Evolving magmas, explosive eruptions and hydrothermal deposits at Nili Patea Caldera, Syrtis Major, Mars

Nili Patera is a 45 km diameter caldera at the centre of the Syrtis Major Planum volcanic province. Nili Patera is unique amongst martian volcanic terrains in that it is now below the surrounding planum and hosts a diverse range of volcanic landforms and mineralogies. Our work addresses the stratigraphic and structural context of the caldera, based on these important, and well-known, initial observations:\ud • Evidence of effusive and explosive volcanism.\ud • A compositional diversity from olivine-rich basalts to dacite and feldspathic units.\ud • Outcrops with spectral features indicative of hydrothermal silica in sinter mounds.\ud • Asymmetric collapse with a maximum subsidence of 1800 m; dropping the caldera floor below the surrounding volcanic shield.\ud • A 300 m high resurgent dome in the western caldera floor.\ud We present a geological map (figure 1) and stratigraphic history of Nili Patera (figure 2) in which these geological findings are put into a nine-part geological history (figure 3). Additionaly, we consider the implications of the caldera’s evolution for the evolution of Syrtis Major Planum and Highland Patera style volcanoes in general.