Lithofacies and eruptive conditions of the southernmost volcanoes in the world (87° S)

Abstract

Neogene volcanic centres are uncommon in the Transantarctic Mountains but at least three basaltic examples occur within 300 km of South Pole, above 2200 m asl and inland of the margin of the West Antarctic Rift System. They are the southernmost volcanoes on Earth and have yielded Early—mid Miocene isotopic ages. Two of the centres, at Mt Early and Sheridan Bluff, have been examined. The centre at Mt Early is unequivocally glaciovolcanic. It formed a tall monogenetic volcanic edifice at least 1 km high and > 1.5 km in diameter. It erupted under significantly thicker-than-modern ice, which was probably a fast-moving ice stream at the eruptive site and resulted in a distinctive constructive architecture and lithofacies. It is the first described example of a glaciovolcano erupted beneath an ice stream. The characteristics of the second centre at Sheridan Bluff indicate that it was also a monogenetic volcano but with a shield-like profile, originally c. 6 km in basal diameter but just c. 400 m high. It probably erupted in a substantial pluvial lake in an ice-poor or ice-free environment. The strongly contrasting eruptive settings now identified by the volcanic sequences at both centres examined testify to a highly dynamic Antarctic Ice Sheet during the Early—mid Miocene.

Evidence for Glaciovolcanic, Phreatomagmatic Tuff Dominated Ridges at Pavonis Mons, Mars

“…The steepest side of the ridge is the near‐vertical face to the southeast (Figure 2b), which corresponds to the inferred up‐flow direction of the Pavonis paleo‐glacier (Figure 1). Terrestrial glaciovolcanic edifices are, in many cases, steeper on their up‐flow sides, even before glacial erosion occurs (e.g., Schopka et al., 2006; Smellie & Panter, 2021); this is because flowing ice confines eruptive products closer to the vent on the up‐flow side than on the lee side. The locally steeper distal margins of the ridge are consistent with confinement of volcanics against the walls of an ice vault (Gudmundsson, 2003).…”