Flux modulated volcanic-style and magmatic architecture of the Chaxas Volcanic Complex, N. Chile constrained by zircon petrochronology

Charles Lewis , Shan de Silva

Zircon petrochronology of the Chaxas Volcanic Complex (N. Chile) reveals dynamic intrusive flux with a corresponding volcanic history that parallels pulses of the regional Altiplano-Puna Volcanic Complex (APVC) flare-up. Two distinct stages of eruptive style and flux are recognized. The Pre-Chaxas stage is comprised of silicic ignimbrites, including the 500 km3 Puripicar Ignimbrite. Pre-Chaxas U-Pb crystallization ages have long durations (∆t) of 1.3–4.1 myr due to efficient cannibalization. Autocrystic subpopulations indicate maximum crystallization durations prior to eruption (∆tY) of 440–950 kyr. Zr/Hf in zircon is partially decoupled from typical proxies for fractionation (e.g., U/Th) and instead track assimilation. Modeled synthetic zircon ages benchmarked by observed zircon ages predict that Pre-Chaxas flux is consistent with flux requirements necessary for supereruptions at 1.2 × 10−4–2.3 × 10−4 km3 yr−1 km−2. An intrusive volume of ~5800 km3 is estimated for the Pre-Chaxas stage. The younger Chaxas Complex stage consists dominantly of a distributed dacitic dome complex. ∆tY is shorter relative to the Pre-Chaxas stage and zircon is less efficiently cannibalized. Predicted flux during this stage is nearly an order of magnitude lower (< 3.2 × 10−5–5.6 × 10−5 km3 yr−1 km−2), with an estimated intrusive volume of 790 km3. This petrochronologic record shows that volcanic style and subvolcanic architecture are sensitive to variations in magmatic flux, shifting by an order of magnitude over only a few hundred kyr.