Reavalia??o das condi??es de cristaliza??o de granitos alcalinos ediacaranos dos domínios Rio Piranhas-Seridó e S?o José do Campestre, Província Borborema, NE-Brasil

摘要

The crystallization conditions (P, T, ?O 2 ) of alkaline granites (A-type) within the Rio Piranhas-Seridó and S?o José do?Campestre domains (NE Borborema Province) were revaluated based on the simultaneous application of multiple geobarometers,?geothermometers and crystallization modelling. The studied bodies are the Caxexa, Serra do Algod?o, Serra do?Boqueir?o, Olho D’água, Japi, and Serra Negra do Norte plutons, and the Flores stock. The results show emplacement?pressures between 3.7 and 3.7 kbar (~11–14 km at depth), except for the Japi pluton, with an average pressure of 5.3 kbar?(~20 km at depth). Crystallization modelling yield liquidus temperatures in the range between 885–917 and 818oC for the?Flores stock, and solidus between 660–700oC. Aegirine-augite, magnesio-ferri-hornblende and biotite crystallize between?813–822, 728–751, and 750–789oC, respectively. Among the accessories, the geothermometer Zr-in-titanite yields temperatures?of about 780oC (maximum of 830oC) for the Caxexa pluton. Crystallization took place under essentially oxidizing?conditions for most of the plutons (+1.0 Δ QFM +2.1), except for the Flores stock, formed under slightly more reduced?conditions (Δ QFM ≈ 0.0). Plutons related to regional shear zones are alkali-richer and, on average, deeper, reinforcing the?role of structural control on the emplacement and chemical contrast among these granites. The new? estimates are more accurate?and contribute to the better understanding of the evolution of the granitic alkaline magmatism within the setentrional?portion of the Borborema Province.