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Dynamics of oceanic slab tearing during transform-fault horizontally-oblique subduction: Insights from 3D numerical modeling
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  • Jie Xin,
  • Huai Zhang,
  • Felipe Orellana-Rovirosa,
  • Zhong-Hai Li,
  • Liang Liu,
  • Yigang Xu,
  • Zhen Zhang,
  • Yaolin Shi
Jie Xin
University of Chinese Academy of Sciences
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Huai Zhang
University of Chinese Academy of Sciences

Corresponding Author:hzhang@ucas.ac.cn

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Felipe Orellana-Rovirosa
Ocean Science and Engineering department, Southern China University of Science and Technology, Shenzhen 518055, P. R. China
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Zhong-Hai Li
University of Chinese Academy of Sciences
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Liang Liu
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
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Yigang Xu
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
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Zhen Zhang
University of Chinese Academy of Sciences
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Yaolin Shi
University of Chinese Academy of Science
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Abstract

Oceanic-plates vertical tearing is seismically-identified in the present-day Earth. This type of plate tearing is frequently reported in horizontally-oblique subduction zones where transform-faulted oceanic plates are subducting (or subducted). However, the mechanisms behind vertical slab tearing are still poorly understood, thus we utilize 3D time-dependent Stokes’ flow thermo-mechanical models to further study this problem. We find that (i) the age offset of transform fault and (ii) the horizontal obliqueness of subduction fundamentally control the tearing behavior of two generic, materially-homogeneous oceanic slabs separated by a low-viscosity zone. The overriding-continental plate bends one slab first, which combined with the age-thickness difference between slabs, causes the differential sinking of them. Based on the modeling results, well-developed slabs vertical tearing would happen when the oblique angle of subduction is ≥30° or the age ratio of the secondly-bent to firstly-bent slab being ~<0.6. Quantifying the horizontal distance-vector between sinking slabs, we find that subduction at medium-low horizontal-obliqueness angles (≤30°) of young lithosphere (slabs-average ~15 Myr) tends to produce fault-perpendicular tearing. Contrastingly, old-age slabs (average ≥ 30 Myr) with medium-large obliqueness angles (~>20°) tend to produce fault-parallel tearing, related to differential slab-hinge retreat or rollback. Correlations between slabs’ (i) computed tearing horizontal-width and (ii) scaling-theory forms of their subduction-velocity differences, are reasonable (0.76-0.97). Our numerically-predicted scenarios are reasonably consistent with plate-tear imaging results from at least 4 natural subduction zones. Our modeling also suggests that continual along-trench variation in subduction dip angle may be related to a special case of oblique subduction.
08 May 2023Submitted to ESS Open Archive
25 May 2023Published in ESS Open Archive