Seeking Signatures of Martian Magmatic Evolution within the Greater Thaumasia Plateau

Abstract:

We characterize a plateau and proximal eastern regions, consisting of Thaumasia, Solis, and Syria Planae, in terms of chemistry, mineralogy, and mapped geology. We determine how such independent and complementary data bear upon the evolution of this region for mantle evolution models[1]. Three chemical provinces make up the Greater Thaumasia (GT) and are less obscured by unconsolidated layers of globally-derived < 40 μm-size sediments [Fig. 5][2]. This enables complementary insight from Visible/Near/Thermal-Infrared data[3]. Depleted H and enriched Si relative to their respective global averages[4] define region 70 to the East, with the southeastern parts of GT exposing many non-volcanic rocks dating to middle-late Noachian[5]. On the West, region 90 marks K and Th depletion. Region 75 is an overlap of regions 70 and 90. GT exposes Hesperian-aged units of mostly volcanic origin in the NW, with region 90 localized in Syria Planum and 75 in Solis Planum. Comparing elemental mass fractions derived from Mars Odyssey GRS of GT sub-regions to the rest of Mars (ROM), confirms Ca depletion in region 70. H₂O depletion relative to ROM gets enhanced eastward to 70. Intriguingly, the intra-regional variation in Ca, as observed by the comparison with ROM, highlights its enrichment in 90 and 75. This may present an elemental signature supporting the detection of High-Ca Pyroxene (HCP) rocks by Rogers et al. [2014]. In detail, this convergence between regions 75 and 90, with the TES compositional class 8[3], indicate a possibility of HCP-rich volcanism. The enrichment of Si accompanied by H and Th depletion, across the Noachian-Hesperian transition in GT, diverges from mantle evolution models[1].

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