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The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record

Abstract : Combining U-Pb ages with Lu-Hf data in zircon provides insights into the magmatic history of rocky planets. The Northwest Africa (NWA) 7034/7533 meteorites are samples of the southern highlands of Mars containing zircon with ages as old as 4476.3 +/- 0.9 Ma, interpreted to reflect reworking of the primordial Martian crust by impacts. We extracted a statistically significant zircon population (n = 57) from NWA 7533 that defines a temporal record spanning 4.2 Gyr. Ancient zircons record ages from 4485.5 +/- 2.2 Ma to 4331.0 +/- 1.4 Ma, defining a bimodal distribution with groupings at 4474 +/- 10 Ma and 4442 +/- 17 Ma. We interpret these to represent intense bombardment episodes at the planet's surface, possibly triggered by the early migration of gas giant planets. The unradiogenic initial Hf-isotope composition of these zircons establishes that Mars's igneous activity prior to similar to 4.3 Ga was limited to impact-related reworking of a chemically enriched, primordial crust. A group of younger detrital zircons record ages from 1548.0 +/- 8.8 Ma to 299.5 +/- 0.6 Ma. The only plausible sources for these grains are the temporally associated Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir, indicating that Mars has been in a stagnant-lid tectonic regime for most of its history. Our results imply that zircon is ubiquitous on the Martian surface, providing a faithful record of the planet's magmatic history.
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Submitted on : Wednesday, July 13, 2022 - 3:35:20 PM
Last modification on : Tuesday, December 6, 2022 - 11:10:07 AM

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Maria M. Costa, Ninna K. Jensen, Laura C. Bouvier, James N. Connelly, Takashi Mikouchi, et al.. The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record. Proceedings of the National Academy of Sciences of the United States of America, 2020, 117 (49), pp.30973-30979. ⟨10.1073/pnas.2016326117⟩. ⟨insu-03684650⟩

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