Comments on the geology, petrography, and chemistry within the resurgent dome area, Valles Caldera, New Mexico
Fraser Goff, Richard G. Warren, Cathy J. Goff, Jennifer Whiteis, K, Emily uk, and Dale Counce
We briefly describe the geology, petrography and chemistry of rocks from the resurgent dome of Valles caldera using recently published 1:24,000 geologic mapping, supported by thin section examinations and chemical analyses. Eruptive rocks consist of lavas and tuffs of rhyolite to high-silica rhyolite. A 110 m-thick section of densely welded ignimbrite exposed along Redondo Border apparently correlates with the two uppermost stratigraphic units of the Tshirege Member, Bandelier Tuff on the Pajarito Plateau east of the caldera. Caldera collapse breccias consist of Quaternary Otowi Member of Bandelier Tuff, Miocene to Pliocene volcanic rocks, Permian to Miocene clastic rocks, and Pennsylvanian limestone. The age, petrography and chemistry of the volcanic collapse breccias resemble those described for the Tschicoma and Paliza Canyon Formations in the surrounding Jemez Mountains. Early caldera-fill debris flow, fluvial, and lacustrine sediments are derived from the above lithologies but tend to have higher silica and less total alkalis than source rocks due to chemical weathering and hydrothermal alteration. Altered rocks and veins are silica-rich and alkali-poor, and generally contain enhanced iron, sulfur and arsenic values. Rhyolite vitrophyre from ignimbrite just northwest of Cerro Seco, one of the post-collapse ring fracture domes, has chemistry very comparable to Seco rhyolite lava. Thus, we interpret these pyroclastic deposits as the initial eruptions that eventually culminated with Cerro Seco dome.
- Goff, Fraser; Warren, Richard G.; Goff, Cathy J.; Whiteis, Jennifer; K;uk, Emily; Counce, Dale, 2007, Comments on the geology, petrography, and chemistry within the resurgent dome area, Valles Caldera, New Mexico, in: Geology of the Jemez Region II, Kues, Barry S.; Kelley, Shari A.; Lueth, Virgil W., New Mexico Geological Society, Guidebook, 58th Field Conference, pp. 354-366.