Geologia do complexo metacarbonatítico de angico dos dias, divisa bahia/piauí, Brasil

Abstract

Paleoproterozoic rocks from Angico dos Dias Metacarbonatite Complex (MCCAD) are intrusive in Archean-Paleoproterozoic migmatitic gneissic rocks of Sobradinho-Remanso Complex, located at the interface between the Craton of São Francisco and Formosa do Rio Preto and Riacho do Pontal fold belts. The complex consists of metacarbonatites, varied metasyenites, metapyroxenites, alkaline metadiorites, tremolitites and metalamprophyres. The rocks are mainly classified as calcium carbonatite and consist predominantly of calcite and apatite and subordinate dolomite, olivine, phlogopite and magnetite. The metacarbonatitic rocks exhibit variation in the content of apatite, iron-magnesium minerals and magnetite, forming a cumulatic magmatic layering allowing individualizing various petrographic rock types. In addition, exhibit a weathering mantle, which results in the residual phosphate ore, called apatitite. The structural and metamorphic framework is identified by Paleoproterozoic deflections S-2 and S-1 and a reliquiar layering S0, locally preserved due to the heavy implementation of Neoproterozoic foliation S1 and S2, associated to the thrust zones and related to the early collisional phases, with crustal thickening. The deformation of mylonitic character (S3) is superimposed on planar features. The rocks of the complex are metamorphosed to high amphibolite facies, presenting retrometamorphic parageneses over medium to high green schist facies, as well as locally characterize fenitization and silicification processes.