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，被认为是最近的板块构造过程（显生宙）的标志。活跃的吸积楔可以反映出长达50年或更长时间的历史，而古老的吸积复合体甚至可以反映出更长的历史，可能包括碰撞变形事件以及刮擦、逆冲和底板。增生复合体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。通过海洋地球物理调查研究了与活动俯冲有关的增生楔的构造，得到了复杂的构造历史，包括海洋岩石圈叠瓦、弧前伸展和/或收缩、超俯冲冲断带和/或宽的m<s:1>蓝带的圈定以及构造楔入。尽管这些海洋地球物理研究在发展对各种构造环境中增生楔形发育的广泛理解方面具有重要意义，但长期增生复合体的变形历史的许多方面仍然知之甚少，需要直接检查暴露的陆地上的例子来探索这些过程。俄勒冈州东北部的复合贝克地体提供了一个天然的实验室，用于研究一个暴露良好的古代增生复合体的结构发育和地壳生长的本质。在这个项目中，研究人员将评估一个构造模型，其中贝克地体是一个复合的超俯冲增生复合体，在北美边缘发育，是蓝山省与碰撞造山运动有关的岩石圈变形的主要焦点。该研究将通过详细的地质和构造填图、放射虫生物地层学、断层相关岩石的微观结构研究、地球化学和Nd和Sr同位素研究、碎屑锆石研究以及U-Pb放射性测年等方法对蓝山的地壳结构进行具体预测。特别值得一提的是，该模型认为贝克地体的北缘是一个基本的岩石圈边界，它将远行的瓦洛瓦岛弧地体与贝克增生复杂地体分开。这项研究将包括对怀俄明大学研究生的培训。本科生也将被聘为地质现场助理。此外，从本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、岩石学和构造地质学课程，以及研究生微观结构分析课程。最后，贝克地体是蓝山省的一个主要组成部分，对这些沉积岩石（即该地区广泛存在的年轻岩石的构造基底）的全面了解对于通过蓝山省进行拟议的地球物理调查（例如，EarthScope项目中的GeoSwath倡议）的成功至关重要。

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).