Picabo volcanic field

Picabo volcanic field
Kbh3rd · Public domain · source
Name	Picabo volcanic field
Location	Butte County, Idaho, Blaine County, Idaho, USA
Range	Snake River Plain
Type	caldera-related volcanic field
Last eruption	~10.5–4.5 million years ago

Picabo volcanic field is a Neogene volcanic province in the eastern Snake River Plain of southwestern Idaho, United States. The field contains widespread silicic ignimbrites, rhyolitic domes, and basaltic lavas that record interactions among the Yellowstone hotspot, Basin and Range extension, and the North American Plate. Its deposits and structures have been studied in relation to regional volcanic provinces such as the Heise volcanic field, Bruneau-Jarbidge volcanic field, and the Yellowstone Plateau.

Geology

The geology of the Picabo volcanic field comprises silicic tuffs, welded ignimbrites, rhyolite domes, and intercalated basaltic flows mapped across the eastern Snake River Plain and adjacent parts of Blaine County, Idaho and Butte County, Idaho. Stratigraphy shows thick units correlated with regional ash-flow sheets that also appear in outcrops near the Craters of the Moon National Monument, the Idaho Batholith, and sediments of the Salmon River drainage. Regional tectonostratigraphic relationships tie the field to the track of the Yellowstone hotspot and extensional faulting associated with the Basin and Range Province and the Neogene Cordilleran orogeny.

Eruptive history

Eruptive history includes multiple large-volume silicic eruptions during the middle to late Miocene (~10.5–4.5 Ma), producing eruptions that are temporally and compositionally related to ignimbrites mapped across the Snake River Plain. The field produced major ash-flow sheets that correlate with units erupted from centers near the Heise dome complex and contemporaneous with volcanism at the Bruneau-Jarbidge volcanic field and early Yellowstone Caldera activity. Intervening mafic volcanism, recorded by basaltic lavas, occurred synchronously with rhyolitic activity and is comparable to basaltic pulses documented in the Columbia River Basalt Group margin and along the Great Rift of Idaho.

Petrology and geochemistry

Petrology of the Picabo suites includes high-silica rhyolites with phenocrysts of quartz, sanidine, plagioclase, and accessory titanite and Fe–Ti oxides similar to xenocryst assemblages in the Idaho Batholith and Yellowstone volcanic province. Geochemical signatures show high silica, high alkali content, and isotopic ratios that indicate crustal assimilation and mantle-derived input attributed to the passage of the Yellowstone hotspot beneath Proterozoic and Mesozoic crust. Trace-element patterns (e.g., rare-earth elements, high field strength elements) resemble those of rhyolites from the Heise volcanic field and show fractional crystallization trends comparable to magmas studied at the Coso volcanic field and Long Valley Caldera.

Structure and tectonic setting

Structural setting is controlled by the eastward-progressing track of the Yellowstone hotspot across the North American Plate and by regional extension within the Basin and Range Province. Basin-scale fault systems, grabens, and caldera-related ring faults influenced vent distribution and emplacement of ignimbrites, linking the field to fault blocks mapped in Blaine County, Idaho and to regional deformation associated with the Neogene Cordillera. The field lies on crust influenced by the Idaho Batholith and overlies Proterozoic basement terranes exposed in regional ranges such as the Bitterroot Range and Sawtooth Range.

Geochronology

Geochronology employs argon–argon and potassium–argon dating of sanidine and biotite, U–Pb zircon geochronology, and magnetostratigraphic correlations to constrain eruptive ages between ~10.5 Ma and ~4.5 Ma. Dates correlate with units in the Snake River Plain chronology and with the magmatic pulse that preceded caldera formation episodes at the Yellowstone Caldera and volcanic centers of the Heise volcanic field. Isotopic age frameworks have been integrated with regional chronostratigraphic markers such as the Bruneau-Jarbidge ash beds and magnetochron boundaries.

Volcanic hazards and geomorphology

Although extinct in the Quaternary, the geomorphology of the Picabo volcanic field preserves extensive ignimbrite plateaus, welded-tuff cliffs, and rhyolite dome remnants that influence modern drainage, soil development, and erosion patterns in Blaine County, Idaho and adjacent basins. Present-day hazards are negligible, but understanding of large-volume silicic eruptions aids hazard assessment for active provinces like the Yellowstone volcanic system and the Long Valley Caldera. Landscapes preserve features comparable to those at Craters of the Moon National Monument and the Snake River Canyon.

Research history and discoveries

Research history includes detailed mapping by state geological surveys and academic investigations at institutions such as the University of Idaho, Idaho Geological Survey, and national laboratories that examined petrography, geochemistry, and geochronology. Key discoveries linked the Picabo field to the Yellowstone hotspot track, established correlations with the Heise volcanic field and Bruneau-Jarbidge volcanic field, and refined Miocene magmatic chronologies using U–Pb zircon and 40Ar/39Ar dating methods. Ongoing studies integrate field mapping, isotopic studies, and geophysical imaging techniques used in regional projects like the EarthScope program and collaborations with the United States Geological Survey.

Category:Volcanic fields of Idaho