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Alexander N. Krot - One of the best experts on this subject based on the ideXlab platform.

  • machiite al2ti3o9 a new oxide mineral from the murchison Carbonaceous Chondrite a new ultra refractory phase from the solar nebula
    American Mineralogist, 2020
    Co-Authors: Alexander N. Krot, K Nagashima, George R Rossman
    Abstract:

    Machiite (IMA 2016-067), Al₂Ti₃O₉, is a new mineral that occurs as a single euhedral crystal, 4.4 μm in size, in contact with an euhedral corundum grain, 12 μm in size, in a matrix of the Murchison CM2 Carbonaceous Chondrite. The mean chemical composition of holotype machiite by electron probe microanalysis is (wt%) TiO₂ 59.75, Al₂O₃ 15.97, Sc₂O₃ 10.29, ZrO₂ 9.18, Y₂O₃ 2.86, FeO 1.09, CaO 0.44, SiO2 0.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al_(1.17)Sc_(0.56)Y_(0.10)Ti4+0.08Ti0.084+Fe_(0.06)Ca_(0.03)Mg_(0.01))(⁠Ti4+2.71Ti2.714+Zr_(0.28)Si_(0.01))O₉. The general formula is (Al,Sc)₂ (Ti⁴⁺,Zr)₃O₉. The end-member formula is Al₂Ti₃O₉. Machiite has the C2/c schreyerite-type structure with a = 17.10 A, b = 5.03 A, c = 7.06 A, β = 107°, V = 581 A3, and Z = 4, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 4.27 g/cm³. The machiite crystal is highly ¹⁶O-depleted relative to the coexisting corundum grain (Δ¹⁷O = –0.2 ± 2.4‰ and –24.1 ± 2.6‰, respectively; where Δ¹⁷O = δ¹⁷O – 0.52 × δ¹⁸O). Machiite is a new member of the schreyerite (V₂Ti₃O₉) group and a new Sc,Zr-rich ultrarefractory phase formed in the solar nebula, either by gas-solid condensation or as a result of crystallization from a Ca,Al-rich melt having solar-like oxygen isotopic composition (Δ¹⁷O~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10⁻⁴–10⁻⁵ bar) conditions in the CAI-forming region near the protosun. The currently observed disequilibrium oxygen isotopic composition between machiite and corundum may indicate that machiite subsequently experienced oxygen isotopic exchange with a planetary-like ¹⁶O-poor gaseous reservoir either in the solar nebula or on the CM Chondrite parent body. The name machiite is in honor of Chi Ma, mineralogist at California Institute of Technology, for his contributions to meteorite mineralogy and discovery of many new minerals representing extreme conditions of formation.

  • addibischoffite ca2al6al6o20 a new calcium aluminate mineral from the acfer 214 ch Carbonaceous Chondrite a new refractory phase from the solar nebula
    American Mineralogist, 2017
    Co-Authors: Alexander N. Krot, K Nagashima
    Abstract:

    Addibischoffite (IMA 2015-006), Ca_2Al_6Al_6O_(20), is a new calcium aluminate mineral that occurs with hibonite, perovskite, kushiroite, Ti-kushiroite, spinel, melilite, anorthite, and FeNi-metal in the core of a Ca-Al-rich inclusion (CAI) in the Acfer 214 CH3 Carbonaceous Chondrite. The mean chemical composition of type addibischoffite measured by electron probe microanalysis is (wt%) Al_2O_3 44.63, CaO 15.36, SiO_2 14.62, V_2O_3 10.64, MgO 9.13, Ti_2O_3 4.70, FeO 0.46, total 99.55, giving rise to an empirical formula of (Ca_(2.00))(Al_(2.55)Mg_(1.73)V^(3+)_(1.08)Ti^(3+)_(0.50)Ca_(0.09)Fe^(2+)_(0.05))_(∑6.01)(Al_(4.14)Si_(1.86))O_(20). The general formula is Ca_2(Al,Mg,V,Ti)_6(Al,Si)_6O_(20). The end-member formula is Ca_2Al_6Al_6O_(20). Addibischoffite has the P1 aenigmatite structure with a = 10.367 A, b = 10.756 A, c = 8.895 A, α = 106.0°, β = 96.0°, γ = 124.7°, V = 739.7 A^3, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.41 g/cm^3. Addibischoffite is a new member of the warkite (Ca_2Sc_6Al_6O_(20)) group and a new refractory phase formed in the solar nebula, most likely as a result of crystallization from an ^(16)O-rich Ca, Al-rich melt under high-temperature (~1575 °C) and low-pressure (~10^(−4) to 10^(−5) bar) conditions in the CAI-forming region near the protosun, providing a new puzzle piece toward understanding the details of nebular processes. The name is in honor of Addi Bischoff, cosmochemist at University of Munster, Germany, for his many contributions to research on mineralogy of Carbonaceous Chondrites, including CAIs in CH Chondrites.

  • 53mn 53cr dating of aqueously formed carbonates in the cm2 lithology of the sutter s mill Carbonaceous Chondrite
    Meteoritics & Planetary Science, 2014
    Co-Authors: Christine E Jilly, Alexander N. Krot, K Nagashima, Qingzhu Yin, G R Huss, Naoji Sugiura
    Abstract:

    Radiometric dating of secondary minerals can be used to constrain the timing of aqueous alteration on meteoritic parent bodies. Dolomite is a well-documented secondary mineral in CM Chondrites, and is thought to have formed by precipitation from an aqueous fluid on the CM parent body within several million years of accretion. The petrographic context of crosscutting dolomite veins indicates that aqueous alteration occurred in situ, rather than in the nebular setting. Here, we present 53Mn-53Cr systematics for dolomite grains in Sutter's Mill section SM51-1. The Mn-Cr isotope data show well-resolved excesses of 53Cr correlated with 55Mn/52Cr ratio, which we interpret as evidence for the in situ decay of radioactive 53Mn. After correcting for the relative sensitivities of Mn and Cr using a synthetic Mn- and Cr-bearing calcite standard, the data yield an isochron with slope corresponding to an initial 53Mn/55Mn ratio of 3.42 ± 0.86 × 10−6. The reported error includes systematic uncertainty from the relative sensitivity factor. When calculated relative to the U-corrected Pb-Pb absolute age of the D'Orbigny angrite, Sutter's Mill dolomites give a formation age between 4564.8 and 4562.2 Ma (2.4–5.0 Myr after the birth of the solar system). This age is contemporaneous with previously reported ages for secondary carbonates in CM and CI Chondrites. Consistent carbonate precipitation ages between the Carbonaceous Chondrite groups suggest that aqueous alteration was a common process during the early stages of parent body formation, probably occurring via heating from internal 26Al decay. The high-precision isochron for Sutter's Mill dolomite indicates that late-stage processing did not reach temperatures that were high enough to further disturb the Mn-Cr isochron.

  • radar enabled recovery of the sutter s mill meteorite a Carbonaceous Chondrite regolith breccia
    Science, 2012
    Co-Authors: Alexander N. Krot, Michael E. Zolensky, Peter Jenniskens, M Fries, S A Sandford, D W G Sears, Robert Beauford, D S Ebel, Jon M Friedrich
    Abstract:

    Doppler weather radar imaging enabled the rapid recovery of the Sutter’s Mill meteorite after a rare 4-kiloton of TNT–equivalent asteroid impact over the foothills of the Sierra Nevada in northern California. The recovered meteorites survived a record high-speed entry of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets (Tisserand’s parameter = 2.8 ± 0.3). Sutter’s Mill is a regolith breccia composed of CM (Mighei)–type Carbonaceous Chondrite and highly reduced xenolithic materials. It exhibits considerable diversity of mineralogy, petrography, and isotope and organic chemistry, resulting from a complex formation history of the parent body surface. That diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to C-class asteroids are interpreted.

  • extremely na and cl rich chondrule from the cv3 Carbonaceous Chondrite allende
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: G J Wasserburg, Alexander N. Krot, K Nagashima, J Aleon, I D Hutcheon, Erick C Ramon, Adrian J. Brearley
    Abstract:

    We report on a study of Al3509, a large Na- and Cl-rich, radially-zoned object from the oxidized CV Carbonaceous Chondrite Allende. Al3509 consists of fine-grained ferroan olivine, ferroan Al-diopside, nepheline, sodalite, and andradite, and is crosscut by numerous veins of nepheline, sodalite, and ferroan Al-diopside. Some poorly-characterized phases of fine-grained material are also present; these phases contain no significant H_2O. The minerals listed above are commonly found in Allende CAIs and chondrules and are attributed to late-stage iron-alkali-halogen metasomatic alteration of primary high-temperature minerals. Textural observations indicate that Al3509 is an igneous object. However, no residual crystals that might be relicts of pre-existing CAI or chondrule minerals were identified. To establish the levels of ^(26)Al and ^(36)Cl originally present, ^(26)Al–^(26)Mg and ^(36)Cl–^(36)S isotopic systematics in sodalite were investigated. Al3509 shows no evidence of radiogenic ^(26)Mg∗, establishing an upper limit of the initial ^(26)Al/^(27)Al ratio of 3 × 10^(−6). All sodalite grains measured show large but variable excesses of ^(36)S, which, however, do not correlate with ^(35)Cl/^(34)S ratio. If these excesses are due to decay of ^(36)Cl, local redistribution of radiogenic ^(36)S∗ after ^(36)Cl had decayed is required. The oxygen-isotope pattern in Al3509 is the same as found in secondary minerals resulting from iron-alkali-halogen metasomatic alteration of Allende CAIs and chondrules and in melilite and anorthite of most CAIs in Allende. The oxygen-isotope data suggest that the secondary minerals precipitated from or equilibrated with a fluid of similar oxygen-isotope composition. These observations suggest that the formation of Al3509 and alteration products in CAIs and chondrules in Allende requires a very similar fluid phase, greatly enriched in volatiles (e.g., Na and Cl) and with Δ^(17)O ~ −3‰. We infer that internal heating of planetesimals by ^(26)Al would efficiently transfer volatiles to their outer portions and enhance the formation of volatile-enriched minerals there. We conclude that the site for the production of Na- and Cl-rich fluids responsible for the formation of Al3509 and the alteration of the Allende CAIs and chondrules must have been on a protoplanetary body prior to incorporation into the Allende meteorite. Galactic cosmic rays cannot be the source of the inferred initial ^(36)Cl in Allende. The problem of ^(36)Cl production by solar energetic particle (SEP) bombardment and the possibility that ^(36)Cl and ^(41)Ca might be the product of neutron capture resulting from SEP bombardment of protoplanetary surfaces are discussed. This hypothesis can be tested comparing inferred "initial" ^(36)Cl with neutron fluencies measured on the same samples and on phases showing ^(36)S∗ by Sm and Gd isotopic measurements.

P Lindgren - One of the best experts on this subject based on the ideXlab platform.

  • elephant moraine 96029 a very mildly aqueously altered and heated cm Carbonaceous Chondrite implications for the drivers of parent body processing
    Geochimica et Cosmochimica Acta, 2016
    Co-Authors: M R Lee, P Lindgren, A J King, I A Franchi, R C Greenwood, R Sparkes
    Abstract:

    Elephant Moraine (EET) 96029 is a CM Carbonaceous Chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM Chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ∼400–600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.

  • aqueous alteration of chondrules from the murchison cm Carbonaceous Chondrite replacement pore filling and the genesis of polyhedral serpentine
    Meteoritics & Planetary Science, 2016
    Co-Authors: M R Lee, P Lindgren
    Abstract:

    Forsterite and clinoenstatite in type IAB chondrules from the Murchison CM Carbonaceous Chondrite have been partially serpentinized, and the mechanisms of their alteration reveal crystallographic and microstructural controls on the reaction of silicate minerals with parent body aqueous solutions. Grains of forsterite were altered in two stages. Narrow veinlets of Fe-rich serpentine formed first and by the filling of sheet pores. Most of these pores were oriented parallel to (010) and (001) and had been produced by earlier fracturing and/or congruent dissolution. In the second stage, the subset of veinlets that were oriented parallel to (001) was widened accompanying the replacement of forsterite by Mg-Fe serpentine. This reaction proceeded most rapidly parallel to [001], and crystallographic controls on the trajectory of retreating vein walls created fine-scale serrations. Murchison clinoenstatite grains have a skeletal appearance due to the presence of abundant veinlets and patches of phyllosilicate. Two alteration stages can again be recognized, with initial water–mineral interaction producing tochilinite-rich veinlets by the filling of (001)-parallel contraction cracks. Pores then formed by congruent dissolution that was guided principally by orthopyroxene lamellae, and they were subsequently filled by submicrometer-sized crystals of polyhedral serpentine. This finding that Murchison forsterite and clinoenstatite grains have been altered demonstrates that aqueous processing of magnesium silicate minerals started much earlier in CM parent body history than previously believed. Our results also show that the occurrence of polyhedral serpentine can be used to locate former pore spaces within the parent body.

  • Clasts in the CM2 Carbonaceous Chondrite Lonewolf Nunataks 94101 : Evidence for aqueous alteration prior to complex mixing
    Meteoritics & Planetary Science, 2013
    Co-Authors: P Lindgren, M. Sofe, M R Lee, Michael E. Zolensky
    Abstract:

    Clasts in the CM2 Carbonaceous Chondrite Lonewolf Nunataks (LON) 94101 have been characterized using scanning and transmission electron microscopy and electron microprobe analysis to determine their degrees of aqueous alteration, and the timing of alteration relative to incorporation of clasts into the host. The provenance of the clasts, and the mechanism by which they were incorporated and mixed with their host material are also considered. Results show that at least five distinct types of clasts occur in LON 94101, of which four have been aqueously altered to various degrees and one is largely anhydrous. The fact that they have had different alteration histories implies that the main part of aqueous activity occurred prior to the mixing and assimilation of the clasts with their host. Further, the presence of such a variety of clasts suggests complex mixing in a dynamic environment involving material from various sources. Two of the clasts, one containing approximately 46 vol% carbonate and the other featuring crystals of pyrrhotite up to approximately 1 mm in size, are examples of unusual lithologies and indicate concentration of chemical elements in discrete areas of the parent body(ies), possibly by flow of aqueous solutions.

  • microstructure of calcite in the cm2 Carbonaceous Chondrite lon 94101 implications for deformation history during and or after aqueous alteration
    Earth and Planetary Science Letters, 2011
    Co-Authors: P Lindgren, M. Sofe, M R Lee, Mark J. Burchell
    Abstract:

    The microstructure of calcite in the CM2 Carbonaceous Chondrite LON 94101 has been characterized using electron backscatter diffraction (EBSD) analysis, to reconstruct the parent body deformation history during and/or after aqueous alteration. The results suggest that at least two events of calcite crystallization have taken place during aqueous alteration, and at least three episodes of deformation are recorded by the calcite. The first event of calcite crystallization produced calcite grains scattered throughout the matrix, and the second event formed a calcite vein via localized fluid flow. The first episode of deformation is recorded in the crystallographic preferred orientations of the calcite grains and occurred via a directed stress probably induced by compaction in shallow crustal levels of the parent body. The second episode of deformation is recorded in an e-twin microstructure and it suggests a deformation induced via directed stress by impact processing, also in shallow crustal levels. The third episode of deformation generated subgrains in the calcite vein and in some calcite grains, and fragmented and disrupted the calcite vein. This could have been a result of a relatively forceful deformation event, perhaps when the meteorite was released from its parent body. This study shows that carbonate microstructures in Carbonaceous Chondrites is a powerful and versatile tool for reconstructing the history of deformation during and/or after aqueous alteration.

Hisayoshi Yurimoto - One of the best experts on this subject based on the ideXlab platform.

  • crystal growth and disequilibrium distribution of oxygen isotopes in an igneous ca al rich inclusion from the allende Carbonaceous Chondrite
    Geochimica et Cosmochimica Acta, 2018
    Co-Authors: Hisayoshi Yurimoto, Naoya Sakamoto, S B Simon, L Grossman, Noriyuki Kawasaki
    Abstract:

    Abstract TS34 is a Type B1 Ca-Al-rich inclusion (CAI) from the Allende CV3 Chondrite, consisting of spinel, melilite, Ti-Al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. Oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in TS34. Using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic evolution of the CAI melt was established. Oxygen isotopic compositions of the constituent minerals plot along the Carbonaceous Chondrite anhydrous mineral line. The spinel grains are uniformly 16O-rich (Δ17O = −22.7 ± 1.7‰, 2SD), while the melilite grains are uniformly 16O-poor (Δ17O = −2.8 ± 1.8‰) irrespective of their akermanite content and thus their relative time of crystallization. The fassaite crystals exhibit growth zoning overprinting poorly-developed sector zoning; they generally grow from Ti-rich to Ti-poor compositions. The fassaite crystals also show continuous variations in Δ17O along the inferred directions of crystal growth, from 16O-poor (Δ17O ∼ −3‰) to 16O-rich (Δ17O ∼ −23‰), covering the full range of oxygen isotopic compositions observed in TS34. The early-crystallized 16O-poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously. The correlation of oxygen isotopic compositions with Ti content in the fassaite imply that the oxygen isotopic composition of the CAI melt evolved from 16O-poor to 16O-rich during fassaite crystallization, presumably due to oxygen isotope exchange with a surrounding 16O-rich nebular gas. Formation of spinel, the liquidus phase in melts of this composition, predates crystallization of all other phases, so its 16O-rich composition is a relic of an earlier stage. Anorthite exhibits oxygen isotopic compositions between Δ17O ∼ −2‰ and −9‰, within the range of those of fassaite, indicating co-crystallization of these two minerals during the earliest to intermediate stage of fassaite growth. The melilite and fassaite yield an 26Al–26Mg mineral isochron with an initial value of (26Al/27Al)0 = (5.003 ± 0.075) × 10−5, corresponding to a relative age of 0.05 ± 0.02 Myr from the canonical Al–Mg age of CAIs. These data demonstrate that both 16O-rich and 16O-poor reservoirs existed in the solar nebula at least ∼0.05 Myr after the birth of the Solar System.

  • young asteroidal fluid activity revealed by absolute age from apatite in Carbonaceous Chondrite
    Nature Communications, 2016
    Co-Authors: Aicheng Zhang, Yangting Lin, Hisayoshi Yurimoto, Naoya Sakamoto, Rucheng Wang
    Abstract:

    Chondritic meteorites formed in the early solar system and may tell us about primary processes at that time. Here, Zhang et al. report an absolute 207Pb/206Pb isochron age (4,450±50 Ma) of apatite from a Carbonaceous Chondrite constraining timing of fluid activity in meteorites.

  • mineralogical characterization of a unique material having heavy oxygen isotope anomaly in matrix of the primitive Carbonaceous Chondrite acfer 094
    Geochimica et Cosmochimica Acta, 2008
    Co-Authors: Yusuke Seto, Naoya Sakamoto, Kiyoshi Fujino, Takashi Kaito, Tetsuo Oikawa, Hisayoshi Yurimoto
    Abstract:

    Abstract We report the mineral compositions and micro-texture of the isotopically anomalous (δ17,18OSMOW ∼ +180‰) Fe–S–Ni–O material recently discovered in matrix of the primitive Carbonaceous Chondrite Acfer 094 [Sakamoto N., Seto Y., Itoh S., Kuramoto K., Fujino K., Nagashima K., Krot A. N. and Yurimoto H. (2007) Oxygen isotope evidence for remnants of the early solar system primordial water. Science 317, 231–233]. Synchrotron radiation X-ray diffraction and transmission electron microscopy studies indicate that this material consists of the symplectitically intergrown magnetite (Fe3O4) and pentlandite (Fe5.7Ni3.3S8) with magnetite/pentlandite volume ratio of ∼2.3. Magnetite forms column-shaped grains (10–30 nm in diameter and 100–200 nm in length); pentlandite occurs as worm-shaped grains or aggregates of grains 100–300 nm in size between magnetite crystals. Although both the X-ray diffraction and electron energy loss spectra support identification of iron oxide as magnetite, the electron diffraction patterns show that magnetite has a weak 3-fold superstructure, possibly due to ordering of vacancies. We infer that the isotopically anomalous symplectite formed by sulfurization and oxidization of metal grains either in the solar nebula or on an icy planetesimal. The intersite cation distribution of pentlandite suggests that timescale of oxidation was no longer than 1000 years.

  • ca al rich inclusions amoeboid olivine aggregates and al rich chondrules from the unique Carbonaceous Chondrite acfer 094 i mineralogy and petrology
    Geochimica et Cosmochimica Acta, 2004
    Co-Authors: Alexander N. Krot, Ian D. Hutcheon, M. I. Petaev, K D Mckeegan, K Keil, T J Fagan, S Sahijpal, Hisayoshi Yurimoto
    Abstract:

    Based on their mineralogy and petrography, ∼200 refractory inclusions studied in the unique Carbonaceous Chondrite, Acfer 094, can be divided into corundum-rich (0.5%), hibonite-rich (1.1%), grossite-rich (8.5%), compact and fluffy Type A (spinel-melilite-rich, 50.3%), pyroxene-anorthite-rich (7.4%), and Type C (pyroxene-anorthite-rich with igneous textures, 1.6%) Ca,Al-rich inclusions (CAIs), pyroxene-hibonite spherules (0.5%), and amoeboid olivine aggregates (AOAs, 30.2%). Melilite in some CAIs is replaced by spinel and Al-diopside and/or by anorthite, whereas spinel-pyroxene assemblages in CAIs and AOAs appear to be replaced by anorthite. Forsterite grains in several AOAs are replaced by low-Ca pyroxene. None of the CAIs or AOAs show evidence for Fe-alkali metasomatic or aqueous alteration. The mineralogy, textures, and bulk chemistry of most Acfer 094 refractory inclusions are consistent with their origin by gas-solid condensation and may reflect continuous interaction with SiO and Mg of the cooling nebula gas. It appears that only a few CAIs experienced subsequent melting. The Al-rich chondrules (ARCs; >10 wt% bulk Al2O3) consist of forsteritic olivine and low-Ca pyroxene phenocrysts, pigeonite, augite, anorthitic plagioclase, ± spinel, FeNi-metal, and crystalline mesostasis composed of plagioclase, augite and a silica phase. Most ARCs are spherical and mineralogically uniform, but some are irregular in shape and heterogeneous in mineralogy, with distinct ferromagnesian and aluminous domains. The ferromagnesian domains tend to form chondrule mantles, and are dominated by low-Ca pyroxene and forsteritic olivine, anorthitic mesostasis, and Fe,Ni-metal nodules. The aluminous domains are dominated by anorthite, high-Ca pyroxene and spinel, occasionally with inclusions of perovskite; have no or little FeNi-metal; and tend to form cores of the heterogeneous chondrules. The cores are enriched in bulk Ca and Al, and apparently formed from melting of CAI-like precursor material that did not mix completely with adjacent ferromagnesian melt. The inferred presence of CAI-like material among precursors for Al-rich chondrules is in apparent conflict with lack of evidence for melting of CAIs that occur outside chondrules, suggesting that these CAIs were largely absent from chondrule-forming region(s) at the time of chondrule formation. This may imply that there are several populations of CAIs in Acfer 094 and that mixing of “normal” CAIs that occur outside chondrules and chondrules that accreted into the Acfer 094 parent asteroid took place after chondrule formation. Alternatively, there may have been an overlap in the CAI- and chondrule-forming regions, where the least refractory CAIs were mixed with Fe-Mg chondrule precursors. This hypothesis is difficult to reconcile with the lack of evidence of melting of AOAs which represent aggregates of the least refractory CAIs and forsterite grains.

M E Zolensky - One of the best experts on this subject based on the ideXlab platform.

  • discovery of primitive co2 bearing fluid in an aqueously altered Carbonaceous Chondrite
    Science Advances, 2021
    Co-Authors: Akira Tsuchiyama, Akira Miyake, Satoshi Okuzumi, Akira Kitayama, Jun Kawano, Kentaro Uesugi, Akihisa Takeuchi, Tsukasa Nakano, M E Zolensky
    Abstract:

    Water is abundant as solid ice in the solar system and plays important roles in its evolution. Water is preserved in Carbonaceous Chondrites as hydroxyl and/or H2O molecules in hydrous minerals, but has not been found as liquid. To uncover such liquid, we performed synchrotron-based x-ray computed nanotomography and transmission electron microscopy with a cryo-stage of the aqueously altered Carbonaceous Chondrite Sutter’s Mill. We discovered CO2-bearing fluid (CO2/H2O > ~0.15) in a nanosized inclusion incorporated into a calcite crystal, appearing as CO2 ice and/or CO2 hydrate at 173 K. This is direct evidence of dynamic evolution of the solar system, requiring the Sutter’s Mill’s parent body to have formed outside the CO2 snow line and later transportation to the inner solar system because of Jupiter’s orbital instability.

  • the isotopic composition of volatiles in the unique bench crater Carbonaceous Chondrite impactor found in the apollo 12 regolith
    Earth and Planetary Science Letters, 2020
    Co-Authors: Romain Tartèse, Yves Marrocchi, M E Zolensky, K H Joy, S Messenger, D Frank, D A Kring
    Abstract:

    Abstract Projectiles striking the Moon have modified its crust and delivered volatile elements to its interior and surface. Direct evidence of impactor origins is recorded by the rare occurrence of sub-cm sized meteorite fragments identified in Apollo samples and lunar meteorites. The Bench Crater meteorite is a millimetre-sized Carbonaceous Chondrite collected in regolith on the rim of Bench impact crater at the Apollo 12 landing site. Transmission electron microscopy has previously shown that Bench Crater contains abundant hydrated silicates, establishing the survivability of hydrated material impacting the lunar surface. To provide further information on the volatile inventory of the Bench Crater meteorite, we report here the isotope compositions of hydrogen, nitrogen, carbon and oxygen. This is the first direct isotopic analysis of meteoritic material delivered to the lunar surface and provides context for volatile and organic element signatures in lunar regolith samples, and the survivability of volatile material delivered to planetary surfaces during impact bombardment. The Bench Crater meteorite is characterised by δD values ranging between −36 ± 40 and 200 ± 40‰, and bulk average δ 13 C of −13 ± 30‰, and δ 15 N of −40 ± 36‰ (all uncertainties at the 2σ confidence level). The oxygen isotope compositions measured in situ in matrix silicates and magnetite in Bench Crater are consistent with those measured in matrix and magnetite in CI and CM Chondrite falls. Altogether, these new H, C, N and O isotope data, coupled to mineralogical and geochemical observations, suggest that Bench Crater may have been derived from an asteroidal parent body not represented in the terrestrial meteorite collection. This is a crucial outcome in the current context of sample-return missions to Carbonaceous asteroids, and more broadly for investigating the flux of material delivered to the Earth-Moon system through time.

  • three dimensional observation and morphological analysis of organic nanoglobules in a Carbonaceous Chondrite using x ray micro tomography
    Geochimica et Cosmochimica Acta, 2013
    Co-Authors: Toru Matsumoto, Akira Tsuchiyama, Kentaro Uesugi, Akihisa Takeuchi, Tsukasa Nakano, Keiko Nakamuramessenger, M E Zolensky
    Abstract:

    Abstract Organic nanoglobules are submicrometer spherical, often hollow organic grains ubiquitously distributed throughout primitive solar materials, such as Carbonaceous Chondrites. Until now, organic nanoglobules have been examined by TEM only after sectioning by ultramicrotomy so it has not been possible to determine whether fluids or mineral grains occur in the hollow cores. H 2 O-rich fluids might be present in hollows of the nanoglobules if they originate from dust particles composed of organic materials and ice prior to or in an early stage of the solar system formation or fluids incorporated into nanoglobules during aqueous alteration on the asteroidal parent body. In order to determine whether or not any fluids or mineral grains are present in the nanoglobules, a Carbonaceous Chondrite sample (Tagish Lake C2 meteorite) was observed non-destructively using synchrotron radiation-based X-ray CT (computed tomography), and then microtomed sections were observed using a transmission electron microscope (TEM). We observed three-dimensional shapes of thirty-eight organic nanoglobules in the meteorite sample. Their size and shape distributions are consistent with a hypothesis that nanoglobules originate from icy dust particles. Nanoglobule candidates observed in CT images were confirmed by the TEM images. However, the presence or absence of fluid could not be judged because CT images of nanoglobules are affected by X-ray refraction. Simulation of CT images by considering X-ray refraction shows that the presence or absence of water in nanoglobules cannot be distinguished with CT images alone. However the outer shapes of nanoglobules can be determined quantitatively and nanoglobules containing silicate cores can be easily identified. The thirty-eight nanoglobules we examined did not have silicate cores.

  • replacement of olivine by serpentine in the Carbonaceous Chondrite nogoya cm2
    Geochimica et Cosmochimica Acta, 2012
    Co-Authors: Michael A Velbel, Eric Tonui, M E Zolensky
    Abstract:

    Abstract Coarse (chondrule and isolated) olivine in some CM Chondrites is replaced by serpentine in both centripetal and meshwork replacement textures. Locally preserved textures formed by partial replacement of coarse olivine by serpentine in the Carbonaceous Chondrite Nogoya (CM2) establish unique associations between each individual mass of serpentine and the specific olivine from which that serpentine formed. Electron probe microanalyses show that the composition of serpentine replacing coarse olivine is uniform throughout all analyzed volumes of Nogoya, and is independent of the composition of the olivine being replaced. If, as previously proposed, late-stage alteration fluids were Mg-rich because Fe-source minerals were depleted in earlier stages, then the uniform Mg-rich composition of the serpentine replacing large silicate grains during advanced stages of alteration may indicate diffusional homogenization of the aqueous solutions over progressively larger spatial scales, enabled by long timescales and previously proposed stagnant or slow-moving fluids. The range of olivine compositions replaced in Nogoya is even larger than previously reported from ALH 81002 (CM2). This militates against hypotheses of strong primary-mineral control on the compositions of alteration products, at least at advanced stages of alteration. The serpentine formed by olivine replacement in Nogoya is more magnesian than the counterpart serpentine replacing all anhydrous primary silicates in ALH 81002. This intermeteorite heterogeneity of replacement-serpentine composition between ALH 81002 and Nogoya indicates that the aqueous solutions in which the olivine-serpentine replacement reactions occurred were of different compositions in the two different CM parent-body volumes sampled by ALH 81002 and Nogoya. The more magnesian character of serpentines in Nogoya than in ALH 81002 indicates that the Nogoya aqueous-alteration environment was even more highly evolved toward Mg-rich solutions than the environment indicated by the composition of the serpentine in ALH 81002. Persistence of primary-silicate remnants within centripetal and meshwork serpentine indicates that either the aqueous alteration episodes in the parent-body volumes represented by individual meteorites were too short to allow complete replacement of olivine by serpentine, or one or more reactants (most likely water) were completely consumed before the coarse primary silicate was completely replaced. Seemingly incompatible arguments for and against primary-mineral control of serpentine composition during CM Chondrite alteration may be reconciled by considering the different grain sizes and reaction timescales that likely existed in different textural settings.

  • Carbonaceous Chondrite rich howardites the potential for hydrous lithologies on the hed parent
    42nd Lunar and Planetary Science Conference, 2011
    Co-Authors: Jason S Herrin, David W. Mittlefehldt, M E Zolensky, J A Cartwright, D K Ross
    Abstract:

    Howardites, eucrites, and diogenites, collectively referred to as the "HED's", are a clan of meteorites thought to represent three different lithologies from a common parent body. Collectively they are the most abundant type of aChondrites in terrestrial collections. Eucrites are crustal basalts and gabbros, diogenites are mostly orthopyroxenites and are taken to represent lower crust or upper mantle materials, and howardites are mixed breccias containing both lithologies and are generally regarded as derived from the regolith or near-surface. The presence of exogenous chondritic material in howardite breccias has long been recognized. As a group, howardites exhibit divergence in bulk chemistry from what would be produced by mixing of diogenite and eucrite end-members exclusively, a phenomenon most evident in elevated concentrations of siderophile elements. Despite this chemical evidence for chondritic input in howardite breccias, chondritic clasts have only been identified in a minority of samples, and typically at levels of only a few percent. Three recent Antarctic howardite finds, the paired Mt. Pratt (PRA) 04401 and PRA 04402 and Scott Glacier (SCO) 06040, are notable for their high proportion of Carbonaceous Chondrite clasts. PRA 04401 is particularly well-endowed, with large chondritic clasts occupying more than half of the modal area of the sections we examined. Previously only a few percent chondritic clasts had been observed to occur in howardites. PRA 04401 is the most Chondrite-rich howardite known

Kazushige Tomeoka - One of the best experts on this subject based on the ideXlab platform.

  • nepheline and sodalite in chondrules of the ningqiang Carbonaceous Chondrite implications for a genetic relationship with those in the matrix
    Geochimica et Cosmochimica Acta, 2017
    Co-Authors: Megumi Matsumoto, Kazushige Tomeoka, Yusuke Seto
    Abstract:

    Abstract Ningqiang is an ungrouped Carbonaceous Chondrite that has a chemical and mineralogical affinity to CV3 Chondrites. The Ningqiang matrix has distinctly higher abundances of Na, K, and Al than CV3 matrices. A recent study by Matsumoto et al. (2014) revealed that the major proportions of these elements can be attributed to the presence of nepheline and sodalite. Scanning electron microscopy revealed that all of the Ningqiang chondrules studied show abundant evidence of extensive Na–Fe metasomatism. Only a small proportion of the chondrules contain primary mesostases in their cores, but the mesostases in their mantles were replaced by fine grains of nepheline, sodalite, Fe-rich olivine, and hedenbergite. The mesostases in the majority of the chondrules were completely replaced by fine grains of the same secondary minerals. Most opaque nodules were also largely replaced by various fine-grained secondary minerals. Nepheline/sodalite form veins penetrating the primary mesostases, providing evidence that aqueous fluids were involved in the alteration reactions. The nepheline/sodalite in the mesostases contain various amounts of inclusions of Fe-rich olivine, diopside, hedenbergite, Fe sulfides, and magnetite. The mineralogical features of the nepheline/sodalite in the mesostases are almost identical to those in the meteorite matrix. These results suggest that a significant fraction of the nepheline/sodalite grains in the Ningqiang matrix originated from the nepheline/sodalite produced in chondrules and refractory inclusions and that they were disaggregated and mixed into the matrix. These processes can be explained consistently by the model of the dynamic formation of Chondrite lithology in a parent body proposed by Tomeoka and Ohnishi (2015). We suggest that after a Ningqiang precursor with a CV3-like lithology was metasomatized, it was fragmented, causing the disaggregation of the fine-grained host matrix and the fine-grained altered mesostases, including nepheline/sodalite, and opaque nodules in the chondrules. The chondrules were thereby separated into multiple fragments. Subsequently, during transportation in a fluidized state, all these materials were homogenously mixed together and later underwent accumulation and lithification.

  • nepheline and sodalite in the matrix of the ningqiang Carbonaceous Chondrite implications for formation through parent body processes
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Megumi Matsumoto, Kazushige Tomeoka, Akira Miyake, Yusuke Seto, Mitsuhiro Sugita
    Abstract:

    Abstract Ningqiang is an ungrouped Carbonaceous Chondrite that chemically and petrologically resembles CV3 Chondrites. The matrix of Ningqiang shows much higher abundances of Na, K, and Al by factors of 4.4, 2.7, and 1.6, respectively, than in CV3 Chondrites. Our scanning and transmission electron microscope observations and synchrotron radiation X-ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite. Rietveld refinement of X-ray diffraction data shows that the feldspathoids constitute 7.7 vol.% of all crystalline phases in the matrix. Nepheline and sodalite occur mostly as discrete, equidimensional grains 2–5 μm in diameter that are dispersed homogeneously in the matrix. Most of the grains contain inclusions of Fe-rich olivine and minor Ca pyroxene, magnetite, troilite, and pentlandite. Despite the high abundances of Na, K, and Al in the matrix of Ningqiang, the bulk meteorite abundances of these elements are comparable to those of the CV group (e.g., Rubin et al., 1988). This means that the chondrules, which constitute a major proportion of the volume other than the matrix in Ningqiang, are depleted in Na, K, and Al. In fact, our analyses and observations show that the chondrules in Ningqiang overall contain very small amounts of these elements. Our interpretation of these findings suggests that nepheline and sodalite in the Ningqiang matrix were originally formed by Na-metasomatism of the chondrules and Ca–Al-rich inclusions in the meteorite parent body. Afterward, they were likely disaggregated and scattered into the matrix. However, it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite. Hence, we suggest that the Ningqiang meteorite underwent these processes before final lithification.

  • a hydrated clast in the mokoia cv3 Carbonaceous Chondrite evidence for intensive aqueous alteration in the cv parent body
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Kazushige Tomeoka, Ichiro Ohnishi
    Abstract:

    Abstract We report the discovery of a highly hydrated clast in the Mokoia CV3 Carbonaceous Chondrite that contains eight chondrules and one amoeboid olivine inclusion (AOI), embedded in a matrix dominated by hydrous phyllosilicates. Anhydrous silicates in the chondrules and AOI were extensively replaced by phyllosilicates. The matrix has a composition intermediate between saponite and serpentine and contains abundant framboidal magnetite, being similar to the matrices of the CI Chondrites. The mineralogy and texture indicate that the clast resulted from intensive aqueous alteration of a precursor equivalent to the host Mokoia meteorite, and it can be regarded as the CV2-type lithology. The results indicate that there was in fact an extremely wet region within the Mokoia parent body and that this clast escaped subsequent thermal metamorphism. This clast reveals abundant evidence of progressive and dynamic aqueous alteration processes. The chondrules were replaced inward from their margins, and the alteration products were disaggregated and mixed into the matrix; as a result, the chondrules increasingly became smaller in size and irregular in shape. Some of the chondrules were separated into pieces. The results indicate that a major proportion of the matrix materials were produced by the alteration of chondrules and inclusions and that there was a stage in which the alteration products and the original matrix material were extensively and uniformly mixed together. The presence of the clast supports a previously proposed model, which suggests that hydrated chondrules, inclusions, and the rims surrounding them in the host Mokoia Chondrite are clasts produced by brecciation within a wet region of the parent body and that they were subsequently transported and incorporated into the dry matrix.

  • Experimental shock metamorphism of the Murchison CM Carbonaceous Chondrite
    Geochimica et Cosmochimica Acta, 1999
    Co-Authors: Kazushige Tomeoka, Yasuhiro Yamahana, Toshimori Sekine
    Abstract:

    Abstract A series of shock-recovery experiments were carried out on the Murchison CM Carbonaceous Chondrite by using a single-stage propellant gun. The Murchison samples were shocked in nine experiments at peak pressures from 4 to 49 GPa. The recovered samples were studied in detail by using an optical microscope, a scanning electron microscope and an electron-probe microanalyzer. Chondrules are flattened in the plane of the shock front at 4 to 30 GPa. The mean aspect ratio of chondrules increases from 1.17 to 1.57 roughly in proportion to the intensity of shock pressure up to ∼25 GPa. At 25 to 30 GPa, the mean aspect ratio does not increase further, and chondrules show increasingly more random orientations and degrade their preferred orientations, and at ∼35 GPa, they are extensively disrupted. Most coarse grains of olivine and pyroxene are irregularly fractured, fracture density increases with increasing shock pressure and at ∼30 GPa almost all are thoroughly fractured with subgrains of Local shock melting occurs as melt veins and pockets at 20 to 30 GPa. Fracture-filling veins of fine grains of matrix are also produced at 25 to 30 GPa. The melts and the fine grains seem to result mainly from frictional heating due to displacement along fractures. At ∼35 GPa, melting occurs pervasively throughout the matrix. The melts are mainly produced from the matrix; however, they are consistently more enriched in Fe, S, and Ca, which indicates that these elements are selectively incorporated into the melts. The melts contain tiny spherules of Fe-Ni metal, Fe sulfide, and numerous vesicles. At 49 GPa, the matrix is totally melted and coarse grains of olivine are partially melted. The melts contain much larger vesicles (50–300 μm in diameter) than those in the samples shocked at lower pressures, which indicates that much more intense devolatilization and gas expansion took place. For the purpose of comparing shock thermal effects between the experimentally shocked samples and naturally shocked targets (surface materials in the Murchison parent body), we calculated internal energy increase for compression by multiple shock wave reflections (experimental case) and for compression by a single shock wave (natural case). The results suggest that postshock thermal effects observed at each experiment may be attained by impact on the natural targets at a considerably lower shock pressure than the peak shock pressure. From the results of our experiments and calculations, we conclude that if the Murchison parent body were shocked on the surface at pressures higher than ∼25 GPa, shocked material would probably undergo drastic increase in the degree of comminution and simultaneous generation of strong expansive forces on pressure release. Thus the results support the hypothesis of Scott et al. (1992) that volatile-rich Carbonaceous Chondrites shocked above 20 to 30 GPa escaped from the parent body and formed particles that are too small to survive as meteorites.