5413

CRYSTALLINE SILICATES IN COMET 81P/WILD 2 FROM THE STARDUST TRACK 81

E. Dobrică and A. J. Brearley. Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, NM 87131-0001, USA. E-mail: edobrica@unm.edu.

**Introduction:** Previous studies of Stardust samples collected from comet 81P/Wild2 have reported abundant crystalline phases, presumably formed in the asteroid belt [1, 2]. In this study, we describe the mineralogical composition of one ultramicrotome section from track 81 (C2092.7.81.1.10) examined by transmission electron microscopy (TEM).

**Results and Discussion:** The microtome section is a polycrystalline aggregate dominated by pyroxenes and plagioclase feldspar. Due to chattering from the microtome sample preparation, it is not possible to determine the exact grain size of the individual phases, but we estimate that the grains are typically submicron to micron in size. We identified low-Ca and Ca-rich pyroxenes (n = 12, En80-95 Wo1-8; n = 5, En52-63 Wo32-38), plagioclase (n = 21, An45-85 Ab13-55 Or0-2) and rare, nanometric sulfides. No olivines were found. Low-Ca pyroxenes are enriched in Cr2O3 (up to 1.8 wt%; avg. 1.1 wt%), MnO (up to 2.4 wt%; avg. 1.3 wt%) and also contain significant Al2O3 (up to 3.8 wt%; avg. 2.6 wt%). Ca-rich pyroxenes contain lower amounts of Cr2O3 (up to 0.9 wt%, avg. 0.5 wt%) and MnO (up to 0.8 wt%, avg. 0.6 wt%) but have TiO2 contents up to 1.3 wt% (avg. 1.1 wt%). The low-Ca pyroxene compositions are extremely unusual having Mn/Fe ratios up to 70× CI, higher that the value of olivines measured previously in Stardust samples [2] (Mn/Fe ratios up to 50× CI). Low-Ca pyroxene Cr2O3 and MnO contents correlate positively with Al2O3, a relationship that is also observed in low-iron, manganese-enriched (LIME) minerals from interplanetary dust particles (IDP) [3]. The LIME silicates have generally been interpreted as condensates from a gas of solar composition [3]. The compositions of Ca-rich pyroxenes in this particle are also distinct from those found in Kool grains from other Stardust particles [1]. The Al2O3 and TiO2 contents are higher and CaO and Cr2O3 lower in the Ca-rich pyroxenes analyzed in this study. However, the average concentrations of Na2O (2.1 wt%) and MnO (avg. 0.5 wt%) are comparable in both studies.

Although the assemblage enstatite, clinopyroxene, and plagioclase feldspar does occur in some plagioclase-bearing chondrules in carbonaceous chondrites [4], the fine-grained character, textural relationships, and unusual compositions of the pyroxenes make this particle quite distinct from any known chondritic material. The ambiguous textural relationships between the different phases due to microtoming also prevent any definitive statement about whether the particle is igneous in origin. However, the compositions of the pyroxenes in this particle share similarities to terrestrial igneous pyroxenes that accept Al³⁺ into the tetrahedral sites, creating a charge imbalance that requires the simultaneous entry of Cr³⁺, Ti⁴⁺, or Fe³⁺ in the octahedral sites [5]. Irrespective of the exact formation mechanism of this particle, it is clear that the pyroxene mineral chemistry is indicative of another unique type of material in comet 81P/Wild 2 that has not been sampled by any known primitive meteorite, but was present within the feeding zone for the accretion of the Jupiter Family comets.

**References:** [1] Joswiak D. J. et al. 2009. *Meteoritics & Planetary Science* 44:1561–1588. [2] Brownlee D. E. et al. 2009. *Cosmic Dust* 157. [3] Klöck W. et al. 1989. *Nature* 339. [4] Scott E. R. D. and Krot A. N. 2005. *Meteorites, comets and planets*. Oxford. [5] Campbell I. H. and Borley G. D. 1974. *Contributions to Mineralogy and Petrology* 47:281–297.

5452

MICROSTRUCTURAL STUDY OF THE TEXTURE AND MINERALOGY OF TIESCHITZ WHITE MATRIX

E. Dobrică and A. J. Brearley. Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, NM 87131-0001, USA. E-mail: edobrica@unm.edu.

**Introduction:** Tieschitz is an unequilibrated ordinary chondrite (UOC) classified as petrologic type H/L3.6 [1]. This meteorite displays several unique features, notably two types of matrices, termed white and black matrix [2, 3]. The white matrix is enriched in Na, K, and Al [2–5] and has been interpreted as a remobilized component of chondrules, i.e., mesostasis glass which had been leached out and redeposited by a fluid phase [4, 5]. Previous studies have reported the presence of plagioclase and nepheline [6] as the major components of white matrix. However, there are still significant uncertainties regarding the origin of white matrix that remain unresolved. Here we report new observations on white matrix carried out using focused ion beam (FIB)/transmission electron microscopy (TEM) techniques.

**Sample and Methods:** A variety of TEM techniques were used to examine two FIB sections of white matrix using a JEOL 2010F FEG TEM/Scanning TEM operating at 200 kV.

**Results and Discussion:** White matrix in Tieschitz is found as veins often surrounded by black matrix. Our TEM observations are in agreement with previous work [7], showing that white matrix is an intergrowth of two or more phases. The intergrowth is composed of an amorphous phase which could be a glass or a crystalline phase that was amorphized during the electron beam irradiation. Compositionally, this phase has similarities to both albite and nepheline. It is enriched in SiO2 (~60 wt%), Al2O3 (~29 wt%), and Na2O (~7 wt%) with minor amounts (< 1 wt%) of MgO, K2O, CaO, and FeO. The second phase is crystalline and occurs as elongate, oriented arrays that define a lamellar intergrowth with the amorphous phase. The composition and the crystal structure of these lamellae are consistent with a Ca-rich pyroxene (En28 Wo43). These pyroxene lamellae are typically ~30 nm wide and range 400 nm to ~2 µm in length. Veins of olivine (Fo56) were also identified within the intergrowth.

Our new observations confirm the complexity of white matrix in Tieschitz [3, 7, 8], but differ somewhat from the observations in previous studies. We have identified the presence of Ca-rich pyroxene, which was observed by [7], but not characterized. Unlike [7], we have not observed a twinned, beam sensitive phase, but instead have found an amorphous material with a composition close to albite or nepheline. A possibility remains that the amorphization could be the result of FIB sample preparation and requires further investigation. None of our observations provide definitive evidence of the involvement of an aqueous fluid in the formation of the white matrix. Nevertheless, the clear evidence of leaching of Na-Al-bearing mesostasis in chondrules [8], indicates that fluid mass transport must have played an important role in the formation of the white matrix.

**References:** [1] Sears D. W. et al. 1980. *Nature* 287:791. [2] Christophe Michel-Levy M. 1976. *Earth and Planetary Science Letters* 30:143–150. [3] Dobrică E. and Brearley A. J. 2011. Abstract #1889. 42nd Lunar and Planetary Science Conference. [4] Ashworth J. R. 1977. *Earth and Planetary Science Letters* 35:25. [5] Hutchison R. et al. 1979. *Nature* 280:116. [6] Ashworth J. R. 1981. *Proceedings of the Royal Society of London. Series A* 374:179–1974. [7] Alexander C. M. O. et al. 1989. *Earth and Planetary Science Letters* 95:187. [8] Hutchison R. et al. 1998. *Meteoritics & Planetary Science* 33:1169–1179.
## MÖSSBAUER STUDY OF Fe-Ni PHASES IN MESOSIDERITES

E. Dos Santos¹, R. B. Scorzelli¹ and M. E. Varela². ¹Centro Brasileiro de Pesquisas Físicas, RJ, Brazil. ²ICATE—CONICET, San Juan, Argentina.

Following previous studies [1] on the applications of Mössbauer spectroscopy to the meteoritic Fe-Ni metal structures, the present work focuses on the study of Fe-Ni alloys in mesosiderites. The metal from this enigmatic rocks has the lowest cooling rates yet determined for meteorites.

We are performing a systematic study on the following mesosiderite: Vaca Muerta, Mincy, Crab Orchard, Estherville, and Hainholz. Thin ~500 µm slices are cut from the metal-rich areas and then polished to thicknesses of ~150 µm.

The Mössbauer spectra of untreated bulk samples exhibit overlapping of Fe-Ni phases, with kamacite being the dominant phase. This abundance makes the detection of the taenite phases difficult, which contains in its microstructure the intergrowth of tetrataenite and antitaenite [2]. In order to determine the presence of tetrataenite/antitaenite intergrowth that have been observed in ataxites, octahedrites and metal particles of chondrites [3, 4] and better define the degree of ordering of tetrataenite, we are analyzing taenite fractions extracted from these mesosiderites by etching the metallic samples with HCl/HNO₃.

The corresponding Mössbauer hyperfine parameters obtained from the analysis of the spectra, although preliminary, seem to support the reported very slow cooling rate of this unique group of meteorites.

**References:** [1] Scorzelli R. B. and Souza Azevedo I. 2001. *Meteoritics & Planetary Science* 36/9:A185. [2] Rancourt D. G. and Scorzelli R. B. 1995. *Journal of Magnetism and Magnetic Materials* 150:30-36. [3] Danon J., Scorzelli R. B., Azevedo I. S., and Michel-Levy M. C. 1979. *Nature* 281:469-471. [4] Danon J., Scorzelli R. B., Azevedo I. S., Curvello W., Albertsen J. F., and Knudsen J. M. 1979. *Nature* 277:283-284.

## EARLY SOLAR SYSTEM PROCESSES REVEALED BY AN INTEGRATED STUDY OF UREILITE METEORITES

H. Downes¹,²,³, C. L. Smith², A. D. Beard¹,² and A. J. Ross²,³. ¹Department of Earth and Planetary Sciences, Birkbeck University of London, Malet St, London WC1E 7HX UK. E-mail: h.downes@ucl.ac.uk. ²Department of Mineralogy, Natural History Museum, Cromwell Road, London, UK. Centre for Planetary Sciences at ³UCL/Birkbeck, UCL, Gower St. London, UK.

**Introduction:** Far from being “bizarre” and “perplexing,” ureilite meteorites provide us with a wealth of information about processes in the early solar system which have important implications for the formation of the Earth and other terrestrial planets. The ureilite parent body (UPB) was formed by accretion from a chondritic precursor (as seen in the distribution of oxygen isotope values), which was rich in carbon (ureilites contain up to 6 wt% C, which exceeds typical values in carbonaceous chondrites). The UPB then underwent differentiation, forming an Fe-rich core and ultramafic silicate mantle, but did not achieve the magma ocean stage experienced by many other planets and asteroids (i.e., its mantle did not homogenize in terms of mg# and δ¹⁸O) [1]. Thus it provides a window into pre-magma ocean processes not available from any other source. Partial melting of the mantle of the UPB (heated by short-lived radioactive isotopes) produced magmatic activity, as revealed by basalt melt droplets, melt inclusions, LREE-depletion in the silicate mantle phases, and some regions of pyroxene-rich mantle. Extensive magmatic differentiation may also have resulted in small volumes of evolved magmas that formed granitoid-like material [2].

**Impact and Reaccretion:** Ureilites also yield information about impact processes in the early solar system, as many of them are polymict regolith breccias [3]. The original UPB was disrupted by a major impact while it was undergoing partial melting [1]. This produced extensive reduction of silicates to metal in the presence of graphite [4], and also caused the formation of Fe-Ni silicides [5]. If incorporated into larger accreting bodies, such silicides may have contributed to strongly reduced cores in early formed terrestrial planets. Graphite was converted to diamonds by this shock event [6]; thus not all of the carbon accreted to terrestrial planets and asteroids was in the form of the low-temperature organic component found in carbonaceous chondrites. Following the disruptive impact, a daughter planetesimal rapidly reformed by reaccretion, producing a rubble-pile asteroid which is the body sampled by present-day ureilite meteorites. On the surface regolith of this asteroid, impact gardening occurred, with accretion of late veneers of chondritic and other material, including many unusual “orphan” clasts that have no equivalent in our meteorite collections [1]. These clasts are more variable than those found in regolith breccias from the HED parent body. A late addition of water formed opal (hydrated silica) in some areas of the regolith of the ureilite asteroid [7].

**References:** [1] Downes H. et al. 2008. *Geochimica et Cosmochimica Acta* 72:4825-4844. [2] Downes H. et al. 2009. Abstract #5036. 72nd Annual Meteoritical Society Meeting. [3] Goodrich C. et al. 2004. *Chemie der Erde* 64:283-327. [4] Warren P. H. and Huber H. 2006. *Meteoritics & Planetary Science* 41:835-849. [5] Smith C. L. et al. 2010. Abstract #5221. 73rd Annual Meteoritical Society Meeting. [6] Ross A. J. et al. 2011. *Meteoritics & Planetary Science* 46:364-378. [7] Beard A. D. et al. This conference.
5020

## GEBEL KAMIL: THE IRON METEORITE THAT FORMED THE KAMIL CRATER IN EGYPT

M. D'Orazio¹, L. Folco², A. Zeoli² and C. Cordier². ¹Dipartimento di Scienze della Terra, Università di Pisa, Italy. E-mail: dorazio@dst.unipi.it.
²MNA, Siena, Italy.

The 45 m-diameter Kamil impact crater (eastern Sahara, Egypt) was formed <5000 years ago within Cretaceous quartz-arenites of the Gilf Kebir Formation [1, 2]. Most of the pristine features of the impact structure are exceptionally well preserved, including thousands of fragments of the iron meteorite impactor, the Gebel Kamil meteorite. With the exception of a single 83 kg regmaglypted individual showing remnants of the fusion crust, all specimens of Gebel Kamil are explosion fragments (shrapnel) weighing from <1 g to 34 kg. The shrapnel shapes vary from flattened, twisted and jagged to rounded and equidimensional. Gebel Kamil is an ungrouped Ni-rich (about 20 wt% Ni) ataxite characterized by high Ge and Ga and relatively low Ir contents (~120, ~50 and ~0.5 µg g⁻¹, respectively), and by a fine-grained duplex plessite metal matrix. The metal matrix often contains spindles of kamacite (15–25 µm in width) nucleated onto small schreibersite crystals, and arranged in a micro-Widmannstätten pattern. Accessory minerals are, in order of decreasing abundance, schreibersite, troilite, daubréelite, and native copper. Schreibersite and troilite are typically enveloped in swathing kamacite. Terrestrial weathering is extremely low and confined to the portions closest to the external surface. Shrapnel fragments are invariably cross-cut by curvilinear shear bands formed during the explosive impact on Earth. These structures are not observed in the individual specimen which detached from the main body prior to impact. In terms of structure and bulk chemical composition Gebel Kamil is similar to the Morradal ungrouped Ni-rich ataxite [3].

Systematic search around the crater revealed that meteorite fragments have a highly asymmetric distribution, with greater concentrations in the southeast sector. A broad maximum in meteorite concentration occurs in the 125°–160° N sector at about 200 m from the crater rim. The mass of meteorite specimens >10 g recovered in the field is 1700 kg, whereas the total mass inferred from the density map compiled in this study is 3400 kg. Field data indicate that the iron bolide approached the Earth's crust from the northwest (305°–340° N), traveling along a moderately oblique (30°–45°) trajectory, following [4]. Upon hypervelocity impact, the projectile was disrupted into thousands of fragments. Shattering was accompanied by some melting of the projectile and of the quartz-arenite target rocks, which also suffered variable degree of shock metamorphism (formation of planar fractures, mosaicism, and planar deformation features in quartz). Interestingly, some of this melted and shocked material stuck onto the shrapnel surfaces and was occasionally preserved from the erosive action of wind-driven sand.

**Acknowledgments:** Supported by EC (Marie Curie Actions–RTNs ORIGINS project), Fondazione Cassa di Risparmio di Torino, Banca Monte dei Paschi di Siena S.p.A., Fondazione Monte dei Paschi di Siena, and Telespazio S.p.A.

**References:** [1] Folco L. et al. 2010. *Science* 329:804. [2] Folco L. et al. 2010. *Geology* 39:179–182. [3] Buchwald V. F. 1975. *Handbook of iron meteorites*, vol. 3. Berkeley, USA: University of California Press. 1416. [4] Melosh H. J. 1989. *Impact cratering. A geologic process*, Oxford Monographs on Geology and Geophysics. Oxford: Oxford University Press. 245 p.

5507

## METAMORPHISM IN THE NEWLY RECOVERED MASON GULLY (H5) ORDINARY CHONDRITE AND ITS CORRELATION TO ANOMALOUS PROPERTIES

K. A. Dyl¹,², G. K. Benedix², P. A. Bland¹, M. C. Towner¹ and P. Spurny³. ¹Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK. E-mail: kdyl@imperial.ac.uk. ²Department of Mineralogy, Natural History Museum, London SW7 5BD, UK. ³Astronomical Institute of the Academy of Sciences, Fričova 298, CZ-251 65 Ondřejov Observatory, Czech Republic.

**Introduction:** Mason Gully (MG) is a new H5 ordinary chondrite recovered by the Desert Fireball Network in November 2010 [1]. The presence of discernable chondrules and the major element composition of olivine, pyroxene, and plagioclase support this classification. It is characterized by unusually high porosity and has an unusual modal composition for an H chondrite with orthopyroxene being more abundant than olivine. We used the EVO 15LS variable pressure scanning electron microscope at the NHM to examine reaction textures, compositional variation, and phase relationships in this meteorite, specifically in porous areas associated with plagioclase. These observations identify several ways to constrain metamorphic conditions and may explain the unusual properties of this new meteorite fall.

**Reaction and Formation of Pyroxene:** The primary metamorphic reaction observed is qualitatively characterized as follows (in terms of major elements):

$$2\text{Mg}_2\text{SiO}_4 + \text{CaAl}_2\text{Si}_2\text{O}_8 \rightarrow \text{Mg}_2\text{Si}_2\text{O}_6 + \text{CaMgSi}_2\text{O}_6 + \text{MgAl}_2\text{O}_4 \text{ olivine} + \text{anorthite} \rightarrow \text{low-Ca px} + \text{high-Ca px} + \text{spinel.}$$

Evidence for this reaction includes: low-Ca pyroxene replacing olivine, spinel (chromite) formation along grain boundaries, and pyroxene growth at plagioclase-olivine phase boundaries.

**Conditions of Metamorphism:** The temperature and oxygen fugacity associated with metamorphism can be constrained via this reaction. Preliminary calculations using olivine-chromite Fe–Mg exchange and two-pyroxene thermometry suggest more oxidizing conditions at lower temperature (IW-1.5 to IW-0.3) [2]. Further investigation is required to determine what this difference means for the evolution on the parent body.

The Na-rich composition of plagioclase in ordinary chondrites is also a consequence of the reaction we have identified [3, 4]. Further work will determine to what extent the Na/Ca content varies and the role of other processes invoked to explain Na-rich plagioclase (i.e., impact melting [5], fluid phase [4]).

**Relationship to Bulk Properties:** Several unusual bulk properties of Mason Gully are consistent with this reaction.

**Modal Abundances.**

The production of pyroxene is one explanation for the modal mineralogy of Mason Gully; the observation of 38% orthopyroxene is significantly higher than the 26% expected in H chondrites [3].

**High Porosity.**

The reaction identified above is commonly observed in granulite-facies metamorphism (high-temperature, low-moderate pressure). There is evidence for the presence of CO₂-rich fluids in these reaction assemblages [6], which may explain the high porosity observed in Mason Gully.

**References:** [1] Towner M. et al. 2011. *Meteoritics & Planetary Science* 46. This conference. [2] Benedix G. K. et al. 2005. *Geochimica et Cosmochimica Acta* 69:5123–5131. [3] McSween H. Y. and Bennett M. E. 1990. *Icarus* 90:107–116. [4] Kovach H. A. and Jones R. H. 2010. *Meteoritics & Planetary Science* 45:246–264. [5] Rubin A. E. 2003. *Geochimica et Cosmochimica Acta* 67:2695–2709. [6] Selverstone J. 1982. *Contributions to Mineralogy and Petrology* 79:28–36.
## SEQUENTIAL ACCRETION AND ANNEALING OF SEPARATE SILICATE AND METAL LAYERS IN A CR CHONDRITE CHONDRULE

D. S. Ebel¹ and M. R. Downen². ¹Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th St, New York, NY 10024, USA. E-mail: debel@amnh.org. ²Geography and Geology, Western Kentucky University, 1906 College Heights Blvd. #31066, Bowling Green, KY 42101-1066, USA.

**Introduction:** Computed tomography (CT) reveals the 3D shapes and metal abundances in spherical, FeO-poor, metal-rimmed chondrules in CR chondrites [1]. Hypotheses for their formation [2, 3] include a mechanical segregation process [4], or vaporization and recondensation of Fe-Ni alloy during cooling. The latter scenario predicts that siderophile element abundances were gradually established during multiple melting events, due to reduction of FeO-bearing olivine and evaporation of S from sulfides. Repeated heating advanced this process, coarsened silicate grains, and promoted a spherical shape of the resulting chondrules [5-9]. Here, an alternative model is proposed, based on texture and chemistry of a large chondrule in Acfer 139 (CR2). This is an extreme example of similar layering observed in CT images of CR chondrite chondrules.

**Methods:** Acfer 139-t2-ch1 was imaged by synchrotron (APS) and conventional CT (AMNH). Serial thick sections to the core of this approximately 3.5 mm chondrule provided detailed chemical and textural information on four discrete, concentric, metal layers surround, sulfide-free, almost metal-free silicate layers.

**Results:** The innermost approximately 1 mm diameter, metal-free, pyroxene-free, Mg#98 core has an annealed barred olivine texture. It is surrounded by many non-connected 5-20 µm metal beads. Next is a 400-600 µm enstatite-bearing, Mg#98, porphyritic olivine layer, with a nearly continuous metal shell up to 150 µm thick. The next silicate layer, 300-500 µm, has olivine/pyroxene approximately 0.7, Mg#98 in both, with a thin, up to 100 µm thick, near-continuous metal shell. The outermost silicate layer is less continuous, 200-400 µm thick, with modal pyroxene > olivine, surrounded by a thin metal shell.

**Discussion:** This texture seems inconsistent with multiple episodes of heating at >1800 K for durations sufficient to evaporate and recondense metal from successive layers [5-9], leaving interior layers intact. But it is consistent with independent accretion and rapid annealing of alternating layers of silicate and metal particles in a reducing, cooling disk environment, as in [10].

**References:** [1] Ebel D. S. et al. 2008. *Meteoritics & Planetary Science* 43:1725-1740. [2] Connolly H. C. Jr. et al. 2001. *Geochimica et Cosmochimica Acta* 65:4567-4588. [3] Campbell A. J. et al. 2005. In *Chondrites and the protoplanetary disk*, edited by Krot A. N. et al. Astronomical Society of the Pacific Conference Series 341:407-431. [4] Wasson J. T. & Rubin A. E. 2010. *Geochimica et Cosmochimica Acta* 74:2212-2230. [5] Kong P. et al. 1999. *Geochimica et Cosmochimica Acta* 63:2637-2652. [6] Zanda B. et al. 2002. Abstract #1852. 33rd Lunar and Planetary Science Conference. [7] Humayun M. et al. 2002. Abstract #1965. 33rd Lunar and Planetary Science Conference. [8] Varley L. R. et al. 2003. Abstract #1899. 34th Lunar and Planetary Science Conference. [9] Humayun M. et al. 2010. Abstract #8004. Chondrules: Their role in early solar system history. [10] Weisberg et al. 1992. *Meteoritics* 27(suppl.):A306.

**Support:** NASA-COS-NNX10AI42G, NSF-EAR-0959384(DSE); NSF-EAR-0622171, DoE-Geo-DE-FG02-94ER14466 (APS).

## THERMODYNAMIC STABILITY OF LOW-IRON MANGANESE-ENRICHED OLIVINE IN THE SOLAR NEBULA

D. S. Ebel¹,³ and M. K. Weisberg¹,²,³. ¹Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th St, New York, NY 10024, USA. E-mail: debel@amnh.org. ²Kingsborough College, CUNY, Brooklyn, NY. ³Graduate Center of the City University of New York, NY, USA.

**Introduction:** A significant fraction of olivine and Ca-poor pyroxene grains in primitive extraterrestrial materials are very low in Fe, and Mn-enriched. These LIME silicates (primarily olivine) have wt% MnO/FeO > 0.1, and usually <1.0 wt% FeO. They occur in Allende (CV3) silicates [1], interplanetary dust particles [2], Type I chondrules [3] and amoeboid olivine aggregates [4, 5] in CR chondrites, and Wild 2 cometary particles [6, 7]. Here, we clarify the reduction/oxidation conditions in which the Mn component (tephroite, Mn-Ol) of olivine solid solution may be more thermodynamically stable relative to the Fe component (fayalite, Fe-Ol), in vapors of solar composition, and in vapors enriched in a dust of CI chondritic composition [8,9].

**Methods:** (1) Reactions involving O₂ (e.g., 2Mn + O₂ = 2MnO) in a G<sub>rxn</sub> = RTln(fO₂) vs. temperature (T) were plotted on the classic nomogram [10, Fig 14-4]. Previous results for CI-dust enriched systems [8] were used to compute the stability (G<sub>rxn</sub>) of olivines with mole fractions 0.1 and 0.5 Mn-Ol and Fe-Ol, relative to solar, 100 × CI and 1000 × CI chemical systems at total pressure (P<sup>tot</sup>) 10<sup>-3</sup> and 10<sup>-6</sup> bar, vs. T. These curves illustrate the relative stability of Mn-Ol and Fe-Ol, by their intersections with RTln(fO₂) calculated for each chemical system. (2) A Mn-, Ni- olivine solid solution model [11] was integrated into the code for vapor-solid-liquid equilibria in cooling gases [8, 12], to predict MnO/FeO in silicates in particular chemical systems.

**Results:** In vapor of solar composition LIME olivines are stable at T where olivine is in equilibrium with vapor, and some Si remains in the vapor. In systems enriched > 50× in CI dust [8, 9], Fe-Ol becomes stable at T higher than Mn-Ol.

**Discussion:** In chemical systems where Mn-Ol becomes stable at higher T than Fe-Ol, significant forsteritic olivine (Mg₂SiO₄) has condensed at even higher T. This is consistent with textures in AOA olivine with Mn-rich rims [4]. LIME olivines are sensitive indicators of oxygen fugacity. In chemical systems investigated here, they are only stable in reduced vapors (solar composition). Silicate melts are not stable in such systems except at P<sup>tot</sup> > 10<sup>-2</sup> bar [9, plate 7], consistent with most (but not all) LIME olivine occurring in melt-free primitive materials.

**Acknowledgments:** Work was supported by NASA-COS-NNX10AI42G (DSE), NASA-COS-NNG06GG44G (MKW).

**References:** [1] Rubin A.E. 1984. *American Mineralogist* 69:880-888. [2] Klöck et al. 1989. *Nature* 339:126-128. [3] Weisberg et al. 1995. *Proceedings of Symposium Antarctic Meteorites* 8:11-32. [4] Weisberg M. K. et al. 2004. *Meteoritics & Planetary Science* 39:1641-1653. [5] Sugiura N. et al. *Meteoritics & Planetary Science* 44:559-572. [6] Zolensky et al. 2006. *Science* 314:1735-1739. [7] Nakamura et al. 2008. *Science* 321:1664-1667. [8] Ebel D. S. and Grossman L. 2000. *Geochimica et Cosmochimica Acta* 64:339-366. [9] Ebel 2006. In *Meteorites & the early solar system II*, 253-277. [10] Darken L. S. and Gurry R. W. 1953. *Physical Chemistry of Metals*. McGraw Hill. [11] Hirschmann M. M. and Ghiorso M. S. 1994. *Geochimica et Cosmochimica Acta* 58:4109-4126. [12] Ghiorso M. S. and Sack R. O. 1995. *Contributions to Mineralogy and Petrology* 119:197-212.
INTER-ELEMENT FRACTIONATION PROCESSES BETWEEN
TARGET MELTS, PROJECTILE MATTER AND SHOCKED
QUARTZ IN CRATERING EXPERIMENTS

M. Ebert¹, L. Hecht¹, A. Deutsch², T. Kenkmann³. ¹Museum für
Naturkunde, Invalidenstrasse 43, D-10115 Berlin, Germany, E-mail:
Matthias.Ebert@mfn-berlin.de. ²Univ. Münster, Wilhelm-Klemm-Str. 10;
D-48149 Münster. ³Univ. Freiburg, Albertstr. 23b, D-79104 Freiburg,
Germany.

**Introduction:** The detection of meteoritic components in impact-derived rocks is of great diagnostic value for confirming an impact origin [1]. The processes of mixing projectile matter into target and impactite materials are far from being understood. We present results of hypervelocity cratering experiments using a natural sandstone target and iron meteorite matter as projectile.

Experiments have been performed at the two-stage acceleration
facilities of the Fraunhofer Ernst-Mach-Institute (Freiburg, GER). Our
results are based on experiment #3298 [2] using a Campo del Cielo
meteorite sphere projectile (Ø 10 mm) accelerated to ~4.5 km s⁻¹ (Eₖin
~43 kJ) and as target a 50 × 50 × 50 cm block of Seeberger Sandstone.
Ejecta material was captured with a catcher system [3] and analyzed by
an electron microprobe.

**Results:** The ejecta fragments show metamorphic shock features (PDFs in Qtz, diaplectic glass, lechatelierite) and partial melting of the clay-bearing sandstone matrix, which involves Qtz too. Droplets of projectile have only entered the sandstone melt.

Projectile residues occur as spheres, spheroids or partly molten
fragments in the ejecta. The residues are enriched in Ni and Co and
depleted in Fe compared to the Campo del Cielo meteorite. The spheres
vary strongly in composition (Ni: 5.6-17.3 wt%, Co: 0.4-1.3 wt%, Fe:
77.7-94.0 wt%). Enrichment of Ni and Co versus Fe correlates negatively
with the sphere-size.

Sandstone melt consists of SiO₂ (51–94 wt%), (1.9–17 wt%), FeO (4.5–32 wt%), and NiO (0.01–0.9 wt%). Components of this mixture are Qtz, clay-bearing sandstone matrix (with FeO = 3.2 wt%) and up to ~20% projectile matter. The Fe/Ni-ratio of the sandstone melt is generally below the projectile ratio.

Shocked quartz with PDFs, diaplectic glass and lechatelierite contain slightly FeO (<1.7 wt%) and NiO (<0.08 wt%). The average FeO content of the high-shocked Qtz is 0.58 wt%.

**Discussion:** Our analyses suggest inter-element fractionation between
projectile and target in different impact stages. (A) After shock
compression with formation of PDFs in Qtz, diaplectic glass or
lechatelierite, and during early unloading, <1% of projectile matter is
added to the glass phases without detectable fractionation. (B) Later,
when waste heat triggers melting of the sandstone, molten projectile is
mixed with the sandstone melt and significant element fractionation
occurs. Fe is selectively enriched in the silicate melt; Ni and Co are
enriched over Fe in coexisting projectile spherules. Comparable processes
have been reported in natural impactites [4–6]. The increase of
fractionation with decreasing spheres-size shows that the fractionation of
Fe, Ni, and Co occurs during solution of the metal spheres in the silicate
melt due to differences in chemical reactivity [6].

**References:** [1] Koeberl C. 1998. *Geological Society Special Publication* 140. pp. 133–153. [2] Poelchau M. et al. 2011. Abstract #1824. 42nd Lunar and Planetary Science Conference. [4] Domke I. et al. Abstract #1605. 41st Lunar and Planetary Science Conference. [3] Reiser F. et al. 2011. Abstract #1733. 42nd Lunar and Planetary Science Conference. [4] Mittlefehldt D. W. et al. 1992. *Meteoritics* 27:316–370. [5] Gibbons R. V. et al. 1976. Proceedings, 7th Lunar Science Conference. pp. 863–880. [6] Kelly W. R. et al. 1974. *Geochimica et Cosmochimica Acta* 38:533–543.

ALMAHATA SITTA MS-17 EL-3 CHONDRITE FRAGMENT: CONTRASTING OLDHAMITE ASSEMBLAGES IN CHONDRULES AND MATRIX AND SIGNIFICANT OLDHAMITE REE-PATTERNS

A. El Goresy¹, M. Boyet² and M. Miyahara³. ¹Bayerisches Geoinstitut,
Universität Bayreuth, 95447 Bayreuth, Germany, E-mail: Ahmed.
Elgoresy@uni-bayreuth.de. ²Université Blaise Pascal, Lab. Magmas et
Volcans, UMR CNRS 6524, BP 10448, F-63000 Clermont-Ferrand,
France. ³Department of Earth and Planetary Materials Science, Graduate
School of Science, Tohoku University, Sendai 980-8578, Japan.

**Introduction:** Almahata Sitta CT₃ 2008 is considered a second-generation polymict asteroid dominated by ureilites [1]. The impact also delivered OCs, EH, and EL chondrites. MS-17 preliminarily classified as shocked EL-3/4 chondrite [1] is full of chondrules and FeNi clasts. We report detailed petrographic studies, mineral chemistries, and REE abundances of oldhamite (CaS) in chondrules and matrix in two large polished thin sections from its unweathered interior.

**Results and Discussion:** MS-17 is a chondrule-rich EL-3 conglomerate with a matrix dominated by fluffy accreted lithologies. The matrix is full of individual oblong FeNi metal objects containing prismatic crystals of enstatite and rarely diopside both grown from the metal outer surfaces into their interiors. FeNi metal objects have fluffy accretionary rims of idiomorphic troilite (FeS) with daubreelite exsolution lamellae, alabandite, and sphalerite crystallites. Chondrules are exceptionally enriched in large amoeboid stoichiometric CaS grains with minor Mg, Mn, and Fe-contents (1.34 mol% MgS, 1.55 mol% MnS, and 0.89 mol% FeS). CaS engulfs stoichiometric enstatite (En) crystals barren of MnO, poor in CaO (0.63 wt%), and FeO (0.76 wt%). In contrast to CaS in chondrules, every CaS in matrix contains (FeNi)₃P inclusions hinting to different f'O₂ conditions. We found no metal-troilite eutectic textures or shock-induced phase transitions of En to majorite or akimotointe. We reclassify MS-17 as a pristine EL-3 chondrite. En in FeNi clasts is barren of MnO but hosts higher FeO (1.19 wt%) than in chondrule En (<0.8 wt%). Metal clasts enclose in their interiors four different graphite types, no shock twinning or inversion to diamond thus refuting origin of the metal clasts by shock melting. LA-ICPMS studies of 11 oldhamites in different settings reveal CI-normalized REE patterns with prominent negative Eu anomalies without Yb depletions. MS-17 is an unshocked EL-3 conglomerate of CaS-rich chondrules and FeNi- enstatite-graphite clasts decorated with FeS fluffy rims prior to accretion. Enstatite compositions point to separate nebular sources of chondrules and metal-bearing clasts.

**Conclusions:** MS-17 contains two different CaS populations: Grains with (Fe, Ni)₃P inclusions in the matrix, and clear amoeboid grains in chondrules. CaS in MS-17 EL-3 depicts REE patterns (negative Eu anomaly) different from the mainstream pattern in EH-3 (positive Eu and Yb anomalies [2]). Presence of (Fe, Ni)₃P in CaS in matrix is strongly suggestive of condensation of schreibersite at 1439 K and C/O ratio >0.83 before condensation of CaS [3]. The two different settings of CaS in chondrules and matrix strongly suggest two different f'O₂ at their condensations.

**References:** [1] Bischoff A. et al. 2010. *Meteoritics & Planetary Science* 45:10–11:1638–1656. [2] Gannoun et al. 2011. *Geochimica et Cosmochimica Acta* 75:3269–3289. [3] Petaev M. I. and Wood J. A. 2000. Abstract #1608. *Meteoritics & Planetary Science* 31.
LOW-T MAGNETIC PROPERTIES OF 5 CM2 CHONDRITES: COMPARISON WITH THE SIGNATURE OF CRONSTEDTITE AND WITH PRELIMINARY RESULTS FROM THE PARIS CHONDRITE

A. Elmaleh¹, S. C. Tarantino², M. Zema², B. Zanda³, B. Devouard⁴ and M. Fialin⁵.
¹Inst. de Minéralogie et de Physique des Milieux Condensés-UPMC-CNRS, Paris, France. E-mail: agnes.elmaleh@impmc.upmc.fr.
²Dip. di Scienze della Terra e dell'Ambiente, U. Pavia, Italy. ³Museum National d'Histoire Naturelle-CNRS, Paris, France. ⁴Laboratoire Magmas et Volcans, Clermont-Ferrand, France. ⁵CAMPARIS, Paris, France.

Here we report on the low-T (2-300 K) magnetic properties of samples of the Fe-rich serpentine cronstedtite (characterized by EMPA, SCXRD), and of a series of CM2 chondrites in which the mineralogy of phyllosilicates (mostly serpentine) has been extensively studied and related to the degree of alteration, as summarized by [1]. Our conclusions [2, 3] are used to interpret the low-T magnetic signal of Paris, newly discovered and considered as a possibly very pristine CM2 [4].

Using single crystals, it is possible to define the low-T magnetic signature of cronstedtite, and to suggest that the Mg content modifies this signature by lowering the T of the susceptibility peak ($T_p$ ≈7 K). A few results on powder samples also suggest that $T_p$ increases, relative to single crystals, in an assembly of interacting fine grain particles. Turning to CM2, the low-T properties of Murray are explained by a mixture of small amounts of stoichiometric magnetite, and of an Fe-rich serpentine close to reference cronstedtite. We observe an evolution of $T_p$ among the CM2 (including Cold Bokkeveld, Migheis, Murchison, and Nogoya) that correlates with the Mineralogical Alteration Index [5] and the FeO/SiO$_2$ content of PCPs [1]. Deviations from the signature of reference cronstedtite are observed, in particular in Cold Bokkeveld (lowest $T_p$). In this meteorite, [6] measured a high (up to 8.8 at%) Mg content in Fe-rich serpentine by TEM-EDS. Although the effects of other parameters (Al, Fe valence, tochilinite layers, grain size) need to be more completely assessed, our results suggest the influence of the Mg content, and would pinpoint differences in the composition of Fe-serpentine with the degree of alteration, rather than only mixing between minerals of fixed compositions. Our approach can also be used for evaluating changes in mineralogy, possibly linked to alteration, in mm-size clasts from a meteorite. Direct application is proposed for the Paris breccia, in which we selected fragments from zones showing different degrees of alteration according to the criteria of [4]. First, all samples show low-T susceptibility peaks in a range compatible with that of reference cronstedtite. Second, the less altered and the more altered zones have contrasting low-T magnetic signatures, with a shift in the position of the peak, from high $T_p$, to a lower one, comparable to what is found in Murray. This would be consistent with the interpretation of Paris as a CM2 breccia partially affected by a low degree of alteration and preserving in some regions a more pristine material, presumably characterized by finer grain and/or Mg-poorer Fe-serpentine.

**References:** [1] Rubin A. E. et al. 2007. *Geochimica et Cosmochimica Acta* 71:2361-2382. [2] Elmaleh A. et al. 2010. Abstract #GP43B-1052. Fall meeting 2010 AGU. [3] Elmaleh A. et al. *Meteoritics & Planetary Science* (submitted). [4] Zanda et al. 2011. Abstract #2040. 27th Lunar and Planetary Conference. [5] Browning L. et al. 1996. *Geochimica et Cosmochimica Acta* 60:2621-2633. [6] Zega T. and Buseck P. 2003. *Geochimica et Cosmochimica Acta* 6 7:1711-1721.

MARTIAN SOIL ANALOGS FROM ANTARCTIC DRY VALLEYS: ELEMENTAL ABUNDANCES AND MINERALOGY SIGNAL WEATHERING PROCESSES

P. Englert¹, J. L. Bishop²,³, L. D. Hunkins²,³,⁴ and C. Koeberl⁵,⁶.
¹University of Hawaii, Mānoa, HI, USA. penglert@hawaii.edu. ²SETI Institute, Mountain View, CA, USA. ³NASA Ames Research Center, Moffet Field, CA, USA. ⁴University of South Florida, FL, USA. ⁵Natural History Museum, Vienna, Austria. ⁶Department of Lithospheric Research, University of Vienna, Vienna, Austria.

**Introduction:** The only Martian samples returned to date are meteorites. They provide important clues about the mineralogy of Mars; however they are not consistent with most of the planet's composition. Studies of soil and sediment alteration in cold and dry environments on Earth can contribute to understanding Martian surface properties. Antarctic Dry Valley soils exhibit complex chemical weathering in a low temperature and dry environment [1, 2]. We present here analyses of elemental abundances and mineralogy of sediments from this area in order to contribute towards our understanding of Mars. Our study focuses on elemental abundances and visible/near-infrared (VNIR) reflectance spectroscopy for comparison with data collected by orbiters and rovers on Mars [e.g., 3-6]. Coordinated evaluation of chemistry and mineralogy of meteorites and Antarctic Dry Valley soils will provide insights into the weathering processes that occurred on Mars.

**Samples:** We characterized 24 samples, collected directly adjacent to Lakes Fryxell, Vanda, and Brownsworth by geochemical analysis and VNIR spectroscopy. This analysis complements results obtained previously for Lake Hoare sediment cores [2, 7].

**Chemistry:** The soils from each of the lakes show distinct major and minor elemental abundance patterns and C concentrations indicating that each lake environment may represent moderately different soil formation and weathering conditions. The majority of the samples have a chemical index of alteration of 55, indicating predominantly physical weathering.

K/Th ratios for the majority of large Martian domains range from about 4000 to 7000 K $Th^{-1}$ ratios in the sample suite range from 522 to 5077, and are below 3000 for all but three samples, with Lake Vanda soils clearly distinguished by ratios systematically below 2000. The low spread of K/Th ratios for both Mars and the soil samples for this study indicate little loss of K through aqueous processes. More detailed analyses may provide model insight into the observation that Martian K/Th ratios do not seem to support aqueous alteration contrary to evidence of significant water/rock interaction [8].

**Spectra:** VNIR spectral analyses indicate orthopyroxene/ clinopyroxene ratios of approximately 40/60 for most samples with higher pyroxene abundances near Vanda and Brownsworth. Weak clay bands are observed for most samples with differences observed among the three sites. The Fryxell samples exhibit CH and carbonate bands, consistent with their presence in the chemical analyses. Mid-IR spectra show the presence of quartz and feldspar.

**References:** [1] Gibson E. K. et al. 1983. *Journal of Geophysical Research* 88:A912-A928. [2] Bishop J. L. et al. 1996. *Geochimica et Cosmochimica Acta* 60:765-785. [3] Gellert R. et al. 2004. *Science* 305:829-832. [4] Boynton W. V. et al. 2007. *Journal of Geophysical Research* 112, doi:10.1029/2007JE002887. [5] Bibring J.-P. et al. 2005. *Science* 307:1576-1581. [6] Murchie S. L. et al. 2009. *Journal of Geophysical Research* 114, doi:10.1029/2009JE003342. [7] Bishop J. L. et al. 2001. *Geochimica et Cosmochimica Acta* 65:2875-2897. [8] Taylor G. J. et al. 2006. *Journal of Geophysical Research* 111, doi:10.1029/2006JE002676.
5301

REDUCTION VERSUS SULFIDATION IN ORDINARY AND ENSTATITE CHONDRITES FROM SPECIATION OF IRON AMONG SILICATES, METALS AND SULFIDES

T. J. Fagan and C. Niki. Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku, Tokyo 169-8050, Japan, E-mail: fagan@waseda.jp.

**Introduction:** Variations in oxidized vs. metallic iron are used to distinguish LL, L, and H ordinary chondrites and the enstatite chondrites [1, 2]. These variations reflect spatial and temporal differences in oxygen fugacity in the solar nebula. Oxidized iron in these meteorites is concentrated in silicates, and metallic iron occurs in Fe, Ni-metals; however, iron also occurs in troilite (and other sulfides in the enstatite chondrites). Sulfur fugacity may have varied independently. This study uses Fe-speciation to address sulfidation in addition to oxidation and reduction during formation of ordinary and enstatite chondrites.

**Analytical Methods:** In this project, we use a mass balance model developed previously to understand reactions that transfer iron among silicates, metals and sulfides [3, 4]. We use two data sets to constrain the speciation of iron in ordinary and enstatite chondrites: (1) mineral modes and compositions determined from thin sections of six meteorites [St. Marks (EH5), Lewis Cliff 88180 (EH5), Northwest Africa 974 (E6), Bensour (LL6), Mt. Tazerzait (L5) and Tamdakht (H5); and (2) a set of wet chemical analyses of H (n = 31), L (n = 57), LL (n = 17) and enstatite (n = 4) chondrites compiled by E. Jarosewich [5, 6].

For data set (1), mineral compositions were analyzed using the JEOL JXA-8900 electron microprobe (EPMA) at Waseda University. Elemental maps were also collected by EPMA. The maps were opened in graphics files and grids were digitally overlain on the maps. The mineral present at each grid node was identified manually by inspection of the elemental maps. The modes and compositions were combined with molar volume data to calculate the distribution of Fe among major minerals.

E. Jarosewich and others determined whole rock analyses in data set (2). They used aliquots of powdered samples to determine the abundances of FeO, FeS and Fe⁰ from their analyses.

**Results:** Iron speciation for each group of samples can be summarized from two numbers: the percentage of Fe as metal and the percentage as sulfide. The percentage of Fe as silicate is not independent. Most LL samples from data set (2) fall in a range from 0-20% Fe as metal and 10-25% as sulfide. The L samples have 20-40% Fe as metal and 10-25% as sulfide. The H samples have 50-70% Fe as metal, 10-15% as sulfide. Results from ordinary chondrites in data set (1) fall within these ranges. Enstatite chondrites from data sets (1) and (2) have nearly no Fe as FeO, and from 60 to 80% Fe as metal.

The LL, L, and H chondrites are well-separated from each other and may show a slight decrease in sulfidation from LL and L to H groups. The enstatite chondrites appear to be more sulfidized than the H chondrites.

**References:** [1] Van Schmus W. R. and Wood J. A. 1967. *Geochimica et Cosmochimica Acta* 31:747-765. [2] Weisberg M. K. et al. 2006. In *Meteorites and the Early solar system II*, edited by Lauretta D. S. and McSween H. S., pp. 19-52. [3] Fagan T. J. et al. 2008. Abstract #1604. 39th Lunar and Planetary Science Conference. [4] Fagan T. J. and Wakai H. 2010. Abstract #5229. 73rd Annual Meteoritical Society Meeting. [5] Jarosewich E. 1990. *Meteoritics & Planetary Science* 25:323-337. [6] Jarosewich E. 2006. *Meteoritics & Planetary Science* 41:1381-1382.

5340

SHOCK METAMORPHIC EFFECTS IN ROCKS AND MINERALS FROM THE NEWLY CONFIRMED LUIZI IMPACT STRUCTURE (DEMOCRATIC REPUBLIC OF CONGO)

L. Ferrière¹, F. R. T. Lubala², G. R. Osinski³ and P. K. Kaseti². ¹Natural History Museum, Burgring 7, A-1010 Vienna, Austria, E-mail: ludovic.ferriere@nhm-wien.ac.at. ²Department of Geology, University of Lubumbashi, P.O. Box 1825, Lubumbashi, Democratic Republic of Congo. ³Departments of Earth Sciences/Physics & Astronomy, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.

**Introduction:** The Luizi structure, ~17 km in diameter, centered at 10°10'13.5"S and 28°00'27.0"E, on the Kundelungu Plateau of the Katanga province, lies in an underexplored region of the southeastern Democratic Republic of Congo. Luizi exhibits, from the periphery to the center of the structure, a rim elevated up to ~300-350 m above the crater interior, an annular depression, an intermediate ring with a diameter of ~5.2 km, and an ~2-km-wide circular central ring around a central depression [1]. In 1990, Dumont [2] was the first to suggest the structure was of impact origin. Evidence for an impact origin was found recently by Ferrière et al. [1, 3].

Here, we report on geological field observations and petrographic examination of rock samples collected during our 2010 field campaign at the Luizi structure.

**Results and Discussion:** The structure formed in tabular massive arkosic sandstone beds, of centimeter to decimeter thickness, with intercalated laminated argillaceous sandstones. Up to 40 cm in size, well-developed shatter cones formed in arkosic sandstone were observed. Shatter cones mostly occur in situ and a few were also found in float samples along rivers. They appear to be restricted only to the inner 3.2 km of the structure.

Monomict lithic impact breccia dikes, up to ~2 m in thickness, and crosscutting sandstone beds, were mapped up to ~3 km from the center of the structure.

Quartz grains with up to five sets of planar deformation features (PDFs) were identified under the universal stage microscope. The dominance of PDF orientations parallel to o{} and the occurrence of a few PDFs parallel to π{} allow us to estimate that the more heavily shocked exposed target rocks have experienced peak shock pressure slightly above 20 GPa. In addition, rare shock deformations in feldspar, notably in perthitic alkali feldspar grains, in which PDFs oblique to the perthite exsolution lamellae were observed. Kink banding in muscovite grains is also common in most investigated samples.

**Conclusion:** The Luizi structure displays characteristic of complex impact craters, i.e., an elevated structural rim, an annular depression, and a central uplifted zone. For the first time, unique evidence of shock metamorphism, in the form of shatter cones and multiple sets of PDFs in quartz and feldspar grains, is described, confirming the meteorite impact origin of the structure, the first one to be confirmed in Central Africa.

**Acknowledgments:** Field campaign was supported by the National Geographic Society/Waitt Grants Program (grant 69-09).

**References:** [1] Ferrière L. et al. 2011. *Geology*, doi: 10.1130/G31990.1. [2] Dumont P. 1990. *Bulletin de la Société Belge de Géologie* 99:57-65. [3] Ferrière L. et al. 2011. Abstract #1637. 42nd Lunar and Planetary Science Conference.
5102

AUGER ANALYSIS OF IMPACT CRATERS FROM THE STARDUST INTERSTELLAR FOILS

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

**Introduction:** The interstellar tray from NASA's Stardust mission collected particles for 229 days during two exposures prior to the spacecraft encounter with comet 81P/Wild 2, and tracked the interstellar dust stream for all but 34 days of that time. Aluminum foils from this collector are being scanned using high resolution SE imaging and the first impact craters located on the foils have recently been identified [1, 2]. Because the number of impact craters found on the foils appears to be significantly higher than estimates made based on interstellar flux calculations [e.g., 3] (extrapolation of the crater densities on the foils examined to date suggests that as many as ~1000 craters may be present on the total exposed interstellar foil area [1]), the Science Council for the Interstellar Preliminary Examination Team (ISPE) recently approved Auger Nanoprobe, SEM-EDX, and FIB-TEM analysis on several of these craters. Here we report the results of our Auger Nanoprobe analysis on three impact craters from the interstellar foils.

**Experimental:** The Auger measurements were done with the PHI 700 Auger Nanoprobe at Washington University, using a 10 kV 10 nA beam rastered over the crater interiors. Spectrum acquisition consisted of three cycles over an energy range of 30–2130 eV for a total acquisition time of 2 min. Based on measurements of a ~200 nm crater from a cometary side foil, these parameters were deemed sufficient for determining residue compositions on the crater bottoms if such residue is present.

**Results and Discussion:** Two impact craters from foil I1061N (036@33 and 188@24, diameters of 350 nm and 650 nm, respectively) and one crater from foil 1033N (11_175, diameter of 1.1 µm) were analyzed with the Auger Nanoprobe. In addition to C, O, and Al, all craters show the presence of Si. Crater 36@33 also shows evidence for Mg and Fe, while crater 11_175 also appears to contain a minor amount of Na. Spectra taken on areas of foil adjacent to the craters do not show evidence for these elements, although Fe is a common inclusion in Stardust foil. The elements observed in these crater residues are in broad agreement with results of SEM-EDX spectra from three other interstellar impact craters [4] and may suggest the presence of residue of extraterrestrial origin. Although Na is present in the residue of one crater, the absence of Ce and Zn suggests that these are not solar cell glass impacts; FIB-TEM analyses are planned to verify this.

**References:** [1] Stroud R. M. et al. 2011. Abstract #1753. 42nd Lunar and Planetary Science Conference. [2] Floss C. et al. 2011. Abstract #1576. 42nd Lunar and Planetary Science Conference. [3] Landgraf M. et al. 1999. *Planetary Space Science* 47:1029–1050. [4] Stroud R. M. et al. 2011. This conference.

5050

FE-XANES MEASUREMENTS ON ANHYDROUS CLUSTER IDPS

G. J. Flynn¹, A. Lanzirotti², S. Wirick² and S. R. Sutton². ¹Department of Physics, SUNY-Plattsburgh, Plattsburgh NY 12901, USA. E-mail: george.flynn@plattsburgh.edu. ²CARS, University of Chicago, Chicago, IL 60637, USA.

**Introduction:** Chondritic porous interplanetary dust particles (CP IDPs), extremely primitive early solar system material [1], are, most likely, not a complete, representative sample of their parent body. A typical ~10 µm CP IDP is an aggregate of >10⁴ submicron grains. But stratospheric collections include many larger non-chondritic, mono-mineralic grains, mostly olivine, pyroxene and sulfide, that have fine-grained, chondritic material (i.e., small bits of CP IDPs) adhering to their surfaces. This indicates at least some of the non-chondritic grains on the stratospheric collectors are fragments from the same parent as the CP IDPs. Cluster IDPs, typically ~100 times the mass of 10 µm CP IDPs containing some large mono-mineralic grains, sample the parent body at a much larger scale than 10 µm CP IDPs. Fe is a major element (~18.5%) in chondritic meteorites, and the Fe-oxidation state distinguishes various meteorite groups [2].

**Measurements:** We have begun a project to systematically determine the Fe oxidation states of anhydrous cluster IDPs by Fe X-ray Absorption Near-Edge Structure (XANES) spectroscopy. We previously reported that cluster IDP L2009R2 is dominated by Fe with a valence near Fe²⁺ [3]. In addition, the absence of large amounts of Fe-metal in L2009R2 suggests that even at the size scale of cluster IDPs the anhydrous IDP parent body is different from the Wild 2 particles analyzed by Ogliore et al. [4], which exhibited significant Fe-metal (24%–14% + 6%).

**Results:** We have now performed Fe-XANES on >75% of the area of the anhydrous cluster IDP L2009R1, a Zn-depleted cluster (Zn/Fe = 0.20 x CI) that likely experienced Zn-loss due to significant atmospheric entry heating. The average spectrum of L2009R1 (shown in Figure 1) plots between Fe²⁺ and Fe³⁺, but is significantly closer to Fe³⁺ than was L2009R2. Again, we see no evidence for significant Fe-metal in this anhydrous cluster IDP, indicating that both large cluster IDPs examined thus far differ significantly from the Wild 2 particles measured by Ogliore [4].

**References:** [1] Ishii H. et al. 2008. 319:447–450. [2] Urey H. C. and Craig, H. 1953. *Geochimica et Cosmochimica Acta* 4:36–82. [3] Flynn G. J. et al. 2011. Abstract #2521. 42nd Lunar and Planetary Science Conference. [4] Ogliore R. et al. 2010. *Earth and Planetary Science Letters* 296:278–286.

<figure><img src="image_9.png" /><figcaption>Fig. 1. Fe-XANES spectrum summed over the entire analyzed area of cluster IDP L2009R1 compared to the spectra of Fe-metal, fayalite (Fe²⁺), and hematite (Fe³⁺) standards.</figcaption></figure>
5017

THE KAMIL CRATER, EGYPT

L. Folco¹, M. Di Martino², A. El Barkooky³, M. D'Orazio⁴, A. Lethy⁵,
S. Urbini⁶, I. Nicolosi⁶, M. Hafez⁵, C. Cordier¹, M. van Ginneken¹,
A. Zeoli¹, A. M. Radwan⁵, S. El Khrepy⁵, M. El Gabry⁵, M. Gomaa⁵,
A. A. Barakat⁷, R. Serra⁸ and M. El Sharkawi³. ¹MNA, Siena, Italy.
E-mail: folco@unisi.it. ²INAF, Pino Torinese, Italy. ³Department of
Geology, Cairo University, Giza, Egypt. ⁴DST, Pisa, Italy. ⁵NRIAG,
Helwan, Egypt. ⁶INGV, Roma, Italy. ⁷EMRA, Cairo, Egypt. ⁸DF,
Bologna, Italy.

We report the detection in southern Egypt of a rayed impact crater
45 m in diameter on a Cretaceous sandstone target. The ejecta rays
highlight the exceptional freshness of the structure. The crater, identified
by V. De Michele during a Google Earth survey in 2008, is named Kamil
crater after the nearby peak Gebel Kamil. A geophysical expedition
undertaken in February 2010 revealed that the crater is bowl shaped and
has an upraised rim (~3 m above pre-impact surface) typical of simple
craters [1]. The true crater floor depth is 16 m and is overlain by a ~6 m-
thick crater-fill material. Morphometric parameters agree with those
predicted by models [2] for explosive impact craters generated by an iron
meteorite 1.3 m in diameter (equivalent to 9.1 × 10³ kg) impacting at a
velocity of 3.5 km s⁻¹, assuming an average meteoroid entry velocity and
entry angle of 18 km s⁻¹ and 45°, respectively. Centimeter-scale masses of
scoriaceous impact melt glass occur in and close to the crater, and
indicate local shock pressures > 60 GPa [1]. We identified over 5000 iron
meteorite specimens totaling ~1.71 tons in the crater and surrounding
area during systematic searches. They consist of <34 kg shrapnel
produced by the explosion of the impactor upon hypervelocity collision
with the target, except one individual fragment of 83 kg. This indicates
that the Kamil crater was generated by an impactor that landed nearly
intact without substantial fragmentation in the atmosphere. The
meteorite, named Gebel Kamil, is classified as an ungrouped Ni-rich
ataxite (Ni ~20 wt%, Ga ~50 µg g⁻¹, Ge ~120 µg g⁻¹, Ir ~0.5 µg g⁻¹;
data by ICP-MS analyses following [3]). Magnetic anomaly data show no
evidence of buried meteorites larger than some tens of centimeters.

Based on systematic meteorite search, the estimated total mass of
the impactor is of the order of 5–10 × 10³ kg, corresponding to a pre-
atmospheric mass of ~20–40 × 10³ kg [4]. According to geophysical
models [4], iron masses <3 × 10⁶ kg normally fragment upon impact with
the Earth’s atmosphere, thereby reducing the energy of the impact at the
Earth’s surface. The present statistics, which include the recently
discovered Whitecourt crater [5] and the Kamil crater, suggest however
that ~35% of the iron meteorites in the above mass range are not
disrupted in the atmosphere. Details of this work are published in [6, 7].

**Acknowledgments:** Supported by EC (Marie Curie Actions–RTNs ORIGINS FP6 project), Fondazione Cassa di Risparmio di Torino, Banca Monte dei Paschi di Siena S.p.A., Fondazione Monte dei Paschi di Siena, and Telespazio S.p.A.

**References:** [1] Melosh H. J. 1989. *Impact cratering. A geologic process*, Oxford Monographs on Geology and Geophysics. Oxford: Oxford University Press. 245 pp. [2] Collins G. S. 2005. *Meteoritics & Planetary Science* 40:817–840. [3] D’Orazio M. and Folco L. 2003. *Geostandards Newsletter* 27:215–225. [4] Bland, P. A. and Artemieva N. A. 2006. *Meteoritics & Planetary Science* 41:607–631. [5] Herd C. D. K. et al. 2008. *Geology* 36:955–958. [6] Folco L. et al. 2010. *Science* 329:804. [7] Folco L. et al. 2010. *Geology* 39:179–182.

5018

SHOCKED QUARTZ AT THE KAMIL CRATER (EGYPT)

L. Folco¹ and M. D'Orazio². ¹MNA, Siena, Italy. E-mail: folco@
unisi.it. ²Dipartimento di Scienze della Terra, Pisa, Italy.

Impact melt glass occurs at the recently discovered Kamil crater in southwestern Egypt – a rayed crater, 45 m in diameter on a Cretaceous sedimentary (mainly quartz-arenites) target [1, 2]. The glass forms centimeter-scale masses scattered up to a distance of 100 m from the crater rim, or is stuck to the surface of some of the thousand shrapnel specimens of the meteorite that formed the crater, the Gebel Kamil iron. It mainly consists of vesicular, brown to colorless siliceous glass and Fe-Ni droplets entraining clasts of quartz-arenites, testifying to melting of the target and—to some extent—of the projectile during the impact, as a result of the local attainment of shock pressure > 60 GPa.

Shock deformation features in the quartz grains of the quartz-
arenite clasts embedded in an impact melt mass stuck to the surface of
one Gebel Kamil shrapnel were studied by optical microscopy. They vary
from clast to clast, ranging from undulose extinction associated with
pervasive planar fractures (PF) spaced 15–20 µm apart, to blocky
undulose extinction associated with undecorated planar deformation
features (PDF), typically spaced 3–5 µm apart. Multiple sets of PDF may
occur in individual crystals, sometimes with differently oriented sets
occurring in different parts of the crystal.

The crystallographic orientation of 28 PDF planes in four quartz
grains <100 µm in size was determined using a U-stage and indexed
following [3]. Critical sets of PDF include those parallel to the
rhombohedra {1013} and {1012}, with less abundant PDF parallel to the
trigonal dipyramid {1122} (Fig. 1). This assemblage indicates shock
pressures >20 GPa, according to [3].

The occurrence of PDF in bedrock quartz crystals embedded in
shock melt provide strong evidence that the Kamil crater was produced
by a hypervelocity impact.

**Acknowledgments:** Supported by Università di Pisa (Fondi di Ateneo per la Ricerca), Banca Monte dei Paschi di Siena S.p.A., Fondazione Monte dei Paschi di Siena.

**References:** [1] Folco L. et al. 2010. *Science* 329:804. [2] Folco L. et al. 2010. *Geology* 39:179–182. [3] Stöffler and Langenhorst 1994. *Meteoritics & Planetary Science* 29:155–181.

<figure><img src="image_10.png" /><figcaption>Fig. 1. Histogram (binned at 5°) showing PDF orientation in quartz crystals embedded in the Gebel Kamil impact melt.</figcaption></figure>
5177

THE BRITISH AND IRISH METEORITE SOCIETY (BIMS):
PREPARING FOR A FALL

M. Ford and M. P. Smith. BIMS, 27 The Street, Rushington, West
Sussex, BN16 3PA, UK. E-mail: britishmeteorite@gmail.com.

**About Us:** The British and Irish Meteorite Society is a group of over 100 UK and Irish meteorite researchers, curators and collectors. The Society was formed in 2004 by Mark Ford, Dave Harris, and a number of likeminded enthusiasts. With a clear focus on sample research, collection and curation, we are the only such group in the UK and one of only a handful of similar groups worldwide.

The aim of the society is to bring together all those involved with meteorites in the UK under one roof, with a view to educating the general public, furthering the interests of meteorite study, and preserving any new or old UK meteorite material for science. It is also an ideal place to share our interests and meet other people with a similar passion for space rocks.

Members are distributed over the whole of Britain; our main form of communication is via the Internet. Until recently we used an email based mailing list, we have now begun using a Web-based forum. New members are always welcome and may join by completing the form on our website.

**Outreach:** BIMS members are well informed and committed to promoting an interest in meteorites. We give talks and presentations, put on exhibitions and help with identification of suspected meteorites found by the public. Our members have been involved in the Brighton Science Festival and have given presentations to groups of children from nursery to secondary school age. In 2005 the Society was able to donate a substantial meteorite collection to the South Downs Planetarium. In the past 2 years our members have also had a number of articles published in Meteorite. Members regularly meet up and have organized visits to the Natural History Museum, Manchester Museum, and Open University. Our website is frequently updated and contains numerous useful resources. We cover the basics of identifying meteorites and classification; have sections on British and Irish meteorites, in addition to a growing number of articles written by our members.

**New Falls:** After the Almhata Sitta fall, 45 students and staff volunteered from the University of Khartoum to begin the search for material [1]. Following the Buzzard Coulee fall many Royal Astronomical Society of Canada members and ConocoPhillips Canada employees aided in the search [2]. The success of these searches validates the use of volunteers in the recovery of new material. Given the size of our membership and their geographical spread across the UK and Ireland it is hoped that in the event of a new meteorite fall in the area we would play a key role in the location and recovery of material, assisting and working with other organizations to preserve as much material as possible for science.

**References:** [1] Shaddad M. H. et al. 2010. *Meteoritics & Planetary Science* 45:1557–1589. [2] Hildebrand A. R. et al. 2009. Abstract #2505. 40th Lunar and Planetary Science Conference.

**Additional Information:** For additional information on the British and Irish Meteorite Society please visit our website at http://www.bimsociety.org or email the chairman Mark Ford at britishmeteorite@gmail.com.

5525

A BI-MODAL DISTRIBUTION OF ALHA77307 MATRIX OLIVINE:
EVIDENCE FOR FINE-GRAINED MIXING FROM MULTIPLE
RESERVOIRS IN THE CO FORMATION ZONE

D. Frank¹, M. Zolensky², A. Brearley³ and L. Le¹. ¹ESCG/NASA
Johnson Space Center, Houston, TX 77058, USA. E-mail: david.r.frank@
nasa.gov. ²ARES/NASA Johnson Space Center, Houston, TX 77058,
USA. ³University of New Mexico, Albuquerque, NM, USA.

**Introduction:** The CO 3.0 chondrite ALHA77307 is thought to be the least metamorphosed of all the CO chondrites [1]. As such, the fine-grained (< 30 µm) olivine found in its matrix is a valuable resource for investigating the CO formation environment since its compositions should be primary. In the CO matrix, we indeed find a wide range of major element compositions (Fa<sub>0.5–71</sub>). However, more importantly, we find that the olivines make up two compositionally distinct populations (Fa<sub>0.5–5</sub> and Fa<sub>21–71</sub>). Grains from both populations are found within an extremely close proximity and we see no obvious evidence of two distinct lithologies within our samples. Therefore, we conclude that the olivine grains found in the ALHA77307 matrix must have crystallized within two unique formation conditions and were later mixed at a very fine scale during the accretion epoch. Here, we propose a possible explanation based on Cr and Mn concentrations in the olivine.

**The Fa<sub>21–71</sub> Reservoir:** We propose that this population consists of fragmental chondrules. We obtained 35 EPMA measurements of olivine found in type IIA chondrules from ALHA77307, which exhibit remarkable compositional similarities to the Fa<sub>21–71</sub> found in matrix. Both groups of olivines begin at around 20 wt.% FeO and their Mn/Fe trends are nearly identical (see figure below). Although the Cr content in the matrix grains is lower and not positively correlated with FeO like in the chondrules, mild metamorphic effects could explain this. Cr is more mobile and will respond faster to metamorphism in smaller grains, dropping to lower values [2].

Fa<sub>0.5–5</sub>: It has been suggested that very low FeO olivines enriched in Mn could have condensed from the solar nebula [3]. As shown, many of our grains in this population are indeed enriched in MnO. However, we note that an elevated amount of MnO is not a requirement for forsterite to have condensed from a gas and suggest that the majority of this population has such an origin.

**References:** [1] Brearley A. J. and Jones R. H. 1997. Reviews in Mineralogy, vol. 36. pp. 3–38. [2] Grossman J. and Brearley A. J. 2005. *Meteoritics & Planetary Science* 40:87–122. [3] Klöck et al. 1989. *Nature* 339:126–128.

<figure><img src="image_11.png" /></figure>
5176

NORTHWEST AFRICA 5492, A UNIQUE UNGROUPED CHONDRITE
P. Friend¹, J. Zipfel², M. Gellissen¹,³, R. Kleinschrodt¹, C. Muenker¹,
T. Schulz¹, U. Ott⁴, S. Herrmann⁴, A. Pack⁵, A. Stracke⁶ and
H. Palme². ¹Institut für Geologie und Mineralogie, Universität zu
Köln, Zülpicherstrasse 49b, D-50674 Köln, Germany. E-mail:
piafriend13@googlemail.com. ²Sektion Meteoritenforschung, Senckenberg
Forschungsinstitut und Naturmuseum Frankfurt/Main, Germany.
³Institut für Geowissenschaften, Universität Kiel, Kiel, Germany. ⁴Max
Planck Institut für Chemie, Mainz, Germany. ⁵Institut für Mineralogie,
Universität Göttingen, Göttingen, Germany. ⁶Institut für Mineralogie,
Universität Münster, Münster, Germany.

Northwest Africa (NWA) 5492 is an unusual chondritic meteorite briefly described by [1, 2]. Here we report additional mineralogical, chemical and isotope data.

**Texture and Mineralogy:** NWA 5492 is brecciated consisting of large and well defined chondrules, chondrule fragments and various clasts and has apparently no matrix. FeNi metal and sulfides occur as large grains in the chondrule interstitials and as small grains within clasts. The mineralogy of NWA 5492 is very reduced with almost pure enstatite (Fs < 0.5%) as dominant mineral followed by forsteritic olivine (Fa < 0.3%). The degree of reduction is much stronger than in CH-chondrites, even exceeding E chondrites. The low CaO in opx and the high CaO in coexisting cpx, as well as the extremely low Fa and Fs contents would imply temperatures at 500 °C or lower [3]. An extremely long duration of low temperature metamorphism would be required to produce the observed unzoned minerals.

The bulk chemistry has high Fe and Ni, indicating excess metal similar to CH. Mg/Si is CI-chondritic. Refractory elements are neither enriched nor depleted, different from CH and E chondrites. Volatiles are strongly depleted similar to CH but different from E chondrites.

Oxygen isotopes on two bulk samples and four sub-mg samples of two macroscopically distinguishable clasts are uniform within error limits. On a δ¹⁷O versus δ¹⁸O diagram all data plot between LL and EC, above the terrestrial fractionation line, in an area not occupied by another meteorite group [2].

W-isotopes of pure metal phases exhibit εw of about -2.5 to -2.9, reflecting very early metal separation. Metal-silicate aggregates separated magnetically have Hf/W ratios of up to 12 with variable εw (+0.7 to +4.5), indicating isotopic disequilibrium between metal phases and aggregates and later, local metal-silicate equilibration, perhaps a result of extensive low temperature metamorphism.

Rare gases were determined on a 167 mg aliquot. Low abundances of trapped Ar, Kr, and Xe are consistent with low volatile elements contents. Cosmic ray exposure ages are around 8 Ma, concordant for ³He, ²¹Ne, and ³⁸Ar.

In summary, NWA 5492 is a brecciated chondritic meteorite with no obvious differences in chemistry, mineralogy, and isotopes among various lithic clasts. The metal-rich meteorite has extremely reduced mineralogy, excess metal, a strong depletion of volatiles and an oxygen isotopic composition close to but different from O and E chondrites. NWA 5492 does not fit into existing classification schemes.

**References:** [1] Friend P. et al. 2011. Abstract #1095. 42nd Lunar and Planetary Science Conference. [2] Weisberg M. K. et al. 2011. Abstract #1198. 42nd Lunar and Planetary Science Conference. [3] Lindsley D. H. 1983. *American Mineralogist* 68:477-493. [4] Clayton R. N. 2004. *Treatise on Geochemistry*, vol. 1. p. 129.

5425

CARBON MINERALOGY—A COMPREHENSIVE APPROACH FOR THE PLANETARY SCIENCES

Marc Fries. Planetary Science Institute, Tucson, AZ, USA. E-mail: fries@psi.edu.

Carbonaceous materials compose a mineral system independent from, and complimentary with, traditional mineralogy when it comes to studies of geologic/geochemical systems. A broad suite of carbonaceous materials occur in rocks which can be analyzed to quantitatively define limits on the pressure, temperature, chemical environment, shock processing, and oxygen fugacity histories of a given lithology. These phases range from graphite, diamond, macromolecular carbon (MMC)*, vitreous carbon, amorphous carbon and even exotic phases such as buckminsterfullerenes, and graphite whiskers. Each of these phases forms under and retains properties of a distinctly limited range of physical and chemical conditions, describing a range of values for a given lithology to produce useful constraints on the formation and alteration history of that lithology. At this point, technology and methodologies in existence are sufficiently mature to define a comprehensive new field of “carbon mineralogy” capable of quantitatively describing the formation/alteration of extraterrestrial materials based on their carbonaceous phases. By assembling expertise and previous work with new work intended to fill gaps, it should be possible to produce a body of work which will serve as a comprehensive reference on the structure, chemical composition, and phase identities of the carbonaceous materials expected for any given pressure, temperature, and chemical environment that a parent lithology was subjected to. Conversely, for any given extraterrestrial lithology, the pressure, temperature, and chemical environment can be described in terms of the fine structure of the carbonaceous material found within. While considerable work has been done on carbonaceous materials in terrestrial settings, additional work needs to be done for extraterrestrial carbon found in meteorites, cometary materials, IDPs, etc., the majority of which formed by condensation from hot, diffuse gases.

**Pressure:** Carbon phases such as amorphous carbon, diamond, lonsdalite, and others constrain a range of temperature and pressure limits for a given lithology. For most extraterrestrial materials this may be most pertinent to shock processing.

**Thermal Metamorphic History:** MMC exists across a range of submicron structure that describes the thermal alteration history of a given material. The presence and microstructure of diamond, crystalline graphite, aliphatic compounds, and other phases also place limits on the thermal history of a given lithology.

**Chemistry:** Carbonaceous phases can be sensitive indicators of the chemical environment of their parent lithology, as seen in the direct measurement of heteroatomic composition of MMC, the presence and structure of vitreous carbon, the chemical composition of aliphatic compounds, and other features.

**Techniques:** Instrumental techniques already exist to measure carbon properties, such as Raman spectroscopy, TEM, SEM/EDS, FTIR, mass spectroscopic techniques, XRD, and others. Quantifying and cross-correlating these results into a noninstrument-specific format will allow generic description of extraterrestrial carbonaceous materials.

*MMC is defined here as a reduced, primarily carbon solid spanning a continuous range of structural ordering between amorphous carbon and graphite.

References for this abstract are omitted with apologies, as they are too numerous for the abstract format.
5390

MINERAL INCLUSIONS IN MONAHANS AND ZAG HALITES: EVIDENCE OF THE ORIGINATING BODY

M. Fries¹, M. Zolensky² and A. Steele³. ¹Planetary Science Institute, Tucson, AZ, USA. ²NASA Johnson Space Center, Houston, TX, USA. ³Geophysical Laboratory, Carnegie Institute of Science, Washington, DC, USA. E-mail: fries@psi.edu.

Halite grains from Monahans (H5) and Zag (H3-6) are remarkable relicts of aqueous processes in the ancient solar system. Previous work has revealed their age of approximately 4.5 Ga through multiple isotope systems, and fluid-bearing inclusions indicate that these grains have experienced a very mild shock/thermal history [1-3]. Their appearance as discrete grains within an H-chondrite matrix free of aqueous alteration implies that the salt grains are xenogenic to the Monahans/Zag parent body (or bodies). We report the results of Raman imaging analyses of opaque inclusions within the halite grains, which have not been previously described. These results reveal unique insights into the nature of the originating body of the salt grains, as they cannot have been heated in excess of 25 °C since being encased in halite.

Examination of Monahans and Zag halite grains with Raman imaging reveals the presence of small (< 10 µm), primarily metal grains with oxidation/hydroxylation products and minor phases inconsistent with H-chondrite mineralogy that must arise from the halite grains' originating body. The grains are generally subrounded and composed largely of metal, magnetite and another phase which is probably fine-grained lepidocrocite (FeO(OH)). Identification of lepidocrocite carries an element of uncertainty at the time of this writing due to broad spectral features shared with clays and glassy phases, but in advance of data from other techniques the identification as lepidocrocite is reasonable given the inclusions' apparent history as largely metallic clasts altered by interaction with a brine. Minor phases include forsteritic olivine (Fo≈98) [4], macromolecular carbon (MMC), pyroxenes, and a feldspar grain with Raman spectral affinity to anorthoclase. One inclusion features aliphatic material with Raman spectral features consistent with a mixture of short-chain aliphatic compounds.

The minerals and compounds discovered thus far within Monahans/Zag halites are indicative of an originating body at least partly composed of equilibrated igneous materials (high Fo olivine, possibly the metal) which was subjected to aqueous alteration (the halite parent brine) and containing a light organic component (the short-chain aliphatic compounds). Finally, this material was ejected from the originating body with little or no disruption, as evidenced with the presence of fluid inclusions. An actively geysering body similar to modern Enceladus [2] may be a reasonable analog in this respect. Also, the originating body should have been within close proximity to the H chondrite parent in order to generate the number of halite grains seen in Monahans and Zag. Other candidates for Monahans/Zag halite parent bodie(s) may include a young Ceres with its possible liquid ocean [3], Main Belt comet(s) [4], or some long-destroyed body.

**References:** [1] Bogard D., Garrison D., and Masarik J. 2001. *Meteoritics & Planetary Science* 36:107–122. [2] Whitby J. et al. 2000. *Science* 288:1819–1821. [3] Zolensky M. E. et al. 1999. *Science* 285, 1:377–1379. [4] Kuebler K. et al. 2006. *Geochimica et Cosmochimica Acta* 70, 24:6201–6222. [5] Postberg F. et al. 2009. *Nature* 459:1098–1101. [6] Rivkin A. et al. 2006. *Icarus* 185:563–567. [4] Hsieh and Jewitt. 2006. *Science* 312:561–563.

5052

THERMAL RELEASE AND DIFFUSION OF HELIUM-4 IMPLANTED INTO LUNAR SIMULANTS

X. Fu¹,², Y. Zou¹, Y. Zheng¹, H. He³ and Z. Ouyang¹. ¹National Astronomical Observatories, Beijing 100012, China. E-mail: fuxh@bao.ac.cn. ²Graduate University of Chinese Academy of Science, China. ³Institute of Geology and Geophysics, China.

**Introduction:** Noble gases and various isotopes in lunar samples and meteorites provide unique and extensive information about a broad range of fundamental questions [1, 2]. Diffusion properties of noble gases are important in the interpretation of such noble gases data. In addition, ³He in the lunar soil is one of the most valuable resources as a fusion fuel. Knowledge of trapping mechanisms and diffusion characteristics of implanted noble gases will enable the optimization of the processes to extract ³He from lunar soil [3]. Here we report ⁴He implantation and extraction experiments. ⁴He release pattern and diffusion mechanism in lunar simulants grains were studied.

**Experiments:** We performed an experiment of solar wind ions implantation and ⁴He extraction. High-Ti mare soil simulant (CAS-1) [4], highland lunar soil simulant (NAO-1) [5], and Panzhihua ilmenite are irradiated in the experiments. The energy of ⁴He ions is 50 keV. The irradiation dose is $5 \times 10^{16}$ ion cm⁻², five times of irradiation saturation dose [6, 7]. After implantation, the samples were analyzed in noble gas mass spectrometry. The samples were heated from 200 to 1500 °C, with 100 °C stepwise interval.

**Results:** Lunar simulants, CAS-1 and NAO-1, display similar ⁴He release patterns in curve shape as lunar soil, but release temperatures are little lower. This is probably a consequence of long-term diffusion after implantation in lunar soil grains. Panzhihua ilmenite displays a different helium release pattern with lunar simulants. Helium release temperatures of Panzhihua ilmenite are higher than those of lunar simulants. Based on the data, we calculated the helium diffusion coefficient (D) and activation energy (Eₐ) using the equation in [8]. In the Arrhenius plots, we note variation of diffusion parameters of CAS-1 and NAO-1 as temperatures were increasing. It is not consistent with simple thermally activated volume diffusion. The variation could be attributed to physical transformation during high temperature. Activation energy of ⁴He in Panzhihua ilmenite is apparently higher than Eₐ of CAS-1 and NAO-1, especially at low temperature range. This result confirms that ilmenite is more retentive for noble gas than other lunar materials.

**References:** [1] Wieler R. 2002. Reviews in mineralogy and Geochemistry, vol. 47. pp. 21–70. [2] Haskin L. and Warren P. 1997. *Lunar Sourcebook*. [3] Kulhman. 2004. Space resources roundtable VI. pp. 6044. [4] Zheng et al. 2009. *Advances in Space Research* 43:448–453. [5] Li et al. 2009. *Journal of Aerospace Engineering* 22:53–57. [6] Futagami et al. 1990. *Earth and Planetary Science Letters* 101:63–67. [7] Borg et al. 1980. The ancient sun: Fossil record in the earth, moon and meteorites. pp. 431–461. [8] Fulda C. and Lippolt H. 2000. *Mathematical Geology* 32:31–47.
5240

## ALTERATION HISTORY IN THE CI CHONDRITE PARENT BODY INFERRED FROM Mn-Cr DATING OF CAROBNATES

W. Fujiya¹, N. Sugiura¹ and Y. Sano². ¹Earth and Planetary Science, The University of Tokyo, Tokyo, Japan. ²Atmosphere and Ocean Research Institute, The University of Tokyo, Tokyo, Japan. E-mail: fujiya@eps.s.u-tokyo.ac.jp.

**Introduction:** CI chondrites are the most compositionally primitive rocks among the solar system materials. However, they experienced pervasive aqueous alteration, during which chemical and isotopic compositions and mineralogy of their constituents were dramatically changed [1]. For a better understanding of the geological history in the CI chondrite parent asteroid, we investigated ⁵³Mn-⁵³Cr ages (half-life: 3.7 Myr) of carbonates to determine the timescale of aqueous alteration. Here we report Mn-Cr ages of dolomite in the Orgueil and Y980115 CI chondrites.

**Samples and Analytical Methods:** For Orgueil, many but small (< approximately 20 µm in diameter) dolomite grains were found in a polished thin section. Four relatively large (approximately 40 µm) grains were chosen for the isotope measurements. For Y980115, most dolomite grains are associated with numerous tiny (submicron-size) magnetite grains, which can result in contamination during the isotope measurements. An exception, for which we obtained Mn-Cr data, is a large (approximately 300 µm) dolomite grain with a clearly distinct morphology, which might have replaced a primordial CAI. Isotope measurements were performed by the NanoSIMS installed at The University of Tokyo. We used a synthetic calcite standard [2] and analytical methods are described elsewhere [3].

**Results and Discussion:** Three out of four dolomite grains in Orgueil have initial ⁵³Mn/⁵⁵Mn ratios of (3.24–3.54) × 10⁻⁶. Combining these data, we obtain the absolute age of 4563.8 ± 0.7/−0.7 Ma for crystallization of dolomite in Orgueil. However, one dolomite grain, which cannot be distinguished from the others by their morphologies, shows a significantly younger age of < 4556 Ma. One dolomite grain in Y980115 shows a slightly higher initial ⁵³Mn/⁵⁵Mn ratio of (4.03 ± 0.46) × 10⁻⁶. This corresponds to the absolute age of 4564.8 ± 0.6/−0.7 Ma.

The absolute age of three dolomite grains is comparable to those of carbonates in CM chondrites [4]. This indicates that CI and CM chondrite parent bodies accreted around the same time and initial abundances of ²⁶Al are similar as heat sources in these asteroids. Therefore, they experienced heating by the ²⁶Al decay to similar extent, although difference in chemical properties of them (such as water abundances) probably resulted in different thermal histories. The younger dolomite in the present study has a comparable ⁵³Mn abundance to the youngest breunnerites analyzed by Petitat et al. [5], indicating a prolonged duration of aqueous alteration for at least 8 Myr.

The dolomite grain in Y980115 is slightly older than those in Orgueil and Ivuna [3]. The initial ⁵³Mn/⁵⁵Mn ratio is consistent with those of Kaidun carbonates [6]. Based on the strange morphology, it may have originated from another pre-existing planetesimal and have not precipitated in the CI chondrite parent body.

**References:** [1] Brearley A. J. 2006. In *Meteorites and the early solar system* II:587–624. [2] Sugiura N. et al. 2010. *Geochemical Journal* 44:e11–e16. [3] Fujiya W. et al. 2011. Abstract #1397. 42nd Lunar and Planetary Science Conference. [4] Fujiya W. et al. 2011. In review. [5] Petitat M. et al. 2009. Abstract #1657. 40th Lunar and Planetary Science Conference. [6] Petitat M. et al. 2011. *Meteoritics & Planetary Science* 46:275–283.

5318

## XENOLITHS IN CARBONACEOUS AND ORDINARY CHONDRITES

C. Funk¹,³, A. Bischoff² and J. Schlüter³. ¹Institut für Geologie und Mineralogie, Zülpicher Straße 49b, 50674 Köln, Germany. ²Institut für Planetologie, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany. ³Mineralogisch-Petrographisches Institut, Grindelallee 48, 20146 Hamburg, Germany. E-mail: claudia_funk@gmx.net.

**Introduction:** Xenoliths in meteorites are rock fragments of different lithologies genetically not related to the host rock [1]. In this study we systematically searched for xenoliths in primitive carbonaceous and ordinary chondrites in order to find: (1) fragments of known meteorite classes, but occurring as exotic clasts in other chondrite classes, (2) materials with mineralogical and textural properties of chemically unprocessed material, (3) unknown or unusual materials, and (4) igneous-textured lithologies that clearly underwent differentiation processes.

**Results:** The investigated samples include 26 thin sections of 23 carbonaceous chondrites and 31 thin sections of 23 ordinary chondrites. Xenoliths are present in Acfer 114 (CR2), Sahara 98645 (H3), Dhajala (H3.8), Tanezrouft 039 (L3), Sahara 98035 (L/LL3), Adrar 003 (L/LL3.1), and Krymka (LL3.1).

In Acfer 114 an optically dark fragment was found and interpreted as a clast of primitive accretionary material consisting predominantly of olivine grains with varying chemical compositions different to olivines in the Acfer/El Djouf host meteorite [2]. The xenolith in *Sahara 98645* has affinities to CI and CM chondrites. The fragment largely consists of fine-grained phyllosilicate-rich matrix. Coarse-grained constituents include several pyrrhotites, minor amounts of pentlandite and troilite, some small clusters of framboidal and isolated magnetites, carbonates (mainly dolomite), and some olivine and pyroxene grains. The *Dhajala* meteorite comprises a fragment that mainly consists of an extremely fine-grained and porous matrix in which several multiphase-aggregates and rounded objects are embedded. The rounded objects show diameters of 10–30 µm and are very similar to the “accretionary objects” found within the fine-grained fragment BK13 in the Krymka LL3.1 chondrite [3]. Within *Tanezrouft 039* (L3) an LL-chondritic xenolith was found. Another fragment in the same thin section predominantly consist of a kind of Fe, Ni-metal groundmass in which chemically almost homogeneous low-Ca-pyroxenes, sulfides, unidentified Fe-oxides, silica, and feldspar is embedded. Olivine is completely absent. The mineral assemblage and the texture of the clast lead to the assumption that this fragment might originate from a mesosideritic parent body. *Sahara 98035* contains an extremely fine-grained fragment with several unusual multi-phase aggregates and very few microchondrules. In addition Kakangari chondrite-like xenoliths were found within the *Adrar 003* and the *Krymka* meteorite.

Future investigations by transmission electron microscopy and secondary ion mass spectrometry will allow to clearly define the origin of some of the observed xenoliths.

**References:** [1] Bischoff et al. 2006. In *Meteorites and the early solar system* II, edited by Lauretta D. S. and McSween H. Y. pp. 679–712. [2] Bischoff et al. 1993. *Geochemica et Cosmochimica Acta* 57:1587–1603. [3] Semenenko et al. 2001. *Meteoritics & Planetary Science* 36:1067–1085.
5400

METAMORPHIC INDICATORS IN STARDUST

Z. Gainsforth¹, A. L. Butterworth¹, D. E. Brownlee², G. R. Huss³, D. Joswiak², K. Nagashima³, R. C. Ogliore³, T. Tyliczszak⁴, A. J. Westphal¹. ¹U. C. Berkeley, USA. ²Hawaii Institute of Geophysics and Planetology, University of Hawaii at Mānoa, USA. ³Astronomy Department, University of Washington, USA. ⁴Astronomy Department, University of Washington, USA. ⁵Advanced Light Source, Lawrence Berkeley National Laboratory, USA. E-mail: zackg@ssl.berkeley.edu.

**Introduction:** Stardust cometary particles are important for understanding solar system formation because comet Wild 2 most likely preserved mineralic components without additional thermal or aqueous alteration. Evidence of thermal alteration of a Stardust particle would be a significant discovery as it would indicate that the particle resided on a large parent body before being transported to the comet, implying that at least some parent bodies formed during or before large-scale solar mixing and formation of KBOs. On the other hand, absence of thermal metamorphism allows for more accurate dating of particle formation using ²⁶Al and other systems.

**Evaluating Metamorphism:** Very few indicators of low-grade metamorphism can currently be applied to Stardust samples. Most involve unidirectional changes in properties of the constituents. One promising indicator for the particle Iris (from Stardust track C2052,2,74), which has many characteristics of a type II chondrule [1], is the Fe/Mg partitioning between olivine and chromite [2]. At temperatures near the liquidus, the assemblage might be expected to be in equilibrium, and rapid cooling quenches the high-temperature equilibrium values. [2] found that the $K_D$ = (Fe/Mg)³⁵/(Fe/Mg)⁴⁵oliv in chondrules from unmetamorphosed chondrites such as Semarkona and ALHA77307 reflects a temperature of approximately 1400 °C. With small degrees of metamorphism, the $K_D$ values increase as the system tries to equilibrate to lower temperature. Although one cannot determine the metamorphic temperature from the $K_D$S of type 3.1–4.0 meteorites because full low-temperature equilibrium was not achieved, it is still possible to roughly estimate the metamorphic grade. Iris olivine is Fo₆₄. Iris chromite contains 6.0 wt% MgO, 28.4 wt% FeO and 16.9 wt% Al₂O₃. This gives ln($K_D$) for spinel/olivine of approximately 1.5. Chondrules from type 2 and 3.0–3.1 chondrites have $K_D$S of 1–2, while those of type 3.3–3.5 have $K_D$S of 2–4 [2]. The $K_D$ of Iris suggests that the system was quenched at high temperature and has experienced little thermal metamorphism since.

Other potential indicators of metamorphic grade include Ca and Cr distribution in Fe-rich olivine [3, 4], degree of devitrification of mesostasis glass [5], Al/Mg ratio in igneous feldspar [6]. However, these indicators presently give disparate results, probably because they were developed for size scales of 10 to 100s of µm, while Iris features are on the scale of a few µm to hundreds of nm. Careful work to calibrate nucleation and growth of phases at the nanometer scale in artificial and natural chondrules will be necessary to apply these indicators to Iris and other Stardust particles.

**References:** [1] Gainsforth Z. et al. 2010. *Meteoritics & Planetary Science* 45:A60. [2] Johnson C. A. and Prinz M. 1991. *Geochimica et Cosmochimica Acta* 55:893-904. [3] McCoy T. J. et al. 1991. *Geochimica et Cosmochimica Acta* 55:601-619. [4] Grossman J. N. and Brearley A. J. 2005. *Meteoritics & Planetary Science* 40:87-122. [5] Huss G. R. et al. 2006. In *Meteorites and the early solar system II*. pp. 567-586. [6] LaTourette T. and Wasserburg G. J. 1998. *Earth and Planetary Science Letters* 158:91-108.

5433

EQUILIBRATION OF FELDSPAR IN PETROLOGIC TYPE 4-6 L AND LL CHONDRITES: METAMORPHIC CONDITIONS ON CHONDRITE PARENT BODIES

J. Gallegos and R. H. Jones. Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA. E-mail: buhhby@unm.edu.

**Introduction:** Examination of feldspar compositions in petrologic type 4-6 ordinary chondrites (OCs) provides insights into early geologic history and metamorphic processes on OC parent bodies [1]. Understanding compositional equilibration of feldspar through diffusion helps establish better criteria for metamorphic conditions. Also, feldspar can potentially record interactions with fluids as well as shock effects, which may have played a significant role in alteration of these chondrites.

Kovach and Jones [1] studied three LL chondrites (of petrologic types 4, 5, and 6), and observed significant changes in feldspar compositions that indicate progressive equilibration during metamorphism. In contrast, feldspar in H chondrites has similar compositions in petrologic types 4, 5, and 6. The goals of our study are twofold. First, we have studied more LL chondrites to determine whether the sequence of progressive equilibration observed by [1] applies more broadly to the LL group. Second, we have studied L chondrites to determine whether they record development of feldspar that is more similar to the H or LL groups.

**Methods:** We studied three LL chondrites: Sevilla (LL4), Olivenza (LL5) and Beeler (LL6) and two L chondrites: Kramer Creek (L4) and Roy (1933) (L5). We analyzed feldspar that is located within relict chondrules, similar to [1]. All the samples chosen for this study have low shock levels and low degrees of terrestrial weathering. We analyzed feldspar using a JEOL 8200 electron microprobe. All grains analyzed are > 10 µm in diameter.

**Results:** LL chondrites. Feldspar compositions in Sevilla (LL4) are similar to Bjurböle (L/LL4) [1] and Bo Xian (LL4) [2]—they have highly varying An/Ab ratios and low Or contents. Olivenza (LL5) is similar to Tuxtuac (LL5) [1] with a narrower range of An/Ab ratios and higher Or content than in type 4. Beeler (LL6) is similar to St. Séverin (LL6) [1]—feldspar in both is homogeneous and albitic (An₁₀Ab₈₅Or₅). Alteration textures in anorthitic feldspar were observed in Sevilla, similar to those in Bjurböle and Bo Xian [1–3]. We did not see exsolution in Olivenza comparable to that in Tuxtuac [1, 4]. Also, Beeler did not exhibit alkali redistribution that was observed in St. Séverin [1], where it is probably attributable to shock.

L chondrites. Feldspar compositions in Kramer Creek (L4) and Roy (1933) (L5) are similar to LL chondrites of the same petrologic types and are much more similar to LL than to H chondrites. Kramer Creek exhibits alteration textures and ablitization similar to Bo Xian and Bjurböle [1, 2], and we observed exsolution in Roy (1933) similar to that in Tuxtuac [1, 4].

**Discussion:** Progressive equilibrium is recorded by feldspar in LL chondrites, and the general trends described by [1] are observed more broadly in a larger number of samples. Feldspar in L chondrites shows similar trends to LL chondrites, indicating similar metamorphic environments for both parent bodies.

**References:** [1] Kovach H. A. and Jones R. H. 2010. *Meteoritics & Planetary Science* 45:246-264. [2] Jones R. H. and Brearley A. J. 2010. Abstract #2133. 41st Lunar and Planetary Science Conference. [3] Jones R. H. and Brearley A. J. 2010. Abstract #5276. 73rd Meteoritical Society. [4] Jones R. H. and Brearley A. J. 2011. This meeting.
RECOGNITION OF REDEFORMED PLANAR DEFORMATION
FEATURES (PDFS) IN LARGE IMPACT STRUCTURES

A. A. Garde¹ and A. Y. Glikson², ¹Geological Survey of Denmark and Greenland. E-mail: aag@geus.dk. ²Australian National University.

**Introduction:** Planar deformation features (PDFs) in quartz constitute a unique criterion for recognition of shock metamorphism. PDFs residing in the brittle upper crust may preserve their initial 2–5 µm spacing, although superposed tectonic deformation associated with rebound and formation of a central uplift and recrystallization/annealing by hydrothermal activity triggered by the impact may result in bent, wavy and decorated PDFs. High shock pressures can penetrate into ductile, midcrustal environments where PDFs are subject to crystal-plastic reformation and high-temperature hydrothermal alteration associated with postimpact processes. In large exhumed impact structures it is therefore appropriate to distinguish primary shock features from secondary deformation and recrystallization of the PDFs.

**Results:** Optical Universal stage studies of quartz PDFs in the recently discovered Maanitsoq structure, southern West Greenland and the Warburton structure, below the Cooper Basin, northwest South Australia, as well as in the established Sudbury, Vredefort, Manicouagan, Charlevoix, and Azuara impact structures, indicate widespread deformation, recrystallization, coarsening, fluid inclusion decoration, and obliteration of planar microstructures. The planar microstructures contain elements diagnostic of primary PDFs, including multiple intersecting planar sets, prevalence of unique Miller indices (i.e., {10–11}, {10–12}, {10–13}), narrow planar spacings (approximately 2–5 µm) and submicron lamella width. Quartz grains may be bent and show undulose extinction, with curved or kinked PDFs preserving near-original crystallographic orientations. Gradual annihilation of planar sets is widespread, increasing the apparent spacing of remaining PDFs. In addition, closely spaced PDFs with *en echelon* overlaps have merged, resulting in small lateral links not seen in pristine PDFs. TEM studies indicate existence of individual quartz lamellae about or less than one micron in width, consistent with PDFs, and resolves existence of both deformed subgrain boundaries as well as relic contiguous planar crystallographic boundaries. Lamellae in large exhumed impact structures may thus retain critical diagnostic features consistent with PDFs, with two or more orientations being common, preserving the specific crystallographic orientations characteristic of shock metamorphism.

**Discussion:** Less than perfectly preserved quartz PDFs are rarely described in the literature or are denoted as metamorphic deformation lamellae (MDLs) and/or planar fractures (PFs), commonly considered unrelated to impacting. However, MDLs and/or PFs may form following initial shock metamorphic effects of target materials, during superposed deformation associated with rebound and formation of a central uplift, and in some instances younger orogenic events. MDLs normally constitute coarser elongate, spindle-shaped panels a few microns across displaying small shifts in their crystallographic orientation. Planar features (PFs) are commonly even more widely spaced than MDLs. We are unaware MDL or PF sets dominated by shock-diagnostic Miller indices, submicron planar quartz microstructures, interplanar spacings down to less than 2–4 µm and multiple intersecting planar sets, relics of which allow a distinction of PDFs from MDLs and PFs in deformed and hydrothermally altered rocks.

BEYOND VREDEFORT, SUDBURY, AND CHICXULUB

A. A. Garde¹, B. A. Ivanov² and I. McDonald³. ¹Geological Survey of Denmark and Greenland, Denmark. E-mail: aag@geus.dk. ²Institute for Dynamics of Geospheres, Moscow, Russia. ³I. McDonald, Cardiff University, U.K.

**Introduction:** The largest known impact structures on the Earth (VSC—Vredefort, Sudbury, and Chicxulub) [1, 2] were originally formed as impact craters with diameters of 180–200 km. On other terrestrial planets we observe much larger craters and impact basins up to thousands of km in diameter. The largest of these structures have been formed during the late heavy bombardment period [3], and nowadays the main asteroid belt delivers only smaller projectiles to planetary crossing orbits. However, Mead (D approximately 270 km), the largest crater on Venus, is younger than approximately 0.5 Ga [4], and a priori we can assume that remnants of structures larger than VSC may be found on Earth.

**Motivation:** Recent research of the Maniitsoq structure, West Greenland [5] opens the problem of the crust and mantle structure under craters larger than VSC. The subsurface dynamic history (shock level, deformation, and uplift) under Vredefort-scale craters has previously been modeled [2]. Here we present the similar modeling for craters larger than Vredefort but smaller than impact basins [6].

**Modeling:** The same 2-D hydrocode as in [2, 6] is used with ANEOS-based equations of state for crust (“granite”) and mantle (“dunite”). The thermal gradient is assumed as in [7]. The projectile strikes the surface vertically with the velocity of 15 km s⁻¹. The projectile diameter varies from 32 km downward to 14 km modeled earlier [2]. Simulated largest craters have diameters approximately 400–480 km at the poorly expressed rim crest and more well-defined apparent diameter D_a approximately 320 km (at the level of preimpact surface). The new feature, not observed in Vredefort modeling but in giant basin modeling [6], is the fate of the impact melt volume in the transient cavity. The collapse of a Vredefort-sized transient cavity lifts the bottom of the impact melt volume upward, while in larger craters the crater collapse compresses it into a subvertical neck near the center. In above-Vredefort-size modeling the central melt neck is a norm both for “cold” and for “hot” targets (see [7] for definitions). At the assumed erosion level of 20–25 km as at Maniitsoq, the central melted neck after the largest modeled impact has a diameter of 40 (“cold” target) up to 90 km (“hot” target). For smaller projectiles the “melted neck” diameter decreases toward zero when the whole melted zone is located above the erosion level.

**Preliminary Results:** Although strongly model depended, a quantitative structural change is expected for larger-than-Vredefort impact craters. The presence of impact melt in deeply eroded crust may therefore constitute field evidence that a giant impact structure was created here. Model-derived estimates for rock strain, shock level and variations in preimpacting crustal depth can be used for comparison with field data.

**References:** [1] Grieve R. and Therriault A. 2000. *Annual Review of Earth and Planetary Sciences* 28:305–338. [2] Ivanov B. A. 2005. *Solar System Research* 39:381–409. [3] Hartmann W. K. et al. 2000. *In: Origin of the Earth and Moon*. Tucson: The University Arizona Press. pp. 493–512. [4] Phillips R. J. et al. 1992. *GSA Special Papers* 465:29–49. [5] Garde A. A. 2010. Abstracts and Proceedings Geological Society, Norway, 1:57–58. [6] Ivanov B. A. et al. 2010. *GSA Special Paper* 465:29–49. [7] Ivanov B. A. and Melosh H. J. 2003. *Geology* 31:8 69–872.
POLYPHASE MICROBRECCIA INJECTITES IN THE MANIITSOQ STRUCTURE, WEST GREENLAND

A. A. Garde¹ and B. Dyck². ¹Geological Survey of Denmark and Greenland, Copenhagen, Denmark. E-mail: aag@geus.dk. ²Lund University, Sweden.

**Introduction:** In large impacts, the short-lived modification from transient cavity to final crater requires temporary strength degradation of the host rocks. Whereas the process of strength degradation is not well understood, it has been possible to model the crater reorganization observed in large impact structures by employing acoustic fluidization of 100 m-scale individual blocks [1]. Evidence of the repeated compression and dilation that is inherent in such modeling of impact crater modification is found in a regional network of polyphase microbreccia dykes with internal dyke-in-dyke and fold structures in Archean orthogneisses in the Maniitsoq region of West Greenland (interpreted as a giant, deeply eroded Archean impact structure [2]).

**Observations:** Along and outside the margins of the central melt body of the Maniitsoq structure there is a >30 km wide zone containing numerous steep, radial dykelets of fluidized quartz-plagioclase-biotite microbreccia derived from thorough in situ crushing of the host quartzo-feldspathic orthogneiss. The microbreccias and their host rocks display intense crushing of quartz, plagioclase and biotite, loss of twinning in plagioclase and K-feldspar (Kfs) exsolution, as well as Kfs films partially surrounding plagioclase and/or quartz clasts. Microclast shapes and distribution patterns indicate intense compression – but no simple shear as observed in crustal shear zones. The dykes vary in thickness from <1 cm to about 5 m, forming up to c. 10% of the local rock volume. Multiple dyke-in-dyke injection and repeated within-dyke compressional folding are common; internal structures and orientations of rare inclusions of rock fragments suggest almost complete final compressional collapse. The microbreccias are accompanied by coarse-grained, monomineralic, 1–3 cm Kfs veins, both interior, pygmatically folded veins and veins along the margins of individual injectite phases. Such veins are confined to the dykes themselves, and the vein Kfs does not display evidence of crushing or shock metamorphism (contrary to quartz and plagioclase in microbreccia and host rocks).

Some of the microbreccia dykes have been superimposed by ductile simple shear and form part of a second-order, 100 m-scale network of metre-thick shear zones in several directions.

**Discussion:** Radial zones of intense crushing of regional extent, fluidised microbreccias with compressional textures, and associated second-order shear zone systems are expected if rarely described in the floors of large impact structures; the Maniitsoq microbreccias may be related to breccia dykes and pseudotachylites in the floors of, e.g., Vredefort and Popigai [3]. The internal structures of the microbreccias at Maniitsoq and their Kfs veins indicate repeated but very short-lived compression and dilation (overlapping in time with fluidization and the Kfs component being mobile). Such oscillatory deformation from a central point is known from earthquakes and is also inherent in acoustic fluidisation modeling of impact crater modification.

**References:** [1] Melosh H. J. and Ivanov B. A. 1999. *Annual Review of Earth and Planetary Sciences* 27:385–415. [2] Garde A. A. 2010. Abstracts and Proceedings of the Geological Society, Norway, 1:57–58. [3] Reimold W. U. 1995. *Earth-Science Reviews* 39:247–265.

EXPERIMENTAL PARTIAL MELTING OF THE LAPAZ ICEFIELD 03639 R4 CHONDRITE

K. G. Gardner-Vandy and D. S. Lauretta. Lunar and Planetary Laboratory, University of Arizona. E-mail: kgardner@lpl.arizona.edu.

**Introduction:** As part of an ongoing study of the petrology, geochemistry and formation conditions of the FeO-rich primitive achondrites [1–3], we perform partial melting experiments of FeO-rich chondritic meteorites. We recently reported that melting experiments of a CK5 chondrite yield compositions similar to those in several ungrouped primitive achondrites, but we also concluded that a more FeO-rich chondritic precursor is needed to yield brachinite compositions [3]. From this, we have begun similar experiments on R4 chondrite LaPaz Icefield (LAP) 03639.

**Methods:** We obtained a thin section and chip (2.7 g) of LAP 03639 from the Meteorite Working Group. We used an approximately 250 mg chip in each experiment to capture textural changes across the experimental conditions. Experiments were run in a Deltech gas-mixing furnace with an oxygen sensor and type R thermocouple. Thus far, we have completed and analyzed two experiments, R1 and R2. Temperature for both was 1250 °C, and each ran for 4 days. The oxygen fugacity for R1 was IW–1 and R2 was IW + 1, controlled with a 1-bar CO + CO₂ gas mixture. We choose fO₂ values based on our previous analyses of the thermodynamic environment of FeO-rich primitive achondrite meteorites [2]. No attempt was made to retain volatiles.

**Starting Material:** LAP 03639 is an R4 chondrite [4–5]. It has chondrules and chondrule fragments ≤1.1 mm across. The matrix is made of olivine, pyroxene and plagioclase with sulfides containing 0–30 wt% Ni. Olivine is Fa₃₈.₈ ± 0.₂, low-Ca pyroxene is Fs₆–2₆, high-Ca pyroxene is Fs₁₀–1₂, and plagioclase is An₅–1₃.

**Experimental Results:** Both the R1 and R2 experiments resulted in significant silicate melting to the extent that homogeneous (Fa₃₅.₅ ± 0.₈ and Fa₃₉.₈ ± 0.₉, respectively) anhedral to subhedral olivine is the only silicate mineral remaining. These grains are surrounded by silicate melt with Mg# 28.0 ± 1.1 and 20.8 ± 0.8, respectively. Significant S loss occurred, but there are several rounded Ni-rich sulfides in each charge; R1 sulfides have 8.5–40 wt% Ni, and R2 sulfides have 63–70 wt% Ni. R1 contains taenite with up to 39 wt% Ni. R2 has a few grains of Fe, Ni-metal with 60–79 wt% Ni. The original chondritic texture remains only in small regions with relict barred olivine grains.

**Discussion:** Olivine compositions generated in the R1 experiment resulted in olivine with compositions matching those of brachinites (Fa₃₂–₃₅) [1]. Those for the R2 experiment, however, resulted in compositions more oxidized than the starting material. This is likely due to the wide range of intrinsic oxygen fugacities (fO₂) calculated for the R chondrites (FMQ–1 to FMQ–3.5) [5], and proves that LAP 03639 formed at more reducing conditions than IW + 1. These initial results indicate that brachinites could form from the partial melting of an R-chondrite at IW–1.

**Acknowledgments:** Research supported by NASA grants NNX09AQ88H and NNX10AH50G (DSL) and UA/Sloan Foundation Indigenous Graduate Partnership Fellowship (KGGV).

**References:** [1] Gardner K. G. et al. 2007. Abstract #2086. 38th Lunar and Planetary Science Conference. [2] Gardner-Vandy K. G. et al. 2009. Abstract #2520. 40th Lunar and Planetary Science Conference. [3] Gardner-Vandy et al. 2011. Abstract #1935. 42nd Lunar and Planetary Science Conference. [4] Kallemeyn G. W. et al. 1996. *Geochimica et Cosmochimica Acta* 60:2243–2256. [5] Righter K. and Neff K. E. 2007. *Polar Science* 1:25–44.
DIAMOND, BUCKY-DIAMOND, GRAPHITE-DIAMOND, Al-SILICATE, AND STISHOVITE IN THE GUJBA CB CHONDRITE

L. A. J. Garvie¹, P. Németh², P. R. Buseck³,⁴. ¹Center for Meteorite Studies, Arizona State University, AZ, USA. ²Institute of Nanochemistry and Catalysis, Chemical Research Center/Hungarian Academy of Sciences, H-1025 Budapest, Hungary. ³School of Earth and Space Exploration, Arizona State University, AZ, USA. ⁴Department of Chemistry and Biochemistry, Arizona State University, AZ, USA.

**Introduction:** Gujba is a coarse-grained carbonaceous chondrite dominated by silicate globules, large metal globules, and dark interstitial matrix [1]. It shows evidence of shock stage S2 [1]. Features indicating higher shock pressures are evident in the matrix, consisting of fine-grained metal and silicate that resembles the shock veins in ordinary chondrites. Several high-pressure (HP), shock-produced phases occur. These include majorite, wadsleyite, and coesite [2]. The wadsleyite and majorite indicate maximum localized pressures and temperatures of approximately 19 GPa and 2000 °C [2]. There are no prior reports of diamonds in Gujba, but they were described from Bencubbin, where some of the diamonds are thought to have formed via solid-state transformation of pre-existing graphitic material from an intense shock event [3]. As part of our ongoing study of the fine-grained materials in primitive meteorites, we used transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and electron energy-loss spectroscopy (EELS) to investigate the acid-insoluble material from Gujba.

**Methods:** The HF/HCl residue was separated by acid digestion of several millimeter-sized pieces of the dark interstitial matrix. The acid removed most silicates, sulfides, and metals, leaving a black powder. A droplet of the residue in suspension with water was dried on a Cu TEM grid coated with lacy-C. TEM data were acquired where electron-transparent areas of the residue protruded over the holes of the grid. High-resolution (HRTEM) and SAED data were acquired with Tecnai F20 and JEOL JEM 4000EX electron microscopes. EELS data were acquired with a GATAN 766 DigiPEELS spectrometer attached to a Philips 400-ST TEM.

**Results and Discussion:** TEM images of the acid residue show abundant carbonaceous aggregates and lath-shaped stishovite. Stishovite laths to 1 µm long are common. A combination of HRTEM, SAED, and EELS measurements from multiple carbonaceous aggregates show a range of crystallinities and structures that include amorphous to poorly graphitized carbon, well-ordered graphite, rounded to euhedral diamonds, and clumps of nanodiamonds. Hollow, amorphous carbonaceous nanoglobules similar to those in primitive meteorites [4] also occur. A crystalline phase with composition Al₁.₉₅±₀.₂SiO₄.₉₸±₀.₅ occurs in the residue, but its cell constants do not match those of any known Al silicate. Prominent in the HRTEM images are 50 nm particles that show various proportions of parallel 0.350 and 0.206 nm fringes that presumably reflect highly local regions of graphite and diamond structure, respectively. Associated with the graphite-diamond are rare bucky-diamond composed of a nanodiamond core surrounded by curved graphite layers. The unique HP mineral assemblage in Gujba may be the result of its unusual macroscopic structure composed of mm-sized spheres surrounded by silicates. Shockwaves traveling through materials of highly variable densities produce heterogeneous and localized shock pressures and temperatures [5].

**References:** [1] Rubin A. E. et al. 2003. *Geochimica et Cosmochimica Acta* 67:3283. [2] Weisberg M. K., Kimura M. 2010. *Meteoritics & Planetary Science* 45:873. [3] Mostefaoui S. et al. 2002. *Earth and Planetary Science Letters* 204:89. [4] Garvie L. A. J., Buseck P. R. 2004. *Earth and Planetary Science Letters* 224:431. [5] Stöffler et al. 1991 *Geochimica et Cosmochimica Acta* 55:3845.

EMPLACEMENT TEMPERATURE OF THE IMPACT BRECCIA AT HAUGHTON IMPACT CRATER

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

**Introduction:** The Haughton impact structure is a well-preserved Eocene structure 23 km in diameter, located on Devon Island in the Canadian Arctic Archipelago [1]. A remarkable feature is the abundance of allochthonous impactites derived from the sedimentary target rock (Paleozoic dolomites and limestones). These impactites were originally interpreted to be lithic or fragmental breccias [2] but have since been interpreted as impact melt breccias/clast-rich impact melt rocks [3, 4]. In this work, we estimate the emplacement temperature of the impact breccia, using a paleomagnetic method known as “conglomerate test.” This consists in sampling oriented samples in several clasts in the breccia, and determine their paleomagnetic direction using thermal demagnetization. The direction will be scattered for emplacement at low temperature, and clustered for emplacement at high temperature.

We sampled a total of 20 oriented clasts in the impact breccia at two sites located 3 km apart. The paleomagnetic measurements show that all clasts give an identical paleomagnetic direction that is unblocked to at least ~350 °C. This direction (D =, I = a95) is well in agreement with the direction of the magnetic field during Eocene or younger times.

Most of the clasts consist of Paleozoic carbonate rocks whose main ferromagnetic mineral is pyrrhotite (as evidenced by our rock magnetism analyses) that has a Curie temperature of 350 °C. As a consequence, these clasts can provide only a lower limit for the emplacement temperature. However, some clasts consist of Precambrian basement rocks, and among this population a few ones are dominated by magnetite that has a Curie temperature of 585 °C. These latter clasts show two components of magnetization: one unblocked up to ~350 °C with the above-mentioned Neogene direction, and a second one unblocked between ~350 °C and 580 °C which is random from clast to clast indicating that the magnetization was not completely reset by heating.

Although additional data are needed from magnetite-bearing clasts, these preliminary results suggest that when the impact melt rocks were emplaced, its temperature was clearly above 350 °C and probably not much higher. This is of interest for reconstructing the P-T history of the melt rocks and for cratering processes in general. The presence of shock-melted quartz clearly indicates that initial temperatures following decompression were >1850 °C [3, 4] and possibly higher. These high temperatures occurred before emplacement of the impactites in to their final resting place (i.e., the outcrop locations we see at the present-day). The co-existence in the impact melt breccias of carbonate melts with liquidus temperatures of ~500–600 °C [4], and clasts that were not heated above 350–400 °C seems to indicate that the temperature in the breccia was heterogeneous at small scale, and that the high clast content of these melt rocks have ensured rapid cooling. This is in agreement with a previous study showing temperature sensitive fossil biological signatures preserved in the same clasts [5].

**References:** [1] Osinski G. R. et al. 2005. *Meteoritics & Planetary Science* 40:1759–1776. [2] Redeker H. J. and Stöffler D. 1988. *Meteoritics* 23:185–196. [3] Osinski G. R. and Spray J. G. 2001. *Earth and Planetary Science Letters* 194:17–29. [4] Osinski G. R. et al. 2005. *Meteoritics & Planetary Science* 40:1789–1812. [5] Lindgren P. et al. 2006. Abstract #1028. Lunar and Planetary Science Conference.
5435

OTISH BASIN: DISCOVERY OF NEARLY 2,1 GA SHOCKED ROCKS POTENTIALLY OWNING TO A D > 500 KM IMPACT STRUCTURE, QUÉBEC, CANADA

S. Genest¹, F. Robert¹ and N. Goulet². ¹Groupe Omégalpha Inc., Canada. E-mail: groupeomegalpha@bellnet.ca. ²Université du Québec à Montréal, Canada. ¹⁻²Groupe de Recherche sur les Impacts Météoritiques de l'Institut Hubert-Reeves (GRIM-IHR).

The Otish Basin (OB) is located in northern Québec, Canada, and is only accessible by air transportation. The palaeoproterozoic sediments of the OB are known as the Otish Group (OG). They are mostly detrital in composition with minor carbonated material and lay unconformably on the archaean basement of the Superior Province, being limited to the south by the Grenville Province. The sedimentary pile of the OG has been studied by the first author in the 80s while performing a basin analysis of the entire OB [1]. Roughly, the OB covers an area of about 5200 km² and its thickness averages an estimated 2.4 km. Four fining upward megacycles have been characterized, two of which, the older ones from the Indicator Formation, express reducing sedimentary environments. The two younger megacycles of the Peribonca Formation are well characterized by the oxidizing conditions of sedimentation. The evolution of the OB has been disturbed by an event which has been responsible for a widespread gabbro emplacement. Thought to be intrusive up to the 80s, more recent works showed that the gabbro has been emplaced in an extrusive manner according to their distribution and their physical relationship with the sediments. Shocked derived material (glass and PDFs) are observed in the sediments under the gabbro sheet and inside the large enclaves found in the gabbro itself. That discovery led to a preliminary re-examination of the thin sections already studied for the basin analysis in the 80s. By paying attention to the shock metamorphism effects, preliminary results allow us to postulate that the overall OB has been subjected to a major impact shockwave between the Indicator and the Peribonca times. Some poorly defined PDFs have been observed up to 1.06 km in depth from drill hole samples located in the center of the basin. The oxidized sediments of the Peribonca Formation are now thought to be intimately associated with the impact event, being coeval to the gabbro emplacement. According to the scale of the event we are facing, our working hypothesis is as followed (1) the OB has been subjected to the shockwave stress associated with a major impact event some 2.1 Ga ago for which the postulated radius of the relevant structure is well over 250 km; (2) since the Mistassini Basin (MB) shows sedimentary and structural similarities with the OB and because of the geomorphic characteristics of the MB showing analogy with the multiring impact structures, we consider MB as an element of our puzzling huge structure; and (3) the gabbro suite is interpreted as a melt sheet which is potentially linked to a large igneous province observed in the Grenville Province to the south, i.e., a gabbro-related anorthosite suite. For future reference, we propose to temporarily call this hypothetical structure the Mistassini-Otish Impact Structure.

**Reference:** [1] Genest S. 1989. Ph.D. thesis, Université de Montréal, Canada.

5314

THE ATMOSPHERIC ENTRY OF I-TYPE SPHERULES

M. J. Genge. Department of Earth Science and Engineering, Impact and Astromaterials Research Centre, Imperial College London, Exhibition Road, London SW7 2AZ, UK. E-mail: m.genge@imperial.ac.uk.

**Introduction:** Micrometeorites (MMs) are extraterrestrial dust particles <2 mm in size recovered from the surface of the Earth and represent that fraction of the interplanetary dust population to survive atmospheric entry. The only iron-dominated particles found amongst MMs are I-type cosmic spherules (CSs) that occur as spheres dominated by wustite and/or magnetite, sometimes containing FeNi metal beads [1]. These particles, like silicate dominated (S-type) cosmic spherules, are formed by extensive melting during atmospheric entry. I-type spherules are present in small abundances of approximately 2% in Antarctic collections [1].

The absence of unmelted metallic MMs and the small abundance of I-type spherules is problematic due to the presence of ordinary chondrite-like materials amongst MMs [2] and the large abundance of metal on these meteorite parent bodies. A numerical model of the entry heating of iron micrometeoroids is presented to evaluate whether the abundance of I-type spherules is a result of atmospheric heating or the nature of their parent bodies.

**Numerical Methods:** The numerical simulations used in this study are based on those of Love and Brownlee [3] and involve the approximation of the equations of motion and heat transfer of particles to determine temperature and mass loss through evaporation. Unlike previous studies [4], oxidation of metallic particles is included and was simulated by considering the mass of atmospheric oxygen encountered whilst particles were at supra-solidus temperatures. Mass loss of oxygen from molten particles was also calculated due to the evaporation of iron oxide liquids that wet the surface of the iron liquid droplets.

**Results:** Simulation results indicate that iron metal particles are more likely to reach their solidus temperatures (1809 K) than silicate particles with equivalent entry parameters due to their higher densities. Iron micrometeoroids are, however, likely to survive entry heating with less mass loss than S-type spherules due to the significantly lower evaporation rates of iron oxide liquids [5]. Contrary to observation, the abundance of I-type spherules would be expected to be enhanced compared with the abundance of metal on their parent asteroids. Metal bead survival is predicted to be greatest for particles that decelerate at the highest altitudes, or large particles that experience significant mass loss of oxide liquids from their surfaces.

**Conclusion:** The low abundance of I-type spherules amongst cosmic spherules is not a consequence of their atmospheric entry and suggests that either metal-poor parent bodies are common, or iron micrometeoroids have a larger mean size than silicates. The low abundance of metal beads amongst I-type spherules suggests that large, high velocity (cometary) iron micrometeoroids are relatively uncommon.

**References:** [1] Genge M. J. et al. 2008. *Meteoritics & Planetary Science* 43:497–515. [2] Genge M. J. 2008 *Geology* 36:687–690. [3] Love S. G. and Brownlee. D. E. 1990. *Icarus* 89, 26-43. [4] Yada T. et al. 1996. Abstract #1732. 28th Lunar and Planetary Science Conference. [5] Wang J. et al. 1994. Abstract #1459. 25th Lunar and Planetary Science Conference.
TEM-EELS STUDY OF TITANIUM OXIDATION STATE IN METEORITIC HIBONITES

M. Giannini¹, T. Boffa Ballaran¹, F. Langenhorst² and A. Bischoff³.
¹Bayerisches Geoinstitut, Universität Bayreuth, D-95447 Bayreuth.
E-mail: Mattia.Giannini@uni-bayreuth.de. ²Institut für Geowissenschaften,
Universität Jena, D-07749 Jena. ³Institut für Planetologie, Universität
Münster, D-48149 Münster.

**Introduction:** Besides corundum, hibonite is the most Al-rich phase found in CAIs. It is considered to be one of the first oxide phases that condensed from the hot solar nebula [1]. The formula of hibonite usually deviates from the ideal end-member composition (CaAl₁₂O₁₉) due to the presence of variable amounts of minor element such as Ti, Mg, Fe, Si, and V [2]. Since Ti can occur in different oxidation states, it appears the ideal candidate for providing insight into the oxygen fugacity (fO₂) at which such mineral has formed and evolved in the solar nebula [3].

**Experimental Methods:** Three CAIs within two petrographic thin sections of chondrites Acfer 182 (CH; PL01036) and one of Dar al Gani (DAG) 203 (CO3; PL96274) were analyzed with a JEOL JXA-8200 electron microprobe. Electron-transparent sections of one hibonite grain from each CAI have been prepared using a FEI Quanta 3D FEG focused ion beam. Hibonites with the same compositions as the selected meteoritic crystals were also synthesized from oxide mixtures at 1430 °C for 12 h both in air and under controlled fO₂ in a gas mixing furnace using a CO/ CO₂ flux. Thin sections of synthetic hibonite pellets were subsequently thinned down to less than 100 nm by aid of a Gatan DuoMill 600 argon ion milling machine. The valence state of Ti was measured both for meteoritic and synthetic hibonites by means of electron energy loss spectroscopy (EELS) using a 200 keV Philips CM20 scanning TEM, equipped with a Gatan PEELS 666 parallel electron spectrometer. The quantification technique used is based on the spectral features and intensities of the L₃,₂ white lines of Ti [4].

**Results and Discussion:** Chemical compositions and Ti³⁺ contents of meteoritic hibonites are reported in the following Table.

The content of Ti³⁺ in hibonite grains from CAIs is very similar with respect to the synthetic samples prepared at -log fO₂ = 11 (e.g., Acfer 182-3's analogous has 35% of Ti³⁺), indicating that this condition may reflect the redox environment in which hibonite has formed. However, even hibonites synthesized in air still have quite large amount of Ti³⁺ (e.g., 20% for Acfer 182-3's analogous), suggesting that its concentration does not only depend on the redox conditions at which hibonite formed, but also on its crystal chemistry. Even at very oxidizing conditions the substitution mechanism Mg²⁺ + Ti⁴⁺ = 2Al³⁺ is not unique and some Ti³⁺ = Al³⁺ substitution takes place.

**Acknowledgments:** We are grateful for the financial support provided by the Deutsche Forschungsgemeinschaft (BO 2550 4-1, LA 830 14-1).

**References:** [1] Grossman L. 1972. *Geochimica et Cosmochimica Acta* 86:597-619. [2] Simons S. B. et al. 1997. *Meteoritics & Planetary Science* 32:259-269. [3] Ihinger P. D. et al. 1986. *Earth and Planetary Science Letters* 78:67-79. [4] Stoyanov E. et al. 2007. *American Mineralogist* 92:577-586.

<table><thead><tr><td>Sample</td><td>Composition</td><td>Ti<sup>3+</sup>/ΣTi (%)</td></tr></thead><tbody><tr><td>Acfer 182-2</td><td>CaA<sub>11.51</sub>Ti<sub>0.80</sub>Mg<sub>0.69</sub>O<sub>19</sub></td><td>20</td></tr><tr><td>Acfer 182-3</td><td>CaA<sub>11.45</sub>Ti<sub>0.36</sub>Mg<sub>0.23</sub>O<sub>19</sub></td><td>35</td></tr><tr><td>DaG 203-1</td><td>CaA<sub>11.52</sub>Ti<sub>0.75</sub>Mg<sub>0.78</sub>O<sub>19</sub></td><td>25</td></tr></tbody></table>

ALH 84001: THE KEY TO UNLOCKING SECRETS ABOUT MARS—15 YEARS AND COUNTING

E. K. Gibson¹, D. S. McKay¹, K. L. Thomas-Keprta² and S. J. Clemett². ¹ARES, NASA/JSC, Mail Code KA, Houston, TX 77058, USA. ²ESCG at NASA/JSC, Mail Code JE23, Houston, TX 77058, USA. E-mail: everett.k.gibson@nasa.gov.

From the December 27, 1984, discovery of ALH 84001, and its subsequent identification as a sample of Mars in 1993, mystery and debate has surrounded the meteorite [1]. With the realization that the ALH 84001 sample was a orthopyroxenite and one of the oldest SNC meteorites (~4.09 Ga) [2] available to study, important and critical information about the Martian hydrosphere and atmosphere along with the early history and evolution of the planet could be obtained by studying the unique carbonate globules (~3.9 Ga) in the sample [3]. The initial work showed the carbonate globules were deposited within fractures and cracks in the host-orthopyroxene by low-temperature aqueous fluids [4]. Ideas that the carbonates were formed at temperatures [5] approaching 800 °C were ruled out by later experiments [6].

The 1996 announcement by McKay et al. [7] that ALH 84001 contained features which could be interpreted as having a biogenic origin generated considerable excitement and criticism. The NASA Administrator Dan Golden said the 1996 ALH 84001 announcement “saved” NASA’s Mars planetary exploration program and injected $6 billion dollars over five years into the scientific research and analysis efforts [8]. All of the original four lines of evidence for possible biogenic features within ALH 84001 offered by McKay et al. have withstood the test of time. Criticism has been directed at the interpretation of the 1996 analytical data. Research has expanded to other SNC meteorites. Despite the numerous attacks on the ideas, the debate continues after 15 years. The 2009 paper by Thomas-Keprta et al. [9] on the origins of a suite of magnetites within the ALH 84001 has offered strong arguments that some of the magnetites can only be formed by biogenic processes and not from thermal decomposition or shock events which happened to the meteorite.

NASA’s Astrobiology Institute was formed from the foundation laid by the ALH 84001 hypothesis of finding life beyond the Earth. The strong astrobiology outreach programs have expanded because of the work done on the Martian meteorites. Despite the criticism on the biogenic-like features in ALH84001, the meteorite has opened a window into the early history of Mars. Clearly low-temperature fluids have left their signatures within the ALH 84001 meteorite and subsequent cratering events on Mars have been recorded on observable features within the meteorite. The 15 years of detailed study on ALH 84001 and its unique carbonate globules have clearly shown formational and secondary processes at work on Mars. Now we need a well-documented Mars sample return mission.

**References:** [1] Meyer C. 1996. *Mars Meteorite Compendium-1996*. NASA-JSC. [2] Lapen T. J. et al. 2010. *Science* 3328:347-351. [3] Borg L. et al. 1999. *Science* 286:90-94. [4] Romanek C. S. et al. 1994. *Nature* 372:655-657. [5] Harvey R. P. and H. Y. McSween 1996. *Nature* 382:49-51. [6] Valley J. W. et al. 1997. *Science* 275:1633-1638. [7] McKay D. S. et al. 1996. *Science* 273:924-930. [8] Sawyer K. 2006. *The rock from Mars*. Randon House. 416 p. [9] Thomas-Keprta K. L. et al. 2009. *Geochimica et Cosmochimica Acta* 73:6631-6677.
5371

LA-ICPMS TRACE ELEMENT COMPOSITION OF METAL AND SULFIDE IN 3 ORDINARY CHONDRITE FALLS

M. D. Giscard¹,², S. J. Hammond³, G. K. Benedix¹,², P. A. Bland¹,²,⁴ and N. W. Rogers³. ¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College, London, UK. E-mail: m.giscard10@imperial.ac.uk. ²Impacts and Astromaterials Research Centre, Department of Mineralogy, Natural History Museum, London, UK. ³Department of Earth Sciences, The Open University, Milton Keynes, UK. ⁴Department of Applied Geology, Curtin University of Technology, Perth, Australia.

**Introduction:** Trace element compositions are a particularly powerful tool for the study of geochemical processes. Indeed, variations of compositions can span several orders of magnitude [1] and the elements themselves have a wide range of condensation temperatures and geochemical behaviors [2]. Chondrites show different trace elements depletion patterns; their cause is still subject to debate [2-4]. Some elemental concentrations might vary with petrological type, this would mean that the trace element composition is also influenced by metamorphism [4-6]. We hope to contribute to these debates by using LA-ICPMS to provide quantitative trace element abundances for chondritic metal and sulfide. Our first test samples were three equilibrated ordinary chondrite falls: Butsura (H6), Ogi (H6), and Mezo-Madaras (L6 fragment of L3.7-6 breccia).

**Method:** In situtrace elements measurements have been performed using the LA-ICPMS at the Open University with LASER settings of 80 µm spot size, 10 passes 5 µm deep on each point and a 180-200 s wash-out time between points. Furthermore, Fe, Ni, and Co concentrations have been measured by Electron Micropobe at the Natural History Museum and Fe concentration used as an internal standard for LA-ICPMS measurements. The CI composition and volatility sequence used for interpreting the trace elements data is from [7].

**Results and Discussion:** Average Co concentration in kamacite are $5.0 \pm 0.2 \text{ mg g}^{-1}$ in Butsura, $5.0 \pm 0.8 \text{ mg g}^{-1}$ in Ogi and $8.4 \pm 0.2 \text{ mg g}^{-1}$ in Mezo-Madaras, which is consistent with the literature [8, 9, 10]. 19 trace elements were above detection limits in metal and sulfide grains: four moderately volatile/normally depleted elements (Cu, Ag, Ga, and Ge) [3, 4] and 15 more refractory elements (Re, Os, W, Ir, Mo, Ru, V, Pt, Rh, Pd, Cr, P, Mn, As, and Au). Individual metal and sulfide grains show a depletion pattern when elements are ordered in a volatility sequence. Individual kamacite grains show a similar pattern while variations in the Ni-rich metal trace element composition seems correlated to the difference in Ni concentration. Sulfide composition is the most widespread—it could be caused by matrix effects related to the choice of standard. We will also discuss the effect of proximity to the fusion crust on trace elements results.

**Acknowledgments:** The first author has been funded by the Marie Curie Research Training network Origin's.

**References:** [1] Shaw D. M. 2006. In Trace elements in magmas—A theoretical treatment, p. 2. [2] Bland P. A. et al. 2005. *Proceedings of the National Academy of Sciences* 102:13755–13760. [3] Larimer J. W. and Anders E. 1967. *Geochimica et Cosmochimica Acta* 31:1239–1270. [4] Wasson J. T. and Chou C.-L. 1974. *Meteoritics & Planetary Science* 9:69–84. [5] Keays R. R. et al. 1970. *Geochimica et Cosmochimica Acta* 35: 337–363. [6] Takahashi H. et al. 1978. *Geochimica et Cosmochimica Acta* 42:1859–1869. [7] Lodders K. 2003. *The Astrophysical Journal* 591:1220–1247. [8] Afiattalab F. and Wasson J. T. 1979. *Geochimica et Cosmochimica Acta* 44:431–446. [9] Sears D. W. and Axon H. J. 1976. *Nature* 260:34-35. [10] Kallmeyn G. W. et al. 1989. *Geochimica et Cosmochimica Acta* 53:2747–2767.

5035

VARIATION IN DISTAL IMPACT EJECTA WITH DISTANCE FROM THE SOURCE CRATER: A MODEL

B. P. Glass¹ and B. M. Simonson². ¹Department of Geological Sciences, University of Delaware, Newark, DE 19716, USA. E-mail: bglass@udel.edu. ²Geology Department, Oberlin College, Oberlin, OH, 44074, USA. bsimonso@oberlin.edu.

**Introduction:** We have used information from six Phanerozoic ejecta/spherule layers to construct a model on how distal impact ejecta vary with distance from the source crater. The model appears to be consistent with theoretical studies of the cratering process and observational data from most Phanerozoic and late Precambrian distal ejecta layers, but not from older (>2.48 Ga), especially Archean spherule layers.

**Impact Spherules:** Distal impact ejecta layers consist primarily of spherules. There are two types of impact spherules: microtektites which do not contain primary crystallites and microkrystites which do. These two types combined with two mechanisms of formation (melt droplets versus condensate droplets) result in four possible categories of impact spherules: (1) microtektites produced as melt droplets, (2) microtektites formed as condensate droplets, (3) microkrystites formed as melt droplets, and (4) microkrystites formed as condensate droplets.

**The Model:** As an ejecta layer thins away from the source crater, the average degree of shock metamorphism increases and therefore the percent melt (spherules) increases. Beyond ~10 crater diameters an ejecta layer consists primarily of spherules and beyond ~100 crater diameters an ejecta layer is essentially a spherule layer containing little, if any, unmelted ejecta >125 µm. Thus, an ejecta layer from a crater > ~200 km in size will contain unmelted, as well as melted ejecta, globally. On average the petrographic and chemical homogeneity of melt-produced microtektites increases with distance from the source crater (i.e., the number of relict inclusions, vesicles, and schlieren decreases away from the source crater) [1]. The ratio of spherule fragments to whole spherules increases toward the source crater probably due to fragmentation caused by thermal stress as they land in water and/or to collisions between the microtektites in the atmosphere. The latter mechanism is supported by an increase in number of high-velocity impact pits per unit surface area on the microtektites toward the source crater [2]. The average size of the microtektites appears to increase toward the source crater beyond ~100 crater diameters, but closer in that trend reverses due to the increase in fragmentation. The maximum size of shocked-quartz grains increases toward the source crater, but the average degree of shock metamorphism, as indicated by the average number of sets of PDFs, increases away from the crater [3].

**Precambrian Spherule Layers:** Spherule layers from at least 11 impacts >2.4 Ga have been identified. The aggregate thicknesses of these layers are generally greater than the thicknesses of the Phanerozoic ejecta layers, but none of these older layers contain shocked-mineral grains except for trace amounts in four layers that were probably formed by just two impacts. Thus, these spherule layers do not fit the Phanerozoic model. This may be because the target rocks were mafic and/or because of much larger impact sizes as suggested by the large sizes of some of the spherules and the greater thicknesses of the spherule layers.

**References:** [1] Folco et al. 2010. *Geology* 38:211–214. [2] Prasad et al. 2010. *Meteoritics & Planetary Science* 45:990–1006. [3] Morgan et al. 2006. *Earth and Planetary Science Letters* 251:264–279.
5108

ASH SHUTBAH: A NEW IMPACT CRATER IN SAUDI ARABIA

E. Gnos¹, A. Al-Wagdani², A. Mahjub², A. A. Al-Solami², S. H. Allah², A. Matter³, B. A. Hofmann⁴, M. Schmieder⁵ and E. Buchner⁵. ¹Natural History Museum, Geneva. E-mail: edwin.gnos@ville-ge.ch. ²Saudi Geological Survey, Jeddah, Kingdom of Saudi Arabia. ³Institut für Geologie, Universität Bern, Switzerland. ⁴Natural History Museum Bern, Switzerland. ⁵Institut für Planetologie, University of Stuttgart, Germany.

**Introduction:** Although Saudi Arabia covers an area of more than two million square kilometers, only the three small, ~300-year-old Wabar impact craters located in sand dunes of the Rub al Khali have been confirmed on the ground [1, 2]. Three additional circular features, the ~5 km Jabal Rayah, the ~2.5 km Ash Shutbah, and the ~17 km Wadi Na'am have been proposed as possible impact craters [3, 4].

**Ash Shutbah:** The Ash Shutbah impact crater is located in flat lying limestones of the Middle Jurassic Tuwayq Mountain Formation at 21°37'N/45°39'E, ~50 km S of the village of Al Haddar. It is located at the edge of the Jabal Tuwayq escarpment. A set of circular features is easily recognizable on satellite images, and two branches of the upper Wadi Ash Shutbah follow the outermost circular feature. The morphological expression as revealed by Shuttle radar data (SRTM) is very weak [4]. Nonetheless, due to lithologic contrast, a dark central area is clearly distinguishable on satellite images.

**Field Observations:** A 4-day exploration in the Ash Shutbah area in May 2011 confirmed that the morphological expression of the Ash Shutbah impact crater has been strongly reduced by desert alteration and wind erosion. Only one possible shatter cone was found in massif sandstone of the central uplift. The weakly expressed central uplift consists of strongly folded, creamy calcareous sandstone of the Dhruma formation containing a 60-cm thick, black weathering, massif sandstone bed. This marker bed has been located in the escarpment outcrop at ca. 130 m below the plateau, indicating a minimal uplift of ca. 140 m, consistent with estimates obtained on complex impact craters of similar size [5]. Outward dipping radial folds occur in the external part of the central uplift. The outer parts of the crater consist of deformed Tuwayq Mountain limestone sheets forming circular rings of hills and depressions.

**Conclusions:** The presence of folded beds and a possible shatter cone confirm that the Ash Shutbah circular feature is a complex meteorite impact crater that is younger than the middle Jurassic limestones of the lower Tuwayq Mountain formation. The presence of an escarpment and a characteristic marker bed provide a unique situation to determine minimum uplift directly.

**References:** [1] Philby H. S. J. B. 1933. *The Geographical Journal* 81:1–21. [2] Wynn J. C. 2002. *Journal of Environmental & Engineering* 7:143–150. [3] Janjou D., Wyns R., Halawani M. A. and Memesh A. 2004. *Saudi Geological Survey Data-file report SGS-DF-2004-3*. [4] Schmieder M., Buchner E., Hofmann B. A. and Gnos E. 2009. Abstract, *The first Arab Impact Cratering and Astrogeology Conference*, Amman, Jordan, 84–85. [5] Grieve R. A. F. 1987. *Annual Reviews in Earth and Planetary Science* 15:245–270.

5338

EL'GYGYTGYN IMPACT CRATER'S FIREBALL LAYER: SPHERULES, IMPACT MELTS, METEORITIC COMPONENT

S. Goderis¹, M. Elburg², F. Vanhaecke³, Ph. Claeys¹, A. Wittmann⁴, and the El'gygytgyn Scientific Party. ¹Vrije Universiteit Brussel, Earth System Science, Department of Geology, B-1050 Brussels, Belgium. E-mail: steven.goderis@vub.ac.be, phclaeys@vub.ac.be. ²Ghent University, Department of Geology & Soil Sciences, B-9000 Ghent, Belgium. E-mail: marlina.elburg@ugent.be. ³Ghent University, Department of Analytical Chemistry, B-9000 Ghent, Belgium. E-mail: frank.vanhaecke@ugent.be. ⁴Lunar & Planetary Institute, Houston, TX 77058, USA. E-mail: wittmann@lpi.usra.edu.

**Introduction:** The 18 km Ø El'gygytgyn impact crater in NE Siberia formed 3.6 Ma ago in a target of 83.2–89.3 Ma old, ~620 m thick, rhyolitic, andesitic, and dacitic volcanics [1, 2]. An International Continental Drilling Program (ICDP) project recovered drill cores from an inner-crater continuous section of impactite deposits that contain scarce, pristine impact melt particles and glass spherules [3, 4]. These deposits allow studying the mixing of target rock components and the meteoritic projectile.

**Samples and Methods:** Three glassy impact melt rocks that were collected near the W' rim of the crater and 17 samples from the ICDP-Lake Drilling Hole D1 were investigated. Powdered bulk samples were characterized for major and trace element abundances, including the platinum group elements (PGE), using ICP-OES and ICP-MS. The compositions of three glassy impact melt rocks, 11 ~mm-size glassy melt particles, and seven glass spherules in suevitic rocks of the upper ~10 m of impactite drill core were determined with electron microprobe X-ray analysis.

**Results:** Major and trace element concentrations for bulk rock samples are in good agreement with previously published data [3, 5] and indicate a moderately homogeneous rhyo-dacitic drill core. A single sample at 391.6 m has a basaltic-trachyandesitic composition and higher than normal concentrations of Ti, Fe, Mn, Mg, Ca, Sc, V, Cr, Co, Ni, and Zn. Although major and trace elements show typical crustal values and ratios (e.g., subchondritic Ni/Cr of ~0.30–0.60), PGE abundances revealed the presence of a meteoritic component (~0.05 wt%) in three samples. The 11 glassy melt particles and the three glassy melt rocks have rhyolitic compositions. In contrast, six spherules range in composition from rhyolitic, dacitic, trachytic, and andesitic.

**Discussion:** Scaling laws suggest the depth of the melt zone at El'gygytgyn was 1.5–2.6 km [6]. Nonetheless, the compositions of glassy melt particles and impact melt rocks indicate melt-mixtures solely derived from the ~620 m thick volcanic succession of rhyolites, dacites, and andesites [5]. In contrast, five of the six spherules record contribution from a mafic target component [7] that is known from regional outcrops and clasts in the ICDP drill core [3, 4]. Thus, the impact melts in suevite deposits appear homogenized but the spherules that presumably condensed from the vapor plume record heterogeneities of an extended target section. A diluted projectile component was detected in a spherule-bearing drill core sample and two melt rock samples.

**References:** [1] Gurov et al. 2007. *Meteoritics & Planetary Science* 42:307–319. [2] Gurov and Gurova. 1991. *Geological structure and rock composition of impact structures*, Naukova Dumka Press, Kiev, pp. 160. [3] Raschke et al. 2011. Abstract #1299. 42nd Lunar and Planetary Science Conference. [4] Wittmann et al. 2011. Abstract #2792. 42nd Lunar and Planetary Science Conference. [5] Gurov et al. 2005. *GSA Special Paper* 384:391–412. [6] Grieve and Cintala. 1992. *Meteoritics* 27:526–538. [7] Adolph and Deutsch. 2009. Abstract #1116. 40th Lunar and Planetary Science Conference.
5067

THERMAL HISTORY OF METAL PARTICLES IN CB CHONDRITES

J. I. Goldstein¹, R. H. Jones², P. G. Kotula³ and J. R. Michael³. ¹University of Massachusetts, Amherst, MA 01003, USA. E-mail: jig0@ecs.umass.edu. ²University of New Mexico, Albuquerque, NM. ³Sandia National Laboratory, Albuquerque, NM, USA.

**Introduction:** The CB chondrites are part of the “CR clan,” a group of metal-rich chondrites that include CH, CB and CR groups [1, 2]. CB chondrites have more metal than CH and much larger metal particles: both groups may have formed from a similar type of impact event [3]. Many metal grains in CH chondrites show evidence for reheating in the form of two-phase metal particles [4]. In general such textures are not observed in metal from CBa chondrites. Plastically deformed and two phase metal particles have been observed in CBb chondrites [5]. The purpose of this study is to obtain microstructural and microchemical information at the nm to µm scale for two-phase metal particles in CBa Gujba and CBb HaH 237 chondrites in order to understand the detailed thermal histories of CB chondrites.

**Method:** Metal particles were observed optically and selected particles were thinned using focused ion beam techniques for transmission electron microscopy (TEM). Chemistry at the nm level was obtained by X-ray analysis in the TEM and structure analysis was performed using electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM).

**Results:** We observed one metal particle in Gujba that contained about 30 grains ~0.1 mm in size with different orientations. Each grain had a two phase microstructure containing µm sized taenite in a recrystallized kamacite matrix. Kamacite and taenite contain 5.5 and 10.5 wt% Ni respectively. We estimate, using the calculation procedures of [6], that this metal particle was reheated to ~675 °C and cooled to ~550 °C in a month or less. A two phase metal particle in HaH 237 was plastically deformed at temperatures above 500 °C, and reheated at about 640 °C. It has a microstructure similar to grains investigated by Meibom et al. [5]. The taenite and kamacite have a close packed bcc-fcc orientation relationship indicating the exsolution of taenite in kamacite at the reheating temperature. Grain boundary diffusion at the nm level indicates cooling to ~500–550 °C in a month or less.

**Discussion:** Evidence of reheating in CB metal particles is consistent with a process in which discrete metal and silicate particles, which possibly originated in an impact plume, were accreted onto a parent body and later subjected to a secondary heating event. Initial formation of metal could have included both condensation of solid metal and solidification of liquid metal. Later heating could be the same as the one in which impact-melt matrix was injected into pre-existing metal and silicate components [7]. This may have reheated metal particles selectively, allowing for plastic deformation and formation of taenite from a kamacite matrix in some metal particles.

**References:** [1] Weisberg M. K. et al. 2001. *Meteoritics & Planetary Science* 36:401–418. [2] Krot A. N. et al. 2002. *Meteoritics & Planetary Science* 37:1451–1490. [3] Krot A. N. et al. 2005. *Nature* 436:989–992. [4] Goldstein J. I. et al. 2007. *Meteoritics & Planetary Science* 42:913–933. [5] Meibom A. et al. 2005. *Meteoritics & Planetary Science* 40:1377–1391. [6] Smith B. A. and Goldstein J. I. 1977. *Geochimica et Cosmochimica Acta* 41:1061–1072. [7] Weisberg M. K. and Kimura M. 2011. *Meteoritics & Planetary Science* 45:873–884.

5066

PRELIMINARY INVESTIGATION INTO THE USE OF SURFACE MODIFICATION TECHNIQUES TO DETECT ORGANIC MATERIALS IN METEORITES

M. D. Goodyear¹,², I. Gilmour¹ and V. K. Pearson¹,². ¹Planetary and Space Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, UK. ²Department of Chemical and Analytical Sciences, The Open University, Milton Keynes, MK7 6AA, UK. E-mail: m.d.goodyear@open.ac.uk.

**Introduction:** Many carbonaceous chondrites (CCs) display evidence of aqueous and/or thermal alteration of their component minerals [1]. In addition, CCs also contain up to ca. 5% carbon [2], much of which is organic, insoluble, involatile and unreactive, and known as insoluble organic material (IOM). It is not known if there is a causal connection between the mineral alteration, and formation or modification of organic materials [3]; however, by understanding the relationships between them, any connections (chemical or physical) could be established.

**Analytical Constraints:** Organic analysis of CCs generally requires extraction or demineralization; mineralogy is often studied in polished surfaces or thin section. None of these methods is suitable for this study, as all spatial information would either be lost, or compromised (e.g. by mechanical redistribution). Scanning electron microscopy (SEM), and Raman spectroscopy are useful complementary techniques, requiring minimal surface preparation and yielding information in situ, on both the mineralogy (from SEM) and organic content (from Raman) of a region under study. It is essential the sample be accurately aligned and imaged, so the same area is studied using both methods.

**Experimental:** We present preliminary work directed towards the application of molecular tags, whereby more-easily detectable atoms or functional groups (i.e. those not typically present in untreated meteorites) are attached to the IOM.

**Ozonolysis:** To increase its reactivity to tagging, IOM is pre-treated with ozone, to introduce oxygen-containing functional groups, such as carboxylic acids or ketones. The resulting compounds can then be converted into a range of derivatives containing the chosen tag. Conditions for ozonolysis were developed by following the reaction of polycyclic aromatic hydrocarbon (PAH) standards, typical of those believed to make up the IOM backbone [4], on inert mineral supports, e.g. silica or sandstone. Samples of Murchison were ozonized and examined by SEM and Raman spectroscopy, the latter incorporating image processing to ensure in each case, the same sample region was being studied.

**Molecular Tagging:** Reaction conditions have been developed to enable the introduction of a range of molecular tags into ozonolysis-generated oxygen-containing functional groups, initially using model compounds again supported on inert minerals. Using these methods, standard acids (carboxylic and amino-), alcohols, phenols, aldehydes, and ketones have been tagged with fragments containing fluorine or chlorine; work to apply this methodology to meteorites is ongoing.

**Results:** Good-quality, aligned and focused images were obtained using both SEM and Raman, allowing mapping of elemental abundance and organic content. The derivatization of IOM by ozonolysis (indicated by the changes observed in the Raman signal), shows that the IOM can next be subjected to molecular tagging.

**References:** [1] Brearley A. J. 2005. Treatise on Geochemistry vol. 1, 1.09:247–268. [2] Sephton M. 2002. *Natural Product Reports* 19:292–311. [3] Zega T. J. et al. 2010. *Geochimica et Cosmochimica Acta* 74:5966–5983. [4] Derrene S. and Robert F. 2010. *Meteoritics & Planetary Science* 45:1461–1475.
## SLOPE 1, OR NOT SLOPE 1, IS THAT THE QUESTION?

R. C. Greenwood¹, I. A. Franchi¹ and C. T. Pillinger¹. ¹PSSRI, Open University, Walton Hall, Milton Keynes MK7 6AA, UK. E-mail: r.c.greenwood@open.ac.uk.

**CCAM v. Slope 1 Line:** The process involved in producing the non mass-dependent oxygen isotope variation observed in primitive meteorites is poorly understood. While self-shielding of CO [1–3] is currently favoured, alternative scenarios have been proposed [4]. An important aspect of this problem relates to the significance of various reference lines on oxygen isotope plots. The most widely used, the carbonaceous chondrite anhydrous mineral line (CCAM), has a slope of 0.94 and was derived from analyses of Allende mineral separates [5, 6]. However, its significance has been questioned and instead a line of slope 1 proposed as more representative of the primordial variation [7]. The fact that a highly ¹⁷,¹⁸O-enriched phase in Acfer 094 plots on the slope 1 line lends support to this proposal [8].

**High-Precision Studies:** Important insights into the relative significance of the slope 1 and CCAM lines are provided by laser fluorination studies. Bulk CR chondrites define a line of slope 0.70, with less aqueously altered samples plotting close to the slope 1 line [9]. This suggests that the composition of pristine CR precursor material may be given by the point at which the CR mixing line intersects the slope 1 line. The acapulcoite-lodranite clan and winonaites also form distinct linear arrays plotting between the slope 1 and CCAM lines. Winonaites define a slope 0.54 line, with the less evolved chondrule-bearing samples plotting at the lower δ¹⁸O values, i.e., closer to the slope 1 line. Acapulcoite and lodranite analyses define a shorter array, with a steeper slope (0.61). Prior to metamorphism the clan may have experienced aqueous alteration, so that their precursor material would also have had a composition closer to the slope 1 line.

**Discussion:** While the primary significance of the slope 1 line is supported by the evidence discussed above, the relevance of the CCAM line is based on the fact that a significant range of meteorite groups, and their constituents, fall either on, or close to it [5, 6]. The suggestion that the lower slope of the CCAM simply reflects late stage disturbance of the slope 1 line requires further evaluation [7]. Based on analyses of Acfer 094 chondrules, a further distinct slope 1 line has recently been proposed [10]. This again indicates that near-slope 1 variation is a characteristic feature of a wide range of primitive materials. Slope values between ~0.6 and 1.8 have been measured in CO photodissociation experiments [11], as a result there is currently a debate about the extent to which CO self-shielding was responsible for the slope 1 anomaly observed in primitive meteorites [12].

**References:** [1] Clayton R. N. 2002. *Nature* 415:860–861. [2] Yurimoto H. and Kurimoto K. 2004. *Science* 305:1763–1766. [3] Lyons J. R. and Young E. D. 2005. *Nature* 435:317–320. [4] Dominguez G. 2010. *The Astrophysical Journal* 713:L59–L63. [5] Clayton R. N. et al. 1977. *Earth and Planetary Science Letters* 34:209–224. [6] Clayton R. N. and Mayeda T. K. 1999. *Geochimica et Cosmochimica Acta* 63:2089–2104. [7] Young E. D. and Russell S. S. 1998. *Science* 282:452–455. [8] Sakamoto N. et al. 2007. *Science* 317:231–233. [9] Schrader D. L. et al. 2011. *Geochimica et Cosmochimica Acta* 75:308–325. [10] Ushikubo T. et al. 2011. Abstract #1183. 42nd Lunar and Planetary Science Conference. [11] Chakraborty S. et al. 2008. *Science* 321:1328–1331. [12] Lyons J. R. 2011. Abstract #2780. 42nd Lunar and Planetary Science Conference.

## REFLECTANCE SPECTRA OF CARBONACEOUS CHONDRITES UNDER CONTROLLED ATMOSPHERE

F. Grisolle¹, P. Beck¹, E. Quirico¹, B. Schmitt¹ and F. Moynier². ¹UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique de Grenoble (IPAG), France. E-mail: pierre.beck@obs.ujf-grenoble.fr. ²Department of Earth and Planetary Sciences, Washington University, St. Louis, MO, USA.

**Introduction:** Carbonaceous chondrites are fine-grained mixtures of silicates, organics and metals. Their connection with asteroid has been studied over the last decades using similarities in the near-infrared reflectance spectra. One of the particularities of carbonaceous chondrites among other chondrites group, is the presence of hydrated silicates, testifying of the action of water at some time of their formation history. Here, we report on the NIR spectra of four carbonaceous chondrites (Tagish Lake [ungrouped CC], Orgueil [CI1], Murchison [CM2] and Allende [CV3]). The specificity of this study is that we pay particular attention to the 3-µm region and then, spectra were measured under controlled atmosphere in order to avoid contamination by indigenous water.

**Reflectance Spectroscopy:** Infrared reflectance spectra were measured using the spectrogonio radiometer available at the Laboratoire de Planétologie de Grenoble [1]. This instrument enables bi-directionnal reflectance spectra measurements with a good photometric accuracy (below 1%). Spectra were measured in the 0.5–4.6 µm range with a sampling interval of 20 nm. Because ambient atmospheric water might adsorb on the surface of the sample and perturb the 3-µm band, spectra were acquired within the SERAC environmental cell [2]. Samples were heated up to 80 °C under vacuum (P = 10⁻³ mbar) to remove adsorbed water. Spectra were measured under normal illumination incidence, and with an observation angle of 30°.

**The 3-micron Band:** -OH (and H₂O) For all three samples, a spectrum was measured after and prior to submitting the sample to a controlled atmosphere. All spectra reveal the presence of a 3-µm band, but which is much weaker for Allende (Band Depth (BD) of 11%) and stronger for Orgueil, (BD of 60%) and Murchison (BD = 47%). In the case of Orgueil and Murchison, a significant evolution is observed after heating to 80 °C and exposure to vacuum, suggesting that a significant amount of indigenous water was lost. This observation confirms previous work performed using transmission spectroscopy [3]. We show here, the shape, band maximum and band center evolves as adsorbed and mesopore water is removed and dry condition reflectance spectra are needed for a good comparison with asteroid observation.

**Organics Signature:** CH₂ and CH₃. The 3-µm region is also precious since traces or organics can be observed around 3.4 µm [4]. These signatures are clearly detected in the case of Orgueil, Tagish Lake and Murchison, but hardly for Allende. This difference can be explained by the fact that the proportion of organic matter in Allende is smaller than the other two samples, and that the object was slightly metamorphosed.

**References:** [1] Brissaud et al. 2004. *Applied Optics* 43:1926–1937. [2] Pommerol et al. 2009. *Icarus* 204:114–136. [3] Beck at al. 2010. *Geochimica et Cosmochimica Acta* 74:8881. [4] Moroz et al. 1998. *Icarus* 134:253–258.
MICROSTRUCTURAL HETEROGENEITY OF METAL IN CHINGA METEORITE: STUDY USING MÖSSBAUER SPECTROSCOPY WITH A HIGH VELOCITY RESOLUTION

V. I. Grokhovsky¹, M. I. Oshtrakh¹, K. A. Uymina¹, M. V. Goryunov¹,² and V. A. Semionkin¹,². ¹Faculty of Physical Techniques and Devices for Quality Control, Ural Federal University, Ekaterinburg, 620002, Russian Federation. E-mail: grokh47@mail.ru. ²Faculty of Experimental Physics, Ural Federal University, Ekaterinburg, 620002, Russian Federation.

**Introduction:** Iron meteorite Chinga was classified as ataxite IVB with about 16.8 wt.% of Ni. The main part of metal consisted of dispersive multi-phase structure that was not optically resolved. It is well known the presence of macroscopic selective reflection zones (Schliren bands) in ataxites IVB [1]. Previously it was conclude that the origin of these zones is due to the martensite transformation peculiarities [2]. Recently we have observed another macroscopic zone in a peripheral part of the Chinga meteorite fragments. Therefore, we used the high velocity resolution Mössbauer spectroscopy for comparative study of microstructural peculiarities of this new found zone and internal part of Chinga metal.

**Experimental:** The typical relief zone along the periphery of the Chinga meteorite fragment was clearly seen after mechanical cutting of the fragment. Its width varies from approximately 0.5 cm to approximately 1.5 cm. Samples of metal powder were prepared from this zone and internal part of Chinga fragment for Mössbauer study. Mössbauer spectra were measured using automated precision Mössbauer spectrometric system with a high velocity resolution [3] at room temperature in 4096 channels.

**Results and Discussion:** Mössbauer spectra of studied samples from different parts of Chinga fragment were similar asymmetrical six lines patterns. However, these spectra appeared to be slightly different that may be seen in difference between Mössbauer spectra of studied parts of Chinga fragment. Measured Mössbauer spectra were better fitted using nine magnetic sextets. These sextets may be a result of the presence of kamacite α-Fe (Ni, Co), martensite α₂-Fe (Ni, Co), secondary kamacite α'-Fe(Ni, Co), taenite γ-Fe (Ni, Co) and tetrataenite γ-FeNi phases with Ni variations. Comparing this result with the SEM data we can suggest microstructural heterogeneity of Chinga metal. Moreover, areas of Mössbauer spectra components as well as their hyperfine parameters were different for different metal samples. This fact may be explained as variation of microstructural heterogeneity in various parts of Chinga fragment as a result of phase composition variations after ablative heat alteration or terrestrial pre-corrosion alteration.

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

**References:** [1] Axon H. J. and Smith P. L. 1972. *Mineralogical Magazine* 38:736–755. [2] Grokhovsky V. I. et al. 2008. *Meteoritics & Planetary Science* 43:A50. [3] Semionkin V. A. et al. 2010. *Bulletin of the Russian Academy of Sciences: Physics* 74:416–420.

ISOTOPIC AND RAMAN ANALYSES OF LOW-DENSITY ORGUEIL CARBON GRAINS

Evan Groopman¹, Brigitte Wopenka² and Ernst Zinner¹. ¹Physics Department and ²Department of Earth and Planetary Sciences, Washington University, St. Louis MO, USA. E-mail: eegroopm@physics.wustl.edu.

**Introduction:** We present isotopic and Raman spectroscopic data for 20 low-density presolar grains from the OR1d (size > 1 µm, ρ = 1.75–1.92 g cm⁻³) size/density separate of the Orgueil CI chondrite [1]. OR1d contains substantial insoluble organic material (IOM) of solar composition, from which the grains must be physically separated via micromanipulation prior to analysis. Some IOM coating may remain on a grain's surface, yielding isotopic compositions that are less anomalous than the true values. Correlated SEM and isotope images allow us to locate uncoated areas on the grains from which we may infer their true isotopic compositions.

**Results:** We measured ¹²,¹³C, ¹⁴,¹⁵N, ¹⁶,¹⁸O, ²⁸,²⁹,³⁰Si, ²⁴,²⁵,²⁶Mg, and ²⁷Al isotopes with the NanoSIMS. Inferred ²⁶Al/²⁷Al ratios in 10 grains are between 0.012 and 0.45, in the range of SiC X grains [2]; additional ¹⁸O excesses in these grains confirm their supernova origin. 18 grains have ¹⁵N excesses. ¹²C/¹³C ranges from 7 to 306, with 9 grains being isotopically heavy, 5 isotopically light, and 6 of solar composition.

N and O isotope images of 6 grains reveal regions of large isotopic anomalies amidst regions of roughly solar composition. From SEM images we may verify the presence of IOM adhered to the grains' surfaces. Four grains with ¹⁶O/¹⁸O ratios of 162, 169, 304, and 139, all highly enriched in ¹⁸O with respect to solar, showed regions of much more extreme ¹⁸O enrichment with ¹⁶O/¹⁸O of 6, 14.4, 40, and 9, respectively, in the ion images. The whole-grain ¹⁶O/¹⁸O ratios differ by 1–2 orders of magnitude from the ratios in uncoated areas of the grains. ¹⁶O and ¹⁸O concentrations are spatially anti-correlated in one grain, implying that low ¹⁶O/¹⁸O regions are representative of the uncoated grain, while solar-valued regions must be IOM on the surface. ¹⁴N/¹⁵N values also correlate with the presence of IOM (whole grain:uncoated area): (141:20), (256:27), (209:30), (261:111) in the same four grains.

There exists a correlation between Raman and isotopic data. Based on 1st and 2nd order Raman spectra [3], 11 grains are Allende-type (i.e., glassy carbon), 3 are graphitic, and 6 are kerogen-type [4]. All grains with unambiguous SN signatures were found to have Allende- or graphitic Raman spectra. Kerogen-type grains all have isotopically normal C and O, but generally have excesses in ¹⁵N.

**Discussion:** Whole-grain isotope ratios of OR1d carbon grains represent lower limits of isotopic anomalies due to the presence of solar- composition IOM on the grains' surfaces. Isotope images allow us to distinguish between regions covered with IOM and those of the true grain, helping us determine the isotopic composition without sputtering too much of the grain away. These grains will be ultramicrotomed for subsequent Raman, TEM, XANES and NanoSIMS analyses of their interiors, therefore preserving as much of the grain is of utmost importance.

**References:** [1] Jadhav M. et. al. 2006. *New Astronomy Reviews* 50:591–595. [2] Zinner E. et al. 2010. *Proceedings of Science* (NIC XI) 148. [3] Wopenka B. et al. This conference. [4] Wopenka B. et al. 2011. Abstract #1162. 42nd Lunar and Planetary Science Conference.
## LUNAR SPINEL-RICH ROCKS BY REACTION BETWEEN PICRITIC MAGMA AND ANORTHOSITIC CRUST, AND IMPLICATIONS FOR M3 OBSERVATIONS

J. Gross and A. H. Treiman. Lunar and Planetary Institute, Houston, TX, USA. E-mail: gross@lpi.usra.edu.

**Introduction:** The lunar crust contains some of the most important and accessible clues to the history of the Moon's chemical evolution [e.g., 1-3]. The M³ near-infrared mapping spectrometer on the Chandrayaan-1 spacecraft [4-6], recently detected a new rock type on the rim of the Moscoviense basin—rock rich in (Mg,Fe)Al₂O₄ spinel, with less than 5% mafic silicate minerals (olivine and pyroxene). No such material had been described from lunar rocks. Here, we describe a rock fragment rich in Mg-Al spinel from lunar meteorite Allan Hills (ALH) A81005. The fragment is not identical to the M³ rock (it contains approximately 20% olivine + pyroxene) but is similar enough to be relevant.

**Sample:** Antarctic meteorite ALH A81005, is a polymict, anorthositic regolith breccia from the lunar highlands [7-9]. It is composed of anorthosites, granulites, isolated mineral fragments, impactites, impact glasses, and mare basalts set in an glassy, agglutinitic matrix [10]. Thin section ALHA81005.9 contains a single rock fragment, 350 x 150 µm, with approximately 30 vol% (Mg,Fe)Al₂O₄ spinel—enough that an outcrop of it would be easily detected by M³. The rest of this clast is approximately 15% olivine, approximately 6% low-Ca pyroxene, and 49% plagioclase. The fragment is so fine-grained (30–50 µm) that it reasonably could represent a larger rock body; it is not spinel-rich merely by chance.

**Discussion and Implications:** The clast is so rich in spinel that it could not have formed by melting a peridotitic mantle or a basaltic lunar crust. The clast's small grain size and its apparent disequilibrium between spinel and pyroxene suggest rapid crystallization at low pressure. A likely origin for its bulk composition is assimilation of anorthosite by a picritic magma. This model explains the petrographic and chemical features of our clast, and is consistent with the regional setting of the spinel-rich regions identified by M³. The spinel-rich area near Moscoviense is associated with two other unusual spectral signatures—rock rich in olivine, and rock rich in orthopyroxene (the “OOS” association [5]). A picritic intrusion into the anorthositic crust, as suggested here, could produce such rocks as cumulate dunite and pyroxenite, in addition to its spinel-rich cumulates. All of these rocks, igneous and metasomatic, could have been brought to the Moon's surface in the impact that produced the Moscoviense basin. Other spinel-bearing rocks of such a picritic intrusion, like the rock fragment described here, may not be detectable by M³ because of their high abundance of mafic minerals. The strength of the NIR spinel signature is masked significantly if the rock contains more than 5% mafic minerals [4]. Thus spinel-rich rocks might be common in the lunar crust but not yet detectable. However, with the advent of high spectral and high spatial resolution instruments, there is every expectation that similar exposures of materials might be found across the entire surface of the Moon [5].

**References:** [1] Taylor G. J. 1982. Planetary Science: A Lunar Perspective LPI. [2] Demidova et al. 2007. *Petrology* 15:386–407. [3] Isaacson et al. 2011. *Journal of Geophysical Research* 116:E00G11. [4] Pieters C. M. 2010. Abstract #1854. 41st Lunar and Planetary Science Conference. [5] Pieters C. M. 2011. *Journal of Geophysical Research* 116:E00G08. [6] Lal et al. 2011. Abstract #1339. 42nd Lunar and Planetary Science Conference. [7] Treiman A. H. and Drake M. J. 1983. *Geophysical Research Letters* 10:783–786. [8] Goodrich C. A. et al. 1984. *Journal of Geophysical Research* 89:C87–C94. [9] Korotev R. L. 2005. *Chemie der Erde* 65:297–346. [10] Gross J. and Treiman A. H. 2010. Abstract #2180. 41st Lunar and Planetary Science Conference.

## MAGMATIC ORIGIN OF CALCITE FROM THE LUNA-20 REGOLITH SAMPLE

J. Götzé¹, A. Gucsik²,³, U. Kempe¹, U. Ott², P. Hoppe², Sz. Nagy⁴, Sz. Bérczi⁵ and M. Veres⁶. ¹Institut für Mineralogie, TU Bergakademie Freiberg, Brennhausgasse 14, Freiberg, D-09596, Germany. ²Max-Planck-Institut für Chemie, Joh.-J.-Becher-Weg 27, D-55128 Mainz, Germany. ³Konkoly Observatory, Hungarian Academy of Sciences, Konkoly-Thege út 15-17, Budapest, H-1121, Hungary. E-mail: ciklamensopron@yahoo.com. ⁴Petrology and Geochemistry, Eötvös Lorand University, Pázmány Péter sétány 1/c, Budapest, H-1117, Hungary. ⁵Department of Material Physics, Institute of Physics, Eötvös University, Pázmány P. s. 1/a, Budapest, H-1117, Hungary. ⁶Research Institute for Solid State Physics and Optics, Konkoly-Thege M. út 29-33, Budapest, H-1121, Hungary.

**Introduction:** Direct investigations concerning the composition and structure of the Moon started with the space missions of Russia (formerly Soviet Union; Luna missions from 1959 to 1976) and the U.S. (Ranger and Surveyor missions in 1964 and 1968). The Apollo missions between 1969 and 1972 as well as Luna 16, 20, and 24 (1971–1976) returned 382 kg of geological material. Their investigation revealed that the mineral compositions of lunar rocks are much simpler than those of terrestrial rocks. Plagioclase is the most abundant mineral of the lunar highland rocks (enriched in Ca and Al), whereas pyroxene, plagioclase and ilmenite are predominant in mare basalts (pyroxene together with plagioclase 75–90%). Olivine and the high-temperature silica phases (tridymite and cristobalite) mostly occur with contents between 1 and 10% [1–5].

**Sample and Experimental Procedure:** We report the existence of small inclusions of calcium carbonate (CaCO₃—calcite) in a clast of granitic rock composition from lunar regolith that was returned by the Luna 20 space mission. Their presence was proved by a combination of high-resolution cathodoluminescence (CL) microscopy and spectroscopy, SEM-EDS, micro-Raman spectroscopy and elemental analysis by NanoSIMS.

**Results and Discussion:** Based on isotope data obtained by NanoSIMS, an origin from a meteorite impact or from an in situ formation process on the surface of the Moon appears highly unlikely. The inclusion of calcite in quartz, intergrown with K-feldspar and displaying an undamaged igneous texture, indicates a magmatic origin of carbonate.

**Conclusion:** Our observations point to a scenario, where granite crystallized during fractionation from a KREEP-rich melt and where the carbonate inclusion is a residue of immiscible CO₂-rich parts (carbonatite?) of this melt. Consequently, our observations provide the evidence for the presence of volatiles during lunar crust formation.

**References:** [1] Smith J. V. 1974. *American Mineralogist* 59:231–243. [2] Smith J. V. and Steel I. M. 1976. *American Mineralogist* 61:1059–1116. [3] Taylor S. R. 1982. *Planetary science: A lunar perspective*. Houston, Texas: Lunar and Planetary Institute. [4] Taylor S. R. 2008. The origin and evolution of the Moon in a planetary context. *Golden Jubilee Memoirs Geological Society of India* 66:13–50. [5] Shearer C. K. and Papike J. J. 1999. Magma evolution of the Moon. *American Mineralogist* 84:1469–1494.
CATHODOLUMINESCENCE PROPERTIES OF THE FORSTERITE FORMED UNDER SUPER COOLING: AN IMPLICATION FOR METEORITICS

A. Gucsik¹, K. Tsukamoto¹, Y. Kimura¹, H. Miura¹, H. Nishido², M. Kayama², K. Ninagawa³ and Y. Endo². ¹Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. E-mail: ciklamensopron@yahoo.com.
²Research Institute of Natural Sciences, Okayama University of Science, 1-1 Ridai-cho, Okayama, 700-0005, Japan. ³Department of Applied Physics, Okayama University of Science, 1-1 Ridai-cho, Okayama, 700-0005, Japan.

**Purpose:** In this study, cathodoluminescence (CL) microscopy and spectroscopy of the experimentally grown forsterite spherule has been characterized to understand more about the mechanism of the crystal growth under the rapid cooling conditions, which may be applied to the study of the meteoritic forsterite.

**Samples and Experimental Procedure:** Forsterite crystals with 1 mm in diameter were grown as a chondrule analogue by the aero-acoustic levitation u floating method [1, 2] and gas jet levitation methods [3]. Since levitated melt crystallizes under very high super cooling due to homogeneous nucleation, the growth rate of crystallization is quite larger compared with that near equilibrium temperature. The lab-chondrule is well reproduced the texture of natural chondrule. CL spectroscopy was made by a SEM-CL system at Okayama University of Science (Okayama, Japan).

**Results and Discussion:** In previous CL studies of the meteoritic forsterite samples in Allende and Murchison, a significant blue center (between 400 and 500 nm) was observed [4-6]. However, these authors were not able to identify the defect-related centers of the CL emission between 400 and 500 nm in the synthetic and meteoritic forsterite samples. In our samples, the red CL color and its heterogeneous distribution were observed in, which show two broad emission bands at around 630 nm in red region and over 720 nm in red-IR region. The former band can be assigned to impurity center of divalent Mn ion as an activator [4-6]. The latter one shows a magnificent red emission in a wide range of wavelength responsible for trivalent Cr ions [4], which possess two components of Cr activator and structural defect caused by interstitial Cr ions. The color CL image of experimentally grown forsterite exhibits significant blue luminescence in the main branches of the interior structure of lab-chondrule, which reflects an order of crystallization. CL spectra from the blue luminescent area give a characteristic broad band emission at around 450 nm, which is associated with a relatively small concentration of Al, Ca, Ti refractory elements [4]. A new CL band centered at 480 nm (blue/green CL color) might be assigned to a microdefect-related center, which was formed due to the rapid growth from super cooled melt of forsterite.

**References:** [1] Tsukamoto et al. 1999. *Antarctic Meteorites* 24:179-181. [2] Tsukamoto et al. 2001. Abstract #1846. 32nd Lunar and Planetary Science Conference. [3] Nagashima et al. 2006. *Journal of Crystal Growth* 293:193-197. [4] Steele 1986. *American Mineralogist* 71:966-970. [5] Vasconcellos M. A. Z. and Steele I. M. 1996. Abstract #1359. 27th Lunar and Planetary Science Conference. [6] Benstock et al. 1997. *American Mineralogist* 82:310-315.

IRON AND NICKEL ISOTOPIC COMPOSITIONS OF PRESOLAR SiC Z GRAINS AND A MYSTERIOUS SiC GRAIN OF UNKNOWN ORIGIN

F. Gyngard and L. R. Nittler. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA. E-mail: fgyngard@dtm.ciw.edu.

**Introduction:** Approximately 1% of presolar SiC grains are of Type Z, characterized by comparatively large $^{30}$Si/$^{29}$Si ratios [1]. These grains are thought to have formed in the ejecta of low-metallicity AGB stars, and as such represent good tracers of galactic chemical evolution. Here we report new isotopic measurements of the Fe-Ni compositions of three Z grains, as well as one accidentally measured SiC grain of unknown type with the largest Fe isotopic anomaly ever observed.

**Experimental:** A residue (IH6) composed mostly of SiC and $Si_3N_4$ grains from the Indarch enstatite chondrite (EH4) was automatically mapped [2] for $^{12,13}$C, $^{12}$C$^{14}$N, $^{12}$C$^{15}$N, and $^{28,29,30}$Si isotopes in multi-collection with the Carnegie NanoSIMS 50L. After SEM imaging, candidate Z grains were selected for further studies based on their physical separation from nearby grains. Two instrumental setups (consisting of two magnetic field steps each) were used to measure the Fe-Ni isotopic compositions. In the first, $^{54,56,57}$Fe and $^{58,60,61,61}$Ni were measured in one magnetic field step, and $^{52}$Cr and $^{28}$Si$_2$ (for locating the grains) in the other step. The other setup consisted of $^{28}$Si, $^{52}$Cr, $^{54,56,57}$Fe, and $^{58,60}$Ni in the first magnetic field step and $^{61,62}$Ni in the second.

**Results:** The candidate Z grains chosen for study were selected based on their enrichments in $^{30}$Si relative to the mainstream correlation line, as has been done previously [3-5]. Due to extreme difficulty in re-locating many of the grains in the NanoSIMS, only three Z grains were able to be successfully analyzed for their Fe-Ni compositions. Two of the grains have isotopically normal Fe and Ni, within 2σ uncertainties. This is not unexpected as many Z grains analyzed previously [5] have shown no anomalies in Fe and Ni, though this may be simply due to poor statistics from low Fe-Ni elemental concentrations. Z grain f3-2-14-6 has a large enrichment in $^{54}$Fe ($\delta^{54}$Fe/$^{56}$Fe = 620 ± 230‰) - its Ni (as well as other Fe) isotopic compositions are normal. As observed before [5, 6], $^{54}$Fe excesses are unexpected; grains believed to come from low-metallicity stars are predicted to have $^{54}$Fe deficits [6]. In an attempt to locate and measure a Type C SiC grain (e2-3-4 [7]), we inadvertently measured a nearby SiC grain that had not been analyzed for its C, N, or Si isotopic compositions; however, it has an Fe composition of $\delta^{54}$Fe/$^{56}$Fe = 2200 ± 150‰ and $\delta^{57}$Fe/$^{56}$Fe = 1860 ± 230‰. The grain's Ni isotopic composition is solar within 2σ errors. This grain was not measured during the automated measurements; yet, re-analysis of the overview ion image taken of the area containing the grain during automated scanning reveals it to have a $^{12}$C/$^{13}$C ratio of approximately 30. Unfortunately, its N and Si compositions are not diagnostic enough to definitively assign it to a given grain type, due to low count rates in the ROI of the grain. More measurements of Z grains and the Type C grain are planned for the future.

**References:** [1] Hoppe P. et al. 1997. *The Astrophysical Journal* 487:L101. [2] Gyngard F. et al. 2010. *The Astrophysical Journal* 717:107. [3] Zinner E. et al. 2007. *Geochimica et Cosmochimica Acta* 71:4786. [4] Nittler L. R. and Alexander C. M. O.D. 2003. *Geochimica et Cosmochimica Acta* 67:4961. [5] Hynes K. M. et al. 2009. *Meteoritics & Planetary Science* 44:A96. [6] Marhas K. K. et al. 2008. *The Astrophysical Journal* 689:622. [7] Gyngard F. et al. 2010. *Meteoritics & Planetary Science* 73:5242.
THE MARIBO CM FALL AND ITS POSSIBLE RELATIONSHIP TO
COMET ENCKE AND THE TAURID METEOR COMPLEX

H. Haack¹, R. Michelsen¹, G. Stober², D. Keuer², W. Singer² and I.
Williams³. ¹Natural History Museum of Denmark, University of
Copenhagen. E-mail: hh@snm.ku.dk. ²Institute of Atmospheric Physics,
Rostock University, Germany. ³Astronomy Unit, Queen Mary, London
E1 4NS, UK.

**Introduction:** The Maribo meteorite is the first carbonaceous chondrite with an instrumental record of its fall [1]. The orbit of Maribo is also the only meteorite orbit to fall within the Taurid complex, a massive swarm of objects including comet Encke, several other large NEOs as well as fireball producing objects. If Maribo is genetically related to these objects it implies that CM chondrites are related to comets.

**CMs and Comets:** Short period comets remain active for approximately 10 ky. After the comet has depleted its source of volatiles the now extinct cometary nucleus remains in the inner solar system as a member of the near Earth population. NEOs have dynamical lifetimes of ca. 100 My and are likely sources of meteorites. We should therefore expect to see samples of extinct nuclei in our collections of meteorites. Studies comparing the available information on chemistry and petrology of comets and chondrites have suggested that CI and CM chondrites could represent samples of extinct cometary nuclei [2, 3].

Recent astronomical observations and space missions to comets have provided new data supporting a connection to chondrites. D/H ratios in water detected in the tails of Halley and Hyakutake are ca. $30 \times 10^{-5}$ [5]. This is within error of the D/H ratios measured in CM chondrites (18–20 $\times 10^{-5}$) [6]. Spitzer Space telescope observations of the Deep Impact ejecta from comet 9P/Tempel 1 gave the first data on the mineralogy in the interior of comets. The observations demonstrated the presence of crystalline silicates, carbonates and phyllosilicates [7] The crystalline silicates (olivine and pyroxene) require annealing temperatures up to 1400 K and thus demonstrate the presence of materials processed at high temperatures. The detection of carbonates and phyllosilicates implies that liquid water was present in the comet at some point in time.

**The Age of the Taurid Complex:** Peaks in the cosmic ray exposure ages of CM chondrites suggest their parent body suffered several large disruption events 0.2, 0.6, and 1.5 My ago [8]. This is difficult to reconcile with the proposed origin of the Taurid complex. It has been suggested that the source of the Taurid complex was a large comet disruption event 20–30 ky ago [9]. If the CM chondrites come from the Taurid complex its age must be at least a few million years.

**Conclusion:** The petrology of CM chondrites and the orbit determined for Maribo suggest that CM chondrites are related to the Taurid complex and comet Encke.

**References:** [1] Haack et al. 2009. Abstract #5085. Meteoritical Society Conference. [2] Lodders K. and Osborne R. 1999. *Space Science Review* 90:289–297. [3] Weisberg M. K. and Connolly H. C. 2008. Abstract #1981. 49th Lunar and Planetary Science Conference. [5] Irvine et al. 1998. In *Protostars and Planets IV*, pp. 1159–1200. [6] Zinner E. 1988. In *Meteorites and the Early solar system*, pp. 956–983. [7] Lisse C. M. et al. 2006. *Science* 313:635–640. [8] Nishiizumi. 2009. Abstract #5358. Meteoritical Society Conference. [9] Asher D. J. et al. 1993. Monthly Notices of the Royal Astronomical Society 264:93–105.

HIGH ABUNDANCE OF STARDUST IN THE CO3.0 CHONDRITE
LAPAZ ICEFIELD 031117

P. Haenecour¹,² and C. Floss¹,³. ¹Laboratory for Space Sciences. ²Department of Earth and Planetary Sciences. ³Department of Physics, Washington University, St. Louis, MO 63130, USA. E-mail: haenecour@wustl.edu.

**Introduction:** Presolar silicate grains have been found in high abundance only in a few highly primitive meteorites, including the carbonaceous chondrites Acer 094 (C ungrouped), ALHA77307 (CO3.0), QUE 99177 (CR3.0), and MET 00426 (CR3.0) [e.g. 1–3]. The recent discovery of a possible new pristine CO3.0 chondrite, LaPaz 031117 [4] has led us to carry out a reconnaissance study in order to evaluate the abundance of presolar grains in this meteorite. Here we report the results for our first search of carbon- and oxygen-bearing presolar grains in LAP 031117.

**Experimental:** Using the Cameca NanoSIMS 50 at Washington University, we carried out raster ion imaging ($12,13\text{C}$ and $16,17,18\text{O}^{-}$) in the matrix material of a thin-section of LAP 031117. A focused primary Cs$^{+}$ beam of ~1 pA (~100 nm in diameter) was rastered over surface areas of $10 \times 10 \text{ µm}^2$ (256$^2$ pixels) and the $12,13\text{C}^{-}$ and $16,17,18\text{O}^{-}$ secondary ions, as well as secondary electrons were collected in multi-collection mode. All measurements were made within the same matrix area and the total area mapped was 1250 $\text{µm}^2$.

**Results and Discussion:** To date we have identified six oxygen-anomalous grains, all of which are $^{17}\text{O}$-rich relative to solar ($^{17}\text{O}/^{16}\text{O}_{\text{solar}} = 3.8 \times 10^{-4}$ and $^{18}\text{O}/^{16}\text{O}_{\text{solar}} = 2.0 \times 10^{-3}$), with $^{17}\text{O}/^{16}\text{O}$ ratios between $5.01 \times 10^{-4}$ and $1.39 \times 10^{-3}$. Three grains also exhibit moderate $^{18}\text{O}$ depletions. Based on the classification proposed by [5], the six $^{17}\text{O}$-rich grains belong to group 1 and are likely to have formed in the envelopes of low- to intermediate-mass red giant or AGB stars with close-to-solar or slightly lower-than-solar metallicity.

We also found two C-anomalous grains in LAP 031117. One is $^{13}\text{C}$-rich ($^{12}\text{C}/^{13}\text{C} = 65.7 \pm 0.9$) and is likely to be a mainstream SiC grain. The other one is $^{12}\text{C}$-rich, with a $^{12}\text{C}/^{13}\text{C}$ ratio of 101.4 ± 2.4.

Based on the limited area measured to date, we estimate an abundance of oxygen-bearing grains of $173 \pm 58$ ppm (without correcting for detection efficiency), comparable to the range of abundances observed in other primitive carbonaceous chondrites (up to 220 ppm) [1–3]. These preliminary results suggest that this meteorite indeed did not undergo significant secondary processing, such as aqueous alteration and thermal processing metamorphism, and may be a promising new source of presolar silicate grains. However, other matrix areas in LAP 031117 will need to be investigated in order to ensure that the high abundance found in our initial survey is indeed representative of the whole meteorite. Auger electron spectroscopy will then be used to obtain the elemental compositions of the grains identified.

**References:** [1] Floss C. and Stadermann F. J. 2009. *Geochimica et Cosmochimica Acta* 73:2415–2440. [2] Nguyen et al. 2010. *The Astrophysical Journal* 719:166–189. [3] Bose et al. 2010. *The Astrophysical Journal* 714:1624–1636. [4] Chizmadia L. J. and Cabret-Lebrónt E. 2009. Abstract #2031. 40th Lunar and Planetary Science Conference. [5] Nittler L. R. et al. 1997. *The Astrophysical Journal* 483:475–495.
5210

HYDROGEN ISOTOPES IN THE NAKHLITES: MAGMATIC AND ATMOSPHERIC MARTIAN RESERVIORS VERSUS TERRESTRIAL CONTAMINATION

L. J. Hallis¹ and G. J. Taylor¹. ¹HIGP/SOEST, NASA Astrobiology Institute, University of Hawaii, Honolulu, HI 96822 USA. E-mail: lydh@higp.hawaii.edu.

**Introduction:** Erosion of Mars' atmosphere via solar wind has led to the preferential loss of the lighter hydrogen isotope from the atmosphere, producing a deuterium enrichment—the present-day Martian δD of 4200‰ [1–2] is approximately 5× higher than that of VSMOW. This enrichment has been detected in a number of primary and secondary phases in the Martian meteorites (e.g., [3–4]). However, varying degrees of terrestrial contamination, and the possible presence of a second magmatic Martian hydrogen isotope reservoir, with a D/H ratio similar to VSMOW (e.g., [5]), have resulted in wide D/H variations both between and within individual meteorites. The purpose of this study is to determine the role of these three hydrogen isotope reservoirs in the formation, and subsequent alteration, of primary and secondary phases in the nakhlite group of Martian meteorites.

**Methods:** Polished thin-sections of MIL 03346 and 090030 were prepared at the NASA Johnson Space Centre without the use of water, and thin-sections of Nakhla were prepared in the same way at the University of Hawaii (UH). We utilised the JEOL JSM-5900LV scanning electron microscope at UH to produce high-resolution backscatter electron images. Secondary-phase major-element chemistry was determined with a JEOL JXA-8500F electron microprobe, also at UH. D, H and Si isotopic compositions were analyzed in situ with the UH Cameca imms 1280 ion microprobe, with a Cs+ primary beam.

**Results and Initial Conclusions:** D/H ratios for iddingsite-like alteration veins in Nakhla are widely variable (–98 to +1165‰), even between analyses from the same alteration vein. The iddingsite alteration veins in MIL 090030,23 (an interior thin-section) are much less variable, with a range of 134–311‰. Petrological analysis also suggests the alteration veins in Nakhla are more heterogeneous than those in MIL 090030. [6] reported the composition of alteration veins in Nakhla as an assemblage of silica gel, siderite and evaporites. Amorphous silica gel is more susceptible to hydrogen exchange with the atmosphere than minerals with structurally bound water, hence areas with lower D/H ratios are probably those rich in silica gel. MIL 03346,174, a thin-section with terrestrially exposed surfaces, contains iddingsite-like alteration veins with D/H ratios entirely within the terrestrial region (–240 to –69‰). However, as this thin-section was prepared with water, and exposed to atmospheric conditions since its preparation in 2006, we aim to analyze newly prepared exterior thin-sections of MIL 090030 to confirm this result. We also aim to analyze apatite grains in Nakhla and compare their D/H ratios with those of ALH 84001 apatites. These comparisons should help to determine if a separate magmatic hydrogen isotope reservoir did affect these samples, and may give some insight into the effect of shock on D/H ratios.

**References:** [1] Bjoraker G. L. et al. 1989. *Geochimica et Cosmochimica Acta*. [2] Owen T. 1992. *Mars* (Eds. H. H. Kieffer et al.). [3] Sugiura N. and Hoshino H. 2000. *Meteoritics & Planetary Science*. [4] Boctor N. Z. et al. 2003. *Geochimica et Cosmochimica Acta*. [5] Leshin L. A. et al. 1996. *Geochimica et Cosmochimica Acta*. [6] Changela H. G. and Bridges J. C. 2011. *Meteoritics & Planetary Science*.

5299

COMBINED CL, OC, AND EBSD IMAGING SHOWS DIFFERENT TYPES OF PDFS IN QUARTZ

M. F. Hamers, G. M. Pennock and M. R. Drury. Faculty of Geosciences, Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD, Utrecht, The Netherlands. E-mail: hamers@geo.uu.nl.

**Introduction:** Planar deformation features (PDFs) in quartz are essential evidence for the impact origin of suspected structures or stratigraphic levels. They can be observed in a light microscope, but can be confused with other (sub) planar microstructures, especially tectonic deformation lamellae (DL). We use scanning electron microscope cathodoluminescence (SEM-CL) and orientation contrast (OC) imaging and electron backscatter diffraction (EBSD) to identify and characterize PDFs in quartz.

**Method and Samples:** SEM-CL images were acquired in an FEI Nova Nanolab 600 SEM with a panchromatic Gatan PanaCL detector (Gatan UK, Oxford, UK). Red, green, and blue filters were used to record color filtered images, which were combined into a colour composite image. OC images and EBSD data were collected in a Philips XL30 SFEG SEM with a Nordlys CCD camera and Oxford Instruments HKL Channel 5 software. Quartz grains containing PDFs were studied in samples from the Ries, Popigai, Rochechouart, and Vredefort impact structures.

**Results and Discussion:** CL: PDFs show two types of CL behavior: red luminescence and non-luminescence. Red luminescent PDFs occur in all impact structures, but the non-luminescent type only in the younger samples (Ries and Popigai). Red luminescent PDFs are narrow (100–200 nm apparent thickness) and straight, while non-luminescent PDFs are often slightly curved features of varying thickness (100–350 nm apparent thickness). Non-luminescent PDFs are more closely spaced and always occur in multiple sets per grain, while red luminescent PDFs can occur as single sets. Some partly red, partly non-luminescent PDFs are also observed.

**OC and EBSD:** In some Ries and Popigai samples red luminescent PDFs are visible as thin grey lamellae in OC images. Band contrast maps suggest that the material within the PDFs gives a weaker diffraction pattern than the host quartz. In grains from Vredefort and Rochechouart, red luminescent PDFs are not visible in OC images, and they do not show up in band contrast maps. All grains with red-luminescent PDFs contain small scale Dauphiné twins that are often parallel to or bounded by the PDFs. Grains with non-luminescent PDFs give no diffraction pattern from within the PDFs and very weak patterns from the host quartz. OC images of these grains often show a submicron-scale blocky structure of lighter and darker grey domains, parallel to PDFs, that might be very small Dauphiné twins.

**Discussion:** Grains with non-luminescent PDFs are interpreted to have suffered high shock pressure, because the PDFs always occur in multiple closely spaced sets and the weak diffraction patterns from the host quartz suggest a disordered crystal structure. The non-luminescent (parts of) PDFs might contain amorphous material, as they show no diffraction patterns and are only present in relatively young impact structures. Red luminescent PDFs might contain disordered, but not completely amorphous SiO₂, or might represent annealed or recrystallized material.

**Conclusions:** SEM-CL and OC imaging and EBSD data reveal different types of PDFs that are probably related to shock level and the presence of amorphous material within the PDFs.