Shoshonitic magmatism in the Southwestern Borborema Province (NE Brazil): The plutons of Campos Sales-Assaré and Padre Marcos

Abstract

The extensive magmatic record and the large network of shear zones are the most striking features in the Borborema Province (BP) northeast of Brazil. In this context, high-potassium magmatism (Itaporanga Suite) is one of the suites with the most significant expression and volume, usually related to a post-collisional period during the transition from the convergent to the transcurrent tectonic regime. Hence, the Campos Sales-Assaré Batholith (CSAB) represents an extensive sigmoidal magmatic body, comprising the extreme west portion of the Transversal Zone, within the BP, cropping out between the Phanerozoic Araripe and Parnaíba basins. Three different trends are recognized in the AFM diagram, named A, B, and C, suggesting that the batholite comprises more than one magmatic series or different plutons. The field aspects and petrography suggest that the main active petrogenetic process was the magmatism mixing between mafic and felsic magmas. The intrinsic parameters obtained for the magmatic body also corroborate the mixing environment, suggesting that the system may have been reheated. Moreover, differences in mineral chemistry and geochemical data indicate that the batholith may be composed of two distinct plutons: Campos Sales-Assaré Pluton (CSAP) and Padre Marcos Pluton (PMP), separated by the Fronteiras shear zone. The estimated oxygen fugacity in amphiboles from one sample of trend B is higher than in amphiboles of trend A. Furthermore, the classification of magmatic bodies as potassic shoshonitic indicates a metasomatized subcontinental lithospheric mantle as a source for the basic rocks and an amphibolite lower crust source for the leucogranites shoshonitic-like. The difference between trends A and B in the multi-elementary diagram suggests a more enriched source for the latter. According to the data, these plutons can be associated with post-collisional within the Brasiliano Orogeny.