DISCRIMINATION AND CORRELATION OF PEACH SPRINGS TUFF AND PEACH SPRING AGE-EQUIVALENT IGNIMBRITES BY GEOCHRONOLOGY, PETROLOGY, AND IMMOBILE ELEMENT GEOCHEMISTRY, NORTHERN COLORADO RIVER EXTENSIONAL CORRIDOR

The Peach Spring Tuff is a laterally persistent rhyolitic ignimbrite (68-76 SiO₂ wt %) deposited at ˜18.5 Ma over 35,000 km² of the Northern Colorado River extensional corridor and adjacent terranes. Although the geochemical signature of the tuff is associated with syn-extensional volcanism in the southwestern Basin and Range province, significant deposition occurred pre-extensionally in the NCREC, establishing a reliable paleo-horizontal reference from which the extensional kinematics of basin formation in the Black Mountain Accommodation Zone (BMAZ) can be determined. The various welding facies of the Peach Springs Tuff exposures in the BMAZ were confirmed by petrography and stratigraphic relations.

The exposures of Peach Spring Tuff in Kingman, AZ, Warm Springs, AZ, Piute Mountains, CA, and Grasshopper Junction, AZ overlay ˜1m of a minor near-source sedimentary unit followed by ignimbrite units of dacitic composition (63-67 SiO₂ wt %). The dacite units also yield Ar⁴⁰/Ar³⁹ dates of ˜18.5 Ma and units underlying the Peach Spring Tuff at Kingman, Warm Springs, and Piute Mountain sampling locations and positively correlated by petrography and immobile element geochemistry to the Cook Canyon Tuff. Patterns in bivariate REE, trace, and major element harker diagrams and parallel trends in multi-element, REE, and trace element spidergrams of the Peach Springs Tuff and the Cook Canyon Tuff strongly suggest relation by either fractional crystallization or partial melting. The potential cogenetic relationship between the Peach Spring and Cook Canyon ignimbrite sheets will be evaluated and elucidated by AMS (anisotropy of magnetic susceptibility)and paleomagnetic studies.