Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal
Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal
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地幔动力学引起的地壳变形：重力岩石圈去除模型的见解
DOI：
10.1093/gji/ggx209
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发表时间：
2017
影响因子：
2.8
通讯作者：
C. Currie
中科院分区：
文献类型：
--
作者：
Huilin Wang;C. Currie
有人提出用幔源应力解释大陆板块内部变形的发生，而不考虑板块边界过程的影响。我们研究如何重力去除致密地幔岩石圈根可能会导致变形的上覆地壳。简化的数值模型和理论分析被用来研究变形的物理机制和评估去除的表面表达。确定了三种行为：（1）在整个地壳都很坚固的地方，来自下涌地幔的应力可以有效地通过地壳传递。几乎没有地壳变形，迁移伴随着地表沉降和负的自由空气重力异常。表面隆起和增加自由空气重力发生后，密集的根分离。(2)如果中地壳是薄弱的，密集的根创建一个横向压力梯度在地壳中，驱动Poiffille流在薄弱层。这导致地壳增厚，表面隆起和轻微的自由空气重力异常以上的根。(3)如果下地壳是软弱的，变形发生通过压力驱动的Poilluille流和Couette流由于基底剪切。这会覆盖地壳，在根部上方产生地形高压和负的自由空气重力异常。在后两种情况下，地表隆起发生在地幔应力消除之前。模拟结果预测，如果地壳粘度小于10^（21）Pa·s，对应于干长英质或湿镁铁质成分的温度大于10400 -500 °C，干镁铁质成分的温度大于10900 °C，则将发生同向抬升。如果地壳温度低于这个温度，岩石圈的移动就以盆地的形成为标志。这些结果可以解释在下降地幔区观察到的表面表现的多样性。此外，地表挠度的观测可以提供一种约束地壳垂直流变结构的方法。
Mantle-based stresses have been proposed to explain the occurrence of deformation in the interior regions of continental plates, far from the effects of plate boundary processes. We examine how the gravitational removal of a dense mantle lithosphere root may induce deformation of the overlying crust. Simplified numerical models and a theoretical analysis are used to investigate the physical mechanisms for deformation and assess the surface expression of removal. Three behaviours are identified: (1) where the entire crust is strong, stresses from the downwelling mantle are efficiently transferred through the crust. There is little crustal deformation and removal is accompanied by surface subsidence and a negative free-air gravity anomaly. Surface uplift and increased free-air gravity occur after the dense root detaches. (2) If the mid-crust is weak, the dense root creates a lateral pressure gradient in the crust that drives Poiseuille flow in the weak layer. This induces crustal thickening, surface uplift and a minor free-air gravity anomaly above the root. (3) If the lower crust is weak, deformation occurs through pressure-driven Poiseuille flow and Couette flow due to basal shear. This can overthicken the crust, producing a topographic high and a negative free-air gravity anomaly above the root. In the latter two cases, surface uplift occurs prior to the removal of the mantle stress. The modeling results predict that syn-removal uplift will occur if the crustal viscosity is less than ∼10^(21) Pa s, corresponding to temperatures greater than ∼400–500 °C for a dry and felsic or wet and mafic composition, and ∼900 °C for a dry and mafic composition. If crustal temperatures are lower than this, lithosphere removal is marked by the formation of a basin. These results can explain the variety of surface expressions observed above areas of downwelling mantle. In addition, observations of the surface deflection may provide a way to constrain the vertical rheological structure of the crust.