HR: 1400h
AN: V23A-04    [Abstracts]
TI: Volcanic Centers of the Northern McCullough Range, Southern Nevada USA: a View of Pre- Extensional Volcanism in the Colorado River Extensional Corridor
AU: Honn, D K
EM: dkhonn@gmail.com
AF: University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, United States
AU: * Johnsen, R
EM: fear.the.pumice@gmail.com
AF: University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, United States
AU: Smith, E I
EM: gene.smith@unlv.edu
AF: University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, United States
AB: The northern McCullough Range, just south of Las Vegas, Nevada, is being developed by the US Bureau of Land Management as the Sloan Canyon National Conservation Area to preserve its natural history. Compared to adjacent ranges, the northern McCullough Range was relatively undeformed by Miocene extension in the Colorado River Extensional Corridor. Therefore, the well preserved volcanic centers within the McCullough Range provide an excellent opportunity to study pre-extensional volcanism. There are at least seven volcanic centers in the northern McCullough Range; this study focuses on the Cactus Hill, McCullough Wash, and Eldorado Valley Volcanoes in the central McCullough Range, and the Henderson Caldera in the northern McCullough Range. The Cactus Hill volcano is a 200 m thick section of flows and agglomerates that form a broad basalt-andesite cone, nearly 2 km in diameter. This cone is cut by two (2-3 m wide) basalt dikes and at least 8 dacite domes. Each of the domes is associated with a broad debris apron. The McCullough Wash volcano is composed of at least 6 dacite domes and carapace breccias that reflect periods of dome growth and collapse. The Eldorado Valley Volcano, another series of dacite domes and flows, is the source of a 250 m thick breccia unit (Eldorado Valley breccia). The breccia is a block and ash deposit (with beds up to 1.5 m thick) containing spectacular blocks (1 cm - 3 m in diameter) and bombs (10 cm - 6 m in diameter) that are interbedded with flows from the McCullough Wash and Cactus Hill volcanoes. Interbedding of dacite breccia of the Eldorado Valley Volcano with dacitic, andesitic and basaltic dome debris from the Cactus Hill volcano reflect coeval mafic and felsic volcanism. The Henderson caldera at the northern tip of the McCullough Range is formed by a arc of domes that erupted a series of biotite dacite flows. The caldera is also filled by domes and flows of hornblende andesite, ash-flow tuff and mesobreccia deposits. The tuff of the Henderson caldera (~20 m thick) grades from a pumice poor base to a pumice rich top and contains lithic fragments of andesite that reflect the explosive truncation of the central McCullough Range stratovolcano (2500 to 3000 m thick section of andesite flows). Mesobreccia occurs along the southern margin of the caldera and contains andesite clasts (< 25 cm) within a matrix of the tuff of the Henderson caldera. The ongoing study the volcanic centers of the McCullough Range provide geologic data for the development of the Sloan Canyon National Conservation Area as well as providing insight into the evolution of the Colorado River extensional corridor.
DE: 3640 Igneous petrology
DE: 8440 Calderas
DE: 8486 Field relationships (1090, 3690)
DE: 9350 North America
DE: 9604 Cenozoic
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly