Dynamic buckling of subducting slabs reconciles geological and geophysical observations
Dynamic buckling of subducting slabs reconciles geological and geophysical observations
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DOI：
10.1016/j.epsl.2011.10.033
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发表时间：
2011-12
影响因子：
5.3
通讯作者：
Changyeol Lee;S. King
中科院分区：
文献类型：
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作者：
Changyeol Lee;S. King
从板块构造理论发展的早期开始，俯冲带就在地质思想中根深蒂固，它是在火山弧之下，稳定的线性板块以恒定的、均匀的倾角下降到地幔中的地方。然而，来自地质和地球物理观测以及模拟和数值模拟的越来越多的证据表明，与主导文献的稳态线性卡通相反，俯冲板块的弯曲是随时间变化的。为了评估地质事件中随时间变化的板块屈曲的含义，我们通过改变660公里不连续面的粘度增加和俯冲板块的强度，进行了一系列二维数值动力学/运动学俯冲实验。结果表明，当槽迁移速率（Vtrench）相对较慢（Vtrench|<2cm/a），且660 km间断面黏度增加大于30倍时，板状屈曲在所有实验中都是一个普遍现象。板块屈曲表现为俯冲板块的交替变浅变陡（从~40°到~100°），与来海板块向海沟收敛速度的增减有关。此外，在我们的实验中，板屈曲与先前建立的板屈曲的标度规律是一致的；根据俯冲板的合理参数，计算得到的屈曲振幅和周期分别为~400km和~25Myr。在我们的实验中，板屈曲行为解释了各种令人困惑的地质和地球物理观测结果。首先，板块屈曲的周期与俯冲带锚定的大洋板块运动的短周期变化（~25Myr）相一致。(2)上地幔板块倾角的分散分布（~20 ~ ~90°）是板块倾角随时间变化的快照。第三，弧后地区当前的挤压和拉伸应力环境与板块屈曲导致的板块倾角变浅和变陡有很好的相关性。第四，安第斯山脉应力环境的时间演化与交替的板块倾角密切相关。这些相关性表明，随时间变化的平板屈曲是控制俯冲带动力学的主要因素。
Ever since the early days of the development of plate tectonic theory, subduction zones have been engrained in geological thinking as the place where steady, linear slabs descend into the mantle at a constant, uniform dip angle beneath volcanic arcs. However, growing evidence from geological and geophysical observations as well as analog and numerical modeling indicates that subducting slabs buckle in a time-dependent manner, in contrast to the steady-state, linear cartoons that dominate the literature. To evaluate the implication of time-dependent slab buckling of geological events, we conduct a series of 2-D numerical dynamic/kinematic subduction experiments by varying the viscosity increase across the 660km discontinuity and the strength of the subducting slab. Our results show that slab buckling is a universal figure in all the experiments when rate of the trench migration (Vtrench) is relatively slow (Vtrench|<2cm/a) and viscosity increases across the 660 km discontinuity are greater than a factor of 30. Slab buckling is expressed as alternate shallowing and steepening dip of the subducting slab (from ~40 to ~100°) which is correlated with increasing and decreasing convergent rate of the incoming oceanic plate toward the trench. Further, the slab buckling in our experiments is consistent with the previously developed scaling laws for slab buckling; using reasonable parameters from subducted slabs the buckling amplitude and period are ~400km and ~25Myr, respectively. The slab buckling behavior in our experiments explains a variety of puzzling geological and geophysical observations. First, the period of slab buckling is consistent with short periodic variations (~25Myr) in the motions of the oceanic plates that are anchored by subduction zones. Second, the scattered distributions of slab dips (from ~20 to ~90°) in the upper mantle are snapshots of time-dependent slab dip. Third, the current compressional and extensional stress environments in back-arcs are well correlated with shallowing and steeping slab dip resulting from slab buckling. Fourth, the temporal evolution of stress environments in the Andes is well correlated with alternate slab dip. These correlations indicate that time-dependent slab buckling is a major factor controlling subduction zone dynamics.