Deciphering the morphostructure of the Tierra del Fuego region from remote-sensing and geophysical data

LODOLO, E,; TASSONE A.; MENICHETTI, M.; COREN, F.; STERZAI, P.

Nice

Simposio; EGS XXV General Assembly; 2000

EGS

The Tierra del Fuego region - the southern tip of the South America - is the supposed locus of the present-day westernmost part the South America-Scotia plate boundary. The nature, the tectonic setting, and the Cenozoic evolution of this plate boundary are still mostly speculative, because the lack of extensive geophysical and geological data, both onshore and offshore. Geometrical extrapolations and sparse available information suggest that the onshore intersection of the plate boundary in the Tierra del Fuego Island is represented by a mainly strike-slip lineament, running from the western part of the North Scotia Ridge to the Chile Trench south 50° S. Two geophysical and geological campaigns have been conducted in the central part of the Island, and a multichannel seismic reflection survey was carried out off its Atlantic coast, in order to better identify, map and analyse the principal geologic elements of this plate boundary. The overall collected data have been then combined with Synthetic Aperture Radar (SAR) images, SPOT maps and some aerial photographs, to correlate in a regional view the field structures found onshore and offshore. A system of E-W-trending asymmetric folds and associated N-verging thrusts, affected by later N-S-trending faults, have been recognized in the central part of the Island and along its Atlantic coast. Along the northern shore of the Lago Fagnano, a major tectonic lineament has been documented, in correspondence of which the affected rocks are strongly deformed and metamorphosed. SAR and SPOT images, in conjunction with the produced onshore gravity and magnetic maps, support the presence of this main E-W-trending lineament, which can be traced eastward till the Atlantic coast of the Island. It presents a significant counterpart offshore, as revealed from the interpretation of seismic profiles. In a regional scale, data strongly suggest that the identified tectonic lineament (and subsidiary structures) is remarkably transtensive in nature, and spatially superimposed on the preexisting tectonic setting of the area. It forms part of the sinistral strike-slip Magallanes-Fagnano fault system reported in literature, which represents the onshore location of the South America-Scotia plate boundary in the Tierra del Fuego Island.