Radar Investigations at Apollinaris Mons, Mars: a non-Volcanic composition for the Fan Deposits and the Potential for a Caldera Paleolake

Apollinaris Mons is a prominent 200 km-wide and 5 km-high Martian shield volcano located near the boundary between the northern plains and southern highlands (174.4°E, 9.3°S) and approximately 200 km north of Gusev Crater, the target of investigations by the Spirit rover. It features a multi-stage caldera complex approximately 80 km in diameter, as well as extensive fan deposits draping the southern flank from summit to base and extending for almost 150 km. A recent study (El Maarry et al., Searching for Evidence of Hydrothermal Activity at Apollinaris Mons, submitted to Icarus) suggests that Apollinaris Mons is a site with high potential for ancient hydrothermal activity based on a suite of geomorphological features that point to a long history of magma-water interaction. In this meeting, we present shallow ground-penetrating radar data for Apollinaris Mons from orbiting spacecraft in conjunction with high resolution images and altimetry that show that the fan deposits are 1.5 to 2 km-thick in some locations and potentially layered. Furthermore, the dielectric properties of the deposits suggest a non-volcanic composition. Finally, we assess the role a caldera paleolake(s) in forming the fan deposits.