The Serra da Acauã Stock: an example of oxidized fractionated type I granite in the Piranhas-Seridó River Domain (PSD), NE of Brazil

Abstract

The Serra da Acauã Stock is inserted in the context of Ediacaran plutonic activity, one of the most important geological features of the Borborema Province, NE of Brazil. The body is divided into two facies: one fine to medium equigranular and other medium to weakly porphyritic unequigranular with K-feldspar phenocrysts. U-Pb determinations in zircon indicated an ediacaran age of c. 578 Ma for its crystallization. Petrographically, the stock consists of hololeucocratic to leucocratic biotite-monzogranites (M = 1.3% – 9.9%), with biotite being the main mafic (0.5 to 8.1%). Opaque minerals, titanite, allanite, apatite and zircon are accessories and the earliest mineral phases. Geochemically, the rocks that form the stock are similar, with a weakly peraluminous character (1.00 ≤ A / CNK ≤ 1.04), with normative corundum and transition signature between alkaline and calc-alkaline rocks. The variation of the amount of oxides and trace elements suggests the fractionation of plagioclase, biotite, titanite, apatite and magnetite during crystallization of magma. The diagram for the rare earth element (REE) groups shows the enrichment of the LREE relative to the HREE, with the La_N/Yb_N ratios between 16.10 and 54.75, and negative anomalies of Eu (Eu/Eu* of 0.66 to 0.90) compatible with plagioclase fractionation. Data related to the temperature of zircon saturation added to geochemical discriminant diagrams have the potential to associate these rocks to a highly fragmented type I granites. The data set allows correlating the magmatism in the context of high-K calc-alkaline granites, late to post-tectonics of Piranhas-Seridó River Domain.