Mapeamento geológico na escala de 1:50.000 da estrutura dômica a Oeste-Sudoeste de São Tomé/RN, faixa seridó

Abstract

The present work aimed at doing a geological-structural mapping, in the scale of 1:50.000, in the surroundings of a domic structure to the west-southwest of São Tomé, Rio Grande do Norte. The mapped area comprises about 120 km2 where several lithotypes have been recognized that could be correlated to regional lithostratigraphic units, such as (in chronological order) gneisses and amphibolites of the Caicó Complex, metasupracrustal of the Seridó Group (Jucurutu and Seridó formations), magmatism (including granite veins and dikes, pegmatite dikes or pegmatitic granites), hydrothermal alteration rocks (calc-silicate, biotite and orthofibrous-cordierite schists / gneisses), diabase dikes and basalt plug related to the Rio Ceará- Mirim and Macao, respectively, and alluvial deposits in riverbeds. Three deformational and metamorphic events were identified and named D1/M1, D2/M2 and D3/M3. The first one affected only the lithotypes of the Caicó Complex, being responsible for the generation of a metamorphic-migmatite banding under conditions of the upper amphibolite fácies. The event D2 / M2 corresponds to a contractional regime that affected the Caicó basement, the granitic orthogneisses and the metassupracrustal rocks of the Seridó Group, being responsible for generating tight to isoclines recumbent folds with transposition of flanks, reaching amphibolite fácies. Finally, the D3/M3 event affected most of the units, with the exception of the basic meso-Cenozoic magmatism. The structures related to this event are dextral transcurrent shear zones and F3 folds with moderate to strong axial plane dip and passive lineations with subparallel stretching and low pitch. The metamorphic peak of this event reached the upper amphibolite fácies and the retrometromorphism occurred in the green shale fácies. The events D2/M2 and D3/M3 correspond to the orogenic processes related to the Brasilian Cycle, during Ediacaran-Cambrian. D1/M1 was part of a process of generation and agglutination of plutonic complexes with metasupracrustal enclaves/host rocks, during Riaciano.