Effects of a Weak Lower Crust on the Flexure of Continental Lithosphere
Effects of a Weak Lower Crust on the Flexure of Continental Lithosphere
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DOI：
10.1029/2021jb022678
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发表时间：
2021-09
期刊：
影响因子：
--
通讯作者：
A. Bellas;S. Zhong
中科院分区：
文献类型：
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作者：
A. Bellas;S. Zhong
以往大陆背景下的挠曲研究认为，多层岩石圈的弹性厚度只受力学能力层厚度的控制，遵循立方法则。更具体地说，立方法则规定Te =（Te 1/3 + Te 23 +... Ten 3）1/3，其中Te是总弹性厚度，而Tei是每个主管层的弹性厚度。然而，不一定清楚的是，Te应该对中间弱层（例如，弱的下地壳），其可以起到使表面载荷与较低的胜任层分离的作用。为了验证这一想法，我们制定了二维粘弹性加载模型与分层粘度计算完全动态的，时间依赖性的响应的多层岩石圈与一个薄弱的下地壳。结果表明，多层岩石圈对表面载荷的弯曲响应最初符合立方律。然而，这种解决方案是短暂的，因为与负载相关的应力不能通过软弱的下地壳长时间传递。地幔岩石圈中的应力随着时间的推移而松弛，最终由于软弱下地壳中流动的解耦效应而完全不支持载荷。多层岩石圈的稳态挠曲完全受机械能力强的上地壳控制，使得Te = Te 1，这一新的规律是本研究的主要发现。我们的新发现现在解释了Te的小估计，在大陆设置厚地幔岩石圈，如北方天山，以前，很难解释的立方法则。
Previous studies of flexure in continental settings assert that the elastic thickness of a multilayer lithosphere is controlled by the mechanically competent layer thicknesses only, following a cubic rule. More specifically, the cubic rule states Te = (Te13+Te23+ … Ten3)1/3, where Te is the total elastic thickness, and Tei is the elastic thickness of each competent layer. However, it is not necessarily clear that Te should be insensitive to the properties of intermediate weak layers (e.g., a weak lower crust) which may act to decouple the surface load from lower competent layers. To test this idea, we formulate 2D viscoelastic loading models with layered viscosity to compute the fully dynamic, time‐dependent response of a multilayer lithosphere with a weak lower crust. Results show that the flexural response of a multilayer lithosphere to a surface load is initially consistent with the cubic rule. However, this solution is transient because the stress associated with the load cannot be transmitted through the weak lower crust on long timescales. Stress in the mantle lithosphere relaxes with time and eventually does not support the load at all due to the decoupling effect of flow in the weak lower crust. The steady state flexure of a multilayer lithosphere is controlled solely by the mechanically competent upper crust such that Te = Te1, and this new rule is the major finding of this study. Our new findings now explain small estimates of Te in continental settings with thick mantle lithosphere such as the Northern Tien Shan, which previously, were poorly explained by the cubic rule.