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

了解糜棱岩中颗粒尺度上脆性和韧性变形机制之间的相互作用对于了解大陆地壳深部剪切局部化是至关重要的。这种相互作用也对孕震地壳底部以下的流体输送的长度规模和速度以及地震周期本身有很大的影响。该项目的主要目标是了解石英中离散重结晶区（DZR）的起源，作为糜棱岩化初期阶段微破裂的潜在指标。这种构造发育在斯科贝尔群（阿尔卑斯山脉中东部的上陶恩山脉）的石英脉中，这些石英脉在c. 450-500°C，并将用作关键研究。更一般地说，该项目旨在提高对DZR结构初始形成过程中不同变形机制（微破裂，亚晶粒旋转和晶界迁移，机械Dauphiné孪生，溶解-沉淀，晶界滑动）相互作用的理解，以及它们的意义如何随着糜棱岩和超糜棱岩显微结构的逐步发展而变化。如果没有一个综合的方法，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，解释石英变形显微结构上面详细描述的是注定要保持投机。该项目包括通过电子背散射衍射（EBSD）、SEM取向对比成像（沟道对比）、SEM阴极发光（CL）、透射电子显微镜（TEM）和二次离子质谱（西姆斯和NanoSIMS）对细粒微结构进行综合微米和纳米分析，用于石英中钛的分析。此外，在高分辨率分析（下至原子尺度）的原子探针的新发展将被应用于获得有关（子）晶粒尺度的扩散过程（特别是Ti）在局部岩石变形的信息。此外，本项目将测试新开发的具有NanoFTIR功能的近场显微镜在纳米至微米尺度下检测石英中的粒内水的适用性。本试验将伴随使用NanoSIMS技术对石英进行（OH-分子离子）分析。如果这两种独立的方法被证明是成功的，它将开辟一个测量细粒矿物（不仅是石英）中水分的新时代，而且还可以专门解决沿着晶界、亚晶界甚至位错结构中水分的测量问题。结合原子探针分析的Ti分布，这将有助于识别过程，如位错管扩散或沿着亚晶界扩散及其对Ti在石英系统的复位的影响。

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.