Collaborative Research: Constraining the Thermal Structure of Fossil Subduction Plate Interfaces Through Combining Petrology and Geodynamics

The evolution of the magmatic arc depends partly on the thermal condition of the forearc region that controls the metamorphic input to the subduction factory. However, the detailed thermal structure of the forearc and its evolution over time is far from clear. On the one hand, pressure-temperature (P-T) estimates from exhumed metamorphic rocks provide constraints to the thermal conditions of fossil subduction zone plate interfaces. On the other hand, these estimates are 200-300°C warmer than the average thermal conditions that are predicted by thermal models for present-day subduction zones. To elucidate this apparent disparity, we take a two-pronged approach of analyzing exhumed rocks from selected fossil subduction localities using quartz-in-garnet elastic thermobarometry and Zr-in-rutile thermometry and developing 2-D thermo-mechanical models that incorporate the tectonic histories of the localities. The model parameters, such as plate age and convergence velocity, are chosen based on global plate reconstruction models and regional geological and petrological studies. Preliminary results indicate that 1) the new P-T estimates do not differ significantly from those based on chemical equilibrium and 2) the model predictions compare well with P-T estimates.