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Alan E. Rubin - One of the best experts on this subject based on the ideXlab platform.
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joegoldsteinite a new sulfide mineral mncr2s4 from the social circle iva iron meteorite
American Mineralogist, 2016Co-Authors: J Isa, Alan E. RubinAbstract:Joegoldsteinite, a new sulfide mineral of end-member formula MnCr_2S_4, was discovered in the Social Circle IVA iron meteorite. It is a thiospinel, the Mn analog of daubreelite (Fe^(2+)Cr_2S_4), and a new member of the linnaeite group. Tiny grains of joegoldsteinite were also identified in the Indarch EH4 Enstatite Chondrite. The chemical composition of the Social Circle sample determined by electron microprobe is (wt%) S 44.3, Cr 36.2, Mn 15.8, Fe 4.5, Ni 0.09, Cu 0.08, total 101.0, giving rise to an empirical formula of (Mn_(0.82)Fe_(0.23))Cr_(1.99)S_(3.95). The crystal structure, determined by electron backscattered diffraction, is a Fd3m spinel-type structure with a = 10.11 A, V = 1033.4 A^3, and Z = 8.
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wassonite a new titanium monosulfide mineral in the yamato 691 Enstatite Chondrite
American Mineralogist, 2012Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:Wassonite, ideally stoichiometric TiS, is a titanium monosulfide not previously observed in nature, that was discovered within the Yamato 691 EH3 Enstatite Chondrite. Twelve Ti-S phase grains were identified in a rare barred olivine (BO) chondrule; three of the grains were extracted by the focused ion beam technique. Because of the submicrometer size of the wassonite grains, it was not possible to determine conventional macroscopic properties. However, the chemical composition and crystal structure were well constrained by extensive quantitative energy-dispersive X-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for wassonite is rhombohedral ( a = 3.42 ± 0.07, c = 26.50 ± 0.53 A) with space group: R 3 m , cell volume: 268.4 ± 0.53 A 3 , Z = 9, density (calculated): 4.452 g/cm 3 , empirical formula: (Ti 0.93 ,Fe 0.06 ,Cr 0.01 )S. The wassonite grains crystallized from the chondrule melt that was itself formed in the solar nebula, not on the parent asteroid. The other crystalline phases in the BO chondrule include forsterite, Enstatite, troilite, metallic Fe-Ni, and osbornite (as well as the new Ti-S-bearing minerals and schollhornite) are highly reduced and indicate formation at low-oxygen fugacities.
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new titanium monosulfide mineral phase in yamato 691 Enstatite Chondrite
LPI, 2011Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:Yamato 691, an EH3 Enstatite Chondrite, was among the first meteorites discovered by chance in Antarctica by the Japanese Antarctic Research Expedition (JARE) team in 1969. This discovery led to follow-up searches for meteorites in Antarctica [1]. These international searches have been very successful recovering over 40,000 total specimens (and still counting), including martian and lunar meteorites. Titanium is partly chalcophile in Enstatite-rich meteorites. Previous occurrences of Ti-bearing sulfides include troilite, daubrelite and ferroan alabandite in Enstatite Chondrites and aubrites [2], and heideite with 28.5 wt% Ti in the Bustee aubrite [3]. Here we report a new mineral from Yamato 691, ideally stoichiometric TiS, titanium monosulfide, a simple two-element mineral phase, yet with a very unique crystal structure that, to our knowledge, has not been observed previously in nature.
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the formation of wassonite a new titanium monosulfide mineral in the yamato 691 Enstatite Chondrite
LPICo, 2011Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, L P Keller, Scott Messenger, Michael I Petaev, K OikawaAbstract:Wassonite, ideally stoichiometric TiS, is a titanium monosulfide not previously observed in nature, that was discovered within the Yamato 691 EH3 Enstatite Chondrite [1]. Because of the submicrometer size of the wassonite grains, it was not possible to determine conventional macroscopic properties. However, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive x-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for wassonite is rhombohedral (a = 3.42 plus or minus 0.07, c = 26.50 plus or minus 0.53 Angstroms) with space group: R(sup 3 raised bar) m (R9 type), cell volume: 268.4 plus or minus 0.53 Angstroms(sup 3), Z=9, density (calculated): 4.452 grams per cubic centimeter, empirical formula: (Ti(sub 0.93), Fe(sub 0.06), Cr(sub 0.01))S. In this study, we discuss possible formation mechanisms of wassonite and its associated minerals based on the petrology, mineralogy, crystallography, thermodynamic calculations, Al/Mg isotopic systematics and the O-isotopic composition of the wassonite-bearing BO chondrule.
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new titanium monosulfide mineral phase in yamato 691 Enstatite Chondrite k nakamura messenger
2011Co-Authors: Simon J Clemett, Alan E. Rubin, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:K.Nakamura-Messenger 1,2 , S. J. Clemett 1,3 , A. E. Rubin 4 , B.-G. Choi 5 , S. Zhang 1,6 , Z. Rahman 1,2 , K. Oikawa 7 , and L. P. Keller 1 . 1 Astromaterials Research and Exploration Science Directorate /NASA Johnson Space Center, Houston, TX 77058, USA, 2 ESCG/ Jacobs Engineering, TX 77058, USA, 3 ESCG/ ERC Inc., TX 77058. USA, 4 Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567,USA, 5 Earth Science Education, Seoul National University, Seoul 151-748, South Korea, 6 Lunar and Planetary Institute, Houston, TX 77058, USA, 6 Lunar and Planetary Institute, Houston, TX 77058, USA, Dept. of Metallurgy, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan. keiko.nakamura-1@nasa.gov
Hisayoshi Yurimoto - One of the best experts on this subject based on the ideXlab platform.
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identification of silicate and carbonaceous presolar grains by sims in the type 3 Enstatite Chondrite alha81189
Applied Surface Science, 2008Co-Authors: Shingo Ebata, T J Fagan, Hisayoshi YurimotoAbstract:Abstract An isotope ratio imaging technique using the HokuDai isotope microscope system has been applied to in situ survey for presolar grains in the type-3 Enstatite Chondrite ALHA81189. Rastered and static ion beam were used for primary beam. Lateral resolution of the isotope image was achieved to be 0.4 μm for static ion beam mode and to be 0.6 μm for rastered ion beam mode. As a result, the abundances of presolar grains are 150–200% larger under the static ion beam mode than under the rastered ion beam mode. Development of image processing introducing isotopography of 32 S − , 24 Mg 16 O − and 56 Fe − succeeded to increase efficiency of presolar grain characterization. Using the static ion beam and introducing appropriate isotopography were very useful methods of in situ characterization of presolar grains in meteorites.
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Identification of Silicate and Carbonaceous Presolar Grains in the type 3 Enstatite Chondrites
AIP Conference Proceedings, 2008Co-Authors: Shingo Ebata, Hisayoshi YurimotoAbstract:We surveyed presolar grains in primitive Enstatite Chondrites by isotopography using the HokuDai isotope microscope system. The mineral identification has been conducted by X‐ray analysis with scanning electron microscopy. The chemical compositions are determined for eight silicate and ten carbonaceous presolar grains. Presolar grains of pyroxene compositions are dominant in the Enstatite Chondrites. This suggests that presolar silicates of Enstatite composition were selectively survived in the Enstatite Chondrite parent body or the Enstatite Chondrite formation area in the solar nebula.
K Keil - One of the best experts on this subject based on the ideXlab platform.
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Enstatite aChondrite meteorites aubrites and the histories of their asteroidal parent bodies
Chemie Der Erde-geochemistry, 2010Co-Authors: K KeilAbstract:Abstract The aubrites are nearly monomineralic Enstatite pyroxenites, consisting mostly of nearly FeO-free Enstatite, with minor albitic plagioclase, nearly FeO-free diopside and forsterite, metallic Fe,Ni, troilite, and a host of rare accessory minerals, many unknown from Earth, that formed under highly reducing conditions. As a result, many of the normally lithophile elements such as Ti, Cr, Mn, Na, etc. behave partly as chalcophiles (i.e., occur in sulfides), and Si is partly siderophile and occurs in metallic Fe,Ni. Aubrites must therefore have formed in a very unique part of the solar nebula, possibly within 1 AU of the Sun. While of the 27 aubrites, 15 are fragmental breccias, 6 are regolith breccias, and 6 are described as non-brecciated, their ingredients are clearly of igneous origin and formed by melting and fractional crystallization, possibly of a magma ocean. This is indicated by the occurrence of a variety of lithic clasts of igneous origin, and by the REE and other trace element distributions. Their highly reduced nature and their oxygen isotopic compositions suggest close kinship to the Enstatite Chondrites. However, they did not form from known EH or EL Chondrites on their parent bodies. Rather, they formed from Enstatite Chondrite-like material on at least two separate parent bodies, the Shallowater parent body and, for all other aubrites, on the aubrite parent body. Visible and near-infrared reflectance spetra of asteroids suggest that the aubrite parent bodies may be asteroids of the E-type and perhaps the E(II) sub-class, such as 3103 Eger and 2867 Steins (the target of the Rosetta Mission). If aubrites formed by the melting and fractional crystallization of Enstatite Chondrite-like parent lithologies, which should have contained ∼10 vol% plagioclase, then meteorites of Enstatite-plagioclase basaltic composition should exist, which is not the case. These early basaltic melts may have been removed from the aubrite parent body by explosive pyroclastic volcanism, and these small pyroclasts would have been destroyed in space long ago. Age dates suggest that the aubrites formed very early in the history of the solar system, within a few Ma of CAI formation, and that the heat sources for heating and melting of their parent bodies were, most likely, short-lived radionuclides such as 26 Al and, perhaps, 60 Fe. Finally, attention has been drawn to the surface composition of Mercury of low bulk FeO and of nearly FeO-free Enstatite, perhaps with plagioclase, diopside and sulfide. While known aubrites clearly did not originate from Mercury, recent calculations suggest that several percent of high-speed ejecta from Mercury reach Earth. This is only factors of 2–3 less than typical launches from Mars and, since there are now 53 Martian meteorites in our collections, meteoriticists should be alert to the potential discovery of a genuine meteorite from Mercury which, superficially, should resemble aubrites. However, recent results from the Neutron Spectrometer of the Messenger Flyby of Mercury have been interpreted to suggest that the planet’s surface may, in fact, contain abundant Fe–Ti-oxides and, if true, a meteorite from Mercury should not resemble any currently known meteorite type.
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northwest africa 2526 a partial melt residue of Enstatite Chondrite parentage
Meteoritics & Planetary Science, 2008Co-Authors: K Keil, A BischoffAbstract:NWA 2526 is a coarse-grained, achondritic rock dominated by equigranular grains of polysynthetically twinned Enstatite (~85 vol%) with frequent 120 triple junctions and ~10-15 vol% of kamacite + terrestrial weathering products. All other phases including troilite, daubreelite, schreibersite, and silica-normative melt areas make up <~1 vol% of the rock. Oxygen isotopic analyses are well within the range of those for Enstatite Chondrites and aubrites. We show that the "Enstatite aChondrite" (Russell et al. 2005) Northwest Africa (NWA) 2526 is actually a partial melt residue of an Enstatite Chondrite-like lithology that experienced ~20 vol% partial melting. We suggest that the heat source was internal to the parent body. The FeS-Fe,Ni and plagioclase-Enstatite partial melts were removed from the parent lithology, leaving NWA 2526 as a residue highly depleted in troilite and lacking plagioclase. Sub-solidus slow cooling and annealing is responsible for the coarsegrained, recrystallized texture of the rock. We also suggest that the parent lithology of NWA 2526, prior to partial melting, experienced a shock event which formed the curvilinear trails of blebs of minor troilite and rare metal that are enclosed in Enstatite crystals; thus, these represent relicts. After partial melting and annealing, NWA 2526 experienced a second, relatively mild impact event (<~20 GPa) that caused formation of the polysynthetic twinning in the Enstatite. We suggest that the meteorite Zaklodzie, which has been referred to as a "primitive Enstatite aChondrite" (Przylibski et al. 2005), did not form from a magma of internal origin, but that it is an impact-melt breccia of Enstatite Chondrite-like parentage, as previously discussed by Burbine et al. (2000) and Keil (2007). Finally, the "metal-rich Enstatite meteorite with achondritic texture" Itqiy (Patzer et al. 2001) formed by processes very similar to those responsible for formation of NWA 2526 and is also the residue of ~20 vol% partial melting of an Enstatite Chondrite-like parent lithology, with the FeS-Fe,Ni and plagioclase-Enstatite partial melts having been removed from the residue. It also experienced an impact event after partial melting that was responsible for the formation of the mixed Mg-Mn-Fesulfides and the shock stage S3 features of the Enstatite. These similarities indicate that NWA 2526 and Itqiy may have formed on the same parent body. This body was different from the EH, EL, Shallowater and aubrite parent bodies, and NWA 2526 and Itqiy may represent samples from yet another, fifth Enstatite meteorite parent body.
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occurrence and origin of keilite fe 0 5 mg 0 5 s in Enstatite Chondrite impact melt rocks and impact melt breccias
Chemie Der Erde-geochemistry, 2007Co-Authors: K KeilAbstract:Keilite (Fe>0.5,Mg 0.5,Fe 0.5,Fe ∼1500 °C, as indicted by the occurrence of euhedral Enstatite that formed from a melt [McCoy, T.J., Dickinson, T.L., Lofgren, G.E., 1999. Partial melting of the Indarch (EH4) meteorite: a textural, chemical, and phase relations view of melting and melt migration. Meteorit. Planet. Sci. 34, 735–746]. Based on the classifications of the keilite-bearing meteorites as impact-melt rocks and impact-melt breccias and my own textural observations, I conclude that this elevated temperature was reached as a result of impact and not internal heating and melting, followed by fast cooling, thus, quenching in keilite. Enstatite Chondrite impact-melt rocks and impact-melt breccias that do not contain keilite may have been more deeply buried after impact and, hence, cooled slowly and were annealed so that FeS exsolved from keilite, concomitant with the formation of niningerite, alabandite or various (Mn,Mg,Fe) mixed sulfides.
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origin and history of impact melt rocks of Enstatite Chondrite parentage
Geochimica et Cosmochimica Acta, 1995Co-Authors: T J Mccoy, K Keil, Donald D Bogard, Daniel H Garrison, I Casanova, Marilyn M Lindstrom, A J Brearley, K Kehm, R H NicholsAbstract:We have conducted petrologic, chemical, and isotopic studies of two impact-produced rocks of Enstatite Chondrite parentage. Ilafegh 009 is a total impact-melt rock with no residual lithic clasts. Formation on the EL Chondrite parent body is suggested by its mineralogy and mineral compositions. Cooling of the impact melt was rapid at melt temperatures and decreased at subsolidus temperatures. In contrast to previous studies, we show that Happy Canyon is not a new Enstatite aChondrite but an impactmelt breccia of Enstatite Chondrite (and not aubrite) parentage. This rock formed by impact melting and incorporation into the melt of clastic material (which resulted in relatively rapid cooling at all temperatures). Mineralogical and bulk compositional data (probably biased by the heterogeneous nature of this rock) do not allow unequivocal determination of its parent body (i.e., EL vs. EH), although some data such as bulk total Fe content seem to favor EL parentage. Both rocks were subjected to post-solidification shock, which was more severe for Ilafegh 009 than for Happy Canyon. It appears that both impact melt rocks could have formed by impact melting ∼4.57 Ga ago, as is indicated by the nearly identical IXe closure ages of 1.6 and 1.4 Ma before Bjurbole for Ilafegh 009 and Happy Canyon, respectively. An apparently younger 39Ar40Ar age of 4.53 Ga for Happy Canyon may be due to small biases in the intercalibration of the IXe and 39Ar40Ar chronometers, whereas the much younger 4.34–4.44 Ga age for Ilafegh 009 reflects thermal resetting during shock metamorphism. Shallowater, which was impact-derived from a different Enstatite aChondrite parent body, has an IXe closure age 0.4 Ma younger than that for Ilafegh 009 and an 39Ar40Ar age of 4.53 Ga. The ancient ages of these three rocks attest to the intense, early bombardment in this region of the solar system.
L P Keller - One of the best experts on this subject based on the ideXlab platform.
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wassonite a new titanium monosulfide mineral in the yamato 691 Enstatite Chondrite
American Mineralogist, 2012Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:Wassonite, ideally stoichiometric TiS, is a titanium monosulfide not previously observed in nature, that was discovered within the Yamato 691 EH3 Enstatite Chondrite. Twelve Ti-S phase grains were identified in a rare barred olivine (BO) chondrule; three of the grains were extracted by the focused ion beam technique. Because of the submicrometer size of the wassonite grains, it was not possible to determine conventional macroscopic properties. However, the chemical composition and crystal structure were well constrained by extensive quantitative energy-dispersive X-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for wassonite is rhombohedral ( a = 3.42 ± 0.07, c = 26.50 ± 0.53 A) with space group: R 3 m , cell volume: 268.4 ± 0.53 A 3 , Z = 9, density (calculated): 4.452 g/cm 3 , empirical formula: (Ti 0.93 ,Fe 0.06 ,Cr 0.01 )S. The wassonite grains crystallized from the chondrule melt that was itself formed in the solar nebula, not on the parent asteroid. The other crystalline phases in the BO chondrule include forsterite, Enstatite, troilite, metallic Fe-Ni, and osbornite (as well as the new Ti-S-bearing minerals and schollhornite) are highly reduced and indicate formation at low-oxygen fugacities.
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new titanium monosulfide mineral phase in yamato 691 Enstatite Chondrite
LPI, 2011Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:Yamato 691, an EH3 Enstatite Chondrite, was among the first meteorites discovered by chance in Antarctica by the Japanese Antarctic Research Expedition (JARE) team in 1969. This discovery led to follow-up searches for meteorites in Antarctica [1]. These international searches have been very successful recovering over 40,000 total specimens (and still counting), including martian and lunar meteorites. Titanium is partly chalcophile in Enstatite-rich meteorites. Previous occurrences of Ti-bearing sulfides include troilite, daubrelite and ferroan alabandite in Enstatite Chondrites and aubrites [2], and heideite with 28.5 wt% Ti in the Bustee aubrite [3]. Here we report a new mineral from Yamato 691, ideally stoichiometric TiS, titanium monosulfide, a simple two-element mineral phase, yet with a very unique crystal structure that, to our knowledge, has not been observed previously in nature.
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the formation of wassonite a new titanium monosulfide mineral in the yamato 691 Enstatite Chondrite
LPICo, 2011Co-Authors: Keiko Nakamuramessenger, Alan E. Rubin, Simon J Clemett, Byeongak Choi, S Zhang, Zia Rahman, L P Keller, Scott Messenger, Michael I Petaev, K OikawaAbstract:Wassonite, ideally stoichiometric TiS, is a titanium monosulfide not previously observed in nature, that was discovered within the Yamato 691 EH3 Enstatite Chondrite [1]. Because of the submicrometer size of the wassonite grains, it was not possible to determine conventional macroscopic properties. However, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive x-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for wassonite is rhombohedral (a = 3.42 plus or minus 0.07, c = 26.50 plus or minus 0.53 Angstroms) with space group: R(sup 3 raised bar) m (R9 type), cell volume: 268.4 plus or minus 0.53 Angstroms(sup 3), Z=9, density (calculated): 4.452 grams per cubic centimeter, empirical formula: (Ti(sub 0.93), Fe(sub 0.06), Cr(sub 0.01))S. In this study, we discuss possible formation mechanisms of wassonite and its associated minerals based on the petrology, mineralogy, crystallography, thermodynamic calculations, Al/Mg isotopic systematics and the O-isotopic composition of the wassonite-bearing BO chondrule.
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new titanium monosulfide mineral phase in yamato 691 Enstatite Chondrite k nakamura messenger
2011Co-Authors: Simon J Clemett, Alan E. Rubin, S Zhang, Zia Rahman, K Oikawa, L P KellerAbstract:K.Nakamura-Messenger 1,2 , S. J. Clemett 1,3 , A. E. Rubin 4 , B.-G. Choi 5 , S. Zhang 1,6 , Z. Rahman 1,2 , K. Oikawa 7 , and L. P. Keller 1 . 1 Astromaterials Research and Exploration Science Directorate /NASA Johnson Space Center, Houston, TX 77058, USA, 2 ESCG/ Jacobs Engineering, TX 77058, USA, 3 ESCG/ ERC Inc., TX 77058. USA, 4 Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567,USA, 5 Earth Science Education, Seoul National University, Seoul 151-748, South Korea, 6 Lunar and Planetary Institute, Houston, TX 77058, USA, 6 Lunar and Planetary Institute, Houston, TX 77058, USA, Dept. of Metallurgy, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan. keiko.nakamura-1@nasa.gov
Jean-noël Rouzaud - One of the best experts on this subject based on the ideXlab platform.
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structure composition and location of organic matter in the Enstatite Chondrite sahara 97096 eh3
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Laurette Piani, François Robert, Olivier Beyssac, Laurent Binet, Sylvie Derenne, Yves Marrocchi, Smail Mostefaoui, Michele Bourotdenise, Corentin Le Guillou, Jean-noël RouzaudAbstract:The insoluble organic matter (IOM) of an unequilibrated Enstatite Chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the Enstatite Chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous Chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine-grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar $\delta^{15}N$ and $\delta^{13}C$; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium-heterogeneity and having mean H- and N-isotopic compositions in the range of values observed for carbonaceous Chondrites. It contains some submicrometer-sized areas highly enriched in $^{15}N$ ($\delta^{15}N$ up to 1600 permil). These observations reinforce the idea that the IOM found in carbonaceous Chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component.
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d depleted organic matter and graphite in the abee Enstatite Chondrite
Geochimica et Cosmochimica Acta, 2012Co-Authors: Laurent Remusat, Jean-noël Rouzaud, E Charon, Le C Guillou, Yunbin Guan, John M. EilerAbstract:A combination of NanoSIMS and High resolution transmission electron microscopy (HRTEM) imaging along with Raman spectroscopy was used to characterize the carbonaceous phases in HF/HCl residue of the Abee Enstatite Chondrite. This acid residue hosts a very D-depleted component (δD = −480‰). This residue is a mixture of graphite and highly disordered insoluble organic matter. The latter exhibits a significant mesoporosity (i.e., 200–500 nm scale), and also shows concentric and elongated stacks of polyaromatic layers. Insoluble organic matter is shown to be the most D-depleted component in Abee. We also determined, by using NanoSIMS, carbon isotopic composition of graphite and insoluble organic matter in the acid residue (δ^(13)C = −11.3 ± 2.9‰ and −28.4 ± 2.2‰, respectively). We identified graphite in metal-rich clasts and in the matrix of Abee, associated with Enstatite, sulfide and metal, but we could not localize highly disordered organic matter in our section. Regardless, given the vulnerability of organic matter to thermal degradation, we suggest that it was added to Abee parent body during the latest stage of its formation, after any thermal metamorphism or partial melting of Abee parent body. A genetic link between organic matter and graphite in Abee is excluded based on our HRTEM and carbon isotopic data. The differences in carbon isotopic compositions between these phases are consistent with previous data obtained by stepwise heating experiments and indicate that graphite is not derived from a pure thermal solid-state graphitization of the organic matter. Rather, we suggest that graphite precipitated from a melt rich in C during the partial melting of the Abee parent body. Insoluble organic matter in Abee has the lowest D/H ratio among the extraterrestrial organics. Organics in most carbonaceous and ordinary Chondrites are believed to have been subjected to irradiations in low temperature environments, resulting in a dramatic isotopic fractionation through exchange and reaction with gaseous molecular hydrogen during their synthesis. In contrast, Abee organic matter was likely synthesized in a neutral (i.e., not ionized) environment where thermodynamic processes at equilibrium most likely controlled its isotopic composition. This organic matter could have been accreted in a minor component of Abee like the dark inclusions without (or prior to) exposure to the radiation responsible for D enrichments in other meteoritic organics. During the last brecciation events that have affected the Abee parent body, these inclusions could have been mixed with other Abee components. The properties of this organic matter can be interpreted as an indication that thermodynamic processes acted in the synthesis of organic matter in the protosolar disk, in addition to ion/molecule and gas/grains reaction witnessed by the D-rich insoluble organic matter contained in carbonaceous Chondrites.
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Structure, composition, and location of organic matter in the Enstatite Chondrite Sahara 97096 (EH3)
Meteoritics and Planetary Science, 2012Co-Authors: Laurette Piani, C. Le Guillou, François Robert, Olivier Beyssac, Laurent Binet, Michèle Bourot-denise, Sylvie Derenne, Yves Marrocchi, Smail Mostefaoui, Jean-noël RouzaudAbstract:The insoluble organic matter (IOM) of an unequilibrated Enstatite Chondrite Sahara(SAH) 97096 has been investigated using a battery of analytical techniques. As the EnstatiteChondrites are thought to have formed in a reduced environment at higher temperatures thancarbonaceous Chondrites, they constitute an interesting comparative material to test theheterogeneities of the IOM in the solar system and to constrain the processes that could affectIOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometergrains in the network of fine-grained matrix occurring mostly around chondrules and asinclusions in metallic nodules, where the carbonaceous matter appears to be moregraphitized. IOM in these two settings has very similar d15N and d13C; this supports the ideathat graphitized inclusions in metal could be formed by metal catalytic graphitization ofmatrix IOM. A detailed comparison between the IOM extracted from a fresh part and aterrestrially weathered part of SAH 97096 shows the similarity between both IOM samples inspite of the high degree of mineral alteration in the latter. The isolated IOM exhibits aheterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, withoutany detectable free radicals and deuterium-heterogeneity and having mean H- and N-isotopiccompositions in the range of values observed for carbonaceous Chondrites. It contains somesubmicrometer-sized areas highly enriched in 15N (d15N up to 1600&). These observationsreinforce the idea that the IOM found in carbonaceous Chondrites is a common componentwidespread in the solar system. Most of the features of SAH 97096 IOM could be explainedby the thermal modification of this main component.
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Graphite and Organic Matter in Abee Enstatite Chondrite
2010Co-Authors: Laurent Remusat, Jean-noël Rouzaud, C. Le Guillou, John M. EilerAbstract:Abee is a EH4 Enstatite Chondrite. It has been described as an impact breccia, with some parts having been exposed to temperature over 880 °C [1]. The shock induced by the impact has likely resulted in the segregation of metal and Enstatite, leading to an heterogeneous structure with metal-rich clasts included in Enstatite sulfide assemblage. It contains 0.36% of carbon [2], mainly described as graphite, but some of the carbon is poorly organized, being likely organic matter [3]. We have extended the data we have already reported by using NanoSIMS and HRTEM [3], to precise the structure of both graphite and organic matter and to understand their relationship in Abee.