Oxygen isotope thermometry of Brazilian potassic volcanic rocks of kamafugitic affinities

Oxygen isotope analyses have been obtained for magnetite and diopside from mafic alkaline volcanic rocks of kamafugitic affinities from Brazil. These rocks are part of the Alto do Paranaı́ba and Santo Antônio volcanic provinces of Cretaceous age. Based on the clinopyroxene–magnetite pair, the isotopic temperatures obtained for the rocks of the two provinces are: mafitites −1140–920°C; leucitites −920–830°C; kalsilitites −820°C; analcimites (originally leucitites) −1060–1050°C; cumulate pyroxenites 750–690°C. The Mata da Corda (Alto Paranaı́ba Province) and Santo Antônio da Barra range in δ18O coincides with typical values for mantle-derived magmas.