Architecture and Evolution of an Accretionary Orogen

增生造山带的构造和演化

• 批准号: 0126004
• 负责人: Scott Johnson
• 金额: $ 13.01万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2005-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126004&HistoricalAwards=false
• 关键词: Architecture; Evolution; Accretionary; Orogen

Much of Earth's continental crust comprises Precambrian through Cenozoic orogens,where preexisting rocks have been variably modified by metamorphism and deformation. Owingto the association between collisional tectonic events and mountain building, this long record oforogenesis provides the most accessible means of reconstructing paleotectonic settings andevents that have shaped our planet. Although the Appalachian mountains are widely used toillustrate Earth's tectonic evolution and associated orogenesis, collisional processes and eventsthat drove the Ordovician Taconian orogeny in the Quebec Maine segment of the northernAppalachians remain enigmatic. Deformational features in this region cannot be satisfactorilyrelated to a specific convergent setting or collisional event(s) because the nature of the eastern(present coordinates) Laurentian margin during the early Paleozoic is poorly understood.Interpretations are divided as to whether the orogeny was caused by ophiolite emplacement,island-arc collision, or microcontinent collision. Because the Taconian orogeny initiated theAppalachian mountain-building cycle, understanding its architecture and evolution is essentialfor understanding the Appalachians as a whole.The PI proposes to investigate structural, metamorphic, and temporal relationships among therock units that make up the Chain Lakes massif and Boil Mountain ophiolite in order to testcompeting models and hypotheses for the Taconian orogeny in the northern Appalachians. Theirmultidisciplinary approach incorporates mapping, structural, microstructural, metamorphic, andgeochronological studies. Integrating field and laboratory studies, the PI will establish: (a) therelative and absolute timing of metamorphic and deformational events within the Chain Lakesmassif, (b) the crystallization age of the mafic portion of the Boil Mountain ophiolite, (c) the ageand kinematics of ophiolite emplacement, (d) whether mafic volcanic rocks near the ophioliterepresent a genetic part of the ophiolite, and (e) the age of possibly rift-related mafic dikes in theChain Lakes massif. The geochronology portion of the project will include in-situ U-Pb analysesof monazite to provide high temporal resolution for metamorphic events, small-numbermultigrain U-Pb analyses of zircon or baddeleyite from gabbro to determine the crystallizationage of the ophiolite, U-Pb analyses of zircon to establish the age of the dikes, and laser step-heating 40 Ar- 39 Ar analysis of muscovite to determine the minimum ophiolite emplacement age.The PI will compare his results with existing interpretations of the Thetford Mines ophiolite andoverlying units in southern Quebec, the Maquereau Dome in the Gaspe Peninsula, and theDashwoods Subzone in Newfoundland in order to evaluate temporal and spatial relationshipsamong these potentially correlative units. Because the extents and boundaries of terranes arefundamental components of the tectonic models, testing the terrane relationships will test themodels. The work will clarify the nature of the Taconian orogeny in the northern Appalachians,and will bear on conceptual models describing Iapetan paleogeographic reconstruction andcollisional accretionary processes.

地球大部分大陆壳包括前寒武纪的前寒武纪，那里已经存在的岩石已被变质和变形而变化。由于碰撞构造事件与山区建筑之间的关联，这种悠久的记录为重建了塑造我们星球的古旋转环境和事件提供了最容易获得的方法。尽管阿巴拉契亚山区被广泛使用，占地地球的构造进化和相关的造山变化，但碰撞过程和事件在北部阿帕拉奇人的魁北克缅因州段中驱动了奥陶纪塔科尼造山基因，仍然是神秘的。该区域中的变形特征不能与特定的收敛设置或碰撞事件相关，因为早期古生代期间东部（目前的坐标）Laurentian边缘的性质被熟悉的理解不足。解释是否会导致生气因素是否导致了蛇状石层次，Island collconcont-collcon-collision collision collision collision colliment collision collision collision collision collision collision collision collision collision collision collision collision collision collision collision collision collision collision colleistion。因为塔科尼山的造山心开始了戏剧性的山区建造周期，因此了解其建筑和进化对于理解整个阿巴拉契亚人至关重要。他们的发展学科方法结合了映射，结构，微观结构，变质和地球人工学研究。 PI将建立集成现场和实验室研究，将建立：（a）链湖中变质和变形事件的治疗和绝对时机，（b）沸腾的山地粘层的结晶年龄； Ophiolite，以及（E）在Thechain Lakes Massif中可能与裂谷相关的镁铁质堤的年龄。 The geochronology portion of the project will include in-situ U-Pb analysesof monazite to provide high temporal resolution for metamorphic events, small-numbermultigrain U-Pb analyses of zircon or baddeleyite from gabbro to determine the crystallizationage of the ophiolite, U-Pb analyses of zircon to establish the age of the dikes, and laser step-heating 40 Ar- 39 Ar分析棉花糖以确定最小蛇落岩的迁移年龄。PI将其结果与魁北克省南部的Thetford Mines ophiolite Andoverlying单元的现有解释，Gaspe Peninsula中的Maquereau Dome，Gaspe Peninsula中的Maquereau Dome，以及纽芬兰的Thedashwoods Subzone在纽芬兰的潜在型临时关系，以评估这些关系。由于地面的范围和边界是构造模型的基本组成部分，因此测试地层关系将测试temodels。这项工作将阐明北阿巴拉契亚人的塔科尼亚造山运动的性质，并将遵循描述IAPETAN古地理重建和汇总增生过程的概念模型。