EVOLUÇÃO ESTRUTURAL DA PORÇÃO SUL DO TERRENO NICO PÉREZ, URUGUAI: REGISTRO DA CONVERGÊNCIA ENTRE AS PLACAS RIO DE LA PLATA E KALAHARI NO FINAL DO NEOPROTEROZÓICO

Abstract

Archean to Eo-Paleozoic lithotectonic units occur in the Nico Perez Terrane (Uruguay), reworked Rio de la Plata Craton, in a complex structural framework. Based on structural analysis of the units from southern Nico Perez Terrane we recognize two structural events (E 1 -E 2 ), with four deformational phases (D 1 -D 2 -D 3 -D 4 ). Both E 1 and E 2 events developed under a transpressive regime during the late Neoproterozoic as result of the oblique convergence between Rio de la Plata (west) and Kalahari (east) plates. The E 1 event ( s 1 ~ S60E-N60W) represents the progression of plate tectonic convergence, and was developed under ductile conditions. The early stages of this event (D 1 ) generated tight to isoclinal folds (D 1 ) that were transposed by top-to-NW thrust shear zones (D 2 ), responsible for the stacking of infracrustal and supracrustal rocks, which are represented by the Carape Complex and the Lavalleja Metamorphic Complex, respectively. Lower greenschist to lower amphibolite metamorphism was associated with this deformation, and temperatures increase from the NW to the SE. There was a temperature decreasing during the late stages of continental collision process, and development of dextral NNE-SSW trending transcurrent shear zones (D 3 ) under lower greenschist facies, due to lateral tectonic escape. The structures of D 3 phase are included here as a minor component of the Sierra Ballena and Dorsal de Cangucu sinistral transcurrent system. The E 2 event ( s 1 ~ S75E-N75W), formed under ductile-brittle to brittle conditions, developed open folds, faults and conjugate fractures (D 4 ), reactivating some structures of the E 1 event.