TY - JOUR

T1 - Tracing the origin and core formation of the enstatite achondrite parent bodies using Cr isotopes

AU - Zhu (朱柯), Ke

AU - Moynier, Frédéric

AU - Schiller, Martin

AU - Becker, Harry

AU - Barrat, Jean-Alix

AU - Bizzarro, Martin

N1 - Funding Information: Constructive comments from Jan Render, Royji Tanaka and Rick Carlson greatly improved this manuscript, and comments and editorial handling from the associate editor Yves Marrocchi are also appreciated. F. M. acknowledges funding from the European Research Council under the H2020 framework program/ERC Starting Grant Agreement (#637503–PRISTINE) and financial support of the UnivEarthS Labex program at Sorbonne Paris Cité (#ANR–10–LABX–0023 and #ANR–11–IDEX-0005-02), and the ANR through a chaire d’excellence Sorbonne Paris Cité. M. B. acknowledges funding the Carlsberg Foundation (CF18-1105), the Danish National Research Foundation (DNRF97) and the European Research Council (ERC Advanced Grant Agreement, #833275–DEEPTIME). M. S. acknowledges funding from the Villum Fonden (#00025333). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Paris–IdF region SESAME (#12015908). Pierre Burckel and Pascale Louvat were appreciated for analysis on ICP-MS and MC-ICP-MS at IPGP, respectively. We thank Ninja Braukmüller, Monika Feth, Maren Saenz, Elis Hoffmann and Yogita Kadlag for technical support at FUB. Discussions with Paolo Sossi about Cr stable isotope fractionation in S-rich core formation helped us interpret the data. K. Z. thanks an Alexander von Humboldt fellowship (for postdoc researchers), China Scholarship Council (CSC) for a PhD fellowship (#201706340161) and guest fellowships from TRR 170 (host: Harry Becker) and Nanjing University (host: Hejiu Hui) during his stay in Berlin (2020 autumn) and Nanjing (2021 Spring) respectively. H.B. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation–#263649064–TRR 170). This is TRR 170 publication no. 135. Publisher Copyright: © 2021 Elsevier Ltd

PY - 2021

Y1 - 2021

N2 - Enstatite achondrites (including aubrites) are the only differentiated meteorites that have similar isotope compositions to the Earth-Moon system for most of the elements. However, the origin and differentiation of enstatite achondrites and their parent bodies remain poorly understood. Here, we report high-precision mass-independent and mass-dependent Cr isotope data for 10 enstatite achondrites, including eight aubrites, Itqiy and one enstatite-rich clast in Almahatta Sitta, to further constrain the origin and evolution of their parent bodies. The ε54Cr (per 10,000 deviation of the mass bias corrected 54Cr/52Cr ratio from a terrestrial standard) systematics define three groups: main-group aubrites with ε54Cr = 0.06 ± 0.12 (2SD, N = 7) that is similar to the enstatite chondrites and the Earth-Moon system, Shallowater aubrite with ε54Cr = −0.12 ± 0.04 and Itqiy-type meteorites with ε54Cr = −0.26 ± 0.03 (2SD, N = 2). This shows that there were at least three enstatite achondrite parent bodies in the Solar System. This is confirmed by their distinguished mass-dependent Cr isotope compositions (δ53Cr values): 0.24 ± 0.03‰, 0.10 ± 0.03‰ and −0.03 ± 0.03‰ for main-group, Shallowater and Itqiy parent bodies, respectively. Aubrites are isotopically heavier than chondrites (δ53Cr = −0.12 ± 0.04‰), which likely results from the formation of an isotopically light sulfur-rich core. We also obtained the abundance of the radiogenic 53Cr (produced by the radioactive decay of 53Mn, T1/2 = 3.7 million years). The radiogenic ε53Cr excesses correlate with the 55Mn/52Cr ratios for aubrites (except Shallowater and Bustee) and also the Cr stable isotope compositions (δ53Cr values). We show that these correlations represent mixing lines that also hold chronological significance since they are controlled by the crystallization of sulfides and silicates, which mostly reflect the main-group aubrite parent body differentiation at 4562.5 ± 1.1 Ma (i.e., 4.8 ± 1.1 Ma after Solar System formation). Furthermore, the intercept of these lines with the ordinate axis which represent the initial ε53Cr value of main-group aubrites (0.50 ± 0.16, 2σ) is much higher than the average ε53Cr value of enstatite chondrites (0.15 ± 0.10, 2SD), suggesting an early sulfur-rich core formation that effectively increased the Mn/Cr ratio of the silicate fraction of the main-group aubrite parent body.

AB - Enstatite achondrites (including aubrites) are the only differentiated meteorites that have similar isotope compositions to the Earth-Moon system for most of the elements. However, the origin and differentiation of enstatite achondrites and their parent bodies remain poorly understood. Here, we report high-precision mass-independent and mass-dependent Cr isotope data for 10 enstatite achondrites, including eight aubrites, Itqiy and one enstatite-rich clast in Almahatta Sitta, to further constrain the origin and evolution of their parent bodies. The ε54Cr (per 10,000 deviation of the mass bias corrected 54Cr/52Cr ratio from a terrestrial standard) systematics define three groups: main-group aubrites with ε54Cr = 0.06 ± 0.12 (2SD, N = 7) that is similar to the enstatite chondrites and the Earth-Moon system, Shallowater aubrite with ε54Cr = −0.12 ± 0.04 and Itqiy-type meteorites with ε54Cr = −0.26 ± 0.03 (2SD, N = 2). This shows that there were at least three enstatite achondrite parent bodies in the Solar System. This is confirmed by their distinguished mass-dependent Cr isotope compositions (δ53Cr values): 0.24 ± 0.03‰, 0.10 ± 0.03‰ and −0.03 ± 0.03‰ for main-group, Shallowater and Itqiy parent bodies, respectively. Aubrites are isotopically heavier than chondrites (δ53Cr = −0.12 ± 0.04‰), which likely results from the formation of an isotopically light sulfur-rich core. We also obtained the abundance of the radiogenic 53Cr (produced by the radioactive decay of 53Mn, T1/2 = 3.7 million years). The radiogenic ε53Cr excesses correlate with the 55Mn/52Cr ratios for aubrites (except Shallowater and Bustee) and also the Cr stable isotope compositions (δ53Cr values). We show that these correlations represent mixing lines that also hold chronological significance since they are controlled by the crystallization of sulfides and silicates, which mostly reflect the main-group aubrite parent body differentiation at 4562.5 ± 1.1 Ma (i.e., 4.8 ± 1.1 Ma after Solar System formation). Furthermore, the intercept of these lines with the ordinate axis which represent the initial ε53Cr value of main-group aubrites (0.50 ± 0.16, 2σ) is much higher than the average ε53Cr value of enstatite chondrites (0.15 ± 0.10, 2SD), suggesting an early sulfur-rich core formation that effectively increased the Mn/Cr ratio of the silicate fraction of the main-group aubrite parent body.

KW - Mn-Cr chronometry

KW - Cr systematics

KW - Aubrites

KW - Core formation

KW - Cr stable isotopes

KW - Enstatite achondrites

KW - Mantle differentiation

KW - Reduced planets

U2 - 10.1016/j.gca.2021.05.053

DO - 10.1016/j.gca.2021.05.053

M3 - Journal article

AN - SCOPUS:85108651795

VL - 308

SP - 256

EP - 272

JO - Geochimica et Cosmochimica Acta. Supplement

JF - Geochimica et Cosmochimica Acta. Supplement

SN - 0046-564X

ER -