238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas
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Abstract
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.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | 238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas |
Series title | Chemical Geology |
DOI | 10.1016/j.chemgeo.2014.10.020 |
Volume | 390 |
Year Published | 2014 |
Language | English |
Publisher | Elsevier |
Publisher location | New York, NY |
Contributing office(s) | Volcano Science Center |
Description | 10 p. |
First page | 109 |
Last page | 118 |
Country | Mexico, United States |
State | Jalisco, Wyoming |
Other Geospatial | La Primavera Caldera, Yellowstone Caldera |
Online Only (Y/N) | N |
Additional Online Files (Y/N) | N |
Google Analytic Metrics | Metrics page |