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Plots of (a) V 2 O 3 vs Sc 2 O 3 and (b) ZrO 2 vs Sc 2 O 3 of pyroxene in R3C-01-U1. Compositions of Sc-, V-, and/or Zr-rich pyroxene from previous studies (Ulyanov et al., 1982; Meeker et al., 1983; Davis, 1984; El Goresy et al., 1984; Armstrong et al., 1985; Bischoff and Palme, 1987; Simon et al., 1996; El Goresy et al., 2002; Lin et al., 2003; Ma and Rossman, 2009a; Ivanova et al., 2012; Ma et al., 2012; Zhang et al., 2015; Ma and Beckett, 2016; Komatsu et al., 2018) and chondritic ratios (Lodders, 2003) are also shown. Gray areas correspond clinopyroxene/melt fractionation ratio determined by previous studies (Simon et al., 1991; Hart and Dunn, 1993). Abbreviations are as in Fig. 4.
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Ultrarefractory (UR) phases in CAIs could have formed at higher T compared to common CAI minerals and thus they potentially provide constraints on very high-T processes in the solar nebula. We report a detailed characterization of an UR phase davisite bearing CAI from a reduced type CV chondrite. Davisite occur only in one lithological unit that co...
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... davisite in R3C-01-U1 shows higher V/Sc and lower Zr/Sc values compared to davisite in the UR inclusions previously studied (Fig. 6). The 50% condensation temperature of elements in a gas of solar composition at 10 −4 bar are 1741 K for Zr, 1659 K for Sc, and 1429 K for V (Lodders, 2003), suggesting that the Zr/Sc ratio of a condensate decreases with increasing V/Sc value as a nebular gas temperature decreases. Therefore, the condensation temperature of Ti,V-rich ...
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... The petrology and mineralogy of these meteorites have been well characterized in previous studies (e.g., Johnson and Lofgren, 1995;Rubin et al., 1997;Benoit et al., 2002;Lin and El Goresy, 2002;Grossman and Brearley, 2005;Gannoun et al., 2011;Quirico et al., 2011;Ishida et al., 2012;Yoshizaki et al., 2019;Bonal et al., 2020). ...
... Mineralogy, petrology and major element compositions of polished sections of the samples were analyzed using scanning electron microscopes (SEM) and electron probe microanalyzers (EPMA) at Tohoku University and University of Maryland, using procedures after Yoshizaki et al. (2019; Section B.1). Trace element compositions of chondritic components were determined using a New Wave frequency-quintupled Nd:YAG laser system coupled to a Thermo Finnigan Element2 singlecollector ICP-MS at University of Maryland, following procedures of Lehner et al. (2014). Operating conditions are summarized in Table 2. Measurements were carried out in low-mass resolution mode (M/∆M = 300), with 15-200 µm laser spot size and a fluence of ∼2-3 J/cm 2 . ...
Chondrites are sediments of materials left over from the earliest stage of the solar system history. Based on their undifferentiated nature and less fractionated chemical compositions, chondrites are widely considered to represent the unprocessed building blocks of the terrestrial planets and their embryos. Models of chemical composition of the terrestrial planets generally find chondritic relative abundances of refractory lithophile elements (RLE) in the bulk bodies (”constant RLE ratio rule”), based on limited variations of RLE ratios among chondritic meteorites and the solar photosphere. Here, we show that ratios of RLE, such as Nb/Ta, Zr/Hf, Sm/Nd and Al/Ti, are fractionated from the solar value in chondrules from enstatite chondrites (EC). The fractionated RLE ratios of individual EC chondrules document different chalcophile affinities of RLE under highly reducing environments and a separation of RLE-bearing sulfides from silicates before and/or during chondrule formation. In contrast, the bulk EC have solar-like RLE ratios, indicating that a physical sorting of silicates and sulfides was negligible before and during the accretion of EC parent bodies. Likewise, if the Earth’s accretion was dominated by EC-like materials, as supported by multiple isotope systematics, physical sorting of silicates and sulfides in the accretionary disk did not occur. Alternatively, the Earth’s precursors were high-temperature nebular condensates that formed prior to the precipitation of RLE-bearing sulfides. A lack of Ti depletion in the bulk silicate Earth, combined with similar silicate-sulfide and rutile-melt partitioning behaviors of Nb and Ti, prefers a moderately siderophile behavior of Nb as the origin of the accessible Earth’s Nb depletion. Highly reduced planets that have experienced selective removal or accretion of silicates or metal/sulfide phases, such as Mercury, possibly yield fractionated, non-solar bulk RLE ratios.
... from Allende (CV3), and one CAI and six amoeboid olivine aggregates (AOA) from Roberts Massif (RBT) 04143 (CV3). The petrology and mineralogy of these meteorites have been well characterized in previous studies (e.g., Johnson and Lofgren, 1995;Rubin et al., 1997;Benoit et al., 2002;Lin and El Goresy, 2002;Grossman and Brearley, 2005;Gannoun et al., 2011;Quirico et al., 2011;Ishida et al., 2012;Yoshizaki et al., 2019;Bonal et al., 2020). ...
... indicate a similar MVE depletion in the Mars-sized impactor. In addition, the CI-like impactor model requires a significant volatile depletion in the proto-Earth, perhaps at levels seen in angrites and calcium-aluminum-rich inclusions (CAIs), which show heavy Mgand Si-isotope enrichment and significant depletion of moderately volatile elements (e.g.,Grossman et al., 2000Grossman et al., , 2008bPringle et al., 2014) due to significant evaporative losses of the major and more volatile elements by impact-induced or transient nebular heating events (e.g.,Stolper and Paque, 1986;Richter et al., 2002;Pringle et al., 2014;Yoshizaki et al., 2019;Young et al., 2019). However, such isotopic signatures are not recognized for Earth (Section 4.4.1). ...
Comparative studies of terrestrial planets have provided important insights into physico-chemical processes that produced their similarities and differences. Chemical composition of terrestrial planets records planetary accretion, differentiation, impact, and surface processes. In order to place new constraints on the origin and evolution of rocky planets, I investigated chemical compositions of terrestrial planets and meteorites from primitive asteroids (chondrites).
Compositional models of planets have found or assumed chondritic relative abundances of refractory lithophile elements (RLE). I challenge this fundamental paradigm by showing highly variable RLE ratios in individual chondrules from enstatite chondrites (EC), which are highly reduced primitive meteorites with Earth-like isotopic signatures. The fractionated RLE compo- sitions of EC chondrules reflect moderately chalcophile behaviors of these elements and sulfide-silicate separation in highly reduced nebular environments. If the Earth’s building blocks were dominated by highly reduced EC-like materials, they should not have been affected by a physical sorting of silicates and sulfides before their accretion. Alternatively, the Earth’s precursors might have been high-temperature nebular materials that condensed before precipitation of the RLE-bearing sulfides. The bulk Mercury might not have chondritic RLE ratios, due to sulfide-silicate separation processes that formed its large metallic core.
Previous compositional models of Mars relied on an assumption of CI-chondritic relative abundance of Mn and more refractory elements, which has been challenged by recent astrophysical observations. Here I propose a new martian model composition that avoids such an assumption, using data from martian meteorites and spacecraft observations. The new model finds that Mars is enriched in refractory elements and show a systematic depletion of moderately volatiles as a function of their volatilities compared to the CI abundance. The Mars’ volatile depletion trend indicates a S-poor composition for the martian core, which requires an incorporation of additional light elements (e.g., O, H) into the core to match the martian geodetic properties.
Earth and Mars are equally enriched in refractory elements, although Earth is more volatile-depleted and less oxidized than Mars. These compositional properties were established by a nebular fractionation, with negligible post-accretionary losses of moderately volatile elements. The degree of planetary and asteroidal volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale. During its prolonged formation, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids.
The correlations between these planetary properties constrain the composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. These observations, combined with the shared refractory enrichment in Earth and Mars, and insights from planetary uncompressed densities, establishes the compositional model of Mercury. Uncompressed den- sities of rocky bodies in the solar system decrease with their heliocentric distance, indicating a role of disk-scale metal-silicate separation before the planetary accretion, rather than post- accretionary modification processes.
Insights presented here update our knowledge of the origin of rocky planets in our solar system, and provide future perspectives on studies of chemistry of (extra)solar system bodies.
... The common MVE depletion in rocky differentiated bodies in the solar system (e.g., sub-solar K/Th ratios; Section 3.1) might indicate a similar MVE depletion in the Mars-sized impactor. In addition, the CI-like impactor model requires a significant volatile depletion in the proto-Earth, perhaps at levels seen in angrites and calcium-aluminum-rich inclusions (CAIs), which show heavy Mg-and Si-isotope enrichment and significant depletion of moderately volatile elements (e.g., Grossman et al., 2000Grossman et al., , 2008Pringle et al., 2014) due to significant evaporative losses of the major and more volatile elements by impact-induced or transient nebular heating events (e.g., Stolper and Paque, 1986;Richter et al., 2002;Pringle et al., 2014;Yoshizaki et al., 2019;Young et al., 2019). However, such isotopic signatures are not recognized for Earth (Section 3.1). ...
Composition of terrestrial planets records planetary accretion, core-mantle and crust-mantle differentiation, and surface processes. Here we compare the compositional models of Earth and Mars to reveal their characteristics and formation processes. Earth and Mars are equally enriched in refractory elements (1.9 × CI), although Earth is more volatile-depleted and less oxidized than Mars. Their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. The degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. During its formation before and after the nebular disk’s lifetime, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids, establishing its marked volatile depletion. A giant impact of an oxidized, differentiated Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth’s mantle composition. Chalcophile and some siderophile elements in the silicate Earth added by the Mars-like impactor were extracted into the core by a sulfide melt (∼0.5% of the mass of the Earth’s mantle). In contrast, the composition of Mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars’ rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. These similarities and differences between the Earth and Mars made the former habitable and the other inhospitable to uninhabitable.
... We also studied two Ca, Al-rich inclusions (CAI) from Allende (CV3), and one CAI and six amoeboid olivine aggregates (AOAs) from Roberts Massiff (RBT) 04143 (CV3). Petrology and mineralogy of these meteorites have been well characterized in previous studies (e.g., Johnson and Lofgren, 1995;Rubin et al., 1997;Benoit et al., 2002;Lin and El Goresy, 2002;Grossman and Brearley, 2005;Gannoun et al., 2011;Quirico et al., 2011;Ishida et al., 2012;Yoshizaki et al., 2019;Bonal et al., 2020), and all of them are classified as the unequilibrated type 3 chondrites. ...
... Mineralogy, petrology and major element compositions of polished sections of the samples were analyzed using scanning electron microscopes (SEM) and electron probe microanalyzers (EPMA) at Tohoku University and University of Maryland, using procedures after Yoshizaki et al. (2019;Section B.1). Trace element compositions of chondritic components were determined using a New Wave frequency-quintupled Nd:YAG laser system coupled to the Thermo Finnigan Element2 singlecollector ICP-MS at University of Maryland. Operating conditions are summarized in Table 2. Measurements were carried out in low-mass resolution mode (M/∆M = 300), with 15-200 µm laser spot size and a fluence of ∼2-3 J/cm 2 . ...
Chondrites are undifferentiated sediments of materials left over from the earliest stage of the solar system history, and are widely considered to represent the unprocessed building blocks of the terrestrial planets. Compositional models of the planets generally find chondritic relative abundances of refractory lithophile elements (RLE) in the bulk planets ("constant RLE ratio rule"), based on limited variations of RLE ratios among chondritic meteorites and the solar photosphere. Here, we show that ratios of RLE, such as Nb/Ta, Zr/Hf, Sm/Nd and Al/Ti, are fractionated in chondrules from enstatite chondrites (EC), which provides limitations on the use of the constant RLE ratio rule in the compositional modeling of planets. The fractionated RLE compositions of EC chondrules document a separation of RLE-bearing sulfides before and/or during chondrule formation and different chalcophile affinities of RLE under highly reducing environments. If the Earth's accretion is dominated by highly reduced EC-like materials, as supported by multiple isotope systematics, the fractionated RLE ratios of the reduced silicates should have been modified during the Earth's subsequent differentiation, to produce CI-like RLE ratios of the bulk silicate Earth. A lack of Ti depletion in the bulk silicate Earth and the similar chalcophile behavior of Ti and Nb under reducing conditions exclude incorporation of Nb into a core-forming sulfide as the origin of the accessible Earth's Nb depletion.
... Oxygen isotopic composition is an important factor of constraining the formation process, nebular condition, and post-formation history of CAIs in chondrites. Based on the models about the oxygen isotope distribution and evolution in the solar system (Clayton 2002(Clayton , 2003Yurimoto and Kuramoto 2004;Lyons and Young 2005;Sakamoto et al. 2007 (Yurimoto et al. 1998;Simon et al. 2011;Katayama et al. 2012;Kawasaki et al. 2012Kawasaki et al. , 2017Park et al. 2012;Zhang et al. 2015;Yoshizaki et al. 2019;Krot et al. 2019aKrot et al. , 2019b. The presence of 16 Opoor gaseous reservoirs might have led to the formation of uniformly 16 O-poor CAIs and CAIs with heterogeneous oxygen isotopic compositions. ...
Calcium‐aluminum‐rich inclusions (CAIs) are the first solid materials formed in the solar nebula. Among them, ultrarefractory inclusions are very rare. In this study, we report on the mineralogical features and oxygen isotopic compositions of minerals in a new ultrarefractory inclusion CAI 007 from the CV3 chondrite Northwest Africa (NWA) 3118. The CAI 007 inclusion is porous and has a layered (core–mantle–rim) texture. The core is dominant in area and mainly consists of Y‐rich perovskite and Zr‐rich davisite, with minor refractory metal nuggets, Zr,Sc‐rich oxide minerals (calzirtite and tazheranite), and Fe‐rich spinel. The calzirtite and tazheranite are closely intergrown, probably derived from a precursor phase due to thermal metamorphism on the parent body. The refractory metal nuggets either exhibit thin exsolution lamellae of Fe,Ni‐dominant alloy in Os,Ir‐dominant alloy or are composed of Os,Ir,Ru,Fe‐alloy and Fe,Ni,Ir‐alloy with troilite, scheelite, gypsum, and molybdenite. The later four phases are apparently secondary minerals. The Zr,Sc,Y‐rich core is surrounded by a discontinuous layer of closely intergrown hibonite and spinel. The CAIs are rimmed by Fe‐rich spinel and Al‐rich diopside. Perovskite has high concentrations of the most refractory rare earth elements (REEs) but is relatively depleted in the moderately refractory and volatile REEs, consistent with the ultrarefractory REE pattern. Based on this unusual Zr,Sc,Y‐rich mineral assemblage, the layered distribution in CAI 007, and the REE concentrations in perovskite, we suggest that CAI 007 is an ultrarefractory inclusion of condensation origin. In CAI 007, hibonite, spinel, and probably Al‐rich diopside are ¹⁶O‐rich (Δ¹⁷O ~–22‰) whereas perovskite and davisite are ¹⁶O‐poor (Δ¹⁷O ~–3‰). Such oxygen isotope heterogeneity suggests that the UR inclusion formed in the various degrees of ¹⁶O‐rich nebular setting or was originally ¹⁶O‐rich and then experienced oxygen isotope exchange with ¹⁶O‐poor fluid on the CV3 chondrite parent body.
Coarse-grained igneous Ca,Al-rich inclusions (CAIs) in CV (Vigarano group) carbonaceous chondrites have typically heterogeneous O-isotope compositions with melilite, anorthite, and high-Ti (>10 wt% TiO2) fassaite being ¹⁶O-depleted (Δ¹⁷O up to ∼ − 3 ± 2‰) compared to hibonite, spinel, low-Ti (<10 wt% TiO2) fassaite, Al-diopside, and forsterite, all having close-to-solar Δ¹⁷O ∼ − 24 ± 2‰. To test a hypothesis that this heterogeneity was established, at least partly, during aqueous fluid-rock interaction, we studied the mineralogy, petrology, and O-isotope compositions of igneous CAIs CG-11 (Type B), TS-2F-1, TS-68, and 818-G (Compact Type A), and 818-G-UR (davisite-rich) from Allende (CV > 3.6), and E38 (Type B) from Efremovka (CV3.1–3.4). Some of these CAIs contain (i) eutectic mineral assemblages of melilite, Al,Ti-diopside, and ± spinel which co-crystallized and therefore must have recorded O-isotope composition of the eutectic melt; (ii) isolated inclusions of Ti-rich fassaite inside spinel grains which could have preserved their initial O-isotope compositions, and/or (iii) pyroxenes of variable chemical compositions which could have recorded gas–melt O-isotope exchange during melt crystallization and/or postcrystallization exchange controlled by O-isotope diffusivity. If these CAIs experienced isotopic exchange with an aqueous fluid, O-isotope compositions of some of their primary minerals are expected to approach that of the fluid.
We find that in the eutectic melt regions composed of highly-åkermanitic melilite (Åk65−71), anorthite, low-Ti fassaite, and spinel of E38, spinel, fassaite, and anorthite are similarly ¹⁶O-rich (Δ¹⁷O ∼ − 24‰), whereas melilite is ¹⁶O-poor (Δ¹⁷O ∼ − 1‰). In the eutectic melt regions of CG-11, spinel and low-Ti fassaite are ¹⁶O-rich (Δ¹⁷O ∼ − 24‰), whereas melilite and anorthite are ¹⁶O-poor (Δ¹⁷O ∼ − 3‰). In TS-2F-1, TS-68, and 818-G, melilite and high-Ti fassaite grains outside spinel have ¹⁶O-poor compositions (Δ¹⁷O range from − 12 to − 3‰); spinel is ¹⁶O-rich (Δ¹⁷O ∼ − 24‰); perovskite grains show large variations in Δ¹⁷O, from − 24 to − 1‰. Some coarse perovskites are isotopically zoned with a ¹⁶O-rich core and a ¹⁶O-poor edge. Isolated high-Ti fassaite inclusions inside spinel grains are ¹⁶O-rich (Δ¹⁷O ∼ − 24‰), whereas high-Ti fassaite inclusions inside fractured spinel grains are ¹⁶O-depleted: Δ¹⁷O range from − 12 to − 3‰. In 818-G-UR, davisite is ¹⁶O-poor (Δ¹⁷O ∼ − 2‰), whereas Al-diopside of the Wark-Lovering rim is ¹⁶O-enriched (Δ¹⁷O < − 16‰). On a three-isotope oxygen diagram, the ¹⁶O-poor melilite, anorthite, high-Ti fassaite, and davisite in the Allende CAIs studied plot close to O-isotope composition of an aqueous fluid (Δ¹⁷O ∼ − 3 ± 2‰) inferred from O-isotope compositions of secondary minerals resulted from metasomatic alteration of the Allende CAIs.
We conclude that CV igneous CAIs experienced post-crystallization O-isotope exchange that most likely resulted from an aqueous fluid-rock interaction on the CV asteroid. It affected melilite, anorthite, high-Ti fassaite, perovskite, and davisite, whereas hibonite, spinel, low-Ti fassaite, Al-diopside, and forsterite retained their original O-isotope compositions established during igneous crystallization of CV CAIs. However, we cannot exclude some gas–melt O-isotope exchange occurred in the solar nebula. This apparently “mineralogically-controlled” exchange process was possibly controlled by variations in oxygen self-diffusivity of CAI minerals. Experimentally measured oxygen self-diffusion coefficients in CAI-like minerals are required to constrain relative roles of O-isotope exchange during aqueous fluid–solid and nebular gas–melt interaction.
