Subduction initiation in the Scotia Sea region and opening of the Drake Passage: When and why?

• Main Authors: Van de Lagemaat, S.H.A., Swart, M.L.A., Vaes, B., Kosters, M.E., Boschman, L.M., Burton-Johnson, A., Bijl, P.K., Spakman, W., van Hinsbergen, D.J.J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2021
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarctic Peninsula; Weddell Sea; Drake Passage; Scotia Sea; Weddell; South Orkney Islands; South Sandwich Trench; Antarc*; Antarctica
• Online Access: http://nora.nerc.ac.uk/id/eprint/529822/; https://nora.nerc.ac.uk/id/eprint/529822/1/1-s2.0-S0012825221000507-main.pdf; https://www.sciencedirect.com/science/article/pii/S0012825221000507?via%3Dihub

During evolution of the South Sandwich subduction zone, which has consumed South American Plate oceanic lithosphere, somehow continental crust of both the South American and Antarctic plates have become incorporated into its upper plate. Continental fragments of both plates are currently separated by small oceanic basins in the upper plate above the South Sandwich subduction zone, in the Scotia Sea region, but how fragments of both continents became incorporated in the same upper plate remains enigmatic. Here we present an updated kinematic reconstruction of the Scotia Sea region using the latest published marine magnetic anomaly constraints, and place this in a South America-Africa-Antarctica plate circuit in which we take intracontinental deformation into account. We show that a change in marine magnetic anomaly orientation in the Weddell Sea requires that previously inferred initiation of subduction of South American oceanic crust of the northern Weddell Sea below the eastern margin of South Orkney Islands continental crust, then still attached to the Antarctic Peninsula, already occurred around 80 Ma. Subsequently, between ~71–50 Ma, we propose that the trench propagated northwards into South America by delamination of South American lithosphere: this resulted in the transfer of delaminated South American continental crust to the overriding plate of the South Sandwich subduction zone. We show that continental delamination may have been facilitated by absolute southward motion of South America that was resisted by South Sandwich slab dragging. Pre-drift extension preceding the oceanic Scotia Sea basins led around 50 Ma to opening of the Drake Passage, preconditioning the southern ocean for the Antarctic Circumpolar Current. This 50 Ma extension was concurrent with a strong change in absolute plate motion of the South American Plate that changed from S to WNW, leading to upper plate retreat relative to the more or less mantle stationary South Sandwich Trench that did not partake in the absolute plate motion ...