THE CATHEDRAL RANGE INTRUSIVE EVENT IN WESTERN NEVADA: NEW CONSTRAINTS

New mapping and geochronology, together with compilations of existing data, indicate that large intrusions of the ca. 95-83 Ma Cathedral Range intrusive event continue out of the Sierra Nevada proper, bending eastward into the Basin and Range. A particularly large, zoned intrusion, flanked by biotite hornblende granodiorite (92.7 ± 1.4 Ma) and cored by a K-feldspar-phenocryst-bearing biotite granite (88.5 ± 2.0 Ma), is centered on the Shawave Range in Pershing County, western Nevada, 50 km northeast of Reno. One lobe of biotite granite (91.2 ± 1.0 Ma) extends across the Nightingale Range to the west, and the intrusion is also tentatively correlated with outcrops in the Trinity Range to the east. Modal mineralogy from stained slabs demonstrates a range of compositions broadly similar to intrusions of the same age in the Sierra Nevada proper, although there are important differences, such as the lack of many K-feldspar megacrysts > 4 cm in size. However, given the oceanic/basinal crustal underpinnings of the Shawave intrusion as contrasted against the continental affinities of the Cathedral Range intrusive suites south of the initial ⁸⁷Sr/⁸⁶Sr = 0.706 line, the overall petrologic similarities are perhaps more surprising than the differences. Although this is the only compositionally zoned pluton in the 95-83 Ma age range yet documented outside the Sierra Nevada proper, most of the basement exposures between Lake Tahoe and Gerlach are intrusions of this age, including some that are quite large; zoning structures in other intrusions may still remain undiscovered due to the extensive Cenozoic cover and disruption by Walker Lane and Basin and Range faulting. The Late Cretaceous Sierra Nevada Batholith may be more continuous than previously thought.