Isotopic age constraints on middle Paleozoic deformation in the northern Sierra Nevada, California

Abstract

Allochthons of the lower Paleozoic Shoo Fly Complex in the northern Sierra Nevada were assembled and internally deformed prior to formation of a Devonian-Permian island-arc sequence. U/Pb data on zircons indicate ages of 423 +5/−15 Ma for a submarine tuff within the uppermost thrust slice of the Shoo Fly Complex and 378 +5/−10 Ma for a granitic intrusion that may be cogenetic with the lower part of the arc sequence. These data indicate late Early Silurian Shoo Fly deposition and proximity to active volcanism, as well as late Middle Devonian initiation of arc-related magmatism.