The dominant driving force for supercontinent breakup: Plume push or subduction retreat?
The dominant driving force for supercontinent breakup: Plume push or subduction retreat?
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超大陆分裂的主要驱动力：羽流推动还是俯冲后退？
DOI：
10.1016/j.gsf.2018.01.010
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发表时间：
2018-07
影响因子：
8.9
通讯作者：
Z.-X. Li
中科院分区：
文献类型：
--
作者：
Nan Zhang;Z. Dang;C. Huang;Z.-X. Li
了解超大陆分裂的主导力量对于建立地球的地球动力学演化至关重要，包括超大陆周期和板块构造。传统上认为有两种力：大陆地幔柱的推动力（称为裂解的主动力）和大洋俯冲后退的拖曳力（称为裂解的被动力）。然而，这两种力量的相对重要性尚不清楚。在这里，我们模拟超大陆分裂与全球地幔对流，以解决这个问题。我们的全球模型具有2度球谐结构，其中包括一个主要的俯冲带和两个大型上升流（超级羽流）系统。基于这种全球地幔结构，我们研究了超大陆边缘的次超大陆地幔上隆和俯冲后退作用下超大陆的伸展应力分布。我们的研究结果表明：（1）在超大陆的中半部分，地幔柱推压应力是俯冲后退应力的1.33倍，（2）在超大陆下方不超过50 K的平均热异常可以产生足以引起超大陆初始解体的推压力;（3）俯冲后退引起的拉张应力主要集中在超大陆边缘约600 km宽的区域内，而对超大陆内部的影响较小。因此，虽然环超大陆俯冲后退有助于超大陆裂解，但次超大陆地幔上涌是主要的动力。
Understanding the dominant force responsible for supercontinent breakup is crucial for establishing Earth's geodynamic evolution that includes supercontinent cycles and plate tectonics. Conventionally, two forces have been considered: the push by mantle plumes from the sub-continental mantle which is called the active force for breakup, and the dragging force from oceanic subduction retreat which is called the passive force for breakup. However, the relative importance of these two forces is unclear. Here we model the supercontinent breakup coupled with global mantle convection in order to address this question. Our global model features a spherical harmonic degree-2 structure, which includes a major subduction girdle and two large upwelling (superplume) systems. Based on this global mantle structure, we examine the distribution of extensional stress applied to the supercontinent by both sub-supercontinent mantle upwellings and subduction retreat at the supercontinent peripheral. Our results show that: (1) at the center half of the supercontinent, plume push stress is ∼3 times larger than the stress induced by subduction retreat; (2) an average hot anomaly of no higher than 50 K beneath the supercontinent can produce a push force strong enough to cause the initialization of supercontinent breakup; (3) the extensional stress induced by subduction retreat concentrates on a ∼600 km wide zone on the boundary of the supercontinent, but has far less impact to the interior of the supercontinent. We therefore conclude that although circum-supercontinent subduction retreat assists supercontinent breakup, sub-supercontinent mantle upwelling is the essential force.
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