Fabric evolution of polydeformed orthogneisses and quartzites along the Curitiba Shear Zone, Curitiba Domain, Southern Brazil

Abstract

In Southern Brazil there is a series of strike-slip shear zones that represent the late-collisional event of Western Gondwana in the Neoproterozoic-Eopaleozoic transition. The Curitiba Shear Zone (CSZ) is a part of this strike-slip regime separating two different domains: the supracrustal metasedimentary rocks and the basement composed of orthogneiss, migmatite and quartzite. The absence of detailed structural data for this discontinuity has motivated us to study this important part of the geology of southern of Brazil. The main purpose of this work is the characterization of meso and microstructures and determination of crystallographic fabric of quartz in orthogneisses and quartzites along the CSZ southern block. Structural data suggest that the CSZ consists of one ductile-brittle strike-slip deformation phase leading to the deformation of orthogneiss and quartzites of the Atuba Complex. The ductile regime was responsible for the formation of low-grade mylonite in greenschist facies. Crystallographic texture indicate a restricted recrystallization of quartz mainy via dislocation creep through activation ob basal <a> slip system. The brittle regime led to the formation of cataclasites, faults and joints, with a mean orientation of N50E/75SE and N33E/80SE, respectively. Extensive dissolution-precipitation creep affected the rocks and infilled veins with carbonate and quartz.