Oxygen isotope compositions and magmatic epidote from two contrasting metaluminous granitoids, NE Brazil

Oxygen isotope compositions of mineral separates were determined from two metaluminous granitoids (Emas and Sao Rafael plutons) from northeastern Brazil. The I-type Emas pluton has high [[delta].sup.18]O (WR) values (11.5-11.8[per thousand]), whereas the Sao Rafael pluton has low [[delta].sup.18]O (WR) values (7.5-8.1[per thousand]), but Sr and Nd are characteristics of S-type granitoids. Measured mineral-mineral fractionations suggest continuous sub-solidus inter-mineral isotope exchange among all minerals except zircon. There is a large and consistent quartz-epidote fractionation that gives apparent temperatures that are much lower than anticipated closure temperatures for epidote. Oxygen isotope fractionation between natural zircon and magmatic epidote is opposite to that predicted from theoretical determinations, as [[delta].sup.18]O (epidote)