Building the Precambrian Laurentian Core of the North American craton: Resolving the Age and Tectonic Setting of the Snowbird Tectonic Zone of Canada

构建北美克拉通前寒武纪劳伦斯核心：解析加拿大雪鸟构造带的时代和构造背景

• 批准号: 1419843
• 负责人: Michael Williams
• 金额: $ 24.02万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419843&HistoricalAwards=false
• 关键词: Building; Precambrian; Laurentian; Core; North

The Canadian Shield, the core of the North American continent, is one of the great Archean ( 2.5 billion year) cratons on Earth and one from which many inferences have been drawn about the early evolution of Earth and the nature of early tectonic processes. It is generally accepted that the core of the continent consists of a number of relatively small Archean microcontinents (or protocontinents) that were stitched together by Proterozoic (2.0-1.8 billion year) orogenic belts. Many workers interpret the boundaries between these crustal blocks in terms of modern plate tectonic processes. That is, it can be argued that by approximately 2 billion years ago, plate tectonic processes were beginning to resemble those that of the modern-day Earth. There is one major crustal boundary that has remained enigmatic and might challenge interpretations about the evolution of North America and of plate tectonics in general. The Snowbird Tectonic Zone of central Canada is a 2,800-kilometer-long linear discontinuity that roughly corresponds to the boundary between the Hearne and Rae geologic domains (microcontinents?) of a mass of ancient rocks that forms the Canadian Shield. This boundary has been interpreted by geologists and geophysicists in terms of very different tectonic processes that have occurred at widely different times in Earth history. This research is aimed at clarifying the origin and significance of the Snowbird Tectonic zone by first constraining the age of the feature itself, and then by comparing and contrasting basement and cover rocks on either side of the enigmatic boundary. In addition to the scientific goals of the research, the project involves a significant intellectual collaboration between Canadian and American researchers from both government and university organizations. The project will contribute to education in a STEM discipline by the training of graduate and undergraduate students and the development of research results into classroom curricula and the creation of an online course for high school Earth Science students. Results of the research will be widely disseminated through presentations at professional geoscience meetings and the peer-reviewed scientific literature. The Snowbird Tectonic zone is the 2800-kilometer-long boundary between the Rae and Hearn domains (proto-continents) in the western Canadian Shield. It is widely taken to be one of the fundamental growth structures, or sutures, within the core of Laurentia, but interpretations of the age and tectonic setting of the zone vary widely with first-order implications for the early Earth tectonics and the history of Laurentia. The purpose of the proposed work is to build on region mapping and petrologic work near the zone and to finally constrain the age and significance of the Snowbird tectonic zone. Research will be carried out within the 600-km-long central segment of the Snowbird tectonic zone. Building on regional mapping and petrologic/structural analysis, new data will be collected and compiled from three transects across the zone. Data will include: (1) the isotopic signature of basement rocks within and on either side of the zone, (2) the age and character of cover sequences, (3) timing and style of deformation and metamorphism within and adjacent to the zone, and finally (4) the age and petrogenesis of the Chipman mafic dike swarm, a ubiquitous component of the Snowbird zone. The working hypothesis is that, unlike other boundaries in the Canadian Shield, the Rae-Hearne boundary is an Archean (not Proterozoic) continental suture, a collisional boundary that may provide an early record of horizontal tectonics in North America. The Snowbird Tectonic Zone, however, is a Proterozoic feature, a rare deep crustal exposure of an incipient and abortive rift and magmatic ?hot zone? that served to localize deformation, metamorphism, and partial melting. Consequently, in addition to placing critical constraints on the tectonic history of North America, the Snowbird Tectonic Zone provides unprecedented exposures of the zone of interaction of mantle magmatism, high-T metamorphism, and deformation within the lower crust. It may provide a model for similar processes occurring on Earth today.

加拿大地盾是北美大陆的核心，是地球上最大的太古代（25亿年）地盾之一，从中可以得出许多关于地球早期演化和早期构造过程性质的推论。一般认为，大陆的核心是由一些相对较小的太古代微大陆（或原大陆）组成，这些大陆是由元古代（20 - 18亿年）造山带缝合在一起的。许多学者根据现代板块构造过程来解释这些地壳块体之间的边界。也就是说，可以说，大约20亿年前，板块构造过程开始类似于现代地球的构造过程。有一个主要的地壳边界一直是个谜，可能会挑战对北美和一般板块构造演化的解释。加拿大中部的雪鸟构造带是一个2,800米长的线性间断，大致相当于赫恩和雷地质域（微大陆？）形成加拿大地盾的古老岩石群地质学家和地球物理学家根据地球历史上不同时期发生的不同构造过程来解释这一边界。这项研究的目的是澄清雪鸟构造带的起源和意义，首先限制特征本身的年龄，然后通过比较和对比神秘边界两侧的基底和盖层岩石。除了研究的科学目标外，该项目还涉及来自政府和大学组织的加拿大和美国研究人员之间的重要智力合作。该项目将通过培训研究生和本科生、将研究成果纳入课堂课程以及为高中地球科学学生创建在线课程，促进STEM学科的教育。研究结果将通过在专业地球科学会议上的介绍和同行审查的科学文献广泛传播。雪鸟构造带（Snowbird Tectonic zone）是加拿大地盾西部雷域（Rae）和赫恩域（Hearn domain）之间的2800英里长的边界。它被广泛认为是劳伦提斯核心内的基本生长结构或缝合线之一，但对该区域的年龄和构造背景的解释差异很大，对早期地球构造和劳伦提斯历史具有一阶影响。拟议工作的目的是建立在区域测绘和岩石学工作附近的地带，并最终限制的年龄和意义的雪鸟构造带。研究将在雪鸟构造带600公里长的中央部分进行。在区域制图和岩石学/结构分析的基础上，将从整个区域的三个断面收集和汇编新的数据。数据将包括：（1）带内和两侧基底岩石的同位素特征，（2）盖层序列的年龄和特征，（3）带内和邻近带的变形和变质作用的时间和类型，以及（4）奇普曼基性岩墙群的年龄和岩石成因，奇普曼岩墙群是雪鸟带的普遍组成部分。工作假设是，与加拿大地盾的其他边界不同，Rae-Hearne边界是太古代（而不是元古代）大陆缝合线，碰撞边界可能提供北美水平构造的早期记录。雪鸟构造带，然而，是一个元古代的功能，一个罕见的早期和流产裂谷和岩浆？危险区域？使变形变质和部分熔融局部化。因此，除了对北美的构造历史施加关键的限制之外，雪鸟构造带还提供了地幔岩浆作用、高温变质作用和下地壳变形相互作用的区域的前所未有的暴露。它可以为今天地球上发生的类似过程提供一个模型。