A kinematic model for evolution of island arc‐trench systems

Abstract

Plate subduction zones are typically characterized by the patterns of surface topography and gravity anomalies consisting of island‐arc high, trench low, and outer‐rise gentle high. These patterns are stable on the time scale of 106–107yr. At some subduction zones, regardless of its age, steady uplift of marine terraces formed by eustatic sea‐level changes during the last 105 yr can be also observed. The stable patterns of topography and gravity anomalies and the steady uplift of marine terraces seem to contradict each other. We constructed a kinematic model which could explain the evolution process of island are‐trench systems and demonstrated that this puzzle could be solved by considering the effect of accretion at plate boundaries. In our model the lithosphere‐asthenosphere system is represented by a stratified visco‐elastic half‐space under gravity, which consists of a high‐viscosity surface layer and a low‐viscosity substratum. The rheological properties of both layers are assumed to be a Maxwell fluid in shear and an elastic solid in bulk. Interaction between oceanic and continental plates is represented by the steady increase of discontinuity in tangential displacement across the plate boundary. The other essential factors considered in our model are accretion of oceanic sediments at plate boundaries, erosion on land, and sedimentation on inner trench wall. We computed the evolution process of island arc‐trench systems by using the kinematic model and obtained the following results: the island are‐trench systems grow at nearly constant rates in the early stage of plate subduction. Therefore, at young subduction zones, we can generally expect the steady uplift of marine terraces. The stable patterns of topography and gravity anomalies are formed within several million years after the initiation of plate subduction. When the accretion process continuously proceeds at plate boundaries, these stable patterns gradually migrate seaward as a whole. In such a case, we can expect the steady uplift of marine terraces even at old subduction zones. We demonstrate that our model can consistently explain the observed surface topography, gravity anomalies, and uplift rates of marine terraces at subduction zones. Copyright © 1993, Wiley Blackwell. All rights reserved