PRELIMINARY DETRITAL AGES AND STRATIGRAPHY FOR THE BASEMENT IN FAMATINA, PROTO-ANDEAN MARGIN OF GONDWANA

COLLO, G.; ASTINI, R.A; CAWOOD, P.A.; BUCHAN, C.

Mendoza

Congreso; Gondwana 12; 2005

Academia Nac. de Ciencias

The Famatina Ranges constitute a complex and ragged region in western Argentina, located within the present-day Andean foreland. This region is thought to have been part of an ancient accretionary margin (Famatinian Orogen) built along western Gondwana in the early Paleozoic. Its low-grade metasedimentary basement together with a largely Ordovician sedimentary and volcano-sedimentary cover allows its differentiation from the surrounding Pampean Ranges and from the Precordillera terrane to the west. An integrated field-based lithofacies, structural and metamorphic study of the region has allowed identification of a mosaic of protolith units, including at least three that compose the bulk of what previously has been included in the “Negro Peinado Formation”. These units are herein named Achavil, Negro Peinado and La Aguadita formations. The latter has previously been shown to be of Ordovician age. We present U–Pb ion microprobe analysis (SHRIMP) on samples from the Achavil and Negro Peinado formations to attempt to constrain their depositional age and to evaluate the age and nature of their source regions. Several age peaks were identified within the obtained detrital zircon populations in both samples, indicating a sequence of events that record the early stages of the Proto-Andes. Despite the possibility of dispersal complexities of detrital grains, this preliminary work facilitates correlation with other peri-Gondwanan regions and a refinement for the suggested geological evolution of western Gondwana in the early Paleozoic.