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

阿拉斯加中南部卡希尔特纳地体变形的时间和运动学

• 批准号: 0309680
• 负责人: Donald Fisher
• 金额: $ 29.3万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-04-15 至 2007-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309680&HistoricalAwards=false
• 关键词: Timing; Kinematics; Deformation; Kahiltna; Terrane

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.

摘要PI将对Kahiltna岩系变形的时间和运动学进行研究，Kahiltna岩系是一个侏罗纪-白垩纪复理石序列，它确定了塔尔凯特纳超岩系（半岛、亚历山大和弗兰格利亚岩系）与北美前侏罗纪边缘之间神秘的碰撞带。这项研究包括层理、劈理、线理和褶皱轴的构造制图。增量应变分析的同构造纤维与区域普遍的板状劈理将被用来约束运动学与早期褶皱和穿透应变。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。对早第三纪岩体接触晕中的变斑晶和组构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）岩体周围接触带内的应变，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40 Ar/39 Ar测年白云母和黑云母颗粒在压力阴影和在记录同解理变形的石香肠的颈部观察，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在氩气阻断温度以下生长的同构造颗粒的年龄来量化。这种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沿着是历时的，或者组构是否不具有区域相关性。通过结合渗透应变和运动学的研究与中生代组构的定年，他将解决一些长期存在的问题有关的科迪勒支构造：什么时候发生的渗透应变在Kahiltna板岩？与这种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将重点关注沿阿拉斯加南部造山带沿着不同位置的Kahiltna山脉的四个特定断面。在这些领域，他记录了纤维增量应变标记的普遍存在，用于增量应变历史的量化。在两个地方（Cantwell地区和Peters Hills），他在黄铁矿簇周围的压力阴影中观察到黑云母和白云母（适用于40 Ar/39 Ar地质年代学）。他提出的所有详细绘图和样品分析的地区都可以通过公路或包机到达。宾州州立大学的候选人萨拉·比尔请求为三名地球科学本科生提供支助，他们将协助进行实地工作，并为自己的本科论文进行研究。地理信息系统对结构、岩性和地质年代学数据的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、美国地质调查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将在非博士学位上就这项研究的各个方面进行演讲和研讨会。授予包括Juniata学院和Ferrum学院在内的机构。