Constraining the temperature conditions of paleo-subduction plate interfaces, Part II: Geodynamic modeling

The pressure-temperature (P-T) conditions that are estimated from exhumed metamorphic rocks in paleo-subduction localities are on average 200-300 °C warmer than those predicted by geodynamic models for modern subduction zones. To elucidate the difference in the paleo and modern subduction zone thermal structures, we investigate the role of regional tectonics at selected paleo-subduction localities, including the Franciscan Complex in California, the Raspas Complex in Ecuador, the Rio San Juan Complex in the Dominican Republic, the Sanbagawa Belt in Japan, and the Pam Peninsula in New Caledonia. We develop 2-D coupled kinematic-dynamic models for these localities, using the paleo-subduction parameters, such as convergence velocity and plate age, that are constrained by global plate reconstruction models and regional geological and petrological studies. The effects of uncertainties in these parameter values on the temperature estimates are also evaluated. As there are no constraints on the geometry of the subducting slab, we construct a range of generic model geometries and quantify the effect of slab geometry on the subduction interface temperature. The effects of ridge subduction, subduction initiation, and slab break-off, where applicable, are also investigated. We compare the model-predicted subduction thermal structures with the P-T conditions that are estimated from exhumed rocks in the selected localities and assess the key factors that contributed to the petrologically constrained P-T conditions.