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Title: The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian

Northwest Africa (NWA) 8159 is an augite-rich shergottite, with a mineralogy dominated by Ca-, Fe-rich pyroxene, plagioclase, olivine, and magnetite. NWA 8159 crystallized from an evolved melt of basaltic composition under relatively rapid conditions of cooling, likely in a surface lava flow or shallow sill. Redox conditions experienced by the melt shifted from relatively oxidizing (with respect to known Martian lithologies, ~QFM) on the liquidus to higher oxygen fugacity (~QFM + 2) during crystallization of the groundmass, and under subsolidus conditions. This shift resulted in the production of orthopyroxene and magnetite replacing olivine phenocryst rims. NWA 8159 contains both crystalline and shock-amorphized plagioclase (An 50–62), often observed within a single grain; based on known calibrations we bracket the peak shock pressure experienced by NWA 8159 to between 15 and 23 GPa. The bulk composition of NWA 8159 is depleted in LREE, as observed for Tissint and other depleted shergottites; however, NWA 8159 is distinct from all other martian lithologies in its bulk composition and oxygen fugacity. Here, we obtain a Sm-Nd formation age of 2.37 ± 0.25 Ga for NWA 8159, which represents an interval in Mars geologic time which, until recently, was not represented in the other martian meteoritemore » types. The bulk rock 147Sm/ 144Nd value of 0.37 ± 0.02 is consistent with it being derived directly from its source and the high initial ε 143Nd value indicates this source was geochemically highly depleted. Cr, Nd, and W isotopic compositions further support a unique mantle source. While the rock shares similarities with the 2.4-Ga NWA 7635 meteorite, there are notable distinctions between the two meteorites that suggest differences in mantle source compositions and conditions of crystallization. Nevertheless, the two samples may be launch-paired. Finally, NWA 8159 expands the known basalt types, ages and mantle sources within the Mars sample suite to include a second igneous unit from the early Amazonian.« less
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [3] ;  [3] ;  [3] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [6] ;  [7] ;  [7] ;  [8] ;  [8] ;  [8] ;  [9] more »;  [9] ;  [9] ;  [10] ;  [11] « less
  1. Univ. of Alberta, Edmonton, AB (Canada). Dept. of Earth and Atmospheric Sciences
  2. Univ. of Alberta, Edmonton, AB (Canada). Dept. of Earth and Atmospheric Sciences; MacEwan Univ., Edmonton, AB (Canada). Dept. of Physical Sciences
  3. Univ. of New Mexico, Albuquerque, NM (United States). Inst. of Meteoritics, Dept. of Earth and Planetary Sciences
  4. NASA Johnson Space Center, Houston, TX (United States)
  5. Aix-Marseille Univ., and CNRS, Aix-en-Provence (France)
  6. Inst. de Physique due Globe de Paris, Paris (France)
  7. Univ. of California, Davis, CA (United States). Dept. Earth and Planetary Sciences
  8. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  9. Univ. of Munster, Munster (Germany). Inst. for Planetology
  10. Univ. of California, Berkeley, CA (United States). Space Sciences Lab.
  11. Purdue Univ., West Lafayette, IN (United States). Dept. of Physics and Astronomy
Publication Date:
Report Number(s):
Journal ID: ISSN 0016-7037
Grant/Contract Number:
AC52-07NA27344; 261740; RES00007057; 10-LASER10–0077; 11-COS11-0066; NNH14AX56I; NNX13AG44G
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 218; Journal Issue: C; Journal ID: ISSN 0016-7037
The Geochemical Society; The Meteoritical Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE; Natural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautic and Space Administration (NASA)
Country of Publication:
United States
58 GEOSCIENCES; Mars; Igneous rocks; Augite-rich shergottites; Amazonian; Mantle sources
OSTI Identifier: