The Magallanes-Fagnano continental transform fault (Tierra del Fuego).

LODOLO, E.; MENICHETTI, M.; TASSONE, A.

Santiago, Chile.

Simposio; VII Simposio Internacional de deformaciones recientes de la corteza terrestre en Sudamérica y alrededores; 2002

SEGEMIN Chile.

Multichannel seismic reflection profiles, gravity measurements and bathymetric soundings, in conjunction with field geological reconnaissance and remote-sensing images, reveal with unprecedented detail the morphostructure of a major segment of the South America-Scotia plate boundary in the Tierra del Fuego region. This segment, known as the Magallanes-Fagnano fault system, is a continental transform margin arranged in an en-echelon geometry, along which prominent asymmetric basins were developed. Data acquired off the Atlantic coast of Isla Grande, the main island of Tierra del Fuego, in its central and eastern part and in the central and western Magallanes Strait, image the surface and sub-surface structure of the transform fault and its associated basins. The Magallanes-Fagnano fault system is composed of distinct tectonic lineaments that are segments of the transform system and are represented by mostly near-vertical faults, with polarities that change along the strike of the fault. In the Atlantic sector, the fault system trends broadly N70°E and seems to be composed by a single master fault, in correspondence of which a highly asymmetric basin has formed. At around 63°W, the fault terminates by splaying into secondary, mostly normal faults, that dissipate the horizontal displacement along the system. In the central-eastern part of Isla Grande, the fault segments have a clear morphological expression, and are associated to localized gravity minima in correspondence of their unconnected ends. Lago Fagnano, a 105-km-long, E-W-trending depression, is a large, mostly asymmetric pull-apart basin developed within the principal displacement zone of the Magallanes-Fagnano fault system. Restraining bends and overlapping step-over geometries that have produced regions of compression and uplift and prominent drag fold axes, characterize the central part of the Magallanes Strait. At the western part of the fault system, in correspondence of the Pacific entrance of the Magallanes Strait, noticeably asymmetric sedimentary basins have also generated. The sedimentary architecture of the asymmetric basins formed within the principal displacement zone, in which the thick end of the depositional wedge abuts the transform fault, suggest simultaneous strike-slip motion and transform-normal extension, a common feature found in other continental transtensional environments.