How and why is deformation localised in continental crust?

变形如何以及为何局限于大陆地壳？

• 批准号: 2500058
• 金额: --
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2500058
• 关键词: How; why; deformation; localised; continental

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.

在该项目中，学生将对挖出的下地壳进行地质实地调查并利用其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。在过去的几年里，对大陆应变的大地测量观测揭示了两种行为模式。在诸如印度-欧亚大陆碰撞带的喜马拉雅前冲断层、阿尔金塔格断层和鲜水河断层等断层带，在断层本身处观察到高大地应变率。在其他地区，包括西藏西部和蒙古，目前的变形是分散的，几乎没有证据表明主要结构的局部化（例如，Zheng et al., 2017）。这种双模式行为的根本原因仍不清楚，并且引起了激烈的争论。了解大陆上存在或不存在应变局部化的过程对于从地震灾害到资源分布等各种问题都很重要。为了解决应变局部化的问题，学生将从挖掘出的下地壳岩石中进行新的观察。格陵兰岛似乎也存在双峰行为，并利用地质和大地测量观测通过运行数值模型来评估拟议的大陆地壳应变（去）局域化机制。格陵兰岛西南部的 Nagssugtoqidian 造山带的特征由地质“块”的不同之处在于是否存在应变定位。这些与当今印度-欧亚大陆碰撞带中不同行为的区域表现出惊人的相似之处。通过对该地区 20 多年测绘的结构和变质数据进行汇编，可以识别代表应变局部化区域、大部分未变形区域和扩散应变区域的感兴趣区域。使用我们免费提供的这个独特的数据集作为指导，学生将进行额外的有针对性的实地工作，以研究当今露出地面的岩石的流变、化学和预变形特性。他们将利用这些结果建立模型，测试当今碰撞所涉及区域的变质、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-欧亚大陆碰撞的最新大地测量应变率模型区域是根据 2500 多个单独的 GPS 速度构建的（Zheng et al., 2017）。利兹的 COMET 科学家 (http://comet.nerc.ac.uk) 正在利用 InSAR 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数据清楚地表明，印度-欧亚大陆碰撞区内有不同的政权在运作。该学生将利用最新的观测结果完善和改进印度-欧亚大陆碰撞带的大地测量模型。我们希望学生能够询问数据，批判性地评估可观察到的应变定位程度及其在空间中的变化（横向和纵向），也可能利用从环境噪声地形中获得的数据（例如，Jiang 等人，2014 年）对于该项目的地质部分，学生将查询丹麦和格陵兰地质调查局过去 20 年地质测绘活动的可用数据，以确定感兴趣的现场区域。然后，将使用最新技术对这些区域进行详细研究，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 & Piazolo，2010），以获得物理化学特性。