Structural geology of the east of the Tierra del Fuego

MENICHETTI, M.; TASSONE, A; LIPPAI, H,

BOLLETTINO DI GEOFISICA TEORICA ED APPLICATA

ISTITUTO NAZIONALE DI OCEANOGRAFIA E DI GEOFISICA

Lugar: Trieste; Año: 2010 vol. 51 p. 150 - 151

0006-6729

The eastern part of Tierra del Fuego, along the Atlantic coast, is characterized by continuous outcrops of Cenozoic rocks pertaining to the Magallanes perisutural basins developed in front of the external margin of the southernmost Andean Cordillera. In the last years, several kinematic models have been proposed based mainly on stratigraphic and sedimentary methodologies, in several cases not supported by field evidence. A simple fold-and-thrust belt geometry with a basal detachment level in the Tertiary mudstone has been proposed for the area without consideration of the structural complexity of the region affected by at least two tectonic phases: compressional, from late Cretaceous to Oligocene, and transtensional, from Late Oligocene on. The basins subsidence, at least until the Late-Middle Eocene unconformity, has been mainly controlled by several transtensional faults running broadly parallel to the compressional front. Since the late Oligocene, a left-lateral strike slip fault system has been overprinting the thrust structures and partitioning the deformation along different fault arrays of the Atlantic Coast, from Cabo S. Diego to Cabo S. Pablo. The main compressional structures mapped along the coast present a northward verging fault-bend fold geometry, with an amplitude of a few km, a detachment level located in the marls layers, low angle thrust planes and a shortening of about 30 %. The external compressional front of the orogen can be located at Punta Gruesa, where the anticline thrusts over the slightly deformed structures of Cabo S.Pablo. The main E-W left lateral strike-slip faults are located at Cabo Leticia, Capo Campo del Medio and Cabo Irigoyen, and are associated with a set of N-S and NE-SE extensional faults. These later fault systems with offsets of many hundreds of meters represent the fault array associated with the Magallanes-Fagnano transform fault. Many seismically-triggered sand intrusions are present throughout the stratigraphic succession in the Late Cretaceous, the Late Palaeocene and the Middle Miocene marking important tectonic events. Several of these sedimentary and structural features can be easily correlated with the structures observable in the off-shore seismic reflection profiles. The joint analysis of these data, document a multi-stage evolution of the basin with the presence of five seismic units, separated by angular unconformities recording different tectonosedimentary events. Several pull-apart basins are located along the off-shore alignment of the principal deformation zone of the Magallanes-Fagnano fault and have their on-shore counterparts in the Cabo Malenguena basin and western Lago Fagnano.