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.

下陆壳的变形和变质作用使其物理力学性质发生重大变化，对山带的地球动力学演化和地震旋回产生重要影响。经典的地壳强度考量表明，下地壳应该流动而不是破裂。然而，一些出土的下地壳岩石的例子具有大量的假玄武岩，这是岩石记录中古地震活动的证据。此外，地球物理研究表明，地震发生在远低于孕震带的地壳中。拟议的项目针对这一矛盾，对脆性和韧性变形进行地壳尺度评估。虽然以前的研究已经令人信服地证明，局部脆性破坏和粘性蠕变引起的变形可以共同评估，但对这种相互作用的地壳规模评估仍然缺乏。必须彻底评估暴露的类似物的构造和运动学背景，以了解导致当今地震活动的机制。为了解决这些根本问题，拟议的项目将针对位于罗福滕群岛(挪威)的一种理想的暴露的类似物。通过仔细评估保存下来的构造关系和运动学参照系，将有可能描绘出下大陆地壳内的一系列变形。此外，使用来自假玄武岩和韧性剪切带的石榴石和磷灰石的Lu-Hf和U-Pb年龄将限制变形的时间。结合详细的构造约束，这些结果将表明脆性(地震)和韧性(非地震)变形之间的周期性转换是否确实发生在地壳尺度上，或者它们是否与脆性变形相继发生，为流体渗透和粘性机制引发变形铺平了道路。最后，这些结果将与名义上无水矿物中H2O的测定相结合，这将允许评估水化的程度和不同流体含量的空间分布。综上所述，拟议项目的结果将极大地促进我们对地壳尺度流变学以及下地壳变形如何与地震周期相联系的理解。