SOUTH GEORGIA MICROCONTINENT: CURRENT TECTONIC SETTING FROM GPS AND MARINE SEISMIC DATA (Invited Presentation)

The South Georgia microcontinent (SGM) is an allochthonous block displaced from south-east Tierra del Fuego. It was transported over the past 80 -100 My as a result of transpressive deformation during the initial mid-Cretaceous phase of Andean orogenesis and subsequent development of the western part of part of the Scotia Plate (SCO). While its trajectory is poorly constrained, SGM is now located near the eastern extremity of the North Scotia Ridge (NSR), approximately 1600 km east of its original position. West of the SGM, the NSR forms the South America plate (SAM) - SCO boundary. Based on Scotia Arc bathymetric morphology and geological history, SGM has been considered part of the SCO, with the plate boundary along its northern side. SGM seismic activity, while very low, is concentrated along its southern border and interpreted, based on a few small thrust mechanisms, to represent underthrusting and uplift of South Georgia Island on a NSR restraining bend along the north-eastern margin of SGM. More recently, also based on this seismicity, the plate boundary has been placed on SGM's south side, suggesting SGM has, or is being, transferred to SAM. We report on marine seismic reflection surveys north and south of the island, and results from a 4-station continuous GPS network installed on the island, to determine the block's current tectonic affinity with respect to the SAM and SCO plates, to examine SGM for internal deformation, and to evaluate the significance of relative sea level change measured by a tide gauge on the island. We will present preliminary geodetic results, based on 4 years of continuous GPS data, indicating SGM motion and deformation. We will also present multi-channel seismic reflection profiles across the margins of SGM showing indications of compression. SGM appears to be moving as an independent microplate. The anomalously high relief of the island relative to the hinterland of the southernmost Andes (~3000m vs. ~1000m) may result from the impingement of the Northeast Georgia Rise on the microcontinent.