Petrogenesis of the Canindé de São Francisco complex: A major Late Proterozoic gabbroic body in the Sergipe Foldbelt, northeastern Brazil

Abstract

The large Canindé de São Francisco gabbroic complex, with its associated volcanic units, has been widely interpreted as a Late Proterozoic island-arc sequence emplaced onto the margin of the São Francisco craton during the development of the Sergipe Foldbelt. Whole-rock major, trace, and rare earth element data and mineral chemistry data are presented here for the Canindé gabbroic complex and the associated Gentileza and Novo Gosto volcanics. These data show that both the gabbros and the volcanics have compositions that bear little resemblance to island-arc sequences. Instead, much of the complex has trace element characteristics that resemble those of continental flood basalts, such as the Paraná. It is more likely that the Canindé Complex has resulted from remobilization of the subcontinental lithosphere during some thermal event in the Late Proterozoic. The Sergipe Foldbelt, therefore, may not necessarily represent a zone of continental collision. Two distinct magma types are recognized in both the gabbro complex and the volcanic sequence. The dominant leucogabbros and the Gentileza basaltic volcanics are relatively enriched in incompatible trace elements and have multi-element patterns that are similar to those Paraná basalts. However, the Novo Gosto volcanics and the FeTi oxide gabbros are much more depleted in light rare earth and other incompatible trace elements, and have more refractory major element compositions. These rocks cannot be related to the rest of the complex by any conceivable scheme involving fractional crystallization. They have more likely resulted from melting of a more refractory mantle component in the subcontinental lithosphere, or they represent second-stage melting of mantle from which a basalt component had already been removed.