Seismic tomography reveals a wide variety of slab deformation in the mantle transition zone and shallow lower mantle. Numerical modeling of subduction has identified several factors that control slab deformation, among them the properties of the mechanical decoupling between subducting and overriding plates was shown to have a major influence on slab velocity, rollback and deformation in the transition zone. Models with weak crust generally yield fast rollback and slab stagnation while stronger crust results in slab penetration into the lower mantle. Here we perform a detailed analysis of the effects of this weak crustal layer. First, in models with constant crustal viscosity, we quantify combined effects of crustal viscosity and thickness. Further we apply nonlinear crustal rheology that combines dislocation creep and pseudoplastic deformation. We test the effects of varying parameterisations of the nonlinear rheological mechanisms and evaluate their effects on slab deformation. We conclude that the variations of subducting slab velocity (controlled by the buoyancy effects of the major phase transitions) induce strong time variations of the crustal viscosity that in turn enforce further acceleration or deceleration of the slab. This feedback between slab velocity and crustal viscosity strenghtens transient behavior of the subducting slabs and enforces slab penetration after a transient period of stagnation.

地震层析成像显示出在地幔过渡带和下部浅地幔中各种平板变形。俯冲的数值模拟已经确定了控制板坯变形的几个因素，其中俯冲板与上覆板之间的机械解耦特性显示出对过渡区板坯速度，回滚和变形的主要影响。地壳较弱的模型通常会产生快速的回滚和板坯停滞，而地壳较强的模型则会导致板坯渗透到下地幔中。在这里，我们对这个薄弱的地壳层的影响进行了详细的分析。首先，在具有恒定地壳粘度的模型中，我们量化了地壳粘度和厚度的综合影响。进一步地，我们应用了结合位错蠕变和假塑性变形的非线性地壳流变学。我们测试了非线性流变机理的各种参数化的影响，并评估了它们对平板变形的影响。我们得出结论，俯冲板速度的变化（受主要相变的浮力作用控制）引起地壳粘度的强烈时间变化，进而迫使板进一步加速或减速。板坯速度和地壳粘度之间的这种反馈加强了俯冲板坯的瞬态行为，并在过渡期停滞后强制了板坯渗透。我们得出结论，俯冲板速度的变化（受主要相变的浮力作用控制）引起地壳粘度的强烈时间变化，进而迫使板进一步加速或减速。板坯速度和地壳粘度之间的这种反馈加强了俯冲板坯的瞬态行为，并在过渡期停滞后强制了板坯渗透。我们得出结论，俯冲板速度的变化（受主要相变的浮力作用控制）引起地壳粘度的强烈时间变化，进而迫使板进一步加速或减速。板坯速度和地壳粘度之间的这种反馈加强了俯冲板坯的瞬态行为，并在过渡期停滞后强制了板坯渗透。