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

GSTDTAP

项目编号	1650219
	Collaborative Research: Strain localization, shear zone connectivity, and magma-deformation interactions by depth within a 65 km thick transpressional continental arc
	Elena Miranda
主持机构	The University Corporation, Northridge
项目开始年	2017
	2017-05-15
项目结束日期	2020-04-30
资助机构	US-NSF
项目类别	Continuing grant
项目经费	106457(USD)
国家	美国
语种	英语
英文摘要	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.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/71054
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Elena Miranda.Collaborative Research: Strain localization, shear zone connectivity, and magma-deformation interactions by depth within a 65 km thick transpressional continental arc.2017.