Silent Canyon Volcanic Centre

The Silent Canyon volcanic centre is located on the eastern Pahute Mesa, southern Nye County, and its dominantly pyroclastic products overlap with those that emanated from the Black Mountain centre further west. The central caldera area is almost completely obscured by later, unrelated volcanic rocks, its position being inferred from the distribution, variation in thickness, xenolith content etc. of chemically and petrographically similar lavas and tuffs (Noble et al., 1968, p. 67). The most important units erupted from the centre are the Tub Spring Member and overlying Grouse Canyon Member, which together comprise the Belted Range tuff (Sargent et al., 1965). Both are compound cooling units of ash-flow tuff, the Grouse Canyon Member originally covering an area of approximately 7500 km2, having a volume greater than 200 km3 and generally being densely welded. The Tub Spring Member had rather less than half this volume and covered some 2500 km2. Other rocks of the centre comprise lava flows, domes and dykes and minor welded and non-welded tuffs and extend over about 1100 km2. The rocks of the centre are predominantly peralkaline, being mainly comendites with subordinate trachytic soda rhyolite and trachyte. Phenocrysts consist of sodic sanidine or anorthoclase, iron-rich clinopyroxene, fayalitic olivine and rare zircon, opaques and apatite, with quartz phenocrysts in the comendites. Arfvedsonite and aegirine are common groundmass and vapour-phase minerals together with alkali feldspar and quartz or cristobalite and tridymite.