Dynamic slab segmentation due to brittle-ductile damage in the outer rise

摘要

Subduction is the major plate driving force, and the strength of the subducting plate controls many aspects of the thermochemical evolution of Earth. Each subducting plate experiences intense normal faulting(1-9) during bending that accommodates the transition from horizontal to downwards motion at the outer rise at trenches. Here we investigate the consequences of this bending-induced plate damage using numerical subduction models in which both brittle and ductile deformation, including grain damage, are tracked and coupled self-consistently. Pervasive slab weakening and pronounced segmentation can occur at the outer-rise region owing to the strong feedback between brittle and ductile damage localization. This slab-damage phenomenon explains the subduction dichotomy of strong plates and weak slabs(10), the development of large-offset normal faults(6,7) near trenches, the occurrence of segmented seismic velocity anomalies(11) and distinct interfaces imaged within subducted slabs(12,13), and the appearance of deep, localized intraplate areas of reduced effective viscosity(14) observed at trenches. Furthermore, brittle-viscously damaged slabs show a tendency for detachment at elevated mantle temperatures. Given Earth's planetary cooling history(15), this implies that intermittent subduction with frequent slab break-off episodes(16) may have been characteristic for Earth until more recent times than previously suggested(17).Numerical subduction models used to determine the consequences of bending-induced plate damage show that slab weakening and segmentation can occur at the outer-rise region of the subducting plate.