Using magma dynamics models to integrate geochemical and geophysical data in a process-based framework: Melt residence and accumulation at Laguna del Maule, Chile

Abstract:

The assembly of large silicic magmatic centers encompasses processes that span many time and length scales from the initial processes of mantle melting and extraction, to the transport, interaction, differentiation, and residence in the crust. These magmatic systems are coupled to their crustal containers, exchanging mass and energy, and responding to evolving tectonic conditions and crustal lithologies. In this work, we use multiscale numerical models in conjunction with recent information from the on-going geophysical and geochemical investigation of one large silicic center, Laguna del Maule (Chile), to examine the response of the crust to sustained input of magmas from the mantle. The Laguna del Maule (LdM) volcanic field in Chile has been one of the most active rhyolitic centers following deglaciation, and this part of the arc has likely been continuously active for ~25 MY (Hildreth et al, 2010).

We use a 3D multiphase model to examine the evolution of the Laguna del Maule system and explore the magmatic flux that is consistent with a range of observations. This model simultaneously calculates heat transfer, melt dynamics, and phase equilibria. We particularly focus of the long-term history of magma in the crust including melt residence and spatio-temporal relationship of melt in the crust. We also report self-consistent phase equilibria based on batch rhyolite-MELTS calculations embedded in the dynamics model, and use crystal tracers to examine populations of crystals and use these in conjunction with geochronology to examine melt dynamics in the upper crust. Additionally we use the melt and phase equilibria histories to compute zircon crystal histories and forward models of geophysical fields including gravity and magnetotellurics (presented in detail in complementary presentations). We find that given numerous realizations of intrusion scenarios, an upper crustal reservoir of silicic melt develops, albeit with low melt fraction with transient high melt fraction bodies of 10s of cubic kilometers. These upper crustal magma bodies exist in a narrow range of flux from the mantle, and upper crustal reservoirs of melt consistent with LDM observations are accompanied by conditions conducive to the formation of complementary lower crustal reservoirs.