Eclogites in the Yukon-Tanana Terrane, Canadian Cordillera: Subduction Erosion of the Overriding Plate?

地球上超过一半的活动俯冲带正在被侵蚀，在这个过程中，俯冲板块的碎片被移走并沿着俯冲通道向下输送。俯冲侵蚀在岩石记录中是很难识别的，但加拿大科迪勒拉育空-塔纳纳弧地体中含有榴辉岩的大陆地壳是一个很好的候选者。人们正在研究育空-塔纳纳弧区局部暴露良好的高压岩石单元，以确定榴辉岩形成的可能环境。这个项目的最终目标是促进我们对碰撞造山带中俯冲板块和俯冲板块之间界面上发生的过程的理解。具体目标是确定育空-塔纳纳地区一致榴辉岩及其寄主岩石(而不是混杂岩)的谱系、变质演化和构造背景；并根据可能的俯冲和折返通道模式对结果进行评估。详细的绘图是该项目的重要组成部分；问题的关键是展示榴辉岩及其围岩的共同变质历史。在伦斯勒理工学院的电子探针上收集的定量矿物化学和分带数据正在与相平衡建模的结果相结合，以产生详细的压力-温度路径。利用美国地质勘探局-斯坦福大学灵敏的高分辨率离子探针(SHRIMP)的U-Pb年代学获得了锆石、钛铁矿和独居石的年龄，然后将这些年龄与俯冲和折返路径上的不同点联系起来。将根据结果对俯冲侵蚀形成榴辉岩的模型进行评估。我们提出的育空-塔纳纳地体中的榴辉岩是由俯冲侵蚀形成的观点，挑战了所有高压变质作用都是在俯冲板块中形成的假设，以及增生地体中的俯冲极性可以仅由榴辉岩的存在来推断的假设。我们的合作包括来自美国、加拿大和德国的研究人员的贡献，并涉及加拿大地质调查局和育空地质调查局的重要科学和后勤支持。研究结果直接与EDGE项目有关，该项目是加拿大联邦、州和省地质调查局之间的合作努力，旨在通过了解北美北部科迪勒拉地体来加强矿产资源勘探。该项目正在为爱荷华大学的研究生和本科生提供STEM学科的重要培训机会，有助于扩大科学界代表性不足的群体，并通过爱荷华大学的自然历史博物馆为K-12学生提供外联努力。

Over half of the active subduction zones on Earth are eroding in a process whereby pieces of the overriding plate are removed and transported down the subduction channel. Subduction erosion is very difficult to recognize in the rock record, but eclogite-bearing continental crust from the Yukon-Tanana arc terrane in the Canadian Cordillera is a good candidate. Locally well-exposed, high-pressure rock units of the Yukon-Tanana arc are being studied to establish the possible settings for eclogite formation. The ultimate goal of this project is to advance our understanding of processes that occur along the interface between the subducting slab and the overriding plate in collisional orogens. The specific goals are to identify the genealogy, metamorphic evolution and tectonic setting of the coherent eclogites and their host rocks, as opposed to mélanges, in Yukon-Tanana; and to evaluate the results in terms of plausible models for subduction and exhumation channels. Detailed mapping is an essential part of the project; the crux of the problem is to demonstrate shared metamorphic histories for the eclogites and their host rocks. Quantitative mineral chemistry and zoning data collected on the electron microprobe at Rensselaer Polytechnic Institute are being combined with the results of phase equilibrium modeling to produce detailed pressure-temperature paths. U-Pb geochronology utilizing the USGS-Stanford sensitive high-resolution ion microprobe (SHRIMP) yields zircon, titanite and monazite ages that are then linked to various points along the subduction and exhumation path. Models for eclogite formation via subduction erosion will be evaluated in light of the results. Our proposed idea that the eclogites in Yukon-Tanana terrane formed via subduction erosion challenges the assumptions that all high-pressure metamorphism forms in the subducting plate and that subduction polarity in accreted terranes can be deduced from the mere presence of eclogites. Our collaboration involves contributions from researchers from the United States, Canada, and German, and involves important scientific and logistical support from the Canadian Geological Survey and Yukon Geological Survey. The research results directly pertain to the EDGES project, a collaborative effort among the federal, state and provincial geological surveys of Canada to enhance mineral resource exploration by understanding the terranes of the northern Cordillera of North America. The project is providing important training opportunities for graduate and undergraduate students at the University of Iowa in a STEM discipline, is contributing to the broadening of underrepresented groups in science, and is providing outreach efforts for K-12 students through the University of Iowa's Natural History Museum.