Title: Potassium-argon ages for plutons in the eastern and southern Sierra Nevada Batholith, California
Abstract:The ages of biotite and/or hornblende separates from 26 plutons in the eastern and southern Sierra Nevada were determined by the K-Ar method.Both biotite and hornblende age determinations were made fo...The ages of biotite and/or hornblende separates from 26 plutons in the eastern and southern Sierra Nevada were determined by the K-Ar method.Both biotite and hornblende age determinations were made for 14 of these samples.Six of the biotite-hornblende pairs give concordant ages; the rest of the biotites give younger ages.Two samples of hornblende give ages considered to be too young, which may be a consequence of post-magmatic potassium metasomatic alteration of hornblende.Most of the dated plutons were emplaced in Late Cretaceous time at the culmination of magmatic activity in the Sierra Nevada.Samples of two plutons not cut by the Independence dike swarm have ages of around 123 Ma; the dike swarm must have been emplaced prior to this time.Read More