Evaluating the construction and evolution of upper crustal reservoirs with coupled U/Pb zircon geochronology and thermal modeling: A case study from the Mt. Capanne pluton (Elba, Italy)

Abstract:

Understanding timescales and mechanisms of magma emplacement and storage in the upper crust is fundamental for evaluating the controls on melt mobility and the tempo and magnitude of volcanic eruptions. U-Pb dating on zircons is commonly used to estimate these processes in upper crustal reservoirs, but increasing precision in zircon ages has lead to increasing difficulty interpreting them in terms of melt emplacement and storage. We present >150 ID-TIMS U/Pb dates on zircon coupled to numerical thermal simulations that 1) constrain the emplacement history and thermal evolution of upper-crustal reservoirs with analytical precision of thousands of years, 2) aid interpretation of complex age spectra and identification of zircon inherited from deeper crustal levels, and 3) provide insight into time-integrated rates of magma recharge and duration of potential eruption windows in active system. Our study of the Late Miocene Mt. Capanne intrusion (Elba, Italy) – a well-documented example of arc-related laccolith emplaced in the upper-continental crust - shows that this reservoir was incrementally built in minimum 300’000 years by accretion of numerous batches of magma. A variety of numerically simulated emplacement scenarios show that maximum volumes that can be erupted correspond to the volume of each pulse injected. Our results also require that the majority of zircon crystallization occurred in zircon-saturated reservoirs at deeper crustal levels prior to final magma emplacement and cooling, which has implications for using zircon U-Pb geochronology to infer upper crustal magma residence times and for accurate interpretation of volcanic ashbed geochronologic data.