Magnetic and gravity anomalies in the central part of the Tierra del Fuego Island, Argentine: evidences of transtensive tectonics.

TASSONE, A.; LIPPAI, H.; COMBA, A.; LODOLO, E.; MENICHETTI, M.; HORMAECHEA, J. L.; VILAS, J. F.

Toulouse. France

Simposio; 5th International Symposium on Andean Geodynamisc (ISAG).; 2002

Université P. Sabatier. Toulouse. France

The Tierra del Fuego region, is one of the of the least known places on Earth because its remoteness and the difficult access to most of its length. The intersection of the South America-Scotia plate boundary in the Tierra del Fuego region is represented by a mainly strike-slip lineament, known as the Magallanes-Fagnano Fault System (MFS), running from the western part of the North Scotia Ridge to the Chile Trench south of 50°S (Fuenzalida, 1972; Dalziel, 1989). The MFS, substantially splits the Tierra del Fuego Island in two continental blocks. The MFS is a mainly transcurrent lineament which runs from the Pacific entrance of the Magellan’s Strait to the Atlantic coast of the Island (Fig. 1), where significant deformation related to left-lateral strike-slip faults has been surveyed both onshore and offshore (Winslow, 1982; Cunningham, 1993; Klepeis and Austin 1997; Olivero et al., 1999; Menichetti et al., 2000; Diraison et al., 2000; Lodolo et al., 2002). Three geophysical and geological field surveys have been carried out in the in the central part of the Tierra del Fuego island. The difficulties of access in most of the study areas have prevented the realization of a regular grid with closely-spaced geophysical and geological data points, and for this reason some parts remain still unsurveyed (Fig.2a: see shaded areas). Gravity and magnetic data points have been acquired on 420 GPS-fixed data points based on the geodetic local net from the Estación Astronómica de Rio Grande, with a LaCoste-Romberg gravimeter and EG&G Geometrics proton magnetometer. The topographic correction necessary for producing the Bouguer anomaly map has been in fact computed using the obtained Digital Elevation Model. Within this area, a paleomagnetic and magnetic anisotropy survey was performed on the outcrops of the Cerro Hewhoepen intrusive.