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

Abstract

Our objective is to determine whether the Chile Rise spreading center, currently subducting south of the Chile Triple Junction in southern Chile, continues or ceases to separate after subduction. A two-dimensional kinematic thermal model is used to predict the temperature history of the subduction zone during spreading center subduction. Density anomalies, calculated from the temperature fields of the thermal model, are then used to define body forces that drive the motion of a dynamic viscous fluid model of spreading center subduction. Viscous models that include only local inplane driving forces 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 predicted, but at a greatly diminished rate. Fully continuing separation of the subducted 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 plates are believed to fragment. Continuing separation but at a greatly diminished rate is believed to be the most plausible hypothesis for spreading center subduction in southern Chile. Dynamic viscous modeling of subduction in the central Andes suggests a viscosity of 2.5 × 1020 Pa s for upper mantle above the 400 km phase transition. Copyright 2001 by the American Geophysical Union.