HR: 1340h
AN: V53A-0605    [Abstracts]
TI: The Physical and Petrologic Evolution of a Multi-vent Volcanic Field Associated With Yellowstone-Newberry Volcanism
AU: * Brueseke, M E
EM: brueseme@muohio.edu
AF: Department of Geology, 114 Shideler Hall Miami University, Oxford, OH 45056 United States
AU: Hart, W K
EM: hartwk@muohio.edu
AF: Department of Geology, 114 Shideler Hall Miami University, Oxford, OH 45056 United States
AB: The Santa Rosa-Calico volcanic field (SC) of northern Nevada is perhaps the most chemically and physically diverse of all volcanic fields associated with mid-Miocene northwestern USA volcanism. SC volcanism occurred from 16.5 to 14 Ma and was characterized by the eruption of a complete compositional spectrum from basalt through high-Si rhyolite. Locally derived tholeiitic lava flows and shallow intrusive bodies are chemically and isotopically identical to the Steens Basalt (87/86Sri=$<$0.7040), the Oregon Plateau-wide mid-Miocene flood basalt. Andesite-dacite lava flows are exposed as at least four geographically and chemically distinct packages representing products of multiple, discrete magmatic systems. The most voluminous of these is calc-alkaline and characterized by abundant granitoid and mafic xenoliths/xenocrysts and radiogenic Sr isotopic ratios. Subalkaline silicic lava flows, domes, and shallow intrusive bodies define three diffuse north-south trending zones. Textural, chemical, and isotopic variability within the silicic units is linked to their spatial and temporal distribution, again necessitating the existence of multiple magmatic systems. The youngest locally derived silicic units are ash flows exposed in the central portion of the SC that erupted in actively forming sedimentary basins at $\sim$15.4 Ma. Underlying the 400-1500m thick package of SC volcanic rocks are temporally ($\sim$103 and $\sim$85 Ma), chemically, and isotopically (87/86Sr at 16 Ma= 0.7045 to 0.7058 and 0.7061 to $>$0.7070) heterogeneous granitoid plutons and a package of $\sim$20-23 Ma calc-alkaline, arc-related intermediate lava flows. The observed disequilibrium textures, xenoliths, and chemical/isotopic diversity suggests that upwelling Steens magma interacted with local crust, siliceous crustal melts, and the mafic plutonic roots of early Miocene arc volcanism in multiple magmatic systems characterized by heterogeneous open system processes. The formation of these systems is tectonically controlled as evidenced by magma eruption/ascent along active zones of lithospheric extension. Thus, the observed physical and chemical diversity in this volcanic field is attributed to a combination of factors; tectonic setting, availability of upwelling mafic magma(s), nature of pre-Miocene crustal addition and lithospheric modification, and the resulting array of magma sources and petrogenetic processes.
DE: 8499 General or miscellaneous
DE: 9350 North America
DE: 9604 Cenozoic
DE: 8110 Continental tectonics--general (0905)
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting