K-Ar dating of a granitic stock in the Delano Mountains, northeastern Elko County, Nevada, documents probable Jurassic tectonism. Permian(?) sedimentary rocks have been cut by low-angle bedding-plane faults and synchronously and (or) later have been folded into one major, and several other minor, broad, symmetrical, open folds. Emplacement of a granitic stock at 135 m.y. B.P. through the previously deformed strata and subsequent Tertiary normal faulting added to the structural complexity of the area. It is suggested that the relatively moderate pre-Tertiary deformation in the Delano Mountains represents the upper tectonic level of a pre-Cretaceous (Jurassic) suprastructure in Elko County and vicinity.

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