Modeling the Inception of Supercontinent Breakup: Stress State and the Importance of Orogens
Modeling the Inception of Supercontinent Breakup: Stress State and the Importance of Orogens
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DOI：
10.1029/2019gc008538
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发表时间：
2019-11
期刊：
影响因子：
3.7
通讯作者：
Chuan Huang;Nan Zhang;Zheng‐Xiang Li;M. Ding;Z. Dang;A. Pourteau;S. Zhong
中科院分区：
文献类型：
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作者：
Chuan Huang;Nan Zhang;Zheng‐Xiang Li;M. Ding;Z. Dang;A. Pourteau;S. Zhong
驱动超大陆分裂的各种地球动力学机制的相对意义尚不清楚。先前对超大陆分裂过程中伸展应力的分析表明，相对于俯冲后退的拖曳力，羽流推力更为重要。在这里，我们将分析扩展到基底牵引（剪切应力）和跨岩石圈的伸展和剪切应力整合，旨在更清楚地了解这些机制在超大陆分裂中的相关重要性。更重要的是，我们评估了岩石圈中先前存在的造山带（活动带）对超大陆分裂过程的影响。我们的分析表明，一个均质超大陆在其内部（距中心点<40°）具有20-50 MPa的拉伸应力。造山带引入后，大陆的伸展应力集中在岩石圈顶部80 km处，平均强度为~160 MPa，而超大陆边缘的伸展应力为5 ~ 50 MPa。在均质和造山嵌套两种情况下，次超大陆地幔上涌都是控制超大陆内部正应力场的因素。与伸展应力相比，超大陆底部的剪切应力要小1 ~ 2个数量级（0 ~ 5 MPa）。在我们的两个端元模型中，有造山带的超大陆的分裂可以在第一次伸展应力波之后实现，而对于没有造山带的假设超大陆，它在分裂之前开始于大陆岩石圈更分散的局部变薄，这表明弱造山带在超大陆的分散中起着关键作用。
The relative significance of various geodynamic mechanisms that drive supercontinent breakup is unclear. A previous analysis of extensional stress during supercontinent breakup demonstrated the importance of the plume‐push force relative to the dragging force of subduction retreat. Here, we extend the analysis to basal traction (shear stress) and cross‐lithosphere integrations of both extensional and shear stresses, aiming to understand more clearly the relevant importance of these mechanisms in supercontinent breakup. More importantly, we evaluate the effect of preexisting orogens (mobile belts) in the lithosphere on supercontinent breakup process. Our analysis suggests that a homogeneous supercontinent has extensional stress of 20–50 MPa in its interior (<40° from the central point). When orogens are introduced, the extensional stress in the continents focuses on the top 80‐km of the lithosphere with an average magnitude of ~160 MPa, whereas at the margin of the supercontinent the extensional stress is 5–50 MPa. In both homogeneous and orogeny‐embedded cases, the subsupercontinent mantle upwellings act as the controlling factor on the normal stress field in the supercontinent interior. Compared with the extensional stress, shear stress at the bottom of the supercontinent is 1–2 order of magnitude smaller (0–5 MPa). In our two end‐member models, the breakup of a supercontinent with orogens can be achieved after the first extensional stress surge, whereas for a hypothetical supercontinent without orogens it starts with more diffused local thinning of the continental lithospheric before the breakup, suggesting that weak orogens play a critical role in the dispersal of supercontinents.