TECTONIC EVOLUTION OF THE SERGIPANO BELT, NE BRAZIL

Abstract

The Sergipano Belt is a ESE-WNW trending, sub-greenschist to amphibolite grade metavolcano-sedimentary wedge between the southern part of the Borborema Province, known as the Pernambuco Alagoas Massif, and the Sao Francisco Craton, in NE Brazil, polydeformed and metamorphosed about 650Ma ago. From S to N the belt comprises a domain of cratonic sediments, and two metavolcano-sedimentary domains, deposited around mantled Archean-Paleoproterozoic basement gneiss domes. The northern part of the belt also encloses a domain of migmatites and two igneous domains, and is intruded by several syn- to late-tectonic granitic bodies. Intensive geological mapping (1:50,000 and 1:100,000 scales) carried out in a key area of the southern part of the belt, has provided abundant stratigraphic and structural data allowing to interpret the tectonic evolution of the belt in terms of the closure of an asymmetric, laterally continuous basin infilled under a syn-depositional extensional regime and evolving into an oceanic basin (the Caninde sea). The structural analysis indicates a basement-involved D 1 -D 3 ductile to brittle-ductile deformational evolution, D 2 -D 3 being associated with a sinistral transpression throughout the belt. The closure of the Caninde sea was probably followed by an oblique collision of the Borborema Province with the Sao Francisco Craton, then leading to the inversion of the extensional faults of the opening of the basin, and providing the ingredients to understand the lithotectonic domains and the evolution of the Pernambuco-Alagoas Massif. Most tectonic features of the Sergipano Belt fit with those found in other mobile belts of the Pan-African/Brasiliano orogeny, and suggest a model compatible with the supercontinent that evolved by fragmentation and amalgamation along long-lived zones of lithosphere weakness throughout the Proterozoic.