Magma storage and evolution of the most recent effusive and explosive eruptions from Yellowstone Caldera

A field trip guide to the petrology of Quaternary volcanism on the Yellowstone Plateau

“…In the crystallization model, the temperature of the system is decreasing though time, which is supported by temporal decreases in titanium-in-quartz temperatures, pyroxene-fayalite temperatures, titanium-in-zircon temperatures, and iron-titanium oxide temperatures (Vazquez and others, 2009;Girard and Stix, 2010;Stelten and others, 2015). The temperatures implied by the progressive crystallization model are also supported by recent experimental work performed on natural Central Plateau Member rhyolites by Befus and Gardner (2016), which suggest minerals in the rhyolites crystallized at 750±25 °C, in excellent agreement with titanium-in-zircon crystallization temperatures of Stelten and others (2015). Conversely, Loewen and Bindeman (2015) present a model where the rhyolites are generated by equilibrium melting of a shallow refractory feldspar-rich source, which can be in a mushy or subsolidus state.…”

“…These data suggest that the Solfatara Plateau flow rhyolite was formed by mixing the rhyolitic magma that fed the extracaldera Gibbon River flow with magma at the margin of the main subcaldera reservoir that had fed the Central Plateau Member flows. A detailed field and geochemical study by Befus and Gardner (2016) demonstrated that the Solfatara Plateau flow is heterogeneous in trace element composition, and the portion sampled by Stelten and others (2013) is likely to be a volumetrically minor compositional component of the Solfatara Plateau flow. Nevertheless, the zircon and sanidine data described above demonstrate that extracaldera magma mixed with the margin of the main subcaldera reservoir during the genesis of the Solfatara Plateau, Gibbon River, and Hayden Valley rhyolites.…”

“…Iddings (1888) noted that some of the lithophysae have been crushed by surrounding glass that was forced into their cavities, in turn suggesting the glass was viscous at the time of formation. However, using oxygen isotope thermometry, Befus (2016) determined that spherulites in another Yellowstone flow (Pitchstone Plateau) formed in the ~300-580 °C temperature interval, which is below the glass transition of 600-700 °C, indicating crystallization from solid volcanic glass. The Obsidian Cliff flow was a source of Native American arrowheads around the greater Yellowstone area, and is an archeological resource.…”

Geologic field-trip guide to the volcanic and hydrothermal landscape of the Yellowstone Plateau

“…Recent petrologic and geochemical studies of Central Basin Member rhyolites by Befus and Gardner (2016), Stix (2010, 2012), Vazquez and others (2009), Loewen and Bindeman (2015), Stelten and others (2015), and Watts and others (2012) have refined the magmatic history of these units. Girard and Stix (2010) suggest that melting of hydrothermally altered low-δ 18 O rhyolitic protolith began at 0.25 Ma, and a large differentiating crystal mush formed beneath much of the caldera.…”

“…Volatiles in Central Plateau Member rhyolites were explored by Befus and Gardner (2016). Through a study of phenocryst-hosted glass inclusions, they found consistent chlorine (Cl) (1,100 ± 100 parts per million [ppm]) and It is conceivable that the slow-rising lavas of the Central Plateau Member also may have suffered from some diffusive loss of volatiles from phenocryst-hosted glass inclusions.…”