238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas
Application of 238U-230Th disequilibrium dating of accessory minerals with contrasting stabilities and compositions can provide a unique perspective on magmatic evolution by placing the thermochemical evolution of magma within the framework of absolute time. Chevkinite, a Th-rich accessory mineral that occurs in peralkaline and metaluminous rhyolites, may be particularly useful as a chronometer of crystallization and differentiation because its composition may reflect the chemical changes of its host melt. Ion microprobe 128U-230Th dating of single chevkinite microphenocrysts from pre- and post-caldera La Primavera, Mexico, rhyolites yields model crystallization ages that are within 10's of k.y. of their corresponding K-Ar ages of ca. 125 ka to 85 ka, while chevkinite microphenocrysts from a post-caldera Yellowstone, USA, rhyolite yield a range of ages from ca. 110 ka to 250 ka, which is indistinguishable from the age distribution of coexisting zircon. Internal chevkinite-zircon isochrons from La Primavera yield Pleistocene ages with ~5% precision due to the nearly two order difference in Th/U between both minerals. Coupling chevkinite 238U-230Th ages and compositional analyses reveals a secular trend of Th/U and rare earth elements recorded in Yellowstone rhyolite, likely reflecting progressive compositional evolution of host magma. The relatively short timescale between chevkinite-zircon crystallization and eruption suggests that crystal-poor rhyolites at La Primavera were erupted shortly after differentiation and/or reheating. These results indicate that 238U-230Th dating of chevkinite via ion microprobe analysis may be used to date crystallization and chemical evolution of silicic magmas.
Citation Information
Publication Year | 2014 |
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Title | 238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas |
DOI | 10.1016/j.chemgeo.2014.10.020 |
Authors | Jorge A. Vazquez, Noel O. Velasco, Axel K. Schmitt, Heather A. Bleick, Mark E. Stelten |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Chemical Geology |
Index ID | 70134476 |
Record Source | USGS Publications Warehouse |
USGS Organization | Volcano Science Center |