Speaker/Affiliation: Genna Chiaro, U.S. Geological Survey
Title: An extensive and short-lived eruption of fayalite-bearing high-silica rhyolite at Mono Craters during the mid-Holocene
When: Wednesday, January 7 at 12:00 PM PST
Location: EMS B214
Abstract: The ~30 high-silica rhyolite domes and flows of the 15 km-long Mono Craters volcanic chain are some of the youngest rhyolitic volcanoes in the western United States. Their ages range from ~42 ka to 0.7 ka with a total erupted volume of ~8.5 km3 and distinctions based on mineralogy (biotite, orthopyroxene, or fayalite-bearing) and crystallinity. Ion microprobe 238U-230Th dating of allanite and zircon surfaces was previously used to date the final crystallization period of the ~40—20 ka biotite-bearing domes and younger ~12—9 ka orthopyroxene-bearing domes (Marcaida et al., 2019). Whole-rock trace-element compositions and zircon-saturation temperatures from these domes reveal compositional trends and provide insight on changing magmatic conditions through time. We report new ion microprobe 238U-230Th isochron ages for all nine fayalite-bearing Mono Craters domes from paired allanite and zircon surfaces. These domes are compositionally indistinguishable in whole-rock major and trace-elements and titanomagnetite compositions despite having the widest spatial distribution of all the Mono domes, with ~12 km separating the northernmost from the southernmost dome. New 1m lidar clarifies previously ambiguous contact relationships, leading to the discovery of a new fayalite-bearing dome and improved relative dating of domes and their associated explosion pits. Overall, our results reveal an unprecedented change in eruptive frequency over the 42 ka history of the volcanic chain, evacuating >0.3 km3 of high-silica rhyolite lava and tephra in a short (<500 yrs) time.
