The cyclic interplay of seismic and aseismic deformation in the lower continental crust

下大陆地壳地震和地震变形的循环相互作用

• 批准号: 461241592
• 负责人: Dr. Sascha Zertani
• 金额: --
• 依托单位: Physics of Geological Processes
• 依托单位国家: 德国
• 项目类别: WBP Fellowship
• 财政年份: 2021
• 资助国家: 德国
• 起止时间: 2020-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/461241592?language=en
• 关键词: cyclic; interplay; seismic; aseismic; deformation

Deformation and metamorphism of the lower continental crust causes significant changes of its physical and mechanical properties that have an important impact on the geodynamic evolution of mountain belts and the earthquake cycle. Classical crustal strength considerations suggest that the lower crust should flow rather than break. Yet, some examples of exhumed lower crustal rocks feature large volumes of pseudotachylytes, which are evidence of paleo-seismicity within the rock record. Additionally, geophysical studies show that earthquakes occur in the crust well below the seismogenic zone. The proposed project targets this contradiction with a crustal scale assessment of brittle and ductile deformation. While previous studies have demonstrated convincingly that locally brittle failure and deformation by viscous creep can be coeval, a crustal scale assessment of this interplay is still missing. It is imperative to thoroughly evaluate the tectonic and kinematic setting of exposed analogues to understand the mechanisms that cause present-day seismicity. To address these fundamental questions the proposed project will target an ideal exposed analogue located in the Lofoten archipelago (Norway). By carefully evaluating the preserved structural relationships and kinematic reference frame it will be possible to delineate a succession of deformation within the lower continental crust. Further, the timing of deformation will be constrained using Lu-Hf and U-Pb dating of garnets and apatite from pseudotachylytes and ductile shear zones. These results in combination with the detailed structural constraints will show whether cyclical switches between brittle (seismic) and ductile (aseismic) deformation indeed occur on a crustal scale, or if they are successive with brittle deformation paving the way for infiltrating fluids and the initiation of deformation by viscous mechanisms. Finally, these results will be combined with the determination of H2O in nominally anhydrous minerals, which will allow to evaluate the magnitude of hydration and the spatial distribution of varying fluid contents. Taken together the results of the proposed project will significantly advance our understanding of crustal scale rheology and how the deformation of the lower crust is linked to the earthquake cycle.

下大陆壳的变形和变质性会导致其物理和机械性能的显着变化，这些变化对山带的地球动力学演变和地震周期产生了重要影响。经典的地壳强度的考虑表明，下壳应该流动而不是断裂。然而，一些挖掘出的下层地壳岩石的例子具有大量伪lly，这是岩石记录中古震动的证据。此外，地球物理研究表明，地震发生在地壳下方以下的地壳中。提出的项目以脆性和延性变形的地壳尺度评估来针对这一矛盾。虽然先前的研究表明，粘液蠕变的局部脆性失败和变形可能是同时的，但对此相互作用的地壳标度评估仍然缺失。必须彻底评估暴露类似物的构造和运动学设置，以了解引起当今地震性的机制。为了解决这些基本问题，拟议的项目将针对位于洛芬群岛（挪威）的理想曝光类似物。通过仔细评估保留的结构关系和运动学参考框架，可以在下部大陆地壳内描绘一系列变形。此外，将使用假石材和磷灰石的LU-HF和U-PB日期来限制变形的时机，并从假果糖和延性剪切带中限制。这些结果与详细的结构约束结合在一起，将表明脆性（地震）和延性（ASE震动）变形之间的周期性开关是否确实发生在地壳尺度上，还是是否连续变形铺平了渗透液体和通过粘性机制的变形启动的脆性变形。最后，这些结果将与名义上无水矿物质中H2O的测定结合，这将允许评估水合的大小和不同流体含量的空间分布。综上所述，拟议项目的结果将显着提高我们对地壳量表流变学的理解，以及下层地壳的变形如何与地震周期相关。