Western Scotia Sea margins: Improved constraints on the opening of the Drake Passage

Abstract

[ 1 ] We present arevised tectonic interpretation (from $ 28 Ma to 3.2 Ma) of the western sector of the Scotia Sea, incorporating new multichannel seismic reflection profiles and magnetic anomaly identifications for the continental margin offt he Tierra del Fuego Island, and available complementary data for the conjugate margin of the northwestern flank of the South Scotia Ridge. Seismic profiles show ar emarkable diversity of the pair of conjugate passive margins of the western Scotia Sea in both their morphology and structural framework. The Tierra del Fuego continental margin can be related to ac lassic rifted passive margin, while the southwestern margin of the Scotia Sea is characterized by steep slopes mostly generated by subvertical faults that abruptly separate the continental crust of the South Scotia Ridge from the oceanic crust of the western Scotia Sea. This structural difference was caused by intense strike-slip tectonism, mostly concentrated along the modern South Scotia Ridge since the early development of the western Scotia Sea. We find evidence for ap reviously unrecognized magnetic anomaly 10 ( $ 28 Ma) at the foot of the Tierra del Fuego continental margin; the same anomaly is present at the conjugate northern flank of the South Scotia Ridge. The timing of events leading to the earliest development of the western Scotia Sea, which determined the opening of the Drake Passage is important because this gateway opening had aprofound effect on global circulation and climate. The thickness and the distribution of the sedimentary cover overall in the abyssal plain offt he two western Scotia Sea margins is different. This is due to the different regimes of the bottom-current flows which affected the western Scotia Sea, both in the past and in the present time.

Tectonic reconstructions for paleobathymetry in Drake Passage

“…Many of the transforms created fracture zone traces in the neighbouring seafloor. Magnetic anomaly profiles crossing the west Scotia Sea are confidently interpretable to show isochrons 8-3 (26-5.5 Ma) on both plates in the spreading corridors created by the actions of segments W1-W5 (Barker and Burrell, 1977;Eagles et al, 2005;LaBrecque and Rabinowitz, 1977;Livermore et al, 1994;Lodolo et al, 2006). These studies also make isolated identifications of isochrons 9 and 10 on one flank or the other over deep water at the extremes of some of these corridors.…”

Heat-flow determinations of basement age in small oceanic basins of the southern central Scotia Sea

“…Magnetic anomaly identification in Drake Passage is undisputed through many publications, from Barker & Burrell (1977) onwards (e.g. LaBrecque 1985Eagles et al 2005;Lodolo et al 2006), and the estimated age for HF09 is compatible. Protector Basin is discussed below.…”

Tectonic activity evolution of the Scotia‐Antarctic Plate boundary from mass transport deposit analysis

“…The fragmentation of South America and the Antarctic Peninsula led to seafloor spreading in the southwestern part of the Scotia Sea during late Eocene and the initiation of the West Scotia Ridge (WSR) during the Oligocene [ Maldonado et al ., ]. Spreading at the WSR led to the creation of most of what is now the Scotia Plate by the late Miocene, when the ridge became extinct [ Barker and Burrell , ; Maldonado et al ., ; Eagles et al ., ; Geletti et al ., ; Livermore et al ., ; Lodolo et al ., ]. The Sandwich Plate has developed since the middle Miocene, when the active East Scotia Ridge (ESR) initiated oceanic spreading (Figure a) [ Larter et al ., ; Nicholson and Georgen , ].…”