South America-Scotia plate boundary of Geophysic Modelling. IN the Tierra del Fuego Island. Argentina

TASSONE A.; LODOLO E.; MENICHETTI, M.; LIPPAI, H,; HORMAECHEA, J. L.; FERRER, C.; CONNON, G.

Strasbourg. France

Congreso; European Union Geophysics (EUG). Meeting XI.; 2001

European Union Geophysics (EUG).

Four geological and geophysical campaigns were carried out in the Argentinean onshore-offshore sector of the Tierra del Fuego Island (1998-2000) along the supposed trend of the Maggallanes Fagnano Fault System (MFFS). A survey of GPS-fixed gravimetric and magnetic data , reflexion multichannel seismic profiles and the execution of field structural geology transects permit to characterize the position, the kinematic evolution and produce a geophysical model of the area. The main structure of the Island are: 1) a system of ESE-WNW-trending asymmetric folds-and-thrusts, N-verging,  originated by a mostly N-S Late Cretaceous to Tertiary shortening of the Magallanes foreland basin and the shallow marine sequences of the Rocas Verdes marginal basin. 2) a superposed Oligocene-Quaternary E-W left-lateral strike-slip faults runs from the Pacific entrance of the magallanes Strait to the Atlantic coast of the Island, where significant deformation is to have been surveyed both in on-shore (Lago Fagnano, Cabo Leticia and Cabo Colorado) and off-shore (continental shelf), as well as in the remote-sensing maps. 3) a Quaternary system of N-S faults with right lateral strike slip attitude cross the previous structures. The magnetic map shows a significant susceptibility contrast at the southeastern tip of Lago Fagnano, related to –the Cerro Hewhoepen alkaline intrusion. Its shape, as reflected by geophysical modelling, the location and petrographic nature, might suggest that the emplacement is due to a releasing bend of the faults.             The Bouguer anomaly map shows a regional decreasing throught South indicating a major thicknnes of continental crust. A delimited maximun in the anomaly is related with higher density of the intrusion body. The sector to E of the Lago Fagnano to Atlantic coast present two minimum anomaly owing to the present of two pull apart basin. The W-E fault system present a stepped style of the boundary the plates as well the presence of the Bouguer minimun anomaly in the Cabo Colorado and the absence the minimun anomaly in the Cabo Leticia are indicating that the boundary plate in the Atlantic coast is shifted in the northern sector. In cross-section, this tectonic lineament is represented by sub-vertical faults and associated asymmetric basins, generated by simultaneous strike-slip motion and transform-normal extension, as imaged by seismic profiles acquired off the Atlantic coast of the Island.