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Title: Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

Abstract

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53Mn- 53Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53Cr/ 52Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than timemore » estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1634288
Alternate Identifier(s):
OSTI ID: 1618999
Report Number(s):
LLNL-JRNL-798577
Journal ID: ISSN 0012-821X; 1001487
Grant/Contract Number:  
AC52-07NA27344; 17-ERD-001; 20-ERD-001
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 542; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
geosciences; Mars; Mn-Cr system; magma ocean; planetary differentiation; chronology; martian meteorites

Citation Formats

Kruijer, Thomas S., Borg, Lars E., Wimpenny, Josh, and Sio, Corliss K. Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry. United States: N. p., 2020. Web. doi:10.1016/j.epsl.2020.116315.
Kruijer, Thomas S., Borg, Lars E., Wimpenny, Josh, & Sio, Corliss K. Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry. United States. doi:10.1016/j.epsl.2020.116315.
Kruijer, Thomas S., Borg, Lars E., Wimpenny, Josh, and Sio, Corliss K. Thu . "Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry". United States. doi:10.1016/j.epsl.2020.116315.
@article{osti_1634288,
title = {Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry},
author = {Kruijer, Thomas S. and Borg, Lars E. and Wimpenny, Josh and Sio, Corliss K.},
abstractNote = {The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53Mn-53Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53Cr/52Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.},
doi = {10.1016/j.epsl.2020.116315},
journal = {Earth and Planetary Science Letters},
issn = {0012-821X},
number = C,
volume = 542,
place = {United States},
year = {2020},
month = {5}
}

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