THERMOMETRY AND GEOCHEMICAL MINERAL ANALYSES OF YELLOWSTONE INTRACALDERA VOLCANIC DEPOSITS REVEAL SEGREGATED MAGMA CHAMBER PRIOR TO 161K ERUPTION

Yellowstone volcano’s most recent episode of rhyolite volcanism, the Central Plateau Member rhyolites (CPM), consisted of at least 22 intracaldera eruptions that occurred in five brief eruption clusters (<1000 years each) from 160 ka to 70 ka. The clustered nature of the CPM eruptions, as well as the prior 250ky eruptive deposits, offer the opportunity to compare the chemical composition and differentiation history of co-erupted magmas through an in-situ analysis of the mineralogy of each flow conducted on the Scanning Electron Microprobe via Electron electron-dispersive spectroscopy; as well as core to rim analyses of sanidine and plagioclase conducted via Electron Microprobe. We present pre-eruptive magma temperatures calculated via two-feldspar thermometry for 3 flows from the first and largest of the CPM eruptive groups erupted at 161 ka (Aster Creek flow, Dry Creek Flow and Tuff of Bluff Point) and 2 flows from prior eruptive intervals; Scaup Lake - 250ka and Middle Biscuit Basin flow – 528ka (±28). These flows display thermal, textural, and chemical characteristics which are distinct and support the view that the eruptive sequence was not derived from a single magma body, but as a series of eruptions sourced from several physically and chemically segregated magma pockets. Yellowstone’s long lived hot spot volcanism combined with its hydrothermal setting presents complex volcanic venting and magmatic storage, which is why petrologic and mineralogic analyses can offer unique insight into the nature of magmatic storage in this tectonic setting.