Geophysical and Geological reconnaissance of the South America-Scotia plate boundary in the Tierra del Fuego Island

TASSONE, A,; LODOLO, E.; GRUPO TESAC

Wellington

Simposio; 8th Internatonal Symposium on Antartic Earth Sciences; 1999

Preliminary magnetic, gravity and tectonic maps of the studied area have been produced and a deep structural model was constructed across the supposed location of the MFS. As revealed by SAR images, analyses performed on the acquired data also indicates the presence of a main lineation elongated in an W-E direction in prosecution both of the trend of the Fagnano Lake to the west and eastwards on the Atlantic Ocean. In the preliminary gravity map, this W-E main lineation is in correspondence with a regional gravity minima, as seen on satellite-derived free-air gravity data, which in some parts is deeper than 500 m, exactly where the South America-Scotia plate boundary is supposed to be located. The field data are in concordance since Cretaceous and Paleogene rocks are strongly sheared and brecciated within the gravity minina area. To the North of MSF three parallel oriented gravimetric minima have been recognised in coincidence with the alignment seen in the Spot and SAR images. In the field this alignment corresponds to north vergent folds and thrusts affected by later N-S trending faults. To the South of the supposed trend of the MFS, the magnetic map shows the presence of significant susceptibility contrasts in the area just east the Fagnano Lake indicating igneous bodies in the subsurface. This area corresponds to the Andes Fueguinos orogenic front where Cretaceous shale intruded by a monzonite pluton has been surveyed in the top of Hewhoepen Hill. The first correlation between the structures found onshore and those present offshore, as seen from available seismic profiles, have allowed to map the main strike of the MFS in the surveyed area, and tentatively reconstruct the tectonic framework of the South America-Scotia plate boundary in the Tierra del Fuego region.