Evolution of a Long-Lived, Supra-Subduction Accretionary Complex (Baker Terrane, NE Oregon): A Study of Structural Development and Crustal Growth During an Arc-Arc Collision

与俯冲有关的增生杂岩是造山带的基本组成部分，被认为是近代板块构造过程（古生代）的标志。活跃的增生楔可以反映一个可能跨越5000万年或更长时间的长期历史，而古老的增生杂岩甚至可以反映一个更长的历史，可能涉及碰撞变形事件以及剥离，下冲和底侵。增生杂岩通常包括不可能在单一构造环境中形成的岩石类型的混合物。海洋地球物理调查研究了与活动俯冲有关的增生楔的结构，得出了复杂的结构历史，涉及海洋岩石圈的叠瓦作用、弧前伸展和/或收缩、俯冲上冲断带和/或广泛的混杂带的划定以及构造楔合。尽管这些海洋地球物理研究的意义，在发展一个广泛的了解的发展，在各种构造环境的增生楔，许多方面的长期增生杂岩的变形历史仍然知之甚少，需要直接检查暴露，在陆地上，例子来探索这些过程。位于俄勒冈州东北部的复合贝克岩为研究一个暴露良好的古代增生杂岩中的构造发育和地壳生长的性质提供了一个天然实验室。在这个项目中，研究人员将评估一个构造模型，其中贝克河是一个复合的超俯冲增生复合体，在北美边缘发展，是蓝山省碰撞造山带相关的岩石圈变形的主要焦点。拟议的研究作出具体预测的地壳结构的蓝山，将通过详细的地质和结构测绘，放射虫生物地层学，显微结构研究断层相关的岩石，地球化学和Nd和Sr同位素研究，碎屑锆石研究，和U-Pb放射性测年进行测试。特别是，提出的模型是，北方边缘的贝克陨石坑是一个基本的岩石圈边界，分开了遥远的瓦洛瓦岛弧陨石坑贝克增生杂岩陨石坑。这项研究将涉及培训的研究生在怀俄明州。本科生也将被聘为地质现场助理。此外，从这项研究中收集的样本和数据将在课堂上广泛使用。例如，样品将用于本科地球系统科学，岩石学和结构地质学课程，并在微观结构分析的研究生课程。最后，贝克岩是蓝山省的一个主要组成部分，对这些增生岩（即，关于该地区广泛分布的较年轻岩石的结构基底）对于通过蓝山省的拟议地球物理调查的成功至关重要（例如，地球范围项目内的GeoSwath倡议）。

Subduction-related accretionary complexes are fundamental building blocks in orogenic belts and are considered to be a hallmark of more recent plate-tectonic processes (Phanerozoic). Active accretionary wedges can reflect a long-lived history that may span 50 or more millions of years, whereas ancient accretionary complexes can even reflect a longer history that may involve collisional deformation events as well as offscraping, underthrusting, and underplating. Accretionary complexes commonly include a mixture of rock types that could not have formed in a single tectonic setting. The architecture of active subduction-related accretionary wedges has been studied by marine geophysical surveys that have yielded complex structural histories involving imbrication of oceanic lithosphere, fore-arc extension and/or contraction, delineation of supra-subduction thrust belts and/or broad zones of mélange, and tectonic wedging. Despite the significance of these marine geophysical studies in developing a broad understanding of the development of accretionary wedges in a variety of tectonic settings, many aspects of the deformational history of long-lived accretionary complexes are still poorly understood and require the direct examination of exposed, on-land, examples to explore these processes. The composite Baker terrane of northeastern Oregon, provides a natural laboratory to study the nature of structural development and crustal growth in a well-exposed, ancient accretionary complex. In this project, the investigators will evaluate a tectonic model in which the Baker terrane is a composite supra-subduction accretionary complex that developed marginal to North America and was the principal focus of lithospheric deformation related to a collisional orogeny in the Blue Mountains province. The proposed study makes specific predictions about the crustal structure of the Blue Mountains that will be tested through detailed geologic and structural mapping, radiolarian biostratigraphy, microstructural studies of fault-related rocks, geochemical and Nd and Sr isotope studies, detrital zircon studies, and U-Pb radiometric dating. In particular, the model proposed is that the northern margin of the Baker terrane is a fundamental lithospheric boundary that separates the far-traveled Wallowa island-arc terrane from the Baker accretionary complex terrane.This research will involve the training of graduate students at the University of Wyoming. Undergraduate students will also be employed as geologic field assistants. In addition, samples and data collected from this research will be used extensively in the classroom. For example, samples will be used in undergraduate Earth systems science, petrology, and structural geology classes, and in a graduate course in microstructural analysis. Finally, the Baker terrane is a major component of the Blue Mountains province, and a thorough knowledge of these accreted rocks (i.e., the structural basement in regard to the widespread younger rocks of the region) is essential to the success of proposed geophysical surveys through the Blue Mountains province (e.g., the GeoSwath initiative within the EarthScope project).