Potassium-argon dates on the Serra Geral Formation of South America

Abstract

The Serra Geral Formation in the Paraná Basin of South America forms the largest known volcanic development in the world. Stratigraphic evidence indicates that this formation is younger than Upper Triassic and older than Upper Cretaceous, and generally it has been assigned to the Lower Jurassic. Potassium-argon age measurements on plagioclase from two lavas of the Serra Geral Formation yield dates of 120 and 123 m.y. Plagioclase and pyroxene from four samples from dolerite intrusions, which are thought to be coeval with the lavas, give dates ranging from 120 to 126 m.y. All the measured ages agree closely and substantiate the correlation of the dolerites with the lavas. The data suggest a Lower Cretaceous age for the main volcanic activity; this is significantly younger than the ages found for similar rocks from South Africa, Antarctica and Tasmania. Show more