Pavonis Mons Fan-shaped Deposits - a Cold-based Glacial Model

Introduction: Each of the three Tharsis Montes volcanoes on Mars has unusual fan-shaped deposits located exclusively to the northwest of each shield. The fan-shaped deposits of the Tharsis Montes generally share three major facies: 1) Ridged facies, 2) Knobby facies, and 3) Smooth facies. Here we examine the Pavonis fan-shaped deposits using new Mars Global Surveyor and Mars Odyssey data. Any explanation for the origin of the fan-shaped deposits must take into account both the similarities and differences in their morphologies, their approximately similar Amazonian age, and the fact that all three occur on the west-northwestern sides of the volcanoes [1]. Based on Vi-king Orbiter data, several models have been proposed for their formation, including massive landslides [2], glacial processes [3,4,5,6] and pyroclastic flows [6]. Williams [3] and Lucchitta [4] suggest that the fan-shaped deposits are the result of the deposition of mo-raines due to recession of local ice caps that formed on the volcanoes from mixtures of emanated volatiles and erupted ash [4]. Scott et al [6] suggest an explanation combining glacial and volcanic processes. The Pavonis fan-shaped deposits (Figure 1) extend approximately 250 km northwest of the shield base along a N35°W trend [5]. These deposits range from 3.0-8.5 km above the Mars datum and cover an area of about 7.5 x 10 4 km