Collaborative Research: Deformation and Magmatic Modification of a Steep Continental Margin, Western Idaho-eastern Oregon

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。华盛顿州、俄勒冈州和加利福尼亚州的大部分土地面积是在过去2亿年里增加到北美大陆的。这个以海洋为主的岩石圈究竟是如何附着到这块大陆上的，目前还不是很清楚，尽管很明显，沿着北美前西部边缘，涉及的过程从北到南是不同的。在爱达荷州和俄勒冈州的交界处，大洋岩石圈和大陆岩石圈之间的边界在一个非常狭窄的高变形带中暴露得很好，这就是所谓的爱达荷州西部剪切带。这个项目提供了对这种尖锐边界是如何形成的，它如何在区域上控制了随后的变形和岩浆活动，以及它在北美形成中所起的作用的洞察。由于俄勒冈-爱达荷州段分隔了加利福尼亚州和加拿大南部科迪勒拉地区不同风格的山体建筑，因此更好地了解这一复杂地区对于开发北美西部构造演化的连贯模型并最终帮助我们了解大陆形成和随时间演变的过程至关重要。来自威斯康星大学、弗吉尼亚理工大学、佛罗里达大学和华盛顿州立大学的研究科学家正在综合地震学、地球化学、地质年代学和构造地质研究的结果，以研究与大陆边缘演化相关的三个主要问题：1)基本岩石圈结构如何如爱达荷州西部剪切带露出的大陆-海洋岩石圈边界，是否指导了后续的变形和岩浆作用？2)岩浆作用和伸展变形是如何改变(破坏)大陆岩石圈的，以及在什么岩石圈水平？3)这种不稳定对岩浆作用、变形和岩石圈强度的演化有什么构造意义？一系列宽带无源地震仪器和一条地震折射线将勾勒出目前主要地质单元的几何形状及其数百公里深的边界。地球化学和地质年代学将描述后西部爱达荷州剪切带岩浆活动的特征，以提供事件的时间和这些过程发生的构造背景。构造地质学将通过定义主要构造边界和建立主要构造的运动学史，提供大陆被改造的运动学和动态变形路径。除了该项目的研究目标外，该奖项还将支持分布在四所大学的四名研究生和八名本科生的教育和培训，并支持佛罗里达大学的一名早期职业研究人员。

This award is funded under the American Recovery and Reinvestment Actof 2009 (Public Law 111-5).Much of the land area of Washington, Oregon, and California was added to continental North America during the last 200 million years. Exactly how this dominantly oceanic lithosphere accreted to the continent is not well understood, although it is clear that the processes involved differed from north to south along North America's former western margin. In the Idaho-Oregon border region, the boundary between oceanic and continental lithospheres is well exposed in a very narrow zone of high deformation known as the western Idaho shear zone. This project is providing insight into how this sharp boundary formed, how it has controlled subsequent deformation and magmatism regionally, and the role it has played in the formation of North America. Because the Oregon-Idaho segment separates distinct styles of mountain building in California and the southern Canadian Cordillera, a better understanding of this complex region is critical for developing a coherent model for the tectonic evolution of western North America and ultimately helping us understand proceses by which continents are created and evolve through time.Research scientists from the University of Wisconsin, Virginia Tech, The University of Florida, and Washington State University are integrating the results of seismological, geochemical, geochronologic, and structural geologic studies in order to investigate three major issues associated with the evolution of this continental margin: 1) How do fundamental lithospheric structures, such as the continental-oceanic lithosphere boundary exposed in the western Idaho shear zone, guide subsequent deformation and magmatism?; 2) How do magmatism and extensional deformation modify (destabilize) the continental lithosphere, and at what lithospheric levels?; and 3) What are the tectonic implications of this destabilization for evolving magmatism, deformation, and lithospheric strength? A swath of broadband passive seismic instruments and a seismic refraction line will delineate the current geometry of the major geologic units and their boundaries to several hundred kilometers depth. Geochemistry and geochronology will characterize post- western Idaho shear zone magmatism to provide the timing of events and the tectonic context in which these processes occurred. Structural geology will provide the kinematic and dynamic deformation path by which the continent was modified, by defining the major tectonic boundaries and establishing the kinematic history of the major structures.In addition to the research objectives of this project, the award will support the education and training of four graduate students and eight undergraduate students distributed between the four universities, and supports an early career researcher at the University of Florida.