. Long lasting high temperature metamorphism in the Sierra de San Luis and its relation to the amalgamation of the Cuyania terrane (Argentina)

STEENKEN, A., LÓPEZ DE LUCHI, M.G., SIEGESMUND, S., FREI, R., WEMMER, K.,

Punta del Este, Uruguay

Simposio; Fifth South American Symposium on Isotope Geology; 2006

Universidad de la República del Uruguay

Results from SHRIMP U/Pb zircon analyses and PbSL leaching experiments on garnet from a granulite facies mylonitic gneiss from the central basement domain, i.e. the Pringles Metamorphic Complex of the Sierra de San Luis (Central Argentina) are discussed under the light of the generally accepted Mid-Ordovician tectonic emplacement of the Cuyania Terrane at its present position in the west of the Pampia/Pampean Terrane. The new geochronological data indicates a period of at least 40 Ma of high temperature, i.e. granulite facies metamorphism in the proximity of various mafic and ultramafic intrusions following a NNE trending belt in the western realm of the basement domain. SHRIMP U/Pb data on metamorphic grown zircon rims at 498 ±10 Ma indicate that the metamorphic episode on the Pampia/Pampean Terrane predates the accretion of the Cuyania Terrane significantly. Therefore metamorphic processes are largely unrelated to collisional tectonics but might be the result of extensional basin formation subsequently followed by its closure probably due to changes in the subduction angle. Cooling down to amphibolite facies conditions at 452 ±19 Ma is documented from PbSL experiments on garnet.