Mn-Cr ages and formation conditions of fayalite in CV3 carbonaceous chondrites: Constraints on the accretion ages of chondritic asteroids

1Kaori Jogo, 2Tomoki Nakamura, 3Motoo Ito, 4Shigeru Wakita, 5Mikhail Yu. Zolotov, 6Scott R. Messenger
Geochmica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.11.027]
1Division of Earth-System Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 406-840, South Korea
2Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
3Kochi Institute for Core Sample Research, JAMSTEC B200 Monobe, Nankoku, Kochi 783-8502, Japan
4Center for Computational Astrophysics, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
5School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287–1404, USA
6Robert M. Walker Laboratory for Space Science, NASA Johnson Space Center, ARES, Mail Code KR, 2101 NASA Parkway, Houston, Texas 77058, USA
Copyright Elsevier

Chondritic planetesimals are among the first planetary bodies that accreted inside and outside water snow line in the protoplanetary disk. CV3 carbonaceous chondrite parent body accreted relatively small amount of water ice, probably near the snow line, and experienced water-assisted metasomatic alteration that resulted in formation of diverse secondary minerals, including fayalite (Fa80–100). Chemical compositions of the CV fayalite and its Mn-Cr isotope systematics indicate that it formed at different temperature (10–300°C) and fluid pressure (3–300 bars) but within a relatively short period of time. Thermal modeling of the CV parent body suggests that it accreted ∼3.2–3.3 Ma after CV CAIs formation and had a radius of >110–150 km. The inferred formation age of the CV parent body is similar to that of the CM chondrite parent body that probably accreted beyond the snow line, but appears to have postdated accretion of the CO and ordinary chondrite parent bodies that most likely formed inside the snow line. The inferred differences in the accretion ages of chondrite parent bodies that formed inside and outside snow line are consistent with planetesimal formation by gravitational/streaming instability.

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