SHRIMP dating of the El Peñon Granite: A time marker at the turning-point between the Pampean and Famatinian Cycles within the Conlara Metamorphic Complex (Sierra de San Luis; Argentina)?

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

La Plata

Congreso; 16 Congreso Geologico Argentino; 2005

Asociación Geologica Argentina, INREMI

SHRIMP U/Pb zircon dating of the El Peñón batholith located in the eastern realm of the Conlara Metamorphic Complex of the Sierra de San Luis attests an early Famatinian emplacement (497±8 Ma) of the granite. Microstructures within the batholith document a continuous temperature decrease as indicated by magmatic to high temperature solid-state deformation, suggesting a syn-kinematic emplacement. A relative time constraint provided by folded xenoliths suggests its emplacement during D3. Consequently, older fabrics (D1 + D2) and metamorphism (M1 + M2a/in the Conlara Metamorphic Complex have to be assigned to the Pampean Orogenic Cycle. Few analysed detrital zircon cores yielded a maximum age of 562 Ma for the deposition of the sediments that later turned into the Conlara Metamorphic Complex. This indicates that the sedimentary protolith could have been deposited previous to the 530 Ma Pampean collision of the Pampia Block and the Río de la Plata Craton. The young detrital age of 562 Ma is within the time interval that was suggested for the deposition of the Puncoviscana Formation along the southwestern margin of Gondwana. Therefore, the extension of the Puncoviscana Formation into the present easternsector of the Sierra de San Luis can not be excluded.