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理解与汇聚板块边界的海洋脊俯冲有关的过程。特别是，我们正在研究太平洋西北地区一个保存完好的古脊俯冲的例子，在那里我们有一个前所未有的机会来记录2000万年的脊俯冲现象历史，从沉积盆地的发展到岩浆活动和中地壳的变质作用。因此，这个古老的例子为现代脊俯冲系统的研究提供了重要的补充，在现代脊俯冲系统中，更深的过程必须间接评估。我们正在测试一个大约6000万到4000万年前山脊位置变化的模型，这个时期标志着从中生代北喀斯喀特弧到现代喀斯喀迪亚的过渡。我们还解决了山脊俯冲的几个核心问题。1)弧前沉积盆地如何响应伴随洋脊俯冲和洋脊位置跳跃的应力应变变化？2)在洋脊俯冲过程中，变形（如断裂）在空间和时间上是如何在大陆边缘上划分的？3)洋脊俯冲后辐合边缘岩浆的诊断地球化学特征。作为我们研究的一部分，我们正在使用地理信息系统来重建6000万到4000万年之间的地质特征分布。我们正在将这项研究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，以便让其他人在我们的努力的基础上建立和补充。总之，这项多学科的合作研究将为理解与脊俯冲有关的过程、一个基本的板块构造过程以及脊俯冲对西北太平洋始新世构造演化的影响提供重要的贡献。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、普吉特海湾大学、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。几名本科生正在参与这项研究。他们的参与包括参加地质实地考察，进行个人研究项目，前往其他大学使用本国机构无法提供的分析设备，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，作为普吉特海湾大学高级本科课程的一部分，学生们正在研究这项研究中收集的岩石，作为一个学期的课堂项目的一部分。研究结果正在专业学会会议（包括学生对其研究的报告）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.