Continental Tip With Thinned Lithosphere and Thickened Crust Is a Favorable Location for Subduction Initiation

Abstract

The collapse of passive margins and subsequent subduction initiation (SI) are key steps in the Wilson Cycle. However, the occurrence and mechanism of SI at passive margins have long been questioned due to the lack of Cenozoic observations. In this study, we propose that the continental tip, where arc/plateau blocks with thinned lithosphere and thickened crust accrete beside the passive margin, is a favorable location for SI. Our three-dimensional numerical model and force analysis demonstrate that the continental tip, with its reduced frictional resistance and increased gravitational instability, is better suited for SI than other parts of the passive margin. Upon completion of SI, the retreat of self-sustained subduction can create a transform plate boundary by tearing the passive margin. Our model explains why SI can occur at continental tips such as the Scotia and the Caribbean, as well as locations with similar tectonic settings, while most parts of the Atlantic margin remain stable over long geological periods.