Cenozoic volcanism in Antarctica: Jones Mountains and Peter I Island

Abstract

Cenozoic volcanism is widespread along the Pacific coast of Antarctica; a relationship to the rifting of the West Antarctic Rift System is obvious, but the possible role for mantle plumes is not established. We compare here complete geochemical and strontium, neodymium, and lead isotopic data for volcanic rocks from one probable plume just off the coast of Ellsworth Land (Peter I Island) with data from rift-related volcanic rocks from the nearby Jones Mountains, Ellsworth Land. The alkali basalts from Peter I Island are similar in most respects to average oceanic island basalt, and we propose recognition of this island as the most southerly known oceanic plume/hotspot—only unusually high 207/204Pb ratios set the Peter I Island plume apart from other oceanic plumes. The volcanics from the Jones Mountains share many trace element and isotopic characteristics with the Peter I volcanics, including isotopic arrays which have as one end member the low 87/86Sr-high 206/204Pb component which is characteristic of Cenozoic volcanism throughout the West Antarctic Rift System. Basalts from the Jones Mountains are distinctive from those of Peter I Island principally in their much lower 207/204Pb ratios, and their low and non-OIB-like Ce/Pb ratios (8.5–17.6). To explain this difference, we propose that a minor component of subduction-impregnated subcontinental lithosphere has been incorporated into the rift-related Jones Mountains volcanics that is not present in the oceanic Peter I Island plume.