Construcción del margen proto-pacifico del sudoeste de Gondwana en el Ordovícico. Evidencias de la cronologia U-Pb y los isótopos de Hf y O en circón

ROBERT JOHN PANKHURST; JUAN ANDRES DAHLQUIST; EDGARDO GASPAR BALDO; CESAR CASQUET; CARLOS RAMACCIOTTI; CARMEN GALINDO; JUAL ALBERTO MURRA; CARLOS WASHINGTON RAPELA; MARK FANNING; SEBASTIÁN OSVALDO VERDECCHIA; ALASINO, P.

San Miguel de Tucumán

Congreso; XX Congreso geológico Argentino; 2017

Asociacíon Geologica Argentina

Growth of the proto-Andean active margin of Gondwana in the Ordovician. Evidence from U-Pb zircon chronology and Hf-O isotope composition. New U-Pb ages and Hf and O isotope determinations in zircon have been obtained from a 500 km transect in the Sierras Pampeanas and two different areas of NE Patagonia that allows us (a) to raise strict isotopic and geochemical constraints on the origin of the Famatinian (Ordovician) magmas and(b) to develop a geodynamic scenario for the construction of the SW Gondwana margin. In the Sierras Pampeanas, the Famatinian orogen has been subdivided into four domains: Western (WFD), Central (CFD), Eastern (EFD) and Foreland (FFD). Early Ordovician magmatism dominates the transect from 485 Ma to 468 Ma, with major flare-ups at 480 ± 3 Ma and 470 ± 2 M. The distribution of ages suggest expansion of the main arc towards the west, as rocks of the older pulse has not been reported in the western sector of the CFD and the WFD: large crustal sections are entirely composed by rocks of the younger pulse.Famatinian basic rocks mostly show the same evolved whole-rock Sr and Nd isotopic signature and zircon sHft values as the intermediate and acid rocks of the same metaluminous sequence. Thus a complete Proterozoic litho - spheric section including the subcontinental mantle has been proposed as the primary magma source. Hybridization of these magmas with high 87Sr/86 initial ratio and high 618O? (zircon) melts of Ediacaran and Early Paleozoic metasediments can account for most of the Famatinian magmas in the Sierras Pampeanas and Patagonia.