Definition of Regional Scale Tectonic Features within the San Jorge Basin, Argentina, and the Implications for Wrench Related Exploration Targets

Walter D. Tomlinson, Coote Wright-Broughton

The integration of mapped surface structural features from satellite imagery and published surface and subsurface geologic data has defined several possible major structural zones of significance to the development of the San Jorge Basin and the resulting structural styles in the area.

The northwest trending zones of the Chubut and Rio Deseado areas are possibly related to the original northwest trending sutures and fault zones which defined the Paleozoic basement during the early Paleozoic. These features subsequently influenced the positions of the major grabens and horsts which resulted from the extensional tectonics of the Triassic-Jurassic breakup of Gondwana and were the precursors to the major oceanic transforms along which the Atlantic development took place. These features appear to be the bounding structural systems which defined the early Jurassic-Cretaceous San Jorge Basin.

The northeast trending Rio Chico zone may possibly exhibit right lateral movement as a result of the translation of compressive forces from the Andean Orogeny along a preexisting fault zone. The San Bernardo Fold Belt and its development may be related to this somewhat isolated zone of translation and possible development of secondary zones with left lateral motion along the Rio Senguerr fault zone and the fault zone to the east of Lago Colhue Huapi.

The high angle normal faults of the San Jorge Basin proper may be related to divergent extension along an associated bend in the Rio Chico zone. This is difficult to speculate on because of the extensive alluvial cover in the area south of the bend in the Rio Senguerr. The Rio Chico zone is similar in trend to the zone which bisects Lago Buenos Aires and may be an extension of this zone. The Lago Buenos Aires zone is similar in trend and may possibly be a onshore continuation of the Tres Montes Fault Zone of the Chilean offshore area.

In light of the regional data presented here it may be worthwhile to consider possible wrench and strike-slip related exploration targets along the Rio Chico zone and other areas.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995