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Desert Workshop: Abstracts

Item Type Article; text

Citation Desert Meteorites Workshop: Abstracts. & Planetary Science, 41(S8), A201-A216 (2006).

DOI 10.1111/j.1945-5100.2006.tb00997.x

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Journal Meteoritics & Planetary Science

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Link to Item http://hdl.handle.net/10150/656174 Meteoritics & Planetary Science 41, Nr 8, Supplement, A201–A216 (2006) http://meteoritics.org

Desert Meteorites Workshop: Abstracts

9008 9031 SHI™R 043 (IIIAB MEDIUM ): THE FIRST THE OF MINQAR ABD EL NABI, WESTERN METEORITE FROM THE OMAN DESERT DESERT, EGYPT A. Al-Kathiri1, 2, B. A. Hofmann3, E. Gnos1, O. Eugster4, K. C. Welten5 and Aly A. Barakat1 and Mitch Sculte2. 1The Egyptian Resource U. Krähenbühl1. 1Institut für Geologie, Universität Bern, Baltzerstrasse 1, Authority, 3 Salah Sa-lem Road, Abbassiya, Cairo, Egypt. 2NASA Ames CH-3012 Bern, Switzerland. 2Directorate General of Commerce and Research Center, Mail Stop 239-4, Building 239, Moffett , California Industry, Ministry of Commerce and Industry, Salalah, Oman. E-mail: 94035-1000, USA [email protected]. 3Naturhistorisches Museum der Burgergemeinde Bern, Bernastrasse 15, CH-3005 Bern, Switzerland. 4Physikalisches Institut, In addition to the catalogued Egyptian meteorites [1] there are several Abteilung für Weltraumforschung und Planetologie, Universität Bern, ones that have not been reported yet. Minqar Abd el Nabi is a new meteorite Sidlerstrasse 5, CH-3012 Bern, Switzerland. 5Space Science Laboratory, 7 found in November 1992, under the foot of Min-qar Abd el Nabi escarpment Gauss Way, University of California, Berkeley, California 94720-7450, USA. at latitude 29°54′32′′N and longitude 29°54′30′′E. 6Department für Chemie und Biochemie, Universität Bern, Freiestrasse 3, The Minqar Abd el Nabi meteorite is a single complete stone of CH-3012 Bern, Switzerland irregular shape measuring roughly 7.2 × 5.4 × 3.5 cm and weighing about 362 grams.The stone is very hard and compact. Its color is brownish-, with Introduction: The Shi∫r 043 is a single mass of 8267 g very thin dull-black to deep brownish-black patches, representing remnants found in the south Omani desert 42 km NE of the Shi∫r village. It is the first of the fusion crust. Rusty patches representing the effect of terrestrial iron identified among the >1400 individual meteorites reported from Oman. moisture on the metallic iron can be easily detected. The meteorite is a slightly elongated mass showing only minor rusting, , different silicate mineral phases, and opaque minerals partially smooth, partially rough surface with octahedral , and embedded in reccrystallized fine-grained groundmass of the same partially preserved metallic fusion crust typically 0.75 mm thick. Iron constituents are noticed. The stone is highly sheared as indicated by extensive meteorites comprise about 5% of falls [1] but are underrepresented in hot and field of fissures that are cross-cutting the whole mass. The constituents are cold desert finds: represent 1.3% of Antarctic finds [2] and 0.4% in the stained by brownish discoloration via fissures. area, Libya [3]. The observed chondrules are of hazily defined outlines and vary in Discussion: The undeformed Widmanstätten pattern with a mean diameters from 0.2 to 1.4 mm, but the most common size is about 0.4 mm bandwidth of 1.0 ± 0.1 mm (n = 97) indicates structural across. The shape of these chondrules varies from irregular to oval, with a classification as a medium octahedrite. From the bulk composition, Ni = few ones of circular shape. However, the granular chondrules, which 8.06 wt%, Ga = 18.8 ppm, Ge = 37.25 ppm, and Ir = 3.92 ppm, the meteorite consist of subhedral to anhedral olivine grains, are the more common types. is classified as IIIAB [4], the most common group of iron meteorites. The In addition, granular olivine plus orthopyroxene chondrules, monosomatic cosmic-ray exposure (CRE) age based on 3He, 21Ne, 38Ar concentrations and olivine chondrules, traces of barred olivine chondrules, and concentric 10Be-21Ne, 26Al-21Ne, and 36Cl-36Ar ratios is 290 ± 20 Ma. This age falls chondrules are also detected. within the range observed for type IIIAB iron meteorites, but does not The meteorite consists essentially of olivine and orthopyroxene, with coincide with the main cluster [5]. The cosmogenic noble gas and other minor silicate minerals including diopside, plagioclase, in addition to radionuclide data indicate that Shi∫r 043 had a relatively small pre- , kamacite, , and minor . Iron are common atmospheric mass. The low degree of weathering is consistent with a young through the fissures that cross-cut the silicate minerals. The iron oxides terrestrial age of <10,000 years based on the saturated 41Ca concentration. contains appreciable concentration of Ni and S, which indicates that they Shi∫r 043 is not paired with any of the other eight known iron meteorites from were formed from oxidizing the metallic minerals and troilite. Microprobe the Arabian Peninsula. analysis indicates that olivine contains 17 ± 2 mol% fayalite (Fa), Reference: [1] McSween H. Y., Jr. 1999. Meteorites and their parent orthopyroxene contains 17 ± 2 mol% ferrosilite (Fs). In terms of the planets. Cambridge, New York, Melbourne: Cambridge University Press. pp. conventional subdivision of meteoritic pyroxene, this falls in the composition 1–310. [2] Bevan et al. 1998. Meteorite flux in the Nullarbor region, range of bronzite [2]. Australia. In Meteorites: Flux with time and impact effects. London: The The composition of olivine (19.2 mol% Fa) in the stone is characteristic Geological Society. pp. 59–73. [3] Schlüter J. et al. 2002. The Dar al Gani of the olivine-bronzite (H group) [3-4]. The composition of the meteorite field (Libyan Sahara): Geological setting, pairing of meteorites, orthopyroxene (17.2 mol% Fs) is also characteristic of H chondrites [5]. The and recovery density. Meteoritics & Planetary Science 37:1079–1093. [4] homogeneity of olivine and orthopyroxene indicates that the stone is of high Mason B. 1971. Handbook of elemental abundance in meteorites. New York: petrologic rank (~6) according to the rules adopted by Van Schmus and Wood Gordon & Breach pp. 1–555. [5] Wieler R. 2002. Cosmic-ray-produced noble [3]. Accordingly, the meteorite can be placed within the olivine-bronzite gases in meteorites. In Noble gases. Washington, D.C.: Mineralogical Society chondrites (H6). of America. pp.125–170. References: [1] Grady M. M. 2000. Catalogue of meteorites. 5th ed. Cambridge: Cambridge University Press. 696 p. [2] Prior G. T. 1920. Mineralogical Magazine 19:51–63. [3] Van Schmus W. R. and Wood J. A. 1967. Geochimica et Cosmochimica Acta 31:747–765. [4] Freer R. 1981. Contributions to and Petrology 76:440–454. [5] Bunch T. E. and Olsen E. 1974. Contributions to Mineralogy and Petrology 43:83–90.

A201 © The Meteoritical Society, 2006. Printed in USA. A202 Desert Meteorites Workshop: Abstracts

9021 9014 EFFECTS OF ALTERATION ON DESERT METEORITES WEATHERING OF CHONDRITIC METEORITES G. K. Benedix1, I. A. Franchi2, R. C. Greenwood2, M. M. Grady2. 1IARC, P. A. Bland 1,2, A. J. T. Jull3, A. W. R. Bevan4. 1Impacts & Astromaterials Department of Mineralogy, The Natural History Museum, Cromwell Road, Research Centre, Department of Earth Science & Engineering, Imperial London, SW7 5BD, UK, E-mail: [email protected]. 2PSSRI, The Open College London, SW7 2AZ, UK. E-mail: [email protected]. University, Milton Keynes, MK7 6AA, UK 2Impacts & Astromaterials Research Centre, Department of Mineralogy, Natural History Museum, London SW7 5BD, UK. 3NSF-University of Introduction: Desert meteorites are subject to a variety of alteration Arizona AMS Laboratory, University of Arizona, Tucson, Arizona 85721, mechanisms. Hot desert meteorites can experience a change in oxygen USA. 4Department of Earth and Planetary Science, Western Australian isotopic compositions due to exposure in the desert atmosphere over long Museum, Francis Street, Perth, WA 6000, Australia periods of time [1]. [2] noted this and stated the need for both petrologic and isotopic measurements to accurately classify samples. Several samples from Ordinary (OC) finds show a clear correlation between degree Northwest Africa have interesting and/or ambiguous mineralogy that conflict of weathering and residence time at the Earth’s surface, with a rapid initial with their oxygen isotopic compositions. Three samples in particular are period followed by more gradual subsequent alteration. Weathering rate also NWA 725, NWA 1463, and NWA 1500. varies substantially between different regions [1], with meteorites in Discussion: NWA 1463 [3] was classified as a based on Antarctica weathering at rates orders of magnitude lower than hot desert mineralogy (Fa5.8; Fs7.5 [2, 3]) and oxygen isotopic composition [2, 3, this samples. Overall, weathering rates in meteorites may be approximated by an work, Fig. 1]. It may also be paired with NWA 725 (Fa6.1; Fs7.5 [4]), which is appropriate power law. It is apparent that weathering rates are distinct for listed as an [4]. We will compare the oxygen isotopic different sites—even for hot deserts with broadly similar climatic regimes. compositions of NWA 725 to 1463 to determine if they are paired. A An explanation for the rapid initial phase, followed by more gradual complication of the classification is the chromite composition of NWA 1463, oxidation, may be found by considering the porosity of meteorites. Unaltered which falls significantly outside the compositions of winonaite . In OCs are porous rocks. Oxidation of metal to substantial volume addition, NWA 1463 does not appear to contain graphite, a phase commonly expansion which may reduce porosity, thus reducing the ability of water to found in . penetrate the sample. We compared porosity and oxidation data for a number NWA 1500 [5, 6] was classified as a based on its mineralogy of weathered meteorites to average data for fresh falls [2]. The results and texture, despite the fact its oxygen isotopic composition is within the indicate an initial rapid decrease in porosity with weathering, until after winonaite field. ~20% of the original iron has been converted to Fe3+, porosity stabilizes. The Two explanations could clarify these ambiguities: 1) oxygen isotopic suggestion is that porosity reduction passivates weathering, restricting water compositions of hot desert meteorites may shift due to exposure in the desert flow throughout the sample [2]. atmosphere; or 2) winonaites extend to lower 18O and to higher Fa and Fs Given the quantitative measure of the degree of weathering provided by values than previously thought. Both possibilities are interesting and will be Mössbauer spectroscopy, we can observe the effect of terrestrial weathering explored further. on other aspects of meteorite composition, e.g., oxygen isotopes. We have References: [1] Bland P. A. et al. 2000. Meteoritics & Planetary analyzed the O-isotope composition of a number of OC finds from both hot Science 35:1387–1395. [2] Rumble D., III et al. 2005. Meteoritics & and cold deserts. The Antarctic samples show a particularly interesting effect Planetary Science 40:A74. [3] Benedix G. K. et al. 2003. Meteoritics & [3]. Ice in the Allan Hills region has an 18O value of ~40‰ [4], which Planetary Science 32:A70. [4] The Meteoritical Bulletin, No. 85. 2001. compares to initial values in the meteorite of ~4.7‰ [5]. Even a small degree Meteoritics & Planetary Science 36:A293–A322. [5] The Meteoritical of alteration should therefore to a large displacement in the isotopic Bulletin, No. 87. 2003. Meteoritics & Planetary Science 38:A189–A248. [6] composition of the meteorite [6]. Surprisingly, we observe no discernible Goodrich C. A. et al. 2005. Abstract #1073. 36th Lunar & Planetary Science shift in oxygen away from fall values until >25% of the iron in the meteorite Conference. [7] Clayton R. N. and Mayeda T. K. 1996. Geochimica et has been converted to Fe3+ [3]. This anomalous behavior may be related to Cosmochimica Acta 60:1999–2018. the microstructure of silicate alteration. Incipient alteration involves a restructuring to clay minerals along nanometer-wide channels within the primary silicate, in which access of water is restricted. The clay shows a topotactic relationship to the primary grain, suggesting some inheritance of structural polymers by the weathering product, and allowing the bulk oxygen isotopic composition to remain comparatively unaffected for some time. This work has significance in the area of asteroidal aqueous alteration, in that substantial modification of chondritic materials may occur without a pronounced isotopic effect. References: [1] Bland P. A. et al. 1996. Monthly Notices of the Royal Astronomical Society 283:551–565. [2] Bland P. A. et al. 1998. Geochimica et Cosmochimica Acta 62:3169–3184. [3] Bland P. A. et al. 2000. Meteoritics & Planetary Science 35:1387–1395. [4] Fireman E. L. and Norris T. L. 1982. Earth and Planetary Science Letters 60:339–350. [5] Clayton R. N. et al. 1991. Geochimica et Cosmochimica Acta 55:2317–2337. [6] Clayton R. N., Mayeda T. K., and Yanai K. 1984. Proceedings of the Ninth Symposium on Antarctic Meteorites. pp. 267–271. Desert Meteorites Workshop: Abstracts A203

9024 9025 WHAT SHOULD WE DO WITH ALL THOSE METEORITES FROM MINERALOGY AND PETROLOGY OF TNZ 057 (C4) AND SAHARA? COMPARISON TO THE CV AND CK GROUPS B. Devouard1, M. Denise2, M. Messaoudi3,1, D. Belhai3, B. Zanda-Hewins2, B. Devouard1, L. Ferriere2*, B. Zanda-Hewins2, and M. Messaoudi1, 3. and C. Perron2. 1Laboratoire Magmas et Volcans, UMR CNRS 6524, 5 rue 1Laboratoire Magmas et Volcans, UMR CNRS 6524, 5 rue Kessler, 63000 Kessler, 63000 Clermont-Ferrand, France. E-mail: [email protected] Clermont-Ferrand, France. E-mail: [email protected]. bpclermont.fr. 2Laboratoire d’Etude de la Matière Extraterrestre, CP 52, 2Laboratoire d’Etude de la Matière Extraterrestre, CP 52, Département Département d’Histoire de la Terre, Muséum National d’Histoire Naturelle, d’Histoire de la Terre, Muséum National d’Histoire Naturelle, 57 rue Cuvier, 57 rue Cuvier, 75005 , France. 3Université des Sciences et Technologie 75005 Paris, France. 3Université des Sciences et Technologie Houari Houari Boumediene (USTHB), BP 32 , 16012 Algeria Boumediene (USTHB). BP 32 El Alia, 16012 Algeria. *Currently at: Department of Geological Sciences, University of Vienna, Althanstrasse 14, Thousands of meteorites are currently collected from hot and cold A-1090 Vienna, Austria deserts every year. By providing new samples of rare groups, or even previously unknown types of meteorites, these systematic collections greatly Tanezrouft (TNZ) 057 is a 5.4 kg meteorite classified as C4 (The improve our knowledge of the solar system. As meteorites from Antarctic Meteoritical Bulletin, No. 87). It is a nearly equilibrated carbonaceous collections are carefully documented and managed, most meteorites from chondrite, with olivine compositions around 32 Fa% and low-Ca Sahara are collected by dealers. Systematic collection campaigns for ranging from 3 to 30 Fs% (average 19). These characteristics would suggest commercial purposes started in Sahara about 1989 in Libya and Algeria, then a classification as CK4, but the meteorite displays abundant dark inclusions spread to nearby countries such as Morocco, Mauritania, Mali, and Niger. (DIs, up to 11 cm) and CAIs (up to 17 mm) that are more characteristic of the The most remarkable samples of Saharan meteorites are usually singled CV group. The abundance of matrix seems to be highly variable, from 50 to out close to the source and eventually reach laboratories for classification. On 80%. Unfortunately, terrestrial alteration impedes the determination of the the other hand, many meteorites are marketed wholesale at low prices, most original abundance of metal. of them ordinary chondrites. In the absence of laboratories capable to handle We investigated the matrix in TNZ 057 and compared it to matrices in the classification of those hundreds of new samples, many stay unreported. Vigarano (reduced CV3), Allende, and Bali (oxidized CV3), and a suite of Among those, however, many interesting samples probably remain CKs of increasing metamorphic degree (DAG 431, CK3–AN; Karoonda, unrecognized. CK4; PCA 82500, CK4–5; EET 90007, CK5; EET 87860, CK5–6; and LEW From a scientific point of view, Saharan collections have to deal with a 87009, CK6). basic problem: the precise find locations are often unknown, or at least The matrix of TNZ 057 is made of large, texturally unequilibrated unreported. This prevents the studies of strewn fields, of the effect of olivine grains (median of the CSD ~75 µm) with large, sometimes zoned terrestrial alteration (which depends on local geographical factors), and plagioclase grains (up to 100 µm), and minor pyroxene and . This is makes pairing very delicate. similar to the matrix in PCA 82500 (CK4–5) and in some parts of DAG 431 Saharan meteorite collections also raise an ethical issue. Some (CK3–AN). Curiously, Karoonda displays a highly clastic matrix different countries, such as Algeria, do not allow the exportation of meteorites. from all the other CV and CK we investigated. Noble metal , typical Moreover, there are currently no market nor scientific facilities for of CK4 meteorites [1], were observed in DAG 431 but not in TNZ 057. meteoritical studies in north African countries. As a consequence, many However, TNZ 057 contains a few Au grains <3 µm. One DI was also stones collected by nomads in the whole Saharan region are currently investigated in TNZ 057; it displays a texture similar to the matrix, but has a marketed in Morocco, and eventually reach the European or North American significantly different mineralogical composition with ~ 35% of pyroxene. markets and scientific institutions. CVs and CKs seem to be distinct groups on the basis of trace element So, what should we do with all those meteorites from Sahara? Should analyses [2], but other arguments point to a possible continuous metamorphic museums trade at the market price, or ignore this sudden bounty of new series between oxidized CV3 and CK4 [3]. Tanezrouft 057 would probably meteorite finds that (arguably) are of lower scientific interest than observed be best classified as a CV4, but it may also just be the “missing link” between falls? Systematic collections in deserts skim out meteorites that fell over CVs and CKs. thousands of years in these regions. This currently apparent abundance of References: [1] Geiger and Bishoff. 1995. Planetary Space Science 43: meteorites from hot deserts should therefore be considered worth preserving 485. [2] Kallemeyn et al. 1991. Geochimica et Cosmochimica Acta 55:881. as a patrimony (scientific, educational, and aesthetic). This is a challenge . . . [3] Greenwood et al. 2003. Meteoritics & Planetary Science 38:A96. A204 Desert Meteorites Workshop: Abstracts

9028 9005 METEORITE RESEARCH COLLABORATION, CURATION, AND NATIVE IN FeNi METAL AND THE ASSEMBLAGE EDUCATION IN NEW YORK CITY CHROMITE-PLAGIOCLASE IN ORDINARY CHONDRITES: D. S. Ebel and J. S. Boesenberg. Department of Earth and Planetary Sciences, DISCARDED AS SHOCK PARAMETERS American Museum of Natural History, Central Park W. at 79th St., New A. El Goresy. Bayerisches Geoinstitut, Universität Bayreuth, 95447 York, NY 10024. USA. E-mail: [email protected] Bayreuth, Germany. E-mail: [email protected]

Collections: The American Museum of Natural History in New York, Introduction: Ramdohr [1, 2] documented the opaque mineral USA [1], is the repository of a large, historic collection of meteorites. The inventory of ordinary, enstatite, and carbonaceous chondrites. Recently, two collection began in 1872 with donations by non-specialists, but major growth of the diverse assemblages reported by him were claimed to have been was through the acquisition of major collections. The core of the AMNH formed during shock melting events on [3, 4], these are 1) native collection was ~580 meteorites of the Bement mineral collection, purchased copper in FeNi metal, abundantly associated with troilite, kamacite, for the museum in 1900. The collection has grown slowly by purchase or tetrataenite, and [1, 2] and 2) chromite-plagioclase enclaves in trade to its present size of ~1300 meteorites [2]. matrices and in chondrules [1, 2]. I investigated these assemblages in Meteorites are catalogued into about 5000 pieces, with sub-samples for chondritic meteorites to inspect the validity of their origin by shock melting research (e.g., thin sections) catalogued with added digits (e.g., 3127-1). and the reliability of their use as shock parameters [3, 4]. Recently, efforts are underway to present the important specimens in the Results: Any reliable petrologic interpretation of the origin of these collection on the web, with additional digital content such as 3D X-ray assemblages requires comprehensive comparison of their mineral inventories tomographic image stacks, 2D surface chemical X-ray maps, and links to with experimentally established phase relations in the system Fe-Cu-S [5] scientific research. and with the shock-induced high-pressure assemblages in real shock-induced Research: A primary role of the museum collections is scientific melt veins and -pockets in ordinary chondrites, on the other hand [6]. research. Many tens of meteorite samples are loaned to researchers 1) In addition to native Cu, [2] reported chalcopyrrhotite (; or worldwide annually, particularly microscope thin sections, or sent as small ISS) and rare (CuFeS2) in 183 meteorites, none of which were samples for destructive testing. The AMNH house petrographic microscopes, observed by [4]. Two additional assemblages occur in the L6 chondrite Usti a scanning electron microscope, electron microprobe, and other basic tools Nad Orlici (S1) a) troilite--chalcopyrite-cubanite- for description and analysis of rocks and minerals. AMNH staff collaborate and Ni , and b) troilite-kamacite-native Cu and a new - extensively with other meteoriticists, at museums, universities and other deficient Fe-Cu (Fe0.989Ni0.005Cu0.015)S0.991 [7]. My investigations institutions, in investigating isotopic, chemical and textural characteristics of reveal that these sulfide-native Cu assemblages are indicative of equilibration meteorites in the collection. down to very low temperatures ≤200º C leading to breakdown of the new Display: The AMNH has had the Arthur Ross Hall of Meteorites since metastable Fe-Cu sulfide to Cu + troilite + kamacite. In addition, troilite in 1976, expanded to about 2200 square feet (204 m2) in 1981 [3, 4]. The current the assemblages does not depict any sign of closely spaced twin lamellae or Hall contains 132 meteorite specimens, plus tektites and other objects, recrystallization with triple junctions characteristic of shock-induced organized around the question: What do meteorites tell us? Reading from deformation. nature, visitors learn about the origin of the solar system (chondrites), planet 2) A careful scrutiny of the heavily shocked L6 chondrites Sixiangkou formation (irons, , ), and the dynamic solar system and (S5) revealed that the assemblage chromite-plagioclase does (impact cratering). Graphics and text, supplemented by two video displays, not contain any lingunite, also in areas near shock melt veins and pockets [6]. support the specimens with stories and explanation. Lighting is a critical Furthermore, Usti Nad Orlici shows no sign of shock veins, and the meteorite concern in public display of meteorites and was a major concern in building is barren of characteristic shock features, local melting or high-pressure this one. phase transitions. The chromite-plagioclase texture observed is typical as Education: The Hall of Meteorites, research labs, and web presence reported by [1, 2, 7]. Furthermore, it depicts in some chondrules and in the are the basis for working directly with student groups, and, more importantly, chondritic matrix characteristic epitaxial intergrowth. The majority of the educating teachers. A teachers’ guide to using the Hall is on the Internet [5]. assemblage in the matrices consists of single plagioclase and phosphate In professional development for middle- and high-school teachers, meteorites crystals sprinkled with idiomorphic chromites but no skeletal quench are an entry point to basic chemistry, physics, and earth sciences. For crystals, thus negating melting. example, the composition of the solar system, differentiation of planets, and Conclusions: My results unambiguously demonstrate that the textures volatility of elements are basic topics, which are made more interesting when and mineral inventories of these two assemblages are genetically unrelated to explained using meteorites. In collaboration with AMNH, teachers use shock events and hence should be discarded as shock parameters. meteorites and planetary exploration to excite students about these and References: [1] Ramdohr P. 1963. Journal of Geophysical Research related topics. 68:2011–2036. [2] Ramdohr P. 1973. The opaque minerals in stony References: [1] http://www.amnh.org. [2] Ebel D. S. 2006. In The meteorites. Amsterdam: Elsevier. 244 p. [3] Rubin A. E. 1994. Meteoritics & history of meteoritics and key meteorite collections: Fireballs, falls, and Planetary Science 29:93–98. [4] Rubin A. E. 2003. Geochimica et finds, edited by McCall G. J. H., Bowden A. J., and Howarth R. J. London: Cosmochimica Acta 67:2695–2709. [5] Cabri J. L. 1973. The Geological Society. pp. 267–289. [3] Ebel D. S. and Boesenberg J. S. 68:443–445. [6] Gillet Ph. et al. 1996. Science 287:1633–1636. [7] 2004. Meteoritics & Planetary Science 39:1761–1762. [4] http:// Bukovanska M. et al. 1983. Meteoritics 18:223–240. www.amnh.org/exhibitions/permanent/meteorites. [5] http://amnh.org/ education/resources/halls/meteorites/index.php. Desert Meteorites Workshop: Abstracts A205

9020 9016 DISCOVERY OF A GROUP OF METEORITES IN THE ISTIFANE CASTENASO: AN “ITALIAN” FIND OF AREA (TINGHIR, MOROCCO): POTENTIAL SEARCH AREA DOUBTFUL (SAHARAN?) ORIGIN M. El Mansouri, A. Ibhi, H. Nachit and A. Ait Touchnt. Laboratory of L. Folco1, M. D’Orazio2, and N. Perchiazzi2. 1Museo Nazionale petrology, Mineralogy and Materials, Ibn Zohr, Faculty of Science, Agadir dell’Antartide, Siena, Italy. Dipartimento di Scienze della Terra, Pisa, Italy. Morocco. E-mail: [email protected] E-mail: [email protected]. 2Dipartimento di Scienze della Terra, Pisa, Italy

Introduction: Istifane is a potential search area where four meteorites Introduction: We discuss the doubtful origin of a 120 g coming from different falls were found. These stones have the following known as Castenaso, Emilia-Romagna, Italy. The meteorite was classified by characteristics: the stone matrix is fine-grained, with a light gray color. It us as an L5, S3, W1 ordinary chondrite and announced in the Meteoritical contains silvery, metallic specks of NiFe. The stones have mostly well- Bulletin No. 89 [1]. The classification was based on macroscopic and preserved fusion crusts, and they are in a very interesting state of petrographic observations carried out on two small sub-samples (3 and 12 g) preservation. Most of the stones are now kept in the Laboratory of Petrology, and three polished thin sections. Samples were provided by the Osservatorio Mineralogy and Materials (Agadir, Morocco) for a possible classification, Astronomico e Museo “G. Abetti” in S. Giovanni in Persiceto, Bologna, Italy declaration, and mineralogical studies. (OAM), which acquired the whole specimen from Mr. F. Merighi, who Method: Polished thin sections of all four pieces were studied with a reported to have found the stone on the right bank of the Idice stream near the polarizing microscope to determine their petrologic type, shock stage, and Castenaso village (44°29′42′′N, 11°21′20′′E) on July 15, 2003. Since it is an weathering grade. The shock stage for each meteorite was determined using unusual find (of the 38 official Italian meteorites, six are finds and only three the shock classification [1]. Weathering features are described according to are stony), we decided to characterize Castenaso in detail. For this purpose, the scale for thin sections proposed by Wlotzka [2]. the complete stone was made available to us by the OAM curator, R. Serra. Results: All four stones show petrographic features that are Macroscopic Features: The sample measures 4.3. × 4.0 × 2.3 cm and characteristic of ordinary chondrites. The first sample (#1) was found as an has a rounded shape. It is covered with an oxidized fusion crust except from individual rock in February 2006, covered by fusion crust (80%) and one side which appears as a rust-stained broken surface. A corner was weighing 51g. Petrographically, the rock displays a few intact, sharp-defined chipped off to produce sub-samples for analyses and revealed a relatively chondrites, and the matrix is partly recrystallized (type 5). It is very weakly fresh grey-green interior, with moderate oxidation of the metal particles. The shocked (S2); olivine shows undulatory extinction and contains irregular sample showed clear evidence of thorough cleaning, however, some of the fractures. Planar fractures are not obvious in the large olivine grains. The material filling the one tiny of its external surface was not completely majority of metal has been removed and replaced by Fe oxides/hydroxides removed and turned out to be mainly composed of fine-grained quartz grains. (W3). Samples #2 and #3 are pieces found in the same area in February 2006, Quartz Grains in Fractures: The morphology of quartz grains up to with a combined mass of 48.9 g and with 15% of fusion crust. They are 1 mm in size were studied in the SEM. They are well-rounded and bear dish- strongly shocked (S5), of petrologic type 5, and weathering category W3. In shaped concavities, upturned silica plates which have been subject to thin section, the replacement of metals by Fe oxides and hydroxides is solution-precipitation and subsequent smoothing. Such features are obvious. In many cases, cracks and mineral fractures are filled with oxides/ diagnostic of prolonged processing in a hot desert aeolian environment [2]. In hydroxides. Sample #4 is a single, 280 g rock, found in April 2006. Only turn, a soil sample taken where Castenaso was reported to be have been found some fusion crust was preserved (10%); it appears brownish and is heavily mainly consists of quartz, alkali feldspars, and angular particles less affected by terrestrial weathering. Abundant oxides due to terrestrial than 100 µm in size. weathering are scattered throughout the sample, suggesting weathering Bulk Chemistry (XRF, ICP-MS): Castenaso has a typical L-chondrite category W4. are fractured heavily in both an irregular and planar major and trace element composition, however, Sr, Ba, and U are fashion, although no planar deformation features could be found. Strong anomalously enriched. A comparison with European and Saharan L- mosaicism was observed in many crystals. No plagioclase was observed. This chondrite finds, specifically analyzed for this work, reveals that Castenaso is consistent with shock stage S5 (strongly shocked). has a significant affinity with the chemically altered Saharan finds (see also Conclusion: The Istifane area has not been prospected well, and [3]). probably many individual meteorites are still to be found there. However, the Conclusions: Both the material filling the cracks of Castenaso and the discovery of meteorites in the Istifane area (Tinghir, Morocco) lets us think altered geochemical signature indicate that this meteorite resided in a hot that the area can be a Saharan . Work is in progress to confirm this desert environment. We therefore strongly suspect that Castenaso is one of hypothesis. Saharan meteorites represent an important scientific record the many ordinary chondrite finds from the Sahara currently available on the which must be preserved. The meteorites found in the Istifane area are market. This forensic study provides an example of how meteorites of undergoing the formal approval process by the Nomenclature Committee of doubtful origin can be authenticated. the Meteoritical Society. Acknowledgement: R. Serra (OAM), G. Consolmagno (Specola References: [1] Stöffler D., Keil. K., Scott E. R. D. 1991. Geochimica Vaticana), B. Zanda (MHN, Paris), F. Zanazzi (DST, Perugia) are thanked for et Cosmochimica Acta 55:3845–3867. [2] Wlotzka F. 1993. Abstract. the donation of samples. Meteoritics 28:460. References: [1] Russell S. et al. 2005. Meteoritics & Planetary Science 40:A201–A263. [2] Krinsley J. C. and Doornkamp J. C. 1973. of quartz and surface textures. Cambridge: Cambridge University Press. [3] Stelzner et al. 1999. Meteoritics & Planetary Science 34:787–794. A206 Desert Meteorites Workshop: Abstracts

9030 9006 MÖSSBAUER ABSORPTION AREA FOR CLASSIFICATION OF WEATHERING OF ORDINARY CHONDRITES IN THE DESERT METEORITES SULTANATE OF OMAN Abbasher M. Gismelseed and Ahmed D. Al-Rawas. College of Science, E. Gnos1, A. Al-Kathiri2, A. J. T. Jull3, and B. A. Hofmann4. 1Institut für Sultan Qaboos University, Box 36 Al-Khoud, 123 Oman Geologie, Universität Bern, Baltzerstrasse 3, 3012 Bern, Switzerland. E- mail: [email protected]. 2Directorate General of Commerce and Industry, Mössbauer spectroscopy at room temperature (295 K) and liquid Ministry of Commerce and Industry, Salalah, Oman. 3National Science nitrogen temperature (78 K) have been applied to unweathered and Foundation-University of Arizona Accelerator Mass Spectromety weathered equilibrated ordinary chondrites collected from the hot deserts of Laboratory, University of Arizona, 1118 East Fourth Street, Tucson, Arizona Oman and Sudan. The measured spectra revealed striking similarities in the 85721, USA. 4Naturhistorisches Museum der Burgergemeinde Bern, major phases and also pronounced differences in the weathering rate in the Bernastrasse 15, 3005 Bern, Switzerland two environments. The resonance area ratio of olivine to pyroxene in each sample is used in the classification of the meteorites. The absorption area of Introduction: Weathering-induced physical, chemical, and the oxides developed as the result of weathering effect is discussed. mineralogical changes of 50 meteorites from various areas in the central Omani desert were studied and compared with 14C terrestrial ages [1]. The weathering range covered W0 to W4. The results were compared with data available from other deserts [2] – [6]. Results and Discussion: The intensity of weathering generally increases with increasing age. The data indicate that ordinary chondrites from Oman disintegrate completely after ~50 ka. This is faster than the onset of alteration of olivine or pyroxene to serpentines. In general, meteorites with weathering grade W0/W1 are <10 ka old, and a weathering grade of W3/W4 indicates and age of >30 ka. However, a few younger meteorites also showed W4. Disintegration of chondrites is interpreted as a combined result of volume increase due to oxidation of metal and sulfide (moisture), diurnal thermal cycling, and infiltration of soil material into cracks due to wind and water. It is more pronounced in sandy areas. Only locally, wind ablation was strong enough to shape meteorites to ventifacts. Due to seasonally changing wind directions, the soils of the interior of Oman are very homogeneous in bulk chemistry, and their influence on can therefore be assumed to be nearly constant over the whole study area. Pronounced geochemical changes are an accumulation of Sr, Ba, and H2O in chondrites, and a loss of S. These changes are correlated with the oxidation of chondritic metal and a retarded oxidation of the sulfide. Sr and Ba uptake are linked to the sulfide oxidation resulting in deposition of Sr and Ba sulfates. Soils under meteorites are contaminated with Ni and Co derived from these meteorites. The Ni/Co ratios are generally higher than chondritic values, indicating a higher mobility of Ni than Co. High contents found in soils are caused by chromite and other Cr derived form peridotites of the Oman Mountains. References: [1] Al-Kathiri A. et al. 2005. Meteoritics & Planetary Science 40:1215–1239. [2] Jull A. J. T. et al. 1990. Geochimica and Cosmochimica Acta 54:2895–2898. [3] Jull A. J. T. et al. 1993. Meteoritics 28:188–195. [4] Bland P. A et al. 1998. Geochimica and Cosmochimica Acta 62:3169–3184. [5] Bland P. A. et al. 2000. Quaternary Research 53:131–142. [6] Welten K. A. et al. 2004. Meteoritics & Planetary Science 34:259–270. Desert Meteorites Workshop: Abstracts A207

9027 9010 THE AT L’AIGLE AND THE REPORT: A UREILITE (UAE 001) FROM THE UNITED ARAB EMIRATES EXPLORING THE CRADDLE OF METEORITICS D. C. Hezel1, T. Schönbeck1, and L. Nasdala2. 1Universität zu Köln, Institut M. Gounelle. LEME-MNHN, CP52, 57 rue Cuvier, 75005 Paris, France and für Geologie und Mineralogie, Zülpicherstraße 49b, 50674 Köln, Germany. IARC, Natural History Museum, London SW7 5BD, UK. E-mail: E-mail: [email protected]. 2Universität Wien, Institut für Mineralogie [email protected] und Kristallographie, Althanstraße 14, 1090 Wien, Austria

“Il est tombée des pierres aux environs de l’Aigle led 6 Floréal an 11.” Introduction: A single stone of 155 g and completely covered by Stones fell around l’Aigle, July 26th, 1803. Thus ends the “Results” section fusion crust was found during an archeological field trip. Officials were of the Biot report [1] read in front of the Institut de France, the 29 messidor informed about this first finding of a meteorite in the United Arab Emirates an 11 (July 17th, 1803). In France that still used the revolutionary calendar, (UAE) and an agreement for future meteorite recovery expeditions in the Jean-Baptiste Biot, a young scientist aged 29, was sent by the Home Office UAE is currently established with the UAE government. Secretary Chaptal to report on the spectacular fall of stones at l’Aigle, 140 km are ultramafic, magmatic rocks, generally believed to northwest of Paris. originate from a once partially molten, originally chondritic . At the time of the l’Aigle fall, the existence of meteorites was harshly Typical ureilites have monomict textures with olivine and pigeonite as major, debated [2, 3]. Chladni’s book, Ironmasses [4], had been published in 1794, metal as minor and sometimes diamond as accessory phases [e.g., 1]. The but his ideas had not yet convinced the savants of the time. Biot himself origin of diamond in ureilites is still a matter of debate. Two competing defended the theory of a lunar volcanic origin for meteorites [5, 6]. This theories exist: 1) Diamond formed by impact shock on their parent bodies might have been the reason why Chaptal, a scientist himself, sent Biot to [e.g., 2–4]; 2) Diamond formed due to vapor growth in the solar nebula [e.g., l’Aigle when rumors started to fill Paris with stupor and astonishment [7]. 5–13]. Despite, or because of, his interest in the matter Biot claimed himself as Results: The meteorite has a typical ureilite texture [1, 14, 15], “a witness foreign to any system” [1] when he departed from Paris to l’Aigle, consisting of ~1–3 mm large anhedral olivines (~90 vol%) and pigeonites with a compass, a 1/86400th map of the area, and a sample of the Barbotan (~10 vol%). Olivines have homogenous cores with Fo79.8–81.8 but Fo meteorite (fall, 1790). He did not start his enquiry at l’Aigle but in the nearby increases toward the rim up to Fo96.1–96.8. Numerous tiny, Ni-poor, Fe- town of Alençon to check on the local mineralogy and human artifacts. hydroxide droplets occur in these rims. Olivines show deformation lamellae, Traveling between Alençon and l’Aigle, he questioned travellers and occasionally kink bands, undulatory extinction and few have subgrain coachmen about the meteor seen on the same day the stones fell. boundaries, indicating medium shock level [14]. Pigeonites have En73.9–75.2. Summarizing his observations, Biot distinguished 2 kinds of evidence Vein material interstitial to silicate grains consist of Fe hydroxide. Diamond of an extraterrestrial origin of the stones. Physical evidence included the grains occur as accessory phases. Micro-Raman analyses of 33 diamond absence of any stone or human artifact in the area similar to the fallen stones, grains gave Raman peak full width of half maximum (FWHM) between 4 and the sudden appearance of a large number of identical stones similar to 13 cm−1, with a maximum around 7 cm−1. previous meteorites such as Barbotan. Moral evidence included the number Discussion: The meteorite is a typical monomict ureilite. The Fe in the of witnesses who saw “a rain of stones thrown by the meteor” as well as their olivine rims and interstitial veins was altered to Fe hydroxide during heavy diversity in term of profession, interests, and social status. Together, these terrestrial weathering. The FWHM of Raman peaks of natural diamond is 2– lines of evidence pointed toward the fact that extraterrestrial stones fell 3 cm−1 of experimentally shock produced 10–120 cm−1 and of vapor grown around l’Aigle on July 26th, 1803 [1]. CVD diamonds 3–25 cm−1 [13, and references therein]. Our Raman With Biot’s report, the existence of meteorites was recognized. In measurements with FWHM between 4 and 13 cm−1 confirm previous results addition to a celebration of the bicentenary of the l’Aigle fall and the Biot from [12, 13] who concluded that the similar FWHM of ureilite and CVD report, our paper will aim at retracing the social context that for the first time diamond favors a vapor growth origin for ureilite diamond. However, a lead a scientist to a thorough enquiry of stones fallen from the sky. narrowing of the FWHM of shock produced diamond due to prolonged References: [1] Biot J.-B. 1803. In: Mémoires de la classe des sciences duration of impact shock might also explain the Raman results. There is also mathématiques et physiques de l’Institut National de France 7. pp. 224–265. evidence from other workers [16, 17] that diamond may have formed in both [2] Westrum R. 1978. Social Studies of Science 8:461–493.[3] Marvin U. B. ways during impact: 1) shock induced and 2) due to vapor growth. 1996. Meteoritics & Planetary Science 31:545–588. [4] E. F. F. Chladni. References: [1] Goodrich C. A. 1992. Meteoritics 27:327–352. [2] Über den Ursprung der von Pallas Gefundenen und anderer ihr ähnlicher Lipschutz M. E. 1964. Science 143:1431–1434. [3] Bischoff A. et al. 1999. Eisenmassen, und über einige damit in Verbindung stehende Abstract #1100. 30th Lunar and Planetary Science Conference. CD-ROM. Naturerscheinungen. Riga: Johann Friedrich Hartknoch. 63 p. [5] Biot J.-B. [4] Nakamuta Y. and Aoki Y. 2000. Meteoritics & Planetary Science 35:487– 1802. Bulletin des Sciences par la Société Philomatique 66:159–160. [6] Biot 493. [5] Fukunaga K. et al. 1987. Nature 328:141–143. [6] Matsuda J. et al. J.-B. 1802. Bulletin des Sciences par la Société Philomatique 68:153–156. 1991. Geochimica et Cosmochimica Acta 55:2011–2023. [7] Matsuda J. et al. [7] Brard C. P. 1824. In Dictionnaire des Sciences Naturelles. Strasbourg. 1995. Geochimica et Cosmochimica Acta 59:4939–4949. [8] G., and Alfvén H. 1971. Earth and Planetary Science Letters 10:253–267. [9] Rai V. K. et al. 2002. Meteoritics & Planetary Science 37:1045–1055. [10] Rai V. K. et al. 2003. Geochimica et Cosmochimica Acta 67:2213–2237. [11] Miyamoto M. et al. 1988. Geophysical Research Letters 15:1445–1448. [12] Miyamoto M. et al. 1989. Abstract. 20th Lunar and Planetary Science Conference. pp. 709–710. [13] Miyamoto M. 1998. Antarctic Meteorite Research 11:171–177. [14] Mittlefehldt D. W. et al. 1998. In Planetary materials. Washington, D.C.: Mineralogical Society of America. [15] Mittlefehldt D. W. 2004. In Meteorites, planets, and . Amsterdam: Elsevier. pp. 291–324. [16] El Goresy A. et al. 2001. American Mineralogist 86:611–621. [17] Hough R. M. et al. 1995. Nature 378:41–44. A208 Desert Meteorites Workshop: Abstracts

9009 9012 THE OMANI-SWISS METEORITE SEARCH PROJECT: A NON-DESTRUCTIVE CHARACTERIZATION OF THE SUMMARY OF 5 FIELD CAMPAIGNS, 2001–2006 BENGUERIR METEORITE BY ULTRASOUND B. A. Hofmann1, E. Gnos2, A. Al-Kathiri3, and A. J. T. Jull4. A. Ibhi1, A. Faiz2, A. Amghar2, H. Nachit1, and A. Moudden2. 1Laboratory 1Naturhistorisches Museum der Burgergemeinde Bern, Bernastrasse 15, CH- for Petrology, Mineralogy and Materials, Ibn Zohr University, Faculty of 3005 Bern, Switzerland. E-mail: [email protected]. 2Institut für Science, Agadir Morocco. E-mail: [email protected]. 2Laboratory Geologie, Universität Bern, Baltzerstrasse 1, CH-3012 Bern, Switzerland. for Meteorology and Information Treatments, Ibn Zohr University, Faculty of 3Directorate General of Commerce and Industry, Ministry of Commerce and Science, Agadir, Morocco. Industry, Salalah, Oman. 4National Science Foundation-University of Arizona Accelerator Mass Spectromety Laboratory, University of Arizona, Introduction: Knowledge of the porosity is very important for the 1118 East Fourth Street, Tucson, Arizona 85721, USA. characterization of some rocks properties (mechanical, electrical, etc.) and it carries information about their origin and evolution. In the case of meteorites, Introduction: After the recognition of the meteorite potential of Oman the porosity is also essential for genesis and age studies, understanding the in 1999 by private collectors, the meteorite search project was initiated to meteorite- connection, as well as calculating or experimentally study in detail the unique meteorite accumulation in Oman and increase the determining the Hugoniat curves [1]. Several methods have been carried out awareness for this natural heritage. The Omani-Swiss Meteorite Search in order to measure rocks’ porosity. In this work, a non-destructive ultrasonic Project is based on over 30 years of scientific collaboration between the method to estimate the porosity is being developed. It involves monitoring of Directorate General of Minerals, Ministry of Commerce and Industry of the the ultrasound reflection and transmission using both the pulse transmission Sultanate of Oman, and the University of Bern. All samples collected during technique and the pulse echo technique. these research activities are used only for scientific purposes. Our five search Materials and methods: In this study, we have used uncrushed sample campaigns confirmed that the Omani desert is an extremely suitable area for of the Benguerir meteorite as a starting material for our experiments. The meteorite searching. The dominant surface type consists of a mixture of Benguerir meteorite is the first fall from Morocco to be scientifically weathered limestone and windblown silt. Other surface types were described. The analysis agree with the classification as type 6 of an LL investigated, but only one meteorite was recovered from alluvial fans close to ordinary chondrite (Fa30.5 1%, Fs25.3 1%), with a shock grade S3 and the Oman Mountains. weathering W0 (Hasnaa Chennaoui Aoudjehane, UHAC; Jambon, Scientific Goals: Main questions addressed are the weathering of UPVI; Michele Bourot Denise, MNHNP). meteorites related to their terrestrial age, the abundance of meteorite types, The porosity and ultrasonic velocities (longitudinal and transverse the abundance of meteorites on different surfaces, a statistical comparison of velocity) was measured using bistatic and monostatic methods. In the first the Omani meteorite collection with observed falls and other hot and cold method, two transducers are used; the ultrasound reflection is measured from desert collections, and the detailed investigation of rare meteorites. the first interface of the rock as a function of incidence angle [2]. In the Collection Statistics: During 5 search campaigns (~600 man days) second method, a contact transducer was used alternatively as a transmitter 4431 numbered meteorite samples (many more fragments) with a mass of and receiver under normal incidence. In both methods the pulse generator 3500 kg were collected, comprising about 300 fall events. Three newly (Sofranel 5052 PR) sends an electrical pulse to the transducer; which is discovered strewn fields contribute largely to the total mass. On average, transformed into an acoustic wave. The incident acoustic wave is partly 55 km driving yielded one meteorite. Assuming the coverage of a 25-m-wide reflected on the rock and partly transmitted through the rock. The reflected stripe, we typically recovered 0.7 meteorites per km2 (strewn fields not acoustic signal, composed of a series of echoes, is converted into analog included). This is in general agreement with an assumed density of ~4 electrical signal and is amplified and collected by a Lecroy digital meteorites/km2 (age <50 kyr), considering the fact that a certain amount of oscilloscope (9310M-300). The data are sent through an IEEE 488 interface meteorites likely is completely buried, and others have been overlooked. to a personal computer where the porosity and ultrasonic velocities are Certain areas yielded higher average find rates of 1.2–1.5 meteorites per km2. calculated. Meteorite Statistics: A mass breakdown of types for campaigns I–IV Results and Discussion: The porosity and ultrasonic velocities yields (wt%; with/without major strewn fields): H 16.4 (30.8), L 78.6 (59.7), measured for dark and light lithologies of the Benguerir meteorite are given LL 1.0 (2.0), 3.1 (6.0), iron 0.6 (1.1). The values in brackets are in Table 1. similar to a mass breakdown of the US Antarctic collection. The majority of >50 14C-dated meteorites has terrestrial ages <50 kyr. Table 1. Conclusions: Within the last 7 years, Oman has yielded a significant Lithology Porosity Long. velocity Trans. velocity proportion of the world’s meteorites. The Omani meteorite accumulation Dark 5 ± 1% 5040 m/s 3010 m/s surfaces are comparable in number of specimens, variety of finds, and mass Light 8 ± 1% 4080 m/s 2850 m/s to the other major recent sources, Antarctica and northwest Africa. The Omani case is unique, however, because fall locations for such a large number of meteorites are preserved. The high porosities indicate that the asteroidal parent bodies from which these chondritic meteorites are derived are porous and contain heterogenic porous regions. The ultrasonic velocity is an important parameter which can provide information about some meteorite proprieties (lithology, tortuesity, etc.) and the work is being continued to determine the relation between the ultrasonic velocity and these properties. The ultrasonic technique developed here is fast, inexpensive, and non- destructive in comparison to other classical methods used for meteorite characterization. References: [1] R. T. Schmitt et al. 1994. Abstract. 25th Lunar and Planetary Conference. pp. 1209–1210. [2] Z. E. A. Fellah et al. 2003. Journal of the Acoustic Society of America 113:2424–2433. Desert Meteorites Workshop: Abstracts A209

9004 9022 TERRESTRIAL AGES OF METEORITES USING 14C AND 14C/10BE OBSERVED METEORITE FALLS FROM FROM DIFFERENT HOT DESERTS N. Laridhi Ouazaa and H. Belghaji. Université de El Manar. Faculté A. J. T. Jull1, L. R. McHargue1, G. Spears1, J. A. Johnson1, K. J. Kim1, and P. des Sciences, Département de Géologie. Campus Universitaire 2092 El A. Bland2. 1NSF-Arizona AMS Laboratory, University of Arizona, Tucson, Manar II. Tunis. Tunisia. Email: [email protected] Arizona 85721, USA. E-mail: [email protected]. 2Imperial College, Department of Earth Science and Engineering, Prince Consort Road, London During the last seventy years, five meteorite falls were recorded in SW7, UK Tunisia and named Tatahouine, Dahmani, , Djoumine, and Beni M’hira. These falls represent five types of different meteorites. Introduction: The terrestrial age, or the terrestrial residence time, of a Tatahouine is an (). At 01:30 hr (local time) on meteorite, together with its exposure history provides us with useful insight June 27th, 1931, a meteorite fell on an unpaved ground in Tatahouine into the history of the meteorite. Although one expects that meteorites might (32°57′N, 10°25′E). On impact with the ground, three pieces of this meteorite weather quickly in humid environments, we find that large numbers of broke into many fragments (weighing approximately 12 kilograms). It is a meteorites found in semi-arid and arid environments can survive for much differentiated rock composed mainly of an orthopyroxene cumulate at 23% of longer times. Meteorites in arid and semi-arid environments can survive for ferrosilite and 1.5% of wollastonite. The orthopyroxene crystals are about a at least 50,000 yr, and there are some meteorites over 250,000 yr old from centimeter in size. This achondrite diogenite results from a magmatic rock these locations. We will show the wide range of terrestrial ages from different which dissolved in a related body of sufficient dimensions to allow the fusion environments. The terrestrial age also gives us information which can be and the magmatic differentiation applied to studies of infall rates, meteorite distributions, weathering of Dahmani is an olivine-hypersthene chondrite (LL6) which belongs to meteorites, and meteorite concentration mechanisms. We would expect that amphoterite group, the least abundant of ordinary chondrites. After the weathering of meteorites and their eventual destruction would be a function appearance of a fireball accompanied by detonations, one (total of the terrestrial age. In addition, weathering would affect trace-element weight 18 kg) was seen to fall on may 25th, 1981, near a village (33°37′N, composition [1]. However, a direct connection of weathering rates to the 8°50′E) not far from Dahmani (NW Tunisia). The specimen is picked up by terrestrial survival times of meteorites was initially shown by Wlotzka et al. soldiers and sent to the Geological Survey in Tunis. Dahmani is an [2] and later by Bland et al. [3, 4]. homogeneous cataclastic . It is formed of olivine (fayalite 31%) and Trends in Terrestrial Ages: Terrestrial ages of meteorites have been orthopyroxene at 25% of ferrosilite. determined by the concentration of 36Cl, 14C or 41Ca, measured independently Sfax is an orthopyroxene chondrite (LL6). Following an explosion a or also in combination. With measurement of more than one radionuclide, we meteorite fell near Sfax (34°45′N, 10°43′E). At least four fragments can correct for shielding effects [5–7]. At our laboratory, we make (weighing 4.2 kg, 500 g, and two others) were recovered from the region of measurements of 14C and 14C/10Be. The ratio of 14C/10Be can be used to get , about 10 km north of Sfax, It fell on October 16th, 1989, 09:30 better precision on terrestrial ages. Recently, we have also revised our hr. Sfax belongs to the most common chemical category of chondrite. The assumption of undertaken some modeling calculations [8] to determine if we silicates are usually olivine at 24% of fayalite and orthopyroxene at 20% of can assume a constant production rate of 14C and 10Be. ferrosilite. We will discuss the application of terrestrial-age measurements to Djoumine is an ordinary chondrite (H5–6). It fell on October 31th, meteorites from desert environments and their significance for understanding 1999, 18:45 to 19:00 hr local time. After a bright fireball was seen traveling of climatic effects in the region of collection. from the southwest to the northeast accompanied by multiple detonations, References: [1] A. Al-Kathiri et al. 2005. Meteoritics & Planetary two meteorites were recovered by children near the village of Djoumine (36° Science 40:1215. [2] F. Wlotzka et al. 1995. Lunar & Planetary Institute 57′N, 9°33′E) located at about 60 km from Tunis. At least five other pieces Technical Report #95–02. p. 72. [3] P. A. Bland et al. 1996. Monthly Notices were recovered at a later time within a 4-km-long strewn field, with the total of the Royal Astronomical Society 238:551. [4] P. A. Bland et al. 2000. mass collected ~10 kg. It is essentially formed of olivine: Fa18.7±0.7 and Quaternary Research 53:131. [5] A. J. T. Jull. 2006. Terrestrial ages of pyroxene: Fs16.3±0.4Wo1.7±0.8. meteorites. In Meteorites in the early solar system II, edited by Lauretta D. et Beni M’hira is an ordinary chondrite (L6). A meteorite was seen to fall al. Tucson: The University of Arizona Press. [6] A. J. T. Jull et al. 1998. in the Beni M’hira region (32°52′N, 10°48′E) by the inhabitants of Ksar Beni Geological Society of London Special Publication #140. p. 75. [7] K. C. M’hira, a small village ~35 km E of Foum , (SE Tunisia). Three Welten et al. 2003. Meteoritics & Planetary Science 38:499 [8] K. J. Kim et fragments weighing 1720, 300, and 200 g were recovered after the fall by al. 2003. Abstract #1191. 35th Lunar and Planetary Science Conference. CD- local soldiers. An additional 7 pieces totaling >14 kg were later recovered by ROM. private collectors in April 2001. The biggest piece made a small 10 cm crater. The major minerals are olivine, orthoenstatite, , augite, troilite, feldspars and FeNi metal (kamacite and minor taenite). The accessory minerals include chromite, , chloroapatite, and . Dahmani, Sfax, Djoumine, and Beni M’hira all exhibit petrographic evidence characteristic of strong shock metamorphism. They were formed by the accumulation of silicated, millimeter-sized chondrules, their fragments, and metallic grains (alloys of ferro-) and sulfides (troilite FeS). The minerals are fractured, deformed but not dissolved. The shock affected only some sulfides and silicates (plagioclase transformed in maskelynite). The products of shock effects are found in five droplets dispersed in the rock or filling some fissures. The recrystallization is relatively important. These meteorites show a medium to coarsely recrystallized granoblastic texture with poorly defined, barred olivine, porphiritic olivine, and granular olivine- pyoxene relic chondrules. There are certainly many other meteorites in Tunisia. It is easier to find meteorite samples on the ground (especially in desert zones) than to observe a fall. A210 Desert Meteorites Workshop: Abstracts

9029 9015 DETERMINING THE PETROLOGIC TYPE OF WEATHERED NOBLE GAS FEATURES OF TWO DESERT METEORITES, SAMPLES: AN APPLICATION OF FAST ELECTRON DHOFAR 008 AND NORTHWEST AFRICA 869 MICROPROBE (FEM) GRIDS J. Matsuda, A. Akane, and C. Nishimura. Department of Earth and Space C. A. Marsh and D. S. Lauretta, University of Arizona, Lunar and Planetary Science, Graduate School of Science, Osaka University, Toyonaka, Osaka Laboratory, Tucson, Arizona 85721, USA. E-mail: [email protected] 560-0043, Japan. E-mail: [email protected]

Introduction: Meteorites collected in desert environments have often Introduction: The desert meteorite Dhofar 008 was discovered in 1999 been present on the surface of the earth for long periods of time. This is in in the desert of Oman. The petrologic type is H3, shock stage S3, and part because of the preservative effects of dry climates, however, inevitably weathering grade W2 [1]. Surely, Fa and Fs% are in the range of H some weathering has occurred. chondrites, but the bulk chemical composition is in the rage of L chondrites. Petrologic type, or the degree of thermal metamorphism a meteorite This meteorite is highly unequilibrated (<3.3) [1]. Another desert meteorite experienced while on its parent body, is a primary classification tool for Northwest Africa 869 (NWA 869) was found in 2000. This meteorite is a meteorites [1]. This method relies on several characteristics. Homogeneity of breccia type and is classified as L4–6. [2]. These two desert meteorites may olivine, distinctiveness of chondrules, and presence of glass are among them. have complex history, and noble gas features may give some light on the Many of these characteristics are made indistinct by weathering processes. origin of these meteorites. Thus, we have measured the elemental abundances Weathering in terrestrial environments primarily alters metals and sulfide and the isotopic compositions of noble gases of these two meteorites. inclusions in meteorites [2]. Only rarely are silicates altered, however, Results and Discussion: In the 84Kr and 132Xe concentrations diagram, stains often develop which overlay any silicate component. Dhofar 008 is in the field of type 3, and NWA 869 is that of type 4–6 of Discussion: We have been developing a new technique for measuring ordinary chondrites, which agrees with the petrologic types determined by the homogeneity of olivine and low-Ca pyroxene, which we call fast electron chemical features. The Ne isotopes of Dhofar 008 show almost pure microprobe (FEM) grids [3, 4]. We applied this technique to Gold Basin and cosmogenic component, and all light noble gases (He, Ne, and Ar) are largely Payson, two meteorites with a high degree of weathering from arid regions of covered by the cosmogenic components. The estimated cosmic-ray exposure Arizona, which have previously been estimated as type 4 and 6, respectively. ages of Dhofar 008 are 13 Myr (T3), 12–15 Myr (T21), and 18–28 Myr Optical observations of these meteorites show a heterogeneous staining (T38), respectively. The Xe isotopic data show the mixing of Q with small on most silicate grains. However, our results show that the composition of amounts of HL component. olivine and low-Ca pyroxene in these samples is homogenous, with olivine NWA 869 is situated closer to the solar wind position, lying on the percent mean deviation (PMD) of 6.5 to 6.6 and standard deviations of 2.0 to mixing line of the solar wind and the cosmogenic components in the 20Ne/ 2.2, while the low-Ca pyroxene PMD values are 6.3 to 6.4 and standard 22Ne and 21Ne/22Ne diagram. It is very much different from the other ordinary deviations are 0.9, similar to other meteorites of their type in our study. It is chondrites where Ne isotopic data are mainly cosmogenic like Dhofar 008. expected that some petrologic type 4s and all type 6s will be essentially The 20Ne/36Ar ratio is as high as 40, indicating that NWA 869 is enriched in homogeneous in olivine and low-Ca pyroxene, which these low standard noble gases of solar wind from both the isotopic and the elemental abundance deviations indicate. ratios. The presence of the solar component of noble gases in NWA 869 Conclusions: Given the heterogeneous distribution of staining, it is should be related to the breccia type of this meteorite. This meteorite should unlikely that weathering preferentially produced the homogenous have been irradiated by the solar wind on the surface of the parent body. The composition for olivine and low-Ca pyroxene. Our data processing technique estimated cosmic-ray exposure ages of NWA 869 are 2 Myr (T3), 3–4 Myr allows us to filter out grains that are not pure olivine and pyroxene. (T21), and 2–5 Myr (T38), respectively. The 136Xe/132Xe ratio of NWA 869 is Therefore, we conclude that olivine and low-Ca pyroxene grains in 0.3179 ± 0.0037 that is not as low as the solar wind value (0.3011) [3] and is weathered samples can retain their original composition and that our method close to the Q (0.3164) of major planetary component [4]. In the 134Xe/132Xe can efficiently classify the degree of metamorphism experienced in the early and 136Xe/132Xe diagram, NWA 869 is situated very much at the Q point and solar system, even in highly weathered meteorite samples. Having tested the there seems no contribution of HL component, which is different from FEM grid technique on equilibrated ordinary chondrite samples, we can carbonaceous chondrites or unequilibrated ordinary chondrites. As NWA 869 confidently apply it to weathered unequilibrated ordinary chondrites (types 3 is L4–6, the thermal metamorphism damaged the HL component as observed and 4). by Huss et al. [5]. Otherwise, it is also likely that solar Xe in NWA 869 is References: [1] Van Schmus W. R. and Wood J. A. 1967. Geochimica contaminated with the terrestrial air. The 129Xe/132Xe ratio of NWA 869 is et Cosmochimica Acta 31:747–765. [2] Wlotzka F. 1993. Meteoritics & 1.2625 ± 0.0090, much higher than the solar and planetary component, Planetary Science 28:460 [3] Marsh C. A. et al. 2005. Abstract #5336. indicating the presence of the radiogenic component of the extinct nuclide Meteoritics & Planetary Science 40:A97. [4] Marsh et al. Personal 129I. communication. References: [1] The Meteoritical Bulletin, No. 84. 2000. Meteoritics & Planetary Science 35:A199–A225. [2] The Meteoritical Bulletin, No. 90 (2006). Forthcoming. Meteoritics & Planetary Science 41. [3] Podosek F. A. et al. 1971. Earth and Planetary Science Letters 10:199–216. [4] Busemann H. et al. 2000. Meteoritics & Planetary Science 35:949–973. [5] Huss G. R. et al. 1996. Geochimica et Cosmochimica Acta 60:3311–3340. Desert Meteorites Workshop: Abstracts A211

9019 9001 1998: THE MOST RECENT EL-IDRISSIA FALL, AND SINCE THEN WEATHERING EFFECTS ON NITROGEN AND NOBLE GASES IN MORE AND MORE UNLOCALIZED FINDS UREILITES FROM HOT AND COLD DESERTS S. Mostefaoui1, L. Bounatiro2, and M. Bourot-Denise1. 1Laboratoire d’Etudes S. V. S. Murty1 and V. K. Rai1,2. 1Physical Research Laboratory, Ahmedabad- de la Matière Extraterrestre, MNHN, 75005 Paris, France. E-mail: 380009, India. 2University of California San Diego, La Jolla, California, [email protected]. 2Université de Blida, Département d’Aéronautique, 9000 92093-0356, USA Blida, Algeria. Introduction: Terrestrial weathering in meteorite finds recovered from Introduction: Algerian desert meteorites (ADMs) are one of the Antarctica and hot deserts cause a variety of elemental and isotopic important contributors to the world meteorite collection that improves our alterations in them [1–3]. Weathering affects different types of meteorites knowledge of the origin of the solar system and evolution of stars and their differently and the finds from hot desert, in general, experience more severe environments. While managing other meteorite collections is well controlled, chemical alteration as compared to those from cold deserts. The degree of Saharan meteorites and especially the Algeria ones, are out of control and alteration is also element dependent. Nitrogen and noble gas (NG) most of them are handled by dealers. Here, we present an overview of the components of weathering origin have been observed in chondrites, and scientific and commercial interests of ADMs. particularly in Martian meteorites [4–7], making it difficult to decipher Overview: According to MetBase [1], Algerian desert count 613 indigenous components. In order to understand weathering effects on N and documented meteorites, representing more than 15% of the worlds total NG isotope systems in ureilites, we have studied a number of ureilites from registered meteorites from hot Sahara. The ADMs (excluding NWA) count 2 hot and cold deserts along with other finds and falls [8–11]. Here we present SNCs and one lunar. Only two meteorites are known to be preserved in the results for FRO 90036 (FRO 36 hereafter), Acfer 277 (AC 277), Kenna Algeria, El-Idrissia (L6) is in the Centre de Recherche d’Astrophysique et (Ken), and Lahrauli (Lah) ureilites. Astronomie et Geophysique (CRAAG) Algiers, and Fortflatters (non-class.) Results and Discussion: Experimental procedure for the analyses of is in the Saharan Museum in Ouargla, southwest of Algeria. bulk samples and acid residues of ureilites are given in [10–11]. Almost all Meteorite Falls and the El-Idrissia Story: Among the ADMs, seven trapped noble gases [with 40Ar/36Ar <<1, 84Kr/132Xe ~1] and most of N are observed falls. The first observed fall is the Aumale (L6) meteorite (fallen [δ15N(‰): –100 and +120, for the two main components] in ureilites reside in the same day as Shergotty in India, in August 25, 1865). The most recent one carbon phases, and are distinctly different from terrestrial atmosphere [40Ar/ is El-Idrissia. It is also an L6 and it fell on March 10, 1998 [2]. While the 36Ar = 295.5, 84Kr/132Xe = 27.8,δ15N(‰) = 0]. Pyrolysis of bulk ureilites at oldest fall Aumale is composed of two stones of 25 kg each, the total number low temperature (<1000 °C) mostly release gases from silicates (which are of stones and weight of El-Idrissia is still controversial. According to our poor in N and NG) and will thus be very sensitive to terrestrial weathering. In records, which are contradictory to what has been registered [1], 4 pieces of Fig. 1, 15N is plotted against 40Ar/36Ar ratios for low temperature pyrolysis the meteorite were collected by the habitants of the region, one of which is a (<1000 ºC) of bulk samples [8–11]. Elevated 40Ar/36Ar values are partly due single piece of 12 kg and it disappeared after it was brought by the Algerian to some radiogenic component and partly due to air (weathering). It can be local authority to the CRAAG. We still do not know where this stone is. seen that the data range for desert finds are indistinguishable from other finds Algeria, a Closed/Open Meteorites Market: El-Idrissia is probably and falls indicating that N and NG in ureilites are not significantly affected by one of the many meteorites that crossed the borders to land in one of the weathering. overseas meteorite collections. Despite an Algerian law explicitly preventing exportation of meteorites, the collect of ADMs is still active. Within the last 10 years, their flow significantly improved in order to supply meteorite markets. The trading was potentially ensured along the Algerian/Morocco borders. Northwest Africa (NWA) meteorites are one of the most concerned by this traffic. To gain profit from these meteorites, scientists preferred to deal with the merchants rather than defeating them. However, since these meteorites were mostly collected by inexperienced persons that usually work under difficult conditions, many scientific information are lost. Among the ADMs, about 25% are NWA mostly of unknown locations and where records of desert alteration conditions are inaccessible. This is also true for many other meteorites collected in different desert locations (Libya, Oman). Meteorites are part of our scientific patrimony; they deserve more consideration and a better preservation for the succeeding generations. The meteoritic community is most qualified to find solutions to this dramatic situation. Two scientific stations are ready to collaborate in Algeria, in Algiers, and in Oran. Fig. 1. References: [1] Koblitz J. 2005. MetBase 7.2, meteorite data retrieval software. [2] Russell S. et al. 2002. The Meteoritical Bulletin, No. 86. References: [1] Crozaz et al. 2003. Geochimica et Cosmochimica Acta Meteoritics & Planetary Science 37:A157–A184. 67:4727–4441. [2] Dreibus et al. 2006. Abstract #1180. 36th Lunar and Planetary Science Conference. CD-ROM. [3] Lee M. R. and Bland P. A. 2004. Geochimica et Cosmochimica Acta 68:893–916. [4] Murty S. V. S. and Mohapatra R. K. 1999. LPI Contribution #997. pp. 57–60. [5] Mohapatra R. K. et al. 2002. Abstract #1532. 33rd Lunar and Planetary Science Conference. CD-ROM. [6] Schwenzer S. P. et al. 2003. Abstract #1694. 34th Lunar and Planetary Science Conference. CD-ROM. [7] Schultz L. et al. 2005. Meteoritics & Planetary Science 40:659–664. [8] Rai V.K. et al. 2002. Meteoritics & Planetary Science 37:1045–1055. [9] Rai V. K. et al. 2003. Geochimica et Cosmochimica Acta 67:2213–2237. [10] Rai V. K. et al. 2003. Geochimica et Cosmochimica Acta 67:4435–4456. [11] Murty S. V. S. and Bhandari N. 1992. Meteoritics 27:264. A212 Desert Meteorites Workshop: Abstracts

9011 9007 EL-QUSS ABU SAID: A CM2 MAGNETIC CLASSIFICATION, WEATHERING AND WITH DECOMPOSED PHYLLOSILICATES TERRESTRIAL AGES OF DESERT ORDINARY CHONDRITES T. Nakamura1, T. Noguchi2, R. Okazaki1, K. Jogo1, and K. Ohtsuka3. 1Dept. P. Rochette1, L. Folco2, C. Berteloot1, J. Gattacceca1, C. Suavet1, and D. S. of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581, Ebel3. 1CEREGE, CNRS/University of Aix-Marseille 3, France. 2Museo Japan. E-mail: [email protected]. 2Department of Materials and Nazionale Antartide Siena Italy, 3American Museum of Natural History, New Biological Sciences, Ibaraki University, Mito, Ibaraki 310-8512, Japan. York, USA. 3Tokyo Meteor Network, Setagaya, Tokyo 155-0032, Japan The great majority of desert meteorites are ordinary chondrites, with El-Quss Abu Said was found in Egypt in 1999 and later classified as thousands of finds every year. Their classification is an activity with lower CM2 chondrite [1], but characterization in depth has not yet reported. We yield than is demanded, leaving the vast majority of Saharan stones have studied petrology and mineralogy of this meteorite in detail. Overall unclassified). Yet, this classification would provide relevant scientific texture suggests that it is a typical CM2 chondrite: chondrules typically from information, including the relative abundance H/L/LL chondrites falling on 200 to 300 microns in size, but occasionally up to 1 mm, are embedded in Earth, with implications for the compositions and delivery of material to fine-grained matrix. Most chondrules have fine-grained rims with thickness Earth from the main belt and near-Earth asteroids. One could, e.g., use the from 30 to 100 microns. PCPs up to 100 microns in size are present vast Saharan collection to shed light on the difference of the H/L ratio ubiquitously in the matrix. The meteorite does not seem to be a breccia, but between Antarctic (1.12) or Libyan finds (1.25) and falls (0.90). It is thus in major part consisting of primary accretionary rocks [2]. In the interior of highly desirable to have a method for partial rapid classification, either as a chondrules, glassy portions and metallic inclusions are altered, but anhydrous first filter before standard classification, or as a way to recover minimum minerals such as olivine and low-Ca pyroxene mostly remain unaltered. This information from collections that will never be declared to the Meteoritical indicates that this meteorite underwent only weak aqueous alteration. Bulletin. Magnetic susceptibility (χ) provides such a tool for easy Electron microprobe analysis showed that compositions of coarse discrimination between LL, L, and H falls [1]. This method allows rapid scan olivine and pyroxene in chondrules are variable: Fa99.5~56.4 and En98.4~77.0 of collections without sample preparation and with portable instruments [2] Wo0.7~4.6, respectively. In a (Si+Al)-Mg-Fe ternary diagram, matrix, and fine- that can be brought to the “meteorite market.” However, its classification grained rims around chondrules are plotted on or close to serpentine solid abilities are hampered by weathering: for example, a weathered solution, suggesting that the major phase existing in both matrix and rims is can yield the same χ as a fresh . The three well-separated serpentine. But the totals of electron probe analyses reached to 90 wt%, Gaussian distributions for fresh LL, L, and H chondrites [1] are skewed and which is higher than the total of normal serpentine analysis in other CMs partially merged by the weathering effect. The measurement of density [3] (~85 wt%). Thus, serpentine in both matrix and rims is dehydrated. This was does not resolve this ambiguity. To quantify the effect of weathering, we confirmed by synchrotron X-ray diffraction analysis of matrix and rims: they propose a simple mathematical model using the log (versus terrestrial age consist mainly of low-crystalline olivine, low-Ca pyroxene, magnetite, and function, and the terrestrial age distribution of the recovered meteorites as troilite. No hydrous phases including serpentine and tochilinite were input data. A best fit of real data with the model can provide the H/L/LL ratio detected. of the aggregate. As a first test, we apply this method to two collections of The lack of phyllosilicate suggests that this meteorite is a thermally unclassified stones from Sahara: one of 565 stones collected by nomads metamorphosed CM chondrite [e.g., 3, 4]: it experienced heating and under the responsibility of Michel Franco, and one of 570 stones at the decomposition of hydrous phases after mild aqueous alteration in a meteorite AMNH (New York). parent body. With an increase of temperature, phyllosilicates in CM We then tried to constrain the model log (χ) versus terrestrial age chondrites become amorphous, then recrystallize to low-crystalline function using meteorites with ages determined using cosmogenic isotopes. secondary anhydrous phases, and grow to larger, well-crystalline anhydrous We will present preliminary data on a suite of Antarctic meteorites, showing silicates and Fe metals or oxides [e.g., 5]. According to the results of our X- a rather significant correlation, at odds with the literature contention that ray diffraction, the secondary phases in El-Quss Abu Said are poorly terrestrial age is independent of weathering grade in Antarctic meteorites. crystalline and not well crystalline. Therefore, this meteorite ranks among This contradiction likely arises from the fact that Antarctic W grade is a color moderately heated CM2 chondrites. index, that does not represent correctly the amount of metal oxidized in non- References: [1] Grossman J. N. 2000. The Meteoritical Bulletin, No. magnetic phase (akagaenite, goethite, paramagnetic Fe3+), which are 84. Meteoritics & Planetary Science 35:A199. [2] Metzler K. et al. 1992. measured by log (χ). Geochimica et Cosmochimica Acta 56:2873–2897. [3] Tomeoka K. 1990. References: [1] Rochette P. et al. 2003. Meteoritics & Planetary Proceedings of the NIPR Symposium on Antarctic Meteorites 3:40–54. [4] Science 38:251–268. [2] Folco L. et al. 2006. Meteoritics & Planetary Nakamura T. 2005. Journal of Mineralogical and Petrological Sciences 100: Science 41:343–353. [3] Consolmagno G. J. et al. 2006. Meteoritics & 260–272. [5] Akai J. 1992. Proceedings of the NIPR Symposium on Antarctic Planetary Science 41:331–342. Meteorites 5:120–135. Desert Meteorites Workshop: Abstracts A213

9003 9002 GERMAN-LIBYAN METEORITE SEARCHES IN THE LIBYAN ACHONDRITES NWA 2268, NWA 4269, AND NWA 4255 FROM SAHARA ALGERIAN SAHARA: CHARACTERISTICS AND ORIGINS J. Schlüter1 and L. Schultz2. 1Mineralogical Museum, University of A. Seddiki1, J. Y. Cottin2, B. N. Moine2, N. Remaci1, C. Renac2, J. Bascou2, Hamburg, 20146 Hamburg, Germany. E-mail: jochen.schlueter@uni- B. Devouard3, M. Bourot-Denise4, V. Sautter4, J. P. Lorand4, D. Belhai5, M. hamburg.de. 2Max-Planck-Institute for Chemistry, 5520 Mainz, Germany Messaoudi5, H. Affalfiz5. 1Laboratoire de Magmatisme et Géodynamique des Bassins Algériens, Université d’Oran Essenia, Oran 31000, Algérie. E-mail: Introduction: A joint German-Libyan group of scientists has visited [email protected]. 2Laboratoire de Pétrologie-Géochimie the central Sahara several times since the year 2000. The purpose of those UMR CNRS 6524, UJM, Saint-Etienne 42023. France. 3Laboratoire Magmas expeditions was the search for meteorites and to understand the existence of et Volcans UMR CNRS 6524, UBP, Clermont-Ferrand, 63368, France. meteorite concentrations in hot deserts. 4Laboratoire de Minéralogie, MNHN Paris, 75005, France. 5Laboratoire de Our group studied the meteorite fields of Dar al Gani and Hamadah al Géodynamique, Géologie de l’Ingénieur et Planétologie, U.S.T.H.B. Alger Hamra and visited further promising areas in the Libyan Sahara. We also 16000, Algérie discussed with our Libyan colleagues current problems of meteorite searches in hot deserts. Subsequently, Libyan scientists participated in the Meteoritical Introduction: Several meteorites were discovered in the southwest of Society meeting in Münster (Germany) and visited several German research Algeria, of which 44 were officially declared. Here, we discuss asteroidal laboratories. achondrites. All main masses of meteorites found are kept in Libya, reference The polymict NWA 2268 paired with the Macibini polymict samples were taken to Germany for classification and further study. These are eucrite [1] contains mineral fragments of plagioclases, low-Ca pyroxene, deposited in the Mineralogical Museum, Hamburg. , olivine, tridymite, iron metal, and troilite. It also contains subophitic Discussion: Our investigations of the two meteorite fields showed that and cumulative basaltic clasts with exsolved pigeonite. Pyroxferroite is the existence of meteorite concentrations in arid hot deserts are the result of a locally destabilized in hedenbergite-fayalite-tridymite association. It was also combination of specific geological and geomorphological conditions: bright observed in lunar basalts and Martian meteorites [2, 3, 4], and associated with colored plateaus with deflation conditions but slow erosion rates, the lack of whitlokite [5]. In NWA 2268, it is associated to plagioclase, explaining the dark terrestrial rocks, rapid elimination of surface water, absence of sand- origin of the depletion in calcium. The ∆17O (–0.4) of NWA 2268 is slightly blast and, most importantly, a carbonatic ground, which retards rusting of the lower to HED group [6]. metallic components in meteorites. Furthermore, a supposed marly soil cover The monomict eucrite NWA 4269 is fine-grained with metal occurrence during pluvial times could have protected older meteorites against physical (mm). We observed a heterogeneous granulitic matrix with plagioclase and and chemical weathering, thus leading to a concentration of meteorites of low- and high-Ca pyroxenes recrystallization associated with silica (quartz?), different periods. fayalite, Ca phosphate, iron metal (Ni% <0.1), sulfide, spinel, and ilmenite. Future activities to other promising areas in Libya are planned. This assemblage are interpreted as recrystallization products [7]. The metal References: [1] Schlüter J., Schultz L., Thiedig F., Al-Mahdi B. O., and may have origin from reduction of Fe-rich pyroxene as also in Camel Donga Abu Aghreb A. E. 2002. Meteoritics & Planetary Science 37:1079–1093. eucrite [8]. Some clasts display residual coarse-grained lithology with ophitic texture. It contain plagioclase and exsolved ferro-pigeonites. This monomict eucrite is a type 5 of the metamorphic sequence [7]. The Fe/Mn atomic ratio in pyroxenes ranges from 27 to 42. This achondrite has an exceptional ∆17O (0.136), 18O = 3.27 and 17O = 1.84 (HED group) [6]. The diogenite NWA 4255 is predominantly composed of low-Ca pyroxene with scarce inclusions of troilite, ilmenite, spinel, olivine and, iron metal (Ni% <0.1). The metal may have originated from reduction of Fe-rich pyroxene [8]. The Fe/Mn atomic ratio in pyroxene range from 23 to 28. The study of whole-rock trace elements indicated that this is one of the that are most depleted in trace elements. It would be a cumulate of a very depleted asteroidal mantle source [9]. ∆17O (–0.38), with δ18O = 3.25 and δ 17O = 1.31. References: [1] Buchanan P. et al. 2000. Meteoritics & Planetary Science 35:1321–1331. [2] Ware N. G., Lovering J. P. 1971. Science 167: 517–520. [3] Jolliff B. L. et al. 1998. Meteoritics & Planetary Science 33: 581–60. [4] Takeda H. et al. 1991. Proceedings of the NIPR Symposium on Antarctic Meteorites 4:3–11. [5] Aramovich et al. 2002. American Mineralogist 87:1351–1359. [6] Clayton R. N. and Mayeda T. K. 1996. Geochimica et Cosmochimica Acta 60:1999–2017. [7] Takeda H. and Graham A. L. 1991. Meteoritics 26:129–134. [8] Palme H. et al. 1988. Meteoritics 23:49–57. [9] Fowler et al. 1995. Geochimica et Cosmochimica Acta 59:3071–3084. A214 Desert Meteorites Workshop: Abstracts

9017 9013 PROPOSAL FOR A WORKSHOP WEATHERING OF ORDINARY CHONDRITES FROM THE AT THE NATURAL HISTORY MUSEUM IN SUMMER 2007 ATACAMA DESERT, CHILE: FIRST RESULTS FROM MAGNETIC C. L. Smith1, G. K. Benedix1, S. S. Russell1, and M. Gounelle1,2. 1Department PROPERTIES AND DENSITY of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 E. M. Valenzuela1, P. Rochette2, J. Gattacceca2, D. Morata1. 1Departamento 5BD, UK. 2Muséum National d'Histoire Naturelle, 57 rue Cuvier, Paris de Geología, Universidad de Chile, Santiago, Chile. E-mail: 5ème, France. E-mail: [email protected] [email protected]. 2CEREGE, Université Aix-Marseille, Aix-en- Provence, France Introduction: With increasing numbers of meteorites being discovered in the hot deserts, specifically northern Africa and the Arabian Peninsula, Introduction: Ordinary chondrites (OC) have very homogeneous there is increased opportunity for scientists from these countries to become magnetic properties (for a given group H, L, or LL) due to metal content. involved in meteorite classification and research. The Natural History Monitoring the oxidation of this metal is easy to perform using magnetic Museum in London is proposing to hold a week-long workshop in the properties (magnetic susceptibility and saturation magnetization, among summer of 2007, to train scientists from countries suitable for meteorite others) that have the advantage of being rapid, non destructive, and collection, meteorite classification techniques, and on aspects of meteorite representing the bulk meteorite [1]. The goals for the study of the weathering collection and curation. processes acting in OC finds from the Atacama Desert, northern Chile are 1) Background: The Natural History Museum is uniquely placed to hold the characterization, quantification and discrimination of the primary and a training workshop on meteorite classification, curation, and collection secondary magnetic mineralogy of these samples; 2) a comparison of these techniques. Not only does the museum hold one of the largest and most results with Mössbauer spectroscopy data from the same set of samples [2], comprehensive meteorite collections in the world, it also houses world-class and 3) a comparison with weathered samples of OC from other deserts. analytical facilities, which include two scanning electron microscopes, an Magnetic Properties: Low-field magnetic susceptibility (χ) was electron microprobe (with a further being purchased in autumn 2006), two measured in 58 fragments from 21 different weathered OC samples (6 H, 12 imaging scanning electron microscopes, as well as ICP-OES and ICP-MS L and 3 LL) using a Kappabridge instrument, following the procedures instruments. It is proposed that the workshop will cover all aspects of described by [1]. The results agree with the values for ordinary chondrite meteorite classification, from initial recognition of meteoritic samples in classes obtained by [1] for finds and allow a preliminary classification for the “hand specimen,” through optical microscope investigation and analytical non-classified meteorites of the set. Hysteresis loops were performed in a electron microscopy. The Museum’s extensive meteorite collection will be MicroMag VSM at room temperature, from which the parameters of heavily utilized during the workshop, allowing workshop attendees to saturation magnetization (Ms), saturation remnant magnetization (Mr), and investigate all the different meteorite classes and types. Additionally, coercive force (Hc) were obtained. The coercitivity of remanence (Hcr) was participants will have the opportunity to see many samples in hand specimen, determined applying a progressively increasing backfield after saturation. both fresh falls and also finds from hot and cold deserts in various stages of The samples show different behaviors for H and L-LL OC with respect to the weathering. values of Ms and χ: H data displays a tendency coherent with a gradual loss Museum meteorite scientists have organized collecting trips to the of metal followed by the formation of maghemite-magnetite, while L-LL Atacama (Chile), Nullarbor (Australia), Sahara (Western Sahara and data display a mixed signal between FeNi metal and maghemite-magnetite Mauritania), and Namib () deserts, and so it is planned that time will extremes. be spent discussing the protocols and policies for collecting meteorites in hot Density and Porosity: Grain density were measured according to the desert environments, and the legality of collection in various countries and procedures describe by [3] using a helium pycnometer, and the bulk density ownership of meteorite finds. We hope that this will assist scientists from was measured using the glass beads method [4]. Porosity was obtained from meteorite-bearing countries to organize successful meteorite collecting the difference of these densities. Compared with recent OC falls, these expeditions themselves. samples show a decrease in density and porosity as a general tendency, with Finally, there will also be an opportunity to discuss the curation and increasing weathering level, as [4] reports for other desert OC finds. care of meteorites within a museum or a university collection, thus allowing Compared Results: Oxidation percentages from Mössbauer participants to start their own scientific meteorite collection at their own spectroscopy show that even for more oxidized samples the value of log χ institutions. remains in the range given by [1] for OC finds, with only two exceptions. The Costs: The Museum will seek funding of £5,000–10,000 to pay for the magnetic signal of 11 samples is mainly carried by FeNi metal, 9 samples workshop. It is proposed that the participants’ air fare, accommodation, and show a mixed signal from FeNi metal and maghemite-magnetite and/or subsistence will be covered by this funding. and one has completely lost all its magnetic minerals. Summary: We have the sincere hope that this workshop will provide References: [1] Rochette P. et al. 2003. Meteoritics & Planetary useful training and assistance to scientists who are keen to collect and Science 38:251–268. [2] Valenzuela M. et al. 2006. Abstract #5203. research meteorites from their own countries. We would welcome Meteoritics & Planetary Science 41. This issue. [3] Consolmagno G. et al. expressions of interest from any scientists who would like to attend the 2006. Meteoritics & Planetary Science 41:331–342. [4] Consolmagno G. and proposed workshop. It is hoped that, if successful, this training workshop will Britt D. 1998. Meteoritics & Planetary Sciences 33:1231–1242. [4] Bland P. be held regularly. We look forward to welcoming you to London in summer A. et al. 1998. Geochimica & Cosmochimica Acta 62:3169–3184. 2007. Desert Meteorites Workshop: Abstracts A215

9026 9023 METEORITES FROM HOT AND COLD DESERTS: WHAT’S GEOCHEMICAL SIGNATURE OF TERRESTRIAL WEATHERING THERE, WHAT’S MISSING, AND WHY WE SHOULD CARE IN HOT-DESERT LUNAR METEORITES L.C. Welzenbach and T. J. McCoy. Department of Mineral Sciences, National R. A. Zeigler, R. L. Korotev, B. L. Jolliff. Department of Earth & Planetary Museum of Natural History, Smithsonian Institution, Washington, D.C., Sciences, Washington University, Campus Box 1169, St. Louis, Missouri 20560 USA 63130. E-mail: [email protected]

Introduction: The hot deserts of northern Africa have produced a Most meteorites recovered on Earth are finds in hot and cold deserts. bounty of meteorites over the last decade, joining Antarctica as one of the These meteorites typically have terrestrial residence times on the order of most productive meteorite recovery areas on Earth. Is it possible that hot many thousands of years [1–2]. Many studies have shown that despite its arid desert environments are a hotter source of interesting meteorites? How is it environment, the desert imparts a compositional and mineralogical signature possible that so many unique types can be produced in less than a decade? upon the resident meteorites, particularly so in the hot deserts [2–4]. Previous Are we making the most of this unique resource? Classification statistics studies have concentrated on ordinary and carbonaceous chondrites. In this offer some interesting insights into differences between hot and cold deserts study, we consider only lunar meteorites, using compositions determined by and future directions for collecting and research. instrumental neutron activation analysis (INAA) as a record of chemical Results: We compared data for modern falls [1], U.S. Antarctic change in hot-desert lunar meteorites relative to cold-desert lunar meteorites. meteorites [2], NWA and Sahara meteorites, and geographically located Over the past 25 years, we have analyzed thousands of samples meteorites from Algeria, Libya, and Morocco [3] for ordinary (OCs), and 488 subsamples (~10–40 mg each) of 60 different numbered stones carbonaceous (CCs), and enstatite chondrites (ECs), primitive achondrites comprising 36 different lunar meteorites (there are ~39 different lunar (PAs), HEDs, lunar, Martian, and irons. meteorites, consisting of ~94 numbered stones [5]). The proportion of hot- Discussion: The abundance of northern African lunar and Martian desert to cold-desert subsamples is nearly equal (44:56). Elements routinely meteorites has led to the perception of high grading. In fact, northern Africa measured by INAA are: Na2O, K2O, CaO, Sc, Cr, FeO, Co, Ni, Zn, As, Se, has yielded meteorites in roughly the same proportion as observed among Br, Rb, Sr, Zr, Ag, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, W, Ir, modern falls. The ratio of OC/total for both is ~80% and the ratio of HED/ Au, Th, and U. non-OC is ~30%. Any apparent overabundance of lunar and Martian We do not observe any substantial differences in bulk composition meteorites may well reflect pairing and the statistics of small numbers. between Antarctic (cold-desert) lunar meteorites, and Apollo samples. Thus, More significant differences are observed between Antarctic and all enrichments in hot-desert lunar meteorites discussed below are relative to northern African meteorites. In particular, Antarctic meteorites exhibit more Antarctic meteorites of similar bulk composition. The most obvious OCs in total (~93%), irons relative to non-OCs (11% versus 4%), CM to total contaminants in hot-desert lunar meteorites (as in chondrites [2]) are Ba (up CCs (50% versus 2%), and OCs under 1 kg (98% versus 80%). Falls exhibit to 18×) and Sr (25×). Two other elements that show modest enrichments are even more irons (~25% of non-OC) and comparable CM/CC (~40%). Br and As, both ranging up to ~4–5× our detection limit for those elements Implications: These differences may point to a harsh weathering (Apollo and Antarctic lunar meteorites are typically below detection). The U: environment for northern Africa where small (<100 g), fragile (e.g., CI and Th ratio in lunar is largely invariant, ~0.3 [6]. Some hot-desert lunar CM) and iron meteorites are preferentially lost during short terrestrial meteorites have U:Th ratios considerably greater than this, up to 9, indicating residence (<150 kyr, [4]). High grading might explain the overabundance of enrichment in U. The Ca-rich nature of most lunar meteorites makes basaltic meteorites (e.g., HED, Martian), but cannot explain a slight observing excess Ca due to the addition of carbonate- or sulfate-mineral overabundance of hard-to-recognize primitive achondrites. contamination more difficult than in chondritic meteorites. When Ca is The loss of small, fragile, and metal-rich meteorites hinders our plotted against Fe (or even better, Al), modest enrichments in Ca are evident, understanding of processes occurring on asteroids, particularly dark, however. An enrichment in the light REEs (LREE) owing to terrestrial presumably carbonaceous C, P, and D type asteroids that dominate the outer weathering is observed in some samples, with a La/Sm ratio of up to ~3 [5]. Small irons, like those in Antarctica, likely sample a broader observed (compared to <2.25 in most Apollo samples). Concentrations of Au population of exposed metallic cores from the asteroid belt [6]. Even the are elevated by up to 75× in some hot-desert subsamples. The exposure history of meteorites, whether in the asteroid regolith of during cause is most likely contamination from human handling, not chemical passage to Earth, is best recorded among small meteorites from showers [7]. weathering, however. Small meteorites from northern Africa—perhaps neglected because of Different hot deserts impart different chemical signatures on lunar limited commercial appeal—can provide powerful clues to the history of the meteorites. The Omani lunar meteorites have high relative concentrations of solar system. Further, Antarctic meteorites less than 10 g in weight have Ba, Sr, As, and U. Whereas the African lunar meteorites show high relative provided adequate material for scientific study. concentrations of As and Br, moderate relative concentrations of Ba and U, References: [1] Grady M. M. 2000. Catalogue of meteorites. and an increase in the LREE/HREE ratio. Meteorites from all desert regions Cambridge: Cambridge University Press. [2] http://www- show elevated Au and Ca concentrations. curator.jsc.nasa.gov/antmet/query.cfm. [3] http://tin.er.usgs.gov/meteor/ Acknowledgements: This work was supported by NASA grant metbull.php [4] Welten K. C. et.al. 2004. Meteoritics & Planetary Science NNG04GG10G. 39:481–498.[5] Burbine T. H. et al. 2002. In Asteroids III, edited by Binzel R. References: [1] Jull A. J. T. 1998. The Geological Society Special et al. Tucson: The University of Arizona Press. [6] Wasson J. T. 1990. Science Publication #140. pp. 75–91. [2] Al-Kathiri A. et al. Meteoritics & Planetary 249:900–902. [7] Welten K. C. et al. 2004. Abstract #2020. 35th Lunar and Science 40:1215–40. [3] Lee M. R. and Bland P. A. 2004. Geochimica et Planetary Science Conference. CD-ROM. Cosmochimica Acta 68:893–917. [4] Rubin A. E. and Huber H. 2005. Meteoritics & Planetary Science 40:1123–30. [5] http://epsc.wustl.edu/ admin/resources/moon_meteorites.html. [6] Korotev R. L. 1998. Journal of Geophysical Research 103:1691–701. A216 Desert Meteorites Workshop: Abstracts

9018 PROPOSED SEARCH FOR METAMORPHOSED CARBONACEOUS CHONDRITES FROM HOT DESERT METEORITE ACCUMULATIONS Michael Zolensky, NASA Johnson Space Center, Houston, Texas 77058 USA. E-mail: [email protected].

We now know that a significant number of carbonaceous (C) chondrites were thermally metamorphosed on their parent asteroid(s). At least 10 carbonaceous chondrites have been naturally heated, variously, from 400 to over 700 ºC [1–6]. Aside from the issues of the identification of the transient heat source, timing of metamorphism, and the relation of these materials (if any) to conventional CM and CI chondrites, there is also a mystery related to their recovery. All the well-characterized metamorphosed C chondrites have been recovered from the Antarctic; none are falls or finds from any place else. Indeed, the majority have been collected in the Yamato Mountains. In fact, one estimate is that these meteorites account for ~64 wt% of the CM C chondrites at the NIPR [7]. The reasons for this are unclear and, in part, might be due to simple sampling bias. I have previously suggested that this recovery difference is related to the particular age of the Yamato Mountains meteorite recovery surfaces, and differences in meteoroid fluxes between the Yamato meteorites and recent falls and substantially older Antarctic meteorites. Others have previously remarked on the remarkable fact that alone among all analyzed meteorite types, the CI and CM chondrites all have cosmic-ray exposure ages below 5 Myr, suggesting derivation from Earth- crossing asteroids rather than directly from the main asteroid belt [8]. The fact that the metamorphosed C chondrites all have very young terrestrial ages (where measured) and come from the youngest Antarctic stranding surfaces suggests further that they derive from Earth-crossing asteroids that broke up very recently—as little as 200 kyr in the past. The fact that there are no metamorphosed CM or CI chondrites among modern falls could represent statistical bias, but it is harder to explain their rarity among the hot desert accumulations. Therefore, we suggest that a systematic reexamination of C chondrites from hot deserts be undertaken, and we predict that many will be found among the numerous CM and possibly CR chondrites. References: [1] Ikeda T. 1992. Proceedings of the NIPR Symposium on Antarctic Meteorites 5:49–73. [2] Matsuoka et al. 1996. Proceedings of the NIPR Symposium on Antarctic Meteorites 9:20–36. [3] Lipschutz M. et al. 1999. Proceedings of the NIPR Symposium on Antarctic Meteorites 12:57– 80. [4] Tonui E. et al. 2002. Antarctic Meteorites Research 15:38–58. [5] Tonui E. et al. 2002. Meteoritics & Planetary Science 38:269–292. [6] Tonui E. et al. Forthcoming. Geochimica et Cosmochimica Acta. [7] Yanai K. and Kojima H. 1995. Catalog of the Antarctic meteorites. Tokyo: National Institute of Polar Research. 230 p. [8] Eugster O. 2003. Chemie der Erde 63: 3–30.