Metamorphism and ductile flow in the deep crust – controls and tectonic consequences

下陆壳的行为控制着山脉带的生长和衰败。特别是，造山过程中的地壳增厚会导致地壳深部融化，导致地壳强度大幅下降。然后，熔融减弱的地壳可以响应与造山相关的压力梯度向外或向上流动，并可能作为地壳中部的水道横向输送数百公里，或重新加工成大型韧性褶皱。被俯冲到地幔深处(=100公里)的大陆地壳的融化甚至可能有助于其返回地表。尽管无法直接观察到深部地壳，但这些过程的地质证据来自深度侵蚀的大陆地壳中的变质片麻岩地体和最近暴露在年轻山脉带上的地区。这些岩石含有矿物组合和结构，其特征是在高温和高压下在数十至数百公里的尺度上流动，结构表明在变形过程中存在熔融。在大陆地壳上部，岩浆向凉爽的近地表地区的输送可以深刻地改变周围岩石的热平衡、强度和行为。

The behaviour of the lower continental crust controls the growth and decay of mountain belts. In particular, crustal thickening during mountain-building can lead to melting in the deep crust, causing a profound reduction in crustal strength. The melt-weakened crust can then flow outward or upward in response to the pressure gradients associated with mountain-building, and may be transported hundreds of kilometres laterally as mid-crustal channels or reworked into large ductile folds. Melting of continental crust that has been subducted to mantle depths (=100 km) may even assist its return to the surface. Although the deep crust is inaccessible to direct observation, geological evidence for these processes comes from metamorphic gneiss terranes in deeply eroded continental crust and recently exposed regions of younger mountain belts. These rocks contain mineral assemblages and structures characteristic of flow on scales of tens to hundreds of kilometres at high temperature and pressure, with textures indicating that melt was present during deformation. In the upper continental crust, transport of magma into cool near-surface regions can profoundly change the heat budget, strength, and behaviour of the surrounding rocks.