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Title: Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy

Abstract

Martian meteorite Northwest Africa (NWA) 7034 and its paired stones are the only brecciated regolith samples from Mars with compositions that are representative of the average martian crust. These samples therefore provide a unique opportunity to constrain the processes of metamorphism and alteration in the martian crust, which we have investigated via U-Pu/Xe, 40Ar/ 39Ar, and U-Th-Sm/He chronometry. U-Pu/Xe ages are comparable to previously reported Sm-Nd and U-Pb ages obtained from NWA 7034 and confirm an ancient (>4.3 billion years) age for the source lithology. After almost 3000 million years (Ma) of quiescence, the source terrain experienced several hundred million years of thermal metamorphism recorded by the K-Ar system that appears to have varied both spatially and temporally. Such protracted metamorphism is consistent with plume-related magmatism and suggests that the source terrain covered an areal extent comparable to plume-fed edifices (hundreds of square kilometers). The retention of such expansive, ancient volcanic terrains in the southern highlands over billions of years suggests that formation of the martian crustal dichotomy, a topographic and geophysical divide between the heavily cratered southern highlands and smoother plains of the northern lowlands, likely predates emplacement of the NWA 7034 source terrain—that is, it formed within themore » first ~100 Ma of planetary formation.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [4]; ORCiD logo [5]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
  2. Scottish Univ., East Kilbride (United Kingdom). Environmental Research Centre; Univ. of Glasgow, Scotland (United Kingdom). School of Geographical and Earth Sciences
  3. Scottish Univ., East Kilbride (United Kingdom). Environmental Research Centre; Univ. of St. Andrews, Scotland (United Kingdom). Dept. of Earth and Environmental Sciences
  4. Univ. of Glasgow, Scotland (United Kingdom). School of Geographical and Earth Sciences
  5. Univ. of Glasgow, Scotland (United Kingdom). School of Geographical and Earth Sciences; Natural History Museum, London (United Kingdom). Dept. of Earth Sciences
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1502038
Report Number(s):
LLNL-JRNL-731792
Journal ID: ISSN 2375-2548; 883329
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 4; Journal Issue: 5; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Cassata, William S., Cohen, Benjamin E., Mark, Darren F., Trappitsch, Reto, Crow, Carolyn A., Wimpenny, Joshua, Lee, Martin R., and Smith, Caroline L. Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy. United States: N. p., 2018. Web. doi:10.1126/sciadv.aap8306.
Cassata, William S., Cohen, Benjamin E., Mark, Darren F., Trappitsch, Reto, Crow, Carolyn A., Wimpenny, Joshua, Lee, Martin R., & Smith, Caroline L. Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy. United States. doi:10.1126/sciadv.aap8306.
Cassata, William S., Cohen, Benjamin E., Mark, Darren F., Trappitsch, Reto, Crow, Carolyn A., Wimpenny, Joshua, Lee, Martin R., and Smith, Caroline L. Wed . "Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy". United States. doi:10.1126/sciadv.aap8306. https://www.osti.gov/servlets/purl/1502038.
@article{osti_1502038,
title = {Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy},
author = {Cassata, William S. and Cohen, Benjamin E. and Mark, Darren F. and Trappitsch, Reto and Crow, Carolyn A. and Wimpenny, Joshua and Lee, Martin R. and Smith, Caroline L.},
abstractNote = {Martian meteorite Northwest Africa (NWA) 7034 and its paired stones are the only brecciated regolith samples from Mars with compositions that are representative of the average martian crust. These samples therefore provide a unique opportunity to constrain the processes of metamorphism and alteration in the martian crust, which we have investigated via U-Pu/Xe, 40Ar/39Ar, and U-Th-Sm/He chronometry. U-Pu/Xe ages are comparable to previously reported Sm-Nd and U-Pb ages obtained from NWA 7034 and confirm an ancient (>4.3 billion years) age for the source lithology. After almost 3000 million years (Ma) of quiescence, the source terrain experienced several hundred million years of thermal metamorphism recorded by the K-Ar system that appears to have varied both spatially and temporally. Such protracted metamorphism is consistent with plume-related magmatism and suggests that the source terrain covered an areal extent comparable to plume-fed edifices (hundreds of square kilometers). The retention of such expansive, ancient volcanic terrains in the southern highlands over billions of years suggests that formation of the martian crustal dichotomy, a topographic and geophysical divide between the heavily cratered southern highlands and smoother plains of the northern lowlands, likely predates emplacement of the NWA 7034 source terrain—that is, it formed within the first ~100 Ma of planetary formation.},
doi = {10.1126/sciadv.aap8306},
journal = {Science Advances},
number = 5,
volume = 4,
place = {United States},
year = {2018},
month = {5}
}

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