MODELING THE THERMAL EVOLUTION OF FOSSIL SUBDUCTION PLATE INTERFACES (Invited Presentation)

In this study, we discuss some of the key challenges in modeling the thermal history of fossil subduction plate interfaces. The solutions of time-dependent thermal models for subduction systems depend on the initial thermal conditions and thus the ages of the tectonic plates at the time of subduction initiation and their geotherms at the model boundaries as subduction continues. The velocity of the subducting plate also impacts the interface temperature as it controls advective heat transfer. Plate reconstruction models provide constraints on the temporally variable ages of tectonic plates and subduction rate for fossil subduction systems, but the level of confidence decreases as we go further back in time. The uncertainties in plate ages and subduction rate can translate into relatively large uncertainties in the estimates of the interface temperature, particularly when young plates are involved. As the slab subducts into the asthenospheric mantle, viscous coupling between the slab and the overlying mantle induces mantle wedge flow that advects heat, impacting the slab surface temperature. The viscous coupling depends on the strength of the subduction interface relative to that of the overlying mantle. Because the rheologies of the slab surface and overlying mantle are strongly temperature-dependent, the coupling strength may also change as subduction continues. Further, weakening mechanisms, such as hydration and melting, likely affect slab-mantle coupling. However, there is very little understanding of how the slab-mantle coupling strength varies as subduction initiates. The geometrical evolution of the subducting slab in fossil subduction zones is mostly unknown, but we found that the impact of the slab geometry on the subduction interface temperature is relatively small.