An extensive and short-lived episode of mid-Holocene fayalite- bearing high-silica rhyolite eruptions at Mono Craters, California
Having last erupted ~ 700 years ago, the Mono Craters volcanic chain is an active system with a history of explosive and effusive high-silica rhyolite eruptions. Approximately ~ 30 lava domes and flows range from ~ 42 to ~ 0.7 ka, form a ~ 15 km curvilinear trend, and change mineralogy (biotite-, orthopyroxene-, or fayalite-bearing) and crystallinity through time. However, the eruptive chronology of this system is incompletely understood. We report new 238 U- 230 Th isochron ages for nine fayalite-bearing domes from paired zircon and allanite crystal surfaces that reveal a major shift in eruptive frequency and volume over the history of the chain, with extrusion of > 0.45 km 3 of high-silica rhyolite lava between 7.1 and 5.2 ka. This contrasts with older biotite- (~ 42–20 ka) and orthopyroxene-bearing (~ 12–9 ka) domes, each of which erupted smaller volumes over a more protracted period. Whole-rock compositions suggest these older domes tapped separate domains within a shared magmatic system because the former are higher in Sr and Ba whereas the latter are lower in SiO 2 , higher in Zr, and more enriched in light rare-earth elements. Titanomagnetite chemistry and zircon saturation temperatures also reflect changing magma compositions and conditions associated with these domes. Fayalite-bearing domes, in contrast, have uniform whole-rock and titanomagnetite compositions which support rapid extrusion of magma over an interval short enough to prevent Fe-Ti oxides from recording any changes in magmatic conditions. The youngest lavas were also produced in a short-lived episode ~ 700 years ago, showing that multivent, geologically brief eruptive episodes occur repeatedly at Mono Craters.