Pre-eruption recharge of the Bishop magma system

By: , and 



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 <10 µm) to have survived magmatic temperatures for more than ∼100 yr. We interpret these observations to indicate heating-induced partial dissolution of quartz, followed by growth of high-temperature rims (made possible by lowering of water activity due to addition of CO2) within 100 yr of the climactic 760 ka eruption. Hot mafic melts injected into deeper parts of the magma system were the likely source of heat and CO2, raising the possibility that eruption and caldera collapse owe their origin to a recharge event.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Pre-eruption recharge of the Bishop magma system
Series title Geology
DOI 10.1130/G23316A.1
Volume 35
Issue 3
Year Published 2007
Language English
Publisher Geological Society of America
Contributing office(s) Volcano Hazards Program
Description 4 p.
First page 235
Last page 238
Country United States
State California
Other Geospatial Bishop Tuff
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