Primary controlling factors of global ocean trench depth and its linkage with subduction zone kinematics

Abstract

An ocean trench is a major surface feature of a subduction zone, formed by the subduction of a lithospheric plate into the mantle. Despite the importance of ocean trench depth, the primary factors controlling it have not been systematically studied. In this study, we collected several global datasets and performed stepwise regression analysis to investigate this issue. Bathymetric data illustrate that the maximum depth of global trenches varies from −3282 m to −10,924 m, with an average depth of −6125.8 m. Global trench depth generally follows a normal distribution, but also shows a bimodal pattern. Our analysis results suggest that slab age (As), slab dip (θs), sediment thickness (Tsed), and crust thickness (Tc) within a trench are the primary factors controlling global trench depth. The influence of As, Tsed, and Tc on trench depth is similar and is much greater than that of θs. Collectively, these four factors account for 77 % of the variation in trench depth, and other factors including data resolution, reheating events on the seafloor or dynamic topography may account for the remaining 23 % of the trench depth variation. Hierarchical cluster analysis indicates that when a trench enters a terminal stage, its exceptionally thick Tsed and Tc will cause the trench depth to significantly shallow, irrespective of how strongly the As and θs vary. Prior to this, the trench depth is mainly controlled by As and θs because Tsed and Tc are generally small. Our study also reveals varying degrees of correlation between trench depth and subduction zone kinematic parameters including subducting plate velocity (Vsubn), upper plate velocity (Vupn), thermal parameter (φ), trench migration velocity (Vtn), subduction velocity (Vsn), back-arc deformation rate (Vd), and subduction polarity (Psub). There seems to be no correlation between subduction duration (Tsub) and trench depth. We consider these linkages between trench depth and subduction kinematic parameters are the result of the correlations between these parameters and As, θs or Tsed in trenches.