Taylor Creek Rhyolite

Taylor Creek Rhyolite
Name	Taylor Creek Rhyolite
Type	Volcanic rock unit
Age	Paleogene
Primary lithology	Rhyolite
Named for	Taylor Creek
Region	Great Basin
Country	United States

Taylor Creek Rhyolite is a Paleogene volcanic unit characterized by high-silica rhyolitic lava flows, domes, and pyroclastic deposits exposed in parts of the western United States. The unit records explosive and effusive volcanism related to major Cenozoic tectonic events, and preserves textural, geochemical, and geochronologic evidence used to link regional magmatism to broader crustal processes. Field relations and laboratory studies tie the unit to local stratigraphy, regional basin development, and mineralization episodes.

Geologic setting

The unit formed during Paleogene magmatism in the western Cordillera, with emplacement contemporaneous with activity documented in Sierra Nevada (United States), Basin and Range Province, Yellowstone hotspot, Cascade Range, and Laramide Orogeny-related provinces. Regional structural context includes proximity to the Walker Lane, San Andreas Fault, Wasatch Fault, and the extensional framework that produced basins such as the Great Salt Lake Desert, Owens Valley, and Death Valley. Volcanism occurred within a continental arc and post-arc extension milieu influenced by plate interactions among the Pacific Plate, North American Plate, and transient microplates like the Farallon Plate remnants and the Juan de Fuca Plate.

Lithology and petrology

Lithologies include porphyritic rhyolite flows, obsidian rich domes, welded tuffs, pumiceous ignimbrites, and lithic breccias similar to units described from Long Valley Caldera, Bishop Tuff, and Morrison Formation-adjacent volcanics. Phenocryst assemblages commonly contain sanidine, quartz, plagioclase, biotite, and rare hornblende, echoing mineralogies reported from Sierra Nevada batholith-related eruptives and from Katmai National Park and Preserve rhyolites. Geochemical signatures show high silica, elevated incompatible elements such as zirconium and yttrium, and negative anomalies in niobium and tantalum consistent with crustal assimilation and fractional crystallization processes observed in studies of Toba Caldera and Crater Lake rhyolites.

Age and geochronology

Radiometric ages obtained by uranium–lead dating on zircon, argon–argon dating on sanidine, and whole-rock K–Ar analyses place emplacement in the early to middle Paleogene interval, comparable to dates reported from Eocene and Oligocene volcanic provinces including portions of the Absaroka Range and Wind River Range. High-precision U–Pb zircon ages and 40Ar/39Ar sanidine results provide constraints that tie the unit to regional magmatic pulses correlated with documented events such as the cessation of Laramide Orogeny deformation and the onset of Basin and Range extension.

Stratigraphic relationships

The unit overlies older Mesozoic plutonic and metamorphic basement exposed in areas like the Sierra Nevada foothills and is intercalated with sedimentary sequences that include conglomerates, sandstones, and lacustrine deposits analogous to those in the Ephraim Formation and Green River Formation. Stratigraphically it is succeeded by continental volcaniclastic and basin-filling units linked to Miocene extension and by rhyolitic to andesitic volcanics comparable to sequences in the Columbia River Basalt Group-adjacent successions. Field contacts show both conformable and unconformable relations with units mapped by the United States Geological Survey and state geological surveys.

Tectonic significance and origin

Petrogenesis models invoke crustal melting driven by heat input from mafic underplating, lithospheric delamination, or passage of mantle thermal anomalies similar to mechanisms proposed for Sierra Nevada ignimbrites and Great Basin rhyolites. Structural and geochemical evidence links emplacement to transtensional deformation along strike-slip systems like the Walker Lane Transfer Zone and to regional extension associated with the fragmentation of the Farallon Plate. Isotopic compositions support mixing between mantle-derived mafic magmas and crystalline crust akin to scenarios developed for Mount St. Helens and Shasta rhyolitic suites.

Distribution and exposures

Exposures occur in fault-bounded blocks, erosional windows, and volcanic centers across parts of the Great Basin, adjacent ranges including the Sierra Nevada (United States), Inyo Mountains, and isolated plateaus near Bodie Hills and White Mountains (California). Key localities are accessible within public lands administered by the Bureau of Land Management, National Park Service, and state agencies, and have been the focus of mapping by the United States Geological Survey and university geology departments from institutions such as University of California, Berkeley, University of Nevada, Reno, and Stanford University.

Economic importance and hazards

The rhyolitic unit hosts high-silica glass and vapor-phase mineralization that can localize deposits of arsenic, mercury, fluorine, and gold, paralleling mineral occurrences in regions like Comstock Lode and Goldfield, Nevada. Hydrothermal alteration has produced clay- and silica-rich zones of interest for geothermal exploration akin to systems exploited at The Geysers and potential sites investigated by the Department of Energy. Hazards include explosive eruption potential comparable to historic rhyolitic eruptions at Mount St. Helens and Novarupta, rockfall from steep domes as documented in Long Valley Caldera, and geohazards related to fault reactivation similar to events on the San Andreas Fault and Wasatch Fault.

Category:Geology of the United States