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A Reappraisal of the Metamorphic History of EH3 and EL3 Enstatite Chondrites Eric Quirico, Michèle Bourot-Denise, C

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A Reappraisal of the Metamorphic History of EH3 and EL3 Enstatite Chondrites Eric Quirico, Michèle Bourot-Denise, C A reappraisal of the metamorphic history of EH3 and EL3 enstatite chondrites Eric Quirico, Michèle Bourot-Denise, C. Robin, Gilles Montagnac, Pierre Beck To cite this version: Eric Quirico, Michèle Bourot-Denise, C. Robin, Gilles Montagnac, Pierre Beck. A reappraisal of the metamorphic history of EH3 and EL3 enstatite chondrites. Meteoritics and Planetary Science, Wiley, 2011, 46 Supplement (S1), pp.A195. 10.1111/j.1945-5100.2011.01221.x. insu-00683399 HAL Id: insu-00683399 https://hal-insu.archives-ouvertes.fr/insu-00683399 Submitted on 28 May 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License Meteoritics & Planetary Science 46, Supplement, A3–A264 (2011) doi: 10.1111/j.1945-5100.2011.01221.x Abstracts 5112 5444 RAMAN, FTIR, AND MO¨SSBAUER SPECTROSCOPY OF A PRELIMINARY STUDY OF MAGMATIC VOLATILES IN OLIVINES FROM THE D’ORBIGNY METEORITE ANGRITES Y. A. Abdu1, M. E. Varela2 and F. C. Hawthorne1. 1Department of F. A. J. Abernethy1, A. Verchovsky1, I. A. Franchi1 and M. M. Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T Grady1,2. 1PSSRI, The Open University, Walton Hall, Milton Keynes 2N2, Canada. E-mail: [email protected]. 2ICATE-CONICET, Av. MK7 6AA, UK. 2Department Mineralogy, The Natural History Museum, Espan˜ a 1512 Sur, CP J5402DSP, San Juan, Argentina. London SW7 5BD, UK. E-mail: [email protected]. Introduction: Olivine is a major basaltic mineral in high-temperature Introduction: Angrites are a rare group of achondrites notable for volcanic rocks and in stony meteorites. The D’Orbigny angrite contains their critical silica undersaturation, lack of shock metamorphic features large olivine crystals (up to 1 cm in size) that are present throughout and ancient crystallization ages [1–3]. They are subdivided into plutonic the rock, mimicking xenocrysts or forming olivinite (polycrystalline or basaltic angrites on the basis of their inferred petrogenesis. Similar olivine) [1–3]. The olivinites are of particular interest, as very little is studies to those already carried out on HEDs and shergottites [4, 5] could known about them. Here, we study three types of D’Orbigny olivines: be used to shed light on magmatic processes on the angrite parent body honey olivine (HOl), green olivine (GOl), and olivinite (POl), by Raman, (APB). Here we present results from carbon and nitrogen stepped Fourier-transform infrared (FTIR), and Mo¨ ssbauer spectroscopy, and combustion experiments on the plutonic angrites Angra dos Reis (AdoR) compare their structural and spectral features. and NWA 2999, and the basaltic angrite D’Orbigny. Experimental: Raman spectroscopy measurements were done using a Results: Magmatic volatiles are released once the silicate matrix starts LabRAM ARAMIS confocal microscope (Horiba Jobin Yvon). A x100 to become plastic, usually between 800 and 1000 °C; depending on the CRE objective microscope was used to focus the laser beam (532 nm excitation age of the specimen, it is possible for this to be mixed with a spallogenic line) on the sample to a size of 1 lm. FTIR spectra over the range component, the effects of which can be removed following correction. We (4000–400 cm)1) were collected on KBr sample pellets using a Bruker have not yet applied this correction to the data but expect it to have little Tensor 27 FTIR spectrometer. Transmission Mo¨ ssbauer spectra were effect on either carbon or nitrogen abundance, and to reduce isotopic acquired at room temperature (RT) using a 57Co(Rh) point source. composition by <2&. We also discount NWA 2999 from further Results and Discussion: The chemical compositions of the three consideration, because it contained large amounts of terrestrial organic olivines were determined by electron microprobe analysis (EMPA). The carbon which swamped all other potential carbon-bearing components. Mg# [=Mg/(Mg+Fe)] is 0.64 for HOl, 0.85 for GOl, and 0.90 for POl. Raman and FTIR spectroscopy. Total C d13C Magmatic C d13C The main feature of Raman spectra of olivines is a doublet with )1 )1 Name (ppm) (&) (ppm) (&) peaks located at 850 cm (j1) and 820 cm (j2) due to the asymmetric ) ) and symmetric vibrations, respectively, of the SiO4 group [4]. For AdoR 801 21.6 63 21.4 )1 ) D’Orbigny olivines, the j1 and j2 peaks occur at 850, 820 cm for HOl; NWA 2999 6990 29.5 – – 854, 823 cm)1 for GOl; 856, 824 cm)1 for POl, reflecting variability in D’Orbigny 199 )8.8 9 )11.4 15 15 composition. Using the x (= j1-j2) – Mg# relation [3], the estimated Name Total N d N Magmatic N d N Mg# for HOl, GOl, and POl are 0.70(4), 0.82(4), and 0.93(4), respectively, (ppm) (&) (ppm) (&) in close agreement with EMPA results. Similarly, the FTIR spectra of the AdoR 15 +8 3 )2 three olivines do not show any differences except the composition NWA 2999 84 )2– – dependence of the bands positions. Furthermore, no structural OH bands D’Orbigny 12 +8 1 +14 are observed in the OH-stretching region (3800-3000 cm)1) for all samples. Discussion: The overall 13C-enrichment of D’Orbigny compared to Mo¨ ssbauer spectroscopy. AdoR is partly the result of carbonates (d13C approximately 0 to +5&) The RT Mo¨ ssbauer spectra of the HOl and GOl consist of two lining vugs in the meteorite. There are also differences in magmatic asymmetric absorption peaks, resulted from the overlap of two carbon and nitrogen between the two meteorites. AdoR has a higher quadrupole doublets due to the presence of Fe2+ at the M1 and M2 abundance of the component, with lighter isotopic composition. This is octahedral sites. On the other hand, the spectrum of POl shows an ) consistent with the petrogeneses of the meteorites, with D’Orbigny having additional weak doublet (CS = 0.35 mm s 1, QS = 0.30 mm s–1, relative outgassed during its ascent: McCoy et al. [6] calculated that the vesicles area = 2%) which is attributed to Fe3+. Because Fe3+ could indicate a present in D’Orbigny could have formed from as little as approximately laihunite-like material similar to that observed in partially oxidized 12.5 ppm CO dissolved in the magma. Stepped combustion analyses of metasomatized mantle olivines [5], olivinites may record the increasing 2 further angrites should reveal whether there is a relationship between oxidizing conditions prevailing during the late metasomatic event that sample petrogenesis and magmatic volatiles. affect angrite formation. References: [1] Mittlefehldt D. W. et al. 1998. In Planetary materials, References: [1] Kurat G. et al. 2001. Abstract #1753. 32nd Lunar Reviews in Mineralogy 36, Chapter 4. Mineralogical Society of America. [2] and Planetary Science Conference. [2] Kurat G. et al. 2004. Geochimica et Mittlefehldt D. W. and Lindstrom M. M. 1990. Geochimica et Cosmochimica Acta 68:1901–1921. [3] Varela M. E. et al. 2005. Cosmochimica Acta 54:3209–3218. [3] Mittlefehldt D. W. et al. 2002. Meteoritics & Planetary Science 40:409–430. [4] Mouri T. and Enami M. Meteoritics & Planetary Science 37:345–369. [4] Grady M. M. et al. 1997. 2008. Journal of Mineralogical and Petrological Sciences 103:100–104. [5] Meteoritics & Planetary Science 32:863–868. [5] Grady M. M. et al. 2004. Banfield J. F. et al. 1992. American Mineralogist 77:977–986. International Journal of Astrobiology 3:117–124. [6] McCoy T. J. et al. 2006. Earth and Planetary Science Letters 246:102–108. A3 Ó The Meteoritical Society, 2011. A4 74th Annual Meeting of the Meteoritical Society: Abstracts 5211 5021 PETROGRAPHIC EVIDENCE OF SHOCK METAMORPHISM IN BAJADA DEL DIABLO, PATAGONIA, ARGENTINA: THE IMPACT CR2 CHONDRITE GRO 03116 OF A SPLIT COMET? N. M. Abreu. Earth Science, Pennsylvania State University—DuBois, R. D. Acevedo, C. Prezzi, M. J. Orgeira, J. Rabassa, H. Corbella, J. F. PA, USA. E-mail: [email protected]. Ponce, O. Martinez, C. Vasquez, I. Subias, M. Gonzalez and M. Rocca. Conicet, Argentina. E-mail: [email protected]. Introduction: CR chondrites are primitive meteorites that show a broad range of aqueous alteration features from nearly pristine [1] to fully An impact origin has been proposed for the almost 200 circular altered [2]. However, evidence of any thermal metamorphism group is structures found in Bajada del Diablo (42° 46¢ to 43° S and 67° 24¢ to 45¢ only beginning to emerge [3, 4]. To better understand the effects and the W), Patagonia, Argentina [1], some of them partially obliterated by source of metamorphism in the CR parent body, an SEM/EPMA/TEM erosion or sediment accumulation, which range in diameter from 100 m study of GRO 03116 is underway. GRO 03116 was chosen because O- up to 400 m. isotopic analyses suggest that it has only suffered limited aqueous The circular structures have been identified in two rock types: the alteration [5], while Raman spectra shows that its organic materials have Quin˜ elaf eruptive complex (Miocene basalts) and Pampa Sastre undergone some thermal metamorphism [4]. GRO 03116 is an Antarctic Formation (Pliocene basaltic conglomerate). CR2 find of terrestrial weathering type C. Thus, disentangling its record Geological and geomorphological strong evidences of involvement of asteroidal versus terrestrial aqueous alteration merits careful analysis on both geologic entities more over the Pleistocene pediment gravels and petrologic analysis.
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