Comprehensive study of carbon and oxygen isotopic compositions, trace element abundances, and cathodoluminescence intensities of calcite in the Murchison CM chondrite

Geochimica et Cosmochimica Acta

Marrocchi

Villeneuve

et al. 2018

Self Cite

Boriskino is a little studied CM2 chondrite composed of millimeter-sized clasts of different lithologies and degrees of alteration. Boriskino thus offers a good opportunity to better understand the preaccretionary alteration history and collisional evolution that took place on the CM parent body. The least altered lithology displays 16 O-poor Type 1a calcite and aragonite grains ( 18 O ≈ 30-37‰,  17 O ≈ 15-18‰ and  17 O ≈-2 to 0‰, SMOW) that precipitated early, before the establishment of the petrofabric, from a fluid whose isotopic composition was established by isotopic exchange between a 16 O-poor water and 16 O-rich anhydrous silicates. In contrast, the more altered lithologies exhibit 16 O-rich Type 2a and veins of calcite ( 18 O ≈ 17-23‰,  17 O ≈ 6-9‰ and  17 O ≈-4 to-1‰, SMOW) that precipitated after establishment of the deformation, from transported 16 O-rich fluid in preexisting fractures. From our petrographic and X-ray tomographic results, we propose that the more altered lithologies of Boriskino were subjected to high intensity impact(s) (10-30 GPa) that produced a petrofabric, fractures and chondrule flattening. Taking all our results together, we propose a scenario for the deformation and alteration history of Boriskino, in which the petrographic and isotopic differences between the lithologies are explained by their separate locations into a single CM parent body. Based on the  13 C- 18 O values of the Boriskino Type 2a calcite ( 13 C ≈ 30-71‰, PDB), we propose an alternative  13 C- 18 O model where the precipitation of Type 2a calcite can occurred in an open system environment with the escape of 13 C-depleted CH 4 produced from the reduction of C-bearing species by H 2 released during serpentinization or kamacite corrosion. Assuming a mean precipitation temperature of 110°C, the observed δ 13 C variability in T2a calcite can be reproduced by the escape of ≈ 15-50% of dissolved carbon into CH 4 by Rayleigh distillation.

Section: Carbon and Oxygen Isotopessupporting

confidence: 88%

Collisional and alteration history of the CM parent body

Geochimica et Cosmochimica Acta

Marrocchi

Villeneuve

et al. 2018

Self Cite

“…Oxygen isotopic compositions of aqueously formed minerals in hydrated chondrites can be also used to better estimate the contribution of interstellar water ices in CM chondrites (Sakamoto et al 2007;Fujiya et al 2015 (Clayton 2002;Lyons & Young 2005;Yurimoto et al 2008). Meteoritic carbonates represent direct snapshots of the isotopic compositions of alteration fluids and can in theory be used to decipher the origin of water in the chondrite-forming region.…”

Section: Introductionmentioning

confidence: 99%

Inward Radial Mixing of Interstellar Water Ices in the Solar Protoplanetary Disk

Marrocchi

Verdier-Paoletti

et al. 2016

ApJL

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The very wide diversity of asteroid compositions in the main belt suggests significant material transport in the solar protoplanetary disk and hints at the presence of interstellar ices in hydrated bodies. However, only a few quantitative estimations of the contribution of interstellar ice in the inner solar system have been reported, leading to considerable uncertainty about the extent of radial inward mixing in the solar protoplanetary disk 4.56 Ga ago. We show that the pristine CM chondrite Paris contains primary Ca-carbonates whose O-isotopic compositions require an 8%-35% contribution from interstellar water. The presence of interstellar water in Paris is confirmed by its bulk D/H isotopic composition that shows significant D enrichment (D/H = (167±0.2)×10 −6 ) relative to the mean D/H of CM chondrites ((145±3)×10 −6 ) and the putative D/H of local CM water ((82±1.5)×10 −6 ). These results imply that (i) efficient radial mixing of interstellar ices occurred from the outer zone of the solar protoplanetary disk inward and that (ii) chondrites accreted water ice grains from increasing heliocentric distances in the solar protoplanetary disk.

“…However, we cannot directly estimate the fO 2 for our synthetic tochilinite due to the limited available information on its stability. Browning and Bourcier (1996) showed that the stability of Fe-rich tochilinite implies extremely reducing conditions compared to cronstedtite, that is, log fO 2 = À91 to À85, though this range of oxygen fugacity is relevant at 0°C (Fujiya et al 2015), too cold for the formation of meteoritic tochilinite. With increasing temperature, the stability fields of Fe-O-S minerals move toward higher fO 2 and fS 2 (Holland 1959), as demonstrated in Fig.…”

Section: Coprecipitation Of Tochilinite and Cronstedtite In CM Chondrmentioning

confidence: 99%

Deciphering the conditions of tochilinite and cronstedtite formation in CM chondrites from low temperature hydrothermal experiments

Meteorit & Planetary Scien

Truche

Fauré

et al. 2019

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Tochilinite/cronstedtite intergrowths are commonly observed as alteration products in CM chondrite matrices, but the conditions under which they formed are still largely underconstrained due to their scarcity in terrestrial environments. Here, we report low temperature (80 °C) anoxic hydrothermal experiments using starting assemblages similar to the constituents of the matrices of the most pristine CM chondrite and S‐rich and S‐free fluids. Cronstedtite crystals formed only in S‐free experiments under circumneutral conditions with the highest Fe/Si ratios. Fe‐rich tochilinite with chemical and structural characteristics similar to chondritic tochilinite was observed in S‐bearing experiments. We observed a positive correlation between the Mg content in the hydroxide layer of synthetic tochilinite and temperature, suggesting that the composition of tochilinite is a proxy for the alteration temperature in CM chondrites. Using this relation, we estimate the mean precipitation temperatures of tochilinite to be 120–160 °C for CM chondrites. Given the different temperature ranges of tochilinite and cronstedtite in our experiments, we propose that Fe‐rich tochilinite crystals resulted from the alteration of metal beads under S‐bearing alkaline conditions at T = 120–160 °C followed by cronstedtite crystals formed by the reaction of matrix amorphous silicates, metal beads, and water at a low temperature (50–120 °C).