3D slab breakoff in laboratory experiments

Carlos Fernández-García,Benjamin Guillaume,Jean-Pierre Brun

doi:10.1016/j.tecto.2019.228223

Carlos Fernández-García, Benjamin Guillaume + Show 1 more

Open Access

https://doi.org/10.1016/j.tecto.2019.228223

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Abstract

We study slab breakoff of subducting plates with variable orientations of passive margins (ocean-continent transition: OCT) using three-dimensional laboratory experiments. Our results show that the initial obliquity of the OCT with the trench determines the depth and timing of slab breakoff. The reference model involves a straight OCT parallel to the trench. Slab breakoff first starts in the central section of the subduction zone at a depth equivalent to ∼250km and then propagates rapidly towards the edges of the subduction zone where it develops at slightly higher depths (∼280km). In the models where passive margin arrives first at the edges of the subduction zone, slab breakoff starts at that location and propagates laterally towards the center of the subduction zone. It results in higher slab breakoff depths at the edges of the subduction zone than at the center (maximum difference of 170km). In models where the passive margin arrives first in the center of the subduction zone, slab-breakoff starts at that location and propagates towards the edges of the subduction zone over a period that can be as large as 31 Ma and with a large range of depths (maximum difference of 170km). The rate of lateral propagation of slab breakoff decreases with the increasing initial obliquity of the OCT with the trench. The model with the maximum obliquity shows a correlation between the surface topography and the slab breakoff at depth. The plate surface is uplifted after the oceanic and continental slab segments are mechanically decoupled, and in the final stage of the experiment, when the slab is educted, subsidence develops as the isostatic and dynamic support diminish.

Highlights

Slab pull is generally considered as the main driving force for plate motions (Forsyth and Uyeda, 1975; Royden, 1993), and is caused by the negative buoyancy of a subducting oceanic lithosphere
Reference model (H-180) The reference model (H-180) consists of a straight oceanic to continental lithosphere transition (OCT) parallel to the trench direction (Fig. 2 and Table 3), similar to what has been done in the previous studies
The depth and the timing of the breakoff following continental subduction in the model H-180 is within the range of previously obtained values in analogue and numerical models (Fig. 1) and those estimated for subduction zones on Earth (e.g., Mahéo et al, 2002; Chen et al, 2015), which indicates that the setup and the scaling adopted here are appropriate at first order to simulate the slab breakoff in subduction systems

Summary

Introduction

Slab pull is generally considered as the main driving force for plate motions (Forsyth and Uyeda, 1975; Royden, 1993), and is caused by the negative buoyancy of a subducting oceanic lithosphere. The positive buoyancy force that results from the continental lithosphere subduction acts as a force opposing to the oceanic lithosphere slab pull, leading to slab stretching, necking and to breakoff (Davies and von Blanckenburg, 1995; Ton and Wortel, 1997). The breakoff of the subducted lithosphere can be indirectly identified by looking at surface changes resulting from perturbations of slab pull and mantle dynamics at depth. It has been proposed that uplift, sudden changes in deformational regime, changes in magmatic products or fast exhumation of High Pressure rocks may result from slab breakoff at depth. Davies and von Blanckenburg (1995) proposed for the first-time slab breakoff in the Alps to explain the evolution of the Tertiary magmatism, uplift, and exhumation of subducted continental rocks. Slab breakoff has an imprint on the geological record and the surface topography that can be recognized and tracked in the field

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