Singlechannel Seismic Survey in Lago Fagnano, Tierra del Fuego

ESTEBAN, F.; TASSONE A.; LODOLO E.; MENICHETTI, M.; LIPPAI, H. F.; DARBO, A.; GROSSI, M.; BARADELLO, L

Buenos Aires

Workshop; Giambiaggi School- Applied and Enviromental Geophysics.; 2012

FCEyN. Dpto. Física.

Lago Fagnano (LF), an E-W elongated basin located in Tierra del Fuego, occupies a structural depression originated along a segment of the Magallanes-Fagnano fault system. Its evolution was mostly conditioned by tectonic process, and later was affected by glacial and glacio-lacustrine depositional events. In order to study the lake’s origin we reconstructed the basement surface, and the geometry and thickness of glacial and glacio-lacustrine sequences. For this, three seismic stratigraphic units were interpreted from the profiles: (1) a bedrock/basement complex, (2) an ice-contact/glacial deposits, and (3) a glacio-lacustrine and lacustrine successions. To convert the two-way travel time of the high resolution profiles in depths, a water sound velocity of 1432 m/s was used. For the lacustrine, fluvial and glacial sediments a sound velocity of 1500 m/s. The seismostratigraphic units were then correlated with the geologic units outcropping around the LF. Horizon’s grids were created with a point Kriging method and with a forcing factor along the E-W direction, given the peculiar geometry of LF. We recognized three main sub-basins within the Lago Fagnano: (1) a medium-size (ca. 21 x 5 km), deep (373 m), and asymmetrical basin to the east; (2) an E-W trending (44 x 3 km), shallower (150 m) central sub-basin; and (3) a smaller (3.5 x 1.3 km), shallow (128 m) sub-basin to the west. The shape of the sub-basins and their location in relation with the Magallanes-Fagnano fault system, along with the distribution, geometry, and thickness of the sedimentary units, show that the general morphology of the LF was mostly controlled by pre-existing tectonic features.