Geophysical modeling of the Kranck pluton. Tierra del Fuego. Argentina.

JAVIER PERONI; ALEJANDRO TASSONE; HORACIO LIPPAI; MARCO MENICHETTI; EMANUELE LODOLO; JUAN FRANCISCO VILAS

19-20 de noviembre. Santiago. Chile

Simposio; International Geological Congress on the Southern Hemisfere (Geosur 2).; 2007

GEOSUR

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 Magallanes-Fagnano Fault System (MFS). At the southeastern tip of the lake a small monzodioritic intrusion crops out, the Jeujepen pluton. Previous aeromagnetic map pointed to the probable presence of another pluton in the central northern margin of the Lago Fagnano, as indicated by an anomaly of around 35 km2. The aeromagnetic anomaly shows an asymmetric distribution of contour lines, with a southeastern maximum and a northwestern minimum; anomaly values range from 50 nT to -30 nT. 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 determinations at each lithologic type completed with petrologic and structural data survey. The regional outcrops correspond to dark schists and sedimentary rocks pertaining to the Lower Cretaceous Beauvior Fm. which are deformed by Late Cretaceous Andean compressive tectonics. This unit hosts an alkaline pluton - the Kranck pluton - composed of basic to acid terms, dominated by gabbro-syenite association enclosing ultrabasic enclaves. The acquired susceptibility data span from 0.001 [SI] - for the most siliceous facies - to 0.0025 [SI] - for the ultrabasic facies-. The pluton is cut across by faults of the MFS, a set of NE-SW striking faults is overprinted by another set of N-S strike. The aeromagnetic survey and magnetic measurements integrated with the geological information allowed to model an N-S cross section through the area. Some common features allow relating Krank and Jeujepén plutons. Both are located on the lake boundaries, which in turn are controlled by transcurrent tectonics, the two plutonic bodies display similar facies assemblages and show transtensive and normal faults.Moreover, the host rocks of Kranck and Jeujepen plutons are stratigraphically equivalent. Ongoing radiometric and paleomagnetic determinations will allow constraining the meaning of both plutons in the regional geodynamic framework.