Collaborative Research: Strain localization, shear zone connectivity, and magma-deformation interactions by depth within a 65 km thick transpressional continental arc

了解大型断裂带是如何在地壳内不同深度随时间发展的，对于评估地震和火山灾害以及寻找包括天然气、石油和水在内的自然资源至关重要。断裂带不仅是集中运动和地震活动的场所，还形成了流体、岩浆和热量在地球上循环的管道。一个尚未解决的主要问题是，近地表断层的行为如何与断层系统最深处的变形有关，包括最下面的地壳和上地幔。解决这一问题最具挑战性的两个方面是：(1)大深度断层的物理性质和行为具有高度的可变性；(2)地球上很少有地方暴露出曾存在于约40公里以下深度并可供直接研究的大片物质。这个项目利用了地球上少数几个可以直接观测到古老断层系统深层根源的地方之一，这个古老的断层系统曾经穿透大陆地壳，深度超过65公里。在新西兰西南部菲奥德兰国家公园的深处，从白垩纪时期曾经居住在10公里到65公里深处的地区，可以连续追踪到厚度达20公里的近垂直断裂带。研究小组将与新西兰研究人员合作，确定这一古老断裂带在不同深度的内部结构、矿物学和行为，并将展示断裂带如何通过地壳垂直连接，并帮助流体、岩浆和地壳熔体从地幔深处移动到近地表环境。这些基本问题对于理解所有大型断裂带都很重要，包括与美国和其他地方一起发生的断裂带。该项目还将通过一个创新的暑期工作坊计划，为南加州少数族裔服务机构中代表性不足的学生提供研究经验，从而促进人们对研究和研究生机会的兴趣，从而促进预期的社会成果。为研究生和本科生提供国际现场经验和接触尖端分析研究设施，将培养一支多样化的、具有全球竞争力的STEM工作队伍。大陆构造学中一个悬而未决的问题是，相互竞争的削弱机制如何将变形定位于大陆弧根深处的断层和剪切带。这个问题在科迪勒系统中尤为严重，在那里，大量的岩浆作用、地壳熔融和高级变质作用迅速改变了地壳深部的成分和流变结构。该项目的目的是确定应变局部化是如何在位于新西兰菲奥德兰的古老科迪勒弧根深处实现和维持的，在岩浆作用和扭压循环中。该项目综合了横断面图、U-Pb地质年代学和热年代学(锆石、钛铁矿)和电子背散射衍射分析，以确定以下内容：(1)竞争削弱机制如何使中、下地壳深度的应变与大的挤压剪切带局部化，(2)高应变带如何垂直连接地壳深部边界，以及(3)岩浆、变质和变形过程的时空变化如何影响剪切带的发展。该项目的成果将包括一个新的四维模型，该模型显示不同深度的高应变带如何在科迪勒弧内物理连接，如何在其中实现和维持应变局部化，以及变形如何与迁移的岩浆和熔体相互作用。这一项目之所以重要，是因为大型断层和剪切带在大陆岩石圈的形成和演化中发挥了关键作用。它们在不同的深度充当弱化和硬化的媒介，它们通过岩石圈平流质量和热量。研究这些特征最具挑战性的方面之一是确定它们在整个地壳和地幔中的可变性。物理实验、数值模型和对包体的研究有助于我们推断物质如何在很深的地方变形，但较低地壳成分的多相流动规律很少，而且还没有关于钙长石-透辉石聚集体的实验研究，还没有熔体参与变形。此外，很少有地方暴露出曾存在于约40公里以下深度的大片物质。为了解决这些问题，该项目涉及对世界上已知的最大和最深(达65公里)的下弧地壳暴露的应变局部化机制进行实地调查。该项目将提供有关下地壳剪切带的几何、成分、热演化和流变学的新信息，这些剪切带曾经穿透地壳至少65公里。地球科学部)和美国国家科学基金会国际科学与工程办公室正在支持这一项目。

Understanding how large fault zones develop over time at different depths within the Earth's crust is vital to the goals of assessing earthquake and volcanic hazards and finding natural resources, including natural gas, petroleum, and water. Not only are fault zones the sites of concentrated movement and seismic activity; they also form conduits by which fluids, magmas, and heat circulate through the Earth. A major unsolved problem centers on how the behavior of near surface faults relates to deformation in the deepest parts of fault systems, including the lowermost crust and upper mantle. Two of the most challenging aspects of resolving this problem are (1) a high degree of variability in the physical properties and behavior of faults at great depths and (2) there are few places on Earth that expose large tracts of material that once resided at depths below approximately 40 km and are available for direct study. This project utilizes one of only a few places on the planet where it is possible to directly observe the deep roots of an ancient fault system that once penetrated continental crust to depths of more than 65 km. Deep within Fiordland National Park, in southwest New Zealand, a near vertical fault zone up to 20 km thick can be traced continuously from areas that once resided at depths of 10 km to depths of 65 km during the Cretaceous time period. The research team, in collaboration with New Zealand researchers, will determine the internal structure, mineralogy, and behavior of this ancient fault zone at different depths and will show how the fault zone connects vertically through the crust and helped move, fluids, magmas, and crustal melts from mantle depths to near-surface environments. These are fundamental issues that are important to the understanding of all large fault zones, including those that occur with the United States and elsewhere. The project will also advance desired societal outcomes through an innovative, summer workshop program that provides research experiences to underrepresented students at minority-serving institutions in southern California, thereby promoting interest in research and graduate school opportunities. Providing graduate and undergraduate students with international field experiences and exposure to cutting-edge analytical research facilities will develop a diverse, globally competitive STEM workforce.An unsolved problem in continental tectonics centers on how competing weakening mechanisms localize deformation into faults and shear zones deep within the roots of continental arcs. This problem is especially acute in Cordilleran systems where episodes of voluminous magmatism, crustal melting, and high-grade metamorphism quickly change the compositional and rheological structures of the deep crust. The aim of this project is to determine how strain localization was achieved and sustained within the deep root of an ancient Cordilleran arc located in Fiordland, New Zealand during a cycle of magmatism and transpression. The project integrates transect maps, U-Pb geo- and thermochronology (zircon, titanite), and electron backscatter diffraction analyses to determine the following: (1) how competing weakening mechanisms localized strain at lower and middle crustal depths with a large transpressional shear zone, (2) how high-strain zones connected vertically across deep crustal boundaries, and (3) how temporal and spatial variations in magmatic, metamorphic, and deformational processes influenced shear zone development. The outcomes of this project will include a new 4-D model that shows how high-strain zones at different depths are physically connected within Cordilleran arcs, how strain localization is achieved and sustained within them, and how the deformation interacts with migrating magma and melts. This project is important because large faults and shear zones play a key role in the formation and evolution of continental lithosphere. They act as agents of weakening and hardening at different depths and they advect mass and heat through the lithosphere. One of the most challenging aspects of studying these features is determining their variability throughout the crust and mantle. Physical experiments, numerical models, and studies of xenoliths help us infer how materials deform at great depths, but polyphase flow laws for lower crustal compositions are scarce and no experimental studies of anorthite-diopside aggregates yet include melt in the deformation. In addition, few places expose large tracts of material that once resided at depths below about 40 km. To address these problems, this project involves a field-based investigation of strain localization mechanisms within the world's largest and deepest (up to 65 km) known exposure of lower arc crust. The project will provide new information on the geometry, composition, thermal evolution, and rheology of lower crustal shear zones that once penetrated the crust to depths of at least 65 km.The Tectonics Program (Div. of Earth Sciences) and the NSF Office of International Science and Engineering are supporting this project.