How and why is deformation localised in continental crust?

在这个项目中，学生将制作和使用挖掘的下地壳的地质实地调查来约束应变局部化模型，并将其与印度-亚洲碰撞的现代大地测量数据进行比较。在过去几年中，对大陆应变的大地测量观测揭示了两种行为模式。在印度-欧亚碰撞带的喜马拉雅前缘冲断带、阿尔金断裂带和鲜水河断裂带等断裂带上，观测到高大地应变率。在其他地区，包括西藏西部和蒙古，现今的变形是分散的，几乎没有证据表明主要结构的局部化（例如Zheng et al.，2017年）。这种双模式行为的根本原因仍然不清楚，并受到高度争议。了解大陆应变局部化存在或不存在的过程对于从地震危险到资源分布的各种问题都很重要。为了解决应变局部化的问题，学生将从格陵兰岛的下地壳岩石中进行新的观察，那里似乎也存在双峰行为，利用地质和大地测量观测，通过运行数值模型，评估大陆地壳应变（去）局部化的拟议机制。格陵兰岛西南部的纳格苏格托奇甸造山带以地质“块体”为特征，不同之处在于是否存在应变定位。这些表现出惊人的相似之处，在今天的印度-欧亚大陆碰撞带看到的不同行为的地区。从该地区20多年的测绘中收集的结构和变质数据的汇编，可以确定代表应变局部化地区、大部分未变形地区和扩散应变地区的感兴趣地区。使用这个独特的数据集，免费提供给我们，作为指导，学生将进行额外的有针对性的实地工作，以调查今天露头的岩石的流变学，化学和预变形特性。他们将利用这些结果来建立模型，以检验当今碰撞所涉及地区的变质、变形和火成岩历史是否是整个造山带流变行为的决定因素。印度-欧亚碰撞带的最新大地应变率模型是根据2500多个单独的GPS速度建立的（Zheng et al.，2017年）。利兹的彗星科学家（http：comet.nerc.ac.uk）正在使用干涉合成孔径雷达观测来增加观测的空间密度（例如，Wang和Wright，2012年; Wang等人，2019年），但即使从GPS数据来看，印度-欧亚大陆碰撞区内也存在不同的机制。该学生将利用最新的观测资料完善和改进印度-欧亚大陆碰撞区的大地测量模型。我们希望学生能够询问数据，以批判性地评估可以观察到的应变局部化程度及其在空间中的变化（横向和纵向），也可能利用来自环境噪声地形的数据（例如，Jiang等人，2014年）对于项目的地质部分，学生将询问过去20年来来自丹麦和格陵兰地质调查局的地质测绘活动的可用数据，以确定感兴趣的野外区域。然后，将使用最新技术对这些区域进行详细调查，以推断不同岩石单元的流变行为，现场分析和微观结构工作（例如Svahnberg和Piazolo，2010年），以获得物理化学性质。

In this project the student will make and use geological field investigations of the exhumed lower crust to constrain models of strain localisation, and compare these against modern geodetic data from the India-Asia collision. Over the last few years, geodetic observations of strain from the continents have revealed two modes of behaviour. At fault zones such as the Himalayan Frontal Thrust, Altyn Tagh and Xianshuihe Faults in the India-Eurasia collision zone high geodetic strain rates are observed at the faults themselves. In other regions, including Western Tibet and Mongolia, present-day deformation is diffuse, with little evidence for localisation on the major structures (e.g. Zheng et al., 2017). The underlying reasons for this bi-modal behaviour remain unclear and are highly debated. Understanding processes responsible for the presence or absence of strain localisation in the continents is important for diverse problems ranging from seismic hazard to the distribution of resources.To address the question of strain localisation, the student will make new observations from exhumed lower-crustal rocks in Greenland, where bi-modal behaviour also appears to be present, and use the geological and geodetic observations to assess proposed mechanisms for strain (de-)localisation in continental crust by running numerical models.The Nagssugtoqidian Orogen in SW Greenland is characterised by geological "blocks" that differ in whether strain localization is present or absent. These exhibit striking similarities to areas of different behaviour seen in the present day India-Eurasia collision zone. Compilation of structural and metamorphic data from over 20 years of mapping in the area allow identification of areas of interest that represent the areas of strain localization, largely undeformed regions and areas of diffuse strain. Using this unique dataset, freely available to us, as a guide, the student will conduct additional targeted field work to investigate the rheological, chemical and pre-deformation properties of the rocks outcropping today. They will use the results to build models that test whether the metamorphic, deformation and igneous history of areas involved in present day collisions is a deciding factor in the rheological behaviour of the whole orogen.The latest geodetic strain rate models for the India-Eurasia collision zone are built from more than 2500 individual GPS velocities (Zheng et al., 2017). Work by COMET scientists at Leeds (http://comet.nerc.ac.uk) is using InSAR observations to increase the spatial density of observations (e.g. Wang and Wright, 2012; Wang et al., 2019), but even from the GPS data it is clear that different regimes operate within the India-Eurasia collision zone. The student would refine and improve geodetic models for the India-Eurasia collision zone using the latest observations. We would expect the student to interrogate the data to critically assess the degree of strain localisation that can be observed and how it varies in space (laterally and vertically), potentially also utilizing data derived from ambient noise topography (e.g. Jiang et al. 2014)For the geological part of the project, the student will interrogate the available data from geological mapping campaigns over the last 20 years available from the Geological Survey of Denmark and Greenland to identify field areas of interest. These areas will then be investigated in detail using latest techniques to infer rheological behaviour of different rock units, field analysis and microstructural work (e.g. Svahnberg & Piazolo, 2010) to derive physico-chemical properties.