Geophysical evidence for doming during the Pan-African/Brasiliano orogeny in the Seridó belt, Borborema Province, Brazil

Abstract

The Neoproterozoic Seridó belt located in the Borborema Province, NE Brazil, was deformed and metamorphosed in the Pan-African/Brasiliano orogeny. The basement rocks of the belt were submitted to intense partial melting to form dome-like structures as documented in the Santa Luzia anatetic dome. The aeromagnetic map of the Seridó belt shows a long-wavelength anomaly with elongated sigmoidal shape, whose limits coincide with shear zones. Comparison with gravity data shows that both anomalies share common sources, which are felsic rocks more magnetic and less dense than the surrounding crust. Correlation with geology shows that the geophysical anomalies are associated with magnetite-rich migmatites and granites. We modelled the geophysical datasets using magnetic susceptibility and density values from measurements in cores of a stratigraphic borehole. The results are consistent with a migmatite-dome system formed in the south-central part of the belt. This large-scale crustal structure is composed of elongated internal domes, which were geophysically modelled as four anomalous bodies, that resulted from partial melting of rocks mostly of the basement. The anomalies define an elongated migmatite-dome system with the main axis in the NNE-SSW direction that progressively bends to E-W approaching to the Patos shear zone, thus indicating that this shear zone had a key role in shaping the domic structure. The migmatitic domes of the Seridó belt compose a fault-related dome system, formed in association with the broad strike-slip shear zone array of the Patos-Seridó system, which evolved through the crustal extrusion resulting from the continental collisions that amalgamated West Gondwana in the Ediacaran.