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、俄勒冈州和加州的大部分土地面积是在过去的2亿年中被添加到北美大陆的。虽然很明显，沿沿着北美前西缘，从北到南，所涉及的过程是不同的，但这种占主导地位的海洋岩石圈究竟是如何增生到大陆的还没有很好的了解。在莎士比亚-俄勒冈州边界地区，大洋和大陆岩石圈之间的边界很好地暴露在一个非常狭窄的高变形区，称为西部爱达荷州剪切带。这个项目提供了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变形和岩浆活动的区域，以及它在北美的形成中所发挥的作用。由于俄勒冈州-爱达荷州部分将加州和加拿大南部科迪勒拉的独特造山风格分开，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至关重要，并最终帮助我们了解大陆的创建和演变过程。来自威斯康星州大学，弗吉尼亚理工大学，佛罗里达大学，和华盛顿州立大学正在综合地震学、地球化学、地质年代学和构造地质学的研究成果，以研究与该大陆边缘演化有关的三个主要问题：1）基本的岩石圈结构，如暴露在西爱达荷州剪切带中的大陆-大洋岩石圈边界，如何引导随后的变形和岩浆作用？2)岩浆作用和伸展变形是如何改变（破坏）大陆岩石圈的？在什么岩石圈层次上？这种不稳定性对岩浆作用、变形和岩石圈强度的演化有何构造意义？一条宽频带无源地震仪器和一条地震折射线将描绘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爱达荷州西部剪切带岩浆活动的特征，以提供事件发生的时间以及这些过程发生的构造背景。结构地质学将通过确定主要构造边界和建立主要构造的运动历史，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位早期职业研究人员。

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.