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Abstract: The Ñirihuau Basin (Patagonia, Argentina): Its Mesozoic Rifting And Neogene Architecture Due To Dextral Andean Transpression

Diraison, M.; P. R. Cobbold; E.A. Rosello; A.J. Amos; and O.R. López - Gamundi

The Ñirihuau Basin (Western Argentina) is located along the eastern flank of the Northern Patagonia Andes. The sedimentary fill of the Ñirihuau Basin began over the Liassic marine shales (Piltriquitrón Fm.) followed by Paleogene volcanics and pyroclastics represented by the Huitera and Ventana formations that alternate with shallow marine sequences, most of them with oil source properties, thus giving room to the possibility of Neogene Petroleum Systems. Major faults and thrusts trend northwest, forming the edges of Cenozoic basins of foreland or ramp style. These units are divided into belts trending nearly N-NW and apparently are inherited from Cretaceous structures.

The geotectonic setting is dominated by pre-Mesozoic basement rocks of the Andean Cordillera thrusting eastwards to the Paleogene volcaniclastic layers and Neogene sediments of the Ñirihuau Basin. On an outcrop scale, fault-slip data provide information on the relative amounts of crustal thickening and strike-slip faulting. Some of these are inverted grabens of Mesozoic age. The dominant strike-slip faults are right-lateral and trend nearly north, parallel to the Cordillera. Conjugate left-lateral faults trend nearly east.

On a regional scale, from the fault-slip data, the principal direction of shortening is northeast, in areas where thrusts predominate, but swings round to north in areas where wrench faults predominate. The results indicate a degree of strain partitioning, but they are broadly compatible with the oblique direction of convergence between the Nazca and South America plates. This tectonic style seems to have lasted throughout the Neogene.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil