Caracterização do magmatismo ediacarano de afinidade shoshonítica nos domínios Rio Piranhas-Seridó e São José do Campestre, NE da Província Borborema

Abstract

In the extreme NE of the Borborema Province, within the tectonostructural context of the São José do Campestre (DJC) and Rio Piranhas-Seridó (DPS) domains, EdiacaranCambrian magmatism is responsible for generating igneous bodies constituting one of the main geological features. These are represented by different magmatic suites formed by various batholiths, plutons, stocks, and dikes. In this context, a range of studies, from a petrographic/textural and chemical (lithochemical and mineral chemistry) perspective, has been conducted for the six identified plutonic suites. However, for the Shoshonitic Suite, despite significant contributions in terms of mapping, petrography, lithochemistry, geochronology, and intensive crystallization parameters, there is a lack of integration of various bodies. Thus, there was an identified opportunity to integrate existing literature data with unpublished data, aiming to characterize the petrogenetic aspects of Shoshonitic magmatism in DJC and DPS. This is based on petrographic, lithochemical, and mineral chemistry data, including intensive crystallization parameters (P, T, and fO2). For the research development, eleven plutons were selected: Casserengue, Japi, Monte das Gameleiras, Poço Verde, Serrinha, Acari, Quixaba, São João do Sabugi, Serra do Caramuru, Tapuio, and Totoró. Through the integration of compiled data, it was observed that rocks belonging to the Shoshonitic Suite in the DJC and DPS domains are transitional between calc-alkaline and alkaline or subalkaline rocks, with chemical peculiarities. These rocks are basic to intermediate, enriched in Fe2O3, MgO, CaO, TiO2, MnO, and K2O, all showing negative correlations in Harker-type variation diagrams, except for K2O, which correlates positively. The rocks of this suite are the oldest among the Ediacaran magmatism in DJC and DPS. Regarding intensive crystallization parameters, pressures were calculated based on empirical and experimental geobarometers of Al in hornblende. Initially, these rocks are relatively similar for DJC and DPS, with average pressures ranging between 4.1 kbar and 5.5 kbar, corresponding to crustal depths of 15 to 23 km. Average temperatures are also slightly different between the two domains, ranging from 909 to 1020°C, under conditions slightly reducing to slightly oxidizing. The estimation of oxygen fugacity conditions based on amphibole composition indicates predominantly high and subordinately intermediate conditions, typical for this rock type.