The age and origin of the central Scotia Sea

Abstract

SUMMARY Opening of the Drake Passage gateway between the Pacific and Atlantic oceans has been linked in various ways to Cenozoic climate changes. From the oceanic floor of Drake Passage, the largest of the remaining uncertainties in understanding this opening is in the timing and process of the opening of the central Scotia Sea. All but one of the available constraints on the age of the central Scotia Sea is diagnostic of, or consistent with, a Mesozoic age. Comparison of tectonic and magnetic features on the seafloor with plate kinematic models shows that it is likely to have accreted to a mid‐ocean ridge between the South American and Antarctic plates following their separation in Jurassic times. Subsequent regional shallowing may be related to subduction‐related processes that preceded backarc extension in the East Scotia Sea. The presence of a fragment of Jurassic–Cretaceous ocean floor in the gateway implies that deep water connections through the Scotia Sea basin complex may have been possible since Eocene times when the continental tips of South America and the Antarctic Peninsula first passed each other.

Tectonic reconstructions for paleobathymetry in Drake Passage

“…Sediment temperature gradients, measured at multiple widelyseparated sites over multi-year timescales, are consistently far shallower than should exist in equilibrium with Miocene oceanic basement (Barker and Lawver, 2000;Zlotnicki et al, 1980). New modelling of the sediment temperature gradient and of isochrons in the magnetic anomalies leads to the conclusion that the central Scotia basement is instead of Mesozoic age (Eagles, 2010b). Possible explanations for the basin's shallow seafloor, if it is so old, have yet to be studied but are suggested to be related to subduction beneath it.…”

“…Subduction in the northwest Weddell Sea, beneath the South Orkney Microcontinent, is thought to have started at a Cretaceous transform fault along the sea's western continent-ocean boundary after it started to accommodate convergence as a consequence of the changing direction of South American-Antarctic plate motion Eagles, 2010b). Oceanic lithosphere on the South American side of the margin was thrust far enough beneath the Antarctic Peninsula and for long enough that subduction was forced to initiate (Leng and Gurnis, 2011).…”

“…South Georgia and Shag Rocks present outcrops of unequivocally continental lithologies (Dalziel et al, 1975;Storey et al, 1977;Tyrrell, 1945). Between Terror Rise and South Georgia, magnetic reversal isochrons in deep water show that part of the eastern margin of the west Scotia Sea consists of oceanic lithosphere of the central Scotia Sea (Eagles, 2010b;Hill and Barker, 1980).…”

Composition and evolution of the Ancestral South Sandwich Arc: Implications for the flow of deep ocean water and mantle through the Drake Passage Gateway

“…This was not universally accepted, however, because of the absence of any obvious ridge axis as defined by symmetrical anomalies or positive topographic features and because of the difficulty in explaining the position of the South Georgia microcontinent. In particular, Eagles (2010) inferred that the South Georgia microcontinent was a southwardfacing margin during Gondwana break-up. This requires that the E-W anomalies in the CSS represent Cretaceous oceanic or transitional crust formed during the early stages of spreading at the southern margin of South Georgia.…”

Deep-sea pre-glacial to glacial sedimentation in the Weddell Sea and southern Scotia Sea from a cross-basin seismic transect

“…2; Table 2; online Supplement 1) for the Weddell Sea and Scotia Sea from published literature (BAS, 1985;LaBrecque and Ghidella, 1997;Nankivell, 1997;Surinãch et al, 1997;Lodolo et al, 1998Lodolo et al, , 2010Bohoyo et al, 2002Bohoyo et al, , 2007Eagles and Livermore, 2002;Ghidella et al, 2002;Kovacs et al, 2002;Eagles et al, 2005Eagles et al, , 2006Galindo-Zaldívar et al, 2006;König and Jokat, 2006;Maldonado et al, 2007;Eagles, 2010). This map compilation has not been published before and is available in the PANGAEA database (Lindeque et al, 2012).…”