Evolution of the Major Gercino Shear Zone in the Dom Feliciano Belt, South Brazil, and implications for the assembly of southwestern Gondwana

Abstract

The Dom Feliciano Belt developed during the Brasiliano–Pan-African orogenic cycle due to the tectonic interaction between the Rio de la Plata, Congo and Kalahari cratons, along with the amalgamation of smaller continental fragments. Together with its prolongations to the south, the Major Gercino Shear Zone constitutes one of the main lineaments of the orogenic system, establishing a more than 1000 km long NE-trending tectonic boundary between a granitic batholith and a metavolcano-sedimentary association. Based on combined field, structural, microstructural and textural data, together with new and published geochronological data, a refined model for the geological evolution of the Major Gercino Shear Zone is presented. Regional NW-verging, low-dipping structures were generated between 650 and 615 Ma, preceding the formation of the shear zone. This was followed by the main deformation phase, corresponding to pure-shear dominated dextral strike-slip, interpreted do be controlled by regional transpression during oblique convergence of the continental terranes. This stage lasted until ca. 585 Ma and was coeval with the continuous emplacement of granitic magmatism along the structure. Strain partitioning and localization led to the development of mylonitic belts along the intrusion borders mostly under greenschist facies metamorphic conditions. Late-stage ductile deformation along the structure was active during the cooling of the intrusions until ca. 550 Ma, while the deformation front of the orogenic system migrated to counterpart orogenic belts in the African continent. After tectonic stabilization, the Major Gercino Shear Zone recorded episodic brittle reactivation, possibly related to the Phanerozoic evolution of the active margins and intracratonic basins in Gondwana.