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

Abstract

Evaluating mechanisms and rates for magma transport and emplacement in the upper crust is important in order to predict the thermal and rheological state of the crust, and understand the relationship between plutonism and volcanism. U–Pb geochronology on zircon is commonly used to constrain magma emplacement and storage time in the crust, but interpreting complex zircon age populations in terms of in-situ crystallization versus crystallization at a deeper level is not trivial. This study focuses on the Mt. Capanne pluton in Elba (Italy), a well-documented example of arc-related laccolith emplaced in the upper continental crust. Previous studies proposed that the Mt. Capanne intrusion was accreted in less than 10 000 yr by distinct and mappable magma pulses. Here, we couple high-precision ID-TIMS U–Pb zircon geochronology with numerical thermal simulations to evaluate emplacement rates, test different emplacement models, inform zircon age interpretations and evaluate the potential for melt storage during construction of the Mt. Capanne pluton. Our results require that the Mt. Capanne intrusion was built in at least 250 000 yr by multiple magma injections. A variety of emplacement scenarios show that melt was preserved for <60 000 yr after each pulse and that the maximum eruptible volumes were approximately equal to the volume of each pulse. 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.