Petrology of Serra da Vaca Stock, Poço Redondo Domain, Sergipano Orogenic System

Serra da Vaca Stock (SSV, 19 km²) is elongated NE-SW, located in the North of Poço Redondo Domain, in the Sergipano Orogenic System. The orientation of this stock cut off the NW-SE regional metamorphic foliation. SVS is composed of biotite gray leucocratic granodiorites of gray color, fine to medium equigranular texture, of isotropic structure. Syenogranites and alkali-feldspar granite are present. The accessory minerals of these rocks are epidote, zircon, apatite, and opaque minerals. Alkaline feldspar is perthitic. Andesine and oligoclase of granodiorites have normal zonation, indicating fractional crystallization. Brown biotite is primary and has Fe/(Fe+Mg) ratio ranging from 0.47-0.84 and exhibits chemical affinity for calc-alkaline suites. The primary epidote (19.9 < %pistacite < 28.85) indicates crystallization under relatively oxidizing conditions at a pressure of 6 kbar (~25 km). Geochemical data indicate that SVS rocks are evolved (70% < SiO₂ < 77.5%), peraluminous and magnesian. The magmatic affiliation of granodiorites is high K calc-alkaline, whereas syenogranites, which are the most evolved, have shoshonitic affinity. The (La/Yb)_N ratios range from 21-70 of granodiorites, 40 in the alkali granite, and 1.4-2.8 in the sienogranites. Eu anomalies are poorly pronounced for most samples (0.57 < Eu/Eu⁎ < 0.94), except for alkali-granite and syenogranites, which exhibit a strong europium negative anomaly (0.16–0.3). Data on trace elements suggest that SVS magma was formed from potassium mafic igneous protoliths. Relations between trace elements (e.g., Th, Ta, Hf, Y, Nb, Rb) indicate that these granites were generated in an orogenic environment in a post-tectonic period. SSV granodiorites are suggested to belong to the Coronel João Sá Intrusive Suite of the Macururé Domain, since they have a geochemical signature of potassic, post-collisional, and intrusive magmatic magmas in a volcanic arch, with the signature of subduction fluids. (author)