Three-dimensional thermal structure of subduction zones: effects of obliquity and curvature

A K Bengtson,P E Van Keken

doi:10.5194/se-3-365-2012

Abstract

Abstract. Quantifying the precise thermal structure of subduction zones is essential for understanding the nature of metamorphic dehydration reactions, arc volcanism, and intermediate depth seismicity. High resolution two-dimensional (2-D) models have shown that the rheology of the mantle wedge plays a critical role and establishes strong temperature gradients in the slab. The influence of three-dimensional (3-D) subduction zone geometry on thermal structure is however not yet well characterized. A common assumption for 2-D models is that the cross-section is taken normal to the strike of the trench with a corresponding velocity reduction in the case of oblique subduction, rather than taken parallel to velocity. A comparison between a full 3-D Cartesian model with oblique subduction and selected 2-D cross-sections demonstrates that the trench-normal cross-section provides a better reproduction of the slab thermal structure than the velocity-parallel cross-section. An exception is found in the case of a strongly curved trench, such as in the Marianas, where strong 3-D flow in the mantle wedge is generated. In this case it is shown that the full 3-D model should be evaluated for an accurate prediction of the slab thermal structure. The models demonstrate that the use of a dynamic slab and wedge, separated by a kinematic boundary, yields good results for describing slab velocities in 3-D.

Highlights

Predictions of temperature in the subducting slab have been of interest since the early days of plate tectonics
While this is a clear simplification from models that treat the slab as a dynamic entity (e.g., Zhong and Gurnis, 1995; Kincaid and Sacks, 1997; van Hunen et al, 2002), this approach allows for the use of observed slab geometries (e.g., England et al, 2004; Syracuse and Abers, 2006; Hayes et al, 2012) and can take into account geodetic and paleomagnetic data to accurately prescribe convergence velocities and plate ages (e.g., DeMets et al, 1994; Muller et al, 2008)
The dynamics of subduction zones is complicated by the structure of the mantle wedge, which is the convecting portion of the mantle above the slab and below the overriding lithosphere

Summary

Introduction

Predictions of temperature in the subducting slab have been of interest since the early days of plate tectonics. One approach to model the thermal structure of the downgoing lithosphere is to kinematically project the slab into the mantle. While this is a clear simplification from models that treat the slab as a dynamic entity (e.g., Zhong and Gurnis, 1995; Kincaid and Sacks, 1997; van Hunen et al, 2002), this approach allows for the use of observed slab geometries (e.g., England et al, 2004; Syracuse and Abers, 2006; Hayes et al, 2012) and can take into account geodetic and paleomagnetic data to accurately prescribe convergence velocities and plate ages (e.g., DeMets et al, 1994; Muller et al, 2008). Models that took into account the dynamics of the wedge often used a simplified isoviscous rheology for the wedge

Objectives

Results

Conclusion