Formation Conditions of Basalts at Gale Crater, Mars from ChemCam Analyses

Abstract:

Surface igneous rocks shed light onto the chemistry, tectonic, and thermal state of planetary interiors. For the purpose of comparative planetology, therefore, it is critical to fully utilize the compositional diversity of igneous rocks for different terrestrial planets. For Mars, igneous float rocks and conglomerate clasts at Gale Crater, as analyzed by ChemCam [1] using a new calibration [2], have a larger range in chemistry than have been analyzed at any other landing site or within the Martian meteorite collection [3, 4]. These rocks may reflect different conditions of melting within the Martian interior than any previously analyzed basalts. Here we present new formation conditions for basaltic and trachybasalt/dioritic rocks at Gale Crater from ChemCam analyses following previous procedures [5, 6]. We then compare these estimates of basalt formation with previous estimates for rocks from the Noachian (Gusev Crater, Meridiani Planum, and a clast in the NWA 7034 meteorite [5, 6]), Hesperian (surface volcanics [7]), and Amazonian (surface volcanics and shergottites [7-8]), to calculate an average mantle potential temperature for different Martian epochs and investigate how the interior of Mars has changed through time. Finally, we will compare Martian mantle potential temperatures with petrologic estimate of cooling for the Earth. Our calculated estimate for the mantle potential temperature (T_P) of rocks at Gale Crater is 1450 ± 45 °C which is within error of previous estimates for Noachian aged rocks [5, 6]. The T_P estimates for the Hesperian and Amazonian, based on orbital analyses of the crust [7], are lower in temperature than the estimates for the Noachian. Our results are consistent with simple convective cooling of the Martian interior.

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