Abstract In contrast to active continental rifting, which is caused by the thermal erosion of active upwelling plumes, passive continental rifting is attributed to the extensional stress acting on the continental lithosphere due to either the basal drag force exerted by the passive mantle flow under the lithosphere or the boundary forces at the continental margins. Although the extension of continental lithosphere by passive continental rifting may cause the breakup of continental margins, such as the separation of Zealandia from Gondwanaland at ca. 100 Ma and the Japanese islands from Eurasia at ca. 25 Ma, the dynamics have not been fully understood from geophysical and geological perspectives. Here, a series of numerical experiments of visco-elasto-plastic thermo-chemical convection with a free surface is performed using 2-D Cartesian models to investigate the localization of strain in the extending continental lithosphere, with an initial depth of 200 km, and the behavior of continental rifting and breakup. Our results demonstrate that when extension rates at the continental margin were set between 1 and 4 cm yr−1, the time taken for seafloor subsidence and subsequent continental breakup under extensional stress is less than a few million years. During continental rifting, high-shear zones (i.e., high-strain-rate zones) develop under the base of the deforming continental lithosphere, with a strain rate of the order of 10−13 s−1, which is approximately two orders larger than the typical value of the mantle interior. Due to accumulating strain along the base of the deforming lithosphere, excess strain is not concentrated on the shallowest part of the underlying mantle; hence, the spreading ridge that breaks the thick continental lithosphere emerges as a locally weak plate boundary on the Earth's surface. This characteristic is more remarkable as the activation volume of the sublithospheric mantle rock and the resultant viscosity are low under wet conditions.

中文翻译：

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二维笛卡尔几何中粘弹塑性热化学对流数值实验的大陆岩石圈伸展和被动大陆裂谷动力学

摘要 与活动上升流羽流热侵蚀引起的活动大陆裂谷不同，被动大陆裂谷归因于岩石圈下方的被动地幔流施加的基底阻力作用于大陆岩石圈的拉伸应力。或大陆边缘的边界力量。虽然大陆岩石圈通过被动大陆裂谷的扩张可能导致大陆边缘的分裂，例如西兰大陆与冈瓦纳大陆的分离。约 100 Ma 和来自欧亚大陆的日本岛屿。25 Ma，从地球物理和地质角度尚未完全了解动力学。这里，使用二维笛卡尔模型对具有自由表面的粘弹塑性热化学对流进行了一系列数值实验，以研究初始深度为 200 公里的扩展大陆岩石圈中应变的局部化以及行为大陆裂谷和分裂。我们的结果表明，当大陆边缘的伸展率设置在 1 到 4 cm yr-1 之间时，在伸展应力下海底沉降和随后的大陆破裂所需的时间不到几百万年。大陆裂谷过程中，在变形大陆岩石圈基底下发育高剪切带（即高应变率带），应变率约为10-13 s-1，约为2个数量级。地幔内部的典型值。由于沿变形岩石圈底部的累积应变，多余的应变不会集中在下伏地幔的最浅部分；因此，打破厚厚的大陆岩石圈的扩张脊作为地球表面局部弱板块边界出现。这种特征在湿润条件下亚岩石圈地幔岩石的活化体积和合成粘度较低时更为显着。