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)科迪勒拉最深部分的许多地壳碎片(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Farewell地体，长期以来一直被认为是起源于加拿大西部的移位地壳块体。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)。这项研究的主要目的是检验与告别地体的起源和构造史有关的下列假说：(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，此后经历了晚期运移至其在北美科迪勒拉的当前位置；(2)告别地体最古老的部分反映了西伯利亚-北极的起源，而较年轻的地体成分记录了早期与科迪勒兰-劳伦斯边缘的碰撞和碰撞。作为该项目的一部分，该研究小组将对构成永别地体中、上古生界部分的沉积盆地沉积进行首批详细的实地研究之一。除了进行地质填图和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进行U-Pb年代学分析。就永别地体而言，晚期运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反映出来。或者，早期的运移模式可能反映为随着时间的推移，碎屑过渡到更多以劳伦斯人为主的物源区。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最北端的基底的地壳块体的构造历史和来源。这项研究的结果还将有助于阿拉斯加以及美国大陆西部、加拿大和西伯利亚东部不断扩大的U-Pb碎屑锆石数据库的建立。地壳碎片向构造板块边界的运输和吸积在整个地球-S历史上都发生过，并被广泛认为是山脉演化和大陆生长的基本过程。就阿拉斯加而言，该州95%以上的土地由堆积的地体组成，每一块都带有继承的地质历史和可能的经济潜力。例如，阿拉斯加北部的北极阿拉斯加地体直接毗邻北坡产油区，也是世界上最大的锌地质来源和生产国？S。Farewell地体的大小大致相当于瑞士，是阿拉斯加山脉中最大的地壳碎片之一，位于北极阿拉斯加以南，位于北美科迪勒拉山脉更偏远、地质上更前沿的地区之一。除了这项研究的科学目标外，该项目还将帮助密歇根州立大学的学生进行实地和实验室培训，并使他们面临在微妙和偏远的偏远地区以及尖端研究实验室设施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，研究小组将与密歇根州地球科学教师小组合作，开发阿拉斯加的吸积构造类比，作为一种理解和识别保存在密歇根州北部裸露岩石记录中的类似(和更古老的)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.