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Frederic Moynier - One of the best experts on this subject based on the ideXlab platform.
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High-precision sulfur isotope composition of Enstatite meteorites and implications of the formation and evolution of their parent bodies
Geochimica et Cosmochimica Acta, 2015Co-Authors: C. Defouilloy, Frederic Moynier, Pierre Cartigny, N. Assayag, Jean-alix BarratAbstract:In order to better understand the formation and evolution of their parent bodies, the three isotope ratios of sulfur were analyzed in 33 Enstatite meteorites (24 Enstatite chondrites and 9 aubrites). The results show that on average all Enstatite chondrite groups are enriched in the lightest isotopes compared to other chondrite groups, with means of δ34S of −0.28 ± 0.22‰ for EH3/4, −0.16 ± 0.16‰ for EH5, −0.32 ± 0.15‰ for EL3, −0.67 ± 0.16‰ for EL6 and −0.64 ± 0.00‰ for EL7 (all 1σ). Aubrites show a larger isotope variability in their composition, with a δ34S varying from −1.350‰ to +0.154‰. Contrary to previously published results, our data show a distinct composition for EL6 compared to other Enstatite chondrites. This could be related to an impact-induced loss of isotopically heavy oldhamite (δ34S = by 3.62 ± 3.02‰ (1σ)) on the EL parent body. Although the bulk sulfur in both Enstatite meteorites and aubrites does not show any significant Δ33S and Δ36S, the oldhamite fraction shows clear evidence of mass independent fractionation on the 36S/32S ratio (in 3 out of 9 analyzes, Δ36S up to +2.2‰), a signal that is not correlated to any 33S/32S anomaly (in 1 out of 9 analyzes, Δ33S down to −0.085‰). Though a nebular or photochemical origin cannot be ruled out, the most plausible mechanism to produce such isolated non-mass dependent 36S/32S anomalies would be a contribution of FeCl2 containing excesses of 36S due to the decay of 36Cl to the leached oldhamite fraction. Even though the sulfur isotopic composition measured in Enstatite meteorites is distinct from the Bulk Silicate Earth (BSE), the isotopically lightest samples of EL6, EL7 and aubrites are approaching the isotopic composition of the BSE and Enstatite meteorites remain the meteorites with the sulfur isotopic composition the closest to the terrestrial one
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
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silicon isotopic variation in Enstatite meteorites clues to their origin and earth forming material
Earth and Planetary Science Letters, 2013Co-Authors: Paul S Savage, Frederic MoynierAbstract:Of the primitive meteorite groups, the Enstatite chondrites are among the most chemically dissimilar to terrestrial, which should preclude them as major components of the proto-Earth. However, for many isotope systems (most notably oxygen), Enstatite chondrites show very little variation away from terrestrial, hinting at a common origin. One isotope system which appears to differ from this trend is silicon, but no satisfactory explanation has been proposed as to why these meteorites should be significantly lighter than both the silicate Earth and other primitive meteorite groups. This study presents a comprehensive investigation into the Si isotope composition of Enstatite chondrites and their differentiated counterparts, the aubrites, and confirms that these meteorites are, with respect to Si isotopes, the lightest macroscale solar system objects so far analysed. Crucially, the results show that EH chondrites are significantly lighter (δ30Si=−0.77±0.08‰) than EL chondrites (δ30Si=−0.59±0.09‰) and aubrites (δ30Si=−0.60±0.11‰). Silicon isotope analyses of the metal-free components of EH and EL reveal that these are identical, within error, to each other and with carbonaceous/ordinary chondrite bulk measurements (viz., δ30Si ∼−0.47), which is taken as evidence that Si isotope variation in the nebular gas is not the cause of the light Si isotope enrichment in Enstatite chondrites. From this, one can infer that silicates condensing from the solar nebula over a wide range of compositions and, presumably, heliocentric distances have very similar Si isotope compositions. A statistically significant negative correlation between bulk δ30Si and Si content in Enstatite chondrite kamacite indicates that the presence of isotopically light Si in the metal phase (as the result of formation under reducing conditions) is the principal cause of the bulk enrichment in lighter Si isotopes. Based on the Si isotope offset between Enstatite meteorites and the silicate Earth, the extant Enstatite meteorites cannot represent a significant proportion of the material that accreted to form the proto-Earth, as unfeasibly large amounts of Si would have to enter the core to satisfy mass balance equations. However, we posit that material enriched in refractory lithophile elements which condensed in the same region as E-chondrites, could still be an important component.
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Nature of volatile depletion and genetic relationships in Enstatite chondrites and aubrites inferred from Zn isotopes
Geochimica et Cosmochimica Acta, 2011Co-Authors: Frederic Moynier, Randal Paniello, Matthieu Gounelle, Francis Albarède, Pierre Beck, Frank Podosek, B. ZandaAbstract:Enstatite meteorites include the undifferentiated Enstatite chondrites and the differentiated Enstatite achondrites (aubrites). They are the most reduced group of all meteorites. The oxygen isotope compositions of both Enstatite chondrites and aubrites plot along the terrestrial mass fractionation line, which suggests some genetic links between these meteorites and the Earth as well. For this study, we measured the Zn isotopic composition of 25 samples from the following groups: aubrites (main group and Shallowater), EL chondrites, EH chondrites and Happy Canyon (impact-melt breccia). We also analyzed the Zn isotopic composition and elemental abundance in separated phases (metal, silicates, and sulfides) of the EH4, EL3, and EL6 chondrites. The different groups of meteorites are isotopically distinct and give the following values (parts per thousand): aubrite main group (-7.08 < delta Zn-66
Paul S Savage - One of the best experts on this subject based on the ideXlab platform.
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
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silicon isotopic variation in Enstatite meteorites clues to their origin and earth forming material
Earth and Planetary Science Letters, 2013Co-Authors: Paul S Savage, Frederic MoynierAbstract:Of the primitive meteorite groups, the Enstatite chondrites are among the most chemically dissimilar to terrestrial, which should preclude them as major components of the proto-Earth. However, for many isotope systems (most notably oxygen), Enstatite chondrites show very little variation away from terrestrial, hinting at a common origin. One isotope system which appears to differ from this trend is silicon, but no satisfactory explanation has been proposed as to why these meteorites should be significantly lighter than both the silicate Earth and other primitive meteorite groups. This study presents a comprehensive investigation into the Si isotope composition of Enstatite chondrites and their differentiated counterparts, the aubrites, and confirms that these meteorites are, with respect to Si isotopes, the lightest macroscale solar system objects so far analysed. Crucially, the results show that EH chondrites are significantly lighter (δ30Si=−0.77±0.08‰) than EL chondrites (δ30Si=−0.59±0.09‰) and aubrites (δ30Si=−0.60±0.11‰). Silicon isotope analyses of the metal-free components of EH and EL reveal that these are identical, within error, to each other and with carbonaceous/ordinary chondrite bulk measurements (viz., δ30Si ∼−0.47), which is taken as evidence that Si isotope variation in the nebular gas is not the cause of the light Si isotope enrichment in Enstatite chondrites. From this, one can infer that silicates condensing from the solar nebula over a wide range of compositions and, presumably, heliocentric distances have very similar Si isotope compositions. A statistically significant negative correlation between bulk δ30Si and Si content in Enstatite chondrite kamacite indicates that the presence of isotopically light Si in the metal phase (as the result of formation under reducing conditions) is the principal cause of the bulk enrichment in lighter Si isotopes. Based on the Si isotope offset between Enstatite meteorites and the silicate Earth, the extant Enstatite meteorites cannot represent a significant proportion of the material that accreted to form the proto-Earth, as unfeasibly large amounts of Si would have to enter the core to satisfy mass balance equations. However, we posit that material enriched in refractory lithophile elements which condensed in the same region as E-chondrites, could still be an important component.
Kun Wang - One of the best experts on this subject based on the ideXlab platform.
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Potassium isotopic compositions of Enstatite meteorites
Meteoritics & Planetary Science, 2019Co-Authors: Chen Zhao, Katharina Lodders, Hannah Bloom, Heng Chen, Zhen Tian, Piers Koefoed, Mária K. Pető, Kun WangAbstract:Enstatite chondrites and aubrites are meteorites that show the closest similarities to the Earth in many isotope systems that undergo mass-independent and mass-dependent isotope fractionations. Due to the analytical challenges to obtain high-precision K isotopic compositions in the past, potential differences in K isotopic compositions between Enstatite meteorites and the Earth remained uncertain. We report the first high-precision K isotopic compositions of eight Enstatite chondrites and four aubrites and find that there is a significant variation of K isotopic compositions among Enstatite meteorites (from -2.34 permil to -0.18 permil). However, K isotopic compositions of nearly all Enstatite meteorites scatter around the Bulk Silicate Earth (BSE) value. The average K isotopic composition of the eight Enstatite chondrites (-0.47 +/- 0.57 permil) is indistinguishable from the BSE value (-0.48 +/- 0.03 permil), thus further corroborating the isotopic similarity between Earth' building blocks and Enstatite meteorite precursors. We found no correlation of K isotopic compositions with the chemical groups, petrological types, shock degrees, and terrestrial weathering conditions; however, the variation of K isotopes among Enstatite meteorite can be attributed to the parent body processing. Our sample of the main group aubrite MIL 13004 is exceptional and has an extremely light K isotopic composition (delta 41K= -2.34 +/- 0.12 permil). We attribute this unique K isotopic feature to the presence of abundant djerfisherite inclusions in our sample because this K-bearing sulfide mineral is predicted to be enriched in 39K during equilibrium exchange with silicates.
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
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the iron isotope composition of Enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
Geochimica et Cosmochimica Acta, 2014Co-Authors: Frederic Moynier, Paul S Savage, Kun WangAbstract:Abstract Despite their unusual chemical composition, it is often proposed that the Enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of Enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the Enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both Enstatite chondrites and achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated Enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from Enstatite achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.
Derek W. G. Sears - One of the best experts on this subject based on the ideXlab platform.
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Pyroxene structures, cathodoluminescence and the thermal history of the Enstatite chondrites
Meteoritics & Planetary Science, 1996Co-Authors: Yanhong Zhang, John M. Dehart, Gary E. Lofgren, Shaoxiong Huang, Diann Schneider, Paul H. Benoit, Derek W. G. SearsAbstract:In order to explore the thermal history of Enstatite chondrites, we examined the cathodoluminescence (CL) and thermoluminescence (TL) properties of 15 EH chondrites and 21 EL chondrites, including all available petrographic types, both textural types 3-6 and mineralogical types alpha-delta. The CL properties of EL3(alpha) and EH3(alpha) chondrites are similar. Enstatite grains high in Mn and other transition metals display red CL, while Enstatite with low concentrations of these elements show blue CL. A few Enstatite grains with greater than 5 wt% FeO display no CL. In contrast, the luminescent properties of the metamorphosed EH chondrites are very different from those of metamorphosed EL chondrites. While the Enstatites in metamorphosed EH chondrites display predominantly blue CL, the Enstatites in metamorphosed EL chondrites display a distinctive magenta CL with blue and red peaks of approximately equal intensity in their spectra. The TL sensitivities of the Enstatite chondrites correlate with the intensity of the blue CL and, unlike other meteorite classes, are not simply related to metamorphism. The different luminescent properties of metamorphosed EH and EL chondrites cannot readily be attributed to compositional differences. But x-ray diffraction data suggests that the Enstatite in EH5(gamma),(delta) chondrites is predominantly disordered orthopyroxene, while Enstatite in EL6(beta) chondrites is predominantly ordered orthopyroxene. The difference in thermal history of metamorphosed EL and EH chondrites is so marked that the use of single 'petrographic' types is misleading, and separate textural and mineralogical types are preferable. Our data confirm earlier suggestions that metamorphosed EH chondrites underwent relatively rapid cooling, and the metamorphosed EL chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field.
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The thermometry of Enstatite chondrites: A brief review and update
Meteoritics & Planetary Science, 1996Co-Authors: Yanhong Zhang, Derek W. G. SearsAbstract:— Due to the discoveries in Antarctica, the number of known Enstatite chondrites has doubled in the last few years, and many rare or previously unknown types have been collected, most notably many EL3 and EH3 chondrites. We have applied the five major Enstatite chondrite thermometers to the new and previously known Enstatite chondrites, the thermometers being: (1) kamacite-quartz-Enstatite-oldhamite-troilite (KQEOT), (2) oldhamite, (3) alabandite-niningerite, (4) sphalerite, and (5) phosphide-metal. Measured temperatures based on the KQEOT and oldhamite systems are 800 °C-1000 °C with the type 3 Enstatite chondrites having values similar to those of type 4–6. It seems likely that these temperatures relate to events prior to parent body metamorphism, such as nebula condensation or chondrule formation, and were not significantly reset by later events. Measured temperatures for alabandite-niningerite, metal-phosphide and sphalerite in EH chondrites increase from 300 °C-400 °C to 600 °C-800 °C with petrographic indications of increasing metamorphism. In contrast, measured temperatures for all EL chondrites, including the most heavily metamorphosed, are generally
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The classification and complex thermal history of the Enstatite chondrites
Journal of Geophysical Research, 1995Co-Authors: Yanhong Zhang, Paul H. Benoit, Derek W. G. SearsAbstract:We have carried out instrumental neutron activation analyses of 11 Enstatite chondrites and electron microprobe analyses of 17 Enstatite chondrites, most of which were previously little described. We report here the third known EH5 chondrite (LEW 88180) and an unusual EL6 chondrite (LEW 87119), new data on four EL3 chondrites (ALH 85119, EET 90299, PCA 91020, and MAC 88136, which is paired with MAC 88180 and MAC 88184), the second EL5 chondrite (TIL 91714), and an unusual metal-rich and sulfide-poor EL3 chondrite (LEW 87223). The often discussed differences in mineral composition displayed by the EH and EL chondrites are not as marked after the inclusion of the new samples in the database, and the two classes apparently experienced a similar range of equilibration temperatures. However, texturally the EL chondrites appear to have experienced much higher levels of metamorphic alteration than EH chondrites of similar equilibration temperatures. Most of the petrologic type criteria are not applicable to Enstatite chondrites and, unlike the ordinary chondrites, texture and mineralogy reflect different aspects of the meteorite history. We therefore propose that the existing petrologic type scheme not be used for Enstatite chondrites. We suggest that while “textural type” reflects peak metamorphic temperatures, the “mineralogical type” reflects equilibration during postmetamorphic (probably regolith) processes. Unlike the ordinary chondrites and EH chondrites, EL chondrites experienced an extensive low-temperature metamorphic episode. There are now a large number of Enstatite meteorite breccias and impact melts, and apparently surface processes were important in determining the present nature of the Enstatite chondrites.
Jennife M Jackso - One of the best experts on this subject based on the ideXlab platform.
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rapid identification of steatite Enstatite polymorphs at various temperatures
Journal of The European Ceramic Society, 2008Co-Authors: Uno Reynard, Jay D Ass, Jennife M JacksoAbstract:The mechanical properties of steatite ceramics after high-temperature processing depend on inversion of high-temperature Mg_2Si_2O_6 protoEnstatite polymorph to low clino- or ortho-Enstatite, which are characterized by Raman spectroscopy. The Raman spectrum of a pure Mg_2Si_2O_6 protoEnstatite is sufficiently distinct from those of low clino- and ortho-Enstatite to allow rapid identification in a bulk sample both at ambient and high temperatures. With its high-lateral resolution (about 2 μm), speed, and ease of application on rough materials, Raman spectroscopy can be used to map transformation sequences of Enstatite in quenched materials or at high temperature during the fabrication of the steatite-type ceramics, and their relationship with microstructural defects such as voids and cracks.