Geophysical survey of the Fagnano pluton.. Tierra del Fuego. Argentina.

VILAS, J. F.; TASSONE, A.; PERONI, J. I.; LIPPAI, H.; MENICHETTI, M.; LODOLO, E.

Perugia. Italia

Simposio; International Union of Geodesy and Geophysics (IUGG); 2007

IUGG

The Lago Fagnano, located in the central area of Tierra del Fuego Island, is the result of transtensive tectonics responsible for several pull-apart basins associated with the transform Magallanes-Fagnano Fault System (MFS). At the southeastern tip of the lake a small monzodioritic intrusion outcrops, the Jeujepen pluton. Previous aeromagnetic map pointed to the probable presence of another pluton in the central northern margin of the Lago Fagnano. There, an aeromagnetic anomaly of around 35 km2 shows an asymmetric distribution of contour lines with the highest values in the east (reaching values > 1200 nT). Last November a geophysical survey was carried on in the area of the aeromagnetic anomaly. Data acquisition in the field involved magnetic measurements at GPS-fixed stations with a proton magnetometer, sampling for susceptibility, paleomagnetic and AMS determinations at each lithologic type completed with petrologic and structural data survey. The outcrops correspond to dark schists and sedimentary rocks pertaining to the Lower Cretaceous Beauvior Fm. which are deformed by Upper Cretaceous Andean compressive tectonics. This unit hosts an alkaline pluton –the Fagnano pluton- composed of basic to acid terms, dominated by gabbro-syenite association enclosing ultrabasic enclaves. The pluton is cut across by faults of the MFS. The aereomagnetic survey and magnetic measurements integrated with the geological information allowed to model an N-S cross section through the area. Preliminary processing of available data along with the location of Fagnano pluton along the strike of MFS allow to propose that its emplacement was governed by a transtensive regime associated with this transform fault activity.