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Yunbin Guan - One of the best experts on this subject based on the ideXlab platform.
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phosphate minerals in the h group of ordinary Chondrites and fluid activity recorded by apatite heterogeneity in the zag h3 6 regolith breccia
American Mineralogist, 2016Co-Authors: Francis M Mccubbin, Rhian H Jones, Yunbin GuanAbstract:Phosphate minerals in ordinary Chondrites provide a record of fluids that were present during metamorphic heating of the Chondrite parent asteroids. We have carried out a petrographic study of the phosphate minerals, merrillite and apatite, in metamorphosed H group ordinary Chondrites of petrologic type 4–6, to understand development of phosphate minerals and associated fluid evolution during metamorphism. In unbrecciated Chondrites, apatite is Cl rich and shows textural evolution from fine-grained apatite-merrillite assemblages in type 4 toward larger, uniform grains in type 6. The Cl/F ratio in apatite shows a similar degree of heterogeneity in all petrologic types, and no systematic change in compositions with metamorphic grade, which suggests that compositions in each meteorite are dictated by localized conditions, possibly because of a limited fluid/rock ratio. The development of phosphate minerals in H Chondrites is similar to that of L and LL Chondrites, despite the fact that feldspar equilibration resulting from albitization is complete in H4 Chondrites but not in L4 or LL4 Chondrites. This suggests that albitization took place during an earlier period of the metamorphic history than that recorded by preserved apatite compositions, and chemical equilibrium was not achieved throughout the H Chondrite parent body or bodies during the late stages of metamorphism. A relict igneous clast in the H5 Chondrite, Oro Grande has apatite rims on relict phenocrysts of (possibly) diopside that have equilibrated with the host Chondrite. Apatite in the Zag H3–6 regolith breccia records a complex fluid history, which is likely related to the presence of halite in this meteorite. The porous dark H4 matrix of Zag, where halite is observed, has a high apatite/merrillite ratio, and apatite is extremely Cl rich. One light H6 clast contains similarly Cl-rich apatite. In a second light H6 clast, apatite compositions are very heterogeneous and more F-rich. Apatites in both H4 matrix and H6 clasts have very low H_2O contents. Heterogeneous apatite compositions in Zag record multiple stages of regolith processing and shock at the surface of the H Chondrite parent body, and apatite records either the passage of fluids of variable compositions resulting from different impact-related processes, or the passage of a single fluid whose composition evolved as it interacted with the Chondrite regolith. Unraveling the history of apatite can potentially help to interpret the internal structure of Chondrite parent bodies, with implications for physical and mechanical properties of chondritic asteroids. The behavior of halogens recorded by apatite is important for understanding the behavior of volatile elements in general: if impact-melt materials close to the surface of a chondritic asteroid are readily degassed, the volatile inventories of terrestrial planets could be considerably more depleted than the CI carbonaceous Chondrite abundances that are commonly assumed.
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oxygen isotopes in calcium aluminum rich inclusions from enstatite Chondrites new evidence for a single cai source in the solar nebula
Earth and Planetary Science Letters, 2000Co-Authors: Yunbin Guan, K D Mckeegan, Glenn J MacphersonAbstract:Calcium–aluminum-rich inclusions (CAIs) from enstatite Chondrites have large 16O excesses, similar to CAIs in carbonaceous and ordinary Chondrites, and are also similar in morphology, mineralogy and Al–Mg isotopic systematics. These similarities provide new evidence that most CAIs might have formed in a single, restricted nebular locale and were then distributed unevenly throughout the various Chondrite accretion regions.
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calcium aluminum rich inclusions from enstatite Chondrites indigenous or foreign
Science, 2000Co-Authors: Yunbin Guan, Glenn J Macpherson, Gary R Huss, G J WasserburgAbstract:The primary mineral assemblages and initial ^(26)Al/^(27)Al ratios of rare calcium-aluminum–rich inclusions (CAIs) from enstatite (E) Chondrites are similar to those of CAIs from other Chondrite classes. CAIs from all Chondrite classes formed under oxidizing conditions that are much different from the reducing conditions under which the E Chondrites formed. Either CAIs formed at an earlier, more oxidizing epoch in the region where E Chondrites ultimately formed, or they formed at a different place in the solar nebula and were transported into the E Chondrite formation region.
Glenn J Macpherson - One of the best experts on this subject based on the ideXlab platform.
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oxygen isotopes in calcium aluminum rich inclusions from enstatite Chondrites new evidence for a single cai source in the solar nebula
Earth and Planetary Science Letters, 2000Co-Authors: Yunbin Guan, K D Mckeegan, Glenn J MacphersonAbstract:Calcium–aluminum-rich inclusions (CAIs) from enstatite Chondrites have large 16O excesses, similar to CAIs in carbonaceous and ordinary Chondrites, and are also similar in morphology, mineralogy and Al–Mg isotopic systematics. These similarities provide new evidence that most CAIs might have formed in a single, restricted nebular locale and were then distributed unevenly throughout the various Chondrite accretion regions.
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calcium aluminum rich inclusions from enstatite Chondrites indigenous or foreign
Science, 2000Co-Authors: Yunbin Guan, Glenn J Macpherson, Gary R Huss, G J WasserburgAbstract:The primary mineral assemblages and initial ^(26)Al/^(27)Al ratios of rare calcium-aluminum–rich inclusions (CAIs) from enstatite (E) Chondrites are similar to those of CAIs from other Chondrite classes. CAIs from all Chondrite classes formed under oxidizing conditions that are much different from the reducing conditions under which the E Chondrites formed. Either CAIs formed at an earlier, more oxidizing epoch in the region where E Chondrites ultimately formed, or they formed at a different place in the solar nebula and were transported into the E Chondrite formation region.
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the distribution of aluminum 26 in the early solar system a reappraisal
Meteoritics, 1995Co-Authors: Glenn J Macpherson, A. M. Davis, Ernst ZinnerAbstract:— A compilation of over 1500 Mg-isotopic analyses of Al-rich material from primitive solar system matter (meteorites) shows clearly that 26Al existed live in the early Solar System. Excesses of 26Mg observed in refractory inclusions are not the result of mixing of “fossil” interstellar 26Mg with normal solar system Mg. Some material was present that contained little or no 26Al, but it was a minor component of solar system matter in the region where CV3 and CO3 carbonaceous Chondrites accreted and probably was a minor component in the accretion regions of CM Chondrites as well. Data for other Chondrite groups are too scanty to make similar statements. The implied long individual nebular histories of CAIs and the apparent gap of one or more million years between the start of CAI formation and the start of chondrule formation require the action of some nebular mechanism that prevented the CAIs from drifting into the Sun. Deciding whether 26Al was or was not the agent of heating that caused melting in the aChondrite parent bodies hinges less on its widespread abundance in the nebula than it does on the timing of planetesimal accretion relative to the formation of the CAIs.
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The distribution of aluminum‐26 in the early Solar System—A reappraisal
Meteoritics, 1995Co-Authors: Glenn J Macpherson, A. M. Davis, Ernst ZinnerAbstract:— A compilation of over 1500 Mg-isotopic analyses of Al-rich material from primitive solar system matter (meteorites) shows clearly that 26Al existed live in the early Solar System. Excesses of 26Mg observed in refractory inclusions are not the result of mixing of “fossil” interstellar 26Mg with normal solar system Mg. Some material was present that contained little or no 26Al, but it was a minor component of solar system matter in the region where CV3 and CO3 carbonaceous Chondrites accreted and probably was a minor component in the accretion regions of CM Chondrites as well. Data for other Chondrite groups are too scanty to make similar statements. The implied long individual nebular histories of CAIs and the apparent gap of one or more million years between the start of CAI formation and the start of chondrule formation require the action of some nebular mechanism that prevented the CAIs from drifting into the Sun. Deciding whether 26Al was or was not the agent of heating that caused melting in the aChondrite parent bodies hinges less on its widespread abundance in the nebula than it does on the timing of planetesimal accretion relative to the formation of the CAIs.
Klaus Keil - One of the best experts on this subject based on the ideXlab platform.
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Calcium-aluminum-rich inclusions in enstatite Chondrites (I): Mineralogy and textures
Meteoritics & Planetary Science, 2000Co-Authors: Timothy Fagan, Alexander N Krot, Klaus KeilAbstract:Abstract— Like calcium-aluminum-rich inclusions (CAIs) from carbonaceous and ordinary Chondrites, enstatite Chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al, Ti-diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na-(±Cl)-rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite Chondrite CAIs and rare Wark—Lovering rims are also similar to CAIs from other Chondrite groups. However, the small size (
Michael K. Weisberg - One of the best experts on this subject based on the ideXlab platform.
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The unequilibrated enstatite Chondrites
Geochemistry, 2012Co-Authors: Michael K. Weisberg, Makoto KimuraAbstract:Abstract The enstatite Chondrites formed under highly reducing (and/or sulfidizing) conditions as indicated by their mineral assemblages and compositions, which are sharply different from those of other Chondrite groups. Enstatite is the major silicate mineral. Kamacite is Si-bearing and the enstatite Chondrites contain a wide variety of monosulfide minerals that are not present in other Chondrite groups. The unequilibrated enstatite Chondrites are comprised of two groups (EH3 and EL3) and one anomalous member (LEW 87223), which can be distinguished by differences in their mineral assemblages and compositions. EH3 Chondrites have >1.8 wt.% Si in their kamacite and contain the monosulfide niningerite (MgS), whereas EL3 Chondrites have less than 1.4 wt.% Si in their kamacite and contain the monosulfide alabandite (MnS). The distinct mineralogies, compositions and textures of E3 Chondrites make comparisons with ordinary Chondrites (OCs) and carbonaceous Chondrites (CCs) difficult, however, a range of recrystallization features in the E3s are observed, and some may be as primitive as type 3.1 OCs and CCs. Others, especially the EL3 Chondrites, may have been considerably modified by impact processes and their primary textures disturbed. The chondrules in E3 Chondrites, although texturally similar to type I pyroxene-rich chondrules, are sharply different from chondrules in other Chondrite groups in containing Si-bearing metal, Ca- and Mg–Mn-rich sulfides and silica. This indicates formation in a reduced nebular environment separate from chondrules in other Chondrites and possibly different precursor materials. Additionally the oxygen isotope compositions of E3 chondrules indicate formation from a unique oxygen reservoir. Although the abundance, size distribution, and secondary alteration minerals are not always identical, CAIs in E3 Chondrites generally have textures, mineral assemblages and compositions similar to those in other groups. These observations indicates that CAIs in O, C and E Chondrites all formed in the reservoir under similar conditions, and were redistributed to the different Chondrite accretion zones, where the secondary alteration took place. Thus, chondrule formation was a local process for each particular Chondrite group, but all CAIs may have formed in the similar nebular environment. Lack of evidence of water (hydrous minerals), and oxygen isotope compositions similar to Earth and Moon suggest formation of the E Chondrites in the inner solar system and make them prime candidates as building blocks for the inner planets.
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Fe‐Ni metal in primitive Chondrites: Indicators of classification and metamorphic conditions for ordinary and CO Chondrites
Meteoritics & Planetary Science, 2008Co-Authors: Makoto Kimura, Jeffrey N. Grossman, Michael K. WeisbergAbstract:We report the results of our petrological and mineralogical study of Fe-Ni metal in type 3 ordinary and CO Chondrites, and the ungrouped carbonaceous Chondrite Acfer 094. Fe-Ni metal in ordinary and CO Chondrites occurs in chondrule interiors, on chondrule surfaces, and as isolated grains in the matrix. Isolated Ni-rich metal in Chondrites of petrologic type lower than type 3.10 is enriched in Co relative to the kamacite in chondrules. However, Ni-rich metal in type 3.15-3.9 Chondrites always contains less Co than does kamacite. Fe-Ni metal grains in chondrules in Semarkona typically show plessitic intergrowths consisting of submicrometer kamacite and Ni-rich regions. Metal in other type 3 Chondrites is composed of fine- to coarse-grained aggregates of kamacite and Ni-rich metal, resulting from metamorphism in the parent body. We found that the number density of Ni-rich grains in metal (number of Ni-rich grains per unit area of metal) in chondrules systematically decreases with increasing petrologic type. Thus, Fe-Ni metal is a highly sensitive recorder of metamorphism in ordinary and carbonaceous Chondrites, and can be used to distinguish petrologic type and identify the least thermally metamorphosed Chondrites. Among the known ordinary and CO Chondrites, Semarkona is the most primitive. The range of metamorphic temperatures were similar for type 3 ordinary and CO Chondrites, despite them having different parent bodies. Most Fe-Ni metal in Acfer 094 is martensite, and it preserves primary features. The degree of metamorphism is lower in Acfer 094, a true type 3.00 Chondrite, than in Semarkona, which should be reclassified as type 3.01.
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thermal history of the enstatite Chondrites from silica polymorphs
Meteoritics & Planetary Science, 2005Co-Authors: Makotoki Kimura, Michael K. Weisberg, Yangting Lin, Akio Suzuki, Eiji Ohtani, Ryuji OkazakiAbstract:Here we report the results of our petrologic and mineralogical study of enstatite (E) Chondrites in order to explore their thermal histories. We studied silica phases in 20 E Chondrites by laser micro Raman spectroscopy to determine the silica polymorphs they contain. Silica phases are commonly present in E Chondrites and their polymorphs reflect the physical conditions of formation. The samples studied here include EH3-5, EL3-6, E Chondrite melt rocks, and an anomalous E Chondrite. We identified quartz, tridymite, cristobalite, and silica glass in the samples studied. EH4 5 and EH melt rocks are divided into high and low temperature classes based on niningeritealabandite solid solutions. EH3, EL3, and some EH melt rocks of the high temperature class contain tridymite and cristobalite. We suggest that tridymite and cristobalite crystallized in chondrules and E Chondrite melts, followed by rapid cooling, leading to the survival of these silica polymorphs. EH4 and EL4 Chondrites also contain tridymite and cristobalite in their chondrules, indicating that these silica polymorphs survived low temperature metamorphism (as estimated from opaque mineral geothermometers) because of the sluggishness of the transition to a more stable polymorph. Tridymite and cristobalite in EL6 Chondrites reflect the high temperature processes experienced by these meteorites. On the other hand, some EH5 Chondrites and EH melt rocks of the low temperature class contain quartz, which may be a product of the transition from tridymite or cristobalite during a long period of low temperature metamorphism. Although the thermal history of E Chondrites have been previously estimated from opaque minerals, such compositions mainly reflect low temperature processes. However, we can reconstruct the primordial thermal processes and subsequent cooling histories of E Chondrites from their silica polymorphs. The E Chondrites have complicated thermal histories, which produced the observed variations among them.
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A new metal-rich Chondrite grouplet
Meteoritics & Planetary Science, 2001Co-Authors: Michael K. Weisberg, Martin Prinz, Robert N. Clayton, Toshiko K. Mayeda, Naoji Sugiura, Shigeo Zashu, Mitsuru EbiharaAbstract:Abstract-A new grouplet of primitive, metal-rich Chondrites, here called the CB (C, carbonaceous; B, bencubbinite) Chondrites, has been recognized. It includes Bencubbin, Weatherford, Hammadah a1 Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627. Their mineral compositions, as well as their oxygen and nitrogen isotopic compositions, indicate that they are closely related to the CR and CH Chondrites, all of which are members of the more inclusive CR clan. CB Chondrites have much greater metal/silicate ratios than any other Chondrite group, widely increasing the range of metal/silicate fractionation recorded in solar nebular processes. They also have the greatest moderately volatile lithophile element depletions of any chondritic materials. Metal has compositional trends and zoning patterns that suggest a primitive condensation origin, in contrast with metal from other Chondrite groups. CB Chondrites, as well as other CR clan Chondrites, have much heavier nitrogen (higher 15N/14N) than that in other Chondrite groups. The primitive characteristics of the CB Chondrites suggest that they contain one of the best records of early nebular processes. Another Chondrite, Grosvenor Mountains 9555 1, is petrographically similar to the CB Chondrites, but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir.
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The K (Kakangari) Chondrite grouplet
Geochimica et Cosmochimica Acta, 1996Co-Authors: Michael K. Weisberg, Martin Prinz, Robert N. Clayton, Toshiko K. Mayeda, Monica M. Grady, Ian A. Franchi, Colin Pillinger, Gregory W. KallemeynAbstract:Abstract The Kakangari, LEW 87232, and Lea Co. 002 Chondrites have a similar set of petrologic and oxygen isotopic characteristics that distinguishes them from other Chondrite groups. They are here established to constitute a single Chondrite grouplet—the K (after Kakangari) Chondrites. The K Chondrites have (1) high matrix abundances (33–77 vol%) as do carbonaceous Chondrites, (2) metal abundances (6–10 vol%) that are similar to the H group ordinary Chondrites, (3) average mafic silicate compositions (average Kakangari olivine = Fa2.2; enstatite Fs4.4) that indicate an oxidation state intermediate between H and E Chondrites, (4) matrix that differs from that in other Chondrite groups in being enstatite-rich with compositions more Mg-rich (average = Fs3) than those in the chondrules, (5) refractory lithophile element abundances (
Yves Marrocchi - One of the best experts on this subject based on the ideXlab platform.
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Oxygen isotopic and chemical composition of chromites in micrometeorites: Evidence of ordinary Chondrite precursors
Meteoritics and Planetary Science, 2019Co-Authors: N. Rudraswami, Yves Marrocchi, M. Shyam Prasad, D. Fernandes, Johan Villeneuve, S. TaylorAbstract:We identified 66 chromite grains from 42 of ~5000 micrometeorites collected from Indian Ocean deep-sea sediments and the South Pole water well. To determine the chromite grains precursors and their contribution to the micrometeorite flux, we combined quantitative electron microprobe analyses and oxygen isotopic analyses by high-resolution secondary ion mass spectrometry. Micrometeorite chromite grains show variable O isotopic compositions with δ18O values ranging from –¬¬0.8 to 6.0‰, δ17O values from 0.3 to 3.6‰, and Δ17O values from –0.9 to 1.6‰, seems majority of them are similar to those of chromites from ordinary Chondrites. The oxygen isotopic compositions of olivine as a proxy to the chromite in chromite-bearing micrometeorites where we could not measure chromite have Δ17O values suggesting largely related to ordinary chondritic with some having carbonaceous Chondrite precursors. Furthermore, the chemical compositions of chromites in micrometeorites are close to those reported for ordinary Chondrite chromites, but some contribution from carbonaceous Chondrites cannot be ruled out. Consequently, carbonaceous Chondrites cannot be a major contributor of chromite-bearing micrometeorites. Based on their oxygen isotopic and elemental compositions, we thus conclude with no ambiguity that chromite-bearing micrometeorites are largely related to fragments of ordinary Chondrites with small fraction from carbonaceous Chondrites, unlike other micrometeorites deriving largely from carbonaceous Chondrites.
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Hydrogen isotopic composition of water in CV-type carbonaceous Chondrites
Earth and Planetary Science Letters, 2018Co-Authors: Laurette Piani, Yves MarrocchiAbstract:Among the different groups of carbonaceous Chondrites, variable concentrations of hydrous minerals and organic matter are observed that might be related to the time and/or place of formation of their asteroidal parent bodies. However, the precise distribution of these volatile-bearing components between Chondrite groups and their chemical and isotopic compositions remain fairly unknown. In this study, we used a novel secondary ion mass spectrometry analytical protocol to determine the hydrogen isotopic composition of water-bearing minerals in CV-type carbonaceous Chondrites. This protocol allows for the first time the D/H ratio of CV Chondrite hydrous minerals to be determined without hindrance by hydrogen contributions from adjacent organic material. We found that water in the altered CV Chondrites Kaba, Bali, and Grosnaja has an average D/H ratio of D/H CV-water = [144 +8 −21 ] × 10 −6 (or δD CV-water = −77 +54 −131 h, 2σ), significantly higher than water in most CM-type carbonaceous Chondrites (D/H CM-water = [101 ± 6] × 10 −6 or δD CM-water = −350 ± 40h, 2σ). We show that because organic matter in CV Chondrites is depleted in deuterium compared to that in CM Chondrites, such differences could result from isotopic exchange between water and organics. Another possibility is that the CM and CV parent bodies sampled different reservoirs of water ice and organics characterized by variable isotopic compositions due to their different time and/or place of accretion.