VOLCANIC HISTORY OF AMPHITRITES AND PENEUS PATERAE, MARS: A TALE OF TWO VOLCANOES

Highland paterae represent a unique class of volcano on the Martian surface and are interpreted to have formed through periods of explosive volcanism. These volcanoes predominantly occur within the Circum-Hellas volcanic province and are characterized by low-relief flanks and a prominent central caldera. Here we present our initial results of our ongoing work addressing the volcanic evolution of two of these paterae – Amphitrites and Peneus Paterae, which are located in northern Malea Planum, southwest of Hellas basin. The two volcanoes are in relatively close proximity (~140 km apart), but appear to have undergone distinct volcanic evolutions. Amphitrites Patera (59° S, 60° E) is ~280 km in diameter (flanks plus caldera) with heavily channeled flanks, which suggests that much of the volcano is comprised loose material that we interpret as representing explosively erupted deposits. The caldera is ~125 km in diameter and appears to host a smaller (~60 km diameter) caldera suggesting a pro-longed and complex magmatic history for this volcano. There is no apparent evidence for effusive volcanism having occurred at Amphtrities, but such deposits may be covered by a surficial deposit that characterizes much of the Malea Planum region. In contrast, Peneus Patera (57° S, 52° E) is ~200 km in diameter (flanks plus caldera), hosts a lot fewer channels on its flanks, and has a singular flat-floored caldera denoted by a suite of concentric graben. A dome ~40 km in diameter appears to extend from the graben in the southwest corner of the caldera and suggests that Peneus underwent a late stage effusive eruption. When taken together, such observations suggest that Peneus, when compared to Amphitrites, may have experienced more effusive rather explosive volcanism and underwent a much simpler caldera collapse history. Although our results are still preliminary, they do indicate that not all highland paterae are created equally.