HR: 0800h
AN: V51C-0707    [Abstracts]
TI: Magmatic construction of the Searchlight magmatic system (Eldorado-Newberry Mountains, Nevada) as revealed through zircon geochemistry and Ti-in-zircon geothermometry
AU: * Leslie, S
EM: shanleslie14@yahoo.com
AF: Dept. of Geology, San Jose State University, San Jose, CA 95192-0102, United States
AU: Miller, J
EM: Jonathan.Miller@sjsu.edu
AF: Dept. of Geology, San Jose State University, San Jose, CA 95192-0102, United States
AU: Miller, C
EM: calvin.miller@vanderbilt.edu
AF: Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37235, United States
AU: Wooden, J
EM: jwooden@usgs.gov
AF: Stanford–USGS Micro-Isotopic Analytical Center, Stanford University, Stanford, CA 94305- 2220, United States
AU: Faulds, J
EM: jfaulds@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 89557, United States
AB: The Miocene Searchlight pluton and coeval volcanic rocks in the Colorado River Extensional Corridor, southern Nevada (USA) provide an excellent record of the growth of a large subvolcanic magmatic system. Mapping, geochronology, geochemistry, and isotopes have established a clear petrogenetic relationship between volcanism and growth and solidification of the Searchlight pluton. The main quartz monzonite pluton grew by repeated intrusion of trachydacite/trachyandesite magma from about 17.0 Ma to 16.2 Ma, with periodic venting of crystal-rich magma as flows and domes. The pluton then underwent fractionation to granite, with eruption of rhyolite as domes, flows, and tuffs (16.2 to 15.8 Ma). This final period of magmatism was also accompanied by new mafic input. Trace elements in zircons from 3 pluton samples (felsic quartz monzonite to high-silica granite), 1 trachydacite dike, and 2 volcanic rocks (a trachydacite and rhyolite that mark the transition from intermediate to silicic volcanism) show patterns typical of igneous fractionation, including deepening of Eu anomalies, higher Hf, and lower Th/U with decreasing temperature as estimated by Ti-in-zircon thermometry. Zoning observed in CL images and Ti-in-zircon temperatures indicate that zircons had diverse and often disparate histories. Zircons from the plutonic samples and the rhyolite show the greatest range of temperature distribution among the analyzed samples, ~150-200°C. Conversely, zircons from the trachydacite dike and trachydacite lava flow show a narrower temperature range ~90-100°C, and for the trachydacite nearly all zircons give temperatures within ~50°C (excluding one analysis). Zircons from the pluton have lower temperature rims surrounding higher temperature interiors and show mainly oscillatory zoning but the range of variation between grain interiors and rims varies dramatically; in some cases <20°C (within uncertainty), and in other cases ~100°C. In contrast, zircons with rounded, resorbed cores surrounded by thinner, euhedral rims are common in the two volcanic samples, and temperatures of the rims are invariably 50- 100°C higher than core temperatures for these zircons. We interpret the data above to indicate that zircons grew in and were transferred between diverse thermal and chemical environments during the growth and solidification of the pluton. Resorption and pronounced temperature increase recorded in rims of zircons from the volcanic rocks likely indicates thermal rejuvenation of the magma chamber accompanied eruption.
DE: 1749 Volcanology, geochemistry, and petrology
DE: 3618 Magma chamber processes (1036)
DE: 3640 Igneous petrology
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting