A geological map of the Scotia Sea area constrained by bathymetry, geological data, geophysical data and seismic tomography models from the deep mantle

Abstract

The Scotia Sea is one of the tectonically most complex and least understood back-arc basins on Earth, which partly results from its remote location making the acquisition of data challenging. Here, we provide a review of current, publicly available geophysical and geological data in the Scotia Sea realm, including magnetic, Bouguer gravity anomaly, high-resolution bathymetric, heat flow and reflection seismic data and rock type data from cored and dredged samples. With this inter-disciplinary data-set, we performed an offshore geological mapping exercise that allowed us to identify lithologies in the predominantly submerged Scotia Sea domain. Cross-sections combining crustal structure and mantle tomography enabled us to address some of the still persisting geological challenges in this tectonically complex area.The data-review revealed that basalt is the dominant lithology in the Scotia Sea area, occupying most of the West and East Scotia Sea (WSS and ESS). Andesitic and more felsic lithologies are identified in the Central Scotia Sea (CSS) and the northern East Scotia Sea (ESS). Mesozoic/Palaeozoic metamorphic/sedimentary lithologies are reported from the highs along the North and South Scotia Ridges (NSR and SSR). These highs originate from a land bridge that, until the late-Mesozoic, connected the South American and Antarctic continents. Scarcely available and contradicting data prevent the age determination of several structural units surrounding and located on the Scotia plate, but our mapping exercise allowed us to confirm the presence of the early Oligocene - late Miocene Ancestral South Sandwich Arc (ASSA) in the east of the CSS, setting the minimum age of the older segment of the CSS crust to Eocene-earliest Oligocene.Three cross-sections cross-cutting the Scotia Sea reveal two high velocity zones, indicating cold mantle material. One is situated below the structural highs along the SSR, which we interpreted as remnant slab material of the ASSA and another below South Georgia and the CSS, which we interpreted as the front of the slab that currently subducts at the South Sandwich Trench (SSaT). The neutral velocity discontinuity below the WSS implies mantle conditions of a recently extinct spreading centre. The upper mantle low velocity anomaly below the CSS is interpreted as warmer toroidal flows around the slab edges of the subducting plate at the SSaT.We have demonstrated that the geological and geophysical data publicly available today allows us to create offshore geological maps in remote, inaccessible offshore domains. This is a less time-consuming, economically advantageous exercise, which re-uses existing geological and geophysical data for a new purpose. It is the most data-inclusive study there is today of the Scotia Sea region and serves as a guideline for future expeditions targeting the CSS and the structural features along the NSR to identify their age and origin. A georeferenced version of the map is provided in the supplementary material.