SUÍTES GRANÍTICAS DO BATÓLITO PELOTAS NO RIO GRANDE DO SUL: PETROGRAFIA, TECTÔNICA E ASPECTOS PETROGENÉTICOS

Abstract

SUÍTES GRANÍTICAS DO BATÓLITO PELOTAS NO RIO GRANDE DO SUL: PETROGRAFIA, TECTÔNICA E ASPEC-TOS PETROGENÉTICOS The Pelotas Batholith, situated in the eastern part of the Sul-Rio-Grandense shield, is 400 km-long and 80-120 km-wide. It is mostly constituted by six intrusive suites: Pinheiro Machado Intrusive Suite, Viamão Intrusive Suite, Encruzilhada do Sul Intrusive Suite, Cordilheira Granitic Suite and the Dom Feliciano Granitic Suite. This association is composed of high-K calc-alkaline rocks, with minor amounts of alkaline granitoids. Alkaline and peralkaline terms are represented by the Bela Vista Granite and rhyolite dikes. The successive emplacement of granitic rock associations is largely related to the activity of extensive, ductile to brittle-ductile shear zones. The suites within the batholith have been affected by three successive deformational events, from which the first two are ductile (D 1 and D 2) and one is ductile-brittle to brittle (D 3). Granitoids from the Pinheiro Machado Intrusive Suite record the oldest deformation event (D 1), which is characterized by flat-lying shear zones with oblique stretching lineations indicating top-to-ESE movement. The structural evolution determined for this region is compatible with a transpressive tectonic model related to oblique plate convergence.