Petrogenesis, alteration, and shock history of intermediate shergottite Northwest Africa 7042: Evidence for hydrous magmatism on Mars?

T. V. Kizovski, M. R.M. Izawa, K. T. Tait, D. E. Moser, J. M.D. Day, B. C. Hyde, L. F. White, L. Kovarik, S. D. Taylor, D. E. Perea, I. R. Barker, B. R. Joy

Research output: Contribution to journalArticle

Abstract

Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of olivine (early zoned olivine Fo41-76, and late-stage fayalitic olivine Fo46-56), complexly zoned pyroxene (En35-64Fs22-46Wo5-34), shock-melted or maskelynitized feldspar (An5-30Ab16-61Or1-47), and accessory merrillite, apatite, ilmenite, titanomagnetite, Fe-Cr-Ti spinels, pyrrhotite, and baddeleyite. The zoned olivine grains have been pervasively modified, containing conspicuous brown Mg-rich cores surrounded by colorless, unaltered Fe-rich overgrowth rims. This textural relationship suggests that the cores were altered at magmatic temperatures prior to crystallization of the rims on Mars. Launch-generated shock veins in NWA 7042 also crosscut and displace several of the altered olivine grains indicating that alteration occurred before ejection of the meteorite. While this type of olivine alteration is rare in shergottites, it is similar to deuterically altered olivine in basalts and gabbros on Earth, caused by residual water-rich magmatic fluids. Transmission electron microscopy analysis of the olivine alteration did not reveal the high-temperature phases expected from this process; however, NWA 7042 has also been subjected to extensive terrestrial weathering, which may explain their absence. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where deuteric alteration of olivine has been observed (the others being NWA 10416, and Allan Hills 77005). The different mantle sources for the parental melts of these three meteorites would suggest many, if not all martian mantle reservoirs have the potential to produce water-rich magmas.

Original languageEnglish
Pages (from-to)103-123
Number of pages21
JournalGeochimica et Cosmochimica Acta
Volume283
DOIs
Publication statusPublished - Aug 15 2020
Externally publishedYes

Keywords

  • Alteration
  • Intermediate compositions
  • Mars
  • NWA 7042
  • Shergottites
  • Shock processes

ASJC Scopus subject areas

  • Geochemistry and Petrology

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    Kizovski, T. V., Izawa, M. R. M., Tait, K. T., Moser, D. E., Day, J. M. D., Hyde, B. C., White, L. F., Kovarik, L., Taylor, S. D., Perea, D. E., Barker, I. R., & Joy, B. R. (2020). Petrogenesis, alteration, and shock history of intermediate shergottite Northwest Africa 7042: Evidence for hydrous magmatism on Mars? Geochimica et Cosmochimica Acta, 283, 103-123. https://doi.org/10.1016/j.gca.2020.05.030