Segmentation of subducting oceanic plates by brittle-ductile damage

T. V. Gerya1, D. Bercovici2 & T. W. Becker3.4
1Swiss Federal Institute of Technology Zurich, Department of Earth Sciences, Zurich, Switzerland.
2Yale University, Earth & Planetary Science, New Haven, CT, United States
3Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, United States
4Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, United States

Subducting oceanic plates experience intense normal faulting during bending that accommodates the transition from horizontal to downward motion at the outer rise at subduction trenches. We investigated the consequences of the plate bending on the mechanical properties of subducting slabs using 2D subduction models in which both brittle and ductile deformation, as well as grain size evolution, are tracked and coupled self-consistently. Numerical results suggest that pervasive brittle-ductile slab damage and segmentation can occur at the outer rise region that strongly affects subsequent evolution of subducting slabs in the mantle. This slab-damage phenomenon explains the subduction dichotomy of strong plates and weak slabs, the development of large-offset normal faults near trenches and the occurrence of segmented seismic velocity anomalies and interfaces imaged within subducted slabs. Furthermore, brittle-viscously damaged slabs show a strong tendency for slab breakoff at elevated mantle temperatures that may have destabilised continued oceanic subduction and plate tectonics in the Precambrian.