Cordilleran infrastructure in the eastern Great Basin

Reconnaissance of the almandine-amphibolite facies rocks of the Raft River, Grouse Creek, and Ruby Ranges in the eastern Great Basin indicates the presence of recumbent folds with axial-surface schistosity displayed on scales up to thousands of feet. The regional structural grain parallels major trends of the Cordilleran geosyncline. The metamorphic facies and fabric of all metamorphic rocks in these areas are due to post-Triassic, pre-Lower Cretaceous metamorphism. Structural analogies with other mountain chains suggest that the medium- and high-grade metamorphic rocks in the eastern Great Basin are part of a Cordilleran infrastructure and that they may be separated from low-grade and nonmetamorphic rocks by a zone of steep metamorphic gradients and complex shearing caused by differential movement of warm fluid rocks flowing beneath a cool competent cover, the suprastructure.