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Noriko T Kita - One of the best experts on this subject based on the ideXlab platform.

  • oxygen isotope systematics of Chondrule olivine pyroxene and plagioclase in one of the most pristine cv3red chondrites northwest africa 8613
    Meteoritics & Planetary Science, 2019
    Co-Authors: Andreas Hertwig, Makoto Kimura, Celine Defouilloy, Noriko T Kita
    Abstract:

    : We performed in situ oxygen three-isotope measurements of Chondrule olivine, pyroxenes, and plagioclase from the newly described CVRed chondrite NWA 8613. Additionally, oxygen isotope ratios of plagioclase in Chondrules from the Kaba CV3OxB chondrite were determined to enable comparisons of isotope ratios and degree of alteration of Chondrules in both CV lithologies. NWA 8613 was affected by only mild thermal metamorphism. The majority of oxygen isotope ratios of olivine and pyroxenes plot along a slope-1 line in the oxygen three-isotope diagram, except for a type II and a remolten barred olivine Chondrule. When isotopic relict olivine is excluded, olivine, low- and high-Ca pyroxenes are indistinguishable regarding Δ17O values. Conversely, plagioclase in Chondrules from NWA 8613 and Kaba plot along mass-dependent fractionation lines. Oxygen isotopic disequilibrium between phenocrysts and plagioclase was caused probably by exchange of plagioclase with 16O-poor fluids on the CV parent body. Based on an existing oxygen isotope mass balance model, possible dust enrichment and ice enhancement factors were estimated. Type I Chondrules from NWA 8613 possibly formed at moderately high dust enrichment factors (50× to 150× CI dust relative to Solar abundances); estimates for water ice in the Chondrule precursors range from 0.2 to 0.6× the nominal amount of ice in dust of CI composition. Findings agree with results from an earlier study on oxygen isotopes in Chondrules of the Kaba CV chondrite, providing further evidence for a relatively dry and only moderately high dust-enriched disk in the CV Chondrule-forming region.

  • the 26al 26mg systematics of feo rich Chondrules from acfer 094 two Chondrule generations distinct in age and oxygen isotope ratios
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: A T Hertwig, Takayuki Ushikubo, Makoto Kimura, C Defouilloy, Noriko T Kita
    Abstract:

    Abstract The 26Al-26Mg ages of FeO-rich (type II) Chondrules from Acfer 094, one of the least thermally metamorphosed carbonaceous chondrites, were determined by SIMS analysis of plagioclase and olivine/pyroxene using a radio frequency (RF) plasma oxygen ion source. In combination with preexisting 26Al-26Mg ages of FeO-poor (type I) Chondrules, the maximum range of formation ages recorded in Chondrules from a single meteorite is determined to help provide constraints on models of material transport in the proto-planetary disk. We also report new SIMS oxygen three-isotope analyses of type II Chondrules in Acfer 094. All but one of the plagioclase analyses show resolvable excesses in 26Mg and isochron regressions yield initial 26Al/27Al ratios of type II Chondrules that range from (3.62 ± 0.86) × 10−6 to (9.3 ± 1.1) × 10−6, which translates to formation ages between 2.71 −0.22/+0.28 Ma and 1.75 −0.11/+0.12 Ma after CAI. This overall range is indistinguishable from that determined for type I Chondrules in Acfer 094. The initial 26Al/27Al ratio of the oldest type II Chondrule is resolved from that of all other type II Chondrules in Acfer 094. Importantly, the oldest type I Chondrule and the oldest type II Chondrule in Acfer 094 possess within analytical error indistinguishable initial 26Al/27Al ratios and Δ17O values of ∼0‰. Ages and oxygen isotope ratios clearly set these two Chondrules apart from all other Chondrules in Acfer 094. It is therefore conceivable that the formation region of these two Chondrules differs from that of other Chondrules and in turn suggests that Acfer 094 contains two distinct Chondrule generations.

  • oxygen isotope systematics of Chondrules in the murchison cm2 chondrite and implications for the co cm relationship
    Geochimica et Cosmochimica Acta, 2018
    Co-Authors: N Chaumard, C Defouilloy, Noriko T Kita
    Abstract:

    High-precision oxygen three-isotope measurements of olivine and pyroxene were performed on 29 Chondrules in the Murchison CM2 chondrite by secondary ion mass spectrometry (SIMS). The oxygen isotope ratios of analyzed Chondrules all plot very close to the primitive Chondrule minerals (PCM) line. In each of 24 Chondrules, the olivine and/or pyroxene grains analyzed show indistinguishable oxygen isotope ratios. Exceptions are minor occurrences of isotopically distinguished relict olivine grains, which were found in nine Chondrules. The isotope homogeneity of these phenocrysts is consistent with a co-magmatic crystallization of olivine and pyroxene from the final Chondrule melts and a significant oxygen isotope exchange between the ambient gas and the melts. Homogeneous type I Chondrules with Mg#'s of 98.9-99.5 have host Chondrule Δ17O values ranging from -6.0‰ to -4.1‰, with one exception (Δ17O: -1.2‰; Mg#: 99.6). Homogeneous Chondrules with Mg#'s 0%) and at dust enrichments of ~300-2000×. Regarding the Mg# and oxygen isotope ratios, the Chondrule populations sampled by CM and CO chondrites are similar and indistinguishable. The similarity of these 16O-rich components in CO and CM chondrites is also supported by the common Fe/Mn ratio of olivine in type II Chondrules. Although they accreted similar high-temperature silicates, CO chondrites are anhydrous compared to CM chondrites, suggesting they derived from different parent bodies formed inside and outside the snow line, respectively. If Chondrules in CO and CM chondrites formed at the same disk locations but the CM parent body accreted later than the CO parent body, the snow line might have crossed the the common Chondrule-forming region towards the Sun between the time of the CO and CM parent bodies accretion.

  • oxygen isotope ratios of feo poor Chondrules in cr3 chondrites influence of dust enrichment and h2o during Chondrule formation
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Travis J Tenner, Michael K. Weisberg, Daisuke Nakashima, Takayuki Ushikubo, Noriko T Kita
    Abstract:

    Abstract We present detailed electron microprobe analyses and oxygen three-isotope measurements by high precision secondary ion mass spectrometry on 45 type I (FeO-poor) Chondrules/fragments and 3 type II (FeO-rich) Chondrule fragments from Meteorite Hills 00426 and Queen Alexandra Range 99177, two of the most primitive CR3 chondrites. Type I Chondrules/fragments have Mg#’s (defined as the Mg# of constituent olivine and/or low-Ca pyroxene) ranging from 94.2 to 99.2; type II Chondrule fragments have Mg#’s of 53–63. Oxygen three-isotope measurements plot on the slope ∼1 primitive Chondrule mineral (PCM) line. Within Chondrules, Δ 17 O (=δ 17 O–0.52 × δ 18 O) values of coexisting olivine, pyroxene, and plagioclase are homogeneous, with propagated uncertainties of 0.3‰. This indicates each phase crystallized from the final Chondrule melt, and that efficient oxygen isotope exchange occurred between ambient gas and Chondrule melt. Among type I Chondrules there is a well-defined increase in Δ 17 O, from –5.9‰ to ∼−1‰, as Mg#’s decrease from 99.2 to ∼96; type II Chondrule fragments are comparatively 16 O-poor (Δ 17 O: ∼0.2–0.6‰). The relationship between Mg# and Δ 17 O among type I Chondrules confirms that addition of a 16 O-poor oxidizing agent to the highest Mg# Chondrule precursors resulted in forming lower Mg# CR Chondrules. Using aspects of existing equilibrium condensation models and a mass balance we estimate that type I CR Chondrules formed at dust enrichments of 100–200×, from dusts with 0–0.8 times the atomic abundance of ice, relative to CI dust. The type II Chondrule fragments are predicted to have formed at CI dust enrichments near 2500×.

  • oxygen isotope systematics of Chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs
    Geochimica et Cosmochimica Acta, 2013
    Co-Authors: Travis J Tenner, Takayuki Ushikubo, Noriko T Kita, E Kurahashi, Hiroko Nagahara
    Abstract:

    High-precision oxygen three-isotope measurements of olivine and pyroxene were performed on 33 Chondrules in the Yamato 81020 CO3.0 chondrite by secondary ion mass spectrometry. In Chondrules where oxygen isotopes were measured in both olivine and pyroxene, the majority of grains have similar values, indicating co-magmatic crystallization. However, many Chondrules contain relict grains with unique oxygen isotope ratios. A striking feature of Yamato 81020 Chondrules is a bimodal distribution of oxygen isotope ratios, as those with Mg# >97 phenocrysts range in Δ17O from −4.8‰ to −6.5‰ (“−5.5‰” group), and those with Mg# 96–36 phenocrysts have Δ17O values of −2.1‰ to −3.0‰ (“−2.5‰” group). A single Mg# 99.6 barred olivine Chondrule has a Δ17O of −3.3‰. We discuss that Δ17O ∼−5.5‰ Chondrules are derivative of a reservoir with limited dust enrichment (100× Solar System), which yielded a relatively reduced Chondrule-forming environment. In contrast, the Δ17O ∼−2.5‰ Chondrules may have been influenced by 16O-poor H2O ice that sublimed and then homogenized with precursor material. The addition of H2O, when combined with high dust enrichment (1000× Solar System) and greater bulk Fe content, could have induced an oxidized environment at high temperatures, forming Mg# 96–36 Chondrules. Among the 33 Chondrules studied, the Al–Mg relative ages of 20 had been obtained previously. Comparing the oxygen isotope ratios and the 26Al ages of these Chondrules, it is likely that the “−5.5‰” and “−2.5‰” oxygen isotope reservoirs existed contemporaneously. This implies that the snow line was spatially fixed during Chondrule formation, and separated the CO chondrite accretion region into two distinct volumes of precursors.

Takayuki Ushikubo - One of the best experts on this subject based on the ideXlab platform.

  • extended Chondrule formation intervals in distinct physicochemical environments evidence from al mg isotope systematics of cr chondrite Chondrules with unaltered plagioclase
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: Travis J Tenner, Daisuke Nakashima, Takayuki Ushikubo, Makoto Kimura, Naotaka Tomioka, Michael K. Weisberg
    Abstract:

    Abstract Al-Mg isotope systematics of twelve FeO-poor (type I) Chondrules from CR chondrites Queen Alexandra Range 99177 and Meteorite Hills 00426 were investigated by secondary ion mass spectrometry (SIMS). Five Chondrules with Mg#’s of 99.0 to 99.2 and Δ 17 O of −4.2‰ to −5.3‰ have resolvable excess 26 Mg. Their inferred ( 26 Al/ 27 Al) 0 values range from (3.5 ± 1.3) × 10 −6 to (6.0 ± 3.9) × 10 −6 . This corresponds to formation times of 2.2 (–0.5/+1.1) Myr to 2.8 (−0.3/+0.5) Myr after CAIs, using a canonical ( 26 Al/ 27 Al) 0 of 5.23 × 10 -5 , and assuming homogeneously distributed 26 Al that yielded a uniform initial 26 Al/ 27 Al in the Solar System. Seven Chondrules lack resolvable excess 26 Mg. They have lower Mg#’s (94.2 to 98.7) and generally higher Δ 17 O (−0.9‰ to −4.9‰) than Chondrules with resolvable excess 26 Mg. Their inferred ( 26 Al/ 27 Al) 0 upper limits range from 1.3 × 10 −6 to 3.2 × 10 −6 , corresponding to formation >2.9 to >3.7 Myr after CAIs. Al-Mg isochrons depend critically on Chondrule plagioclase, and several characteristics indicate the Chondrule plagioclase is unaltered: (1) SIMS 27 Al/ 24 Mg depth profile patterns match those from anorthite standards, and SEM/EDS of Chondrule SIMS pits show no foreign inclusions; (2) transmission electron microscopy (TEM) reveals no nanometer-scale micro-inclusions and no alteration due to thermal metamorphism; (3) oxygen isotopes of Chondrule plagioclase match those of coexisting olivine and pyroxene, indicating a low extent of thermal metamorphism; and (4) electron microprobe data show Chondrule plagioclase is anorthite-rich, with excess structural silica and high MgO, consistent with such plagioclase from other petrologic type 3.00-3.05 chondrites. We conclude that the resolvable ( 26 Al/ 27 Al) 0 variabilities among Chondrules studied are robust, corresponding to a formation interval of at least 1.1 Myr. Using relationships between Chondrule ( 26 Al/ 27 Al) 0 , Mg#, and Δ 17 O, we interpret spatial and temporal features of dust, gas, and H 2 O ice in the FeO-poor Chondrule-forming environment. Mg# ≥ 99, Δ 17 O ∼−5‰ Chondrules with resolvable excess 26 Mg initially formed in an environment that was relatively anhydrous, with a dust-to-gas ratio of ∼100×. After these Chondrules formed, we interpret a later influx of 16 O-poor H 2 O ice into the environment, and that dust-to-gas ratios expanded (100× to 300×). This led to the later formation of more oxidized Mg# 94-99 Chondrules with higher Δ 17 O (−5‰ to –1‰), with low ( 26 Al/ 27 Al) 0 , and hence no resolvable excess 26 Mg. We refine the mean CR chondrite Chondrule formation age via mass balance, by considering that Mg# ≥ 99 Chondrules generally have resolved positive ( 26 Al/ 27 Al) 0 and that Mg# 26 Mg, implying lower ( 26 Al/ 27 Al) 0 . We obtain a mean Chondrule formation age of 3.8 ± 0.3 Myr after CAIs, which is consistent with Pb-Pb and Hf-W model ages of CR chondrite Chondrule aggregates. Overall, this suggests most CR chondrite Chondrules formed immediately before parent body accretion.

  • the 26al 26mg systematics of feo rich Chondrules from acfer 094 two Chondrule generations distinct in age and oxygen isotope ratios
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: A T Hertwig, Takayuki Ushikubo, Makoto Kimura, C Defouilloy, Noriko T Kita
    Abstract:

    Abstract The 26Al-26Mg ages of FeO-rich (type II) Chondrules from Acfer 094, one of the least thermally metamorphosed carbonaceous chondrites, were determined by SIMS analysis of plagioclase and olivine/pyroxene using a radio frequency (RF) plasma oxygen ion source. In combination with preexisting 26Al-26Mg ages of FeO-poor (type I) Chondrules, the maximum range of formation ages recorded in Chondrules from a single meteorite is determined to help provide constraints on models of material transport in the proto-planetary disk. We also report new SIMS oxygen three-isotope analyses of type II Chondrules in Acfer 094. All but one of the plagioclase analyses show resolvable excesses in 26Mg and isochron regressions yield initial 26Al/27Al ratios of type II Chondrules that range from (3.62 ± 0.86) × 10−6 to (9.3 ± 1.1) × 10−6, which translates to formation ages between 2.71 −0.22/+0.28 Ma and 1.75 −0.11/+0.12 Ma after CAI. This overall range is indistinguishable from that determined for type I Chondrules in Acfer 094. The initial 26Al/27Al ratio of the oldest type II Chondrule is resolved from that of all other type II Chondrules in Acfer 094. Importantly, the oldest type I Chondrule and the oldest type II Chondrule in Acfer 094 possess within analytical error indistinguishable initial 26Al/27Al ratios and Δ17O values of ∼0‰. Ages and oxygen isotope ratios clearly set these two Chondrules apart from all other Chondrules in Acfer 094. It is therefore conceivable that the formation region of these two Chondrules differs from that of other Chondrules and in turn suggests that Acfer 094 contains two distinct Chondrule generations.

  • oxygen isotope ratios of feo poor Chondrules in cr3 chondrites influence of dust enrichment and h2o during Chondrule formation
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Travis J Tenner, Michael K. Weisberg, Daisuke Nakashima, Takayuki Ushikubo, Noriko T Kita
    Abstract:

    Abstract We present detailed electron microprobe analyses and oxygen three-isotope measurements by high precision secondary ion mass spectrometry on 45 type I (FeO-poor) Chondrules/fragments and 3 type II (FeO-rich) Chondrule fragments from Meteorite Hills 00426 and Queen Alexandra Range 99177, two of the most primitive CR3 chondrites. Type I Chondrules/fragments have Mg#’s (defined as the Mg# of constituent olivine and/or low-Ca pyroxene) ranging from 94.2 to 99.2; type II Chondrule fragments have Mg#’s of 53–63. Oxygen three-isotope measurements plot on the slope ∼1 primitive Chondrule mineral (PCM) line. Within Chondrules, Δ 17 O (=δ 17 O–0.52 × δ 18 O) values of coexisting olivine, pyroxene, and plagioclase are homogeneous, with propagated uncertainties of 0.3‰. This indicates each phase crystallized from the final Chondrule melt, and that efficient oxygen isotope exchange occurred between ambient gas and Chondrule melt. Among type I Chondrules there is a well-defined increase in Δ 17 O, from –5.9‰ to ∼−1‰, as Mg#’s decrease from 99.2 to ∼96; type II Chondrule fragments are comparatively 16 O-poor (Δ 17 O: ∼0.2–0.6‰). The relationship between Mg# and Δ 17 O among type I Chondrules confirms that addition of a 16 O-poor oxidizing agent to the highest Mg# Chondrule precursors resulted in forming lower Mg# CR Chondrules. Using aspects of existing equilibrium condensation models and a mass balance we estimate that type I CR Chondrules formed at dust enrichments of 100–200×, from dusts with 0–0.8 times the atomic abundance of ice, relative to CI dust. The type II Chondrule fragments are predicted to have formed at CI dust enrichments near 2500×.

  • oxygen isotope systematics of Chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs
    Geochimica et Cosmochimica Acta, 2013
    Co-Authors: Travis J Tenner, Takayuki Ushikubo, Noriko T Kita, E Kurahashi, Hiroko Nagahara
    Abstract:

    High-precision oxygen three-isotope measurements of olivine and pyroxene were performed on 33 Chondrules in the Yamato 81020 CO3.0 chondrite by secondary ion mass spectrometry. In Chondrules where oxygen isotopes were measured in both olivine and pyroxene, the majority of grains have similar values, indicating co-magmatic crystallization. However, many Chondrules contain relict grains with unique oxygen isotope ratios. A striking feature of Yamato 81020 Chondrules is a bimodal distribution of oxygen isotope ratios, as those with Mg# >97 phenocrysts range in Δ17O from −4.8‰ to −6.5‰ (“−5.5‰” group), and those with Mg# 96–36 phenocrysts have Δ17O values of −2.1‰ to −3.0‰ (“−2.5‰” group). A single Mg# 99.6 barred olivine Chondrule has a Δ17O of −3.3‰. We discuss that Δ17O ∼−5.5‰ Chondrules are derivative of a reservoir with limited dust enrichment (100× Solar System), which yielded a relatively reduced Chondrule-forming environment. In contrast, the Δ17O ∼−2.5‰ Chondrules may have been influenced by 16O-poor H2O ice that sublimed and then homogenized with precursor material. The addition of H2O, when combined with high dust enrichment (1000× Solar System) and greater bulk Fe content, could have induced an oxidized environment at high temperatures, forming Mg# 96–36 Chondrules. Among the 33 Chondrules studied, the Al–Mg relative ages of 20 had been obtained previously. Comparing the oxygen isotope ratios and the 26Al ages of these Chondrules, it is likely that the “−5.5‰” and “−2.5‰” oxygen isotope reservoirs existed contemporaneously. This implies that the snow line was spatially fixed during Chondrule formation, and separated the CO chondrite accretion region into two distinct volumes of precursors.

  • primordial oxygen isotope reservoirs of the solar nebula recorded in Chondrules in acfer 094 carbonaceous chondrite
    Geochimica et Cosmochimica Acta, 2012
    Co-Authors: Takayuki Ushikubo, Noriko T Kita, Makoto Kimura, John W Valley
    Abstract:

    Abstract Highly precise and accurate ion microprobe analyses of oxygen three-isotope ratios in Chondrules from the Acfer 094, one of the most primitive carbonaceous chondrites, show that Chondrules preserve evidence for oxygen isotope heterogeneity in Chondrule-forming regions of the solar nebula. Identical Δ 17 O values in most minerals and glass within each Chondrule indicate that the oxygen isotope ratio in Chondrule melt did not change during or after crystallization. Nearly half of the Chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same Chondrule. Most Chondrules in Acfer 094 can be classified into two oxygen isotope groups (Δ 17 O ∼ −2‰ and Δ 17 O ∼ −5‰) indicating that the final melting of Chondrules occurred within two distinct oxygen isotope reservoirs, probably representing the local protoplanetary disk immediately before planetesimal formation. One of these reservoirs (Δ 17 O ∼ −2‰) is observed from Chondrules in other carbonaceous chondrites and from crystalline silicates in comet Wild 2, suggesting that crystalline silicates formed in an oxygen isotope reservoir of Δ 17 O ∼ −2‰ were widely distributed in the outer asteroid belt and throughout the outer solar nebula. Oxygen three-isotope ratios of minerals in Chondrules from Acfer 094 are distributed along a newly defined Primitive Chondrule Minerals (PCM) line, which has slope ∼1 [δ 17 O = (0.987 ± 0.013) × δ 18 O − (2.70 ± 0.11)] and intersects the terrestrial fractionation line at δ 18 O = 5.8 ± 0.4‰. These data are distinct from, and plot between, the CCAM, and Young and Russell lines. The PCM line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the Earth.

Emmanuel Jacquet - One of the best experts on this subject based on the ideXlab platform.

  • collisions and compositional variability in Chondrule forming events
    arXiv: Earth and Planetary Astrophysics, 2021
    Co-Authors: Emmanuel Jacquet
    Abstract:

    Compound Chondrules, i.e. Chondrules fused together, make a powerful probe of the density and compositional diversity in Chondrule-forming environments, but their abundance among the dominating porphyritic textures may have been drastically underestimated. I report herein microscopic observations and LA-ICP-MS analyses of lobate Chondrules in the CO3 chondrites Miller Range 07193 and 07342. Lobes in a given Chondrule show correlated volatile and moderately volatile element abundances but refractory element concentrations are essentially independent. This indicates that they formed by the collision of preexisting droplets whose refractory elements behaved in closed system, while their more volatile elements were buffered by the same gaseous medium. The presence of lobes would otherwise be difficult to explain, as surface tension should have rapidly imposed a spherical shape at the temperature peak. In fact, since most Chondrules across chondrite groups are nonspherical, a majority are probably compounds variously relaxed toward sphericity. The lack of correlation of refractory elements between conjoined compound Chondrule components is inconsistent with derivation of Chondrules from the disruption of homogenized melt bodies as in impact scenarios and evokes rather the melting of independent mm-size nebular aggregates. Yet a "nebular" setting for Chondrule formation would need to involve not only increased solid concentration, e.g. by settling to the midplane, but also a boost in relative velocities between droplets during Chondrule-forming events to account for observed compound Chondrule frequencies .

  • Oxygen isotopic diversity of Chondrule precursors and the nebular origin of Chondrules
    Earth and Planetary Science Letters, 2018
    Co-Authors: Yves Marrocchi, Johan Villeneuve, Valentina G. Batanova, Laurette Piani, Emmanuel Jacquet
    Abstract:

    Abstract FeO-poor (type I) porphyritic Chondrules formed by incomplete melting of solid dust precursors via a yet-elusive mechanism. Two settings are generally considered for their formation: (i) a nebular setting where primordial solids were melted, e.g. by shock waves propagating through the gas and (ii) a collisional planetary setting. Here we report a method combining high-current electron microprobe X-ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from Chondrule precursors. We find that these olivine crystals are Ca–Al–Ti-poor relative to host olivine crystals. Their variable Δ 17 O, even in individual Chondrule, is inconsistent with derivation from planetary interiors as previously argued from 120 ° triple junctions also exhibited by the Chondrules studied herein. This indicates that Chondrule precursors correspond to solid nebular condensates formed under changing physical conditions. We propose that porphyritic Chondrules formed during gas-assisted melting of nebular condensates comprising relict olivine grains with varying Δ 17 O values and Ca–Al–Ti-rich minerals such as those observed within amoeboid olivine aggregates. Incomplete melting of Chondrule precursors produced Ca–Al–Ti-rich melts (CAT-melts), allowing subsequent crystallization of Ca–Al–Ti-rich host olivine crystals via epitaxial growth on relict olivine grains. Incoming MgO and SiO from the gas phase induced (i) the dilution of CAT-melts, as attested by the positive Al–Ti correlation observed in Chondrule olivine crystals, and (ii) buffering of the O-isotope compositions of Chondrules, as recorded by the constant Δ 17 O values of host olivine grains. The O-isotopic compositions of host olivine grains are Chondrule-specific, suggesting that Chondrules formed in an array of environments of the protoplanetary disk with different Δ 17 O values, possibly due to variable solid/gas mixing ratios.

  • Chondrule Transport in Protoplanetary Disks
    arXiv: Earth and Planetary Astrophysics, 2015
    Co-Authors: Aaron Z. Goldberg, James E. Owen, Emmanuel Jacquet
    Abstract:

    Chondrule formation remains one of the most elusive early Solar System events. Here, we take the novel approach of employing numerical simulations to investigate Chondrule origin beyond purely cosmochemical methods. We model the transport of generically-produced Chondrules and dust in a 1D viscous protoplanetary disk model, in order to constrain the Chondrule formation events. For a single formation event we are able to match analytical predictions of the memory Chondrule and dust populations retain of each other (complementarity), finding that a large mass accretion rate ($\gtrsim 10^{-7}$~M$_\odot$~yr$^{-1}$) allows for delays on the order of the disk's viscous timescale between Chondrule formation and chondrite accretion. Further, we find older disks to be severely diminished of Chondrules, with accretion rates $\lesssim 10^{-9}$~M$_\odot$~yr$^{-1}$ for nominal parameters. We then characterize the distribution of Chondrule origins in both space and time, as functions of disk parameters and Chondrule formation rates, in runs with continuous Chondrule formation and both static and evolving disks. Our data suggest that these can account for the observed diversity between distinct chondrite classes, if some diversity in accretion time is allowed for.

  • trace element geochemistry of ordinary chondrite Chondrules the type i type ii Chondrule dichotomy
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Emmanuel Jacquet, Olivier Alard, Matthieu Gounelle
    Abstract:

    We report trace element concentrations of silicate phases in Chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine ∼10 K/h) than type I Chondrules. Appreciable Na concentrations (3–221 ppm) are measured in olivine from both Chondrule types; type II Chondrules seem to have behaved as closed systems, which may require Chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II Chondrule forming regions may explain the higher oxygen fugacities they record compared to type I Chondrules. Type I and type II Chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that Chondrule formation models must account for.

  • Trace element geochemistry of ordinary chondrite Chondrules: The type I/type II Chondrule dichotomy
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Emmanuel Jacquet, Olivier Alard, Matthieu Gounelle
    Abstract:

    We report trace element concentrations of silicate phases in Chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine < pyroxene < mesostasis, and heavy REE (HREE) being enriched by 1–2 orders of magnitude (CI-normalized) relative to light REE (LREE) in ferromagnesian silicates, although no single olivine with very large LREE/HREE fractionation has been found. On average, olivine in type II Chondrules is poorer in refractory lithophile incompatible elements (such as REE) than its type I counterpart by a factor of ∼2. This suggests that olivine in type I and II Chondrules formed by batch and fractional crystallization, respectively, implying that type II Chondrules formed under faster cooling rates (>∼10 K/h) than type I Chondrules. Appreciable Na concentrations (3–221 ppm) are measured in olivine from both Chondrule types; type II Chondrules seem to have behaved as closed systems, which may require Chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II Chondrule forming regions may explain the higher oxygen fugacities they record compared to type I Chondrules. Type I and type II Chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that Chondrule formation models must account for.

Alan E Rubin - One of the best experts on this subject based on the ideXlab platform.

  • multiple melting in a four layered barred olivine Chondrule with compositionally heterogeneous glass from ll3 0 semarkona
    Meteoritics & Planetary Science, 2013
    Co-Authors: Alan E Rubin
    Abstract:

    Chondrule K7p from LL3.0 Semarkona consists of four nested barred-olivine (BO) Chondrules. The innermost BO Chondrule (Chondrule 1) formed by complete melting of an olivine-rich dustball. After formation, the Chondrule was incorporated into another olivine-rich dustball. A second heating event caused this second dustball to melt; the mesostasis and some of the olivine in Chondrule 1 were probably also melted at this time, but the Chondrule 1 structure remained largely intact. At this stage, the object was an enveloping compound BO Chondrule. This two-step process of melting and dustball enshrouding repeated two more times. The different proportions of olivine and glass in Chondrules 1–4 suggest that the individual precursor dustballs differed in the amounts of Chondrule fragments they contained and the mineral proportions in those fragments. The final dustball (which ultimately formed Chondrule 4) was somewhat more ferroan; after melting, crystallizing, and quenching, Chondrule 4 contained olivine and glass with higher FeO and MnO contents than those of the earlier formed Chondrules. Subsequent aqueous alteration on the LL parent body transformed the abundant metal blebs and stringers at the Chondrule surface into carbide, iron oxide, and minor Ni-rich metal. Portions of the mesostasis underwent dissolution, producing holes and adjacent blades of more resistant material. Much of the glass in the Chondrule remained isotropic, even after minor hydration and leaching. The sharp, moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution.

  • physical properties of Chondrules in different chondrite groups implications for multiple melting events in dusty environments
    Geochimica et Cosmochimica Acta, 2010
    Co-Authors: Alan E Rubin
    Abstract:

    Chondrite groups (CV, CK, CR) with large average Chondrule sizes have low proportions of RP plus C Chondrules, high proportions of enveloping compound Chondrules, high proportions of Chondrules with (thick) igneous rims, and relatively low proportions of type-I Chondrules containing sulfide. In contrast, chondrite groups (CM, CO, OC, R, EH, EL) with smaller average Chondrule sizes have the opposite properties. Equilibrated CK chondrites have plagioclase with relatively low Na; equilibrated OC, R, EH and EL chondrites have more sodic plagioclase. Enveloping compound Chondrules and Chondrules with igneous rims formed during a remelting event after the primary Chondrule was incorporated into a dustball. Repeated episodes of remelting after Chondrules were surrounded by dust would tend to produce large Chondrules. RP and C Chondrules formed by complete melting of their precursor assemblages; remelting of RP and C Chondrules surrounded by dust would tend to produce porphyritic Chondrules as small dust particles mixed with the melt, providing nuclei for crystallizing phenocrysts. This process would tend to diminish the numbers of RP and C Chondrules. Correlations among these Chondrule physical properties suggest that chondrite groups with large Chondrules were typically surrounded by thick dust-rich mantles that formed in locally dusty nebular environments. Chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away. Slow cooling led to enhanced migration of sulfide to Chondrule surfaces and more extensive sulfide evaporation. These Chondrules also lost Na; the plagioclase that formed from equilibrated CK chondrites was thus depleted in Na.

  • Non-spherical lobate Chondrules in CO3.0 Y-81020: General implications for the formation of low-FeO porphyritic Chondrules in CO chondrites
    Geochimica et Cosmochimica Acta, 2005
    Co-Authors: Alan E Rubin, John T Wasson
    Abstract:

    Non-spherical Chondrules (arbitrarily defined as having aspect ratios ≥1.20) in CO3.0 chondrites comprise multi-lobate, distended, and highly irregular objects with rounded margins; they constitute ∼70% of the type-I (low-FeO) porphyritic Chondrules in Y-81020, ∼75% of such Chondrules in ALHA77307, and ∼60% of those in Colony. Although the proportion of non-spherical type-I Chondrules in LL3.0 Semarkona is comparable (∼60%), multi-lobate OC porphyritic Chondrules (with lobe heights equivalent to a significant fraction of the mean Chondrule diameter) are rare. If the non-spherical type-I Chondrules in CO chondrites had formed from totally molten droplets, calculations indicate that they would have collapsed into spheres within ∼10−3 s, too little time for their 20-μm-size olivine phenocrysts to have grown from the melt. These olivine grains must therefore be relicts from an earlier Chondrule generation; the final heating episode experienced by the non-spherical Chondrules involved only minor amounts of melting and crystallization. The immediate precursors of the individual non-spherical Chondrules may have been irregularly shaped Chondrule fragments whose fracture surfaces were rounded during melting. Because non-spherical Chondrules and “circular” Chondrules form a continuum in shape and have similar grain sizes, mineral and mesostasis compositions, and modal abundances of non-opaque phases, they must have formed by related processes. We conclude that a large majority of low-FeO Chondrules in CO3 chondrites experienced a late, low-degree melting event. Previous studies have shown that essentially all type-II (high-FeO) porphyritic Chondrules in Y-81020 formed by repeated episodes of low-degree melting. It thus appears that the type-I and type-II porphyritic Chondrules in Y-81020 (and, presumably, all CO3 chondrites) experienced analogous formation histories. Because these two types constitute ∼95% of all CO Chondrules, it is clear that Chondrule recycling was the rule in the CO Chondrule-formation region and that most melting events produced only low degrees of melting. The rarity of significantly non-spherical, multi-lobate Chondrules in Semarkona may reflect more-intense heating of Chondrule precursors in the ordinary-chondrite region of the solar nebula.

  • Size‐frequency distributions of Chondrules and Chondrule fragments in LL3 chondrites: Implications for parent‐body fragmentation of Chondrules
    Meteoritics & Planetary Science, 2002
    Co-Authors: Victoria E. Nelson, Alan E Rubin
    Abstract:

    We measured the sizes and textural types of 719 intact Chondrules and 1322 Chondrule fragments in thin sections of Semarkona (LL3.0), Bishunpur (LL3.1), Krymka (LL3.1), Piancaldoli (LL3.4) and Lewis Cliff 88175 (LL3.8). The mean apparent diameter of Chondrules in these LL3 chondrites is 0.80 Φ units or 570 um, much smaller than the previous rough estimate of ~900 μm. Chondrule fragments in the five LL3 chondrites have a mean apparent cross-section of 1.60 phi units or 330 μm. The smallest fragments are isolated olivine and pyroxene grains; these are probably phenocrysts liberated from disrupted porphyritic Chondrules. All five LL3 chondrites have fragment/Chondrule number ratios exceeding unity, suggesting that substantial numbers of the Chondrules in these rocks were shattered. Most fragmentation probably occurred on the parent asteroid. Porphyritic Chondrules (porphyritic olivine + porphyritic pyroxene + porphyritic olivine-pyroxene) are more readily broken than droplet Chondrules (barred olivine + radial pyroxene + cryptocrystalline). The porphyritic fragment/Chondrule number ratio (2.0) appreciably exceeds that of droplet-textured objects (0.9). Intact droplet Chondrules have a larger mean size than intact porphyritic Chondrules, implying that large porphyritic Chondrules are fragmented preferentially. This is consistent with the relatively low percentage of porphyritic Chondrules within the set of the largest Chondrules (57%) compared to that within the set of the smallest Chondrules (81%). Differences in mean size among Chondrule textural types may be due mainly to parent-body Chondrule-fragmentation events and not to Chondrule-formation processes in the solar nebula.

  • petrologic geochemical and experimental constraints on models of Chondrule formation
    Earth-Science Reviews, 2000
    Co-Authors: Alan E Rubin
    Abstract:

    Abstract The petrologic and geochemical properties of Chondrules as well as results of experimental studies provide strong constraints on Chondrule-formation models. Nebular formation is indicated by the non-mass-fractionated oxygen isotopic compositions of bulk Chondrules. Chondrule formation from a melt is required by the prototypical spheroidal shapes and the presence of euhedral phenocrysts and glassy mesostases. Incomplete melting is indicated by the abundance of porphyritic Chondrules (which experiments demonstrate require relict nuclei) and coarse relict grains. The length of time that Chondrules were hot is constrained by their retention of relict grains and moderately volatile elements. Rapid cooling of Chondrules after formation is supported by the presence of zoned phenocrysts, isotopic anomalies and dynamic crystallization experiments. It is clear from the presence of relict grains, enveloping compound Chondrules and igneous rims that many Chondrules were heated again after cooling. The heating mechanism responsible for Chondrule formation seems to have operated at varying intensities over large regions of the inner solar nebula for at least the time it took ambient nebular temperatures to cool from above ∼900 to below ∼600 K. The Chondrule-formation mechanism provided a repeatable source of energy capable of highly localized melting, characteristic of flash heating. The occurrence of ferroan microChondrules with low melting temperatures within some Chondrule rims indicates that Chondrule formation did not occur exclusively in high-temperature regions near the Sun as required in bipolar outflow models. Mechanisms for forming Chondrules that are consistent with the constraints include various flash-heating models: nebular lightning, magnetic reconnection flares, gas dynamic shock waves and radiative heating.

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  • An unusual compound object in Yamato 793408 (H3.2‐an): The missing link between compound Chondrules and macroChondrules?
    Meteoritics and Planetary Science, 2020
    Co-Authors: Jens Barosch, Dominik Hezel, Yves Marrocchi, Andrey Gurenko, Christoph Lenting
    Abstract:

    We found a large (~2 mm) compound object in the primitive Yamato 793408 (H3.2‐an) chondrite. It consists mostly of microcrystalline material, similar to Chondrule mesostasis, that hosts an intact barred olivine (BO) Chondrule. The object contains euhedral pyroxene and large individual olivine grains. Some olivine cores are indicative of refractory forsterites with very low Fe‐ and high Ca, Al‐concentrations, although no 16O enrichment. The entire object is most likely a new and unique type, as no similar compound object has been described so far. We propose that it represents an intermediate stage between compound Chondrules and macroChondrules, and formed from the collision between Chondrules at low velocities (below 1 m s−1) at high temperatures (around 1550 °C). The macroChondrule also trapped and preserved a smaller BO Chondrule. This object appears to be the first direct evidence for a genetic link between compound Chondrules and macroChondrules. In accordance with previous suggestions and studies, compound Chondrules and macroChondrules likely formed by the same mechanism of Chondrule collisions, and each represents different formation conditions, such as ambient temperature and collision speed

  • Sectioning effects of porphyritic Chondrules: Implications for the PP/POP/PO classification and correcting modal abundances of mineralogically zoned Chondrules
    Meteoritics and Planetary Science, 2020
    Co-Authors: Jens Barosch, Dominik Hezel, Lena Sawatzki, Lucia Halbauer, Yves Marrocchi
    Abstract:

    Mineralogically zoned Chondrules are a common Chondrule type in chondrites. They consist of olivine cores, surrounded by low‐Ca pyroxene rims. By serial sectioning porphyritic Chondrules from carbonaceous, ordinary, and enstatite chondrites, we demonstrate that the 2‐D textural appearances of these Chondrules largely depend on where they are cut. The same Chondrule may appear as a porphyritic pyroxene (PP) Chondrule when sectioned through the low‐Ca pyroxene rim, and as a porphyritic olivine‐pyroxene (POP) or porphyritic olivine (PO) Chondrule when sectioned close or through its equator. Chondrules previously classified into PP/POP/PO Chondrules might therefore not represent different types, but various sections through mineralogically zoned Chondrules. Classifying Chondrule textures into PP, POP, and PO has therefore no unequivocal genetic meaning, it is merely descriptive. Sectioning effects further introduce a systematic bias when determining mineralogically zoned Chondrule fractions from 2‐D sections. We determined correction factors to estimate 3‐D mineralogically zoned Chondrule fractions when these have been determined in 2‐D sections: 1.24 for carbonaceous chondrites, 1.29 for ordinary chondrites, and 1.62 for enstatite chondrites. Using these factors then shows that mineralogically zoned Chondrules are the dominant Chondrule type in chondrites with estimated 3‐D fractions of 92% in CC, 52% in OC, and 46% in EC

  • Oxygen isotopic diversity of Chondrule precursors and the nebular origin of Chondrules
    Earth and Planetary Science Letters, 2018
    Co-Authors: Yves Marrocchi, Johan Villeneuve, Valentina G. Batanova, Laurette Piani, Emmanuel Jacquet
    Abstract:

    Abstract FeO-poor (type I) porphyritic Chondrules formed by incomplete melting of solid dust precursors via a yet-elusive mechanism. Two settings are generally considered for their formation: (i) a nebular setting where primordial solids were melted, e.g. by shock waves propagating through the gas and (ii) a collisional planetary setting. Here we report a method combining high-current electron microprobe X-ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from Chondrule precursors. We find that these olivine crystals are Ca–Al–Ti-poor relative to host olivine crystals. Their variable Δ 17 O, even in individual Chondrule, is inconsistent with derivation from planetary interiors as previously argued from 120 ° triple junctions also exhibited by the Chondrules studied herein. This indicates that Chondrule precursors correspond to solid nebular condensates formed under changing physical conditions. We propose that porphyritic Chondrules formed during gas-assisted melting of nebular condensates comprising relict olivine grains with varying Δ 17 O values and Ca–Al–Ti-rich minerals such as those observed within amoeboid olivine aggregates. Incomplete melting of Chondrule precursors produced Ca–Al–Ti-rich melts (CAT-melts), allowing subsequent crystallization of Ca–Al–Ti-rich host olivine crystals via epitaxial growth on relict olivine grains. Incoming MgO and SiO from the gas phase induced (i) the dilution of CAT-melts, as attested by the positive Al–Ti correlation observed in Chondrule olivine crystals, and (ii) buffering of the O-isotope compositions of Chondrules, as recorded by the constant Δ 17 O values of host olivine grains. The O-isotopic compositions of host olivine grains are Chondrule-specific, suggesting that Chondrules formed in an array of environments of the protoplanetary disk with different Δ 17 O values, possibly due to variable solid/gas mixing ratios.

  • Magmatic sulfides in the porphyritic Chondrules of EH enstatite chondrites
    Geochimica et Cosmochimica Acta, 2016
    Co-Authors: Laurette Piani, Yves Marrocchi, Guy Libourel, Laurent Tissandier
    Abstract:

    The nature and distribution of sulfides within 17 porphyritic Chondrules of the Sahara 97096 EH3 enstatite chondrite have been studied by backscattered electron microscopy and electron microprobe in order to investigate the role of gas-melt interactions in the Chondrule sulfide formation. Troilite (FeS) is systematically present and is the most abundant sulfide within the EH3 chondrite Chondrules. It is found either poikilitically enclosed in low-Ca pyroxenes or scattered within the glassy mesostasis. Oldhamite (CaS) and niningerite [(Mg,Fe,Mn)S] are present in ! 60 % of the Chondrules studied. While oldhamite is preferentially present in the mesostasis, niningerite associated with silica is generally observed in contact with troilite and low-Ca pyroxene. The Sahara 97096 Chondrule mesostases contain high abundances of alkali and volatile elements (average Na 2 O = 8.7 wt.%, K 2 O = 0.8 wt.%, Cl = 7000 ppm and S = 3700 ppm) as well as silica (average SiO 2 = 63.1 wt.%). Our data suggest that most of the sulfides found in EH3 chondrite Chondrules are magmatic minerals that formed after the dissolution of S from a volatile-rich gaseous environment into the molten Chondrules. Troilite formation occurred via sulfur solubility 2 within Fe-poor Chondrule melts followed by sulfide saturation, which causes an immiscible iron sulfide liquid to separate from the silicate melt. The FeS saturation started at the same time as or prior to the crystallization of low-Ca pyroxene during the high temperature Chondrule forming event(s). Protracted gas-melt interactions under high partial pressures of S and SiO led to the formation of niningerite-silica associations via destabilization of the previously formed FeS and low-Ca pyroxene. We also propose that formation of the oldhamite occurred via the sulfide saturation of Fe-poor Chondrule melts at moderate S concentration due to the high degree of polymerization and the high Na-content of the Chondrule melts, which allowed the activity of CaO in the melt to be enhanced. Gas-melt interactions thus appear to be a key process that may control the mineralogy of Chondrules in the different classes of chondrite.