The Magallanes-Fagnano Fault System in the Lago Fagnano. Tierra del Fuego Island: morphology and Structure

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

Nice

Simposio; XXVI General Assembly. European Geophysical Society; 2001

European Geophysical Society (EGS)

            The Lago Fagnano, located in the central part of the Tierra del Fuego Island (southernmost South America), is an E-W-trending major depression which highlights an important segment of the South America - Scotia plate boundary. This structure, known as the magallanes-Fagnano Fault System (mFS), is a mainly transcurrent lineament which runs from the Pacific entrance of the magallanes Strait to the Atlantic coast of the Island, where significant deformation related to left-lateral strike-slip faults has been surveyed both in onshore and offshore.             Field geological mapping, combined with the bathymetric data, integrated with a Digital Elevation Model (DEm) produced from Synthetic Aperture Radar (SAR) data and SPOT multispectral images, provide new insights into the structural and morphologic framework of the Lago Fagnano area.             A bathymetric map of the eastern part of the Lago Fagnano has been produced for the first time, in order to identify the morphostructural expression of the mFS, and to delineate the main submerged features of the plate boundary in this sector of the Tierra del Fuego Island. The most important feature comprises a prominent scarp which parallels the northern shore of the Lago Fagnano and aligns with a weak E-W-trending depression located onshore to the east which has been identified from the DEm map. The N-S profile shows an asymmetric shape with the steepest slope in the northern margin and maximum deeps up to 201 m.             The analysis of the outcrop data integrated with the DEM map has shown the continuity in surface of this scarp, specially in the northern flank of the Lago Fagnano. Here Upper Cretaceous mudstones have been involved in a thrust shear zone which is superposed by a strong strike-slip E-W left lateral component . The Quaternary sediments mainly located along the southern and southeastern shorelines are also affected by the E-W strike-slip deformation.