Tracking the Siberian-Laurentian Detrital Transition in the Farewell Terrane, Southwestern Alaska

构成阿拉斯加山脉（阿拉斯加南部）科迪勒拉山脉最深处的许多地壳碎片（即地体）的起源和构造历史在很大程度上是未知的。该项目的重点是阿拉斯加西南部的告别地体，长期以来，该地体一直被认为是起源于加拿大西部的流离失所的地壳块。然而，最近的研究表明，告别地体可能起源于环北极地区（例如东西伯利亚）。本研究的主要目的是检验以下与告别地体的起源和构造历史相关的假设：（1）告别地体的所有组成部分在古生代都是西伯利亚-北极边缘的一部分，并经历了晚期搬运到目前在北美科迪勒拉山脉的位置； (2)告别地体最古老的部分反映了西伯利亚-北极的起源，而地体较年轻的部分则记录了与科迪勒拉-劳伦特边缘的早期吸积和碰撞。作为该项目的一部分，该研究小组将对构成告别地体中上古生代部分的沉积盆地沉积物进行首次详细的实地研究之一。除了进行地质测绘并记录这些地层的厚度和范围外，还将对这些单元的碎屑锆石颗粒进行 U-Pb 地质年代学分析。就告别地体而言，晚期迁移的碎屑记录很可能通过与环北极岩浆源区年龄相当的锆石来反映。或者，早期输运模型可能反映为随着时间的推移，碎屑过渡到劳伦斯主导的源区。在最广泛的科学范围内，该项目将有助于更好地了解构成阿拉斯加西南部北美科迪勒拉山脉最北端基底的地壳块的构造历史和起源。这项研究的结果还将有助于不断扩大的 U-Pb 碎屑锆石数据库，该数据库来自阿拉斯加以及美国大陆西部、加拿大和西伯利亚东部。地壳碎片向构造板块边界的迁移和增生贯穿了地球的整个历史，并被广泛认为是山地带演化和大陆生长的基本过程。就阿拉斯加而言，该州 95% 以上的面积由增生地体组成，每块地体都承载着继承的地质历史和潜在的经济潜力。例如，阿拉斯加北部的北极阿拉斯加地体直接毗邻北坡石油产区，也是世界上最大的锌地质来源和生产地。告别地体的大小与瑞士相当，是阿拉斯加山脉最大的地壳碎片之一，位于阿拉斯加北极以南，是北美科迪勒拉山脉较偏远和地质前沿的地区之一。除了本研究的科学目标外，该项目还将有助于密歇根州立大学学生的现场和实验室培训，让他们接触到在脆弱和偏远的偏远地区以及尖端研究实验室设施中进行研究的挑战和回报。作为该项目教育推广部分的一部分，研究小组将与一组密歇根地球科学教师合作，开发阿拉斯加的增生构造类似物，作为理解和识别密歇根州北部暴露岩石记录中保存的类似（而且更古老）事件的手段。

The origin and tectonic history of many of the crustal fragments (i.e. terranes) that make up the deepest parts of the Cordillera in the Alaska Range (southern Alaska) are largely unknown. The focus of this project is on the Farewell terrane of southwestern Alaska, which has long been considered to be a displaced crustal block that originated in western Canada. However, recent studies indicate that the Farewell terrane may have instead originated in circum-Arctic regions (e.g. eastern Siberia). The primary goal of this study is to test the following hypotheses related to the origin and tectonic history of the Farewell terrane: (1) All components of the Farewell were part of the Siberian-Arctic margin during the Paleozoic and have since undergone late-stage transport to their current position in the North American Cordillera; (2) The oldest parts of the Farewell reflect Siberian-Arctic origins while the younger components of the terrane record the early-stage accretion and collision with the Cordilleran-Laurentian margin. As part of this project, this research group will conduct one of the first detailed field studies on sedimentary basin deposits that make up the middle and upper Paleozoic parts of the Farewell terrane. In addition to carrying out geologic mapping and documenting the thickness and extent of these strata, U-Pb geochronologic analyses on detrital zircon grains from these units will be conducted. In the case of the Farewell terrane, the detrital record of late-stage transport would most likely be reflected through zircons that are age equivalent with circum-Arctic magmatic source areas. Alternatively, an early-stage transport model may be reflected by a detrital transition through time to more Laurentian-dominated source areas. At the broadest scientific scale, this project will contribute a better understanding on the tectonic history and provenance of crustal blocks that make up the basement to the northernmost extent of the North American Cordillera in southwest Alaska. Results from this study will also contribute to an ever-expanding U-Pb detrital zircon database that is emerging from Alaska as well as the western parts of the continental U. S., Canada, and eastern Siberia.The transport and accretion of crustal fragments to tectonic plate boundaries has occurred throughout Earth?s history and is widely recognized as a fundamental process by which mountain belts evolve and continents grow. In the case of Alaska, greater that 95 per cent of the state consists of accreted terranes, each of which carries with it an inherited geologic history as well as possible economic potential. For example, the Arctic Alaska terrane of northern Alaska is directly adjacent to petroleum-producing regions of the North Slope and is also the world?s largest geologic source and producer of zinc. At roughly the size of Switzerland, the Farewell terrane is one of the largest crustal fragments in the Alaska Range and is located just south of Arctic Alaska in one of the more remote and geologically frontier regions of the North American Cordillera. In addition to the scientific objective of this study, this project will also contribute to the field and lab training of students from Michigan State University and expose them to the challenges and rewards of conducting research in delicate and remote backcountry settings as well as in cutting-edge research lab facilities. As part of an educational outreach component to this project, the research team will be working with a group of Michigan Earth Science teachers to develop accretionary tectonic analogs from Alaska as a means for understanding and recognizing similar (and much older) events that are preserved in the exposed rock record of northern Michigan.