Mendenhall Postdoctoral Research Seminar
Christy Till, Volcano Science Center, USGS-Menlo Park, CA
When: Wednesday, September 18, 2013 – 12 Noon
Where: National Center, Room 4C315
Quantifying Time Scales of Magma Evolution at Yellowstone Caldera
Caldera-forming eruptions represent the most catastrophic volcanic events and pose the greatest volcanic hazard on Earth. Yet the rate at which this type of volcano amasses voluminous rhyolite magma in subsurface magma chambers and their eruption-triggers is poorly constrained. Dr. Till will present new results on the time interval between the thermal rejuvenation and eruption of magma during the youngest episode of effusive volcanism at Yellowstone Caldera using ultra high-resolution ion-microprobe (NanoSIMS) diffusion dating, radioisotopic dating, and chemical analyses of single crystals.
She will focus on the youngest of the Upper Basin Member intra-caldera effusive rhyolite lavas, the Scaup Lake flow (SCL), which erupted ca. 257 ka after a volcanic hiatus of approximately 200 k.y. The SCL contains zoned phenocrysts of quartz, clinopyroxene, orthopyroxene, plagioclase, and sanidine with accessory zircon and Fe-Ti oxides that show petrographic evidence for magmatic recycling of plutonic crystals. SCL clinopyroxene commonly exhibit exsolution lamellae in their cores, signifying that subsolidus conditions were attained during the early evolution of these rhyolites. Results from U-Pb dating indicate that the SCL magma experienced initial crystallization in the Yellowstone reservoir ca. 350 ka followed by subsequent rejuvenation ca. 240 ka. The crystal chemistry and sanidine and pyroxene diffusion dating indicate that the Yellowstone magma chamber which sourced the SCL was heated and rejuvenated ~1000 years prior to eruption. Together these techniques and observations imply millennial timescales for the rejuvenation of silicic intrusions and the generation of eruptible magma at Yellowstone.
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