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Dominik C Hezel - One of the best experts on this subject based on the ideXlab platform.
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fe isotope composition of bulk chondrules from murchison cm2 constraints for parent body alteration nebula processes and chondrule matrix complementarity
Earth and Planetary Science Letters, 2018Co-Authors: Dominik C Hezel, Johanna S Wilden, Daniel Becker, Sonja Steinbach, Frank Wombacher, Markus HarakAbstract:Abstract Chondrules are a major constituent of primitive meteorites. The formation of chondrules is one of the most elusive problems in cosmochemistry. We use Fe isotope compositions of chondrules and bulk chondrites to constrain the conditions of chondrule formation. Iron isotope compositions of bulk chondrules are so far only known from few studies on CV and some ordinary chondrites. We studied 37 chondrules from the CM chondrite Murchison. This is particularly challenging, as CM chondrites contain the smallest chondrules of all chondrite groups, except for CH chondrites. Bulk chondrules have δ 56 Fe between −0.62 and +0.24‰ relative to the IRMM-014 standard. Bulk Murchison has as all chondrites a δ 56 Fe of 0.00‰ within error. The δ 56 Fe distribution of the Murchison chondrule population is continuous and close to normal. The width of the δ 56 Fe distribution is narrower than that of the Allende chondrule population. Opaque modal abundances in Murchison chondrules is in about 67% of the chondrules close to 0 vol.%, and in 33% typically up to 6.5 vol.%. Chondrule Al/Mg and Fe/Mg ratios are sub-chondritic, while bulk Murchison has chondritic ratios. We suggest that the variable bulk chondrule Fe isotope compositions were established during evaporation and recondensation prior to accretion in the Murchison parent body. This range in isotope composition was likely reduced during aqueous alteration on the parent body. Murchison has a chondritic Fe isotope composition and a number of chondritic element ratios. Chondrules, however, have variable Fe isotope compositions and chondrules and matrix have complementary Al/Mg and Fe/Mg ratios. In combination, this supports the idea that chondrules and matrix formed from a single reservoir and were then accreted in the parent body. The formation in a single region also explains the compositional distribution of the chondrule population in Murchison.
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the chemical relationship between chondrules and matrix and the chondrule matrix complementarity
Earth and Planetary Science Letters, 2010Co-Authors: Dominik C Hezel, H PalmeAbstract:Chondrules and matrix are the two major components of carbonaceous chondrites (CC). The Mg/Si ratios of chondrules and matrices in CV, CR, CO and CM chondrites are complementary: chondrules have super CI chondritic and matrices sub CI chondritic Mg/Si ratios. Bulk samples of CC have always CI chondritic Mg/Si ratios, indicating that chondrules and matrix are chemically connected. Such a chemical relationship places important constraints on the chondrule formation process and the chemical evolution of the protoplanetary disk. The chondrule matrix complementarity excludes separate origins and later mixing of chondrules and matrix. Redistribution of Fe and Mg between chondrules and matrix or leaching of Si from chondrule mesostasis into the matrix on the parent body can be excluded. Both, chondrules and matrix must have formed from the same chemical reservoir. The Mg/Si complementarity was probably established in the nebula before parent body accretion by the extraction of a Mg-rich component from a CI chondritic reservoir. This component then served as precursor for chondrules, leaving behind Mg-depleted material, the parent material of matrix. This interpretation excludes all chondrule forming processes that involve a separate origin for chondrules and matrix, such as, for example, the X-wind model. The existence of this complementarity in CV, CR, CO and CM chondrites also suggests that chondrules and matrix are formed by similar processes.
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constraints for chondrule formation from ca al distribution in carbonaceous chondrites
Earth and Planetary Science Letters, 2008Co-Authors: Dominik C Hezel, H PalmeAbstract:Abstract Chondritic meteorites and their components formed in the protoplanetary disk surrounding the nascent sun. We show here that the two volumetrically dominating components of carbonaceous chondrites, chondrules and matrix did not form independently. They must have been derived from a single, common source. We analyzed Ca and Al in chondrules and matrix of the CV type carbonaceous chondrites Allende and Y-86751. The Ca/Al-ratios of chondrules and matrix of both chondrites are complementary, but in case of Allende chondrules have sub-chondritic and matrix super-chondritic Ca/Al-ratios and in case of Y-86751 chondrules have super-chondritic and matrix sub-chondritic Ca/Al-ratios. This rules out the redistribution of Ca between chondrules and matrix during parent body alteration. Tiny spinel grains in the matrix produce the high Al in the matrix of Y-86751. In Allende these spinels were most probably included in chondrules. The most plausible explanation for this Ca- and Al-distribution in the same type of chondrite is that both chondrules and matrix formed from the same chemical reservoir. Tiny differences in nebular conditions during formation of these two meteorites must have led to the observed differences. These are severe constraints for all models of chondrule formation. Any model involving separate formation of chondrules and matrix, such as the X-wind model can be excluded.
M Van Ginneken - One of the best experts on this subject based on the ideXlab platform.
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intense aqueous alteration on c type asteroids perspectives from giant fine grained micrometeorites
Geochimica et Cosmochimica Acta, 2019Co-Authors: Luigi Folco, M D Suttle, Matthew J Genge, S. S. Russell, Jens Najorka, M Van GinnekenAbstract:Abstract This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of
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the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites
Geochimica et Cosmochimica Acta, 2017Co-Authors: M Van Ginneken, J Gattacceca, P Rochette, Corinne Sonzogni, Anne Alexandre, V Vidal, Matthew J GengeAbstract:High-precision oxygen isotopic compositions of eighteen large cosmic spherules (> 500 mu m diameter) from the Atacama Desert, Chile, were determined using IR-laser fluorination - Isotope Ratio Mass spectrometry. The four discrete isotopic groups defined in a previous study on cosmic spherules from the Transantarctic Mountains (Suavet et al., 2010) were identified, confirming their global distribution. Approximately 50% of the studied cosmic spherules are related to carbonaceous chondrites, 38% to ordinary chondrites and 12% to unknown parent bodies. Approximately 90% of barred olivine (BO) cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites. Similarly, similar to 90% porphyritic olivine (Po) cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites. Other textures are related to all potential parent bodies. The data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters. We propose that the Po texture may essentially be formed from a coarse-grained precursor having an ordinary chondritic mineralogy and chemistry. Coarse-grained precursors related to carbonaceous chondrites (i.e. chondrules) are likely to either survive atmospheric entry heating or form V-type cosmic spherules. Due to the limited number of submicron nucleation sites after total melting, ordinary chondrite-related coarse-grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline (Cc) textures instead of BO textures. Conversely, the BO textures would be mostly related to the fine-grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases, allowing the preservation of submicron nucleation sites. Independently of the nature of the precursors, increasing peak temperatures form glassy textures.
William F Mcdonough - One of the best experts on this subject based on the ideXlab platform.
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variable refractory lithophile element compositions of planetary building blocks insights from components of enstatite chondrites
Geochimica et Cosmochimica Acta, 2021Co-Authors: Takashi Yoshizaki, R D Ash, Marc D Lipella, Tetsuya Yokoyama, William F McdonoughAbstract:Abstract Chondrites are sediments of materials left over from the earliest stage of the solar system history. Based on their undifferentiated nature and less fractionated chemical compositions, chondrites are widely considered to represent the unprocessed building blocks of the terrestrial planets and their embryos. Models of chemical composition of the terrestrial planets generally find chondritic relative abundances of refractory lithophile elements (RLE) in the bulk bodies (“constant RLE ratio rule”), based on limited variations of RLE ratios among chondritic meteorites and the solar photosphere. Here, we show that ratios of RLE, such as Nb/Ta, Zr/Hf, Sm/Nd and Al/Ti, are fractionated from the solar value in chondrules from enstatite chondrites (EC). The fractionated RLE ratios of individual EC chondrules document different chalcophile affinities of RLE under highly reducing environments and a separation of RLE-bearing sulfides from silicates before and/or during chondrule formation. In contrast, the bulk EC have solar-like RLE ratios, indicating that a physical sorting of silicates and sulfides was negligible before and during the accretion of EC parent bodies. Likewise, if the Earth’s accretion was dominated by EC-like materials, as supported by multiple isotope systematics, physical sorting of silicates and sulfides in the accretionary disk did not occur. Alternatively, the Earth’s precursors were high-temperature nebular condensates that formed prior to the precipitation of RLE-bearing sulfides. A lack of Ti depletion in the bulk silicate Earth, combined with similar silicate-sulfide and rutile-melt partitioning behaviors of Nb and Ti, prefers a moderately siderophile behavior of Nb as the origin of the accessible Earth’s Nb depletion. Highly reduced planets that have experienced selective removal or accretion of silicates or metal/sulfide phases, such as Mercury, possibly yield fractionated, non-solar bulk RLE ratios.
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variable refractory lithophile element compositions of planetary building blocks
arXiv: Earth and Planetary Astrophysics, 2020Co-Authors: Takashi Yoshizaki, R D Ash, Marc D Lipella, Tetsuya Yokoyama, William F McdonoughAbstract:Chondrites are undifferentiated sediments of materials left over from the earliest stage of the solar system history, and are widely considered to represent the unprocessed building blocks of the terrestrial planets. Compositional models of the planets generally find chondritic relative abundances of refractory lithophile elements (RLE) in the bulk planets ("constant RLE ratio rule"), based on limited variations of RLE ratios among chondritic meteorites and the solar photosphere. Here, we show that ratios of RLE, such as Nb/Ta, Zr/Hf, Sm/Nd and Al/Ti, are fractionated in chondrules from enstatite chondrites (EC), which provides limitations on the use of the constant RLE ratio rule in the compositional modeling of planets. The fractionated RLE compositions of EC chondrules document a separation of RLE-bearing sulfides before and/or during chondrule formation and different chalcophile affinities of RLE under highly reducing environments. If the Earth's accretion is dominated by highly reduced EC-like materials, as supported by multiple isotope systematics, the fractionated RLE ratios of the reduced silicates should have been modified during the Earth's subsequent differentiation, to produce CI-like RLE ratios of the bulk silicate Earth. A lack of Ti depletion in the bulk silicate Earth and the similar chalcophile behavior of Ti and Nb under reducing conditions exclude incorporation of Nb into a core-forming sulfide as the origin of the accessible Earth's Nb depletion.
Roberta L Rudnick - One of the best experts on this subject based on the ideXlab platform.
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highly siderophile element composition of the earth s primitive upper mantle constraints from new data on peridotite massifs and xenoliths
Geochimica et Cosmochimica Acta, 2006Co-Authors: Harry Becker, Mary F. Horan, Richard J Walker, Jean-pierre Lorand, Roberta L RudnickAbstract:Osmium, Ru, Ir, Pt, Pd and Re abundances and 187 Os/ 188 Os data on peridotites were determined using improved analytical techniques in order to precisely constrain the highly siderophile element (HSE) composition of fertile lherzolites and to provide an updated estimate of HSE composition of the primitive upper mantle (PUM). The new data are used to better constrain the origin of the HSE excess in Earth’s mantle. Samples include lherzolite and harzburgite xenoliths from Archean and post-Archean continental lithosphere, peridotites from ultramafic massifs, ophiolites and other samples of oceanic mantle such as abyssal peridotites. Osmium, Ru and Ir abundances in the peridotite data set do not correlate with moderately incompatible melt extraction indicators such as Al2O3. Os/Ir is chondritic in most samples, while Ru/Ir, with few exceptions, is ca. 30% higher than in chondrites. Both ratios are constant over a wide range of Al2O3 contents, but show stronger scatter in depleted harzburgites. Platinum, Pd and Re abundances, their ratios with Ir, Os and Ru, and the 187 Os/ 188 Os ratio (a proxy for Re/Os) show positive correlations with Al2O3, indicating incompatible behavior of Pt, Pd and Re during mantle melting. The empirical sequence of peridotite-melt partition coefficients of Re, Pd and Pt as derived from peridotites (D s=l Re < D s=l Pd < D s=l Pt < 1) is consistent with previous data on natural samples. Some harzburgites and depleted lherzolites have been affected by secondary igneous processes such as silicate melt percolation, as indicated by U-shaped patterns of incompatible HSE, high 187 Os/ 188 Os, and scatter off the correlations defined by incompatible HSE and Al2O3. The bulk rock HSE content, chondritic Os/Ir, and chondritic to subchondritic Pt/Ir, Re/Os, Pt/Re and Re/Pd of many lherzolites of the present study are consistent with depletion by melting, and possibly solid state mixing processes in the convecting mantle, involving recycled oceanic lithosphere. Based on fertile lherzolite compositions, we infer that PUM is characterized by a mean Ir abundance of 3.5 ± 0.4 ng/g (or 0.0080 ± 0.0009*CI chondrites), chondritic ratios involving Os, Ir, Pt and Re (Os/IrPUM of 1.12 ± 0.09, Pt/IrPUM = 2.21 ± 0.21, Re/OsPUM = 0.090 ± 0.002) and suprachondritic ratios involving Ru and Pd (Ru/IrPUM = 2.03 ± 0.12, Pd/IrPUM = 2.06 ± 0.31, uncertainties 1r). The combination of chondritic and modestly suprachondritic HSE ratios of PUM cannot be explained by any single planetary fractionation process. Comparison with HSE patterns of chondrites shows that no known chondrite group perfectly matches the PUM composition. Similar HSE patterns, however, were found in Apollo 17 impact melt rocks from the Serenitatis impact basin [Norman M.D., Bennett V.C., Ryder G., 2002. Targeting the impactors: siderophile element signatures of lunar impact melts from Serenitatis. Earth Planet. Sci. Lett, 217–228.], which represent mixtures of chondritic material, and a component that may be either of meteoritic or indigenous origin. The similarities between the HSE composition of PUM and the bulk composition of lunar breccias establish a connection between the late accretion history of the lunar surface and the HSE composition of the Earth’s mantle. Although late accretion following core formation is still the most viable explanation for the HSE abundances in the Earth’s mantle, the ‘‘late veneer’’ hypothesis may require some modification in light of the unique PUM composition.
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highly siderophile element composition of the earth s primitive upper mantle constraints from new data on peridotite massifs and xenoliths
Geochimica et Cosmochimica Acta, 2006Co-Authors: Harry Becker, Mary F. Horan, Richard J Walker, Jean-pierre Lorand, Roberta L RudnickAbstract:Osmium, Ru, Ir, Pt, Pd and Re abundances and 187 Os/ 188 Os data on peridotites were determined using improved analytical techniques in order to precisely constrain the highly siderophile element (HSE) composition of fertile lherzolites and to provide an updated estimate of HSE composition of the primitive upper mantle (PUM). The new data are used to better constrain the origin of the HSE excess in Earth’s mantle. Samples include lherzolite and harzburgite xenoliths from Archean and post-Archean continental lithosphere, peridotites from ultramafic massifs, ophiolites and other samples of oceanic mantle such as abyssal peridotites. Osmium, Ru and Ir abundances in the peridotite data set do not correlate with moderately incompatible melt extraction indicators such as Al2O3. Os/Ir is chondritic in most samples, while Ru/Ir, with few exceptions, is ca. 30% higher than in chondrites. Both ratios are constant over a wide range of Al2O3 contents, but show stronger scatter in depleted harzburgites. Platinum, Pd and Re abundances, their ratios with Ir, Os and Ru, and the 187 Os/ 188 Os ratio (a proxy for Re/Os) show positive correlations with Al2O3, indicating incompatible behavior of Pt, Pd and Re during mantle melting. The empirical sequence of peridotite-melt partition coefficients of Re, Pd and Pt as derived from peridotites (D s=l Re < D s=l Pd < D s=l Pt < 1) is consistent with previous data on natural samples. Some harzburgites and depleted lherzolites have been affected by secondary igneous processes such as silicate melt percolation, as indicated by U-shaped patterns of incompatible HSE, high 187 Os/ 188 Os, and scatter off the correlations defined by incompatible HSE and Al2O3. The bulk rock HSE content, chondritic Os/Ir, and chondritic to subchondritic Pt/Ir, Re/Os, Pt/Re and Re/Pd of many lherzolites of the present study are consistent with depletion by melting, and possibly solid state mixing processes in the convecting mantle, involving recycled oceanic lithosphere. Based on fertile lherzolite compositions, we infer that PUM is characterized by a mean Ir abundance of 3.5 ± 0.4 ng/g (or 0.0080 ± 0.0009*CI chondrites), chondritic ratios involving Os, Ir, Pt and Re (Os/IrPUM of 1.12 ± 0.09, Pt/IrPUM = 2.21 ± 0.21, Re/OsPUM = 0.090 ± 0.002) and suprachondritic ratios involving Ru and Pd (Ru/IrPUM = 2.03 ± 0.12, Pd/IrPUM = 2.06 ± 0.31, uncertainties 1r). The combination of chondritic and modestly suprachondritic HSE ratios of PUM cannot be explained by any single planetary fractionation process. Comparison with HSE patterns of chondrites shows that no known chondrite group perfectly matches the PUM composition. Similar HSE patterns, however, were found in Apollo 17 impact melt rocks from the Serenitatis impact basin [Norman M.D., Bennett V.C., Ryder G., 2002. Targeting the impactors: siderophile element signatures of lunar impact melts from Serenitatis. Earth Planet. Sci. Lett, 217–228.], which represent mixtures of chondritic material, and a component that may be either of meteoritic or indigenous origin. The similarities between the HSE composition of PUM and the bulk composition of lunar breccias establish a connection between the late accretion history of the lunar surface and the HSE composition of the Earth’s mantle. Although late accretion following core formation is still the most viable explanation for the HSE abundances in the Earth’s mantle, the ‘‘late veneer’’ hypothesis may require some modification in light of the unique PUM composition.
Matthew J Genge - One of the best experts on this subject based on the ideXlab platform.
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intense aqueous alteration on c type asteroids perspectives from giant fine grained micrometeorites
Geochimica et Cosmochimica Acta, 2019Co-Authors: Luigi Folco, M D Suttle, Matthew J Genge, S. S. Russell, Jens Najorka, M Van GinnekenAbstract:Abstract This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of
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the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites
Geochimica et Cosmochimica Acta, 2017Co-Authors: M Van Ginneken, J Gattacceca, P Rochette, Corinne Sonzogni, Anne Alexandre, V Vidal, Matthew J GengeAbstract:High-precision oxygen isotopic compositions of eighteen large cosmic spherules (> 500 mu m diameter) from the Atacama Desert, Chile, were determined using IR-laser fluorination - Isotope Ratio Mass spectrometry. The four discrete isotopic groups defined in a previous study on cosmic spherules from the Transantarctic Mountains (Suavet et al., 2010) were identified, confirming their global distribution. Approximately 50% of the studied cosmic spherules are related to carbonaceous chondrites, 38% to ordinary chondrites and 12% to unknown parent bodies. Approximately 90% of barred olivine (BO) cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites. Similarly, similar to 90% porphyritic olivine (Po) cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites. Other textures are related to all potential parent bodies. The data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters. We propose that the Po texture may essentially be formed from a coarse-grained precursor having an ordinary chondritic mineralogy and chemistry. Coarse-grained precursors related to carbonaceous chondrites (i.e. chondrules) are likely to either survive atmospheric entry heating or form V-type cosmic spherules. Due to the limited number of submicron nucleation sites after total melting, ordinary chondrite-related coarse-grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline (Cc) textures instead of BO textures. Conversely, the BO textures would be mostly related to the fine-grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases, allowing the preservation of submicron nucleation sites. Independently of the nature of the precursors, increasing peak temperatures form glassy textures.
