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Title: The early differentiation of Mars inferred from Hf–W chronometry

Mars probably accreted within the first 10 million years of Solar System formation and likely underwent magma ocean crystallization and crust formation soon thereafter. In this study, to assess the nature and timescales of these large-scale mantle differentiation processes we applied the short-lived 182Hf– 182W and 146Sm– 142Nd chronometers to a comprehensive suite of martian meteorites, including several shergottites, augite basalt NWA 8159, orthopyroxenite ALH 84001 and polymict breccia NWA 7034. Compared to previous studies the 182W data are significantly more precise and have been obtained for a more diverse suite of martian meteorites, ranging from samples from highly depleted to highly enriched mantle and crustal sources. Our results show that martian meteorites exhibit widespread 182W/ 184W variations that are broadly correlated with 142Nd/ 144Nd, implying that silicate differentiation (and not core formation) is the main cause of the observed 182W/ 184W differences. The combined 182W– 142Nd systematics are best explained by magma ocean crystallization on Mars within ~20–25 million years after Solar System formation, followed by crust formation ~15 million years later. Finally, these ages are indistinguishable from the I–Pu–Xe age for the formation of Mars' atmosphere, indicating that the major differentiation of Mars into mantle, crust, and atmospheremore » occurred between 20 and 40 million years after Solar System formation and, hence, earlier than previously inferred based on Sm–Nd chronometry alone.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [2] ;  [4] ;  [2] ;  [5]
  1. University of Munster (Germany). Institut fur Planteologie; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
  2. University of Munster (Germany). Institut fur Planteologie
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
  4. Univ. of Washington, Seattle, WA (United States). Department of Earth and Space Sciences
  5. University of New Mexico, Albuquerque, NM (United States). Institute of Meteoritics
Publication Date:
Report Number(s):
LLNL-JRNL-728324
Journal ID: ISSN 0012-821X; TRN: US1702966
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 474; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 58 GEOSCIENCES; martian meteorites; Hf–W chronometry; Sm–Nd chronometry; planetary differentiation; magma ocean; crust formation
OSTI Identifier:
1409996

Kruijer, Thomas S., Kleine, Thorsten, Borg, Lars E., Brennecka, Gregory A., Irving, Anthony J., Bischoff, Addi, and Agee, Carl B.. The early differentiation of Mars inferred from Hf–W chronometry. United States: N. p., Web. doi:10.1016/j.epsl.2017.06.047.
Kruijer, Thomas S., Kleine, Thorsten, Borg, Lars E., Brennecka, Gregory A., Irving, Anthony J., Bischoff, Addi, & Agee, Carl B.. The early differentiation of Mars inferred from Hf–W chronometry. United States. doi:10.1016/j.epsl.2017.06.047.
Kruijer, Thomas S., Kleine, Thorsten, Borg, Lars E., Brennecka, Gregory A., Irving, Anthony J., Bischoff, Addi, and Agee, Carl B.. 2017. "The early differentiation of Mars inferred from Hf–W chronometry". United States. doi:10.1016/j.epsl.2017.06.047. https://www.osti.gov/servlets/purl/1409996.
@article{osti_1409996,
title = {The early differentiation of Mars inferred from Hf–W chronometry},
author = {Kruijer, Thomas S. and Kleine, Thorsten and Borg, Lars E. and Brennecka, Gregory A. and Irving, Anthony J. and Bischoff, Addi and Agee, Carl B.},
abstractNote = {Mars probably accreted within the first 10 million years of Solar System formation and likely underwent magma ocean crystallization and crust formation soon thereafter. In this study, to assess the nature and timescales of these large-scale mantle differentiation processes we applied the short-lived 182Hf–182W and 146Sm–142Nd chronometers to a comprehensive suite of martian meteorites, including several shergottites, augite basalt NWA 8159, orthopyroxenite ALH 84001 and polymict breccia NWA 7034. Compared to previous studies the 182W data are significantly more precise and have been obtained for a more diverse suite of martian meteorites, ranging from samples from highly depleted to highly enriched mantle and crustal sources. Our results show that martian meteorites exhibit widespread 182W/184W variations that are broadly correlated with 142Nd/144Nd, implying that silicate differentiation (and not core formation) is the main cause of the observed 182W/184W differences. The combined 182W–142Nd systematics are best explained by magma ocean crystallization on Mars within ~20–25 million years after Solar System formation, followed by crust formation ~15 million years later. Finally, these ages are indistinguishable from the I–Pu–Xe age for the formation of Mars' atmosphere, indicating that the major differentiation of Mars into mantle, crust, and atmosphere occurred between 20 and 40 million years after Solar System formation and, hence, earlier than previously inferred based on Sm–Nd chronometry alone.},
doi = {10.1016/j.epsl.2017.06.047},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 474,
place = {United States},
year = {2017},
month = {7}
}