GoTriple - Mass-independent and mass-dependent Cr isotopic composition of the Rumuruti (R) chondrites: Implications for their origin and planet formation

authors

Contributors

Institut de Physique du Globe de Paris (IPGP) ; Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP),

Centre for Star and Planet Formation (STARPLAN) ; Globe Institute ; Faculty of Health and Medical Sciences ; University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU)-Faculty of Health and Medical Sciences ; University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU),

Carnegie Institution for Science [Washington],

Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR) ; Institut Universitaire Européen de la Mer (IUEM) ; Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Centre National de la Recherche Scientifique (CNRS)-Université de Brest (UBO),

Institut für Planetologie [Münster] ; Westfälische Wilhelms-Universität Münster (WWU),

F. M. acknowledges funding from the European Research Council under the H2020 framework program/ERC grant agreement (ERC starting grant, #637503-PRISTINE) and financial support of the UnivEarthS Labex program at Université de Paris (#ANR-10-LABX-0023 and #ANR-11-IDEX-0005-02), and the IPGP platform PARI, and the Region Île-de-France Sesame grant no. 12015908. M. S. acknowledges funding from the Villum Fonden (#00025333). M. B. acknowledges funding from the Carlsberg Foundation (#CF18-1105), the Danish National Research Foundation (#DNRF97) and the European Research Council (ERC Advanced Grant Agreement, #833275-DEEPTIME). A. B. thanks the support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, #263649064) – TRR 170 (subproject B05). This is TRR170 Publication No. 116. K. Z. thanks the China Scholarship Council (CSC) for the PhD fellowship (#201706340161) and IPGP for the funding support of traveling, “Aide à la MOBILITE INTERNATIONALE des doctorants de l’IPGP” (2019), to visit Earth and Planetary Laboratory, Carnegie Institution for Science.,

ANR-10-LABX-0023,UnivEarthS,Earth - Planets - Universe: observation, modeling, transfer(2010),

ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011),

European Project: 637503,H2020,ERC-2014-STG,PRISTINE(2015)

+ 9

Publisher

HAL CCSD

Abstract

International audience Chromium (Cr) isotopes play an important role in cosmochemistry and planetary science because they are powerful tools for dating (Mn-53-Cr-53 short-lived chronometry), tracing (Cr-54 nucleosynthetic anomalies) the origins of the materials, and studying the processes involved in volatile element fractionation and planetary differentiation (Cr stable isotopic fractionation). To use Cr isotopes for these purposes, it is essential to precisely know the compositions of the various chondritic reservoirs. However, the Cr isotope composition of Rumuruti (R) chondrites remains unknown. Here, we report high-precision mass-independent (average 2SE uncertainty of similar to 0.02 and similar to 0.06 for epsilon Cr-53 and epsilon Cr-54, respectively; epsilon indicates 10,000 deviation) and mass-dependent (uncertainty of average 0.03 parts per thousand for delta Cr-53; .delta indicates 1000 deviation) Cr isotope data for 12 bulk R chondrites of petrologic types 3-6 (including R chondrite breccias), and one R chondrite-like clast (MS-CH) in the Almahata Sitta polymict ureilite. All the R chondrites show homogeneous bulk epsilon Cr-54 values, -0.06 +/- 0.08 (2SD), similar only to those of the Earth-Moon system and enstatite chondrites. This first epsilon Cr-54 dataset for R chondrites provides significant addition to the epsilon Cr-54-A, Delta O-17 diagram, and positions them as a potential endmember for planetary precursors. The R chondrites possess a higher Mn-55/Cr-52 of 0.68 +/- 0.04 relative to most of carbonaceous chondrites and higher epsilon Cr-53 values 0.23 +/- 0.05 (2SD) relative to most of chondrite groups. This likely results from the lower chondrule abundance in R chondrites compared to that of ordinary and enstatite chondrites. The stable Cr isotope composition of R chondrites is homogeneous with a delta Cr-53 = -0.12 +/- 0.03%e (2SD). Combined with previous data of other groups of chondrites, we show that the stable Cr isotopic composition of all the chondrites is homogeneous with delta Cr-53 of -0.12 +/- 0.04%e (2SD, N = 42) and is independent of the petrologic type and redox conditions. The lack of mass-dependent fractionation between all groups of chondrites suggests that the average chondrite delta Cr-53 value is also representative for the initial composition of all differentiated planets in the Solar System. Finally, the MS-CH clast in Almahata Sitta has a Cr isotopic composition (epsilon Cr-53 = 0.18 +/- 0.04, epsilon Cr-54 = 0.16 +/- 0.07, and delta Cr-53 = -0.11 +/- 0.05%e) that is consistent (within error) with it being an R chondrite-like clast. (C) 2020 Elsevier Ltd. All rights reserved.