Influence of Heterogeneities on the Initiation of Shear Zones in the Ductile Regime

应变局部化到变尺度剪切带是构造过程的共同特征。以往的许多研究都集中在上地壳脆性断裂带的演化上，但对更深层韧性剪切带的形成和扩展知之甚少。这些剪切带发展的一个可能的起源是结构非均质性的存在，可能在局部产生应力集中，导致脆性或塑性软化机制的激活。为了检验这种情况，我们提出了一项新的实验研究，探索高温剪切带的成核和生长过程，以及相关的力学和微观结构响应。扭转实验将在卡拉拉大理石样品上进行，这些样品含有人工制备的不同形状和不同流变行为的内含物。建议的实验条件为温度500-1000℃，围压300-400 MPa，应变速率在10-3 s-1和10-5 s-1之间。采用最新开发的应变作图技术，利用微米尺度应变标记确定包裹体附近的局部应变和应力分布。此外，还将进行详细的微观结构分析，包括透射电子显微镜和通过电子背散射衍射确定首选晶体取向。实验结果将与Morcles推覆体（Helvetic Alps）方解石岩石的自然剪切带微观结构进行比较。本提案的目标是表征应变局部化的过程，从韧性体系的初始结构异质性开始，并制定捕捉机制关键方面的本构定律。

Strain localization into shear zones of variable scales is a common feature in tectonic processes. A number of previous studies focused on the evolution of brittle fault zones in the upper crust, but little is known about the initiation and propagation of ductile shear zones at greater depth. One possible origin of the development of these shear zones is the presence of structural heterogeneities that may locally produce stress concentrations leading to the activation of brittle or plastic softening mechanisms. To examine this scenario, we propose a novel experimental study exploring the processes of high temperature shear zone nucleation and growth, and the associated mechanical and microstructural response. Torsion experiments will be conducted on Carrara marble samples that contain artificially prepared inclusions of different shapes and contrasting rheological behavior. Suggested experimental conditions are 500-1000°C temperature, 300-400 MPa confining pressure, and strain rates between 10-3 s-1 and 10-5 s-1. The local strain and stress distribution in the vicinity of the inclusions will be determined using µm-scale strain markers by adopting a recently developed strain mapping technique. In addition, a detailed microstructural analysis will be performed, including transmission electron microscopy and the determination of preferred crystallographic orientations via electron backscatter diffraction. The experimental results will be compared with microstructures of natural shear zones in calcite rocks of the Morcles nappe (Helvetic Alps). The goal of this proposal is to characterize the processes involved in strain localization from an initial structural heterogeneity in the ductile regime and to formulate constitutive laws that capture key aspects of the mechanisms.