CONICET | Buscador de Institutos y Recursos Humanos

The Eastern Sierras Pampeanas are constituted by the Neoproterozoic to early Cambrian basement of the Sierras de Córdoba, San Luis and eastern Rioja (29°00 33°30S, 64°00 68°00W) outcropping in the east of the Chaco-Paraná basin. High-grade metamorphic gneisses and schists dominate the basement. The intrusion of magmatic rocks took place during the Pampean, Famatinian and Achalian cycles. The basement is divided in different lithological and structural domains by ~N-S trending ductile shear-zones. The east-dipping compressive LosTúneles and Guacha Corral shear-zones at the western limit of the Sierras de Córdoba are the most important with respect to the exhumation history of the Sierras. An extensive survey on the cooling history by K/Ar biotite and muscovite dating of the basement rocks of the Sierras de Córdoba and San Luis was carried out and interpreted in terms of a differential exhumation history of the different blocks. Beginning of cooling in the Sierra de San Luis is documented by large muscovite booklets from pegmatites yielding ages between 438 Ma and 448 Ma. Slow cooling rates (~3°/Ma) led to a systematic reset of the K/Ar ages in the fine-grained muscovites forming two groups between 430 Ma and 410 Ma and 410 Ma and 380 Ma resulting from the Achalian deformation in the Devonian. In contrast to the Upper Ordovician/-Llandoverian cooling onset in the Sierra de San Luis, large pegmatitic muscovites from the Sierras de Córdoba record late Cambrian to Early Ordovician ages between 493 Ma and 474 Ma. The limit between those age domains is marked by the Los Túneles and Guacha Corral shear-zones accommodating the vertical displacement responsible for the different ages. Cooling ages from the shear-zone rocks at ~430 Ma define the upper limit for the contraction that is related to the collision with the Cuyania Terrane to the western outboard of Gondwana.