Research Article| May 01, 2003 Rapid generation of both high- and low-δ18O, large-volume silicic magmas at the Timber Mountain/Oasis Valley caldera complex, Nevada Ilya N. Bindeman; Ilya N. Bindeman 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar John W. Valley John W. Valley 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2003) 115 (5): 581–595. https://doi.org/10.1130/0016-7606(2003)115<0581:RGOBHA>2.0.CO;2 Article history received: 27 Dec 2001 rev-recd: 24 Sep 2002 accepted: 10 Oct 2002 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ilya N. Bindeman, John W. Valley; Rapid generation of both high- and low-δ18O, large-volume silicic magmas at the Timber Mountain/Oasis Valley caldera complex, Nevada. GSA Bulletin 2003;; 115 (5): 581–595. doi: https://doi.org/10.1130/0016-7606(2003)115<0581:RGOBHA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We present an oxygen isotope and petrologic study of four voluminous, zoned ash-flow sheets of the Southwestern Nevada Volcanic Field (SWNVF): Topopah Spring (TS, >1200 km3, 12.8 Ma), Tiva Canyon (TC, 1000 km3, 12.7 Ma), Rainier Mesa (RM, 1200 km3, 11.6 Ma), and Ammonia Tanks (AT, 900 km3, 11.45 Ma). The δ18O values of quartz, sanidine, sphene, magnetite, and zircons in rhyolites and latites of each tuff were measured and used to estimate δ18O(melt) at 700–900 °C. Temperatures were determined by Δ18O(quartz-magnetite) and Fe-Ti thermometers. Each tuff is characterized by a distinct range of δ18O(melt): 8.0–9.0‰ (TS), 7.1–7.8‰ (TC), 7.4–8.6‰ (RM), and 5.4–6.0‰ (AT), with higher δ18O values for rhyolites in each unit. The distinct δ18O of rhyolitic versus latitic portions of each tuff suggests that they can not be related by in situ fractionation and assimilation in a single zoned magma chamber. It is more likely that latite and rhyolite represent two magmas that were juxtaposed prior to eruption. Low-δ18O AT and normal-δ18O TC tuffs were erupted from the same nested caldera complex only 100–150 k.y. after eruption of voluminous high-δ18O TS and RM magmas, respectively. These short time intervals, distinct δ18O, 87Sr/86Sri, and εNd of each tuff, the same loci of their eruption, and energy-constrained assimilation modeling suggest that TS, TC, RM, and AT represent independent magma batches that were rapidly generated, fractionated, and erupted from shallow, sheet-like magma chambers. Such geometry is a result of extensional tectonics in the Basin and Range province, and it favors nearly total evacuation of the magma chamber during a single eruption. Each silicic magma unit was generated by a shallow influx of new mafic magma that melted 18O/16O-depleted (as in the case of AT) or 18O/16O-enriched (RM, TS) rocks. The AT tuff and associated pre- and post-caldera lavas are 2.5‰ lower in δ18O than in the RM tuff and represent the largest known low δ18O magma. We find that all units of the AT cycle contain isotopically zoned zir cons that have up to 2‰ core-to-rim zoning and correspondingly smaller, out-of-equilibrium quartz-zircon and melt-zircon fractionations. Air-abraded cores of quartz and sphene do not preserve any δ18O zoning. The higher-δ18O zircon cores in low-δ18O magmas of SWNVF are similar to zoned zircons in low-δ18O lavas at Yellowstone. In both places, normal-δ18O zircons have been inherited from precursor volcanic rocks in that the matrix suffered depletion in δ18O (down to +4% to +5% according to AFC modeling), but zircons and quartz survived hydrothermal alteration. These precursor rocks were later rapidly remelted to form low-δ18O melt and caused progressive exchange of oxygen with normal-δ18O zircon and quartz xenocrysts. Based on modeling of oxygen diffusion in zircon and quartz, the time between xenocryst entrapment and eruption is estimated to be 104 yr in SWNVF versus 103 yr for Yellowstone. We suggest that zircon recycling is a common feature of low-δ18O magmas worldwide and is a signature of nearly total remelting of hydrothermally altered roof rocks, in hot-spot (Yellowstone) and in extensional (SWNVF) environments. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Bindeman et al. (2003) studied this question.