6249–6262.

<table><caption>Table 1. Comparison of measured samples with literature values shown in grayed rows. Error is 1σ.</caption><thead><tr><th></th><th>56/54Fe</th><th>57/54Fe</th><th>Fe wt%</th><th>δ<sup>65</sup>Cu</th><th>Cu (ppm)</th></tr></thead><tbody><tr><td><strong>Lunar Basalts</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>12053, 284</td><td>0.02 ± 0.04</td><td>-0.08 ± 0.07</td><td>14.0 ± 0.7<br>14.3-15.6</td><td>1.59 ± 0.2</td><td>5.4 ± 0.37<br>7.1-26</td></tr><tr><td>12056, 20</td><td>-0.08 ± 0.03<br>-0.04</td><td>-0.18 ± 0.04<br>-0.10</td><td>20.3 ± 0.5<br>16.79</td><td>2.02 ± 0.2</td><td>6.07 ± 0.30</td></tr><tr><td>12063, 329</td><td>-0.03 ± 0.05<br>0.07</td><td>-0.05 ± 0.03<br>0.12</td><td>15.0 ± 0.4<br>16.5-16.7</td><td>1.60 ± 0.2</td><td>4.56 ± 0.33<br>5.0-12.9</td></tr><tr><td>12021, 597</td><td>-0.03 ± 0.05<br>0.01-0.06</td><td>0.00 ± 0.07<br>0.05-0.08</td><td>15.8 ± 0.4<br>14.9-15.6</td><td>1.90 ± 0.2</td><td>3.73 ± 0.42<br>8.1-14</td></tr><tr><td>12022, 297</td><td>0.00 ± 0.06</td><td>0.04 ± 0.08</td><td>16.9 ± 0.4<br>16.7-17.2</td><td>2.13 ± 0.2</td><td>3.74 ± 0.31<br>5.0-17.6</td></tr><tr><td>12075, 90</td><td>-0.07 ± 0.04</td><td>-0.07 ± 0.04</td><td>15.5 ± 0.2<br>15.7-16.8</td><td>1.68 ± 0.2</td><td>3.81 ± 0.26<br>6.0-8.5</td></tr></tbody></table>

<figure><img src="image_18.png" /></figure>

5184

**SINGLE CRYSTAL ⁴⁰Ar/³⁹Ar AGES FROM GRA 06128**

F. N. Lindsay¹,³, G. Turrin²,³, G. F. Herzog¹,³ and C. C. Swisher III²,³. ¹Chemistry and Chemical Biology ²Earth Planetary Science ³Rutgers University, Piscataway, NJ 08854, USA.

**Introduction:** Lindsay et al. [1] reported the feasibility of dating single feldspar grains from the unusual, brachinite-like achondrite GRA 06129. An age difference of 100 My between GRA 06128 (4.34 ± 0.01 Ga, [2] and GRA 06129 (4.42 ± 0.03 Ga, [1]) (hereafter GRA8 and GRA9) was noted (4.34 ± 0.01 Ga, [2] versus 4.42 ± 0.03 Ga, [1], respectively); this discrepancy prompted us to date GRA8 using our single grain method. We now report an age for GRA8 of 4.34 ± 0.02 Ga, which confirms the results of [2] and strengthens the arguments for a long, complicated thermal history on the parent body of these paired achondrites [3–9].

**Experimental Methods:** We separated 30 feldspar grains (0.004 < volume [µm³] < 0.112; 1 < mass [µg] < 30) from GRA8 by handpicking techniques. Eight feldspar grains (endmember composition An₂₅Ab₇₂Or₃- An₂₄Ab₇₃Or₃, which is slightly less albitic than reported by [4, 9, 10]) were irradiated (with Cd shielding) for 80 h at the USGS Triga reactor along with reference minerals FC-2 sanidine (28.02 Ma) and Hb3Gr amphibole (1073.6 Ma). Single grains were heated in 8–10 steps with a CO₂ laser. The Ar isotopes were analyzed using a MAP 215-50 spectrometer operated in pulse-counting mode. For grains of 3–29 µg with 0.16–0.29 K wt%, the total gas released (10⁻¹² mol g⁻¹): ⁴⁰Ar = 3493–10826; ³⁹Ar = 6.54–18.15; typical system blank (10⁻¹⁸ mol) is: ⁴⁰Ar = 748 ± 24; ³⁹Ar = 7.7 ± 1.0; ³⁸Ar = 0.6 ± 0.2; ³⁷Ar = 24 ± 0.2; ³⁶Ar = 2.4 ± 0.14. With a few exceptions, each heating increment yielded 1/6th to 1/8th of the total amount of gas.

**Results and Discussion:** Our single grain ages for GRA8 and GRA9 are comparable to published whole rock dates for GRA9 (4.46 ± 0.02 [9], 4.39 ± 0.04 [11]) and a plagioclase separate date for GRA8 (4.35 ± 0.02 [2]). Our method allows us to use substantially less sample (30 µg versus 3–13 mg) and yields spectra that are simple to interpret. Figure 1 shows the range of ages of 28 grains; we believe this range points to fine scaled heterogeneities between oligoclase grains, which may show differential amounts of resetting due to metamorphism and/or metasomatism over a span of 100 My.

**References:** [1] Lindsay F. et al. 2010. Abstract #5322. *Meteoritics & Planetary Science* 45. [2] Park J. et al. 2010. Abstract #1365. 41st Lunar and Planetary Science Conference. [3] Usui T. et al. 2010. *ibid*. Abstract #1186. [4] Arai T. et al. 2008. Abstract #2465. 39th Lunar and Planetary Science Conference. [5] Zeigler R. A. et al. 2008 *ibid*. Abstract #2456. [6] Mikouchi T. and Miyamoto M. 2008 *ibid*. Abstract #2297. [7] Nyquist L. E. et al. 2009. Abstract #1290. 40th Lunar and Planetary Science Conference. [8] Day J. M. D. et al. 2009. *Nature* 457:179–182. [9] Shearer C. K. et al. 2010 *Geochimica et Cosmochimica Acta* 74:1172–1199. [10] Trieman A. H. et al. 2008. Abstract #2215. 39th Lunar and Planetary Science Conference. [11] Bajo T. et al. 2010. *Meteoritics & Planetary Science* 45. Abstract #5089.

<figure><img src="image_19.png" /></figure>
A HETEROGENEOUS SOLAR NEBULA AS SAMPLED BY CM HIBONITES

Ming-Chang Liu¹,², Marc Chaussidon¹, Christa Göpel³ and Typhoon Lee². ¹CNRS-CRPG, Nancy, France. E-mail: mcliu@crpg.cnrs-nancy.fr.
²ASIAA, Taipei, Taiwan. ³IPGP, Paris, France.

**Introduction:** The degree of uniformity of isotope distribution in the solar nebula has long intrigued cosmochemists, as it is crucial for the use of short-lived radionuclides for chronometry. Model simulations showed that in a marginally gravitationally unstable disk, initial isotope variations, if any, could be well mixed to ~10% level spatial heterogeneity within a few thousand years [1]. From this view, the formation time of refractory inclusions plays a key role in understanding the observed isotopic compositions.

Hibonite (CaAl₁₂O₁₉), primarily found in CM meteorites as 20–80 µm individual inclusions in the matrix, is believed to be one of the oldest solar system solids [2]. The inferred ²⁶Al abundances split CM hibonite grains into two distinct groups [e.g., 3]. ²⁶Al/²⁷Al in individual Spinel-HIBonite spherules (SHIBs) is consistent with ~5 × 10⁻⁵ within large analytical errors. In contrast, PLAty hibonite Crystals (PLACs) display a range of Δ²⁶Mg* (deviation from a mass dependent fractionation line) from +2‰ to -4‰. Negative Δ²⁶Mg in PLACs indicates that these grains must have formed prior to the presence of ²⁶Al in the solar nebula [4]. However, the chronology for SHIBs is still not clear, primarily due to large analytical uncertainties. Here we report new high precision Mg data of hibonite, in hopes of better constraining the formation time of SHIBs.

**Experimental:** Forty-three new hibonite samples (9 PLACs and 34 SHIBs) studied here were hand-picked from a Murchison acid residue (Courtesy of A. Davis), and a high density fraction of Paris meteorite, and are on average ~40 µm in size. High precision Mg isotopic analysis was performed on the Cameca 1280HR2 at CRPG-CNRS. Polished, epoxy-mounted hibonite grains were sputtered with a 20 nA ¹⁶O⁻ beam (? ~30–40 µm). Secondary ions were collected simultaneously with four faraday cups. Instrumental mass fractionation and relative sensitivity factor were determined and corrected for by using Madagascar hibonite. The inferred ²⁶Al/²⁷Al for each grain was calculated by connecting the data point to the origin (Δ²⁶Mg* = ²⁷Al/²⁴Mg = 0).

**Results and Discussion:** The Mg isotopic compositions of Murchison and Paris hibonite are consistent with previous discoveries, but the higher precision enables us to resolve an ²⁶Al/²⁷Al scatter from 1 to 6 × 10⁻⁵ in SHIBs, although analytical errors for grains with 6 × 10⁻⁵ would also allow for overlapping with 5.2 × 10⁻⁵, the “canonical ratio” defined in CV CAIs [5]. Such a variation could result from early formation of SHIBs before ²⁶Al was homogenized or contemporaneous formation of SHIBs and CAIs followed by subsequent disturbance in SHIBs. However, each measurement here is analogous to “bulk” analysis, which should be insensitive to internal re-equilibration, unless the disturbance was an open-system behavior. Furthermore, if the grains were indeed subject to loss of radiogenic ²⁶Mg, one should expect to see some SHIBs without any ²⁶Al. Therefore, we explain the observed ²⁶Al/²⁷Al variation in SHIBs as recording ²⁶Al heterogeneity in the disk, possibly prior to the CAI formation.

**References:** [1] Boss A. P. 2008. *Earth and Planetary Science Letters* 268:102–109. [2] Grossman L. 1972. *Geochimica et Cosmochimica Acta* 36:597–619. [3] Ireland T. R. 1988. *Geochimica et Cosmochimica Acta* 52:2827–2839. [4] Liu M.-C. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5051–5079. [5] Jacobsen B. et al. 2008. *Earth and Planetary Science Letters* 272:353–364.

NEW STORY OF SHERGOTTITE EETA79001

Yang Liu¹, Cyrena. A. Goodrich² and Lawrence A. Taylor¹. ¹Planetary Geosciences Institute, Department of Earth and Planetary Science, University of Tennessee, Knoxville, TN 37996, USA. E-mail: yangl@utk.edu. ²Planetary Science Institute, Tucson, AZ 85719, USA.

**Introduction:** Elephant Moraine (EET) A79001 is a unique shergottite, containing two juxtaposing lithologies: A and B [1]. The origin of Lithology A has been a point of debate since its collection (e.g., [1–5]). Here we report new observations suggesting assimilation/mixing at high P and followed by crystallization in a closed system.

**Mineral Inclusions in Lithology A:** We observed round olivine and orthopyroxene (opx) inclusions in olivine (ol) megacrysts. The round opx inclusion is Mg-rich in the interior (Mg# 79.6, En₇₈Wo₂) and more Fe-rich at the rim near the interface (Mg# 76.5, En₇₇Wo₂), both of which are NOT in equilibrium with the host olivine (Mg# 67). This is opposite to what is expected for crystallization at low P, where ol would be enclosed by opx. A subhedral ol (Fo₆₈) is also enclosed in a megacrystic ol (Fo₆₈). The similar composition between ol inclusion and host can be explained by re-equilibration as the Fe-Mg diffusion is fast in olivines.

The round shape of the mineral inclusions indicates resorption event(s) due to interaction with melt. Two possible scenarios can cause dissolution (1) mixing with melt of a different composition; (2) decrease in pressure so that opx becomes unstable. If (2) is the sole process, we would expect more Mg-rich ol (Mg# > 70) than Mg-rich opx. This is not consistent with the available literature data [1, 6], where there is comparable modal abundances of Mg-rich olivine and orthopyroxene. Furthermore, occurrence of Mg-rich ol and opx as individual megacrysts in other sections [1, 4, 5] indicates both Mg-rich ol and opx are stable liquidus phases, a feature typical for crystallization at high P [7].

**“Melt” Inclusions in Olivine:** We measured bulk trace element abundances of “melt” (now devitrified) inclusions in olivines using LA-ICP-MS. Melt inclusions in Mg-rich olivines (Fo₇₅–₇₃) suggest that these olivines crystallized from incompatible-element depleted melt (I[La/Yb]N = 0.04–0.15, N denotes CI chondrite normalized), similar to shergottites with depleted incompatible elements (e.g., Yamato-980459, [8]). Melt inclusions from more Fe-rich olivines is similar to whole-rock data of EETA79001B.

**Implications:** Based on the above observations, we suggest that EETA79001A was formed by: (1) crystallization of Mg-rich ol + opx at high P; (2) mixing at high P with a magma containing slightly more enriched incompatible elements (not enriched basaltic shergottites!) that assimilated some ol + opx; (3) crystallization of megacrystic ol and opx at high P, (4) eruption/ascent to lower P. Different from previous models, we emphasize that (1)–(3) occurred at pressure >0.7 GPa (>60 km) (inferred from [7]).

**References:** [1] McSween H. Y. and Jarosewich E. 1983. *Geochimica et Cosmochimica Acta* 47:1501–1513. [2] Wadhwa M. et al. 1994. *Geochimica et Cosmochimica Acta* 58:4213–4229. [3] Mittlefehldt D. W. et al. *Meteoritics & Planetary Science* 34:357–367. [4] Steele I. M. and Smith J. V. Proceedings, 13th Lunar and Planetary Science Conference, JGR, 87, supplement, A375–384. [5] Goodrich C. A. 2003. *Geochimica et Cosmochimica Acta* 67:3735–3771. [6] Melin M. 2008. Masters thesis. [7] Filiberto J. and Treiman A. H. 2009. *Chemical Geology* 263:60–68. [8] Shirai N. and Ebihara M. 2004. Abstract #1511. 35th Lunar and Planetary Science Conference.
CALCULATIONS ON PHOTOPHORETIC MOTION OF CHONDRULES IN THE EARLY SOLAR SYSTEM AND TEMPERATURE DISTRIBUTIONS IN ILLUMINATED CHONDRULES

C. Loesche¹, J. M. Friedrich², J. Teiser¹ and G. Wurm¹. ¹Faculty for Physics, University Duisburg-Essen, AG Wurm. E-mail: christoph.loesche@uni-due.de. ²Department of Chemistry, Fordham University, Bronx, New York.

Chondrules play an important role in the formation process of planets [1]. We study if the effect of photophoresis might transport particles to the asteroid belt. Photophoresis has been proposed as an efficient mechanism for radial material transport. However, these models are based on idealized assumptions concerning the particle geometry and material properties [2, 3]. We present calculations/simulations in order to complement ongoing lab experiments on photophoresis and to develop more realistic transport models.

First, tomographic data from chondrules of the L/LL4 chondrite Bjurböle are used to extract the geometric shape and to define material functions using Mathematica-Code. After that, a finite elements method (FEM) is used to calculate the temperature distribution inside the tomographed chondrules resulting from solar irradiation. With these results it is possible to improve the understanding of chondrule motion and sorting in the early solar system as a result from the photophoretic force.

Currently first preliminary results are available. Comparison with experimental data by Hesse et al. (in prep.) shows that the numerical simulations give realistic data, including effects of rotating chondrules under irradiation. Further goals are to get information about torques influencing chondrule rotation and to improve materials equations of state.

**References:** [1] Scott E. R. D. 2007. *Annual Review of Earth and Planetary Science* 35:577-620. [2] Wurm G. and Krauss O. 2006. *Icarus* 180:487-495. [3] Wurm G. and Haack H. *Meteoritics & Planetary Science* 44:689-699.

**Additional Information:** If you have any questions regarding the preparation of your abstract, call the LPI at 281-486-2142 or -2188 (or send an e-mail message to publish@lpi.usra.edu).

SPATIAL ANALYSIS OF PLANAR DEFORMATION FEATURES

A. Losiak¹, I. Golebiowska² and C. Koeberl¹,³. ¹Dept. Lithospheric Research, Univ. Vienna, 1090 Vienna, Austria. E-mail: anna.losiak@univie.ac.at. ²Univ. Warsaw, Faculty of Geography and Regional Studies, Poland. ³Natural History Museum, 1010 Vienna, Austria.

**Introduction:** Planar deformation features (PDFs) are multiple sets of parallel planes of amorphous material in minerals, ≤2 µm thick and spaced 2-10 µm apart, which form due to shock in specific crystallographic orientations [e.g., 1, 2]. PDFs are usually measured on randomly selected grains from a thin section, thus microtextural context information is lost. We attempt to measure PDF orientations of all quartz grains within the field of view in a thin section to check if any spatial relations exist between grains containing PDFs. This project will help the understanding of PDF formation mechanisms and shock wave propagation on the single grain scale.

**Methods:** Planar deformation features are measured using a U-stage and indexed using the program of [3]. Care has been taken to keep a constant orientation of the thin section in relation to the U-stage, ensuring that all measured azimuths have the same reference system. All measured grains were referenced on a map of a thin section based on a microphotograph. A database with information about the orientation of c-axes and PDFs as well as the number and type of PDFs present in each grain was referenced to a thin section photo-map using ArcGIS software. Spatial associations between grains in relation to their various characteristics (e.g., number of PDFs present) were analyzed.

The studied test sample is a meta-graywacke from the Bosumtwi crater (Ghana) from 271.4 m depth in the LB-08A drill core [e.g., 4]. It consists mostly of large multigrain aggregates of quartz (≤1 mm) and large feldspar grains (≤1.5 mm) set in a fine-grained crystalline matrix.

**Results:** We measured 102 quartz grains within a total area of 9.62 mm²; the average number of PDFs per grain was 1.76 (including 15 grains with no PDFs). The following observations were made: (1) quartz grains with no PDFs are located on the external part of the quartz aggregates, while ones with a strongly distorted crystallographic lattice are located in the center of quartz aggregates; (2) grains sharing boundaries often contain similar numbers of PDFs; (3) grains sharing borders and having similar orientations of their c-axes can have different numbers of PDFs; (4) grains with the same PDF indices tend to occur close to each other.

**Discussion:** Firstly, clustering of PDFs of specific types suggest that, on a micro-scale, the formation of PDFs within the grain is dependent on the surroundings of the grain. Secondly, the angle between the c-axis of a quartz grain and the shock wave propagation direction is not a main factor influencing development of PDFs. However, it is also possible that the observed differences in a number of PDFs are due to differences in the c-axis orientation (Dauphiné twining). Thirdly, stress within quartz aggregates is not distributed evenly.

**References:** [1] Stöffler D. and Langenhorst F. 1994. *Meteoritics & Planetary Science* 29:155-181. [2] Ferrière L. et al. 2009. *Meteoritics & Planetary Science* 44:925-940. [3] Losiak A. et al. 2011. Abstract #1286. 42nd Lunar and Planetary Science Conference. [4] Ferrière L. et al. 2008. *Science* 322:1678-1681.
## ISOTOPIC CONSTRAINTS OF MODERATELY VOLATILE AND SIDEROPHILE ELEMENTS DURING CORE FORMATION

B. Luais. CRPG-CNRS, Nancy-Université, BP 20, 54501 Vandoeuvre-lès-Nancy Cedex, France. E-mail: luais@crpg.cnrs-nancy.fr.

**Introduction:** Scenarios of core-mantle formation and subsequent processes of planetary accretion leading to the observed elemental composition of the Earth upper mantle are based on experimental metal-silicate partitioning of siderophile elements. Recent models require homogeneous accretion at high P (≈30–40 GPa), T (≈3000 °K) conditions with an increase with time of oxygen fugacity to account for the budget (depletion) of moderately siderophile elements in the mantle [1,2]. However, these models differ on the (P, T, fO₂) conditions relevant to the depletion of the moderately volatile siderophile element (e.g., Ge) in the Earth upper mantle. These elements provide additional constraints on the possible loss of volatile elements during impact processes, which are linked to the main metal-silicate differentiation stage. Specifically, isotopes of these elements can be strongly fractionated during evaporation processes, which makes isotopic composition an appropriate tool for testing the role of volatility processes.

**Results and Discussion:** New germanium isotopic data (δ⁷⁴Ge relative to JMC standard, 2σ ± 0.2‰) were obtained on Earth silicate mantle (peridotites, basalts) and carbonaceous chondrites (CC), and then compared with Ge isotopic composition of iron meteorites [3]. Earth silicate mantle samples have δ⁷⁴Ge = +0.892 ± 0.062‰, which is significantly lower than the mean value for magmatic iron meteorites (δ⁷⁴Ge = +1.77 ± 0.22‰). First δ⁷⁴Ge data of some carbonaceous chondrites indicate light isotopic composition.

The heavy Ge isotopic composition of Fe-meteorites and Earth silicates with respect to CC would indicate a major loss of Ge during core formation, most probably due to evaporation induced by a Moon-forming impact. This isotopic effect of evaporation leads to a strong isotopic fractionation which would hide the small if detectable kinetic isotopic fractionation associated to diffusion of Ge from the silicate to the metal phase under the reducing conditions of metal-silicate segregation [4]. The light Ge isotopic composition of the Earth silicate mantle cannot represent the resulting silicate phase (Bulk Silicate Earth) after core segregation, this silicate depleted reservoir (≈ 1 ppm Ge) would have in this case heavier Ge isotopic composition than the core. It is suggested that the δ⁷⁴Ge value of +0.892‰ is representative of the Earth Upper Mantle. The Ge isotopic composition of the silicate phase at the P, T, fO₂ conditions of core segregation would reflect the change in oxidation state and valence of Ge associated with pressure [1, 2].

**References:** [1] Siebert J. et al. 2011. *Geochimica et Cosmochimica Acta* 62:1631–1642. [2] Righter K. 2011. *Earth and Planetary Science Letters* 304:379–388. [3] Luais B. 2007. *Earth and Planetary Science Letters* 262:21–36. [4] Luais et al. 2007. *Eos Trans. AGU*, 88(52), Fall Meet. Suppl. Abstract #V51E-0833.

## PHOTOCHEMISTRY AND THE OBSERVED ENRICHMENT OF O, C, N, AND H ISOTOPES IN METEORITE IOM

J. R. Lyons¹. ¹Institute of Geophysics & Planetary Physics, UCLA, Los Angeles, CA 90095-1567, USA. E-mail: jimlyons@ucla.edu.

**Introduction:** The remarkable O MIF signatures seen in acid-insoluble organic matter (IOM) from a CR2 meteorite [1] show some correlation with enhanced δ¹³C values, suggesting that both enrichments may be a result of CO photochemistry. ²H and ¹⁵N enrichments in the same IOM do not correlate with ¹⁷O and ¹⁸O and/or ¹³C enrichments, but do show some correlation with each other [1]. Both N and H isotopes have been shown to be strongly fractionated by ion-molecule reactions in molecular clouds [2, 3]. Here, the question I address is whether these results, particularly those for meteorite IOM [1], are consistent with expected photochemical and ion-molecule processes.

**Photochemical Models of Clouds and the Solar Nebula:** It is well established that in model calculations CO self-shielding produces large enrichment in product ¹⁷O and ¹⁸O, which are then stored in H₂O. Product C is similarly enriched in ¹³C, although by a factor of ~2 less than the enrichment in ¹⁷O and ¹⁸O [4]. Self-shielding enrichment of ¹³C is predicted by photochemical models of disks [5], but CO exchange with C⁺ and CO condensation [6, 7], are also important. Disk model calculations, including ¹³C at temperatures well above CO condensation (> 20 K), are in progress using the oxygen isotope code of [8]. Shielding functions from [4] are used for C¹³O. As with CO, N₂ also undergoes self-shielding, producing enriched N and N(²D), with the N stored in HCN. The N(²D) rapidly forms NH, leading to reformation of N₂ by reaction of N and NH, and thus erasing much of the photo-induced fractionation. Large initial ¹⁵N enrichments are possible by N₂ self-shielding, but the total amount of enriched material produced is small [9]. Finally, H₂ also has a line-type absorption spectrum, and so also undergoes self-shielding at the edges of clouds and high surface of disks. At greater depths into these objects, where CO and N₂ self-shielding become important, H₂ lines are highly broadened and will shield HD lines, thus reducing D enrichment. These results are consistent with a photochemical origin for O and (possibly) C isotopes signatures in IOM, and ion-molecule origin for H and N isotopes signatures in IOM.

**References:** [1] Hashizume K. et al. 2011. *Nature Geoscience* 4:165. [2] Rodgers S. D. and Charnley S. B. 2008. *MNRAS* 385:L48. [3] Aleon J. and Robert F. 2004. *Icarus* 167: 424. [4] Visser R. et al. 2009. *Astronomy & Astrophysics* 503: 323. [5] Woods P. and Willacy K. 2009. *The Astrophysical Journal* 693: 1360. [6] Smith R. et al. 2011. Abstract #1281. 42nd Lunar and Planetary Science Conference. [7] Young E. and Schauble E. 2011. Abstract #1323. 42nd Lunar and Planetary Science Conference. [8] Lyons J. R. and Young E. D. 2005. *Nature* 435:317–320. [9] Lyons J. R. 2010. Abstract #5424. 73rd MetSoc.