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


Gaudio, S.J.; Varga, R.J.; Bettison, V.L.

Abstracts with Programs - Geological Society of America 35(4): 17

2003


The Peach Spring Tuff is a laterally persistent rhyolitic ignimbrite (68-76 SiO (sub 2) wt %) deposited at approximately 18.5 Ma over 35,000 km (super 2) 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 approximately 1m of a minor near-source sedimentary unit followed by ignimbrite units of dacitic composition (63-67 SiO (sub 2) wt %). The dacite units also yield Ar (super 40) /Ar (super 39) dates of approximately 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.