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.

陆壳下地壳的变形变质作用使其物理力学性质发生显著变化，对造山带的地球动力学演化和地震周期有重要影响。经典的地壳强度理论认为，下地壳应该是流动的而不是破裂的。然而，一些下地壳岩石的例子以大量的假玄武玻璃为特征，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，地震发生在孕震区下方的地壳中。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的评估。虽然以前的研究已经令人信服地表明，局部脆性破坏和变形的粘性蠕变可以同时进行，地壳尺度的评估，这种相互作用仍然是失踪。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。为了解决这些基本问题，拟议的项目将针对位于罗弗敦群岛（挪威）的理想暴露类似物。通过仔细评估保存下来的构造关系和运动学参照框架，将有可能描绘出下大陆地壳内部的一系列变形。此外，变形的时间将受到限制，使用Lu-Hf和U-Pb测年的石榴石和磷灰石的假玄武玻璃和韧性剪切带。结合详细的结构约束，这些结果将显示脆性（地震）和韧性（地震）变形之间的周期性转换是否确实发生在地壳尺度上，或者如果它们是连续的脆性变形为渗透流体和粘性机制的变形的开始铺平了道路。最后，这些结果将结合H2O在名义上无水矿物，这将允许评估水化的大小和不同的流体含量的空间分布的测定。总之，拟议项目的结果将大大提高我们对地壳尺度流变学的理解，以及下地壳变形如何与地震周期联系在一起。