The Early Jurassic Subcordilleran Belt of Patagonia (42º - 44º S): proto-Pacific subduction coeval with the Karoo mantle plume

RAPELA, C.W.; PANKHURST, R.J; FANNING, C.M.

Concepción

Congreso; 10º Congreso Geológico Chileno, Concepción, Extended Abstract Volume (CD-ROM), 9p.; 2003

Sociedad Geológica de Chile

New SHRIMP U-Pb zircon ages, geochemical data and Sr-Nd isotope analyses have been obtained for three granite bodies in the ‘Subcordilleran Plutonic Belt’ of Patagonia which lies between the eastern Andes and the North Patagonian Massif in western Chubut province. The granites are ah Early Cretaceous (ca. 185 Ma): they are thus contemporaneous with the Marifil Formation rhyolites of northeastern Patagonia. However, their petrology and geochemistry clearly identifies them as subduction-related volcanic arc granites whereas the rhyolites are thought to be crustal melts related to the rifting Gondwana under the influence of the Karroo mantle plume. The Triassic to earliest Cretaceous tectonic and magmatic scenario of the region is summarised in the light of the new results. It is suggested that the Subcordilleran granites were generated in a continuous are with the isotopicaly similar earliest Jurassic quartz monzonites of the Deseado Massif, during relative westward migration of southern Patagonia, perhaps as a number of discrete crustal blocks.