Marysvale volcanic field

Marysvale volcanic field
Name	Marysvale volcanic field
Location	Utah, United States
Type	Volcanic field
Last eruption	Miocene–Pliocene

Marysvale volcanic field is an extensive volcanic province in western Utah characterized by diverse volcanic centers, calderas, and associated intrusive rocks formed mainly during the Neogene. The field lies within a broader landscape shaped by the Sevier Orogeny, Basin and Range extension, and regional magmatism that also affected parts of Nevada and Idaho. It has attracted study from geologists associated with institutions such as the United States Geological Survey, University of Utah, and Brigham Young University.

Geology

The field occupies the Tushar Mountains, Pavant Range, and adjacent basins within the Great Basin province and sits atop Paleozoic sedimentary strata and Mesozoic plutons related to the Cordilleran orogeny. Volcanic rocks overlie folded and thrust-faulted rocks emplaced during the Sevier Orogeny and are cut by normal faults attributed to Basin and Range Province extension and the Wasatch Fault. The region records interactions between crustal shortening from the Laramide orogeny and later extension influenced by the Yellowstone hotspot track and plate boundary forces from the Pacific Plate and North American Plate.

Volcanic History and Chronology

Volcanism spanned from roughly 32 to 3 million years ago, with peak eruptive activity in the Miocene and Pliocene as documented by radiometric studies such as potassium-argon and argon-argon dating conducted by teams linked to the USGS and Geological Society of America. Major eruptive pulses correspond to regional magmatic episodes that affected the Cascade Range-to-Silver Island Range corridor and coincide temporally with ignimbrite flare-ups recorded in the Colorado River Extensional Corridor. Sequence stratigraphy ties explosive eruptions to ash-flow tuffs, lava domes, and rhyolitic flows with younger basaltic vents marking late-stage activity synchronous with extension along the Wasatch Front.

Major Volcanoes and Caldera Complexes

Key centers include the Mount Belknap-Tushar caldera cluster, the Big John and Indian Peak calderas, and the Clear Creek and Paunsaugunt volcanic centers with associated lava domes and tuff sheets. Calderas in the field are comparable in scale to those in the San Juan Mountains and the Coso Volcanic Field and have produced voluminous ash-flow tuffs analogous to deposits in the Latir volcanic field and Valles Caldera. Numerous intrusive bodies, including granitic and monzonitic plutons, are exposed at localities such as Fremont and Piute ranges.

Petrology and Geochemistry

Rocks range from basaltic andesite to high-silica rhyolite, with cambial suites showing transitional and calc-alkaline affinities typical of continental arc-related magmatism. Geochemical fingerprints include high-silica rhyolite with elevated incompatible elements similar to tuffs of the Mogollon-Datil volcanic field and isotopic ratios indicative of crustal assimilation comparable to studies from the Sierra Nevada and Wasatch Range. Trace-element patterns and rare-earth element distributions reveal contributions from enriched mantle and Proterozoic to Paleozoic crustal components, paralleling petrogenetic models used for the San Juan and Snake River Plain provinces.

Tectonic Setting and Magmatic Sources

The volcanic field developed at the intersection of regional extensional tectonics and magmatic flux influenced by subduction rollback of the Farallon Plate and subsequent interactions with remnants such as the Gorda Plate. Magmatism reflects decompression melting associated with Basin and Range extension and thermal input from mantle upwelling similar to processes inferred for the Yellowstone-Snake River Plain track. Structural controls by strike-slip and normal faults, including offsets related to the Wasatch Fault Zone, localized magma ascent and caldera formation.

Economic and Environmental Impacts

Volcanic and hydrothermal activity produced mineralization exploited in Pioche District, Mercury-style ore zones, and porphyry- and epithermal-style deposits mined historically for gold, silver, lead, and fluorite. The field’s tuffs and andesites supply construction aggregate for communities such as Beaver, Utah and Fillmore, Utah. Environmental concerns include acid-sulfate alteration zones that affect groundwater chemistry near springs and reservoirs monitored by the Utah Division of Water Quality and legacy mining impacts addressed by the Environmental Protection Agency Superfund programs where applicable.

Research History and Notable Studies

Systematic investigation began with mapping and mineral assessments by the USGS and state geological surveys in the mid-20th century, followed by radiometric dating and petrogenetic studies published in journals affiliated with the Geological Society of America, American Geophysical Union, and universities including the University of California, Berkeley and Massachusetts Institute of Technology. Notable researchers include geochronologists and petrologists who compared the field to contemporaneous provinces such as the San Juan Mountains and Lunar Crater Volcanic Field, advancing models of ignimbrite flare-ups and crustal magma chamber evolution. Ongoing work integrates seismic imaging by institutions like Stanford University and geochemical modeling from the Scripps Institution of Oceanography to refine magmatic source models and tectonic linkages.

Category:Volcanic fields of Utah Category:Miocene volcanoes Category:Pliocene volcanoes