Slab tearing in non-collisional settings: Insights from thermo-mechanical modelling of oblique subduction

Andrić-Tomašević, N., Koptev, A., Maiti, G., Gerya, T. and Ehlers, T. A. (2023) Slab tearing in non-collisional settings: Insights from thermo-mechanical modelling of oblique subduction. Earth and Planetary Science Letters, 610, 118097. (doi: 10.1016/j.epsl.2023.118097)

Abstract

The propagation of slab break-off (slab tearing) is usually attributed to laterally variable plate convergence systems with a spatial transition between simultaneous oceanic subduction and continental collision. To study the process of slab tearing in a non-collisional geodynamic context, here we use a 3D thermo-mechanical numerical approach to model the oblique subduction of a homogeneous oceanic plate. We investigate the effects of the following parameters: (1) subduction obliquity angle, (2) age of oceanic slab, and (3) partitioning of boundary velocities (i.e., the ratio between the subduction component and the advance of the overriding plate in the total convergence). In our simulations, the retreat of the subduction zone leads to a thinning of the fore-arc and back-arc lithosphere, which are decoupled from the subducting slab by the rise of the hot asthenosphere from the underlying mantle wedge. As a consequence of the initial obliquity of the active plate margin, slab roll-back velocities are subject to progressive along-trench variations. Consistent with the gradual rotation of the trench, the front of the decoupling between the overriding and downgoing plates (together with predicted magmatic activity and topographic uplift) migrates in a horizontal direction. In the experiments with low angles of subduction obliquity (< 15°), relatively old subducting plates (> 50 Ma), and in the absence of the subduction component in the overall shortening, slab detachment either develops simultaneously along the entire length of the subduction zone or does not occur at all. In contrast, with higher subduction obliquity (≥ 15°), younger slabs (≤ 50 Ma) and in the presence of a boundary push on the oceanic side, the initial slab break-off is followed by the gradual growth of the “tear” window in the direction opposite to the migration path of the previously established plates decoupling. The sharp contrast in trench retreat rates between subduction zone segments affected and unaffected by slab detachment results in the arcuate shape of the trench. Furthermore, the direction of slab tearing may change from horizontal to vertical, eventually leading to the formation of a transform fault on the subducting plate. Our results show striking similarities with several features – such as trench curvature, subduction zone segmentation, magmatic production, lithospheric stress/deformation fields, and associated topographic changes – observed in many subduction zones (e.g., Marianas, New Hebrides, Mexico, Calabrian).

• Item Type: Articles
• Additional Information: This study is supported by the Start-up research fund from the Excellence Strategy of the Karlsruhe Institute of Technology and the Excellence Strategy of the University of Tübingen, IG-Tomase-2019-02 to N. Andrić-Tomašević, and by an Alexander von Humboldt Foundation fellowship to A. Koptev. G. Maiti acknowledges support from the Start-up research fund from the Excellence Strategy of the Karlsruhe Institute of Technology to N. Andrić-Tomašević. T.A. Ehlers and N. Andrić-Tomašević thank the German Science Foundation (DFG) for support (grants EH 329/24-1 and TO 1364/1-1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ehlers, Professor Todd A.
• Authors: Andrić-Tomašević, N., Koptev, A., Maiti, G., Gerya, T., and Ehlers, T. A.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Earth and Planetary Science Letters
• Publisher: Elsevier
• ISSN: 0012-821X
• ISSN (Online): 1385-013X
• Published Online: 20 March 2023
• Copyright Holders: Copyright © 2023 The Authors
• First Published: First published in Earth and Planetary Science Letters 610:118097
• Publisher Policy: Reproduced under a Creative Commons licence