Pre-eruption recharge of the Bishop magma system

• Published in: Geology (Boulder) 2007-03, Vol.35 (3), p.235-238
• Main Authors: Wark, D. A, Hildreth, W, Spear, F. S, Cherniak, D. J, Watson, E. B
• Format: Article
• Language: English
• Subjects: Bishop Tuff; calderas; California; carbon dioxide; cathodoluminescence; Cenozoic; crystal growth; eruptions; experimental studies; framework silicates; geologic thermometry; geothermal gradient; heat sources; igneous and metamorphic rocks; Igneous rocks; Long Valley Caldera; Magma; magma chambers; magma transport; magmas; metals; mineral-water interface; Mono County California; Petrology; phenocrysts; Pleistocene; precursors; pyroclastics; quartz; Quaternary; reaction rims; silica minerals; silicates; Stratigraphy; Temperature; titanium; tuff; United States; volcanic features; volcanic rocks; Volcanoes
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G23316A.1

The 650 km3 rhyolitic Bishop Tuff (eastern California, USA), which is stratigraphically zoned with respect to temperatures of mineral equilibration, reflects a corresponding thermal gradient in the source magma chamber. Consistent with previous work, application of the new TitaniQ (Ti-in-quartz) thermometer to quartz phenocryst rims documents an ∼100°C temperature increase with chamber depth at the time of eruption. Application of TitaniQ to quartz phenocryst cores, however, reveals lower temperatures and an earlier gradient that was less steep, with temperature increasing with depth by only ∼30°C. In many late-erupted crystals, sharp boundaries that separate low-temperature cores from high-temperature rims cut internal cathodoluminescent growth zoning, indicating partial phenocryst dissolution prior to crystallization of the high-temperature rims. Rimward jumps in Ti concentration across these boundaries are too abrupt (e.g., 40 ppm across a distance of