The significance of granite fabrics in the neoproterozoic amalgamation of Western Gondwana (Dom Feliciano Belt, Santa Catarina, Brazil)

Abstract

The analyses of microstructures in combination with the reconstruction of the spatial distribution of linear and planar fabrics within plutonic rocks can make them delicate kinematic indicators in the unravelling of complex orogenic processes. Within the Dom Feliciano Belt of south-eastern Brazil and Uruguay large volumes of granitoid melts have formed extensive batholiths throughout the Neoproterozoic, that document the diachronic agglutination of the different basement domains during the Rio Doce orogeny. In Santa Catarina collision started at ~610 Ma with the juxtaposition of the Brusque metamorphic complex against the Florianópolis batholith. This was followed by the thrusting of the Brusque metamorphic complex on top of the Itajaí foreland basin at ~535 Ma. Under the focus of the presented project is the understanding of the emplacement kinematics of three closely related granitoid suites within the Brusque metamorphic complex, i.e. the Sao Joao Batista, the Valsungana and the Nova Trento granitoid suites. All suites have been considered to be synto post-kinematically emplaced with respect to the collision between the Florianópolis batholith and the Brusque metamorphic complex. The determination of the anisotropy of magnetic susceptibility has proven to be highly useful in the analyses of the weakly developed linear and planar fabrics in igneous rocks. These in combination with a microstructural study of the magmatic vs. sub-solidus origin of fabrics will elucidate the regional stress field during the latest stages of the juxtaposition of Eastern and Western Gondwana. Geochronological and petrographic data will be discussed in terms of rotational exhumation of the granitoids and their host. Results will verify the original orientation of magmatic fabrics at the time of magma emplacement. (AU)