2007 GSA Denver Annual Meeting (2831 October 2007)
Paper No. 169-8
Presentation Time: 3:45 PM-4:00 PM

ORIGIN AND EVOLUTION OF SILICIC MAGMATISM AT YELLOWSTONE BASED ON THE ION MICROPROBE ANALYSIS OF ISOTOPICALLY-ZONED ZIRCONS

BINDEMAN, Ilya N.1, FU, Bin2, KITA, Noriko2, and VALLEY, John W.2, (1) Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, bindeman@uoregon.edu, (2) Department of Geology and Geophysics, Univ of Wisconsin, Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA, Madison, WI 53706

The present a high-resolution look at Yellowstone magmatism using ion microprobe analysis for &delta18O in zircons with precision of 0.2 and a 10um spot size. We report 357 analyses of cores and rims, and isotope profiles of 142 zircons in 11 units that represent Yellowstone ignimbrites and post-caldera lavas that were earlier studied by laser fluorination, and previously dated in the same spots by SHRIMP. New observations are the following. 1) Most zircons from ~0.5 Ma post-caldera low-&delta18O Upper Geyser Basin lavas are zoned with higher-&delta18O and highly variable U-Pb ages in cores, that suggest inheritance from pre-caldera >0.64 Ma rocks. 2) Many higher-&delta18O zircon cores in these lavas have 0.64-0.50 Ma U-Pb ages that postdate the caldera formation, but predate the lava's eruption age by <20 ky, and represent inheritance of unexposed post-Lava Creek tuff intracaldera subvolcanic units, formed by cooling the LCT batholith. 3) These 0.5Ma zircons suggest that zircon crystallization, hydrothermal alteration, and zircon re-incorporation in later low-&delta18O magma happened quite rapidly, < 10 to 20 ky. 4) Voluminous 0.25-0.1 Ma intracaldera Central Plateau lavas contain zircons with both high-, and low-&delta18O cores. These youngest lavas were formed after LCT mush was crystallized, by remelting a variety of rocks from high-d18O pre-caldera and low-&delta18O post-caldera units followed by residence in a common intermediate-d18O melt prior to eruption. 5) 2Ma Huckleberry Ridge tuff contains zoned zircons with lower-&delta18O cores suggesting zircon inheritance from the low-&delta18O hydrothermally-altered carapace as an important process during formation of large magma bodies prior to caldera collapse. Large-volume silicic magmatism at Yellowstone reflects rapid, shallow-level remelting of earlier erupted and hydrothermally-altered Yellowstone source rocks. Pulses of basaltic magma provided the heat that drove postcaldera volcanism. Each post-caldera Yellowstone lava was variable in &delta18O, but inherited zircons that retained earlier the age and &delta18O values, and represents an independent magma batch that was generated rapidly by remelting of source rocks of various ages and &delta18O. The LCT magma was already an uneruptable mush by the time of the first post-LCT eruption, ca. 0.1 My after the climatic caldera forming eruption.

2007 GSA Denver Annual Meeting (2831 October 2007)
General Information for this Meeting
Session No. 169
The Track of the Yellowstone Hot Spot II: What do Neotectonics, Climate Indicators, Volcanism, and Petrogenesis Reveal about Subsurface Processes?
Colorado Convention Center: 401/402
1:30 PM-5:30 PM, Tuesday, 30 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 456

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