Collaborative Research: Evaluating the Influence of Eocene Ridge Subduction on Magmatism, Deformation, and Basin Evolution, Pacific NW

我们正在利用地球科学中的多个学科来更好地了解与汇聚板块边界处的洋脊俯冲有关的过程。特别是，我们正在研究太平洋西北部保存完好的古代海脊俯冲的例子，在那里我们有一个前所未有的机会来记录从沉积盆地的发展到中地壳的岩浆和变质作用的2000万年海脊俯冲现象的历史。因此，这个古老的例子为现代海脊俯冲系统的研究提供了一个重要的补充，在现代海脊俯冲系统的研究中，必须间接评估更深层次的过程。我们正在测试一个从大约6000万年到4000万年前海脊位置变化的模型，这一时期标志着从中生代北喀斯喀兹弧向现代卡斯卡迪亚的过渡。我们还讨论了海脊俯冲的几个核心问题。1)弧前沉积盆地如何响应伴随海脊俯冲和洋脊位置跳跃而来的应力和应变的变化？2)在海脊俯冲过程中，大陆边缘的变形(如断层)在空间和时间上是如何划分的？3)海脊俯冲后收敛边缘内岩浆的特征是什么。作为我们研究的一部分，我们正在使用地理信息系统重建6000-4000万年间地质特征的分布。我们正在将这项研究得出的数字古构造和古地理地图和数据提供给其他研究人员和教育工作者，以便使其他人能够在我们努力的基础上再接再厉，补充我们的努力。总之，这项多学科的合作研究将对理解与海脊俯冲有关的过程，一个基本的板块构造过程，以及海脊俯冲对太平洋西北地区始新世构造演化的影响做出重大贡献。我们的项目涉及几所不同性质的大学之间的合作，包括圣何塞州立大学、普吉特湾大学、北亚利桑那大学和麻省理工学院。研究生和本科生的参与是这个项目的关键组成部分。几名本科生参与了这项研究。他们的参与包括参与地质实地调查，开展个人研究项目，前往其他大学使用本国机构没有的分析设施，以及根据他们的研究准备本科论文。这项研究的结果也被整合到地质学课堂课程中，作为普吉特湾大学一门高级本科课程的一部分，学生们正在学习在这项研究中收集的岩石，这是一个为期一学期的课程项目的一部分。研究结果正在专业学会会议(包括学生对其研究的陈述)和同行评议的科学文献中传播。

We are utilizing multiple disciplines in the Earth Sciences to better understand processes associated with the subduction of oceanic ridges at convergent plate boundaries. In particular, we are studying a well-preserved example of ancient ridge subduction in the Pacific Northwest, where we have an unprecedented opportunity to document a 20 million year history of ridge subduction phenomena from development of sedimentary basins to magmatism and metamorphism in the middle crust. This ancient example thus offers a critical compliment to studies of modern ridge subduction systems where deeper processes must be evaluated indirectly. We are testing a model of the changing position of the ridge from approximately 60 to 40 million years ago, a period that marks the transition from the Mesozoic North Cascades arc to modern Cascadia. We are also addressing several central questions for ridge subduction. 1) How do fore-arc sedimentary basins respond to changes in stresses and strains that accompany ridge subduction and jumps in the positions of oceanic ridges? 2) How is deformation, such as faulting, partitioned in space and time across the continental margin during ridge subduction? 3) What are the diagnostic geochemical features of magmas within a convergent margin after ridge subduction. As part of our research, we are using a geographic information system to reconstruct the distribution of geological features during the interval of 60-40 million years. We are making the digital paleotectonic and paleogeographic maps and data derived from this study available to other researchers and educators in order to allow others to build upon and supplement our efforts. In summary, this multidisciplinary collaborative research should provide significant contributions to understanding of processes associated with ridge subduction, a fundamental plate tectonic process, and the effects of ridge subduction on the Eocene tectonic evolution of the Pacific Northwest. Our project involves a collaboration between several universities of diverse character, including San Jose State University, University of Puget Sound, Northern Arizona University, and the Massachusetts Institute of Technology. Involvement of graduate and undergraduate students is a critical component of this project. Several undergraduate students are participating in the research. Their involvement includes participating in the geologic fieldwork, conducting individual research projects, traveling to other universities to use analytical facilities not available at their home institutions, and the preparation of undergraduate theses based on their research. The results are of the research are also being integrated in geologic classroom curricula as part of an advanced undergraduate course at the University of Puget Sound where students are studying the rocks collected during this study as part of a semester-long class project. Results of the research are being disseminated at professional society meetings (including student presentations on their research) and the peer-reviewed scientific literature.