El basamento pre-jurásico medio en el anticlinal Malargüe: evolución magmática y tectónica

LLAMBIAS, E.J.; SATO, A.M.; BASEI, M.A.S.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2005 p. 567 - 578

The basement of Neuquén basin crops out in the Chihuido anticline of southern Mendoza Province, and it consists of three volcano-sedimentary units separated by angular unconformities. The oldest unit is El Fortín volcano-sedimentary Complex, consisting of andesitic breccia, lava flows and domes, as well as conglomerates and sandstones. The last event recognized within this unit is the intrusion of a thick rhyolitic to monzogranitic dike, dated by conventional U-Pb zircon method at 250 ± 5 Ma. According to this age, the El Fortín Complex can be correlated to the Choiyoi Group of Frontal Cordillera and San Rafael Block. In angular unconformity over the former unit is found the 370 m-thick Upper Triassic Tronquimalal Group. It is composed of sedimentary rocks with abundant volcanogenic components that are intercalated with andesitic breccia. The layers show lateral thinning because of the temporary character of depocenters and partly catastrophic nature of deposition.  The unconformity separating the Tronquimalal Group from the El Fortín Complex is assigned to the Huarpic diastrophic phase which shows widespread regional extent. On top of the Tronquimalal Group there is a set of conglomerates intercalated with sandstones and mudstones that has been compared with Remoredo Formation. The conglomerate clasts are mainly of igneous origin, derived from volcanic and granitic rocks similar to those of the El Fortín Complex. Therefore, our interpretatrion favours their derivation from the destruction of Permo-Triassic volcanoes, in a process helped by the diastropic movements.The Remoredo Formation is followed in apparent conformity by Bardas Blancas Formation of Bajocian age. The volcanic activity in the studied area was continuous during Permian to Late Triassic times, and its intensity decayed after the action of the Huarpic phase.