Rb-Sr Isotopic Age for the Precambrian Lavas of the Seton Formation, East Arm of Great Slave Lake, Northwest Territories

Abstract

Spilitic basalts from the Proterozoic Seton Formation at the type locality of Seton Island in the East Arm of Great Slave Lake, Northwest Territories, have a Rb–Sr isotopic age of 1872 ± 10 m.y. The age, representing either the time of eruption or a subsequent metasomatic (spilitization) event, provides a minimum age for the Great Slave Supergroup of the district. An initial 87 Sr/ 86 Sr ratio of 0.7018 ± 0.0005 for the lavas is, together with their age, in accordance with previously proposed theories on continental separation and mantle derived magmatism during Aphebian times.