CONSTRAINING PAST THERMAL CONDITIONS OF THE PALEO-SUBDUCTION PLATE INTERFACE AT NEW CALEDONIA AND THE DOMINICAN REPUBLIC: COMBINING PETROLOGY AND GEODYNAMICS (Invited Presentation)

Pressure-temperature (P-T) estimates from exhumed metamorphic rocks, including eclogites and blueschists, are often used to constrain the thermal conditions of paleo-subduction zone plate interfaces. However, the exhumed rock record on average indicates temperatures 100-300°C warmer than those predicted by geodynamic models for modern subduction zones. To elucidate the difference in the ancient and modern subduction zone thermal structures, we compare newly acquired P-T estimates from petrologic data to newly constructed geodynamic models for the thermal evolution of the paleo-subduction localities exposed in New Caledonia and the Dominican Republic. We chose these two subduction systems because they represent endmembers of relatively short-lived and longer-lived subduction respectively. We evaluate the P-T history of these localities using quartz-in-garnet elastic thermobarometry combined with Zr-in-rutile thermometry. This permits us to test assumptions about chemical equilibrium that are the basis for thermobarometers commonly utilized to reconstruct P-T paths. We develop 2-D coupled kinematic-dynamic models that incorporate the paleo-subduction parameters, such as convergence velocity and plate age that are constrained by global plate reconstruction models. Data from regional geological and petrological studies also help constrain the duration of subduction and the thermal history of the subducting plate. We compare the model-predicted subduction thermal structures with the P-T conditions estimated from the exhumed rock record to assess key factors that contribute to the apparent disparity between ancient and active subduction systems and to provide insight into characteristics not preserved from the ancient systems, such as plate dip and the depth of slab-mantle coupling.