Mesozoic to recent evolution of intraplate stress fields under multiple remote stresses: The case of Signy Island (South Orkney Microcontinent, Antarctica)

Abstract

Palaeostresses inferred from approximately 3200 brittle mesostructures measured at 43 sites in Signy Island show a stress field characterized by compressional, strike-slip and extensional stress states. There is a dominant NW–SE horizontal compression direction as well as three (NNW–SSE, WNW–ESE and ENE–WSW) secondary σ1 horizontal stress directions. Orientation of σ3 shows a main mode trending NW–SE together with secondary north–south and NE–SW extensional stress directions. The NNW–SSE horizontal compression is consistent with the stretching–shearing direction defined from the fold-axis trend. This is owing to a subduction-related tectonic regime during early to middle Jurassic times. In middle Jurassic/early Cretaceous times, the tectonic regime changes to extensional with north–south extensional stress directions. The early processes of subduction of the northern sector of the Weddell Sea oceanic crust below the South Orkney Microcontinent, from the Paleocene until the middle Miocene, is related to the σ1 direction WNW–ESE to NW–SE. The spreading of Powell Basin took place from the late Eocene to the early Miocene and is the cause of east–west and NE–SW extensional processes in the southern South Orkney Microcontinent. Finally, the NW–SE σ3 direction is related to the current left-lateral strike-slip movement between the Scotia and Antarctic plates.

Eocene-Oligocene paleoenvironmental changes in the South Orkney Microcontinent (Antarctica) linked to the opening of Powell Basin

“…Estimates of the timing of SOM´s break from the Antarctic Peninsula range from the mid-Eocene to the early Oligocene (40-30 Ma; King and Barker, 1988;Coren et al 1997;Eagles and Livermore, 2002). The SOM drifted and rotated eastward in conjunction with the rifting and subsequent opening of Powell and Jane Basins (King and Barker, 1988;Trouw et al, 1997;Maldonado et al, 1998;Busetti et al, 2000;Bohoyo et al, 2002;Maestro et al, 2013), attaining its current location during the early Miocene (King and Barker, 1988;Coren et al, 1997).…”

3D Geophysical and Geological Modeling of the South Orkney Microcontinent (Antarctica): Tectonic Implications for the Scotia Arc Development

“…The positive isostatic anomaly in the northern SOM reflects an uplift of the area, most likely related to an active strike-slip movement along the northern margin (King & Barker, 1988). In terms of crustal composition, outcrops in South Orkney Islands indicate that the upper continental crust consists mainly of low-grade metamorphic rocks of Paleozoic to Cretaceous age, intruded by bodies of igneous rocks of Cretaceous age (Dalziel, 1984;King & Barker, 1988;Maestro et al, 2013;Rodriguez-Fernandez et al, 1997). Barber et al (1991) dredged rock from around Powell Basin and the margins of the SOM and differentiated between two groups of samples.…”

“…The tectonic evolution of the SOM since the Mesozoic has been inferred by the analysis of lineaments and brittle structures measured in rock outcrops in the South Orkney Islands, the only exposed part of the microcontinent (Maestro et al, 2013;Trouw et al, 1997). Trouw et al (1997) established up to five phases of deformation.…”