TECTONIC EVOLUTION OF THE SIERRA DE SAN LUIS AND ITS IMPLICATIONS FOR THE EARLY PALEOZOIC ACCRETIONAL HISTORY IN THE SOUTHWEST OF GONDWANA

The Sierra de San Luis occupies a critical position between the Pampean orogen and the southern extension of the Famatina magmatic arc. From east to west it is made up by the Conlara (CMC), Pringles (PMC) and Nogoli Metamorphic Complexes (NMC) that are separated by the low grade San Luis Formation. The CMC registers the Pampean orogeny, i.e. its main deformation and peak metamorphic conditions were acquired prior to 500 Ma. Therefore the Conlara sediments were deposited in a southern extension of the Puncoviscana trough that underwent their first compressive deformations (D1 + D2) during the Pampean compression. Our model for the pre-Devonian evolution considers that after the Pampean orogeny inception of west dipping subduction along the western margin of the Pampean terrane controlled the development of a Cambrian to Early Ordovician back arc basin that was filled with Pampean derived sediments that later made up the PMC. As a result of the extension mafic magma supplied the thermal input for granulite facies metamorphism that took place during the resumption of compressive deformation along the margin of Gondwana.. Constraints for the timing of the Ordovician metamorphism are provided by the 500-480 Ma crystallization age of mafic rocks and the 480-470 Ma emplacement of calc-alkaline tonalites. The latter were syn-kinematic to D1 of the San Luis Formation ,i.e. D2 of the PMC. Compression may have resulted from the approaching Cuyania Terrane. The earliest ca. 500 Ma D1 syn-kinematic metasedimentary derived intrusions of the PMC, i.e the Paso del Rey granite, would indicate that initial compression resulted rather from changes in the geometry of the subduction zone than from the docking of the Cuyania Terrane which is considered to have occurred shortly before 460 Ma. The NMC records Ordovician metamorphism and magmatism but timing of deposition of the original sediments is dubious