New isotopic dating of intrusive rocks in the Sierra de San Luis (Argentina): implications for the geodynamic history of the Eastern Sierras Pampeanas

Abstract

U–Pb datings of zircons from intrusions in the metamorphic complex of the Sierra de San Luis (Eastern Sierras Pampeanas, Argentina) suggest that the depositional, tectonic, metamorphic, and magmatic history in this part of the Pampean Terrane spans the Proterozoic through Early Paleozoic time interval. The Paso del Rey Granite intruded a clastic succession at 608+26/−25Ma and, afterward, was deformed together with the country rocks. The intrusions of the Rı́o Claro Granite and La Escalerilla Granite at 490±15 and 507±24Ma, respectively, mark the onset of Famatinian arc plutonism due to east-directed subduction beneath the Eastern Sierras Pampeanas. The new data, along with structural analyses and published results of isotopic dating, allow an interpretation of the history in this segment of the Pampean Terrane. After basement formation, Late Proterozoic turbiditic sedimentation in a passive margin setting was accompanied by block faulting and continued at least to the Early Cambrian. It is assumed that the Pampean Terrane represents a detached fragment of the Rı́o de La Plata Craton in the east. The first deformation in the Micaschist Group was an effect of an early stage of the compressive Pampean event, which is related to the collision of the Pampean Terrane with the Rı́o de La Plata Craton. The Early Cambrian is recorded by injections of acid magmatic sills and dykes, probably under overall crustal extension. This also indicates an age of the turbiditic sediments comparable to that of the Puncoviscana Formation s.l. of northwest Argentina. After cessation of Famatinian arc plutonism, compression and regional metamorphism affected the intrusives, clastic succession, and older basement units. The related amalgamation of the Cuyania (Precordillera) Terrane with the Eastern Sierras Pampeanas was completed during the Early Devonian.