EP017-07
A new type of hydrous alteration on Mars? Investigating the unique textures of olivine in martian meteorite NWA 7042
Wednesday, 9 December 2020: 04:18
Virtual
Tanya Kizovski1,2, Matthew R Izawa3, Kimberly Tait1,2, Desmond Moser4, James M Day5, Brendt C Hyde2,4, Lee Francis White1,2, Libor Kovarik6, Sandra D Taylor6, Daniel E. Perea7, Ivan Barker8 and Brian R Joy9, (1)University of Toronto, Earth Sciences, Toronto, ON, Canada, (2)Royal Ontario Museum, Centre for Applied Planetary Mineralogy, Toronto, ON, Canada, (3)Okayama University, Institute for Planetary Materials, Misasa, Japan, (4)University of Western Ontario, Earth Sciences, London, ON, Canada, (5)Scripps Institution of Oceanography, Geosciences Research Division, Scripps Isotope Geochemistry Laboratory, La Jolla, CA, United States, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (8)University of Western Ontario, London, ON, Canada, (9)Queen's University, Geological Sciences and Geological Engineering, Kingston, ON, Canada
Abstract:
In the absence of return samples, martian meteorites provide us with the only opportunity to directly analyze the martian crust at scales and precision not possible with
in-situ rover and remote sensing techniques. Analysis of these rare samples is particularly valuable if they have been altered by martian fluids. The chemical analysis of the resulting aqueous alteration products can provide new insight into the chemistry of water reservoirs on Mars, the conditions under which these rocks were altered, and possibly the timing of the alteration. However, determining the origin of alteration products in meteorites is difficult as the majority have also been exposed to terrestrial weathering on the Earth’s surface. Here, we present our geochemical and petrographic analysis of the uniquely modified olivine within martian meteorite Northwest Africa (NWA) 7042 and examine the possibility of both martian alteration, and terrestrial weathering formation mechanisms.
The olivine grains in NWA 7042 have been pervasively modified, containing brown Mg-rich cores surrounded by colorless, unaltered Fe-rich rims. This textural relationship suggests that the cores were altered at magmatic temperatures prior to crystallization of the rims on Mars. Shock veins generated during the ejection of NWA 7042 from the martian surface also crosscut and displace several of the altered grains indicating that alteration occurred before ejection. While this type of alteration is rare in martian meteorites, 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 terrestrial weathering which may have overprinted such evidence. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where this alteration has been observed (see NWA 10416 and ALH 77005). The different mantle sources for the parental melts of these three meteorites suggests many martian mantle reservoirs could have produced water-rich magmas.
