South Orkney microcontinent

The South Orkney microcontinent (Fig. 5) is the biggest continental element of the South Scotia Ridge (250 x 350 km), an E-W-trending submarine morphological feature along which the present-day Antarctica-Scotia plate boundary is identified. The exposed rocks on the South Orkney Island are mainly metamorphic in origin, closely resembling oucrops of metamorphic complexes of teh paleo-Pacific margin found on the Antarctic Peninsula.

South Orkney Islands Bathymetric Map
Fig. 5 - General bathymetric map of the South Orkney Islands and surroundings. The thick segment crossing the ODP site represents the part of profile in Fig. 9.

Geodynamic reconstructions have postulated that this microcontinent represents a dispersed fragment of the terrains connecting the southern South America and the northern Antarctic Peninsula, prior to the opening of the Drake Passage during Oligocene time (Barker & Burrell, 1977). It drifted away from the northern tip of the Antarctic Peninsula as a consequence of the development of the Powell Basin (Coren et al., 1997), a restricted oceanic basin presently separating the microcontinent from the northern Antarctic Peninsula. Seismic and gravity data (King & Barker, 1988; Kavoun & Vinnikovskaya, 1994; Maldonado et al., 1998), have documented the continental character of the crust for the South Orkney block, and have reconstructed the deep structure of the fragment, which presents three main N-S-trending epicontinental basins, possibly ancestral structures related to Late Mesozoic rifting.

Two sites drilled during the Ocean Drilling Program (ODP) Leg 113 (Barker, Kennett et al., 1988), on the southeast margin of the South Orkney microcontinent, have allowed the seismostratigraphic correlation with the existing grid of seismic profiles back to the Late Miocene sedimentary sequences, which are of mixed terrigenous, volcanic, and pelagic origin, with the most prominent characteristic the abundance of biosiliceous components.

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