Cretaceous–Paleogene tectonic reconstructions of the South Scotia Ridge and implications for the initiation of subduction in the Scotia Sea

Abstract

The Cenozoic development of the Scotia Sea and the opening of Drake Passage led to the dispersal of crustal blocks of the North and South Scotia ridges, which today have a strong influence on the pathway of the Antarctic circumpolar current. The pre-translation positions of the crustal fragments of the Scotia ridges are uncertain, with correlations to both the Antarctic and South American plates. We present direct geochronology results ( 40 Ar/ 39 Ar) from the Bruce and Jane banks of the South Scotia Ridge that yield Late Cretaceous–Paleogene ages, indicating a pre-translation magmatic history. The basaltic magmatism from Bruce Bank is calc-alkaline, akin to the Cenozoic magmatism of the South Orkney microcontinent and the South Shetland Islands, and agrees with pre-translation tectonic models that place the crustal blocks of the South Scotia Ridge adjacent to the northern Antarctic Peninsula arc. The intra-oceanic arc magmatism at Jane Bank is Late Cretaceous in age (97.2 ± 1.1 Ma) and is therefore inconsistent with models suggesting a Miocene origin as part of the ancestral South Sandwich arc. The development of westwards-directed subduction adjacent to Jane Bank is predicted in some tectonic models as a consequence of Late Cretaceous plate dynamics that developed prior to the Oligocene–Miocene ancestral arc. Supplementary material: Full 40 Ar/ 39 Ar datasets and GPlates reconstruction files are available at https://doi.org/10.6084/m9.figshare.c.6639909