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

合作研究：65公里厚的挤压大陆弧内按深度的应变局部化、剪切带连通性和岩浆变形相互作用

• 批准号: 1650183
• 负责人: Keith Klepeis
• 金额: $ 28.01万
• 依托单位: University of Vermont & State Agricultural College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-05-15 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650183&HistoricalAwards=false
• 关键词: Collaborative; Research; Strain; localization; shear

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.

了解地壳内不同深度的大型断层带是如何随着时间的推移而发展的，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。断裂带不仅是运动和地震活动集中的场所；它们还形成了流体、岩浆和热量在地球上循环的管道。一个尚未解决的主要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，包括最下层的地壳和上地幔。要解决这一问题，最具挑战性的两个方面是：(1)深层断层的物理性质和行为具有高度的可变性；(2)地球上很少有地方能暴露出曾经存在于大约40公里以下深度的大片物质，并可供直接研究。这个项目利用了地球上仅有的几个地方之一，在那里可以直接观察一个古老断层系统的深层根源，这个断层系统曾经穿过大陆地壳，深度超过65公里。在新西兰西南部峡湾国家公园的深处，可以连续追踪到一条近20公里厚的垂直断裂带，从白垩纪时期的10公里深处一直延伸到65公里深处。该研究小组与新西兰研究人员合作，将确定这个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、岩浆和地壳融化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，包括那些发生在美国和其他地方的断层带。该项目还将通过一个创新的暑期研讨会项目来推进预期的社会成果，该项目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，从而提高他们对研究和研究生院机会的兴趣。为研究生和本科生提供国际实地经验和接触尖端分析研究设施的机会，将培养一支多元化的、具有全球竞争力的STEM劳动力队伍。大陆构造学中尚未解决的一个问题是，相互竞争的弱化机制如何将变形局部化为大陆弧根部深处的断层和剪切带。这个问题在科迪勒拉体系中尤其严重，在那里，大量岩浆活动、地壳熔融和高变质作用的发作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在岩浆活动和挤压循环期间，位于新西兰峡湾的古科迪勒拉弧的深层根部是如何实现和维持应变定位的。该项目整合了样带图、U-Pb地质和热年代学（锆石、钛矿）和电子后向散射衍射分析，以确定以下内容：(1)相互竞争的弱化机制如何在大的跨洋剪切带下、中地壳深处局部化应变；(2)高应变带如何跨越地壳深部边界垂直连接；(3)岩浆、变质和变形过程的时空变化如何影响剪切带的发育。该项目的成果将包括一个新的4-D模型，该模型显示了科迪勒拉弧内不同深度的高应变带是如何物理连接的，应变局部化是如何实现和维持的，以及变形是如何与迁移的岩浆和熔体相互作用的。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到弱化和硬化的作用，并通过岩石圈输送质量和热量。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是如何在极深的地方变形的，但是对于较低地壳成分的多相流动规律却很少，而且对于钙长石-透辉石聚集体的实验研究也没有将熔体包括在变形中。此外，很少有地方暴露出曾经存在于深度约40公里以下的大片物质。为了解决这些问题，该项目涉及在世界上最大和最深（高达65公里）的已知弧下地壳暴露中进行应变定位机制的实地调查。该项目将提供有关下地壳剪切带的几何结构、组成、热演化和流变学的新信息，这些剪切带曾经渗透到地壳深处至少65公里。大地构造计划（地球科学部）和NSF国际科学与工程办公室支持这个项目。

项目成果

What we can learn in the kitchen sink: an example from garnet granulite

我们可以在厨房水槽中学到什么：以石榴石麻粒岩为例

• 发表时间: 2021
• 期刊: America Geophysical Union
• 作者: Stowell, H.H.

PRELIMINARY GARNET GROWTH AGES FROM THE ANITA SHEAR ZONE AND ADJACENT ROCKS, NORTHERN FIORDLAND, NEW ZEALAND

新西兰北部峡湾安妮塔剪切带和邻近岩石的石榴石初步生长年龄

• DOI: 10.1130/abs/2019am-340485
• 发表时间: 2019
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Dickson, Hannah;Stowell, Harold H.;Bollen, Elizabeth M.;Schwartz, Joshua J.;Klepeis, Keith A.;Miranda, Elena A.
• 通讯作者: Miranda, Elena A.

MICROKINEMATIC ANALYSIS OF STRAIN GRADIENTS IN THE MIDDLE CRUST OF THE GEORGE SOUND SHEAR ZONE, NEW ZEALAND

新西兰乔治湾剪切带中地壳应变梯度的微观运动分析

• DOI: 10.1130/abs/2021am-370033
• 发表时间: 2021
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Brown, Virginia;Miranda, Elena;Klepeis, Keith;Schwartz, Joshua
• 通讯作者: Schwartz, Joshua

Shear zone evolution by depth in the continental lithosphere, SW New Zealand

新西兰西南部大陆岩石圈深度剪切带演化

• DOI: 10.6084/m9.figshare.12674636.v1
• 发表时间: 2020
• 期刊: Tectonics Community Science Workshop
• 作者: Klepeis, K.A.

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

新西兰峡湾中部长期地壳边界白垩纪压变形与大陆弧岩浆作用的相互作用

• DOI: 10.1130/ges02251.1
• 发表时间: 2020
• 期刊: Geosphere
• 影响因子: 2.5
• 作者: Blatchford, Hannah J.;Klepeis, Keith A.;Schwartz, Joshua J.;Jongens, Richard;Turnbull, Rose E.;Miranda, Elena A.;Coble, Matthew A.;Kylander-Clark, Andrew R.
• 通讯作者: Kylander-Clark, Andrew R.