Thermochemical inversion of zircon age populations: A new approach to determine the state of subvolcanic magma reservoirs

Abstract:

Understanding the present state and size of magma reservoirs is crucial to mitigate the hazards associated with volcanic eruptions. The spatial resolution of geophysical imaging techniques is often too low to fully quantify the volume of eruptible magma stored in the system, and the eruptive history of a volcano through geological and geochemical records does not provide a defined picture of the state of the subvolcanic magmatic system. We applied a novel approach based on zircon geochronology, trace element geochemistry and thermal modelling to Nevado de Toluca volcano in Mexico to determine the rate of magma supply and accumulation of potentially eruptible magma in the subvolcanic reservoir. Our calculations constrain the average rate of magma input in the upper crust to values between 5.8×10^-6 and 7.5×10^-6 km³ km^-2 yr^-1. We also show that only a few percent of the supplied magma erupted and that a maximum melt volume of ∼350 km³ is potentially residing within the upper crustal plumbing system of the volcano today. The presence of eruptible magma at Nevado de Toluca is transiently associated with recharge events over timescales of years to centuries. We emphasize that dormant stratovolcanoes, such as Nevado de Toluca, may transition into unrest and eruption over short periods of time potentially without geophysical evidences for melt-rich magma bodies in the shallow crustal storage region. This calls for the need to extend monitoring networks and to combine multi-parametric monitoring with petrology and modelling to gather a quantitative understating of the current status of dormant volcanic systems. Our approach can be widely applied and provides vital quantitative information to better assess the potential magnitude of future volcanic eruptions.