Depth Seismic Migration Modelling Offshore “Tiera del Fuego”, Argentina (54º 25´ S).

COMINGUEZ, A. H.; FLORES, J.; TASSONE, A

Acapulco . México.

Otro; American Geophysical Union . Joint Assembly; 2007

AGU

Within the framework of the TESAC Project (Tectonic Evolution of the South America-Scotia plate boundary during the Cenozoic), about 900 km of multichannel seismic reflection profiles were acquired off the Atlantic coast of the Tierra del Fuego Island. The profiles cut across the South America-Scotia plate boundary, a transform margin which traverses in an E-W direction the Island. Data processing and interpretation of a seismic reflection profile is presented in this contribution. A robust post-stack technique involved depth-migration of the seismic section, using an interval-velocity model of the upper Crust adjusted by iterative processing. An interpreted seismic- velocity section (which trends roughly NW-SE), shows a complex superposition of different tectonic structures, with presence of extensional, compressional and transtensional features in the area located to the north of Isla de los Estados. The profile, which crosses the offshore part of the Magallanes fold-and-thrust belt, images the deep structural framework of part of this tectonic province. The identification of acoustic fabrics and seismic discontinuities allowed us to recognize four main units. Overlaying the acoustic basement (Seismic unit 1), there is another unit (Seismic unit 2) which exhibits some reflector packages of high amplitude; this unit must be related to the volcanic and volcaniclastic sequences of Tobífera/Lemaire Fms. The Seismic Unit 3 displays internal reflector configurations of moderate amplitude and continuity and low-to-moderate frequency; the Yaghán/Beauvoir Fms must be the onshore equivalent of this unit. An uppermost seismic layer (Unit 4) may be correlated with the Tertiary sediments of the Magallanes foreland basin which were involved in the fold and thrust belt. A major structure identified in the studied seismic profile is a SE structural high (which involves the units 1, 2 and 3) and a NW down-faulted area. The latter display folds of kilometric size (3-4 km). Steeply dipping (mainly to the south) reverse faults cut through the folds. Some of these faults represent old extensional faults of the Middle- Mesozoic Rocas Verdes marginal basin rifting, which have been subsequently inverted by compressional stress fields. In addition, a noticeable flower fault system is recognized in the seismic profile, which involves both the sedimentary cover and the acoustic basement. This fault is interpreted as the result of shear stresses produced along the transcurrent South America-Scotia plate boundary.