The effects of plate interface rheology on subduction

12 Tectonic plate motions predominantly result from a balance between the potential energy 13 change of the subducting slab and viscous dissipation in the mantle, bending lithosphere, 14 and slab–upper plate interface. A wide range of observations from active subduction zones 15 and exhumed rocks suggest that subduction interface shear zone rheology is sensitive to the 16 composition of subducting crustal material— for example, sediments versus mafic igneous 17 oceanic crust. Here we use 2-D numerical models of dynamically consistent subduction to 18 systematically investigate how subduction interface viscosity influences large-scale subduc19 tion kinematics and dynamics. Our model consists of an oceanic slab subducting beneath an 20 overriding continental plate. The slab includes an oceanic crustal/weak layer that controls 21 the rheology of the interface. We implement a range of slab and interface strengths and 22 explore how the kinematics respond for an initial upper mantle slab stage, and subsequent 23 quasi-steady-state ponding near a viscosity jump at the 660-km-discontinuity. If material 24 properties are suitably averaged, our results confirm the effect of interface strength on plate 25 motions as based on simplified viscous dissipation analysis: a ∼ 2 order of magnitude in26 crease in interface viscosity can decrease convergence speeds by ∼ 1 order of magnitude. 27 However, the full dynamic solutions show a range of interesting behavior including an inter28 play between interface strength and overriding plate topography and an end-member weak 29 interface-weak slab case that results in slab breakoff/tearing. Additionally, for models with 30 a spatially limited, weak sediment strip embedded in regular interface material, as might be 31 expected for the subduction of different types of oceanic crust through Earth’s history, the 32 transient response of enhanced rollback and subduction velocity is different for strong and 33 weak slabs. Our work substantiates earlier suggestions as to the importance of the plate 34 interface, and expands the range of quantifiable links between plate reorganizations, the 35 nature of the incoming and overriding plate, and the potential geological record. 36