Age of the magma chamber and its physicochemical state under Elbrus Greater Caucasus, Russia: Zircon petrochronology and modeling insightsтезисы доклада
Аннотация:Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for LatePleistocene and Holocene eruptions, but the size and state of its magma chamber remain poorlyconstrained. We report that high spatial resolution co-registered U-Th-Pb ages, as well as O and Hf isotopicvalues in zircon and these span ~0.6 Ma in each lava, documenting magmatic initiation that forms thecurrent edifice. We use a 2D thermochemical modeling of Melnik et al. (2021, JGR) of magma fluxes byeither basaltic or rhyolitic magma fluxes adjusted to Elbrus parameters. The model computes zirconcrystallization ages and O and Hf isotopic ratios, by using a 50k individual points within a mesh, by usingBindeman and Melnik (2016 JPet) code with zircon crystallization from a melt cell. The best-fit of the modelconstrains magmatic fluxes at 1.2 km3/1000 yr in the form of random dike and sill intrusions by hot (900°C),zircon-free dacite from depth into a vertically extensive magma body, which has developed since ~0.6 Mabetween depths of 4 and 8 km. Incubation periods without major accumulations of eruptible magma atthese recharge rates are 0.4 Ma, whereas a volcanic episode with eruptible magma present only extendsover the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~180 km3 and temporally oscillating δ18O and εHf values in zircon, and wide-range of zircon age distributionsin each sample. Zircons in 0.7 Ma ignimbrites in the western base of Elbrus also contain diverse zircons butappear unrelated to the current activity. These data provide insight into the current state and the potentialfor future activity of Elbrus and demonstrate that similar zircon records worldwide require continuousintrusive activity by magmatic accretion of silicic magmas generated at depths.