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

了解地壳内不同深度的大型断层带如何随着时间的推移而发展，对于评估地震和火山灾害以及寻找天然气，石油和水等自然资源的目标至关重要。断层带不仅是集中运动和地震活动的场所，它们还形成了流体、岩浆和热量在地球上循环的管道。一个主要的未解决的问题集中在近地表断层的行为如何与断层系统最深处的变形有关，包括最低地壳和上地幔。解决这个问题的两个最具挑战性的方面是（1）在很深的地方断层的物理性质和行为的高度可变性，以及（2）地球上很少有地方暴露出曾经位于大约40公里以下深度的大面积物质，可供直接研究。该项目利用地球上仅有的几个地方之一，可以直接观察曾经穿透大陆地壳超过65公里深处的古老断层系统的深层根源。在新西兰西南部峡湾国家公园的深处，一个近垂直的断层带厚达20公里，可以连续地从白垩纪时期曾经居住在10公里深处的地区追溯到65公里深处。该研究小组与新西兰研究人员合作，将确定这一古老断层带在不同深度的内部结构、矿物学和行为，并将展示断层带如何通过地壳垂直连接，并帮助将流体、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层带都很重要，包括美国和其他地方发生的断层带。该项目还将通过一个创新的夏季研讨会计划，为加州南部少数民族服务机构中代表性不足的学生提供研究经验，从而促进对研究和研究生院机会的兴趣，从而推动预期的社会成果。为研究生和本科生提供国际领域经验和接触尖端分析研究设施的机会，将培养一支多元化、具有全球竞争力的STEM劳动力队伍。大陆构造学中一个未解决的问题集中在竞争性弱化机制如何将变形定位到大陆根部深处的断层和剪切带中。弧。这一问题在科迪勒支系统中尤为严重，在那里，大量岩浆活动、地壳熔融和高级变质作用的发生迅速改变了深部地壳的成分和流变结构。该项目的目的是确定应变本地化是如何实现的，并在位于峡湾，新西兰的一个古老的科迪勒拉弧的深根内持续在一个周期的岩浆作用和挤压。该项目综合了样带图、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）相互竞争的弱化机制如何使应变局部化在地壳中、下部，并形成一个大的压扭剪切带，（2）高应变带如何垂直地跨越地壳深部边界，（3）岩浆的时空变化，变质作用和变形作用影响剪切带的发育。该项目的成果将包括一个新的四维模型，该模型显示了不同深度的高应变区如何在科迪勒拉弧内物理连接，应变局部化如何在其中实现和维持，以及变形如何与迁移的岩浆和熔体相互作用。由于大断裂和剪切带在大陆岩石圈的形成和演化中起着关键作用，因此该项目具有重要意义。它们在不同的深度起着弱化和硬化的作用，它们通过岩石圈输送物质和热量。研究这些特征最具挑战性的方面之一是确定它们在地壳和地幔中的变化。物理实验，数值模型和捕虏体的研究有助于我们推断材料如何在很深的地方变形，但多相流动的法律较低的地壳成分是稀缺的，还没有实验研究钙长石透辉石聚集体包括熔融变形。此外，很少有地方暴露出曾经存在于大约40公里以下深处的大面积物质。为了解决这些问题，该项目涉及在世界上最大和最深（达65公里）的已知下弧地壳暴露的应变局部化机制的实地调查。该项目将提供关于下地壳剪切带的几何形状、组成、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公里的深度。美国国家科学基金会国际科学与工程办公室（NSF Office of International Science and Engineering）支持该项目。

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.