5405

THE "BASAL ONAPING INTRUSION": POTENTIAL ROOF ROCKS OF THE SUDBURY IGNEOUS COMPLEX

D. T. M. Brillinger¹, R. A. F. Grieve¹,², G. R. Osinski¹ and D. E. Ames². ¹Department of Earth Sciences, University of Western Ontario, London, ON, Canada. ²Earth Sciences Sector, Natural Resources Canada, Ottawa, ON, Canada.

**Introduction:** The origin of the Sudbury Igneous Complex (SIC) as the remnant of the coherent impact melt sheet at the Sudbury impact structure is now generally accepted. Hindering its early recognition were the fact that is was differentiated, due to its great thickness, and is not flat-lying but somewhat funnel-shaped, due to almost immediate postimpact folding and thrusting. It also has no apparent foot and roof rocks, which are relatively finer-grained melt rocks, with high lithic and mineral clast contents, as observed at the base and top of coherent melt sheets at other impact structures. Here, we present the results of field, petrographic and geochemical studies of the so-called Onaping Intrusion, and discuss its relationship to the SIC.

**Results:** The so-called basal Onaping Intrusion occurs at approximately 50% of the upper contact of the Granophyre of the SIC and the overlying breccias of the Onaping Formation [1]. Near Joe Lake, in the North Range of the SIC, this lithology has a fine-grained (0.2–0.5 mm) igneous-textured matrix, consisting mainly of interlocking intergrowths of plagioclase, quartz, K-feldspar, amphibole, clino-pyroxene and biotite. It also contains >5 to approximately 50% mineral and lithic clasts, with corroded margins indicative of partial melting, corresponding to the lithologies of the original target area. Some quartz grains, usually within granitoid or quartzite clasts, exhibit partially annealed, decorated PDFs. Locally, clast content decreases and matrix grain-size increases toward the contact with the underlying Granophyre of the SIC. Samples closer to the Granophyre exhibit fine-grained granophyric matrix textures and the contact with the Granophyre can be described as gradation over a few meters. X-ray fluorescence analyses of the Onaping Intrusion at Joe Lake show that it is average composition is more siliceous (approximately 67%) than the average of the currently exposed SIC (approximately 63%) and the North Range Offset dikes (approximately 59.2–61.9%) [2, 3].

**Discussion:** The matrix texture and the presence of clasts with PDFs demonstrate that the basal Onaping Intrusion conforms to the descriptive definition of an impact melt rock. This, together with the geochemical similarities to the SIC and the field relations suggest that the basal Onaping Intrusion may be the roof rocks of the SIC. The early failure to recognize the basal Onaping Intrusion as the potential roof rocks of the SIC may be attributable to the fact that it only occurs at 50% of the SIC's upper contact with the Onaping Formation. Its absence is likely due to its destruction as a coherent lithology and local removal by explosive melt-fuel-coolant interactions (MFCI) between incoming sea-water and the superheated proto-SIC impact melt within the Sudbury impact structure [4]. These interactions led to the formation of the bulk of the lithologies of the Onaping Formation as a series of impact melt-related "phreatomagmatic" breccias, containing vitric proto-SIC clasts and only a minor component of impact-related shocked materials.

**References:** [1] Ames D. E. et al. 2008. *Economic Geology* 103:1057–1077. [2] Ames D. E. et al. 2002. *Economic Geology* 97:1541–1562. [3] Carter W. M. et al. 2009. Geological Survey of Canada Open File 6134. [4] Grieve R. A. F. 2010. *Meteoritics & Planetary Science* 45:759–782.

5403

TEM STUDY OF MATRIX IN THE CO3 CHONDRITE ALHA77307: CLUES ABOUT THE FIRST STAGES OF METAMORPHISM IN CHONDRITES

C. E. Brunner and A. J. Brearley. Department of Earth and Planetary Sciences, MSC03-2040, 1 University of New Mexico, Albuquerque, NM 87131, USA. E-mail: cbrunner@unm.edu, brearley@unm.edu

**Introduction:** The fine-grained matrices of carbonaceous chondrites are sensitive recorders of both nebular and asteroidal processes in the early solar system. The matrices of type 3.0 carbonaceous chondrites consist of a complex assemblage of very fine-grained, unequilibrated materials (silicates, sulfides, oxides, etc.) that are particularly susceptible to modification by aqueous alteration and thermal metamorphism [1]. Only in very pristine chondrites (type 3.0) is matrix minimally altered, preserving a primary nebular record. We are examining matrix silicates in the most pristine CO3 chondrite, ALHA77307 (type 3.0), as part of study to investigate the formation and metamorphism of crystalline silicates in type 3.0 carbonaceous chondrite matrices.

**Experimental:** Electron-transparent sections of ALHA77307 matrix were prepared using focused ion beam (FIB) techniques. The chemical and microstructural properties of the FIB sections where characterized in detail using a JEOL 2010F FEG/STEM.

**Results and Discussion:** All FIB sections of ALHA77307 matrix are composed largely of extremely fine-grained materials (<100 nm in size). Each FIB section contains similar silicate assemblages that occur in clusters surrounded by amorphous matrix material, consistent with previous observations [1]. The FIB sections are dominated by an amorphous silicate groundmass in which nanoparticles of iron oxides, Fe and Fe,Ni sulfides (<200 nm), olivine and pyroxene grains are embedded [1]. In addition, our new studies have also revealed what appears to be a population of distinct, amorphous ferromagnesian grains that were not recognized in the previous study [1].

ALHA77307 contains a population of Mg-rich olivine and pyroxene grains that are probably primary in origin [1]. Each FIB section contains several distinct, fine-grained (>400 nm) subhedral to anhedral forsterite grains that usually occur in clusters, but also occur as isolated crystals. Dark field STEM imaging of the olivine and amorphous Mg-Fe silicate grains shows distinct Fe-rich rims on these grains which are usually 10–30 nm in width. STEM EDS analysis and STEM line profiles across these grains confirm the Fe-enrichment in their rims. The olivine core compositions lie in the range Fo<sub>78–99</sub> while Fe-enriched rims range from Fo<sub>40–80</sub>. Fine-grained (>400 nm) low-Ca pyroxenes (En<sub>75–99</sub>) show no evidence of Fe-enrichment at their grain edges.

We interpret the presence of narrow Fe-rich rims on olivine and amorphous silicate grains as representing the very first stages of metamorphic equilibration in the matrix of ALHA77307. These features were not recognized previously by conventional TEM studies [1]. Nevertheless, the effects are so limited and subtle that it further confirms the highly pristine nature of this meteorite. However, it does demonstrate that ALHA77307 has not completely escaped metamorphism, consistent with the arguments of [1], but provides the first glimpse of the process of metamorphism in the finest grain fraction of chondritic materials.

**References:** [1] Brearley A. J. 1993. *Geochimica et Cosmochimica Acta* 57:1521–1550. [2] Brearley A. J. and Jones R. H. 1998. In *Planetary materials* 3-1:3–398. [3] Brearley A. J. 1995. In Chondrules and the Protoplanetary Disk. pp. 137–151.
5048

A POSSIBLE NEW IMPACT SITE NEAR NALBACH (SAARLAND, GERMANY)

E. Buchner¹,³, W. Müller² and M Schmieder³. ¹Rieskrater-Museum Nördlingen, Eugene-Shoemaker-Platz 1, 86720 Nördlingen, Germany. E-mail: elmar.buchner@geologie.uni-stuttgart.de. ²Diefflerstr. 217, 66809 Nalbach/Saar, Germany. ³Institut für Planetologie, Universität Stuttgart, Herdweg 51, 70174 Stuttgart, Germany.

**Introduction:** The two impact craters Nördlinger Ries and the Steinheim Basin (S Germany) represent the only confirmed impact structures in Germany. Although a great number of possible impact structures in many parts of Germany were proposed in the past, none of them was confirmed. We suggest a new possible impact site in the German state of the Saarland (W Germany) on the base of possible impact glasses and potential traces of an iron meteorite in melt particles that are distributed within an area of some square kilometers in the surroundings of the village of Nalbach. The possible impact melt particles were recently discovered by one of the authors (W. Müller).

**Petrographic and Geochemical Analyses:** Externally, the melt particles exhibit a bluish to black color and are often aerodynamically deformed (tear- or spindle-shaped). The particles contain a homogenous, schlieren- and vesicle-textured glassy melt groundmass; roundish sandstone particles are incorporated into the melt matrix. Geochemically, the melt matrix yielded a Si-, Al-, and K-rich mixed silicatic composition. We have not detected shocked quartz grains with PDFs so far, however, some of the melt particles show conspicuous ballen-textured α-cristobalite (Fig. 1A) and contain spherule-shaped iron droplets (Fig. 1B). Preliminary geochemical SEM-EDX analyses showed that the Fe droplets commonly contain higher amounts of Ni (up to ~10 wt%), together with variable amounts of S, P, Ni, and Co. We also detected metallic fragments that exhibit a composition close to taenite, troilite, and schreibersite as known from meteorites. Further analyses are in progress.

**Conclusions:** Ballen α-cristobalite, detected in some melt particles, was recently suggested as an impact-diagnostic feature [1]. Externally and internally, the Nalbach melt particles closely resemble impact glasses from Wabar [2,3] and other terrestrial impact sites by their color, texture, composition, and content of metallic particles. The metallic droplets and fragments in the melt particles may be interpreted as the molten and fragmented remnants of an iron meteorite. The melt particles are distributed over some km² that could represent an (eroded or covered) impact crater or an area affected by a larger meteoritic airburst.

**References:** [1] Ferrière L. et al. 2009. *European Journal of Mineralogy* 21:203–217. [2] Schmieder M. and Buchner E. 2009. Abstract volume of the 1st AICAC Conference, Amman, Jordan, CD-ROM. [3] Schmieder M. et al. 2011. This volume.

<figure><img src="image_4.png" /><figcaption>Fig. 1. Nalbach glass. A: Ballen α-cristobalite and B: Fe-Ni droplets (white) in a vesicular glassy melt matrix (backscattered electron images).</figcaption></figure>

5135

MAPPING OF MICROSTRUCTURAL DEFORMATION IN EXPERIMENTAL IMPACT CRATERS FORMED IN SANDSTONE

E. Buhl¹,², M. H. Poelchau¹, T. Kenkmann¹ and G. Dresen². ¹A.-L.-Univ. Freiburg, Germany, E-mail: e.buhl@gmx.de. ²German Research Center for Geosciences, Potsdam, Germany.

**Introduction:** As part of the MEMIN project experimental hypervelocity impacts into porous sandstone were conducted at the Ernst-Mach-Institut (EMI), Germany [1]. In combination with real-time investigations of the ejection process and ultrasound signals, spatially resolved impact damaging of the target was systematically investigated with a scanning electron microscope (SEM). As first result four distinct subsurface zones can be discriminated by their deformation mechanisms.

**Methods:** A 2.5 mm sphere of high alloyed steel impacted into a 20 cm sandstone cube with a velocity of 4.8 km s⁻¹. Acceleration was achieved by a two stage light gas gun (Space Gun, EMI) [2, 3]. The sandstone has a porosity of ca. 22% and a quartz content of 94 wt%. The sub-rounded quartz grains are cemented by quartz and clay mineral coatings. For investigations the impacted block was bisected parallel to the impact direction and thin sections were prepared directly underneath the crater floor. For a detailed mapping ca. 300 SEM photomicrographs (160×, BSE) were merged to a high resolution image of the crater subsurface.

**Results:** The formed crater has a diameter of 5.76 cm and a depth of 1.1 cm. Deformation gradually decreases with increasing distance from the crater floor. The outermost zone (> 3.6 projectile diameters (Øₚ) from the impact center) of apparent deformation is dominated by concussion fractures which are well known from natural impacts [4]. These intragranular fractures occur on grain-grain contacts and have a preferred radial orientation. Macroscopic radial fractures as described for cratering in basalt [5] were not detected. The second zone of deformation (2.9–3.6 Øₚ from the impact center) is characterized by localized compactional shear bands in which grain comminution along with shearing and compaction occurs. This zone has a hemispherical appearance beneath the crater floor with a thickness of ca. 2.2 mm. In the third zone (1.7–2.9 Øₚ from the impact center) the compaction and grain crushing is pervasive. Pore space is completely crushed and filled with small quartz fragments and clay mineral aggregations. This zone has a maximum thickness of 3.1 mm. The innermost zone (1.4–1.7 Øₚ from the impact center) of deformation in contact to the crater floor has a maximum thickness of 0.9 mm. In addition to the deformation described for zone three, tensional fractures occur sub-parallel to the crater floor. These fractures are up to 1.2 mm long and formed new pore space in the compacted host rock. Macroscopic spall fractures are traceable laterally at distances > 5 Øₚ from the impact center.

**Conclusion:** The sub-surface deformation in shocked porous sandstone can be differentiated into four different zones by the occurrence of different deformation types. A more detailed analysis of deformational modes is planned to give further insights into deformation mechanisms in porous targets during shock loading.

**References:** [1] Kenkmann T. et al. 2011. *Meteoritics & Planetary Science*, in press. [2] Schäfer F. et al. 2006. *ESA SP-612*. [3] Poelchau M. H. 2011. Abstract #1824. 42nd Lunar and Planetary Science Conference. [4] Kieffer S. W. 1971. *Journal of Geophysical Research* 76:5449–5473. [5] Polanskey C. A. and Ahrens T. J. 1990. *Icarus* 87:140–155
## OXYGEN ISOTOPES IN PYROXENES FROM TWO VIGARANO CAIs VARY INDEPENDENTLY OF fO₂

E. S. Bullock¹, G. J. MacPherson², A. N. Krot², K. Nagashima², T. Ushikubo³ and N. T. Kita³. ¹US National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20560 USA. E-mail: BullockE@si.edu. ²Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA. ³Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA.

**Introduction:** A hallmark of Ca-Al-rich inclusions (CAIs) is enrichment in most of their constituent minerals in ¹⁶O, taken to be the isotopic signature of the gas in which they formed. Other minerals that are ¹⁶O-poor likely underwent later exchange with a different isotopic reservoir after formation [e.g., 1]. However, recent work [2] has shown that some CAIs sampled multiple distinct reservoirs during their primary formation, either as a result of temporal variations in the composition of the gas or because the CAIs were transported to different isotopically-distinct regions, before being accreted into the parent body. Analyses of the isotopic and chemical compositions of pyroxene from two different Vigarano CAIs (F6; a compact type A, and F8; a fluffy type A) sheds new light on the environment in which the CAIs underwent isotopic exchange.

**Methods:** Minerals were analyzed with a JEOL 8900 electron probe at the Smithsonian Institution. Oxygen isotopes were analyzed using the University of Hawai'i Cameca ims 1280, in multicollector mode (see [3]). Al-Mg isotopes were analyzed using the University of Wisconsin Cameca ims 1280 (see [4]).

**Results and Discussion:** High-precision Al-Mg dating of F6 and F8 [4] gives initial ²⁶Al/²⁷Al ratios of (5.3 ± 0.3)×10⁻⁵ (F8) and (4.2 ± 0.4)×10⁻⁵ (F6), corresponding to a approximately 200,000 yr time difference. The Ti-rich pyroxene in F6 plots on the ²⁶Al isochron and is ¹⁶O-rich (Δ¹⁷O = -20.6 ± 1.6‰ and -23.8 ± 2.0‰); similar pyroxene in F8 plots on the F8 ²⁶Al isochron but is consistently ¹⁶O-poor (Δ¹⁷O = -2.6 to -4.1 ± 1.5‰). The pyroxene in F8 rims (replaces) perovskite, which also is ¹⁶O-poor, so the pyroxene must postdate perovskite exchange. Pyroxene in both F6 and F8 contains on average approximately 60% Ti³⁺. Pyroxene in the Wark-Lovering rim (WL) of both inclusions is ¹⁶O-rich (Δ¹⁷O approximately -22 to -23 ± 2.8‰). F6 is almost uniformly ¹⁶O-rich, even melilite. Melilite in F8, however, is variably depleted in ¹⁶O.

During the time of F6 and F8 evolution, O-isotopes in their environs varied greatly yet fO₂ did not. This is hard to reconcile with CAIs transport from dust-poor to relatively dust-rich environments [2]. Low fO₂ persisted during the formation of the WL rims [5], yet these two CAIs solidified 200,000 yr apart. Either the rims themselves formed at different times, or else all rims formed late at a time that postdated the formation of F6.

**References:** [1] Clayton R. N. et al. 1977. *Earth and Planetary Science Letters* 34:209–224. [2] Yurimoto H. et al. 2008. Reviews in Mineralogy and Geochemistry vol. 68:141–187. [3] Makide K. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5018–5050. [4] MacPherson G. J. et al. 2010. Abstract #2356. 41st Lunar and Planetary Science Conference. [5] Simon S. et al. 2007. *Geochimica et Cosmochimica Acta* 71:3098–3118.

## NORTHWEST AFRICA 6698: A HIGH TEMPERATURE “DIORITIC” ACHONDRITE WITH OXYGEN ISOTOPE COMPOSITION IN THE LL CHONDRITE FIELD

T. E. Bunch¹, A. J. Irving², J. H. Wittke¹ and D. Rumble III³. ¹Geology Program, SESES, Northern Arizona University, Flagstaff, AZ 86011, USA, E-mail: tbearl@cableone.net ²Earth & Space Sciences, University of Washington Seattle, WA 98195, USA. ³Geophysical Laboratory, Carnegie Institution, Washington, DC 20015, USA.

**Petrography:** NWA 6698 is a small (38.4 g), fresh stone with unusual mineralogical and isotopic characteristics. It is a fine to medium grained (<2 mm) “dioritic” assemblage of relatively sodic plagioclase (69 vol %), pyroxenes (27 vol %) and accessory taenite, chromite (cr# = 90), chlorapatite and troilite. Plagioclase displays simple albite and Carlsbad twinning, is mostly equigranular, and contains included pyroxene chadacrysts. Two pyroxenes (augite and *unexsolved pigeonite*) are present as grains of highly variable size (up to 2 mm), and contain included plagioclase chadacrysts. Sparse pockets of brown, glassy late stage residuum with microlites occur between the other phases. Undulatory extinction in plagioclase and some pyroxenes implies mild shock levels.

**Silicate Compositions:** Most plagioclase ranges in composition from An₂₂.₄Or₂.₀ to An₃₆Or₂.₂; a few zoned grains have cores of An₅₂-₅₆Or₂.₁ and rims of An₃₆Or₂.₁, and albite in residuum pockets is An₁₀Or₅.₇. Both augite (Fs₁₈.₅-₂₇.₀Wo₃₆.₇-₄₁.₂; FeO/MnO = 14–17, Al₂O₃ = 2.2 wt%, Na₂O = 1.2 wt%; TiO₂ = 1.2 wt%; Cr₂O₃ = 1.6 wt%) and pigeonite (Fs₃₄.₄-₃₉.₇Wo₈.₆-₁₄.₅; FeO/MnO = 20, Al₂O₃ up to 3.2 wt%) are notably aluminous. Residuum glass contains (in wt%): SiO₂ 70, Al₂O₃ 13.8, FeO 2.8, CaO 2.1, Na₂O 9.4 and K₂O 2.9.

**Oxygen Isotopes:** Results obtained by laser fluorination of acid-washed material (δ¹⁸O = 4.80, 4.73; δ¹⁷O = 3.72, 3.75; Δ¹⁷O = 1.199, 1.265 per mil, respectively) plot well above the TFL in the field for LL chondrites [1].

**Discussion:** Several aspects of this achondrite imply that it is a rapidly cooled, high temperature igneous rock. The coexistence of pigeonite and subcalcic augite is possible only at temperatures above 1175°C in Fe-free systems at 1 bar [2], but even in Fe-bearing systems the coexistence of these two pyroxenes would indicate temperatures probably above 900–1000°C, which are consistent also with the elevated aluminum contents of both pyroxenes. The partly glassy intergranular residuum is consistent with rapid quenching of a partly crystallized magmatic liquid. The possibility that NWA 6698 might represent an impact melt rock is not in concert with the overall texture and complete lack of included clasts. Although the oxygen isotopic composition and sodic plagioclase suggest affinities with LL chondrites, the pyroxene compositions and especially their very low FeO/MnO ratios are quite unlike those for pyroxenes in LL chondrites.

**References:** [1] Clayton R. et al. 1991. *Geochimica et Cosmochimica Acta* 55:2317–2337. [2] Longhi J. and Bertka C. 1996. *American Mineralogist* 81:685–695.
ACAPULCOITE NORTHWEST AFRICA 6557 AND PROPOSED ESTABLISHMENT OF THE ACAPULCOITE-LODRANITE CLAN AS A SINGLE METEORITE CLASS

T. E. Bunch¹, A. J. Irving², J. H. Wittke¹ and D. Rumble III³. ¹Geology Program, SESES, Northern Arizona University, Flagstaff, AZ 86011, USA, E-mail: tbear1@cableone.net ²Earth & Space Sciences, University of Washington Seattle, WA 98195, USA. ³Geophysical Laboratory, Carnegie Institution, Washington, DC 20015, USA.

**Petrography:** NWA 6557 is a very fresh 68 g crusted achondrite with a mean grainsize (gs) of 240 µm exhibiting equigranular metamorphic texture with triple grain junctions. It is composed of 38 vol% orthopyroxene (Fs₁₂.₅Wo₂.₁, FeO/MnO = 12), 35 vol% olivine (Fa₁₃.₉, FeO/MnO = 16), 12 vol% sodic plagioclase (An₆.₈Or₅.₅), 7 vol% subcalcic augite (Fs₈.₁Wo₃₆.₈), and 8 vol% chromite (cr# = 87] + kamacite (Ni = 6.2 wt%).

**Oxygen Isotopes:** Results obtained by laser fluorination of acid-washed NWA 6557 material (δ¹⁸O = 3.05, 2.79; δ¹⁷O = 0.64, 0.55; Δ¹⁷O = -0.962, -0.913 per mil, respectively) plot within the relatively broad field for acapulcoites and lodranites.

**Nomenclature Issues:** Since the falls of Acapulco (mean gs 170 µm) and Lodran (mean gs 580 µm), more than 45 separate related meteorites have been found in Antarctica, Africa and elsewhere. There is a continuous range in mean grainsize among specimens assigned the names acapulcoite and lodranite (based on the arbitrary division at 340 µm proposed by [1]), and grainizes range widely even within single specimens of some of these achondrites (e.g., 50–1700 µm with a mean of 550 µm in NWA 4448). In the column chart below the apparent peak in the 500–550 µm range is an artifact of grainsize estimates reported simply as “0.5 mm” by some classifiers, rather than a precise value.

**Proposal:** We suggest that the term *acapulcoite-lodranite clan* be applied to all of the members of this group (which oxygen isotopes and CRE ages suggest derive from different portions of the same parent body [2]). The terms acapulcoite and lodranite could still be used informally for members at either end of the range, but it seems imprudent to attempt to arbitrarily assign a specific grainsize at which the name changes. The term *transitional* has also been used for specimens of “intermediate” grainsize, but this also seems quite arbitrary and of limited usefulness.

**References:** [1] McCoy T. et al. 1996. *Geochimica et Cosmochimica Acta* 60:2861–2908. [2] Irving A. et al. 2007. Abstract #1338. 38th Lunar and Planetary Science Conference; Eugster O. and Lorenzetti S. 2005. *Geochimica et Cosmochimica Acta* 69:2675–2685.

<figure><img src="image_5.png" /></figure>

ICE IMPACTS ON AEROGEL AND STARDUST Al FOIL

M. J. Burchell¹, M. J. Cole¹, M. C. Price¹ and A. T. Kearsley². ¹School of Physical Science, University of Kent, Canterbury, CT2 7NH, UK, E-mail: m.j.burchell@kent.ac.uk. ²Impacts & Astromaterials Research Centre (IARC), Department of Mineralogy, Natural History Museum (NHM), London SW7 5BD, UK.

**Introduction:** The NASA Stardust mission to comet Wild 2 returned a dust collector to Earth in 2006 (see [1] for first results and [2] for a recent summary). The main collection substrate was SiO₂ aerogel, with a smaller area of aluminum (Al) foil. As a low density, highly porous material, aerogel can retain much relatively unprocessed material from many types of hypervelocity particles [3] within tracks of diverse shape, instead of as the highly disrupted and partially melted residue found in Al foil impact craters. Stardust flew close to the comet nucleus (236 km) at 6.1 km s⁻¹, and captured numerous mineral particles in aerogel tracks [4–5] and foil craters [6–7]. So far, it has been assumed that no impact features were produced by ice, as modeling suggests small ice grains should have rapidly sublimated following release into the coma, disappearing before reaching Stardust (see [2] for discussion of dust transit time to the collector). However, live-time data recorded during the fly-by show a late burst of impacts, as if a larger ejected boulder broke up after leaving the comet surface [8]. Might this have still been carrying ice? Images from comet Hartley 2, taken by the EPOXI mission in 2010, show cm-scale ice-rich grains above the comet surface [9]. We therefore ask how we might recognize if ice did impact on Stardust, and have made analogue experimental impacts on aerogel and Al foil at 6.1 km s⁻¹.

**Method:** We used the Kent two stage light gas gun [10]. Modifications to breech and launch tube mounts for active cooling and pre-cooling of the launch tube allow mm-size solid ice projectiles to be fired. Projectiles fragment due to shock during acceleration, and a spreading shower of fragments proceeds to the target.

**Discussion:** Our preliminary results show ice impacts at appropriate velocity (higher than previous work [11]), by particles similar in size to Stardust impactors. Foils and Al support plates show shallow craters lined by collapsed vesicles. Broad projectile dispersion has so far yielded fewer impacts on aerogel, the first tracks are currently being characterized; they show no terminal grain or fine projectile fragments lining the wall, consistent with loss of a volatile impactor. Given the polydisperse size distribution of grains striking the targets, we do not yet have a calibration for track vs. impactor size, but this is being investigated. In summary, we can now fire ice at Stardust speeds in the gun, and have impacts corresponding to those that might have occurred from ice grains from comet Wild 2 impacting onto the Stardust collector.

**References:** [1] Brownlee D. E. et al. 2006. *Science* 314:1711–1716. [2] Burchell M. J. and Kearsley A. T. 2009. *Planetary and Space Science* 57:1146–1161. [3] Burchell M. J. et al. 2006. *Annual Review of Earth and Planetary Sciences* 34:385–418. [4] Hörz F. et al. 2006. *Science* 314:1716–1719. [5] Burchell et al. 2008. *Meteoritics & Planetary Science* 43:23–40. [6] Kearsley A. T. et al. 2008. *Meteoritics & Planetary Science* 43:41–74. [7] Price M. C. et al. 2010. *Meteoritics & Planetary Science* 45:1409–1428. [8] Tuzzolino A. J. et al. 2006. *Science* 304:1776–1780. [9] A’Hearn M. F. et al. 2011. Abstract #2516. 42nd Lunar and Planetary Science Conference. [10] Burchell M. J. et al. 1999. *Meas. Sci. Technol.* 10:41–50. [11] Yano H. et al. 1999 Abstract #1961. 30th Lunar and Planetary Science Conference.
SYNCHROTRON FOURIER TRANSFORM INFRARED SPECTROSCOPY ON FRAGMENTS OF INTER-PLANETARY DUST PARTICLES (IDPS)

H. Busemann¹, S. Bajt², N. H. Spring¹ and L. R. Nittler³. ¹SEAES, University of Manchester, UK. E-mail: henner.busemann@manchester.ac.uk. ²DESY, Hamburg, Germany. ³DTM, Carnegie Institution of Washington DC, USA.

**Introduction:** IDPs are among the most primitive materials available for laboratory analysis and contain pristine material essentially unaltered since solar system formation [1]. As > 80% may originate from comets [2], they allow the study of comets in the laboratory without sample return [3]. Our ultimate goal will be the (destructive) examination of the heavy noble gases in IDPs to assess the volatile contents in comets [4]. Before we will perform various correlated analyses including Raman spectroscopy [5] to identify the material that is most likely of cometary origin.

Here we present preliminary FTIR results from a first set of IDP fragments. The IDP analyses yield large spectral variations in the organic matter.

**Experimental:** Without any sample preparation, several fragments (typically 3–4 to up to 10 µm diameter) were split off bulk IDPs on NASA glass slides and transferred onto KBr windows. All particles were analyzed with the FTIR microscope at the ALS Berkeley (~600–4000 cm⁻¹) in mapping mode with diffraction-limited spatial resolution [6]. The IDPs were not pressed to allow removal for future NanoSIMS analysis.

**Results and Discussion:** Four IDPs from collector L2036 clusters 4 and 20 show the typical aliphatic hydrocarbon signatures observed earlier [e.g., 7,8]. Two of those may also indicate primary amine functionality, as one IDP from L2006. Both Raman [5] and FTIR spectroscopy of L2011 cluster 1 IDP fragments suggest only little OM, consistent with their non-chondritic-porous, metal-rich nature. A fragment from a L2005 cluster 26 IDP did not yield IR bands for OM above the detection limit, whereas another fragment shows the typical Raman parameters indicative of disordered C. Comet Grigg-Skjellerup collection IDPs were analyzed so far as two fragments of a L2054 cluster 1 IDP. Whilst one fragment does not yield IR results for OM above detection limit, the other shows potentially the signature of NO₂ compounds, but no aliphatic hydrocarbon bands. Raman spectroscopy on a different fragment indicates particularly disordered OM. One IDP from L2006 suggests carbonate.

These analyses will be supplemented by SEM and NanoSIMS examinations of both the fragments analyzed here by FTIR and their main IDP masses to determine chemistry and mineralogy, and the presence of isotopically anomalous organic matter and presolar grains. The preliminary tentative detection of carbonate, NO₂, primary amine and widespread aliphatic hydrocarbon (CH₂ and CH₃ stretch) functionality in the IDPs is consistent with their primitive, essentially unheated character and their origin from a variety of parent bodies including comets, where the OM did not experience homogenization and destruction.

**References:** [1] Bradley J. P. 2003. Treatise on Geochemistry vol. 1:689–711. [2] Nesvorný D. et al. 2010. *The Astrophysical Journal* 713:816–836. [3] Busemann H. et al. 2009. *Earth and Planetary Science Letters* 288:44–57. [4] Busemann H. et al. 2010. Abstract #1947. 41st Lunar and Planetary Science Conference. [5] Spring N. H. and Busemann H. 2011. *Meteoritics & Planetary Science* 46: this volume. [6] Bajt S. et al. 2009. *Meteoritics & Planetary Science* 44:471–484. [7] Matrajt G. et al. 2005. *Astronomy & Astrophysics* 433:979–995. [8] Flynn G. J. et al. 2003. *Geochimica et Cosmochimica Acta* 67:4791–4806.

INSIGHTS ON THE THERMAL HISTORY OF THE PARIS CM CHONDRITE BASED ON THE PHASE RELATIONS OF ITS OPAQUE ASSEMBLAGES

C. Caillet Komorowski¹, O. Boudouma², B. Reynard³, B. Van de Moortèle³ and A. El Goresy⁴. ¹Muséum National d'Histoire Naturelle, LMCM, UMR CNRS 7202, Paris, France. E-mail: ccaillet@mnhn.fr. ²UPMC-ISTEP, Paris. ³ENS-Laboratoire de Géologie de Lyon, UMR CNRS 5276. ⁴Bayerishes Geoinstitut, Universität Bayreuth, Germany.

We studied the characteristic features of FeNi metals and sulfides in matrix, around clasts and in chondrules of the primitive Paris CM chondrite [1] to explore its thermal history. Two polished thin sections were optically studied and at the FESEM. EMPA and Raman spectra were obtained on selected minerals.

Paris is a primitive microbrecciated chondrite with well-preserved chondrules containing large quantities of FeNi metal globules, heterogeneously distributed refractory inclusions, altered clasts (PCP), phenocrysts, 150–300 µm rounded metal grains surrounded by accretionary rims and a fine-grained matrix locally altered. The opaque minerals consist of FeNi metal, FeNi sulfides, rare phosphides and oxides. X-ray mapping shows the ubiquitous presence of sulfur-bearing components in matrix. Here, we describe sulfides: mainly pyrrhotite, pentlandite (Pn), other FeNi-sulfides, and very rare stoichiometric troilite. They occur as (1) tiny matrix grains, (2) ubiquitous large grains of pyrrothite containing blebs or flames of Pn, and (3) associated with Fe-rich olivine as isolated entities plastered around clasts or chondrules. No Hg minerals were found [2].

Chemical compositional of sulfides in matrix and chondrule rims is identical suggesting similar formation conditions. Pn crystals have up to 1.35 wt% Co. Only sulfides associated with Fe-rich olivines contain Cr. The Ni content of metal ranges between 4 and 15 wt% and is positively correlated with Co content (0.17–0.6 wt%). P is up to 0.4 wt% and Cr up to 1 wt%. Tetrateanite contains 1.7 wt% Co. Kamacite is far more abundant than taenite.

Other opaques in matrix include tiny grains of (FeNi)₃P and a 100 µm idiomorphic Pn grain. These grains formed before accretion on the Paris parent body. Presence of Pn limits the upper temperature bound of heating of bulk Paris to <610 °C in agreement with [3]. Several broken sulfates, PCP-rich clumps, carbonates (about 40 µm) were incorporated and further altered on the parent body. Gypsum surrounds some carbonates.

Idiomorphic (hexagonal or trigonal) and rounded silica inclusions, up to 4 µm large, are present in large isolated metallic globules in the matrix, often surrounded by accretion rims, or occur in metal of chondrules. We identified cristobalite and silica glass. SiO₂ glass was found as hexagonal inclusion in kamacite. High temperature silica polymorph demonstrates that a high thermal event at high fO₂ (probably formation by oxidation of Si-bearing FeNi; [4]) followed by rapid quenching prior to accretion of the metal in the meteorite. Presence of glass, cristobalite, and large fragments of Pn strongly suggests that only low temperature metamorphism occurred in the meteorite after accretion. FIB-TEM of these idiomorphic inclusions are in progress.

**References:** [1] Bourot-Denise M. et al. 2010. Abstract #1683. 31st Lunar and Planetary Science Conference. [2] Caillet Komorowski C. et al. 2010. *Meteoritics & Planetary Science* 45:A28. [3] Kimura M. et al. 2011. *Meteoritics & Planetary Science* 46:431–442. [4] Hewins and Zanda B. 1992. *Meteoritics* 27:233.
5242

SERS INVESTIGATION OF NUCLEOBASES DEPOSITED ON EVAPORITE MINERALS: A TEST CASE FOR ANALOG MARS REGOLITH

S. Caporali¹,², V. Moggi-Cecchi¹, M. Pagliai², G. Pratesi³, V. Schettino²,⁴. ¹Museo di Scienze Planetarie, Provincia di Prato, Via Galcianese, 20/h, I-59100 Prato, Italy. ²Dipartimento Chimica, Università di Firenze, Via della Lastruccia, 3, I-50019, Sesto Fiorentino, Italy. E-mail: stefano.caporali@unifi.it. ³Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira, 4, I-50121, Florence, Italy. ⁴European Laboratory for NonLinear Spectroscopy (LENS) Università di Firenze, Via Carrara 1, I-50019, Sesto Fiorentino, Italy.

**Introduction:** Traditionally, Micro-Raman spectroscopy is one of the primary analytical techniques for the detection of minerals and organic molecules in the laboratory. However, in owe of its versatility and capability to interrogate samples without preliminary purification or concentration treatments, it is one of the frontrunners for the next generation of in situ instrument designed to explore solar system bodies. In particular the Raman capability to unambiguously detect organic molecules and biomarkers might result of great importance to understand if and how primitive life generates in extraterrestrial environments (e.g., Mars). The technique's analytical sensitivity towards organic molecules can be further enhanced by means of the interaction with coin metals nanoparticles [1]. This approach, named Surface Enhanced Raman Scattering (SERS) has proved to be able to detect traces amount of nucleobases adsorbed on Terrestrial [2] or Martian [3, 4] substrates. Even if these studies have shown the suitability of SERS to detect tiny amounts of biomarkers in magmatic rocks, other substrates such as evaporites should result more prone to host biomolecules. According to orbital and rover observations [5, 6] as well as the presence of tiny amounts of evaporitic minerals in nakhlites (Martian meteorites) [7], Martian evaporites are considered to be constituted by carbonates, sulfates and clay minerals. In the present study we focused on the identification of nucleobases on Martian analog material in order to test the SERS response on such kind of mineral substrates.

**Experimental and Results:** Two different nucleobases (adenine and hypoxanthine) were deposited on crushed samples made of carbonates (calcite, dolomite, magnesite and siderite) and sulfates (anhydrite and gypsum). Then the Raman spectra were collected under air at room temperature on every single mineral phase. Without depositing Ag nanoparticles (Ag-nps) only the bands attributable to the substrate were observed. However, the addition of Ag-nps enhanced the intensity of the Raman bands of the two nucleobases allowing their unambiguous identification and assessing the SERS capability to deal with subpicogram amounts of nucleobases.

**Acknowledgments:** The authors would like to thank Regione Toscana for financial support of the project LTSP through the found POR FSE 2007-2013 (Obiettivo 2,Asse IV).

**References:** [1] K. Kneipp et al. (eds). 2006. Surface-Enhanced Raman Scattering: Physics and Applications. [2] M. Muniz-Miranda et al. 2010. *Journal Raman Spectroscopy* 41:12–15. [3] El Amri C. et al. 2004. *Journal Raman Spectroscopy* 35:170–177. [4] S. Caporali et al. 2011. Abstract #1401. 42nd Lunar and Planetary Science Conference. [5] Bibring J.-P. et al. 2005. *Science* 307:1576–1581. [6] Chevrier V. and Math P. E. 2007. *Planetary and Space Science* 55:289–314. [7] Bridges J. C. and Grady M. M. 2000. *Earth and Planetary Science Letters* 176:267–279.

5465

Ar-Ar CRYSTALLIZATION AGES OF SHERGOTTITE RBT 04262 MINERAL SEPARATES

J. A. Cartwright¹ and R. Burgess². ¹Max Planck Institute for Chemistry, J.-J.-Becher-Weg 27, 55128, Mainz, Germany. ²SEAES, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. E-mail: julia.cartwright@mpic.de

**Introduction:** For most chronometers including Ar-Ar, the crystallization ages of shergottites show groupings at 165–180 Ma, 375 Ma and 474–900 Ma [1–3]. However, crystallization ages determined by Pb-Pb dating suggest ages of ~4 Ga, with [4] citing isotopic resetting as the cause for younger ages in other chronometers. In addition, the presence of trapped ⁴⁰Ar components, including terrestrial atmosphere, has been suggested as a cause for elevated ages in both nakhlites and shergottites [5]. Having observed evidence for trapped air in previously reported Xe analysis of Roberts Massif 04262 (RBT 04262) [6], here we report apparent ages based on the Ar-Ar technique for RBT 04262 mineral separates, to assess whether and to what extent trapped air can account for variable ages.

**Meteorite description and Methodology:** Enriched shergottite RBT 04262 shows two distinctive lithologies. The first has coarse-grained pyroxene oikocrysts and rare olivine, whilst the second is fine-grained with pyroxene, olivine and maskelynite [7]. Previous research reported crystallization ages of 225 ± 21 Ma (Lu-Hf, [8]), 167 ± 6 Ma (Rb-Sr, [9]) and 174 ± 14 Ma (Sm-Nd, [9]). As in [6], a small chip of RBT 04262,14 (2nd lithology) was crushed and mineral separates hand-picked into 8 aliquots: 4 of olivine-pyroxene (Olpx), 3 of maskelynite (Mask) and 1 of opaque (Opq). Following neutron irradiation, the aliquots were analyzed for Ar isotopes using a laser step-heating technique on an MS1 noble gas mass spectrometer (Manchester).

**Results and Discussion:** RBT 04262 showed an average apparent K-Ar age of ~321.0 ± 0.3 Ma, with total Ar-Ar ages ranging between ~310–1355 Ma. The Olpx aliquots yield older apparent ages (625 ± 19, 644 ± 3, 723 ± 17, 1355 ± 47 Ma) than the Mask (309 ± 1, 340 ± 2, 348 ± 3 Ma) and Opq (575 ± 31 Ma), and show overall increasing age with temperature during stepped heating. These apparent ages are older than previously reported Lu-Hf and Sm-Nd ages of RBT 04262, and may suggest the presence of a trapped ⁴⁰Ar component. In addition, correcting for ⁴⁰ArK (assumed age 174 Ma [9]) does not significantly reduce the ⁴⁰Ar content, leaving a putative trapped ⁴⁰Ar/³⁰Ar of ~1000. There is a clear correlation in the Mask between ⁴⁰Ar and K, and correlation in Olpx between ⁴⁰Ar and Cl. This may suggest multiple trapped components including an aqueous Cl-bearing phase or Cl-rich melt inclusions in olivine. In addition, there is no obvious overall correlation between ⁴⁰Ar concentration and mineral separate, which may suggest its location within a minor phase (e.g., melt/fluid inclusion).

**References:** [1] Borg L. et al. 2001. Abstract #1144. 32nd Lunar and Planetary Science Conference. [2] Nyquist L. E. et al. 2001. *Space Science Reviews* 96:105–164. [3] Symes S. J. K. et al. 2008. *Geochimica et Cosmochimica Acta* 72:1696–1710. [4] Bouvier A. et al. 2008. *Earth and Planetary Science Letters* 266:105–124. [5] Bogard D. et al. 2009. *Meteoritics & Planetary Science* 44:905–923. [6] Cartwright J. A. et al. 2010. *Meteoritics & Planetary Science* 45:1359–1379. [7] Mikouchi T. et al. 2008. Abstract #2403. 39th Lunar and Planetary Science Conference. [8] Lapen T. J. et al. 2008. Abstract #2073. 39th Lunar and Planetary Science Conference. [9] Shih C.-Y. et al. 2009. Abstract #1360. 40th Lunar and Planetary Science Conference.
## "SOLAR-WIND-RICH" HOWARDITES: TRUE REGOLITH VS. CM-IMPLANTED COMPONENTS

J. A. Cartwright¹, D. W. Mittlefehldt², J. S. Herrin², S. Herrmann¹ and U. Ott¹. ¹Max Planck Institut für Chemie, J.-J.-Becher-Weg 27, 55128, Mainz, Germany. ²NASA/Johnson Space Center, Houston, Texas, USA. E-mail: julia.cartwright@mpic.de.

**Introduction:** Howardite, eucrite and diogenite meteorites (collectively HED) likely originate from asteroid 4 Vesta [1], one of two asteroids targeted by NASA's Dawn mission. Many howardites (polymict breccias of E and D material) contain "regolithic" features, including impact-melt clasts, fragmental breccia clasts, and carbonaceous chondrite fragments. True regolithic nature can be determined through noble gas analysis, as solar wind (SW) is implanted into the upper-most surfaces of solar system bodies. While previous work [2] suggested that high siderophile element contents (e.g., Ni of 300–1200 µg g⁻¹) were regolith indicators, we found no obvious correlation between SW and these indicators in our initial howardite noble gas analyses [3]. We observed CM-like fragments in a number of our howardites, whose textures suggest late addition to the breccia assemblage [4]. As typical CMs contain mixtures of SW (in matrix) and planetary (in clasts) components [5], we investigate the dominance of such components in SW-rich howardites. This will help determine the extent of implanted SW in HED grains vs. SW and planetary gases from CM fragments, and allow better understanding of regolith processes.

**Results:** Noble gas analysis was performed using furnace step-heating on an MAP 215-50 noble gas mass spectrometer. Our results are shown in Table 1. Only 4 howardites show potential SW (e.g. GCR-SW mixing $^{20}$Ne/$^{22}$Ne 1–13.75, $^{21}$Ne/$^{22}$Ne 0.85–0.03 [6]), of which 3 contain CM fragments. A pure CM clast (PRA CM) was analyzed to assess CM dominance compared to bulk PRA. LEW (no CM) has the highest $^{20}$Ne, concentration and SW-Ne ratios. The CM-rich samples show typical mixes of SW (seen in Ne) and planetary (seen in Xe) components as observed for CM Murchison ($^{20}$Ne/$^{22}$Ne ~9, $^{136}$Xe/$^{132}$Xe ~0.322). Our estimated CM fractions (from petrological analysis [4]) are roughly consistent with observed heavy noble gas concentrations. Significant late addition of CM (with matrix) to howardite assemblages may thus overprint latent SW components. The effects are thus not as strong with low CM fractions (e.g. MET)—possibly due to less incorporated matrix. Elevated Xe concentrations may help identify potential CM-rich howardites.

**References:** [1] Drake M. J. 2001. *Meteoritics & Planetary Science* 36:501–513. [2] Warren P. H. et al. 2009. *Geochimica et Cosmochimica Acta* 73:5918–5943. [3] Cartwright J. A. et al. 2011. Abstract #2655. 42nd Lunar and Planetary Science Conference. [4] Herrin J. S. et al. 2011. Abstract #2806. 42nd Lunar and Planetary Science Conference. [5] Nakamura T. et al. 1999. *Geochimica et Cosmochimica Acta* 63:257–273. [6] Grimberg A. et al. 2008. *Geochimica et Cosmochimica Acta* 72:626–645.

<table><caption>Table 1. "SW-rich" Howardite noble gas results.</caption><thead><tr><th>Noble<br>Gas (cc/g)</th><th>LEW</th><th>MET</th><th>SCO</th><th>PRA</th><th>PRA</th></tr></thead><tbody><tr><td></td><td>85313</td><td>00423</td><td>06040*</td><td>04401</td><td>CM</td></tr><tr><td><sup>22</sup>Ne (10<sup>-8</sup>)</td><td>36.7 (8)</td><td>19.6 (6)</td><td>2.7 (2)</td><td>6.6 (3)</td><td>4.9 (2)</td></tr><tr><td><sup>20</sup>Ne/<sup>22</sup>Ne</td><td>9.68 (4)</td><td>8.90 (1)</td><td>1.61 (2)</td><td>3.22 (4)</td><td>3.57 (3)</td></tr><tr><td><sup>21</sup>Ne/<sup>22</sup>Ne</td><td>0.157 (1)</td><td>0.272 (2)</td><td>0.814 (7)</td><td>0.670 (6)</td><td>0.567 (4)</td></tr><tr><td><sup>20</sup>Ne<sub>t</sub> (10<sup>-8</sup>)</td><td>347 (22)</td><td>169 (9)</td><td>2.3 (2)</td><td>16.9 (11)</td><td>14.3 (9)</td></tr><tr><td><sup>132</sup>Xe<sub>t</sub> (10<sup>-10</sup>)</td><td>2.1 (1)</td><td>0.64 (2)</td><td>5.1 (2)</td><td>39.9 (13)</td><td>78.0 (27)</td></tr><tr><td><sup>129</sup>Xe/<sup>132</sup>Xe</td><td>1.023 (3)</td><td>1.004 (8)</td><td>0.992 (2)</td><td>1.046 (3)</td><td>1.042 (3)</td></tr><tr><td><sup>136</sup>Xe/<sup>132</sup>Xe</td><td>0.334 (1)</td><td>0.358 (3)</td><td>0.334 (1)</td><td>0.324 (1)</td><td>0.323 (1)</td></tr><tr><td>CM fraction</td><td>—</td><td>&lt; 1%</td><td>~10%</td><td>~60%</td><td>~100%</td></tr></tbody></table>

Errors in parentheses. *t* = trapped. *incomplete analysis.

## METEORITE BENDEGÓ, A BRAZILIAN COMICS SUPER HERO

W. P. Carvalho and D. C. Rios. Instituto de Geociências, Universidade Federal da Bahia. E-mail: wilton@atarde.com.br.

**Introduction:** Comics are mainly written for children, but everyone knows that many grown-up readers are fond of such a visual storytelling medium. Because comics' colorful pages, characters expressions and the funny dialogue balloons attract, at a first glance, most people for its contents, that medium has been used in Brazil as a non-technical educational tool to make meteoritics more popular among kids and adults. The Bendegó iron, the most known meteorite in the Brazilian collection, is the super hero who interacts visually with school children to tell its rich history and scientific facts regarding the entrance, fall, finding, analysis and classification of meteorites.

<figure><img src="image_6.png" /></figure>

**Results:** Starting in October 2008 the authors and a team of nine professors and students of geology executed a 2-year academic project to identify, recover and register meteorites in Brazil. That project has opened a communication channel to teach high school students and laymen about the importance of meteorites to science and how to distinguish space rocks from terrestrial ones. A 16-page comics titled Bendegó: a visitor from space [1] was designed and 10,000 full color copies were printed in Portuguese and freely distributed to people who attended educational events such as lectures, geology congresses, astronomy parties and scientific expositions. Children and adults have enjoyed Bendegó's comics so much that other 10,000 copies are being printed to attend demand. Looking forward to make Bendegó's comics international, an English version has been set up and hopefully will be followed by other languages.

**Discussion:** In every country there is one meteorite which is the master-piece and the most popular among all, as Bendegó in the 60-specimen Brazilian collection. "Comics have a lot of communication power in development and education." [2], so why not use that characteristic to design and execute information campaigns about meteoritics?

**Acknowledgments:** We are grateful to Fundação de Apoio à Pesquisa do Estado da Bahia (FAPESB) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) for the financial support granted.

**References:** [1] Rios D. C. and Carvalho W. P. 2009. *Bendegó: um visitante do espaço*. Editora Cedraz, Salvador. 16 p. [2] Packalém L. and Odoi F. 2004. Comics with an attitude... A Guide to Use of Comics in Development Information. Hakapainos. 97 p.
5334

NATURAL HISTORY MUSEUM (LONDON) METEORITE
COLLECTION DIGITIZATION PROJECT

D. J. Cassey, D. A. Smith and C. L. Smith. Department of Mineralogy, The Natural History Museum, London, SW7 5BD, UK, E-mail: deboc@nhm.ac.uk

**Introduction:** The Meteorite Collection housed at the Natural History Museum (NHM) in London is one of the world's leading collections encompassing some 1975 individual meteorites as 4845 registered specimens with associated preparations (e.g., thin sections, powders) and curatorial documentation. The collection is a heavily used resource for scientists around the world, for example over the last five years the Museum has carried out 297 individual loans, of 1156 specimens to 93 individual borrowers. A key strategy of the NHM is to increase access to the collections and enhance the value of the collections through the integration new scientific data for each specimen. With the implementation of the KeEMu database system [1] we have initiated a number of projects to provide more detailed information on the Meteorite Collection, which be made available to scientists, historians and members of the public.

**Digitization Strategy:** The first element of the project was a thorough audit of the carbonaceous chondrites and achondrite meteorites. This work included weighing of all samples (including fragments, chips and powders at the milligram level), re-housing specimens into conservation grade storage, photographing all specimens and associated "permanent labels" - the permanent label is the original paper label that is created on specimen registration and all information relating to that specimen is added to the label as and when curatorial action occurs. All of this data is now entered into the EMu database adding to the level of information readily available for each specimen. Importantly this work has provided up to date holdings information for scientifically valuable samples, which we use when evaluating requests for material for study [2].

The second element of the project (still ongoing) is the digitization of all information relating to fall meteorites held in the collection (the NHM currently holds 682 of the 1095 recognized fall meteorites). This includes a full audit, photography of all specimens and permanent labels and digitization of all locally held paper records and archives including register entries, correspondence, newspaper/magazine articles, paper-held data records, chemical data and scans of thin sections.

A third element is the acquisition of compositional imagery of thin sections by automated analytical electron microscopy, which will allow for the "virtual loan" of specimens [3].

Value to the community: The NHM's significant investment in a holistic approach to collections digitization provides unrivalled levels of information on each registered specimen, considerably enhancing the collection for present and future users. In return we expect users of the collection to provide us with information obtained during their studies. Using this model, meteorite collections enhancement is a dual responsibility of both institutions and collections users. We encourage the community to consider this approach to ensure the sustainability of limited resources for the continued benefit of all.

**References:** [1] Sendino C. 2009. *Collections: A Journal for Museum and Archives Professionals* 5:149-158. [2] Smith C. L. and Welzenbach L. C. 2006. *Meteoritics & Planetary Science* 41:A164. [3] Kearsley A. T. et al. 2011. This volume.

5149

DO WE HAVE ANY IRONS RELATED TO THE IIAB GROUP BY
CRYSTALLIZATION AT THE FE-FES EUTECTIC?

Nancy L. Chabot¹, ¹Applied Physics Laboratory, Johns Hopkins Rd, Laurel, MD, 20723, USA, E-mail: Nancy.Chabot@jhuapl.edu.

**Introduction:** Most previous modeling work on the crystallization of iron meteorites has focused on the fractional crystallization of a molten metallic liquid up to the Fe-FeS eutectic composition [e.g. 1-5]. These models have had success at explaining the trends of irons in major magmatic groups, even if there remains disagreement on the details such as the bulk S composition [e.g., 3-5]. There is general agreement that the trends observed in these iron meteorite groups resulted from fractional crystallization, and these fractional crystallization models end when the eutectic composition is reached, even though liquid remains.

Many irons are from silicate-bearing, or non-magmatic groups, or are ungrouped irons whose chemical compositions are not explained by simple fractional crystallization. This project aims to model the expected composition of irons formed at the eutectic in the Fe-Ni-S system and to compare the model results to these irons. Here I present results of such modeling for the IIAB group, the largest magmatic group of iron meteorites.

**Modeling Approach:** At the eutectic composition, both FeNi solid metal and FeS troilite crystallize. For the calculations in this model [6], it is assumed that the troilite would be pure FeS and that all Ni and siderophile trace elements would partition completely into the crystallizing solid metal, similar to the approach of [7]. The eutectic composition of the Fe-Ni-S system was expressed mathematically as a function of the liquid Ni and S contents. Published parameterizations of the solid metal/ liquid metal partition coefficients as a function of the liquid S content were used for 17 siderophile elements [8,9].

**Results:** For the IIAB group, the predicted eutectic solid metal composition was calculated and a mixing line was determined between the pre-eutectic solid metal and the eutectic solid metal. Irons with a component of the IIAB eutectic solid metal are characterized by: highly elevated concentrations of Sb; Au, As, and Co contents near those of late crystallizing IIAB irons; elevated Ni contents with values up to ~30 wt%; low Ga, Ge, and Ir concentrations. Iron meteorites with compositions near these predictions include the sHH subgroup of the IAB complex [10] and the Twin City duo, as previously noted by [7] based on similar modeling with fewer trace elements. The sHL subgroup of the IAB complex [10] also falls intriguingly close to the IIAB eutectic mixing line calculation. Current work is further evaluating the feasibility that these meteorites may be genetically related to the IIAB group.

**References:** [1] Jones J. H. and Drake M. J. 1983. *Geochimica et Cosmochimica Acta* 47:1199-1209. [2] Haack H. and Scott E. R. D. 1993. *Geochimica et Cosmochimica Acta* 57:3457-3472. [3] Wasson J. T. 1999. *Geochimica et Cosmochimica Acta* 63:2875-2889. [4] Chabot N. L. 2004. *Geochimica et Cosmochimica Acta* 68:3607-3618. [5] Wasson J. T. et al. 2007. *Geochimica et Cosmochimica Acta* 71:760-781. [6] Chabot N. L. 2010. *Meteoritics & Planetary Science*. Abstract #5021. [7] Kracher A. 2002. 33rd Lunar and Planetary Science Conference. Abstract #1421. [8] Chabot et al. 2003. *Meteoritics & Planetary Science* 38:1425-1436. [9] Chabot et al. 2007. *Meteoritics & Planetary Science* 42:1735-1750. [10] Wasson J. T. and Kallemeyn G. W. 2002. *Geochimica et Cosmochimica Acta* 66:2445-2473.
## NANOGLOBULE ABUNDANCES IN IOM EXTRACTS: CORRELATION WITH PARENT BODY PROCESSING

H. G. Changela¹,², R. M Stroud², B. T. De Gregorio³, L. R. Nittler⁴, C. M. O'D. Alexander⁴ and G. D. Cody⁴. ¹George Washington University, Department of Physics, Washington, District of Columbia 20052, USA. ²Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, District of Columbia 20375, USA. E-mail: changela@anvil.nrl.navy.mil. ³Johnson Space Center, Houston, Texas 77058, USA. ⁴Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.

**Introduction:** Nanoglobules are a form of Insoluble Organic Matter (IOM) found in chondrites [1], IDPs [2] and Comet 81P/Wild2 [3]. Some nanoglobules exhibit large ¹⁵N and D enrichments relative to solar values, indicating that they likely originated in the ISM or the outskirts of the protoplanetary disk [4]. Recent studies of samples from the Tagish Lake meteorite with varying levels of hydrothermal alteration suggest that nanoglobule abundance decreases with increasing hydrothermal alteration [5]. The aim of the present study is to further constrain the morphologies of IOM from a range of primitive chondrites in order to determine any correlation between morphology and petrographic grade and chondrite class.

**Methods:** We are performing a comprehensive scanning transmission electron microscopy (STEM) survey of IOM residues prepared by methods described in [3]. STEM annular dark-field (ADF) imaging surveys were performed with NRL's JEOL 2200FS on residues from Murchison (CM2), EET 92042 (CR2) and QUE 97008 (L3). IOM textures were classified as either having a 'globular' morphology, i.e. spherical, non-porous regions approximately 50-1000 nm in size; 'fluffy', i.e. porous material with fine scale heterogeneity below 50 nm; and 'dense-irregular', i.e. uniformly dense, non-spherical material > 50 nm. ADF images were taken of each chondrite, sampling approximately 100 µm² of IOM. The different morphologies were manually identified from the images and masked using Adobe Photoshop. Area fractions were then obtained using Image J software. Because some small globules (< 100 nm) are difficult to distinguish from the background of fluffy IOM, our results reflect a lower limit on globular abundances.

**Results and Discussion:** Globular to fluffy and dense irregular to fluffy IOM fractions in these chondrites show distinctive variations. Murchison contains the highest abundance of nanoglobules (approximately 7%), followed by EET 92042 (approximately 5%) and then QUE 97008 (approximately 1%). The abundances of dense irregular IOM fractions are similar for Murchison and EET 92402, but have much higher abundance (approximately 20% of measured IOM) in QUE 97008. We will also present new analyses of residues from types 1, 2 and 3 CR and other chondrites to identify any links between nanoglobule abundances and petrographic grade. It has been shown that isotopic enrichment within the IOM is not just localized to globular species, but to some 'fluffy' components as well [6]. It is not clear whether some of the 'dense irregular' morphologies of IOM contain similar enrichments. Coordinated analyses of these extracts and in situ IOM studies will enable us to further constrain the nature of these morphologically distinct components and how they vary with petrographic grade or chondrite class.

**References:** [1] Nakamura-Messenger K. et al. 2006. *Science* 314:1439-1442. [2] Flynn G. J. et al. 2003. *Geochimica et Cosmochimica Acta* 4791-4806. [3] De Gregorio B. T. et al. 2010. *Geochimica et Cosmochimica Acta* 74:4454-4470. [4] Alexander C. M. O'D. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4380-4403. [5] Herd C. D. K. et al. 2011. *Science*, in press. [6] De Gregorio et al. 2010. Abstract #2108. 41st Lunar and Planetary Science Conference.

## ABUNDANCES OF Cl, F, H, AND S IN APATITES FROM SNC METEORITES

M. B. Channon, J. W. Boyce, E. M. Stolper and J. M. Eiler. California Institute of Technology, Pasadena, CA 91125, USA. E-mail: mchannon@gps.caltech.edu.

**Introduction:** Magmatic volatiles influence igneous phase equilibria, eruptive behavior, atmospheric composition, and climate. Several lines of evidence suggest that Mars is rich in halogens and S relative to Earth. However, magmatic volatile abundances and their effects on magmatic processes on Mars are controversial. Here we examine igneous apatites in SNC meteorites as indicators of magmatic volatile abundances.

**Methods:** We measured Cl, F, H (reported as wt% H₂O), and S in 25 apatites from 3 basaltic shergottites (JaH 479, NWA 856, and NWA 2986), 1 lherzolitic shergottite (NWA 1950), and 1 nakhlite (NWA 998) using Caltech's 7f SIMS. We compared our data to literature data for volatiles in SNC apatites [1-8].

**Results:** Our measurements of Cl, F, and H in SNC apatites are similar to previous data, but the increased size of the collective data set sheds light on systematic variations. Our 3 basaltic shergottites have 0.33-0.95 wt% H₂O (literature data: 0.18-0.64 wt% [1-2]), those from the lherzolitic shergottite have 0.07-0.27 wt% (the only previously measured apatite from such a sample has 0.43 wt% [3]); and those from the nakhlite have 0.07-0.11 wt%. Data are also available for apatites from Chassigny (0.21 wt% [4]) and ALH 84001 (0.08 wt% [2] and 0.22 wt% [4]). Apatites from basaltic shergottites appear to be on average H₂O-rich relative to apatites from other lithologies. S contents are variable (<0.01-0.82 wt%; previous measurements are <0.01-0.08 wt% [5-8]). As with H₂O, S contents are lower in the nakhlite (<0.01 wt%) and lherzolitic shergottite (0.02-0.04 wt%) than in the basaltic shergottites (0.05-0.82 wt%).

**Discussion:** The H in apatites from basaltic shergottites spans a range similar to apatites from terrestrial mafic igneous rocks. The higher H and S contents of basaltic shergottites relative to other SNC rock types may indicate higher initial volatile contents or lower extents of degassing prior to apatite crystallization.

Based on our results, apatites in SNCs, particularly basaltic shergottites, are significantly richer in S (by approximately 2x) than those in mafic terrestrial igneous rocks. S is typically incorporated into apatite as SO₄²⁻, and thus is expected to be more strongly partitioned into igneous apatite at higher *f*O₂ (i.e., where sulfate dominates over sulfide in basaltic melts). As expected, terrestrial S-rich apatites are found in lavas that are oxidized (ΔQFM +2 to +6 log units). Estimates of *f*O₂ in shergottite parent magmas (ΔQFM -4 to +0.5 log units) would indicate that S²⁻ was the primary sulfur species. The high S contents of SNC apatite despite low *f*O₂ could reflect (1) high total magmatic S contents; (2) apatite crystallized late when *f*O₂ levels rose above estimates; or (3) some S in SNC apatites is present as sulfide in the halogen site.

**References:** [1] Leshin L. A. 2000. *Geophysical Research Letters* 27:2017-2020. [2] Greenwood J. P. et al. 2008. *Geophysical Research Letters* 35:L05203. [3] Guan Y. et al. 2003. Abstract #1830. 34th Lunar and Planetary Science Conference. [4] Boctor N. Z. et al. 2003. *Geochimica et Cosmochimica Acta* 67:3971-3989. [5] Harvey R. P. et al. 1993. *Geochimica et Cosmochimica Acta* 57:4769-4783. [6] Xirouchakis D. et al. 2002. *Geochimica et Cosmochimica Acta* 66:1867-1880. [7] Greenwood J. P. et al. 2003. *Geochimica et Cosmochimica Acta* 67:2289-2298. [8] Treiman A. H. and Irving A. J. 2008. *Meteoritics & Planetary Science* 43:829-854.
## INTERACTION BETWEEN IMPACT MELT MATRIX AND METAL PARTICLES IN THE WEATHERFORD CBa METEORITE

H. M. Chappell¹, R. H. Jones¹ and J. I. Goldstein². ¹University of New Mexico, Albuquerque, NM 87131, USA. E-mail: hchappel@unm.edu.

²University of Massachusetts, Amherst, MA 01003, USA.

**Introduction:** The CB meteorites, which are subdivided into CBa and CBb subgroups, are metal rich members of the CR clan [1]. Metal and silicate material in CB meteorites possibly formed by condensation from a vapor plume generated during a major impact event [2]. Weatherford is a CBa that has chondrule-like silicate particles and metal particles which are highly deformed, especially compared to the elliptical particles found in the CBa meteorite Gujba. Weatherford, like all the CBa meteorites, also contains a silicate-dominated impact melt matrix which may have been injected at a much later time than when the large particles formed and accreted [3, 4]. The purpose of this study is to investigate the extent to which reheating during injection of impact melt affected the physical nature of pre-existing metal particles.

**Results:** We examined two thin sections of Weatherford (UNM 259 and 260) using reflected light microscopy, SEM and EDS analysis. We observed abundant evidence of physical interaction between the impact melt matrix and metal particles. Metal particles of all sizes have very fine droplets of Fe,Ni metal dissociating from their edges. In places, the impact melt has infiltrated into and begun to disaggregate the metal particles along grain boundaries. Embayments up to 500 µm in size within the metal particles appear to be areas in which metal-rich silicate material, consistent in composition with the impact melt, has invaded the grains.

Many metal grains in CBa meteorites are sulfide-rich and contain Cr-rich troilite (FeS) as tiny blebs within the body of the metal particles, as well as arcuate troilite along grain boundaries [1, 5]. In Weatherford, we observed that some sulfide-rich metal grains, up to 300 µm across, entrained in the impact melt, have inclusions with a Fe-Ni-S eutectic texture [6]. The inclusions are rounded, ranging in size from 5–50 µm, and contain smaller, somewhat elongated, blebs of Fe,Ni metal in a FeS matrix. These inclusions may be the same as what Rubin [7] described as “cellular troilite” in Gujba.

**Discussion:** Deformation and disassociation of metal particles by an invading silicate-rich impact melt matrix, and reheating of entrained metal particles to the eutectic temperature of Fe-Ni-S (1223 K) provides evidence that there was significant interaction between the melt and pre-existing metal particles. Reheating from this process may also have produced two-phase metal particles [8]. Late formation of impact melt (e.g., at 4.2 Ga [4]) may have had a significant effect on the chemical and isotopic properties of CBa meteorites.

**References:** [1] Weisberg M. K. et al. 2001. *Meteoritics & Planetary Science* 36:401–418. [2] Campbell A. et al. 2002. *Geochimica et Cosmochimica Acta* 66:647–660. [3] Barber D. J. and Hutchison R. 1991. *Meteoritics* 26:83–95. [4] Marty B. et al. 2010. *Geochimica et Cosmochimica Acta* 74:6636–6653. [5] Mason B. and Nelen J. 1968. *Geochimica et Cosmochimica Acta* 32:661–664. [6] Scott E. R. D. 1982. *Geochimica et Cosmochimica Acta* 46:813–823. [7] Rubin A. E. et al. 2003. *Geochimica et Cosmochimica Acta* 67:3283–3298. [8] Goldstein J. I. et al. 2011. This conference.

## COMPOSITIONS OF SINGLE CHONDRULES IN THE CR2 CHONDRITE NWA 801 BY MEDICAL X-RAY MICRO-COMPUTED TOMOGRAPHY

C. R. J. Charles¹, P. J. A. McCausland². J. Umoh³, D. Holdsworth³, D. W. Davis¹, D. Gregory⁴, K. Tait⁴ and I. Nicklin⁴. ¹Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, ON, Canada. E-mail: christopher.charles@utoronto.ca. ²Department of Earth Sciences, University of Western Ontario, London, ON, Canada. ³Robarts Imaging Institute; University of Western Ontario, London, ON, Canada. ⁴Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada.

**Introduction:** CR2 chondrites are some of the most primitive and pristine meteorites that contain abundant mm-sized silicate and “armored” chondrules. Armored chondrules show rims of thin Fe-Ni metal on their surfaces or in their interiors, which are thought to be remnants of melting events in a dusty nebular environment [1]. X-ray computed tomography (CT) is an ideal technique to nondestructively map the compositions of such chondrules in 3D, due to variable attenuation of X-rays in different silicates and metal. Synchrotron radiation has been very successful in this respect (i.e., [2]–[4]). However the new generation of “medical” laboratory-based CT scanners also provide excellent spatial resolutions (< 50 µm), high sample throughput, and efficient image acquisition and reconstruction algorithms. Here we report the mineral compositions of chondrules separated from the CR2 chondrite NWA 801 using a GE eXplore specCZT scanner.

**Experimental:** Five hundred and twenty—three individual mm-sized chondrules and chondrule fragments were extracted from 12 g of NWA 801 (loaned by the Royal Ontario Museum) using automated freeze–thaw disaggregation [5]. All objects were sieved and grouped by size onto glass mounts with up to 12 objects/mount. 3D renderings were obtained for all objects along with enstatite, olivine, augite, Si and Fe “standards” through 900 views at 16 ms exposure (110 kVp, 32 mA) at 50 µm/voxel. CT grayscale numbers were converted to Houndsfield units (HU) and all final images were manipulated and examined by GE Microview and custom MatLab scripts.

**Results:** Histograms of HU-values versus number of voxels show one or more distinct peaks throughout the range of 2886 (Si) < HU < 25427 (Fe; saturated). These peaks correspond to the chemical compositions of the objects, which are approximately constrained by the standards. To quantify the compositions of the chondrules obtained by CT imaging, 14 fragments that span the range of HU values, together with the olivine, enstatite and augite “standards” were analyzed by an SX-50 electron microprobe (EMP) to obtain their mineral chemistries and structures. The fragments showed high forsteritic olivine with variable amounts of mesostasis containing low-Ca pyroxene, and Fe-oxide veins and nodules.

**References:** [1] Rubin A. E. 2010. *Geochimica et Cosmochimica Acta* 74:4807–4828. [2] Ebel D. S. and Rivers M. 2007. *Meteoritics & Planetary Science* 39:531–544. [3] Fredrich J. M., Wignarajah D. P., Chaudary S., Rivers M. L., Nehru C. E. and Ebel D. S. 2008. *Earth and Planetary Science Letters* 275:132–180. [4] Uesugi M., Uesugi K. and Oka M. 2011. *Earth and Planetary Science Letters* 299:359–367. [5] Charles C. R. J. 2011. *Review of Scientific Instruments*, in press.
5410

## TEXTURES OF SINGLE CHONDRULES IN CR2 CHONDRITE NWA 801 BY MEDICAL X-RAY MICRO-COMPUTED TOMOGRAPHY

C. R. J. Charles¹, P. J. A. McCausland². J. Umoh³, D. Holdsworth³, D. W. Davis¹, D. Gregory⁴, K. Tait⁴ and I. Nicklin⁴. ¹Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, ON, Canada. E-mail: christopher.charles@utoronto.ca. ²Department of Earth Sciences, University of Western Ontario, London, ON, Canada. ³Robarts Imaging Institute; University of Western Ontario, London, ON, Canada. ⁴Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada.

**Introduction:** "Armored" chondrules contain one or more concentric rings of Fe-Ni metal on their exterior surfaces or throughout their interiors. These chondrules are found in the CR2-class of carbonaceous chondrites, and the 3D distributions of metal and silicates inside these chondrules are important to constrain the nebular environment where they formed. Petrography suggests that many CR2 chondrules are remnants of precursor chondrules that were incorporated into dustballs, which were remelted in one or more episodes in a dusty nebular setting [1]. X-ray computed tomography (CT) is an ideal way to test this idea, since 3D renderings of chondrule textures can be obtained nondestructively. Synchrotron radiation has been very successful for imaging chondrule textures due to its very high spatial resolutions (approximately 1 µm; i.e., [2]–[4]). However new laboratory-based medical CT scanners have received less attention, although these instruments offer high resolutions, rapid data acquisition and processing times, the ability to image large numbers of samples, and are more widely available than synchrotron facilities. Here we investigate the use of two General Electric CT scanners, the Locus and eXplore speCZT, for mapping the 3D textures of single chondrules removed from the CR2 chondrite NWA 801.

**Experimental:** Automated freeze thaw disaggregation was used to extract 523 individual mm-sized chondrules and chondrule fragments from 12 g of NWA 801 [5]. All objects were sieved and grouped by size onto glass mounts with up to 12 objects/mount. 3D renderings were obtained for all objects along with enstatite, olivine, augite and Fe "standards" on the eXplore speCZT through 900 views at 16 ms exposure (110 kVp, 32 mA) at 50 µm/voxel. One mount containing several large chondrules was imaged on the Locus through 900 views at a 4500 ms exposure (80 kVp, 0.45 mA) at 20 µm/voxel. CT grayscale numbers from both scanners were converted to Houndsfield units (HU) and all final images were manipulated and examined by GE Microview and custom MatLab scripts.

**Results:** Twelve percent of chondrules contain distinct multiple Fe-Ni rims and 75% showed only a single Fe-Ni rim usually on the exterior surface of the chondrule. A total of 13% of the objects were either "metallic" chondrules or large Fe-Ni blebs of approximately 1 mm or less in diameter. This suggests that enveloping compound chondrules [1] in NWA 801 formed at about the same frequently as the large Fe-Ni blebs, but that both these objects formed less frequently as noncompound chondrules. Thus the majority of NWA 801 chondrules are not products of compound mergers.

**References:** [1] Rubin A. E. 2010. *Geochimica et Cosmochimica Acta* 74:4807–4828. [2] Ebel D. S. and Rivers M. 2007. *Meteoritics & Planetary Science* 39:531–544. [3] Fredrich J. M., Wignarajah D. P., Chaudary S., Rivers M. L., Nehru C. E. and Ebel D. S. 2008. *Earth and Planetary Science Letters* 275:132–180. [4] Uesugi M., Uesugi K. and Oka M. 2011. *Earth and Planetary Science Letters* 299:359–367. [5] Charles C. R. J. 2011. *Review of Scientific Instruments*, in press.

5521

## DATING OF SECONDARY MINERALS IN NAKHLITES

B. L. A. Charlier¹, A. W. Needham² and M. M. Grady²,³. ¹Department of Earth and Environmental Science, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK. ²PSSRI. The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK. ³Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. E-mail: m.m.grady@open.ac.uk.

**Introduction:** Nakhlites are a group of Martian clinopyroxenites, currently 13 in number, that have a tightly-constrained crystallization age of 1320 ± 40 Ma [1]. They are thought to emanate from either a single lava flow, or closely-allied series of flows [2], and following their crystallization, have experienced aqueous alteration. Secondary alteration products include clay minerals, carbonates, sulfates and halite, which form complex assemblages and intergrowths. It is not clear what the relationship is between the different minerals: they may have formed by gradual evaporation following a single episode of fluid incursion [3], or over an extended period of time following several episodes of aqueous activity. The latter case is supported by spectral data from widespread regions of the Martian surface, where overlying units of secondary minerals have been employed to produce a relative chronology [4]. Direct measurement of the age of the secondary products in the meteorites has been difficult—the minerals are fine-grained and not easy to separate from their host silicates. Where results have been obtained, they indicate formation ages of around 600 Ma for phyllosilicates [5]. We have used Rb-Sr dating of Nakhla and Y 000593 in an attempt to determine a series of ages for different components within the meteorites.

**Technique:** We carried out a sequence of leaches on samples of between 200 and 500 mg powdered whole rock meteorite. The sequence was designed to remove increasingly insoluble components, and started with cold water, followed by hot water, cold then hot 0.025 M HCl, cold then hot 0.25 M HCl, then hot 2.5 M HCl, hot 6 M HCl and finally hot HNO₃-HCl. Each leachate was split, with one aliquot analyzed by ICP-MS to determine Rb and Sr abundances, and the remainder taken for Sr isotope analysis by TIMS.

**Results:** Were a bit bizarre, to say the least, with a maximum ⁸⁷Sr/⁸⁶Sr ratio in the cold water leachate from Nakhla of 0.7574. Ratios of this magnitude are more usually associated with evolved rocks rather than soluble components within basalts. The ⁸⁷Sr/⁸⁶Sr decreased with increasing acid strength, converging on a value around 0.702, compatible with an age of > 1000 Ma.

**Discussion:** Our modeling of the components extracted by sequential leaching suggests that halite will be dissolved in cold water, phyllosilicates will start to give up their loosely-bound ions in weak HCl, with those more firmly bound dissolving out in stronger HCl. Carbonates (mainly siderite) will be removed by hot 0.25 M HCl, then the silicates will start to be attacked by 6 M HCl. Duplicate measurements from two separate splits of Nakhla gave elevated values of ⁸⁷Sr/⁸⁶Sr in the cold water extract thought to be associated with halite. Further interpretation will be forthcoming in the fullness of time.

**References:** [1] Nyquist L. E. et al. 2001. *Space Science Reviews* 96:105–164. [2] Treiman A. H. 2005. *Chemie der Erde* 65:203–270. [3] Bridges J. C. and Grady M. M. 2001. *Earth and Planetary Science Letters* 176:267–279. [4] Bibring J.-P. et al. 2006. *Science* 312:400–404. [5] Swindle T. D. et al. 2000. *Meteoritics & Planetary Science* 35:107–115.
## CARBONS IN ACAPULCO AND LODRAN AT THE NANOSCALE: COMPARISON WITH EXPERIMENTAL ANALOGS

E. Charon¹,², J. Aléon² and J. N. Rouzaud¹. ¹Laboratoire de Géologie de l'Ecole Normale Supérieure, UMR CNRS 8538, 24 rue Lhomond 75005 Paris France. ²Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS/IN2P3 UMR 8609, 91405 Orsay Campus France. E-mail: charon@geologie.ens.fr.

**Introduction:** Acapulcoites and Lodranites (A-L) are very primitive partially differentiated objects and can bring essential insights on planetesimal accretion and differentiation within the first 1-2 Myr of the solar system [1]. Here, we study the origin and evolution of carbons in A-L as tracers of early differentiation stages. The study is focused on the relationship between carbons and Fe-based metal. We coupled, on the same micrometer-sized grains, structural characterization by Raman uspectrometry and mapping and High Resolution TEM on Focused Ion Beam (FIB) sections. The carbon phases of A-L are systematically associated with metal and are partially graphitized [2]. In order to show the possible catalytic role of iron on the graphitization, experimental analogs have been produced using blends of 10% saccharose-based chars analogous to the insoluble organic matter (IOM) of chondrites and 90% iron powder, heated between 650 and 1600 °C and compared to carbons in Acapulco and Lodran.

**Results:** Raman spectra corrected from polishing effects reveal as strong structural heterogeneity at the micrometer scale (defect bands of various intensities). Raman mapping shows that carbons in contact with metal are more graphitized, suggesting a catalytic effect of metal on the graphitization of organic matter, thus allowing formation of graphite at temperature <1200 °C. Experimental analogues completely reproduce the range of structural heterogeneity and relationships with metal observed in Acapulco and Lodran.

HRTEM results specify iron-carbon interactions from the micrometer to the nanometer scales. Again micro- and nano-structures observed in Acapulco and Lodran are correctly reproduced in our pyrolysis experiments. Furthermore, the degree of order of carbons and the morphology of metal nano-inclusions in carbons suggest different mechanisms of graphitization as a function of temperature. At low temperature (650 °C), iron diffusion is limited (solid-solid interactions) and mesoporous turbostratic carbons and carbides can be formed. At higher temperature, iron becomes liquid and its diffusion is favored. In both cases 'catalytic' graphitization is favored by the presence of iron and sensu stricto graphite can be obtained at temperatures as low as 1200 °C.

**Conclusion:** Our experimental study shows that carbon structural heterogeneities in Acapulco and Lodran meteorites result from the catalytic graphitization by Fe-Ni metal of an organic precursor having the typical structure of chondritic IOM and probably not from the preservation of preaccretional heterogeneities [3].

**References:** [1] Touboul et al. 2009. *Earth and Planetary Science Letters* 284:168-178. [2] Charon et al. 2009. *Meteoritics & Planetary Science* 44:A48. [3] El Goresy A. et al. 2005. *Geochimica et Cosmochimica Acta* 69:4535-4556.

## O ISOTOPIC CONSTRAINTS ON THE ORIGIN OF Mg-RICH OLIVINES FROM ALLENDE CHONDRULES: PLANETARY OR NOT ?

M. Chaussidon¹, A. Gurenko¹, T. H. Luu¹, C. Rollion-Bard¹. ¹CRPG-CNRS, BP 20, 54501 Vandoeuvre-lès-Nancy, France. chocho@crpg.cnrs-nancy.fr.

**Introduction:** If chondrites parent bodies accreted late, ≈4-5 Myr after the condensation/crystallization of type B CAIs (when $^{26}$Al/$^{27}$Al = 5.2 × 10⁻⁵) as imposed by chondrule ages, there are several evidences that planetesimal accretion (up to sizes of ≈1000 km) started very early, perhaps nearly at the same time than CAIs formed [1]. Developments of high precision Mg isotopic analysis by multi-collector ion microprobe allow to determine both the slopes ($^{26}$Al/$^{27}$Al) and the initial (δ$^{26}$Mg$_0$) of $^{26}$Al isochrons in chondrules and CAIs. This can be used to test the homogeneous distribution of $^{26}$Al and Mg isotopes in the accretion disk at the time of formation of CAIs [2] and to try to calculate model $^{26}$Al ages (under the assumption of an homogeneous distribution) for chondrule precursors [2] or for minerals devoid of Al such as Mg-rich olivines in chondrules [3]. This suggests that some of the chondrule precursors and Mg-rich olivines were formed very early, within 1 Myr or less than CAIs [2, 3]. One possibility would be that these Mg-rich olivines are precursors of type I chondrules and could be the fragments of the mantle of pre-existing disrupted planetesimals [4]. In the present study we explore what constraints could be derived on the origin of Mg-rich olivines in Allende (either in type I chondrules or isolated in the matrix) from high precision measurements of their O isotopic compositions and from their major and trace elements concentrations.

**Experimental:** The O isotopic compositions were measured with the CRPG-CNRS (Nancy) ims 1270 and ims 1280HR2 multi-collector ion microprobes. In each olivines numerous (from 10 to 25) spots were made in order to reach an analytical precision on the level of ± 0.01-0.02‰ (2σ) on $^{17}$O excesses relative to mass fractionation (i.e., $\Delta^{17}$O).

**Results and Discussion:** Mg-rich olivines in type I chondrules from Allende cluster around a few modes (less than 10) of $\Delta^{17}$O values ranging from -7.5 to 0‰. They do not show a continuum of $\Delta^{17}$O values contrary to bulk $\Delta^{17}$O values for Allende type I chondrules [5]. Bulk $\Delta^{17}$O values are likely the result of variable isotopic exchange with the nebular gas during chondrule melting. In most cases Mg-rich olivines appear relict (predating chondrule melting) from their $\Delta^{17}$O values. The most populated mode for Mg-rich olivines is at $\Delta^{17}$O = -5.56 ± 0.09‰. Within a given mode of $\Delta^{17}$O values, a large range of mass fractionation (up to ≈ 6‰ for $\delta^{18}$O values) is observed. This is consistent with previous (but less precise) measurements [4]. Correlations between $\Delta^{17}$O, $\delta^{18}$O, major and trace element concentrations, allow to better constrain the origin of the olivines and to test the possibility that they originate from a restricted number of planetesimals which differentiated very early in the disk.

**References:** [1] Dauphas N. and Chaussidon M. 2011. *Annual Review of Earth and Planetary Sciences* 39:351-386. [2] Villeneuve J. et al. 2009. *Science* 325:985-988. [3] Villeneuve J. et al. 2011. *Earth and Planetary Science Letters* 301:107-116. [4] Libourel G. and Chaussidon M. 2011. *Earth and Planetary Science Letters* 301:9-21. [5] Clayton R. N. et al. 1983. In "Chondrules and their Origins" LPI 37-43.
Ca ISOTOPIC ANALYSIS AS A TOOL FOR EXPLORING GENETIC RELATIONSHIPS AMONG ACHONDRITES

H. -W. Chen¹, T. Lee¹,², D. -C. Lee¹ and J. -C. Chen¹. ¹Institute of Earth Sciences, Academia Sinica. E-mail: typhoon@asiaa.sinica.edu.tw.
²Institute of Astronomy and Astrophysics, Academia Sinica.

**Introduction:** Lord Kelvin would probably put meteoritics as a "stamp collection" science. In this paper we aim to evaluate the potential of helping this endeavor by using the widespread $^{48}$Ca anomalies.

**Method:** Ca was extracted by conventional cation exchange. For each run 2 µg Ca was analyzed by double filament TIMS. Four runs were binned to yield one grand mean that is shown in Fig. 1. NIST SRM 915a was used as the normal standard. Two standard deviations of the population (2σ) consisting of 18 such grand means were measured over 6 months to test our long term reproducibility. They were found to be 0.87, 0.13, 4.6, and 0.42ε for $^{40}$Ca/$^{44}$Ca, $^{43}$Ca/$^{44}$Ca, $^{46}$Ca/$^{44}$Ca, and $^{48}$Ca/$^{44}$Ca after correcting for instrumental fractionation by normalizing $^{42}$Ca/$^{44}$Ca to 0.31221. A plagioclase sample from the Uzen volcano, Japan, was processed the same way as meteorites samples. Fig. 1 plots the deviation of $^{48}$Ca/$^{44}$Ca relative to the normal which is represented by the average of all 18 grand means of SRM 915a. Each symbol is the grand mean of 4 runs. The two Uzen results agree with each other and normal within 0.2ε. For each sample we take the long term reproducibility or 2σ of 4 runs which is greater. To further test our ability to resolve epsilon level of isotope shift.

**Ca-48 anomalies:** Two to four meteorites from each of the five classes of achondrites were studied. Meteorites in the same class seem to share the same characteristic ε$^{48}$Ca isotopic shift. Ureilite, diogenite, angrites, eucrites, and Martian meteorites show ε$^{48}$Ca of -2.0, -1.6, -1.2, -0.9 and -0.1ε respectively. Previously δO were used most successfully in classifying meteorites. Our preliminary data show that ε$^{48}$Ca is probably as effective as δO. Moreover, ε$^{48}$Ca may carry different record than δO. An interesting example is ureilite. Among achondrite, ureilite was thought to be related to carbonaceous chondrites, indeed, their δO fall on the same 1:1 line. However, all four ureilites have ε$^{48}$Ca around -2±0.5ε while the only whole rock ε$^{48}$Ca data for carbonaceous chondrite seems to show effect of opposite direction (+5±2ε) [1].

**Reference:** [1] Chen J. H. et al. 2011. Abstract #2440. 42nd Lunar and Planetary Science Conference.

<figure><img src="image_7.png" /><figcaption>Fig. 1.</figcaption></figure>

PLANAR DEFORMATION FEATURES IN QUARTZ FROM THE XIUYAN CRATER, CHINA

M. Chen¹, C. Koeberl², W. Xiao¹, X. Xie¹ and D. Tan¹. ¹Guangzhou Inst. Geochem., Chinese Academy of Sciences, Guangzhou 510640, China. E-mail: mchen@gig.ac.cn. ²Depart. Lithos. Res., Univ. Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

**Introduction:** The 1.8-km-diameter Xiuyan crater is located in the Liaodong Peninsula in northeastern China. The crater is exposed in a Proterozoic metamorphic rock complex composed of granulite, hornblendite, gneiss, tremolite marble, and marble. A drilling positioning at the center of the crater reveals the geological structure and stratum of the crater [1]. The bottom at the center of the crater covers about 100 m thick lacustrine sediments underlain by 188 m thick crater-fill breccia. A layer of impact breccia composed of clasts of granulite, gneiss, hornblendite and fragments of glass as well as clastic matrix, occurs at the lower part of the breccia units in the depth interval from 260 to 295 m. We have examined abundant planar deformation features (PDFs) in quartz from the impact breccia.

**Results and Discussion:** Quartz with multiple PDFs was identified in the fine-grained matrix and within the clast of granulite. One to five sets of PDFs are observed in a single quartz crystal. A quantity of 70 quartz grains from five thin sections made from the clasts of granulite in the impact breccia recovered at the depth of 290 m were measured in detail by using a Universal stage to determine the orientations of PDFs relative to the optical axis. Total 13 forms of PDFs correspond to rational crystallographic orientations of quartz have been indexed, and these orientations of PDFs include the forms with miller indices of e{1014}, ω{1013}, π{1012}, ξ{1122}, r, z{1011}, s{1121}, p{2131}, {2241}, {3141}, t{4041}, x{511}, m{100} and a{110}. PDFs parallel to the basal (0001) plane is absent. 44% of the quartz grains contain 3 sets of PDFs, and other 40% contain 2 sets of PDFs. Of all the PDFs measured, 11.2% of them, which did not correspond to rational crystallographic orientations of quartz, were not indexed. The most abundant PDFs are rhombohedron forms of π{102}, ω{103}, and r/z{101} with frequency of 33.5%, 22.3% and 9.6%, respectively. The predominant occurrence of PDFs {102} + {103} and the absence of PDFs parallel to (0001) indicate a high intensity shock of the samples [2-4]. A predominant PDF form of {102} in quartz suggests a shock pressure >20 GPa [4]. The occurrence of PDFs in quartz from the impact breccia provides crucial evidence for shock metamorphism of target rocks and confirms the impact origin of this crater.

**Acknowledgments:** This research was supported by CAS (Kzcx2-yw-140), NNSF of China (40872041) and President Foundation of CAS. The University of Vienna provided partial assistance to M.C. during a research visit in Vienna.

**References:** [1] Chen M. et al. 2010. *Chinese Science Bulletin* 55:1777-1781. [2] Robertson P. and Grieve R. A. F. 1977. In *Impact and explosion cratering*, by Roddy D. J. et al. Pergamon Press, New York. 687-702. [3] Stöffler D. and Langenhorst F. 1994. *Meteoritics & Planetary Science* 29:155-181. [4] Grieve R. A. F. et al. 1996. *Meteoritics & Planetary Science* 31:6-35.
5325

A NEW METEORITE FIND IN BOU AZARIF, ALNIF AREA (SOUTH MOROCCO)

H. Chennaoui Aoudjehane¹,², A. Jambon², N. Larouci¹,² and H. Gako¹.
¹Laboratoire GAIA, Equipe patrimoine géologique du Maroc, Université Hassan II Casablanca Faculté des Sciences Ain Chock BP 5366 Maārif Casablanca Maroc. E-mail: h.chennaoui@fsac.ac.ma.
²UPMC-PARIS 6, ISTEP 4 place Jussieu, 75005 Paris France. CNRS UMR 7193.

During a field trip in the south of Morocco in December 2010, which aimed to collect the coordinates of two recent falls in the Morocco-Algerian border, we visited a minerals and fossils store in Alnif (South of Morocco). The dealer Mohamed Bouiri showed us a sample of a badly weathered meteorite that he claimed to know the exact provenance. Then he called the finder of the meteorite Hassan Belaid that agreed to accompany us to the find place a few kilometers from Alnif. We collected many samples with the coordinates N 31°09.386'; W 005°09.157', in less than one hour, on a hillside. The finder estimates that he collected about 100 kg of this meteorite that is regularly discovered after rain showers. The fall is old as the samples are recovered by sediments that are eroded by the rain. The weathering grade provides evidence of this old age.

We collected SEM images (UPMC ISteP) to see the size of minerals, their layout, and the mode. Listed minerals are olivine, pyroxene, plagioclase, weathered kamacite, taenite less weathered than kamacite, troilite, phosphates (chlorapatite and merilite).

EMP analyses (SX100- UPMC ISteP) on olivines, pyroxenes and plagioclases: Olivine Fa 18.2; Pyroxene Fs 17.9, Wo 2.3; that allowed us to classify the meteorite as an ordinary chondrite H5. The shock intensity is S3 and the weathering grade is W4. The magnetic susceptibility is $log \chi = 4.75$.

By searching in the Meteoritical Bulletin database, we found that the name "Alnif" has already been given to an 8 kg sample, purchased in April 1992 by A. Carion in a mineral shop in Rissani, Morocco. The seller said it had been collected with trilobites near Oum-Jrane, 60 km south of Alnif. Microprobe analyses of Alnif meteorite yield: olivine, Fa19.3; pyroxene Fs17.3, Wo1.7; plagioclase, An10.6; that corresponds to an ordinary H5 chondrite, shock stage S2; weathering grade W2; submitted by the MNHN Paris, in 1998.

Even for an ordinary chondrite, it is important to avoid the NWA nomenclature whenever possible. This meteorite will have a proper geographic name that could be "Bou Azarif" (Bou Izarif) as the hill is named in the topographic 1/100,000 map of Alnif. It will be added to meteorites that have been submitted by a Moroccan French team, as Benguerir [1], Al Haggounia [2], Tamdakht [3], with a proper geographic name.

It could be interesting to measure the terrestrial age of this meteorite and try to find its history, if it is a fossil meteorite, how deep are the samples, to compare it with the Alnif meteorite in order to assess whether they are paired stones.

**References:** [1] Chennaoui Aoudjehane H. et al. 2006. *Meteoritics & Planetary Science* 41:231-238. [2] Chennaoui Aoudjehane et al. H. 2007. Abstract #5329. *Meteoritics & Planetary Science* 42. [3] Chennaoui Aoudjehane H. et al. 2009. Abstract #5038. *Meteoritics & Planetary Science* 44.

5078

THE PATHS OF ICE GRAINS IN THE SOLAR NEBULA: IRRADIATION AND THE FORMATION OF ORGANICS

F. J. Ciesla¹, S. A. Sandford² and R. M. Mastrapa².
¹Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637. E-mail: fciesla@uchicago.edu.
²NASA-Ames Research Center, Moffett Field, CA 94035.

**Introduction:** Organic compounds have been found in a number of meteorites, leading many to suggest that Earth's prebiotic material was delivered through the accretion of cometary and chondritic-like planetesimals. While formation of organic molecules during aqueous alteration of a parent body can occur [1], the D/H ratios in these compounds have led many to investigate a low temperature origin [2]. Among the favored pathways is the UV irradiation of ice-mantled grains, where photons break up molecules in solid grains, leaving behind reactive ions and radicals, which form more complex species. Most studies have considered an interstellar setting for such reactions [e.g., 3, 4]. Here we explore whether ice-mantled grains in the outer solar nebula could have absorbed enough UV photons to contribute significantly to the organic inventory of the solar system.

**Model:** We have developed a particle-tracking model that calculates vertical and radial paths of dust particles through a diffusive protoplanetary disk [5, 6]. This allows us to determine the amount of time that particles spend at different locations throughout an evolving disk. By assuming an incident flux of UV radiation on the disk, we can then determine the flux wherever the particles reside and determine an irradiation history (number of incident UV photons) for each particle.

**Results:** We tracked the motions of 5000 ice grains released from the midplane of a disk where temperatures were <50 K—low enough for molecular species like H₂O, CO₂, NH₃, and CH₃OH to be frozen onto grain surfaces—for a period of $10^6$ years. We find that, because the UV flux is rapidly attenuated through the disk as small dust particles readily absorb the incident radiation, ices only see significant fluences of UV photons when lofted to high altitudes in the disk. Thus only small, <10 µm grains, are exposed to large fluences of UV photons. However, in many cases, these fluences can be large enough to lead to the production of significant amounts of organic molecules.

**Discussion:** Throop (2011) [7] suggested organics could have been produced in the outer solar nebula if the Sun formed in an Orion-like setting, such that a nearby massive star would have irradiated the disk at $10^6$ × the current interstellar UV flux ($G_0$). In that model, UV photons were assumed to be evenly distributed among all ice particles at a given location in the disk, and as such, high UV fluxes were necessary to produce high yields of organics. We find that turbulence would have lofted small grains to high altitudes, exposing many to enough UV radiation that significant organic synthesis could have occurred, even at low incident UV fluxes (< $10^3 G_0$), such as those expected for a young star irradiating its own disk or one in a small cluster. This suggests organic synthesis can occur in most protoplanetary disks, meaning organic compounds should be commonly found in young planetary systems.

**References:** [1] Peltzer E. T. et al. 1984. *Advances in Space Research* 4:69-74. [2] Sandford S. A. et al. 2001. *Meteoritics & Planetary Science* 36:1117-1133. [3] Bernstein M. P. et al. 2002. *Nature* 416:401-403. [4] Muñoz Caro G. M. et al. 2002. *Nature* 416:403-405. [5] Ciesla F. J. 2010. *The Astrophysical Journal* 723:514-529. [6] Ciesla F. J. 2011. *The Astrophysical Journal*. Submitted. [7] Throop H. B. 2011. *Icarus* 212:885-895.
## PETROGRAPHY AND CHEMISTRY OF DJERFISHERITE IN ENSTATITE CHONDRITES

P. L. Clay¹, H. Busemann¹ and A. El Goresy². ¹SEAES, University of Manchester, M13 9PL, UK. ²BGI, Universität Bayreuth, Germany. E-mail: Patricia.Clay@manchester.ac.uk.

**Introduction:** Establishing a precise chronology of events in the early solar system is crucial for understanding its evolution from parent molecular cloud to the planetary bodies. Various chronometers can be applied to date formation, thermal resets, and differentiation. While short-lived chronometers date events in the first few tens of Ma with a high chronological resolution, they require calibration with a long-lived chronometer for absolute ages. However, mineral phases that can be dated simultaneously with both a long- and a short-lived system are rare. The K-Cl-bearing sulfide djerfisherite [1, 2], found in several E-chondrites, offers such an opportunity with the application of short (I-Xe)-and long-lived (Ar-Ar, Rb-Sr) chronometers. It is a good target for these isotopic systems, as correlated release of ¹²⁹Xe* excess and ⁴⁰Ar* has previously been shown for St. Mark's (EH5), where djerfisherite is one suspected carrier of Ar and Xe [3, 4]. Here, we present initial petrographic and chemical analyses of djerfisherite grains that will be extracted from two E chondrites for correlated I-Xe and Ar-Ar analysis, with a further subsection reserved for Rb-Sr analysis.

**Petrography & Mineral Chemistry:** Petrography, texture, and mineral chemistry of several djerfisherite grains have been investigated using reflected light microscopy, BSE imaging, element mapping, and quantitative EPMA analysis in ALHA77295 ("A77", EH3), and Sahara 97096 ("S97", EH3). Djerfisherite in A77 is present in several forms: matrix grains, included in metal-troilite and accreted around metal-troilite, idiomorphic grains, as well as larger veins; forms previously described for oldhamite distribution in A77 [5]. Chemically, these grains are relatively indistinct, with consistent mineral-chemical formulae, represented by: (K, Na)5.6-6.1 (Fe, Ni, Cu)25.4-27, S27 Cl1.0-1.4, consistent with previous studies. BSE images reveal chemically unzoned and pristine grains. S97 contains less idiomorphic djerfisherite than A77, and shows the characteristic Qingzhen 'breakdown' reaction into porous troilite and other phases, previously described in Qingzhen and Y-691[6].

**Results & Discussion:** Idiomorphic djerfisherite in A77 is pristine, primary djerfisherite from nebular condensation, whilst the more common porous 'broken down' djerfisherite of S97 is disturbed, due most likely to a thermal event at ~2 Ga [7]. However, chemically, there is minimal difference between the two pristine djerfisherite populations in both meteorites. Evidence for further disturbances of other sulfide phases, such as eutectic melt textures, as reported in paired SAH 97072 [8], are encountered in S97, again supporting a more complex history for this sample related to thermal metamorphic episodes. Moreover, these textural features could provide additional evidence that these EH3s originated from and evolved in different parent bodies [5].

**References:** [1] Fuchs L. H. 1966. *Science* 153:166-167. [2] Lin Y. and El Goresy A. 2002. *Meteoritics & Planetary Science* 20:577-599. [3] Busemann, H. et al. 2002. Abstract. *Meteoritics & Planetary Science* 37:A28. [4] Busemann H. et al. 2002. *Geochimica et Cosmochimica Acta* 66: A112. [5] Gannoun A. et al. 2011. *Geochimica et Cosmochimica Acta* 75:3269-3289. [6] El Goresy A. 1985. *Meteoritics* 20:639. [7] Torigoye N. and Shima M. 1993. *Meteoritics* 28:515-527. [8] Lehner S. W. et al. 2010. *Meteoritics & Planetary Science* 45:289-303.

## IODINE AND XENON SYSTEMATICS OF GRA 06129

J. L. Claydon¹, S. A. Crowther¹, C. K. Shearer² and J. D. Gilmour¹. ¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK, E-mail: jennifer.claydon@postgrad.manchester.ac.uk. ²Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.

**Introduction:** GRA 06129 (GRA 9) is an ancient ungrouped achondrite that has experienced a series of processes on its parent asteroid [1]. Our previous analyses of unirradiated GRA 9 [1] showed excess ¹²⁹Xe from decay of ¹²⁹I, either *in situ* or inherited, and ¹³¹⁻¹³⁶Xe from fission of ²⁴⁴Pu. Excess ¹²⁹Xe was thought to be hosted in a minor phase. An I-Xe age of ~75 Ma after Shallowater and an evolved trapped component have been reported [2].

**Experimental:** Whole rock fragments (~1 mg) of GRA 9 were neutron irradiated (~10¹⁹ n cm⁻²) converting the stable isotope ¹²⁷I to ¹²⁸Xe. Following irradiation the samples were laser step-heated at high resolution and Xe isotopes analyzed using RELAX [3,4]. ¹³¹Xe is produced in the irradiation from Ba or Te and ¹³¹⁻¹³⁶Xe are produced by neutron-induced fission of ²³⁵U, allowing some mineralogical information about phases releasing gas at any temperature to be determined. A correlation between ¹²⁹Xe and ¹²⁷I during step-heating of a sample would indicate that some of the ¹²⁹Xe had been derived from *in situ* decay of ¹²⁹I. When this is the case, the ratio of excess ¹²⁹Xe and ¹²⁷I corresponds to the closure age of the material [5, 6].

**Results:** Three samples of GRA 9 have been analyzed producing 116, 64 and 60 individual releases respectively. High concentrations of excess ¹²⁸Xe (corresponding to 10–30 ppm of I) released at low temperatures are attributed to Antarctic contamination [7]. Excess ¹³¹Xe released at higher temperatures corresponds to Ba concentrations of 10–50 ppm, consistent with an origin in plagioclase [1].

A series of distinct high temperature releases were observed; each with contributions from Ba- and I-derived Xe alongside fission xenon and a trapped component. The systematics suggest an “original” phase with a consistent I/Ba ratio overprinted by contributions from a later phase containing iodine alongside U/Pu. Given the mineralogy of GRA 9, this may be attributed to the addition of (U/Pu-bearing) apatite to (Ba-rich) plagioclase.

Small ¹²⁹Xe excesses were observed alongside these releases, but no overall correlation with I-derived ¹²⁸Xe was observed. This discordant behavior suggests endmember models involving either inheritance of excess ¹²⁹Xe during secondary phase formation after complete decay of ¹²⁹I, or production of distinct secondary phases in a series of separate events distributed through time. In neither case can a closure age be reliably determined.

**References:** [1] Shearer C. K. et al. 2010. *Geochimica et Cosmochimica Acta* 74:1172-1199. [2] Bajo K. et al. 2010. Abstract. *Meteoritics & Planetary Science* 45:A5089. [3] Gilmour J. D. et al. 1994. *Review of Scientific Instruments* 65:617-625. [4] Crowther S. A. et al. 2008. *Journal of Analytical Atomic Spectrometry* 23:921-1044. [5] Brazzle R. H. et al. 1999. *Geochimica et Cosmochimica Acta* 63:739-760. [6] Gilmour J. D. et al. 2006. *Meteoritics & Planetary Science* 41:19-31. [7] Heumann K. G. et al. 1987. *Geochimica et Cosmochimica Acta* 51:2541-2547.
5010

OXYGEN AND NITROGEN ISOTOPES IN THE EARTH AND THE SUN

R. N. Clayton. Enrico Fermi Institute, Department of Chemistry, Department of the Geophysical Sciences, University of Chicago, IL, USA. E-mail: r-clayton@uchicago.edu.

By analogy with CO, it has been suggested that photochemical self-shielding may have been important for N₂ in the early solar system [1]. Self-shielding in CO has led to an enrichment on Earth, relative to the Sun and solar nebula, in the rare heavy isotopes of oxygen by about 6% [2]. Nitrogen isotope measurements in the Genesis solar wind collectors imply an enrichment of ¹⁵N on Earth of about 40%. [3]. A similar enrichment in the heavy nitrogen isotope was not seen in ammonia on Jupiter [4], implying that the photochemical process operated in the inner solar system, and also implying that the young Sun was the source of UV radiation. An obvious question is: why is the nitrogen isotope effect so much larger than that in oxygen? A possible solution lies in the nature of the photolysis products in the two cases:

$$CO(^{1}\Sigma) \rightarrow C(^{2}\text{P}) + O(^{3}\text{P}) \text{ (both atoms in the ground state)} \text{ [5] (1)}$$

$$N_{2}(^{1}\Sigma) \rightarrow N(^{4}\text{S}) + N(^{2}\text{D}) \text{ (one atom in an excited state)} \text{ [6]. (2)}$$

The subsequent “trapping reactions” are much faster for the excited N (²D) than those for the ground-state atoms (C (³P), O (³P) and N (⁴S)). The first (and rate-limiting) step in trapping is probably reaction with the abundant molecular hydrogen:

$$N + H_{2} \rightarrow NH + H \text{ (3)}$$

$$O + H_{2} \rightarrow OH + H \text{ (4)}$$

It was shown [7] that a depletion of about a factor of five in ¹²C¹⁷O/¹²C¹⁶O and ¹²C¹⁸O/¹²C¹⁶O can be found in a molecular cloud, implying almost complete photodissociation of the rarer isotopologues in the cloud interior. If the same degree of dissociation applies also to ¹⁴N¹⁵N in the solar nebula, then the atom ratio ¹⁵N¹⁵D/¹⁷O is near unity. The implication is that the larger “isotopic anomaly” observed for terrestrial nitrogen relative to oxygen is not due to the primary photochemical process, and likely reflects the greater “trapping” reactivity of N (²D) relative to O (³P). The observed ratio of isotope effects is consistent with a trapping reaction temperature of about 1400K, and is inconsistent with lower temperatures, due to the large activation energy (and consequent large temperature dependence) for the oxygen trapping reaction.

Note that there is no large isotope effect in carbon, since its lower ionization potential leads to rapid isotope “scrambling”:

$$C + H^{+} \rightarrow C^{+} + H, \text{ and (5)}$$

$$^{12}\text{C}^{+} + ^{13}\text{C} \rightarrow ^{12}\text{C} + ^{13}\text{C}^{+}, \text{ (6)}$$

There are, of course, many measurements of ¹⁵N/¹⁴N ratios in solar system materials that are greater than the terrestrial atmospheric value, usually associated with high D/H ratios in organic materials. These have been interpreted as the result of low-temperature ion-molecule reactions [8,9] either in the solar nebula or in the precursor molecular cloud.

**References:** [1] Clayton R. N. 2002. *Nature* 415:860. [2] McKeegan K. D. et al. 2011. *Science* 332. in press. [3] Marty B. et al. 2011. *Science* 332. in press. [4] Owen T. et al. 2001. *The Astrophysical Journal* 553:L77. [5] Gaydon A. G. and Penney W. G. 1945. *Proceedings of the Royal Society* 183:374. [6] Walter C. W. et al. *Physical Review A* 50:2930. [7] Sheffer Y. et al. 2002. *The Astrophysical Journal* 574:L171. [8] Terzieva R. and Herbst E. 2000. *Monthly Notices Royal Astronomical Society* 317:563. [9] Charnley S. B. and Rodgers S. D. 2002. *The Astrophysical Journal* 569:L133.

5024

THE EFFECTS OF PLANETESIMAL COLLISIONS

G. S. Collins¹, T. M. Davison¹,² and F. J. Ciesla². ¹Impacts and Astromaterials Research Centre, Dept. Earth Science and Engineering, Imperial College London, SW7 2AZ, UK. E-mail: g.collins@imp-erial.ac.uk. ²Dept. of Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60430, USA.

**Introduction:** As planetesimals are expected to form via gentle aggregation of smaller bodies, the first generation of large solid bodies likely possessed significant (> 50%) porosity [1–3]. The compaction of a substantial volume of pore space can dramatically decrease the peak shock pressure and increase the post-shock temperature of impact-processed materials [4,5].

Critical to understanding the consequences of planetesimal collisions in the early solar system is quantification of (1) the disruption threshold for weak, porous first-generation planetesimals; (2) the evolution of planetesimal porosity with time through impact-induced compaction; and (3) the redistribution, retention and cooling of heated material in sub-catastrophic collisions. Here we simulate sub-catastrophic planetesimal collisions to late times, quantifying momentum transfer and compaction as well as the ejection and redistribution of impact heated material.

**Method:** We used the 2D iSALE hydrocode [6,7] to simulate sub-catastrophic head-on collisions between planetesimals. ANEOS-derived equation of state tables for dunite were used to represent the non-porous planetesimal material. Pore-space compaction was modeled using the improved epsilon-alpha porosity model [6,8]. Material strength was modeled according to [7] with parameters for weak rock. Target planetesimals 100 km and 500 km in diameter with a uniform initial temperature (300 K) and initial porosities of 0–50%, were modeled. Impacting planetesimals with diameters 0.1–0.3 times target planetesimal diameter, and with identical material properties, collided with the target at 0.1–7 km s⁻¹. The gravity field was updated periodically during the calculation using a self-gravity algorithm, inspired by [9].

**Results:** The compaction of pore space during a planetesimal collision increases shock heating and reduces ejection velocities relative to the non-porous case. Hence, if planetesimals are sufficiently porous, collisions can cause localized heating and, even in large sub-catastrophic collisions, the vast majority of the heated material is retained on the target planetesimal. As the energy of the collision approaches the disruption threshold, the fate of the heated material changes considerably, with important implications for post-collision thermal evolution. In small collisions, the small volume of heated material is buried beneath an insulating lens of breccia in the crater. In larger collisions, the heated material is localized within the impacted hemisphere, forming a deep plug beneath the impact site. Close to the disruption threshold, the heated material is distributed in a thin layer over the entire surface of the planetesimal. Secondary compaction occurs across the surface of the rear-side, which may reduce the potential for subsequent impacts to further heat the planetesimal.

**References:** [1] Wurm G. et al. 2001. *Physical Review E* 64:046301. [2] Cuzzi et al 2008. *The Astrophysical Journal* 687:1432–1447. [3] Johansen et al. 2007. *Nature* 448:1022–1025. [4] Zel'dovich, Y. B. and Raizer, Y. P. *Physics of shock waves and high-temperature hydrodynamic phenomena*. Academic Press, New York. 1966. [5] Davison T. M. et al. 2010. *Icarus* 208:468–481. [6] Wünnemann K., Collins G. S. and Melosh H. J. 2006. *Icarus* 180:514–527. [7] Collins G. S., Melosh H. J., and Ivanov B. A. 2004. *Meteoritics & Planetary Science* 39:217–231. [8] Collins G. S., Melosh H. J. and Wünnemann K. 2010. *International Journal of Impact Engineering*, in press. [9] Barnes J. E. & Hut P. 1986. *Nature* 324:446–449.
## ALLENDE 3509 HC-2: A COMPACT TYPE A—'F' INCLUSION WITH A SNAKE-LIKE MORPHOLOGY

H. C. Connolly Jr.<sup>1,2,3</sup>, J. R. Beckett<sup>4</sup>, G. R. Huss<sup>5</sup>, K. Nagashima<sup>5</sup>, E. D. Young<sup>6</sup>, K. Ziegler<sup>6</sup>, C. Ma<sup>4</sup> and G. R. Rossman<sup>4</sup>. <sup>1</sup>Dept. Physical Sci., Kingsborough Community College of CUNY, Brooklyn NY 11235 & Dept. Earth & Envir. Sci., The Graduate Center of CUNY, New York, NY 10016, USA. <sup>2</sup>Dept. Earth & Planet. Sci., AMNH, New York, NY 10024, USA. <sup>3</sup>LPL, Univ. of Arizona, Tucson, AZ 85721, USA. <sup>4</sup>Div. of Geol. & Planet. Sci., Caltech, Pasadena, CA 91125, USA. <sup>5</sup>Hawai'i Institute of Geophysics & Planetology, Univ. of Hawai'i at Mānoa, Honolulu, HI 96822, USA. <sup>6</sup>Dept. of Earth & Space Sci., UCLA, Los Angeles, CA 90095, USA. E-mail: chondrule@haroldconnolly.com.

**Introduction:** Calcium-, aluminum-rich inclusions (CAIs) are the first rocks to form in the solar system. Some inclusions are igneous and a very few of these (called F inclusions) experienced significant mass dependant fractionation in oxygen [1], and in some cases, other isotopic systems (FUN inclusions). Increasing the number and types of F inclusions will provide additional constraints on CAI formation and their formation environments. We report here on a Compact Type A (CTA) inclusion from Allende with an overall snake-like morphology, is an F inclusion, and initial <sup>26</sup>Al/<sup>27</sup>Al that was canonical.

**Analytical Methods:** The entire inclusion, HC-2, was recovered from a slab of Allende 3509 (USNM). Major and minor element abundances were determined with the Cameca SX-50 at the LPL UAz. Oxygen isotopes and Al-Mg isotopic systematics were analyzed for on the Cameca 1280 ion microprobe at the Univ. of Hawai'i, Mānoa [2]. Si isotopes were analyzed by LA-MC-ICPMS at UCLA.

**Results:** HC-2 has an overall morphology that is snake-like, wrapping throughout a 1.5 cm thick (total width is approximately 0.75 cm) section of the meteorite, inspiring it to be nicknamed The Snake. It has a Wark-Lovering rim on both sides, although the rim is thicker on one side. The inclusion has experienced some brittle deformation. HC-2 is dominated by spinel (Ti = 0.14–0.37; V = 0.44–0.64; Cr = 0.08–0.14; all wt%) and melilite (Ak = approximate 4 to approximate 50). Perovskites are numerous, ranging in size from sub-micron to approximately 0.5 mm. There appear to be two smaller (approximately 400 µm) CAIs that are mineralogically layered included.

SIMS analysis on spinel and melilite yield an isochron with an initial <sup>26</sup>Al/<sup>27</sup>Al of (4.9 ± 0.2) × 10<sup>-5</sup>. ÅÅ<sup>25</sup>Mg (variations from the standard in stable Mg isotope) range from approximately 5 to 13‰. Oxygen isotopes: Melilites have δ<sup>18</sup>O- δ<sup>17</sup>O- values that span approximately 10‰ and plot on the CCAM line near the TF line. Two perovskite grains are isotopically different with δ<sup>18</sup>O, δ<sup>17</sup>O of (in ‰) approximately -28, -31 in one and -40, -44 in the other. Overall, the spinels are <sup>16</sup>O-rich and show a clear mass fractionation of 4‰ amu<sup>-1</sup>, (δ<sup>18</sup>O = -34 to -42‰; δ<sup>17</sup>O = -41 to -45‰) with the overall trend to the right of the CCAM line.

**Conclusion:** HC-2 is clearly igneous. The reason for its unusual shape is not clear, but it must have formed while plastic. Based on the stable isotope data, HC-2 experienced considerable mass-dependent isotopic fractionation, most likely while molten and while <sup>26</sup>Al was present. We will compare our data to other 'F' inclusions to place new constraints on CAI formation and the environment in which they formed.

**References:** [1] Bullock E. S. et al. 2011. Abstract #2312. 42nd Lunar and Planetary Science Conference. [2] Kentaro et al. 2009. *Geochimica et Cosmochimica Acta.* [3] Shahara and Young. 2009. *Earth and Planetary Science Letters.*

## MAJOR AND TRACE ELEMENTS AND OXYGEN ISOTOPES IN DIFFERENTIATED COSMIC SPHERULES RELATED TO VESTA-LIKE ASTEROIDS

C. Cordier<sup>1</sup>, L. Folco<sup>1</sup>, C. Suavet<sup>1</sup>, P. Rochette<sup>2</sup> and C. Sonzogni<sup>2</sup>. <sup>1</sup>MNA, Siena, Italy. E-mail: cordier@uniis.it. <sup>2</sup>CEREGE, Aix-en-Provence, France.

Cosmic spherules (CSs) are extraterrestrial particles <2 mm in size, captured by the Earth's gravitational field and melted during atmospheric entry. Generally, CSs have geochemical affinities with chondritic material [1]. The ongoing investigation of large and unbiased collections of CSs from the South Pole Water Well and the Transantarctic Mountains (TAM) have, however, led to the identification of new types, including nine differentiated CSs [2, 3]. Here, we define the geochemical characteristics of this new type of CSs from the TAM collection [4] in terms of major (n = 11, EPMA), trace element (n = 6, LA-ICP-MS) and oxygen isotope (n = 15, IRMS) compositions.

The 11 differentiated CSs have high Fe/Mg ratios (0.6–1.6) and homogeneous Fe/Mn ratios (31 ± 4). Oxygen isotope compositions (δ<sup>18</sup>O = 14.37% to 20.12 ‰ and Δ<sup>17</sup>O = -0.47% to -0.65%) suggest a Vesta-like parent body. Systematic variations in refractory major and trace elements result from differences of the mineralogy of the spherule precursors. Type-1 spherules (n = 4) are akin to bulk eucrites, with high CaO and Al₂O₃ contents, flat REE patterns and high REE contents (La/Yb<sub>N</sub> = 0.4 to 1.0, REE<sub>N</sub> = 8.5 to 14 × CI). They derive from fine-grained precursors with typical eucritic mineralogy. Type-2 spherules (n = 4) have lower CaO and Al₂O₃ contents, higher MgO, FeO, and Sc contents, and strong LREE depletions (La/Yb<sub>N</sub> < 0.2) relative to eucrites. These compositions suggest large amounts of pigeonite in their precursors. Type-3 spherules (n = 2) have flat REE patterns with chondritic REE abundances (REE<sub>N</sub> = 1.5 to 2.2 × CI), and are enriched in Co (> 50 µg g<sup>-1</sup>) and Ni (> 17 µg g<sup>-1</sup>) relative to eucrites. Their composition suggests they derive from howardite-like precursors rich in orthopyroxene. The mineralogies proposed for the differentiated precursors are consistent with those expected for micrometeoroids deriving from the regolith of Vesta-like asteroids [5].

The combination of elemental and isotopic data shows that the elemental ratios and contents (Fe/Mg and Fe/Mn, REEs, Ni and Co, V, Zn) previously proposed to identify the differentiated CSs and their parent body [3] are suitable, provided that the mineralogical control is understood. Differentiated CSs deriving from pigeonite-rich precursors (Type 2) tend to have slightly lower Fe/Mg and Fe/Mn ratios and higher V contents than basaltic eucrites, whereas large amount of opx in spherule precursor may result in lower Fe/Mg and higher Ni and Co contents.

The relative frequency of Vesta-like micrometeorites in the TAM micrometeorite collection (1.6%) is consistent with the proportion amongst meteorites of eucrites and howardites (1.8%), which are the main constituents of the regoliths of Vesta-like asteroids.

**Acknowledgments:** This work was supported by the PNRA and by the EU-funded ORIGINS Marie Curie Action.

**References:** [1] Engrand C. and Maurette M. 1998. *Meteoritics & Planetary Science* 33:565–580. [2] Taylor S. et al. 2007. *Meteoritics & Planetary Science* 42:155–304. [3] Cordier et al. 2011. *Geochimica et Cosmochimica Acta* 75:1199–1215. [4] Rochette P. et al. 2008. *Proceedings of the National Academy of Sciences* 105:18206–18211. [5] Burbine T. H. et al. 2009. *Meteoritics & Planetary Science* 44:1331–1341.
THE GEOCHEMICAL FRACTIONATION RECORDED BY CHONDRITIC GLASS COSMIC SPHERULES DURING ATMOSPHERIC ENTRY

C. Cordier¹, L. Folco¹, C. Suavet¹, P. Rochette² and C. Sonzogni².
¹MNA, Siena, Italy. E-mail: cordier@unisi.it. ²CEREGE, Aix-en-Provence, France.

**Introduction:** Cosmic spherules (CSs) are extraterrestrial particles <2 mm in size, captured by the Earth's gravitational field and melted while penetrating through the atmosphere. The diversity in quench textures and chemistry among stony CSs has been ascribed to variable peak temperatures and evaporative loss during atmospheric entry [1], with glass CSs forming under very high temperature regimes. Here, we combine the major (n = 187, EPMA) and trace element (n = 76, LA-ICP-MS) and oxygen isotope (n = 6, IRMS) compositions obtained on glass CSs from the Transantarctic Mountains [2] with literature data [1, 3-6] to discuss the processes occurring during their atmospheric entry.

**Results:** A total of 31 CSs closely resemble the FeO-poor (Fe/Si < 0.06), Mg-rich (Mg/Si > 0.9), colorless, glass CAT-like spherules [3]. 45 "high Ca-Al" CSs have high CaO, Al₂O₃ and TiO₂ contents (CaO + Al₂O₃ > 9 wt%, Ti/Si = 0.005 ± 0.002), but higher FeO (Fe/Si > 0.6) and lesser MgO contents (Mg/Si < 0.9) than CAT-like CSs. The 393 other chondritic CSs form the normal group. From normal group to high Ca-Al group, through CAT-like group, CaO, Al₂O₃, TiO₂ and REE contents increase, whereas SiO₂, MgO and volatile element contents decrease. Siderophile and chalcophile elements show a different behavior: their depletion increases from the normal group, to the high CAT-like group, through the high Ca-Al group.

**Atmospheric Entry Processes:** Chemical differences between the three groups of CSs record variations in the degree of heating and evaporation. Based on progressive enrichment in major (Ca, Al, Ti) and trace (Zr, REEs) refractory elements relative to moderately refractory elements (Mg, Si) and volatile elements (Rb, Na, Zn, Pb), we propose that the mass lost by evaporation increases from the normal group (40-50 wt% mass loss), through the CAT-like group (50-60 wt%), to the high Ca-Al group (80-90 wt%). However, siderophile and chalcophile elements in CSs appear to be not governed only by evaporation process. As there is no correlation between siderophile and chalcophile element contents, the processes governing their abundances during melting and melt evolution are, however, different. Siderophile elements probably record the mechanical extraction of metal (plus sulfide) beads resulting from immiscibility between metallic and silicate liquids under reducing conditions [7]. Chalcophile elements may record the extraction of chromite relict grains. The relative importance of evaporation vs. segregation is controlled by interdependent factors: parent body, precursor mineralogy and thermal and redox conditions during atmospheric entry.

**Acknowledgments:** This work was supported by the PNRA and by the EU-funded ORIGINS Marie Curie Action.

**References:** [1] Taylor S. et al. 2000. *Meteoritics & Planetary Science* 35:651-666. [2] Rochette P. et al. 2008. *Proceedings of the National Academy of Sciences* 105:18206-18211. [3] Alexander C. M. O. et al. 2002. *Geochimica et Cosmochimica Acta* 66:173-183. [4] Taylor S. et al. 2005. *Geochimica et Cosmochimica Acta* 69:2647-2662. [5] Yada T. et al. 2005. *Geochimica et Cosmochimica Acta* 69:5789-5804. [6] Cordier C. et al. 2011. *Geochimica et Cosmochimica Acta* 75:1199-1215. [7] Brownlee D. E. et al. 1997. *Meteoritics & Planetary Science* 32:157-175.

THE OLD WOMAN, CALIFORNIA, METEORITE

C. M. Corrigan¹, R. S. Clarke Jr.¹, H. Plotkin² and T. J. McCoy¹. ¹Smithsonian Institution, NMNH, P.O. Box 37012, Washington, D.C., 20013-7012, USA. E-mail: corriganc@si.edu.
²University of Western Ontario, London, ON, Canada.

**Introduction:** The Old Woman meteorite, discovered in March 1976, by two prospectors searching for a fabled lost Spanish gold mine in mountains approximately 270 km east of Los Angeles, achieved legendary status among meteorite collectors.

**History of the Old Woman Meteorite:** The question of the ownership of the meteorite gave rise to 4 yr of disputes. Ultimately, ownership of the meteorite was transferred to the Smithsonian under the powers of the 1906 Antiquities Act, a ruling upheld in a U.S. District Court and a U.S. Court of Appeals. After additional debate, the Smithsonian removed a 0.5 m² cut for study and curation, and for disbursement of specimens to qualified researchers. The main mass was then returned to California on long-term loan to the Bureau of Land Management way station in Barstow. The Old Woman meteorite litigation served as an important test case for the ownership and control of meteorites found on federal lands.

**Scientific Importance of the Old Woman Meteorite:** The Old Woman meteorite, a 2753 kg group IIAB meteorite, is the second largest meteorite (approximately 0.8 × 0.9 × 1.0 m) ever found in the United States. The large slice retained at the Smithsonian reveals distinct regions that show the transition between hexahedral IIA and octahedral IIB iron meteorite structures, a greater understanding of the solid-state transformation that occurs during cooling. The slice is comprised of a polycrystalline mass with grain sizes ranging from <1 cm to >40 cm in maximum dimension, with a strongly bimodal distribution. At high temperature, each grain was an independently oriented austenite crystal. Seven large grains comprise approximately 85% of the surface area and comprise the hexahedral structure within the meteorite, with the remaining 15% of the surface sampling the octahedral polycrystalline regions up to 20 cm in maximum dimension with grain sizes of 1-3 cm. More rarely, smaller grains are found completely enclosed (at least in two-dimensions) within the larger grains.

Within the larger grains (hexahedrite, Region 1), kamacite is the only Fe,Ni metallic phase identified. Taenite was not seen. Numerous schreibersite grains up to several cm in length suggest remnant Widmanstätten, similar to Zacatecas [1]. Shock-melted sulfide inclusions contain troilite and daubreelite. Within Region 2, which might be called a coarsest octahedrite in isolation, smaller parent austenite grains are converted completely to kamacite and lack any remnant Widmanstätten pattern [2]. Thin ribbons of schreibersite and sulfides are seen. Traverses across schreibersites yield identical compositions of unzoned schreibersite in both remnant Widmanstatten pattern of the hexahedral structure in Region 1, and at kamacite-kamacite grain boundaries in Region 2.

If sampled separately, the individual lithologies of Old Woman might well have been classified as three distinct meteorites. Instead, we now recognize that transitional textural types do occur in close proximity and can provide clues to unraveling the unique combinations of chemistry and nucleation and cooling history [3] that produce these textures.

**References:** [1] Buchwald V. 1975. Zacatecas (1792), in *Handbook of meteorites*. Berkeley and Los Angeles: University of California Press, 3:1361. [2] Clarke R. S., Jr. 1979/2011, personal communication. [3] Yang and Goldstein. 2005. *Meteoritics & Planetary Science* 40:239.
ELEMENTS MAGAZINE: A NEW FORM OF OUTREACH FOR THE METEORITICAL SOCIETY

C. M. Corrigan¹, H. Y. McSween Jr.² and E. R. D. Scott³. ¹Smithsonian Institution, NMNH, Washington, D.C. 20560, USA. E-mail: corriganc@si.edu. ²University of Tennessee, Knoxville, TN, USA. ³HIGP, University of Hawai'i at Mānoa, Honolulu, HI, USA.

**Introduction:** In 2010, the Meteoritical Society joined *Elements* magazine, a bimonthly magazine of mineralogy, geochemistry, and petrology, published jointly by 16 professional societies [1]. *Elements* offers a great way for the Meteoritical Society to inform its members and others about society activities. The Meteoritical Society's first "Society News" page appeared in the October, 2010, issue of the magazine [2]. Three more have since been published, one in an issue highlighting current research in cosmochemistry [3].

*Elements Magazine:* *Elements* is read by approximately 15,000 geoscientists and students. Each issue provides invited, peer reviewed articles to the greater, international geochemical science population. Each issue is organized around an individual, relevant, topic in the geosciences. A guest editor compiles a list of invited authors to cover relevant topics around the issue's main theme. The Impact Factor of Elements has tripled since its launch in 2005 and has climbed from an initial 1.562 to 3.569 in 2009.

**The Meteoritical Society and Elements Magazine:** On a society scale, Elements provides the members, council and officers of the Meteoritical Society with a broad stage on which to publicize events, meeting announcements and reports, award winners, society news, membership and other information both to its fellow members and to the broader community.

On an even broader scale, Elements provides the Meteoritical Society with the opportunity to engage with, and link itself to, the broader geochemical and petrologic communities. With issues such as the February, 2011 issue on cosmochemistry (ed. Dante Lauretta) [3], current hot topics in our field were presented in a fashion both attractive and informative to scientists not necessarily intimately familiar with the details of our research. The February, 2010 issue on mineral evolution (ed. Robert Hazen) [4], linked meteoritical research to the ever-expanding research climate surrounding the topics of biogeochemistry. The August 2009 issue featured an article on mineral magnetism in extraterrestrial materials by Pierre Rochette [5], and February 2009 issue (ed. John Delano) focused on the Moon [6]. Many other issues [7–13] have featured articles written by our members, as well.

In addition, the Meteoritical Society has agreed to increase its contribution to Elements from the June, 2011 issue forward, by providing two pages per issue. Every other issue (roughly) will alternate between two society news pages and a new feature called CosmoElements which will be akin to a one page news article highlighting a hot scientific topic (i.e., the June 2011 page will cover the status of water in meteorites to align itself with the theme of the issue, Global Water Sustainability).

**References:** [1] http://www.elementsmagazine.org/index.htm. [2] Richet, Henderson, Neuville, eds. 2010. *Elements* 6, 5, 327. [3] Lauretta D., ed. 2011. *Elements* 7:1. [4] Hazen, ed. 2010. *Elements* 6:1. [5] Feinberg, Harrison, eds. 2009. *Elements* 5, 4, 223. [6] Delano, ed. 2009. *Elements* 5, 1, 223. [7] Bodnar, ed. 2005. *Elements* 1, 1, 39. [8] Harlow and Davies, eds. 2005. *Elements* 1, 2, 85 & 97. [9] Valley, ed. 2006. *Elements* 2:4. [10] McSween, ed. 2006. *Elements* 2:3. [11] Brenan and Mungall, eds. 2008. *Elements* 4:4. [12] Hochella, ed. 2008. *Elements* 4:6. [13] Mandeville, ed. 2010. *Elements* 6:2.

PRELIMINARY INVESTIGATIONS INTO THE TOMOGRAPHY OF PALLASITES: IMPLICATIONS FOR PALLASITE FORMATION

A. L. Couch and R. G. Mayne. ¹Monnig Meteorite Collection, Texas Christian University, TCU Box 298830, Fort Worth, TX 76129 E-mail: amanda.couch@tcu.edu.

**Introduction:** Pallasites consist almost entirely of coarse olivine ((Mg,Fe)₂SiO₄) and FeNi metal. They are traditionally thought to have formed at the core-mantle boundary of a differentiated parent body [1], where the olivine from the mantle would mix with molten metal in the core. However, there are several problems with this theory. The cooling rate of pallasites is much slower than that of any irons [2]. The density difference between the olivine and metal is so great that one would expect to find only a small volume of pallasites, as the zone of mixing would be very limited in a core-mantle formation [3]. However, for every 12 iron meteorites, we have roughly one pallasite [4].

Other formation models theorize that pallasites could have formed i) near the center [5, 6], ii) near the surface [7, 8], or iii) at contact zones between an olivine mantle and isolated metallic pools [9]. Model (i) states that pallasites formed close to the center of the parent body, which essentially negates the problem with density difference. Model (ii) requires an external heat source, which would melt the surface of the chondritic parent body, causing differentiation. Model (iii) proposed that partial crystallization of a melt yielded the olivine, and the remaining melt was forced out by liquid metal pools.

Here we present the preliminary results of a tomographical study of pallasite. The goal of this study is to examine the relationship between the olivine and the metal in terms of models for pallasite petrogenesis.

**Methods:** Pallasites are usually sliced thinly to allow light to shine through the olivine crystals. In order to see the 3D relationship between the olivine and the metal in pallasites, it is important that we use samples that are still in 'block' form. For the purposes of this preliminary work, we analyzed the sample Fukang from the Monnig Meteorites Collection at TCU. The tomography scans were taken at the High Resolution X-Ray CT Facility at the University of Texas at Austin using a BIR ACTIS scanner. The scans are to be analyzed using the program Blob3D. Characteristics that we will be looking at include the interconnectivity of the olivine and metal, along with the grain size, shape, and orientation of the olivine.

**Future Work:** We are currently researching other meteorite collections to find more suitable pallasite samples for tomographic analysis. We plan to scan and analyze samples from the main group and Eagle Station pallasites. These two groups are suggested to derive from different parent bodies [10]. We will use tomography to assess any differences between the formations.

**References:** [1] Yang J. et al. 2010. *Geochimica et Cosmochimica Acta* 74:4471-4492. [2] Mittlefehldt D. W. et al. 1998. *Planetary materials* (ed. J. J. Papike) 36:4-1-4-195. [3] Scott E. R. D. 1977. *Geochimica et Cosmochimica Acta* 41:693-710. [4] Scott E. et al. 2010. www.psrd.hawaii.edu/June10/pallasites-origin.html [5] Buseck P. R. and Goldstein, J. I. 1968. *Science* 159:300-302. [6] Wahl W. 1965. *Geochimica et Cosmochimica Acta* 29:177-181. [7] Mittlefehldt D. W. 1980. *Earth and Planetary Science Letters* 51:29-40. [8] Davis A. M. and Olsen, E. J. 1991. *Nature* 353:637-640. [9] Urey H. C. 1956. *The Astrophysical Journal* 124:623-637. [10] Scott E. R. D. 1977. *Geochimica et Cosmochimica Acta* 41:349-360.
## MAGNETIC STUDY OF PARIS METEORITE

C. Cournede¹, J. Gattacceca¹, B. Zanda² and P. Rochette¹. ¹CEREGE, CNRS/Université Aix-Marseille, Aix-en-Provence, France. ²LMCM, Museum national d'Histoire naturelle, CP52, 61 rue Buffon, 75005 Paris, France.

The *Paris* meteorite is a unique carbonaceous chondrite find (CM2/3) with almost no traces of terrestrial weathering [1]. Indeed, this CM chondrite is characterized by the co-existence of FeNi metal and magnetite, the latter mineral being formed during aqueous alteration on the parent body.

Magnetic measurements offer a non-destructive method to quantify the respective abundances of metal and magnetite over a wide range of spatial scales (mm to decimeter). Moreover the comparison of the magnetization obtained for metal-rich and magnetite-rich samples may provide constraints on the chronology of the parent body alteration, and brecciation of this meteorite.

We conducted a magnetic study of several oriented samples of this meteorite, with masses ranging from several mg up to 17 g. Preliminary rock magnetism results show that Paris has a magnetic mineralogy that is notably different from that of other CM chondrites, with a significant contribution of FeNi metal which confirms that *Paris* suffered less aqueous alteration than other CM chondrites. We will discuss the small-scale variability of the magnetic mineralogy. We will also discuss the results of measurements of anisotropy of magnetic susceptibility, a proxy to the petrofabric intensity and orientation [2], in relation with the brecciation history of the meteorite.

Paleomagnetic data show that despite having being exposed to an artificial strong magnetic field (magnet), a pre-terrestrial magnetization, apparently carried by magnetite, is still preserved in the meteorite. Because crystallization of magnetite likely occurred only several Myr after the formation of the solar system [3], i.e., after the possible existence of strong solar and nebular magnetic fields, the homogeneity of the magnetization within the meteorite may indicate the existence of an internally generated field at that time. This would imply a partially differentiated parent body with a convecting metallic core, as recently proposed for the parent body of CV chondrites [4,5]. However, the brecciation history of Paris meteorite needs to be better understood before this conclusion can be confirmed.

**References:** [1] Zanda et al. 2010. *Meteoritics & Planetary Science* 45:222-222. [2] Gattacceca et al. 2005. *Earth and Planetary Science Letters* 234:351-368. [3] Petitat and Gounelle. 2010. Abstract #1673, Lunar and Planetary Science Conference. [4] Carporzen et al. 2011. Proceedings of the National Academy of Sciences 108:6386-6389. [5] Elkins-Tanton et al. 2011. *Earth and Planetary Science Letters* 305:1-10.

## THE LIFE MARKER CHIP—EXTRACTING POLAR AND NONPOLAR BIOMARKERS FROM THE MARTIAN SOIL USING A SURFACTANT-BASED SOLVENT

R. W. Court¹, O. A. Baki¹, M. R. Sims², D. Cullen³, M. A. Sephton¹. ¹Dept. of Earth Science and Engineering, Imperial College London. E-mail: r.court@imperial.ac.uk. ²Space Research Centre, University of Leicester. ³Cranfield Health, Cranfield University.

**Introduction:** The Life Marker Chip (LMC) is designed to detect the chemical evidence of past or present Martian life [1]. To achieve this it will use an antibody-based detection system, but the organic solvents best suited to extracting organic matter from the Martian soil are incompatible with the LMC antibodies. Instead, an aqueous solvent must be used, but water-based solvents are typically ineffective at dissolving the nonpolar organic compounds of most interest to the LMC. A surfactant-based solution of 20:80 (vol:vol) methanol:water with 1.5 mg ml⁻¹ of polysorbate 80 solves this dilemma, with the surfactant forming micelles that promote the dissolution of nonpolar molecules [2]. Here, we report on the ability of this surfactant solution to dissolve organic standards spiked on to analogues to the Martian soil, and on the tendency of common spacecraft materials to adsorb these standards from solution.

**Results:** Addition of 1.5 mg ml⁻¹ of the surfactant polysorbate 80 to a 20:80 (vol:vol) methanol:water solution results in an increase in solubility of approximately two orders of magnitude for the standards hexadecane, phytane, squalene, anthracene, pyrene, stigmasterol and coprostane, resulting in solubilities in the range of ~1–50 µg ml⁻¹. Tests on a range of Martian analogs, including the palagonitic tephra JSC Mars-1 [3], goethite and hematite, demonstrates its ability to extract organic compounds spiked on to their surfaces without debilitating adsorption. The addition of iron compounds such as iron (III) sulfate, iron (III) perchlorate and iron (III) chloride to JSC Mars-1 similarly has no significant deleterious adsorption or chemical effects. However, the addition of the clay-rich Jurassic Blue Lias shale to JSC Mars-1 results in significant adsorption of the standards and a greatly reduced efficiency of extraction of the standards. Further testing is required to determine whether this applies to clay minerals in Martian environments.

The ability of common spacecraft material to adsorb standards dissolved in the surfactant solution has also been investigated. Passage of solvent through 0.2 µm syringe filters shows that polytetrafluoroethylene (PTFE) is least prone to adsorb the standards from surfactant solution, while cellulose acetate adsorbs the most. Polyethersulfone, polypropylene and nylon filters show intermediate levels of adsorption. The fluoropolymer Viton™ shows a small adsorption effect, but not one large enough to significantly inhibit the operation of the LMC.

**References:** [1] Sims M. R. et al. 2005. *Planetary and Space Science* 53:781-791. [2] Court R. W. et al. 2010. *Planetary and Space Science* 58:1470-1474. [3] Allen C. C. et al. 1998. In *Space '98: Proceeding of the Conference of American Society of Civil Engineers.*
## VOLATILE PRODUCTION FROM ABLATING MICROMETEORITES—EVIDENCE FROM STEPPED PYROLYSIS-FTIR

R. W. Court, M. A. Sephton. Dept. of Earth Science and Engineering, Imperial College London. E-mail: r.court@imperial.ac.uk.

**Introduction:** Pyrolysis-Fourier transform infrared (FTIR) spectroscopy has recently been used to simulate the atmospheric entry of micrometeorites and to quantify the production of water, carbon dioxide, methane and sulfur dioxide produced by the thermal processing of their organic and mineral phases [1–4]. However, these attempts to quantify micrometeoritic volatile contributions to the atmospheres of terrestrial planets have assumed that the entire infalling micrometeorite flux is heated to the same temperature. In reality, micrometeorites of a range of varying masses, densities and mineralogies enter the atmosphere at a range of velocities and angles, experiencing variable degrees of heating. As such, a more sophisticated simulation of atmospheric entry should account for variations in volatile production with temperature. Here, we have subjected samples of five carbonaceous chondrites—CI1 Orgueil, CM1 ALH 88045, CM2 Cold Bokkeveld, CM2 Murchison and CV3 Mokoia—to stepped pyrolysis and used FTIR to identify and quantify the volatiles produced at each temperature step.

**Results:** The yields of water, carbon dioxide and sulfur dioxide at temperature steps from 250 °C to 1000 °C have been quantified. The yields of the volatiles, and their patterns of release, can be related to the degree of aqueous alteration experienced by the chondrite on the meteorite parent body. The relatively strongly aqueously altered chondrites Orgueil and Cold Bokkeveld show prominent low-temperature yields of sulfur dioxide and water that are absent or greatly reduced in Murchison and Mokoia. The CM1 chondrite ALH 88045 shows patterns of volatile release more closely related to the considerably less aqueously altered CM2 Murchison and CV3 Mokoia, an anomaly interpreted in terms of terrestrial alteration while this meteorite was exposed on the Antarctic ice sheet [3,5,6]. Carbon dioxide release is more pronounced at higher temperatures, representing the stability of carbon dioxide sources such as carbonates, and the carbon dioxide yield is lower in samples having experienced less aqueous alteration, reflecting the lower abundance of carbonates and organic matter in chondrites such as Mokoia. Combination of these data, revealing volatile production across a range of temperatures, with temperature models of infalling micrometeorites can produce superior estimates of the micrometeoritic contributions to the volatile budgets of terrestrial planets.

**References:** [1] Court R. W. and Sephton M. A. 2011. *Geochimica et Cosmochimica Acta* 75:1704–1717. [2] Court R. W. and Sephton M. A. 2009. *Earth and Planetary Science Letters* 288:382–385. [3] Court R. W. and Sephton M. A. 2009. *Geochimica et Cosmochimica Acta* 73:3512–3521. [4] Court R. W. and Sephton M. A. 2009. *Analytica Chimica Acta* 639:62–66. [5] Shima M., Shima M., and Hintenberger H. 1973. *Earth and Planetary Science Letters* 19:246–249. [6] Sephton M. A. et al. 2004. *Meteoritics & Planetary Science* 39:747–754.

## TIC AND RUTILE WITHIN A SUPERNOVA GRAPHITE

T. K. Croat¹, M. Jadhav¹,², E. Lebsack¹ and T. J. Bernatowicz¹.
¹Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA. E-mail: tkc@wustl.edu. ²HIGP, University of Hawaii at Mānoa, Honolulu, HI, USA.

**Introduction:** The origin of rutile grains (TiO₂) found within presolar graphites (e.g., primary condensate or from secondary alteration) is unclear, given that the host graphites form in C-rich environments and rutile likely in O-rich ones [1]. The Orgueil graphite OR1dm3-6 has ¹²C, ¹⁵N and ¹⁸O excesses indicative of a supernova (SN) origin [2, 3], and also contains hundreds of Ti-rich internal grains, both TiC and rutile [4]. Detailed studies of the chemistry, phase, O isotopic composition and spatial distribution of Ti-rich grains within g6 SN graphite strongly suggest that the rutile grains do not form secondarily (e.g., via oxidation of existing TiCs), but rather are also a primary SN condensate and are indicative of compositional changes (mixing) in SN ejecta.

**Experimental Methods:** After isotopic studies [2, 3], OR1d3m-6 was ultramicrotomed and studied in TEM [4]. Subsequent NanoSIMS measurements of ¹⁶O, ¹⁸O, ²⁸Si, ²⁹Si, and ³⁰Si were made on TiC and rutile-containing graphite sections.

**Results and Discussion:** Chemical compositions (EDXS) and images were collected from 118 separate Ti-rich internal grains within 7 g6 graphite cross-sections. Due to their unusually high O content, SN TiCs cannot be distinguished from rutile grains on that basis, so 76 Ti-rich grains were identified by their distinctive electron diffraction patterns (TiC, FCC, a = 4.4Å and TiO₂ tetragonal, a = 4.9Å, c = 3.1Å). Fifty-two rutile grains and 13 TiCs were found, along with 4 Ti-rich grain patterns that may indicate a different Ti-oxide polymorph. Three SiC and two kamacite grains were also found. The TiCs fall into two groups based on size and composition, with the larger ones (80–130 nm) showing significantly higher V and lower Al content (avg. V/Ti and Al/Ti at. ratios of 0.30 and 0.01 as opposed to 0.15 and 0.40 respectively from smaller (<30 nm) TiCs. The clear increase in V/Ti ratio vs. grain size is consistent with large TiCs experiencing extended growth times at lower T and thus incorporating more V (since VC is less refractory than TiC). The high Al content in some small carbides (not seen previously among SN TiCs) may indicate formation of the structurally-similar Ti₃AlC phase (4.2 Å cubic). Other than having somewhat higher O content, the rutile grains are similar in size and composition to the small TiCs. Analysis of several central cross-sections show TiCs predominantly clustered towards the outside of the graphite's surface, whereas rutile grains are spread throughout its volume. Thus, oxidation of existing TiCs to form rutile after encapsulation in graphite is unlikely to occur, which gives credence to primary condensation of rutile in SN ejecta. NanoSIMS O isotopic images of a g6 cross-section containing two large TiC show ¹⁶O/¹⁸O of 156 ± 33 in the carbides and 315 ± 23 in the graphite (2 σ errors). The ¹⁸O counts from small TiCs and rutiles were insufficient to allow a separate determination of their isotopic composition. Along with more extreme O anomalies in TiC than in graphite, O isotopic dilution towards normal nearer the graphite's surface is also present, effects similar to those seen in [5].

**References:** [1] Croat T. K. 2007. *Meteoritics & Planetary Science* 42:A34. [2] Croat T. K. et al. 2009. 40th Lunar Prospector Spacecraft A2175. [3] Jadhav M. et al. 2006. *New Astronomy Review* 50:591–595. [4] Jadhav M. et al. 2008. 39th Lunar Prospector Spacecraft A1047. [5] Stadermann F. J. et al. 2005 *Geochimica et Cosmochimica Acta* 69:177–188.
5354

PB-PB AGES OF APOLLO 15 ZIRCONS

C. A. Crow¹, K. D. McKeegan¹ and D. J. Taylor¹. ¹Department of Earth and Space Sciences, University of California Los Angeles, USA. E-mail: ccrow@ucla.edu.

**Introduction:** Crystallization ages of lunar zircons provide insight into the timing of early magmatic and/or impact events on the Moon. We report new Pb-Pb ages for Apollo 15 zircons and previously unreported zircon ages for Apollo 17. We also report on the REE, Ti temperatures, and U/Th data for Apollo 15 zircons.

**Sample:** The ages reported here are for zircons from two Apollo 15 samples, 15405 and 15455. Both are impact-melt breccias. 15405 is comprised mainly of dark lithology KREEP basalt [1]. 15455 is a mixture of dark basalt and light anorthosite lithologies [2]. These samples were chosen for their enrichment in KREEP, REE, and U concentrations.

**Method:** Individual zircons were separated from crushed clasts (4.25 g of 15405,75, 3.91 g of 15405,9, and 2.10 g 15455,226) and analyzed using the UCLA Cameca ims-1270 ion microprobe. U-Pb and Pb-Pb ages, REE, and trace element data were collected for all Apollo 15 zircons.

**Results:** The Pb-Pb ages of the Apollo 15 zircons show a peak at approximately 4.33 Ga, which is also present in Apollo 17 [3] and Apollo 14 data [4]. Meyers et al. 1996 suggest that the peaks in U-Pb age distribution of lunar zircons correlate with episodes of KREEP magmatism and zircon crystallization. These Apollo 15 ages, when analyzed in conjunction with other reported zircon ages from two other Apollo landing sites (14 and 17), provide strong empirical support for a widespread (possibly global) zircon-forming event at approximately 4.33 Ga. The REE patterns of the Apollo 15 zircons reported herein are similar to those reported in [5].

**References:** [1] Meyer C. 2006, Lunar Sample Compendium, 15455, (http://curator.jsc.nasa.gov/lunar/compendium.cfm). [2] Meyer C. 2004. Lunar Sample Compendium, 15405, (http://curator.jsc.nasa.gov/lunar/compendium.cfm). [3] Taylor et al. 2009. *Earth and Planetary Science Letters* 279:157-164. [4] Meyers et al. 1996. *Meteoritics & Planetary Science* 31:370-387. [5] Nemchin et al. 2010. *American Mineralogist* 95:273-283.

Apollo 15 Zircon Pb-Pb Ages

<figure><img src="image_8.png" /><figcaption>Fig. 1. Pb-Pb ages for zircons from Apollo samples 15405,9, 15405,75, and 15455,226.</figcaption></figure>

5328

ABUNDANCE AND ISOTOPIC COMPOSITION OF SOLAR WIND XENON COLLECTED BY THE GENESIS MISSION

S. A. Crowther and J. D. Gilmour. SEAES, University of Manchester, UK. E-mail: sarah.crowther@manchester.ac.uk.

**Introduction:** One of the major objectives of NASA's Genesis mission is to determine the elemental and isotopic noble gas composition of the present-day solar wind [1]. However concentrations of implanted noble gases in the Genesis collector targets are very low, and the most sensitive techniques and instruments are required to make precise and accurate measurements. Our work focuses on measuring the concentration and isotopic composition of solar wind Xe implanted in CZ-Si targets from the bulk collector array, using the RELAX mass spectrometer [2, 3].

**Experimental:** The implanted solar wind is extracted by UV laser ablation (Nd:YAG, 355 nm, ~350 mJ). The laser beam covers and ablates the whole surface of the square samples typically ~3-5 mm in dimension, without the need to raster over the surface. Preliminary experiments suggested that ~30 laser shots extracted all the solar wind [4, 5], however extractions of gas from a further 120 laser shots show a systematic enrichment in Xe in the flight samples relative to the non-flight samples. The "excess" Xe in these releases amounts to approximately 55% of the total Xe in these releases, and if this excess is assumed to be solar wind it accounts for ~15% of the total. Our preferred extraction protocol now uses ~150 laser shots to extract all the implanted solar wind.

Instrumental mass discrimination can best be corrected for if sample sizes are matched to those of calibration aliquots. The predicted 2-year fluence for solar wind Xe implanted into the bulk collector arrays is ~3 × 10⁶ atoms Xe cm⁻² [1]. RELAX calibration aliquots contain 1.2 × 10⁵ atoms of atmospheric ¹³²Xe [3]. Therefore we have analyzed approximately square samples, with typical areas of ~0.09–0.25 cm², such that the expected amount of ¹³²Xe closely matches that in the air calibration aliquots. Our approach, which tests the reproducibility of the data through a large number of separate analyses, is complementary to the analysis of gas released from large areas of collector material, which can be analyzed at higher precision on conventional instruments. Notably, the expected ~400 atoms of ¹²⁴Xe per sample make determination of the ¹²⁴Xe/¹³²Xe ratio challenging.

**Results:** Blank Xe, as measured by the same protocol in non-flight samples, is isotopically consistent with air, but the concentration varies by a factor of ~20. Variations in Xe concentration are also observed in flight samples. The isotope ratios measured in the flight samples correlate with the reciprocal of the measured concentration suggesting a variable concentration blank mixes with a uniform concentration implanted solar wind component.

16 flight and 15 non-flight samples have been analyzed using the 150-shot extraction protocol. From the distribution of Xe concentrations measured in these samples we calculate the concentration of the implanted solar wind to be 1.20(9) × 10⁶ atoms ¹³²Xe cm⁻². The isotopic composition calculated from this concentration is consistent with the solar wind measured in the young lunar regolith [6], there is no evidence of fractionation.

**References:** [1] Burnett D. S. et al. 2003. *Space Science Reviews* 105:509-534. [2] Gilmour J. D. et al. 1994. *The Review of scientific instruments*. 65:617-625. [3] Crowther S. A. et al. 2008. *Journal of Analytical Atomic Spectrometry* 23:938-947. [4] Crowther S. A. and Gilmour J. D. 2010. *Meteoritics & Planetary Science* 45. Abstract #5335. [5] Crowther S. A. and Gilmour J.D. 2011. Abstract #1969. 42nd Lunar and Planetary Science Conference. [6] Wieler R. 2002. *Reviews in Mineralogy & Geochemistry* 47:21-70.
THE HYPERVELOCITY ARTIFICIAL METEOROID EXPERIMENT (HAM•E): A MISSION CONCEPT STUDY

D. C. Cullen¹, P. C. E. Roberts² and HAM•E Cranfield MSc Group Design Project Team². ¹Cranfield Health. ²Space Research Centre, Cranfield University, Bedfordshire, UK. E-mail: d.cullen@cranfield.ac.uk

The hypervelocity atmospheric entry of natural bodies—meteoritic, asteroidal and cometary—has relevance to the evolution of the solar system. Relevance includes contribution to early planetary inventories of volatile and organic materials and including possible lithopanspermia questions and the current threat of Near Earth Objects. Present understanding of such events is limited given for all observed natural events the detailed boundary conditions are not known—e.g., the size, shape, detail composition of bodies prior to atmospheric entry. Observational data is limited since for natural bodies of significant mass, no event has been predicted with sufficient notice to allow deployment of the best observational techniques currently available.

The scientific community's current understanding of hypervelocity atmospheric entry of natural bodies is from extensive modeling, hypervelocity laboratory experiments and meteorite record interpretation. Absence of detailed observations of natural events means this large body of work suffers poor validation and for the meteorite record, uncertainty in pre-entry conditions.

To address the absence of relevant data, we propose the Hypervelocity Artificial Meteoroid Experiment (HAM•E) which aims to enter, from space, into the Earth's atmosphere fully characterized bodies (artificial meteoroids) representative of natural bodies at velocities relevant to natural events and at known times and locations allowing the deployment of the best available observational techniques. Resultant data would enable validation and refinement of existing models and laboratory experiments and a re-interpretation of the existing meteorite record.

A preliminary HAM•E mission study has been performed to assess feasibility. Requirements were: enter four artificial meteoroid bodies into the Earth's atmosphere at velocities greater than 11 km s⁻¹; entry times and locations to be compatible with a single observation campaign; entry profiles to be compatible with two bodies undergoing ablation only and two bodies undergoing both fragmentation and ablation. Various mission concepts were proposed and trade-off studies perform to result in a baseline mission. The mission comprised the following key points: Payload of two 236 kg basalt spheres to undergo fragmentation and two 25 kg spheres, one each of basalt and sedimentary rock for ablation only. Dedicated Soyuz launch with a Fregat upper stage on a lunar free-return trajectory. Sequenced release of artificial meteoroids on return leg with atmospheric entry of meteoroids above the Woomera Prohibited Area, Australia at 11.1 km s⁻¹, separated in a 70 min period and 6.3 days after launch. Spacecraft design included meteoroid containment and release mechanisms, propulsion system, instrumentation for monitoring meteoroid integrity and sub-systems for power and communication. Resultant spacecraft mass of 1564 kg including payload.

A detailed science case including more refined payload definition and an observational campaign case, comprising space-borne, air-borne and ground based techniques and including resultant meteorite campaign is the subject of on-going studies.

In summary we have proposed the HAM•E concept and produced a preliminary mission design that implements HAM•E.

QUANTIFICATION OF THE POST-IMPACT THERMAL EVOLUTION OF PLANETESIMALS

T. M. Davison¹, F. J. Ciesla¹ and G. S. Collins². ¹Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA. ²Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK. E-mail: tdavison@uchicago.edu.

**Introduction:** Impacts between planetesimals were common in the early solar system. In some cases, these collisions were energetic enough to cause significant changes to the planetesimal materials; evidence for shock metamorphism, alteration and melting are found in meteorites. While short-lived radionuclides ($^{26}$Al) can account for most of the heating observed in the meteoritic record, hypervelocity impacts have also been invoked as a possible heat source [1–3]. Planetesimals are thought to have formed through low velocity accretionary collisions of smaller bodies [4–6], a process which is expected to have created planetesimals with significant pore space; a recent observational study supports this theory [7]. Numerical modeling has shown that localized heating in porous planetesimals could be higher than previously realized [8]. Here we quantify the post-impact cooling of a planetesimal and compare the thermal evolution to that inferred for primitive meteorites [9, 10].

**Modeling:** We simulate hypervelocity planetesimal collisions using the iSALE hydrocode [11, 12] for a range of planetesimal impact scenarios: parameters investigated include porosity, impact velocity, target and impactor sizes and impact angle. A recent addition to the iSALE model is a self-gravity algorithm [13–15], allowing simulations to extend to later times than in [8]. After the resulting planetesimal has relaxed to its final shape, the density, porosity and temperature structure is extracted from the hydrocode model. This information is passed into a finite volume thermal evolution model to track the redistribution and loss of the deposited impact energy, allowing us to determine the cooling rates throughout the planetesimal. The thermal model solves the heat diffusion equation and accounts for the porosity of the material by altering the thermal diffusivity according to [16].

**Results:** We find peak temperatures of 700–1500 K and cooling rates in the range 0.1–100 K Myr⁻¹ are easily achieved. These values are consistent with those inferred from chondritic meteorites [10]. Cooling rates for initially porous material are lower than for fully consolidated bodies—for a 50% porous parent body that was impacted at 4 km s⁻¹, cooling rates are ~1 K Myr⁻¹, but in an equivalent collision into a non-porous parent body, cooling rates are typically > 10 K Myr⁻¹. We are determining the full range of thermal histories that would be achieved in collisions and will present results from our full parameter study, and a comparison with the predictions of recent radiogenic thermal models [17].

**References:** [1] Rubin A. E. 1995. *Icarus* 113:156–167. [2] Wasson J. T. et al. 1987. *Meteoritics & Planetary Science* 22:525–526. [3] Cameron A. G. W. et al. 1990. 21st Lunar and Planetary Science Conference. pp. 155–156. [4] Cuzzi J. N. et al. 2008. *The Astrophysical Journal* 687:1432–1447. [5] Johansen A. et al. 2007. *Nature* 448:1022–1025. [6] Teiser J. and Wurm G. 2009. *Monthly Notices of the Royal Astronomical Society* 393:1584–1594. [7] Bland P. A. et al. 2011. *Nature Geoscience* 4:244–247. [8] Davison T. M. et al. 2010. *Icarus* 208:468–481. [9] Taylor G. J. et al. 1987. *Icarus* 69:1–13. [10] Kleine T. et al. 2008. *Earth and Planetary Science Letters* 270:106–118. [11] Wünnemann K. et al. 2006. *Icarus* 180:514–527. [12] Collins G. S. et al. 2004. *Meteoritics & Planetary Science* 39:217–231. [13] Collins G. S. et al. 2011. 42nd Lunar and Planetary Science Conference. [14] G. S. Collins et al. This meeting. [15] Barnes J. E. and Hut P. 1986. *Nature* 324:446–449. [16] Warren P. H. 2011. *Meteoritics & Planetary Science* 46:53–78. [17] Harrison K. P. and Grimm R. E. 2010. *Geochimica et Cosmochimica Acta* 74:5410–5423.
TEXTURAL AND COMPOSITIONAL VARIATIONS OF CR-
BEARING SPINEL MINERALS IN REDUCED CV3 CHONDRITES

J. Davidson, D. S. Lauretta, and D. L. Schrader. LPL, Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721-0092, USA. E-mail: davidson@lpl.arizona.edu.

**Introduction:** The CV3 and CK chondrites have been hypothesized to originate from a single parent body [1]. During our ongoing study of the links between opaque phases from CV3/CK chondrites we found less Cr in Fe, Ni metal grains of reduced CV3 (CV3Red) chondrites than expected when compared to a more oxidised CK3 [2]. Since the CV3/CK chondrites have approximately bulk solar abundance of Cr [1], Cr must be present in different phases for each group/sub-group. Cr in oxidized CV3s is most abundant in magnetites but these are absent in CV3Red [2]. Instead Cr appears to be present, with variable abundance, in the spinel phases of CV3Red. Here we investigate the partitioning of Cr between different phases in unequilibrated CV3Red chondrites.

**Analytical:** Polished sections of the reduced CV3 chondrites RBT 04133 [3], MET 01017, and Dhofar 1612 were studied via (1) optical microscopy, (2) X-ray mapping, and (3) major/minor elemental analysis of individual mineral phases with the LPL's Cameca SX-50 electron probe microanalyzer (EPMA).

**Results:** Cr-bearing spinel grains in RBT 04133, MET 01017, and Dhofar 1612 are located exclusively in FeO-rich (type II) chondrules. However, not all FeO-rich chondrules observed are spinel-bearing. Chromium-composition appears to correlate with morphology, with the most euhedral grains being generally the most Cr-rich; RBT 04133 (euhedral; 46.6-52.4 wt.% Cr₂O₃), Dhofar 1612 (rounded, euhedral; 28.6-41.4 wt.% Cr₂O₃), and MET 01017 (subhedral; 18.2-34.9 wt.% Cr₂O₃). Cr-bearing spinels in MET 01017 have Fe-rich rims (increasing from approximately 22 wt.% Fe₂O₃ in the core to approximately 33 wt.% at the rim). No zoning was seen in Cr-bearing spinels from RBT 04133 or Dhofar 1612.

**Discussion:** Chromites from unequilibrated chondrites are reported to be entirely euhedral, with subhedral chromites only present in equilibrated chondrites [4]. The presence of subhedral spinels in MET 01017 may suggest that it has experienced higher degrees of thermal metamorphism than the other CV3s analyzed. This is consistent with a classification of CV3.7 for MET 01017 determined by Raman spectral analysis of its insoluble organic matter [5]. Therefore, we suggest that spinel morphology may also be an indicator of the degree of thermal metamorphism experienced by unequilibrated CV3Red chondrites.

Zoning in the Cr-bearing spinels of MET 01017, the most thermally altered CV3, suggests mobilization of elements with increasing degrees of heating. Cr-bearing spinels appear to become less Cr-rich with increasing parent body thermal alteration. The Cr-composition of FeO-rich olivine grains in carbonaceous chondrites is known to decrease with increasing metamorphic grade [6], forming Cr-rich rims and chromites. This appears to contradict our results. We will determine the Cr-composition of co-existing silicate phases to address this issue.

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

**References:** [1] Greenwood R. G. et al. 2010. *Geochimica et Cosmochimica Acta* 74:1684. [2] Davidson J. et al. 2011. Abstract #1886. Lunar and Planetary Science Conference. [3] Davidson J. et al. 2009. *Meteoritics & Planetary Science* 44:A57. [4] Johnson C. A. and Prinz M. 1991. *Geochimica et Cosmochimica Acta* 55:893. [5] Busemann H. et al. 2007. *Meteoritics & Planetary Science* 42:1387. [6] Grossman J. N. and Brearley A. J. 2005. *Meteoritics & Planetary Science* 40:87.

LATE ACCRETION TO THE MOON AND VESTA

James M. D. Day¹ and Richard J. Walker². ¹Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0244, USA, E-mail: jmdday@ucsd.edu. ²Department of Geology, University of Maryland, College Park, MD 20740, USA.

**Introduction:** We present new highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance and ¹⁸⁷Os/¹⁸⁸Os data for low-Ti mare basalt meteorites, Apollo 12 samples, and diogenite meteorites to explore the late accretion histories of the Moon and asteroid (4) Vesta, the probable diogenite parent body. Moon/Vesta comparisons are potentially useful because both bodies are considered to have witnessed magma ocean differentiation, are relatively volatile depleted (e.g., low ⁸⁷Sr/⁸⁶Sr), and because recent work has identified the possibility of massive (D = 100's to 1000's km, respectively) impactors striking the Moon and Earth subsequent to the major phases of core formation [1]. Thus, interpretation of HSE signatures for differentiated asteroids like Vesta may provide complementary information on the timing, size distribution and distribution within the solar system of potential late accretion impactors to bodies such as the Moon [2-4], Earth [5], Mars [6], and the angrite parent body [7].

**Results and Discussion:** Apollo 12, 15, 17 mare basalts, and mare basalt meteorites have HSE abundances (~1 × 10⁻³ to 1 × 10⁻⁷ × CI-chondrite) that extend the abundance range measured for lunar picritic glass bead interiors (~1 × 10⁻³ to 1 × 10⁻⁵ × CI [2]), and exhibit relatively flat chondrite-relative HSE patterns. Current HSE abundance data for lunar derivative melts and pristine crustal rocks support their derivation from a relatively homogenized lunar mantle with HSE abundances <20× lower than for the terrestrial or Martian mantles, consistent with stochastic late accretion [1]. Diogenite meteorites have chondritic relative abundances of the HSE and close-to-chondritic ¹⁸⁷Os/¹⁸⁸Os [8], and span a range of HSE concentrations from close to terrestrial upper mantle values, to HSE concentrations observed in lunar mare basalts. If it is assumed that the HSE characteristics of most diogenites are reflections of processes internal to Vesta, then their generally chondritic natures, suggests chondritic additions following core formation, but prior to completion of mantle crystallization [8]. If interpretations of stochastic late accretion are valid [1], Vesta, and other asteroids, are smaller targets than Earth, the Moon, or Mars, so the largest early impactors to strike them may have been D < 100 km. Consequently, perhaps only a portion of the Vesta was affected by late accretion, such that some HSE signatures are more consistent with regional rather than global effects. Planetesimals like Vesta, therefore, may be expected to retain compositional heterogeneity that records their magnitude and frequency of late accretion and provides a complementary record to that retained in terrestrial, lunar, and Martian rocks and achondritic meteorites.

**Acknowledgments:** This research was partially supported by NASA LASER grant (NNX11AG34G).

**References:** [1] Bottke W. F. et al. 2010. *Science* 330:1527. [2] Walker R. J. et al. 2004. *Earth and Planetary Science Letters* 224:399. [3] Day J. M. D. et al. 2007. *Science* 315:217. [4] Day J. M. D. et al. 2010. *Earth and Planetary Science Letters* 289:595. [5] Walker R. J. 2009. *Chemie der Erde* 69:101. [6] Brandon A. D. et al. 2010. *Geochimica et Cosmochimica Acta* 74:A117. [7] Riches A. J. V. et al. 2010. *Meteoritics & Planetary Science* 45:A171. [8] Day J. M. D. et al. 2010. Abstract #1942. 41st Lunar and Planetary Science Conference.
5495

HIGH PRESSURE MINERALS IN RC106 REVEAL ITS DEPTH IN ITS PARENT BODY

P. S. De Carli, Z. Xie, R. Trickey, C. A. Weaver, T. G. Sharp. Poulter Laboratories, SRI International.

The present work is based on the study of a 1.3 mm-wide melt vein in the L6 chondrite RC106. This vein contains an assemblage of high pressure phases that constrain the pressure history of the vein as it solidified and cooled to a temperature low enough for survival of the phases. Cooling rate calculations constrain the temperature history of the vein [1, 2]. Thus the pressure-time history is constrained. Since shock pressures are relieved by rarefaction waves from the nearest free surface, shock duration is a measure of the depth of the meteorite in its parent body at the time of the vein-forming shock. Preliminary calculations with the Autodyn® hydrocode indicate the RC106 must have been at least 10 km below the surface of its parent. More refined heat flow and hydrocode calculations are in progress.

**References:** [1] Langenhorst F. and Poirier J. P. 2000. *Earth and Planetary Science Letters* 184:37–55. [2] Sharp T. G. and De Carli P. S. 2006. MESS II, eds. Lauretta and McSween, The University of Arizona Press. pp. 653–677.

5152

METEORITE CURATION AND RESEARCH IN BELGIUM

Walter De Vos. Royal Belgian Institute of Natural Sciences, Brussel, Belgium.

The Royal Belgian Institute of Natural Sciences (RBINS) has held meteorites in its collections since the nineteenth century. Among them are four meteorites that are documented falls in Belgium between 1855 and 1934. In the last few years a new interest in meteorites arose for different reasons. In 2006 a newly discovered mass of the Mont Dieu iron meteorite, weighing 435 kg, was purchased. It is now part of the permanent exhibit of the museum. In 2009, a collection of 361 pieces was acquired from a private collector, including many Saharan meteorites found after 1995.

At present, the RBINS holds 511 pieces from 307 different meteorites, 72 of which, all from The Sahara, have not yet officially been described.

In a separate development, an agreement was signed between Belgian and Japanese scientists to search for meteorites in Antarctica from 2009 to 2014, in the larger neighborhood of the Belgian Princess Elisabeth Station, which was opened in 2009 near the Sor Rondane Mountains. The first field season yielded 635 new meteorites, the second one 218 new meteorites; several ureilites and at least one carbonaceous chondrite were identified on macroscopic inspection. After a first characterization at the Japanese National Institute of Polar Research, half the collected meteorites will be transferred to the RBINS in Belgium for curation.

Starting in 2001, two universities in Brussels carry out research on meteorites and impact structures. Several master students have been at work, notably on the IIE iron Mont Dieu, and on chondrites from The Sahara. One Ph.D. work was concluded this year, and ongoing research at Ph.D. and postdoc level includes research on meteorites from the RBINS collection, both chondrites and achondrites.

At the RBINS itself a fifth Belgian meteorite, Hautes Fagnes, a LL5 chondrite, was studied in collaboration with other institutions, and at present analytical facilities are being upgraded to produce accurate microanalyses. Research themes include classification of chondrites from The Sahara, magnetic susceptibility measurements, and bulk analyses on chondrites in collaboration with university laboratories. In addition, occasionally genuine meteorites are submitted for identification by the public, and some research has started on these.

Given the perspective of a growing collection through the Antarctic prospection program, the RBINS is gradually improving its research infrastructure and its curation facilities for meteorites.
5310

MANTLE OVERTURN AS REVEALED BY NAKHLITES: WHAT
HAPPENED AFTER?

V. Debaille¹ and A. D. Brandon². ¹Département des Sciences de la Terre et de l'Environnement, Université Libre de Bruxelles, Brussels, Belgium. E-mail: vinciane.debaille@ulb.ac.be. ²Department of Earth and Atmospheric Sciences, University of Houston, Houston, USA.

During early stages of differentiation, terrestrial planets may undergo extensive melting, resulting in deep and global magma oceans (MO). For Mars, after its solidification, the contrast of density between early formed Mg-rich MO cumulates located at the bottom of the Martian mantle, and later Fe-rich MO cumulates at the top of the mantle is expected to induce mantle overturn [1]. During the overturn, deep cumulates are brought up to shallower depths and can melt by adiabatic decompression, with large degrees of partial melting of up to 60–65% [2]. While shergottites record the progressive crystallization of the magma ocean [3], nakhlites provide the first geochemical evidence that a mantle overturn occurred [2]. Following the mantle overturn, the large volumes of magma produced above the upwelling cumulates may have resurfaced the whole planet, hence creating an early Martian crust [4], and potentially generating the Martian crustal dichotomy [2].

Using the hypothesized mineralogy of the Martian mantle [5], the evolution of the Fe/Mg ratio during the crystallization of the Martian magma ocean results in Mg# > 80 for cumulates deeper than 13 GPa. Consecutively to the mantle overturn, the direct product of 60% partial melting of these cumulates is magmas with Mg# > 79. These high Mg#s are comparable to terrestrial Archaean komatiites, despite that the Martian mantle is, as a whole, slightly more enriched in Fe (or depleted in Mg) compared to the terrestrial mantle (Mg# of 75 and 81 respectively for the Martian and terrestrial bulk silicate mantle).

However, high Mg# magmas are not apparent in the geological record of Mars, not only in orbiting spacecraft and lander data [6], but also in Martian meteorite parental magma models [7]. This implies that this primordial komatiite-like crust has been altered and/or covered by following eruptive episodes and sediment deposits, and is not exposed anymore in the present crust of Mars. Mineral segregation within thick komatiite lava flows during crystallization could also lead to biased observations from spacecrafts.

References: [1] Elkins-Tanton et al. 2003. *Meteoritics & Planetary Science* 38:1753-1771. [2] Debaille et al. 2009. *Nature Geoscience* 2:548-552. [3] Debaille et al. 2007. *Nature* 450:525-528. [4] Elkins-Tanton et al. 2005. *Journal of Geophysical Research* 110: E12S01. [5] Bertka and Fei. 1997. *Journal of Geophysical Research* 102:5251-5264. [6] McSween et al. 2009. *Science* 324:736-739. [7] Usui et al. 2008. *Geochimica et Cosmochimica Acta* 72:1711-1730.

5061

MAGMA MUSH ON MARS

C. D. Deering, S. Kuehner and O. Bachmann. Dept. of Earth and Space Sciences, University of Washington, Mailstop 351310, Seattle, WA 98195-1310, USA. E-mail: cdeering@u.washington.edu.

Introduction: Magmatic differentiation on Earth appears to be governed by the extraction of interstitial melt from long-lived magma mushes [1]. Recent numerical models [2] indicate that effective melt extraction from crystal-rich reservoirs is confined to a “most probable” crystallinity window (approximately 50–70 vol.%) due to (1) low crystal settling rates at low crystallinity (as magma convects) and (2) the extremely slow melt extraction rate at high crystallinity (low permeability). A key factor in such models is that cooling, and hence crystallization rates, are slow enough for a given reservoir to remain within the optimal crystallinity window long enough for the melt extraction to occur. However, Mars is known to have a significantly lower thermal gradient (1/4 to 1/3) than Earth [3]. Consequently, the ability of magmas to remain at the optimal window of melt extraction for any appreciable length of time on Mars against this low thermal gradient may be severely restricted.

To assess differentiation processes on Mars, we performed a detailed examination of the texture and composition of pyroxene grains in the Martian meteorite NWA 5298 [4]. NWA 5298 is coarse-grained and composed predominately of large euhedral to subhedral elongated pyroxene grains (up to 4 mm in length) and interstitial subhedral laths of maskelytanized plagioclase. BSE images reveal a complex textural and chemical zoning pattern in the pyroxenes, consisting of a well defined augite core that is irregularly truncated and bounded by a distinctly more ferroan mantle (sometimes discontinuous) of augite and/or pigeonite, which in turn is also irregularly truncated by an even more Fe-rich rim. The core-mantle and mantle-rim textural discontinuities are consistent with dissolution surfaces formed during magma recharge events, a common feature found in igneous rocks on Earth. Pyroxene-only modes indicate that the first recharge occurred when the crystal fraction was at least 25% and the second recharge was at least 65%. This evaluation indicates that crystal-rich mushes exist on Mars, and are maintained at intermediate crystallinities by hot recharge.

Using the MELTS software [5], we examined whether or not the most evolved Mars meteorites (Los Angeles) represent extracted liquids from a more mafic mush. We modeled the crystallization path and melt evolution of NWA 5298 at 1 kbar, QFM-3 and anhydrous. Results show that the Los Angeles meteorite composition can be produced when this mush reaches 50–70% crystals. Relative to Earth, however, separation of even more evolved melts at higher crystal fractions is severely hindered on Mars by its lower thermal gradient and resultant higher degree of undercooling. This ensures that the probability of generating any significant amounts of evolved liquid (analogous to terrestrial basaltic-andesite) on Mars is extremely low.

References: [1] Sinton J. M. and Detrick R. S. 1992. *Journal of Geophysical Research* 97:197-216. [2] Dufek J. and Bachmann O. 2010. *Geology* 38:687-690. [3] Solomon S. C. and Head J. W. 1990. *Journal of Geophysical Research* 95:11073-11083. [4] Irving A. J. and Kuehner S. M. 2008. Abstract #5332. Meteoritical Society Annual Meeting. [5] Ghiorso M. S. and Sack R. O. 1995. *Contributions to Mineralogy and Petrology* 119:197-212.
## ISOTOPIC RATIO AND ORIGIN OF HYDROGEN IN IRON METEORITES

C. Defouilloy¹, R. Duhamel¹, F. Robert¹. ¹LMCM, CNRS-MNHN Paris, France. E-mail: cdefouilloy@mnhn.fr.

**Introduction:** We generally see Iron meteorites as pieces of differentiated bodies, whether from a totally segregated core or from droplets. Yet, Irons present some inconsistencies with the classically assumed chronology of the solar system. Their parent bodies are thought to come from the differentiation of a chondritic ancestor, but the Hf-W chronometer situates the core segregation in less than a Myr after the CAIs [1]. One way to explore the story of Iron meteorite is to trace the hydrogen's. Indeed, The D/H ratio being significantly different between the protosolar hydrogen ((D/H)$_{H2}$ = 20 ± 5 × 10⁻⁶ [2]) and hydrogen coming from water reduction during planetesimal differentiation ((D/H)$_{condritic water}$ = 150 × 10⁻⁶ [2]) it can be used as an indicator of the origin of hydrogen in the iron meteorites. Therefore, an analytical technique for measuring the D/H ratio of Iron meteorites using ion microprobe has been developed.

**Method:** hydrogen isotopic composition is determined with the CAMECA IMS 3f at the National Museum of Natural History in Paris [3]. Samples are mounted either in epoxy and Au-coated or as polished thin sections and sputtered with a primary positive Cs⁺ beam. All slits are kept wide open. Under these conditions, the mass resolution is <300 (note that with the Cs⁺ primary beam, the possible mass interference between H₂⁻ is D⁻ is negligible). To reduce to a minimum the contribution of absorbed water at the surface of the sample, we use a large ion spot (500 µm) combined with a 150 µm aperture field, so that the ions from the center of the “crater” are selectively collected. The intensity of the primary beam varies from 1 nA to 40 nA in order to keep as much as possible a secondary beam around 10⁵ cps for H and 10 for D. Data were collected in peak jumping mode, with counting time of 5 and 15 s. for H⁻ and D⁻, respectively.

**Results:** A total of seven meteorites have been studied as well as a terrestrial metallic sample from Disko Island. D/H have been calibrated with an internal standard of our own, made by rusting a sample with a water whose D/H was precisely known. Corrected from this instrumental fractionation, D/H ratios lie between 92 ± 5 × 10⁻⁶ measured in Mont Dieu and 126 ± 12 × 10⁻⁶ in Coahuila. H concentrations have been calibrated by comparing the IMS secondary beam responses to those obtained on an H-implanted golden sample. [H] varies from 0.48 ± 0.12 ppb to 119 ± 100 ppb. There is no evident correlation between D/H ratio and [H] between samples. Though, a correlation has been noticed internally for one particular sample. This last observation is thought to be a proof of spallation, which is not noticeable on any other sample. A particular care has been taken to assess terrestrial pollution and minimize any possible source of additional contamination during the measures.

Analyses of additional elements parallel to H showed a correlation between H and O and H and C, which indicates two possible carriers of H in Irons, respectively water (terrestrial contamination) and residual organic carbon (?).

**References:** [1] Kleine T. et al. 2005. *Geochimica et Cosmochimica Acta* 69:5805-5818. [2] Deloule E. and Robert F. 1995. *Geochimica et Cosmochimica Acta* 59:4695-4706. [3] Defouilloy C. et al. 2010. Abstract #1340. 41st Lunar and Planetary Science Conference.

## THERMAL HISTORIES OF CHONDRULES IN VERY LARGE PLANETESIMAL BOW SHOCKS: DID MARS MAKE CHONDRULES?

S. J. Desch and M. A. Morris. School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA. E-mail: steve.desch@asu.edu

**Introduction:** It is widely accepted that the majority of chondrules formed by passage through solar nebula shocks [1, 2], but the source of the shocks is debated, with either planetesimal bow shocks [3] or shocks driven by gravitational instabilities [4] favored [5]. Previous studies of bow shock models have indicated that the shocked region would be comparable in size to the planetesimal, approximately 10³ km, and so chondrules would necessarily pass through the region in <10³ s, and experience cooling rates >10³ K h⁻¹, inconsistent with the porphyritic textures of most chondrules [6, 7]. Additionally, the observed mass of chondrules can be produced only by assuming large numbers of 2000 km diameter planetesimals or other extreme input parameters [7, 8].

The majority of extant chondrules formed at approximately 2 Myr after the birth of the solar nebula [9]. Modeling of planetary growth [10] indicates that planetary embryos the size of Mars can grow in approximately 2 Myr, and recent Hf-W isotopic systematics indicate Mars did, in fact, form and differentiate within 2 Myr [11]. If true, then Mars formed in the presence of nebular gas and chondrules. Recent dynamical simulations further suggest Mars formed at <1 AU and by 2 Myr was ejected into an eccentric orbit (e > 0.25) centered near its current orbit at 1.5 AU [12]. A proto-Mars with a = 1.5 AU and perihelion 1.0 AU would move at up to 7 km s⁻¹ relative to local gas at aphelion at 2.0 AU and could drive a bow shock capable of melting chondrules. So did Mars form chondrules?

**Results:** We have conducted preliminary calculations using the methodology of [7], including heating by H₂ recombinations [13], to study bow shocks around planetesimals, but assuming a 3400 km radius planetesimal (Mars). We find that chondrule cooling rates are 10-100 K h⁻¹ assuming an opacity equal to a solids-to-gas ratio of 0.13 in 300 µm radius chondrules (equivalent to a solids-to-gas ratio 0.01 in 20 µm particles), so that the optical depths through the shocked region exceed unity. These cooling rates are consistent with the porphyritic textures of most chondrules [14].

**Discussion:** If Mars formed as a planetary embryo at 1 AU and was ejected into its present orbit within 2 Myr, it would have driven very large planetesimal bow shocks capable of melting chondrules in a manner consistent with constraints. We note that the presence of a magma ocean on an early formed Mars (heated by ²⁶Al) could introduce Na and other volatiles into the gas in the chondrule-forming region around the planet, possibly explaining the high inferred Na vapor pressures during chondrule formation [15]. We estimate that Mars alone could shock approximately 10²⁶ g of chondrules per Myr. We plan more detailed numerical simulations to test the provocative possibility that Mars formed chondrules.

**References:** [1] Desch S. J. et al. 2011. *Meteoritics & Planetary Science* (submitted). [2] Desch S. J. et al. 2010. *The Astrophysical Journal* 725:692. [3] Hood L. L. 1998. *Meteoritics & Planetary Science* 33:97. [4] Boss A. P. and Durisen R. H. 2005. *The Astrophysical Journal Letters* 621:137. [5] Desch S. J. et al. 2005. *CPPD* 341:849. [6] Ciesla F. J. et al. 2004. *Meteoritics & Planetary Science* 29:1809. [7] Morris M. A. et al. 2010. Abstract #293. 31st Lunar and Planetary Science Conference. [8] Hood L. L. et al. 2009. *Meteoritics & Planetary Science* 44:327. [9] Villeneuve et al. 2009. *Science* 325:985. [10] Weidenschilling S. J. 2000. *SSRv* 92:295. [11] Dauphas N. and Pourmand A. 2011. Abstract #1040. 42nd Lunar and Planetary Science Conference. [12] Hansen B. M. S. 2009. *The Astrophysical Journal* 703:1131. [13] Morris M. A. and Desch S. J. 2010. *The Astrophysical Journal* 722:1474. [14] Desch S. J. and Connolly H. C. 2002. *Meteoritics & Planetary Science* 37:183. [15] Alexander C. M. O'D. et al. 2008. *Science* 320:1617.
SPHERULES IN CHICXULUB EVENT BED DEPOSITS FROM NE
MEXICO: CLUES FROM TRACE ELEMENTS

A. Deutsch¹, P. Schulte², S. Ebert², and J. Berndt³. ¹Institut f. Planetologie, WWU Münster, D-48149 Münster, Germany. ²GeoZentum Nordbayern, Universität Erlangen, D-91054 Erlangen, Germany. ³Institut f. Mineralogie, WWU Münster, D-48149 Münster, Germany. E-mail: deutsca@uni-muenster.de.

**Introduction:** The Chicxulub impact ("K-Pg") event bed is characterized by its diversity in terms of thickness, mineralogical content, geochemical characteristics, and of processes that caused this enormous diversity [1, 2]. In this context, the amount of Chicxulub ejecta and of the local component, and the contribution of projectile matter to the event bed turned out to be much more complicated than previously thought; this development is mainly due to spatial high-resolution in situ analysis by laser-ablation-mass spectrometry (LA-ICP-MS) [3].

Specifically, the Chicxulub event bed around the Gulf of Mexico contains different types of spherules, composed either of calcium carbonates or silicate glass and their alteration products, or of complicated-textured carbonate and silicate compositions [4]. Compared to the Si-Al-rich ejecta spherules present elsewhere in the Gulf of Mexico area [1, 2], the event bed in NE Mexico contains unusually, Fe-, Mg-, and K-rich (nearly) isotropic spherules [5]. To constrain the origin of these materials in the La Popa area, we performed a series of micro-chemical investigations using electron microprobe and LA-ICP-MS.

**Methods:** The particles were characterized by electron optical methods, and than analyzed in > 100 µm-thick thin sections. Spot size of the LA-ICP-MS at the WWU was between 50 and 100 µm. Details of the analytical methods are given in [3].

**Results:** All analyzed glass spherules are hydrated yielding analytical totals of 88 to wt%; we distinguish Fe-Mg-, and a Si-Al-K-rich particles. The first group is composed of up to 28 wt% FeO and 12 wt% MgO the Si-Al-K-rich particles contain up to 48 wt% SiO₂, 25 wt% Al₂O₃, and 8 wt% K₂O. The particles may consist entirely of one of these phases or both phases occur within one particle as blobs or sharply separated schlieren; mixed phases have not been observed.

The spherules have generally low trace element contents; rare earth elements (REE) are sub-chondritic (0.1 × C1) to chondritic with flat C1-normalized distribution patterns. The lack of Ce and Eu anomalies indicates a closed water-rock system during diagenesis. The Ni/Cr ratio is approximately 1 in the Fe-Mg-rich, and approximately 0.8 in the Si-Al-K-rich spherules.

**Outlook:** Bulk material from the K-Pg event beds usually display REE abundances and distribution patterns similar to that one of the upper continental crust (e.g., [6]). Our high-resolution in situ analyses allow for the first time constraining the presence of materials with obviously different precursor lithologies.

**References:** [1] Schulte P. et al. 2010. *Science* 327:1214–1218. [2] Schulte P. et al. 2011. *Sedimentology*, in press. [3] Berndt J. et al. 2011. *Geology* 39:279–282. [4] Deutsch A. et al. 2010. *Meteoritics & Planetary Science* 45:A45. [5] Schulte P. and Kontny A. 2005. *GSA Special Paper* 384:291–221. [6] Martinez-Ruiz F. et al. 2006. *Chemical Geology* 232:1–11.
We appreciate funding by the DFG.

AL HAGGOUNIA 001: A WEATHERED EL6 CHONDRITE

A. Devaux¹, A. Jambon¹, O. Boudouma¹, D. Badia¹, E. Charon², J. N. Rouzaud² and J.-A. Barrat³. ¹UPMC-PARIS 6, ISTEP 4 place Jussieu, 75005 Paris France. CNRS UMR 7193. ²Laboratoire de Géologie de l'ENS, UMR CNRS 8538, 24 rue Lhomond, 75005 Paris, France ³UBO I.U.E.M., Place Nicolas Copernic, 29280 Plouzané Cedex, France. CNRS UMR 6538

**Introduction:** Al Haggounia (AHa) 001 is a significant find (several tons), the strewnfield of which extends over nearly 50 km [1]. The fall was dated 23 ka B.P. by ¹⁴C; therefore it is not a fossil meteorite as confirmed by field evidences [1]. Its classification is however controversial: AHa 001 was classified as an aubrite [2] but paired stones were classified as EL3, EL6, EL7, enstatite achondrite and aubrite [2, 3]. One obvious reason for this disagreement resides in its severely weathered state and possibly in the variability among such a large number of stones of varied sizes. This can be illustrated in its magnetic susceptibility (log(χ)), which varies from 2.8—an aubrite like value—up to 4.9 as for a slightly weathered enstatite chondrite (fresh 5.5 ± 0.2). The present study is based on the observation of a large number of hand specimens, five polished sections and one thin section. Two types of rocks are typical: (1) brownish, heavily rusted samples with fractures filled of iron oxide-hydroxides and (2) bluish samples or remnant cores of several cm to dm surrounded by variable amounts of brownish material and limited by oxide-hydroxide filled fractures.

**Results:** Faint chondrules about 1 mm in size are quite rare (less than 0.2 per cm² on the average) and therefore not found in every section. Bulk chemical composition is of no help to discriminate between E chondrite and aubrite, as metal and sulfide have been heavily weathered when not leached away. The blue-grey sections in particular exhibit a porosity of about 40% as a result of leaching of all sulfides and metal. Brownish fractions however have some preserved sulfide and metal cores. Minor components in sulfides are useful in determining the type and metamorphic grade [4]. This approach however in hampered by the small size of preserved relict crystals. The Si content of kamacite (1 wt%) favors an EL type. The organization degree of carbon as obtained from Raman spectra has been used in order to characterize EH3 and EL3 [5]. As proposed by [6] we used the width of the G band as a reliable parameter of graphitization and not the classical ID/IG affected by polishing artifacts [6]. In AHa the carbon component is well ordered since its FMWH G (19 cm⁻¹) is close to the canonical graphite value. In contrast matrix carbon in type 3 exhibits a broad G band (FMWH-G > 60 cm⁻¹) and well developed D1 and D2 defect bands characteristic of a still disordered carbon [5]. It follows that all matrix carbon in AHa was subject to a significant metamorphism.

**Conclusions:** From the texture and carbon crystallinity the metamorphic grade is as high as a type 6. According to the presence of ghost chondrules, an aubrite classification is not justified. Search for preserved sulfides will help confirming this diagnosis.

**References:** [1] Chennaoui-Aoudjehane H. et al. 2007. *Meteoritics & Planetary Science* 42:5329. [2] *Meteoritical Bulletin* 84, 87, 89–91, 94, 96. [3] Irving A. et al. 2006. *Meteoritics & Planetary Science* 41:5264. [4] Zhang et al. 1995. *Journal of Geophysical Research* 100:9417. [5] Quirico E. et al. 2011. *Geochimica et Cosmochimica Acta* 75:3088. [6] Ammar and Rouzaud J.-N. 2011. *Journal of Raman Spectroscopy*, in press.