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。在过去的2亿年间，华盛顿州、俄勒冈州和加利福尼亚州的大部分土地被并入北美大陆。这个以海洋为主的岩石圈究竟是如何吸积到大陆上的，目前还不太清楚，尽管很明显，沿着北美以前的西部边缘，所涉及的过程从北向南是不同的。在爱达荷州和俄勒冈州的边界地区，海洋和大陆岩石圈的边界在一个非常狭窄的高变形带中被很好地暴露出来，这个带被称为西爱达荷剪切带。该项目旨在深入了解这个尖锐的边界是如何形成的，它是如何控制随后的区域变形和岩浆活动的，以及它在北美形成过程中所起的作用。由于俄勒冈-爱达荷地区将加利福尼亚和加拿大南部的科迪勒拉山脉的独特风格分开，因此更好地了解这一复杂地区对于为北美西部的构造演化建立一个连贯的模型至关重要，并最终帮助我们了解大陆的形成和演变过程。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们正在综合地震学、地球化学、地质年代学和构造地质学的研究结果，以调查与这一大陆边缘演化有关的三个主要问题：1)爱达荷西部剪切带暴露出的陆洋岩石圈边界等基本岩石圈结构如何引导后续的变形和岩浆活动；2)岩浆活动和伸展变形如何改变（破坏）大陆岩石圈，以及在哪些岩石圈水平上改变（破坏）？3)这种不稳定对演化中的岩浆活动、变形和岩石圈强度的构造意义是什么？一条宽带被动地震仪器和一条地震折射线将勾勒出主要地质单元的当前几何形状及其数百公里深度的边界。地球化学和地质年代学将描述后西爱达荷剪切带岩浆活动，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历史，提供大陆被修改的运动学和动力学变形路径。除了该项目的研究目标外，该奖项还将支持四名研究生和八名本科生的教育和培训，这些学生分布在四所大学之间，并支持佛罗里达大学的一名早期职业研究员。

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.