Subandean thrust and fold belt of northwestem Argentina:: Geometry and timing of the Andean evolution

The Subandean ranges of northwestern Argentina are an active thin-skinned fold and thrust belt. The main detachment level in Silurian shales dips 2-3degreesW, and all the major east-verging faults detach from it. Important intermediate detachment levels in the Devonian shales generate lift-off structures and the decoupling of the lower and upper structural levels. The Subandean thrust belt has a minimum shortening of about 60 km (36%) at about 22degrees40' latitude. The deformation started at about 8.5-9 Ma with the uplift of the El Pescado range and the formation of an important back thrust at the Cinco Picachos range Fault generation gets young to the east; the Pintascayo range uplift started at 7.6 Ma, while the Baja Oran range uplift began at about 6.9 Ma. These two ranges continued growing simultaneously until at least 4.7 Ma. At San Antonio range, fault movement began at approximately 4.4 Ma, and the Aguarague uplift started at about 2.7 Ma. An important stage dominated by out-of-sequence movements spans from about 4.5 Ma to present. For both proposed models of shortening, the Quaternary rates of shortening between 8 and 11 mm/yr coincide well with global positioning system results from the area. The hydrocarbon generation and migration is contemporaneous with the deformation, enhancing the possibilities of hydrocarbon entrapment in the area.