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 将研究 Kahiltna 地体的变形时间和运动学，这是一个侏罗纪-白垩纪复理石序列，定义了塔尔基特纳超级地体（半岛地体、亚历山大地体和兰格利亚地体）与前侏罗纪边缘之间的神秘碰撞带。北美的。这项研究涉及层理、解理、线纹和折叠轴的结构绘图。与区域普遍的板条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。最终，他希望描述应变大小、方向和历史的空间分布特征，并在区域结构模式的背景下评估这些结果。对早期第三纪岩体接触光环中的成斑细胞和织物的分析将用于评估碰撞后渗透应变的模式。他已成功评估了克利尔沃特山脉的岩体周围接触光环内的应变，但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 对在压力阴影和记录同裂变形的布丁颈部中观察到的白云母和黑云母颗粒进行测年，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的阻塞温度以下生长的同构造晶粒的年代来量化。可以对这些结果进行逐个区域的比较，以确定碰撞过程中的变形是否是历时的，或者织物是否在区域上不相关。通过将穿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存在的问题：卡希尔特纳板岩中何时出现穿透应变？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 将重点关注阿拉斯加南部山坡沿线不同位置的卡希尔特纳地体的四个特定横断面。在这些领域，他记录了纤维增量应变标记的普遍存在，可用于量化增量应变历史。在两个地点（坎特韦尔地区和彼得斯山），他在黄铁矿簇周围的压力阴影中观察到了黑云母和白云母（适合 40 Ar/39 Ar 地质年代学）。他提出的详细测绘和样本分析的所有区域都可以通过公路或包机到达。该提案要求提供资金来支持博士生的研究。宾夕法尼亚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持，他们将协助实地考察并为自己的本科论文进行研究。结构、岩性和地质年代数据的 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。萨拉·比尔将在朱尼亚塔学院和费鲁姆学院等非博士学位授予机构就这项研究的各个方面进行演讲并举办研讨会。