Architecture and Evolution of an Accretionary Orogen

地球的大部分大陆地壳由前寒武纪到新生代造山带组成，在这些造山带中，先前存在的岩石已经被变质作用和变形所改变。由于碰撞构造事件和造山运动之间的联系，这一漫长的造山运动记录为重建古构造环境和塑造我们星球的事件提供了最容易获得的手段。虽然阿巴拉契亚山脉被广泛用来说明地球的构造演化和相关的造山作用，碰撞过程和事件，驱动奥陶纪塔康造山带在魁北克缅因州部分的北部阿巴拉契亚山脉仍然是个谜。该地区的变形特征不能与特定的会聚背景或碰撞事件相联系，因为对早古生代东部劳伦阶边缘（现在的坐标）的性质了解甚少。由于塔康造山带开启了阿巴拉契亚山脉的造山周期，了解其结构和演化对于了解整个阿巴拉契亚山脉是至关重要的。PI建议调查构成链湖群和布尔山蛇绿岩的岩石单元之间的结构、变质和时间关系，以检验北方阿巴拉契亚山脉塔康造山带的竞争模型和假设。他们的多学科方法包括制图、构造、显微构造、变质和年代学研究。综合实地和实验室研究，PI将建立：（a）Chain湖群内变质和变形事件的相对和绝对时间f;（B）Boil山蛇绿岩基性部分的结晶年龄;（c）蛇绿岩侵位的年龄和运动学;（d）蛇绿岩附近的基性火山岩是否代表蛇绿岩的成因部分;和（e）年龄的可能裂谷相关基性岩脉在theChain Lakese 100 f。该项目的地质年代学部分将包括独居石的原位U-Pb分析，以提供变质事件的高时间分辨率，辉长岩中锆石或斜锆石的少量多颗粒U-Pb分析，以确定蛇绿岩的结晶年龄，锆石的U-Pb分析，以确定脉岩的年龄，激光步进加热40 Ar-对白云母进行39 Ar分析，以确定蛇绿岩的最小侵位年龄。PI将把他的结果与南部特福德矿山蛇绿岩和上覆单位的现有解释进行比较。魁北克、加斯佩半岛的马克罗穹丘和纽芬兰的达什伍兹分区，以评估这些潜在相关单元之间的时间和空间关系。由于断层的范围和边界是构造模型的基本组成部分，因此检验断层关系将检验模型。这项工作将阐明北方阿巴拉契亚山脉的塔科尼造山带的性质，并将对描述Iapetan古地理重建和碰撞增生过程的概念模型产生影响。

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.