O Batólito Catolé do Rocha (RN-PB): reavaliação de um magmatismo granítico de tipo-A no Domínio Rio Piranhas Seridó, Província Borborema, NE do Brasil

Abstract

The Catolé do Rocha Batolith (CRB) belongs to the geological context of the northerncentral portion of Borborema Province (NE Brazil), to the west of the Rio Piranhas Seridó Domain, and is an important example of the tectono-magmatic event that affected this geotectonic unit during the Brasiliano Cycle (ca. 571 ±3 Ma). The CRB is composed of metaluminous to slightly peraluminous syenogranites to quartz syenites (granitic facies), basic-intermediate rocks and subordinate microgranitic dykes and / or pockets. These rocks intrude paleoproterozoic rocks of the Caicó Complex and Poço da Cruz Suite. The CRB has been considered a member of the porphyritic high-K calc-alkaline granitic suite in this part of the Borborema Province, that encompasses rocks with chemical affinities akin to the Itype granites. This work presents a review of the geology, petrography, mineralogy and chemistry (whole-rock and mineral chemistry) of the CRB, in order to better define its chemical and typological classification. The CRB granites present alkali-calcic to alkaline affinities, given by relatively high alkali contents relative to CaO. They also have ferroan character, with high Fe/Mg ratios, as well as significant concentrations of LIL and HFS elements, and relative enrichment of light over heavy rare earth elements. Their mafic minerals are Fe-enriched, including annitic biotite and ferro-edenite and hastingsite. Based on the geochemical characteristics, the CRB granites classify as post-collisional A2-type granites. Geothermobarometric calculations point to crystallization temperatures at ~750– 950oC and pressures between 4.6–6.3 kbar. Oxygen fugacity estimates, obtained from the amphiboles, biotite and zircon chemical compositions, indicate that CRB was formed under reduced conditions (-4 < ΔQFM < -1). Therefore, the CRB can also be interpreted as a reduced A2-type granite batholith. Chemical evidences and contrasting redox crystallization conditions for the CRB granites and basic-intermediate rocks suggest they represent distinct magma batches, with local mixing and mingling. An inferred petrogenetic model involve partial melting of a enriched (metasomatized) source and magmatic differentiation driven mainly by fractional crystallization processes (FC). The predominance of FC processes for the CRB granites is supported by petrographic evidences (e.g. concentrically zoned plagioclase) and by multielement diagrams showing pronounced troughs for Ti, P, and Sr, which suggest ilmenite, apatite, and plagioclase and/or hornblende fractionation.