Ancient geologic events on Mars revealed by zircons and apatites from the Martian regolith breccia NWA 7034

1,2,3Sen Hu,1,2,3Yangting Lin,1Jianchao Zhang,1Jialong Hao, 1Weifan Xing,1,2,3Ting Zhang,1,2,3Wei Yang,1Hitesh Changela
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13256]
1Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
2Institutes of Earth Science, Chinese Academy of Sciences, Beijing, 100029 China
3College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049 China
Published by arrangement with John Wiley & Sons

Zircons and apatites in clasts and matrix from the Martian breccia NWA 7034 are well documented, timing ancient geologic events on Mars. Furthermore, in this study, zircon trace elemental content, apatite volatile content, and apatite volatile isotopic compositions measured in situ could constrain the evolution of those geologic events. The U‐Pb dates of zircons in basalt, basaltic andesite, trachyandesite igneous clasts, and the matrix are similar (4.4 Ga) suggesting intense volcanism on ancient Mars. However, two metamict zircon grains found in the matrix have an upper intercept date of ~4465 Ma in crystalline, whereas amorphous areas have a lower intercept date of 1634 ± 93 Ma. The younger date is consistent with the date of apatites (1530 ± 65 Ma), suggesting a metamorphic event that completely reset the U‐Pb system in both the amorphous areas of zircon and all apatites. δD values in all apatites negatively correlate with water content in a two‐endmember mixing trend. The D (δD up to 2459‰) and 37Cl heavy core (3.8‰) of a large apatite grain suggest a D‐, 37Cl‐rich fluid during the metamorphic event ~1.6 Ga ago, consistent with the trace elements Y, Hf and Ti and P in zircons. The fluid was also therefore P‐rich. The D‐, 37Cl‐poor H2O‐rich rim (<313‰) suggests the degassing of water from the Martian Cl‐poor interior at a later time. This D‐, 37Cl‐poor Martian mantle reservoir could have derived from volcanic intrusions postdating the younger metamorphic event recorded in NWA 7034.

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