Thermal history of the southern Antarctic Peninsula during Cenozoic oblique subduction

Abstract

Apatite (U–Th)/He and apatite fission-track thermochronology is used to constrain the cooling and uplift history of the southern Antarctic Peninsula where easterly-directed subduction of the Phoenix Plate, including ridge–trench collisions, has been taking place along its western margin since the Late Cretaceous. Apatite ages and thermal history models are similar on eastern Palmer Land but are younger and vary across westernmost Palmer Land and Alexander Island. Transformation of thermal history models to a single plot shows how cooling rates varied as a function of distance from the trench zone. Eastern Palmer Land preserves a record of uplift during the Late Cretaceous that coincides with changes in Phoenix Plate convergence rates and direction. In contrast, western Palmer Land and Alexander Island experienced a period of increased rates of cooling between c. 25 and 15 Ma. This younger phase of exhumation is bounded by major fault zones related to the extension and rifting that formed the present-day George VI Sound. It was probably triggered by cessation of subduction owing to trench collision of a ridge segment NE of the Heezen fracture zone. No evidence was found for slab window influences as seen along the northernmost part of the Antarctic Peninsula. Supplementary material: QTQt thermal models, a PDF with analytical protocols and supplementary tables are available at https://doi.org/10.6084/m9.figshare.c.6086234