Volatile abundances and hydrogen isotope ratios of apatite in Martian basaltic breccia NWA 11522—A paired stone of NWA 7034

Abstract

AbstractThis study aimed to determine the volatile content (Cl, F, OH) and hydrogen isotope (D/H) ratios of apatite grains within the Martian meteorite NWA 11522, a paired stone of the ungrouped polymict breccia NWA 7034. Apatite F:Cl:OH ratios were measured via SEM‐EDS analyses, and found to be strikingly similar in all grains, and dominated by Cl. Apatite D/H ratios were measured in situ via the Cameca ims 1280 SIMS at the University of Hawai'i. Results varied between δDvalues of 782 and 52 ‰ and between water contents of 0.127 and 0.510 wt%. The data form a mixing line between two endmembers. The first endmember, a high D/H ratio and low water content endmember, represents a fluid present during the thermal event that lithified the breccia at 1.5 Ga, resetting apatite volatile content, D/H ratio, and U‐Pb ages at this time. The D/H ratio of this fluid suggests that it was derived from the crust/cryosphere (e.g., melted groundwater ice). The second endmember, a low D/H ratio and high water content endmember, represents a second Martian fluid that interacted with the breccia after lithification. The low D/H ratio of this later fluid indicates it was derived from the deeper Martian interior, and may be evidence of an impact‐related hydrothermal system on Mars during the Amazonian period. The presence of these fluids within NWA 11522 suggests that subsurface impact crater environments were still host to liquid water during the past 1.5 Ga on Mars, and still could be to this day.