How subduction—the sinking of cold lithospheric plates into the mantle—is initiated is one of the key mysteries in understanding why Earth has plate tectonics. One of the favored locations for subduction triggering is at passive margins, where sea floor abuts continental margins. Such passive margin collapse is problematic because the strength of the old, cold ocean lithosphere should prohibit it from bending under its own weight and sinking into the mantle. Some means of mechanical weakening of the passive margin are therefore necessary. Spontaneous and accumulated grain damage can allow for considerable lithospheric weakening and facilitate passive margin collapse. Grain damage is enhanced where mixing between mineral phases in lithospheric rocks occurs. Such mixing is driven both by compositional gradients associated with petrological heterogeneity and by the state of stress in the lithosphere. With lateral compressive stress imposed by ridge push in an opening ocean basin, bands of mixing and weakening can develop, become vertically oriented, and occupy a large portion of lithosphere after about 100 million y. These bands lead to anisotropic viscosity in the lithosphere that is strong to lateral forcing but weak to bending and sinking, thereby greatly facilitating passive margin collapse.

俯冲 - 岩石圈冷板块沉入地幔 - 是如何引发的，是理解地球为什么具有板块构造的关键谜团之一。俯冲触发的有利位置之一是被动边缘，海底紧邻大陆边缘。这种被动的边缘坍塌是有问题的，因为古老的寒冷海洋岩石圈的强度应该会阻止它在自身重量下弯曲并沉入地幔。因此，需要一些机械削弱被动边缘的方法。自发和累积的颗粒破坏会导致岩石圈显着减弱并促进被动边缘塌陷。当岩石圈岩石中的矿物相之间发生混合时，晶粒损伤会增强。这种混合是由与岩石学异质性相关的成分梯度和岩石圈中的应力状态驱动的。在开放的洋盆中，由于脊推施加的横向压应力，混合和弱化带可以发展，成为垂直方向，并在大约 1 亿 y 后占据岩石圈的大部分。这些带导致岩石圈中的各向异性粘性强，侧向强迫强，弯曲和下沉弱，从而极大地促进了被动边缘塌陷。