INTERMEDIATE AND FELSIC MAGMATISM IN EARLY MARS: IMPLICATIONS IN THE COMPOSITION OF THE ANCIENT MARTIAN CRUST (Invited Presentation)

Evidences of a diverse volcanic activity on Mars are increasing over the years. Most martian meteorites, orbital observations of the surface of Mars, and Mars Exploration Rovers showed the dominantly mafic composition of igneous rocks. Yet, the Curiosity rover that landed in Gale crater was the first to reveal intermediate and felsic rocks with trachytic and dacitic compositions of Noachian age (> 3.8 Ga; [1-2]), as well as minerals like tridymite pointing out silicic explosive volcanism [3-4]. Several clasts within the martian meteorite Northwest Africa (NWA) 7533 and its paired rocks dated at 4.48 Ga are felsic, and isotope analyses unveil that they originated from an enriched andesitic primary crust that was extracted from the mantle 4.547 Ga ago, i.e, 20 Myr after the Solar System formation [5]. Both Gale crater and the ejection site of NWA 7533 are located within the Terra Sirenum/Cimmeria (TSC) region that displays relatively higher Th and K content compared to the surroundings, potentially indicating evolved magmatism (SiO₂ > 53 wt.%; [6-8]). In this region, visible/near infrared (VNIR) orbital observations combined with mid-infrared thermal emission data demonstrated the occurrence of several early and mid-Noachian (> 4.2 Ga) feldspar-rich (> 60 wt.%) intermediate terrains below the surface exposed by impacts and erosion [9]. Along with the detection of additional Noachian feldspar-rich evolved terrains identified with VNIR spectroscopy in the southern hemisphere [10-11], these key findings challenge the assumption of a homogeneous mafic martian crust, revealing at least one ancient crustal component at TSC that is evolved, potentially andesitic in composition, underneath the mafic surface, questioning the formation and evolution of the early martian crust.

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