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

追踪阿拉斯加西南部告别地体中的西伯利亚-劳伦斯碎屑转变

• 批准号: 1405049
• 负责人: Brian Hampton
• 金额: $ 2.31万
• 依托单位: New Mexico State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-20 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1405049&HistoricalAwards=false
• 关键词: Tracking; Siberian; Laurentian; Detrital; Transition

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.

构成阿拉斯加山脉（阿拉斯加南部）科迪勒拉山脉最深部分的许多地壳碎片（即地壳碎片）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火山，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，告别仪式可能起源于环北极地区（例如西伯利亚东部）。本研究的主要目的是检验与Farewell岩的成因和构造历史有关的以下假设：（1）Farewell岩的所有组分在古生代时都是西伯利亚-北极边缘的一部分，并在此后经历了晚期搬运，到达了北美科迪勒拉山脉的现今位置;（2）Farewell最古老的部分反映了西伯利亚-北极的起源，而Farewell较年轻的部分则记录了早期的增生和与Cordilleran-Laurentian边缘的碰撞。作为该项目的一部分，该研究小组将对构成告别盆地中、上古生界部分的沉积盆地沉积物进行首次详细的实地研究。除了进行地质测绘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颗粒进行U-Pb年代学分析。在这种情况下，告别的岩石，后期运输的碎屑记录将最有可能反映通过锆石的年龄相当于环北极岩浆源区。或者，一个早期阶段的传输模型可能反映了通过时间的碎屑过渡到更多的劳伦主导的源区。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最北端基底的地壳块体的构造历史和来源。这项研究的结果也将有助于一个不断扩大的U-Pb碎屑锆石数据库，该数据库正在从阿拉斯加以及美国大陆西部出现。美国，地壳碎片向构造板块边界的迁移和增生在整个地球都发生过？这是一个历史性的过程，被广泛认为是山脉演化和大陆生长的基本过程。以阿拉斯加为例，该州95%以上的土地是由加积的珊瑚礁组成的，每一个珊瑚礁都有其继承的地质历史和可能的经济潜力。例如，阿拉斯加北方的北极阿拉斯加州与北坡产油区直接相邻，也是世界？中国最大的锌地质资源和生产商。在大约瑞士的大小，告别海是阿拉斯加山脉中最大的地壳碎片之一，位于阿拉斯加北极南部，在北美科迪勒拉的一个更偏远和地质前沿地区。除了本研究的科学目标，该项目还将有助于密歇根州立大学学生的实地和实验室培训，并使他们接触到在微妙和偏远的穷乡僻壤环境以及尖端的研究实验室设施中进行研究的挑战和回报。作为该项目的教育推广组成部分，研究小组将与密歇根州地球科学教师合作，开发阿拉斯加的增生构造类似物，作为理解和识别保存在密歇根州北方裸露岩石记录中的类似（和更古老）事件的一种手段。