Thermal and dynamic modeling of deep subduction of a spreading center: Implications for the fate of the subducted Chile Rise, southern Chile

Our objective is to determine whether the Chile Rise spreading center, curr ently subducting south of the Chile Triple Junction in southern Chile, cont inues or ceases to separate after subduction. A two-dimensional kinematic t hermal model is used to predict the temperature history of the subduction z one during spreading center subduction. Density anomalies, calculated from the temperature fields of the thermal model, are then used to define body f orces that drive the motion of a dynamic viscous fluid model of spreading c enter subduction. Viscous models that include only local inplane driving fo rces predict that the Chile Rise spreading center ceases to separate after ridge subduction. If global in-plane plate forces are also included in the viscous model, continuing separation of the subducted Chile Rise is predict ed, but at a greatly diminished rate. Fully continuing separation of the su bducted Chile Rise only occurs if the subducted Nazca and Antarctic plates remain rigid, allowing the lateral transmission of global plate forces from along strike; however, this situation is unlikely as young subducted plate s are believed to fragment. Continuing separation but at a greatly diminish ed rate is believed to be the most plausible hypothesis for spreading cente r subduction in southern Chile. Dynamic viscous modeling of subduction in t he central Andes suggests a viscosity of 2.5 x 10(20) Pa s for upper mantle above the 400 km phase transition.