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

PI将对Kahiltna地体变形的时间和运动学进行研究，Kahiltna地体是一个侏罗纪-白垩纪复理石序列，定义了Talkeetna超地体(半岛地体、Alexander地体和Wrangellia地体)与北美前侏罗纪边缘之间的神秘碰撞带。这项研究涉及层理、劈理、线理和褶皱轴线的构造映射。与区域普遍存在的板条解理有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穿透应变有关的运动学。最终，他想要描述应变大小、方向和历史的空间分布，并在区域构造模式的背景下评估这些结果。对早第三纪岩体接触晕中的成斑细胞和组构的分析将被用来评估碰撞后的穿透应变模式。他已经成功地评估了清水山脉深渊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部分。他还计划使用激光消融40Ar/39Ar对白云母和黑云母颗粒进行测年，这些颗粒在压力阴影中观察到，并在记录同理变形的束状物的颈部观察，以评估组构形成事件的时间。变形的年龄可以通过选择性地测定生长在Ar阻挡温度以下的同构造颗粒来定量。这样的结果可以从一个地区到另一个地区进行比较，以确定变形是否沿碰撞是历时的，或者面料是否在地区上没有相关性。通过将渗透应变和运动学的研究与中生代组构的测年相结合，他将解决一些与科迪勒构造有关的长期问题：渗透应变何时出现在卡希尔特纳板岩中？与此变形相关的运动学是什么？第三系碰撞后变形的运动学是什么？PI将集中在沿阿拉斯加南部造山带不同位置的卡希尔特纳地体上的四个特定横断面上。在这些领域，他记录了无处不在的纤维增量应变标记，用于量化增量应变历史。在两个地点(坎特威尔地区和彼得斯山)，他在黄铁矿丛生周围的压力阴影中观察到了黑云母和白云母(适用于40Ar/39Ar年代学)。他提出的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。这项提议要求资金支持宾夕法尼亚州立大学博士候选人Sara Bier的研究。请求为三名地学本科生提供支持，他们将协助进行实地考察，并为自己的本科生论文进行研究。构造、岩性和地质年代学数据的地理信息系统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将在包括Juniata学院和Ferrum学院在内的非授予博士学位的机构就这项研究的各个方面发表演讲并举办研讨会。

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.