Petrologia do Stock Altos Verdes, Domínio Macururé, Província Borborema

Abstract

The Altos Verdes Stock (SAV), with a U-PbShrimp age of 625 ± 4 Ma, is part of the magmatism synchronous to the Brasiliana collision (≈630 Ma), present in the Sergipano Orogenic System. The SAV occurs intrusive in metasedimentary rocks of the Macururé Domain and to the south it is tectonic, through the São Miguel do Aleixo Shear Zone, with the VazaBarris Domain and to the north, the Belo Monte-Jeremoabo Shear Zone, with the Marancó Domain. The SAV rocks have a light gray color, an anisotropic structure marked by mineral alignment, porphyritic, allotriomorphic and medium grain textures. The presence of microgranular mafic enclaves, centimetric to metric, with rounded or elongated shapes and in the form of syn-plutonic dykes indicate that the mixing process between mafic and felsic magmas was important in the structuring of the SAV. The SAV rocks have compositions of diorite, monzonite and monzodiorite (enclave) and consist of plagioclase, quartz, biotite, amphibole, epidote, alkali feldspar, titanite, apatite, opaque minerals and zircon. In metasedimentary rocks the presence of oligoclase, biotite, muscovite, ilmenite and garnet, associated with rocks with albite, muscovite, epidote, ilmenite and chlorite, indicate the presence of regional metamorphism of the conditions of greenschist and amphibolite facies. The mineralochemical study allowed us to infer that the presence of oscillatory-normal chemical zones suggest that the magma has evolved by fractional crystallization. However, the oscillatory zonation can be the record of the mafic magma inputs responsible for the enclaves present in the SAV. Using amphibole crystals as a geobarometer, it was possible to infer the depth of crystallization of amphibole as 25 km. The composition of biotite crystals indicates orogenic affinity for the SAV magma. The geochemistry of the SAV rocks allowed classifying this magmatism as potassic, metaluminous, with affinities with shoshonitic and calcium-alkaline suites of high K2O. The magma generation environment responsible for the SAV was orogenic, of the volcanic arc type.