Abstract
Nili Patera is a 50 km diameter caldera at the center of the Syrtis Major Planum volcanic province. The caldera is unique among Martian volcanic terrains in hosting: (i) evidence of both effusive and explosive volcanism, (ii) hydrothermal silica, and (iii) compositional diversity from olivine-rich basalts to silica-enriched units. We have produced a new geological map using three mosaicked 18 m/pixel Context Camera digital elevation models, supplemented by Compact Remote Imaging Spectrometer for Mars Hyperspectral data. The map contextualizes these discoveries, formulating a stratigraphy in which Nili Patera formed by trapdoor collapse into a volcanotectonic depression. The distinctive bright floor of Nili Patera formed either as part of a felsic pluton, exposed during caldera formation, or as remnants of welded ignimbrite(s) associated with caldera formation—both scenarios deriving from melting in the Noachian highland basement. After caldera collapse, there were five magmatic episodes: (1) a basaltic unit in the caldera's north, (2) a silica-enriched unit and the associated Nili Tholus cone, (3) an intrusive event, forming a ~300 m high elliptical dome; (4) an extrusive basaltic unit, emplaced from small cones in the east; and (5) an extreme olivine-bearing unit, formed on the western caldera ring fault. The mapping, together with evidence for hydrated materials, implies magmatic interaction with subsurface volatiles. This, in an area of elevated geothermal gradient, presents a possible habitable environment (sampled by the hydrothermal deposits). Additionally, similarities to other highland volcanoes imply similar mechanisms and thus astrobiological potential within those edifices.
Highlights
Nili Patera (Figure 1) is a 50 km diameter caldera within the caldera complex at the center of the Syrtis Major Planum volcanic province
We have produced a new geological map using three mosaicked 18 m/pixel Context Camera digital elevation models, supplemented by Compact Remote Imaging Spectrometer for Mars Hyperspectral data. The map contextualizes these discoveries, formulating a stratigraphy in which Nili Patera formed by trapdoor collapse into a volcanotectonic depression
The distinctive bright floor of Nili Patera formed either as part of a felsic pluton, exposed during caldera formation, or as remnants of welded ignimbrite(s) associated with caldera formation—both scenarios deriving from melting in the Noachian highland basement
Summary
Nili Patera (Figure 1) is a 50 km diameter caldera within the caldera complex at the center of the Syrtis Major Planum volcanic province. Syrtis Major Planum is a Hesperian-aged, low-angle volcanic shield located in the Martian highlands on the rim of the Isidis basin [Meyer and Grolier, 1977; Scott and Carr, 1978; Plescia and Saunders, 1979; Greeley and Guest, 1987; Tanaka et al, 2014a, 2014b] consisting of a gently sloping “shield” of lava plains 1100 km wide and estimated to have a mean thickness of 500 m [Hiesinger and Head, 2004]. The subsidence of the whole caldera complex has been linked to magma reservoir drainage and cooling [Kiefer, 2004; Dufek et al, 2014]
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