Petrogenesis of Challis volcanics from central and southwestern Idaho: trace element and Pb isotopic evidence

Challis volcanics comprise Eocene age mafic, intermediate, and silicic lavas and ash flow tuffs erupted from fissure vents and calderas in central and southwestern Idaho. We have analysed a suite of mafic to intermediate composition lava flows from central Idaho, and ash flow tuffs and dikes from southwestern Idaho for major elements, trace elements, and Pb isotopic compositions. These data provide constraints on the petrogenesis of the Challis volcanics and on the tectonic setting of the northwestern United States during the Eocene. The authors favour a model for the generation of the Challis volcanics by melting entirely within the lithospheric mantle and lower crust, possibly in response to the tectonic thickening and subsequent extension experienced by the region following late Mesozoic and early Cenozoic compressional deformation. -from Authors