Near surface geohysics on Magallanes-Fagnano Fault System. Tierra del Fuego. Argentina.

TASSONE, A. A.; PERONI J. I,; VILAS, J.F,; LIPPAI H. F.

New Orleáns, Los Angéles. USA.

Otro; AGU Joint Assembly; 2005

AGU

A main portion of the South America-Scotia plate boundary related to the Magallanes-Fagnano Fault System (MFS) is occupied by the lago Fagnano. Just at the eastern end of lago Fagnano a sag pond area -which is the surface expression of one basin associated with the MFS- is flanking the Hewhoepen monzodioritic intrusion. The MFS overprints the fold-and-thrust-belt of the Fuegian Orogene and is associated with basin formationalong its length. These basins display the greater sedimentary thickness against the main fault in the major displacement zone. Both Paleogene and Quaternary outcrops show transtensional structures associated with MFS. An electric resistivity survey was carried on at the eastern lago Fagnano with the purpose of constraining the subsurface continuation of W-E faults related to MFS and the unexposed portion of the Hewhoepen body. A Syscal R1+Switch 48 resistivity-meter system was employed to perform the 1.6 km-long, N-S, two-dimensional electrical imaging/tomography survey. The roll all on method was applied with a Wenner array using 48 electrodes (with 10 m of constant spacement) connected to a 480 m-long multi-core cable, with four sections and 48 channels. The pseudo section and the obtained 2D inversion model allow inferring two lithologies in the subsurface which display at least two contrasted resistivities, i.e. the uppermost peat blanket and lower sandstones. Both litologies show a network of vertical and horizontal discontinuities defining small fragments dipping southwards. A high resistivity body was also recognized in correspondence with the magnetic anomaly of the Hewhoepen intrusive.