The Mina Gonzalito gneiss: Early Ordovician metamorphism in northern Patagonia

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

Pucón

Simposio; III South American Symposium on Isotope Geology; 2001

SERNAGEOMIN

Understanding the Palaeozoic tectonic evolution of Patagonia is vital to any assessment of the assembly of this part of the southwestern Gondwana margin. Evidence has been slow to appear and difficult to interpret, due to the small, isolated exposures of pre-Jurassic rocks and the failure of geochronological studies to produce precise and reliable ages for the main igneous and metamorphic events. Modern U-Pb zircon dating is beginning to provide data of sufficient quality to resolve some of the previously obscure relationships, and the ion-microprobe technique is proving very successful in this advance (see Baldo et al., 2001; Rapela et al., 2001a: Pankhurst et al., 2001a). This communication shows for the first time that high — grade metamorphism occurred in northern Patagonia synchronously with that associated with collision of the Precordillera terrane in the Sierras Pampeanas (Casquet el al., 2001; Rapela el al., 2001a).