Timing and Kinematics of Deformation of the Kahiltna Terrane, South Central Alaska

【摘要】项目将对Kahiltna地体的变形时间和运动学进行研究。Kahiltna地体是一个侏罗纪-白垩纪的复理石层序，它定义了Talkeetna超地体（半岛、亚历山大和弗兰格里亚地体）与北美前侏罗纪边缘之间的神秘碰撞带。这项研究包括层理、解理、线理和褶皱轴的构造作图。与区域性普遍的板岩解理相关的同构造纤维的增量应变分析将用于约束与早期褶皱和渗透应变相关的运动学。最后，他想描述应变大小、方向和历史的空间分布，并在区域结构模式的背景下评估这些结果。对早第三纪深部岩体接触光圈中的卟啉母细胞和织物的分析将用于评价碰撞后渗透应变的模式。他已经成功地评估了克利尔沃特山脉（Clearwater Mountains）岩体周围接触光圈内的应变，但他希望将这些分析扩展到阿拉斯加山脉的其他地区。他还计划使用激光烧蚀法，对在压力阴影中观察到的白云母和黑云母颗粒进行40ar / 39ar测年，并记录共裂变形，以评估织物形成事件的时间。变形的年龄可以通过选择性地测定生长在氩气阻塞温度以下的同构造颗粒的年代来量化。这样的结果可以从一个区域到另一个区域进行比较，以确定变形是否沿碰撞是历时的，或者织物是否不具有区域相关性。通过将渗透应变和运动学研究与中生代构造的年代测定相结合，他将解决一些与科迪勒拉构造有关的长期问题：渗透应变是什么时候发生在Kahiltna板岩中的？和这个变形相关的运动学是什么？第三纪碰撞后变形的运动学是什么？PI将专注于沿阿拉斯加南部造山斜不同位置的横跨Kahiltna地块的四个特定横断面。在这些领域，他记录了普遍存在的纤维增量应变标记，用于增量应变历史的量化。在两个地点（Cantwell地区和Peters Hills），他在黄铁矿群周围的压力阴影中观察到黑云母和白云母（适合40 Ar/39 Ar地质年代学）。他建议详细测绘和样本分析的所有地区都可以通过公路或包机到达。该提案要求资金支持宾夕法尼亚州立大学博士候选人萨拉·比尔的研究。申请资助三名地球科学本科生，他们将协助实地考察并为自己的本科论文进行研究。构造、岩性和地质年代学数据的GIS汇编将为感兴趣的学术机构（高中、学院和大学）和组织（国家公园管理局、美国地质勘探局和阿拉斯加州地球物理和地质调查局）提供一个可访问的数字数据库。Sara Bier将在非博士阶段就该研究的各个方面进行演讲和研讨会。授予机构包括朱尼亚塔学院和费伦姆学院。

AbstractThe PI will conducut a study of the timing and kinematics of deformation in the Kahiltna terrane, a Jurassic- Cretaceous flysch sequence that defines the enigmatic collision zone between the Talkeetna superterrane (the Peninsular, Alexander, and Wrangellia terranes) with the pre-Jurassic margin of North America. This study involves structural mapping of bedding, cleavages, lineations, and fold axes. Incremental strain analysis of syntectonic fibers associated with a regionally pervasive slaty cleavage will be used to constrain the kinematics associated with early folds and penetrative strain. Ultimately, he would like to characterize the spatial distribution of strain magnitudes, orientations, and histories and evaluate these results in the context of regional structural patterns. Analysis of porphyroblasts and fabrics in contact aureoles of early Tertiary plutons will be used to evaluate patterns of post-collision penetrative strain. He has successfully evaluated strain within contact aureoles around plutons in the Clearwater Mountains but would like to extend these analyses to other parts of the Alaska Range. He also plans to use laser ablation 40 Ar/39 Ar dating of muscovite and biotite grains observed in pressure shadows and in the necks of boudins that record syncleavage deformation to assess the timing of fabric-forming events. The age of deformation could be quantified by selectively dating syntectonic grains that grew below the blocking temperature of argon. Such results could be compared from area to area to determine if deformation was diachronous along the collision or if fabrics are not regionally correlative. By combining studies of penetrative strain and kinematics with dating of Mesozoic fabrics, he will address a number of longstanding questions related to Cordilleran tectonics: When did the penetrative strain occur in the Kahiltna slates? What is the kinematics associated with this deformation? What is the kinematics of post-collision deformation in the Tertiary? The PI will focus on four specific transects across the Kahiltna terrane at different positions along the southern Alaska orocline. In these areas, he has documented the ubiquitous occurrence of fibrous incremental strain markers to be used for quantification of incremental strain histories. At two localities (the Cantwell area and Peters Hills), he has observed biotite and muscovite (suitable for 40 Ar/39 Ar geochronology) in pressure shadows around pyrite clusters. All the areas where he proposes detailed mapping and sample analysis are accessible by road or charter flight.This proposal requests funds to support the research of a Ph.D. candidate at Penn State,Sara Bier. Support is requested for three geoscience undergraduates who will assist with fieldwork and conduct research for their own undergraduate theses. The GIS compilation of structural, lithologic, and geochronological data will provide an accessible digital database to interested scholastic institutions (high schools, colleges, and universities) and organizations (National Park Service, USGS, and the State of Alaska Geophysical and Geological Surveys). Sara Bier will give presentations and conduct workshops on aspects of this research at non-PhD.-granting institutions including Juniata College and Ferrum College.