Nano-analytics of natural quartz deformation microstructures at the brittle-viscous transition

了解糜棱岩在颗粒尺度上的脆性和韧性变形机制之间的相互作用，对于理解大陆地壳深部剪切局部化至关重要。这种相互作用对发震地壳底部以下流体传递的长度尺度和速度以及地震周期本身也有很强的影响。该项目的主要目标是了解石英中离散再结晶带（DZR）的起源，作为糜棱岩化初期微压裂的潜在指标。这种构造发育在Schober群（阿尔卑斯中东部的Hohe Tauern山脉）的石英脉中，这些石英脉在450-500℃时变形，将作为重点研究对象。更广泛地说，该项目旨在提高对DZR构造形成初期不同变形机制（微破裂、亚晶旋转和晶界迁移、机械dauphin<s:1>孪晶、溶解-沉淀、晶界滑动）相互作用的认识，以及它们的重要性如何随着糜棱岩和超糜棱岩微观结构的逐步发展而变化。如果没有综合的方法，使用不同的高分辨率显微结构和微化学（微量元素）分析的最新技术，上述石英变形显微结构的解释注定是推测性的。该项目包括通过电子背散射衍射（EBSD）、扫描电镜定向对比成像（通道对比）、扫描电镜阴极发光（CL）、透射电子显微镜（TEM）和二次离子质谱（SIMS和NanoSIMS）对细粒微结构进行综合微观和纳米分析。此外，原子探针的高分辨率分析（低至原子尺度）的新发展将应用于获得局部岩石变形过程中（亚）晶粒尺度扩散过程（特别是Ti）的信息。此外，该项目将测试新开发的具有纳米红外能力的近场显微镜在纳米到微米尺度上检测石英颗粒内水的适用性。该测试将伴随着（OH-分子离子）分析石英使用NanoSIMS技术。如果这两种独立的方法被证明是成功的，它将开启一个测量细粒矿物（不仅仅是石英）中的水的新时代，进一步，可以专门解决沿晶界，亚晶界甚至位错结构的水的测量。结合原子探针分析的Ti分布，这将有助于识别位错管扩散或沿亚晶界扩散等过程及其对Ti-in- quartz体系重设的影响。

Understanding the interplay between brittle and ductile deformation mechanisms at the grain scale in mylonites is essential for understanding shear localization at depth in the continental crust. This interplay also has a strong influence on the length-scale and velocity of fluid transfer below the base of the seismogenic crust, and on the seismic cycle itself. The main goal of the project is to understand the origin of discrete zones of recrystallization (DZR) in quartz as potential indicators of microfracturing during the incipient stages of mylonitization. Such structures are developed in quartz veins from the Schober Group (Hohe Tauern mountains in the Central Eastern Alps), which were deformed at c. 450-500°C, and will be used as a key study. More generally, the project aims to improve the understanding on interaction of different deformation mechanisms (micro-fracturing, subgrain rotation and grain boundary migration, mechanical Dauphiné twinning, dissolution-precipitation, grain boundary sliding) during the initial formation of DZR structures and, how their significance changes with progressive development of the mylonitic and ultramylonitic microstructures. Without an integrated approach, using different up-to-date techniques of high-resolution microstructural and microchemical (trace element) analysis, interpretations of the quartz deformation microstructures detailed above are destined to remain speculative. The project includes integrated micro- and nano-analyses on fine-grained microstructures by means of: electron backscatter diffraction (EBSD), SEM orientation contrast imaging (channeling contrast), SEM cathodoluminescence (CL), transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS and NanoSIMS) for Ti-in-Quartz analysis. Additional, new developments in high resolution analysis (down to atomic scale) by atom probe will be applied to obtain information about (sub)grain-scale diffusion processes (especially of Ti) during localized rock deformation. Furthermore this project will test the applicability of a newly developed Near Field Microscope with NanoFTIR capability to detect intragranular water in quartz at nano- to micrometer scales. This test will be accompanied by (OH- molecular ions) analysis in quartz using NanoSIMS technique. If these two independent methods prove successful, it will open up a new era of measuring water in fine-grained minerals (not only quartz) and, further, could specifically address the measurement of water along grain boundaries, subgrain boundaries and even dislocations structures. Combined with the Ti distribution analysed by the atom probe, this would help in recognizing processes such as dislocation pipe diffusion or diffusion along subgrain boundaries and their effects on the resetting of the Ti-in-Quartz system.