The study of subduction channels: Progress, controversies, and challenges

Abstract

The subduction channel is defined as a relatively thin and weak zone with coherent kinematics between the descending and overriding plates during subduction. The materials in the channel, showing the characteristics of melange, consist of low-density, low-viscosity, highly sheared metasediments and/or serpentinite-rich matrix with relatively rigid blocks. The channel materials flow downwards and upwards, forming a kind of channel convection. Based on geophysical and geological observations on active oceanic subduction zones, combined with numerical simulations, the subduction channel model was initially set to shallow depths With the development of numerical simulation technology and fossil subduction zone investigations, the subduction channel model was extended to depths of 80–100 km to describe deeper geodynamic environments of oceanic subduction zones and explore the exhumation of high to ultrahigh pressure metamorphic rocks. It is also extended to continental subduction zones in order to explain the exhumation of metamorphic rocks in different grades as well as fluid activity and crust-mantle interaction during continental subduction. Although there are a series of differences in material composition and slab/mantle interface property between the upper and lower plates, continental subduction channels exhibit many similarities in structure and dynamics to oceanic subduction channels. Existing studies have provided a fundamental understanding of the structural and dynamic characteristics of subduction channels, but many problems still need to be solved and clarified. In particular, the fundamental characteristics of subduction channels obtained by numerical simulation need to be confirmed and modified through geological investigations of fossil subduction channels.