Evolution of the Pacific margin of the northern Antarctic Peninsula: an overview

Abstract

The sector of the northern Antarctic Peninsula between the Tula and Shackleton Fracture Zones provides evidence for the subduction of south-east Pacific oceanic crust under Antarctic continental crust during Late Mesozoic through Miocene times. The pre-subduc-tion depositional history of this sector includes the formation of a marine siliciclastic turbidite wedge (?Permian — Triassic) deposited in a marginal basin setting. It was folded and thrust retroarc before the Middle Jurassic to form the Trinity accretion foldbelt, which extended for several hundred kilometres along the Pacific margin of Gondwanaland. The foldbelt was deeply eroded and levelled under subaerial conditions, then unconformably covered either by Middle —Upper Jurassic alluvial to lacustrine deposits (in the north) or by Early Cretaceous basic lavas (in the south).

The subduction-related magmatism, in the form of acidic effusions and intrusions, began in the northern Antarctic Peninsula during Middle Jurassic times and continued as predominantly basic lavas and agglomerates intruded by basic, intermediate and acidic plutons, and by a succession of dykes, during the Early to Late Cretaceous. Thus the inner magmatic arc of the northern Antarctic Peninsula (northern Graham Land —Trinity Peninsula) was formed.

An outward (north-westerly) migration of centres of magmatic activity with time (Cretaceous — Tertiary) towards the subduction trench, coupled with a northeastward shift of these centres along the Arc’s length due to the counterclockwise rotation of Antarctica, produced the outer magmatic arc of the South Shetland Islands.

Slight folding of Late Mesozoic and Tertiary magmatic suites occurred at several stages of subduction. Stronger folding and retroarc thrusting appeared locally as a result of the collision of the Aluk Ridge — Antarctic Peninsula during the Mid-Miocene. The latest plate tectonic event was the opening of the Bransfield Rift (Oligocene — Recent) as a spreading back-arc basin, associated with terrestrial and submarine volcanic activity.