Cenozoic tectonic history of the South Georgia microcontinent and potential as a barrier to Pacific-Atlantic through flow

Andrew Carter,James Schwanethal,Mike Curtis

doi:10.1130/g35091.1

Andrew Carter, James Schwanethal + Show 1 more

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https://doi.org/10.1130/g35091.1

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Abstract

Cenozoic opening of the central Scotia Sea involved the tectonic translation of crustal blocks to form the North Scotia Ridge, which today is a major topographic constriction to the flow of the deep Antarctic Circumpolar Current that keeps Antarctica thermally isolated from warmer ocean waters. How this ridge developed and whether it was a topographic barrier in the past are unknown. To address this we investigated the Cenozoic history of the South Georgia microcontinental block, the exposed part of the ridge. Detrital zircon U-Pb geochronology data confirm that the Cretaceous succession of turbidites exposed on South Georgia was stratigraphically connected to the Rocas Verdes backarc basin, part of the South America plate. Apatite thermochronometry results show that South Georgia had remained connected to South America until ca. 45–40 Ma; both record a distinct rapid cooling event at that time. Subsequent separation from South America was accompanied by kilometer-scale reburial until inversion ca. 10 Ma, coeval with the cessation of spreading at the West Scotia Ridge and collision between the South Georgia block and the Northeast Georgia Rise. Our results show that the South Georgia microcontinental block could not have been an emergent feature from ca. 40 Ma until 10 Ma.

Highlights

Cenozoic opening of the central Scotia Sea involved the tectonic translation of crustal blocks end of the North Scotia Ridge and that South to form the North Scotia Ridge, which today is a major topographic constriction to the flow of Georgia once belonged to part of an extended the deep Antarctic Circumpolar Current that keeps Antarctica thermally isolated from warmer continental margin along the Falkland Plateau ocean waters
To discriminate between competing plate reconstruction models and remove uncertainty surrounding the pre-breakup location of the South Georgia microcontinental block, we compared detrital zircon U-Pb age signatures of the Cretaceous turbidite sequences exposed on South Georgia with potential source areas; namely, the Cordillera
Evidence from South America shows that this basin was inverted and obducted onto the continental margin of South America, metamorphosed, and the equivalents of the Early Cretaceous turbidites of South Georgia folded before intrusion of the Late Cretaceous Beagle Suite granitoids (Mukasa and Dalziel, 2009); South Georgia was likely a topographic feature by the Late Cretaceous

Summary

Introduction

Cenozoic opening of the central Scotia Sea involved the tectonic translation of crustal blocks end of the North Scotia Ridge and that South to form the North Scotia Ridge, which today is a major topographic constriction to the flow of Georgia once belonged to part of an extended the deep Antarctic Circumpolar Current that keeps Antarctica thermally isolated from warmer continental margin along the Falkland Plateau ocean waters How this ridge developed and whether it was a topographic barrier in the past are that formed as Gondwana broke up in Jurassic unknown. Considerable effort has been directed at un- lera, that drove inversion of the marginal ba- as an early proximal barrier to deep Pacificderstanding the geological evolution of the Sco- sins, and the obduction of the Rocas Verdes Atlantic flow To resolve these issues we examtia Sea region as seafloor spreading in the West ophiolitic basement onto the continental mar- ined the provenance of Cretaceous turbidites. Scotia Sea caused the opening of the deep Drake gin can be followed along strike from Tierra exposed on South Georgia using detrital zircon

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