Physics of Geological Processes (PGP), The Njord Centre, Department of Geosciences, University of Oslo, Oslo, Norway.
Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA.
Nature. 2018 Apr;556(7702):487-491. doi: 10.1038/s41586-018-0045-y. Epub 2018 Apr 25.
The structural and metamorphic evolution of the lower crust has direct effects on the lithospheric response to plate tectonic processes involved in orogeny, including subsidence of sedimentary basins, stability of deep mountain roots and extension of high-topography regions. Recent research shows that before orogeny most of the lower crust is dry, impermeable and mechanically strong . During an orogenic event, the evolution of the lower crust is controlled by infiltration of fluids along localized shear or fracture zones. In the Bergen Arcs of Western Norway, shear zones initiate as faults generated by lower-crustal earthquakes. Seismic slip in the dry lower crust requires stresses at a level that can only be sustained over short timescales or local weakening mechanisms. However, normal earthquake activity in the seismogenic zone produces stress pulses that drive aftershocks in the lower crust . Here we show that the volume of lower crust affected by such aftershocks is substantial and that fluid-driven associated metamorphic and structural transformations of the lower crust follow these earthquakes. This provides a 'top-down' effect on crustal geodynamics and connects processes operating at very different timescales.
下地壳的结构和变质演化对岩石圈对造山过程中涉及的板块构造过程的响应有直接影响，包括沉积盆地的沉降、深山区根的稳定性和高地形区的扩展。最近的研究表明，在造山之前，大部分下地壳是干燥的、不可渗透的和机械强度高的。在造山事件期间，下地壳的演化受沿局部剪切或断裂带的流体渗透控制。在挪威西部的卑尔根弧形构造中，剪切带最初是由下地壳地震产生的断层。干燥下地壳中的地震滑动需要在只能维持短时间或局部弱化机制的水平上的应力。然而，地震活动区的正常地震活动会产生应力脉冲，从而引发下地壳的余震。在这里，我们表明，受这种余震影响的下地壳体积相当大，并且下地壳的流体驱动相关变质和结构变形紧随这些地震发生。这对地壳地球动力学产生了自上而下的影响，并将在非常不同的时间尺度上运行的过程联系起来。
