Evolution and demise of passive margins through grain mixing and damage
Evolution and demise of passive margins through grain mixing and damage
复制标题
DOI：
10.1073/pnas.2011247118
复制
发表时间：
2021-01-26
影响因子：
11.1
通讯作者：
Mulyukova, Elvira
中科院分区：
文献类型：
--
作者：
Bercovici, David;Mulyukova, Elvira
俯冲--寒冷的岩石圈板块下沉到地幔--是如何开始的，这是理解为什么地球有板块构造的关键之谜。俯冲触发的有利位置之一是被动边缘，海底与大陆边缘相邻。这种被动的边缘塌陷是有问题的，因为古老的冷海洋岩石圈的强度应该阻止它在自身重量下弯曲并沉入地幔。因此，有必要采取一些机械削弱被动边缘的措施。自发的和累积的颗粒损伤可以使岩石圈相当大的弱化，并促进被动边缘塌陷。在岩石圈岩石中矿物相之间发生混合的地方，颗粒损伤增强。这种混合是由与岩石学不均匀性相关的成分梯度和岩石圈的应力状态驱动的。在一个开放的洋盆中，由于洋脊的推挤作用而产生的侧向压应力，混合带和弱化带可以发展，并在大约1亿年后垂直定向，占据岩石圈的很大一部分。这些条带导致岩石圈中的各向异性粘性，对侧向力强，但对弯曲和下沉弱，从而极大地促进了被动边缘塌陷。
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.