The lower Colorado River extensional corridor in southern Nevada, western Arizona and southeastern California is an ideal natural laboratory in which to examine the interplay between continental extension and magmatism. Most of the >100% extension was concentrated over a rather short time interval (1-4 m.y.) after which both faulting and volcanism decreased rapidly. This study will focus on the structural/tectonic and petrological evolution of the northern Eldorado Mountains in Nevada, where a good data base of geological mapping, high precision 40Ar/39Ar geochronology and structural analysis already exists. Changes in major element geochemistry in the volcanic rocks erupted before, during and after large-scale extension will show how the magmatic rocks responded to rheological changes in the lower crust and mantle during extension. The results of this study will provide direct documentation of the relationship between rates of extension and changes in the composition of mafic magmas in highly extended continental terranes, and will have wide-reaching application to other extensional tectonic environments.
