权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Ductile strain in the footwall of a metamorphic core complex: A field example to test models for dynamics, timescales, and controls of mid-crustal flow.

变质核复合体下盘的延性应变：测试中地壳流动力学、时间尺度和控制模型的现场示例。

基本信息

批准号：
1728227
负责人：
James Vogl
金额：
$ 11.06万
依托单位：
University of Florida
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-01 至 2022-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1728227&HistoricalAwards=false
关键词：
Ductile strain footwall metamorphic core

项目摘要

As is the case of many mountain belts, the western North American Cordillera underwent horizontal stretching that thinned the Earth?s crust. In the Pacific Northwest thinning began around 50 to 55 million years ago immediately following the end of mountain building, and was highly localized along faults and shear zones that commonly record tens of kilometers of extension. The manner in which the deeper levels of the crust respond to this localized stretching and thinning is presently debated. A currently popular model is that the deep crust is weak enough that it flows from unextended areas into the region of localized thinning due to the lessened gravitational stresses in the areas of thinning. This study will test this model and address the controls that determine whether or not this type of weak gravitationally induced flow occurs. The research conducted during this study will contribute to important societal outcomes by providing support for the training of graduate and undergraduate students in an important STEM (science, technology, engineering, and mathematics) discipline, thus contributing to development of a globally competitive workforce. The project will provide opportunity for undergraduate students to be involved in the research, including the completion of theses based on their research. The project also contains important outreach and educational activities through the University of Florida's "Florida Future Scientists" summer program for high school students, the graduate student will gain mentoring experience by assisting these "future scientists" in the universities analytical laboratories. Thus, the project contributes to increased scientific literacy and public engament with STEM. This project will use new and existing NSF-funded analytical facilities at the University of Florida. Funding for the project will therefore insure that these facilities are actively used for geological research and fully calibrated and operational for future NSF projects, including collaborations outside of the University of Florida. Continuous research and educational use of these instruments is critical for maintaining research infrastructure. Technical results of the research obtained during this study will be widely disseminated through presentations at professional geoscience meetings and the peer-reviewed scientific literature. The highly localized extension that characterizes metamorphic core complexes is thought to lead to lateral flow of the weak lower crust into the extending region in response to topographically induced pressure gradients brought about by localized exhumation. While there is significant support from indirect observations for this isostatically induced flow, direct field examples of this process in core complex footwalls are few. In the examples where this process has been inferred, the geochronology does not typically unambiguously demonstrate synchroneity of strain at the different levels. Furthermore, some of the often cited examples lack evidence for convergent flow, which is predicted from inflow. Numerical models of isostatically induced flow predict specific convergent structures that strongly resemble a small number of field examples. However, it is likely that there are controls in natural settings that are not able to be adequately addressed in numerical models. These differing characteristics likely lead to a spectrum of structures, the full range of which is yet to be identified in the field. In the Pioneer core complex (Idaho), we have identified a well-exposed abrupt vertical transition in lineation directions that may be interpreted as a zone of decoupled isostatically induced flow. Importantly, extensive suites of both deformed and undeformed dikes are exposed above and below the lineation transition. Uranium-lead geochronology applied to these dikes offers a rare opportunity to test whether these fabrics formed synchronously or sequentially. This geochronology integrated with detailed kinematic analysis, metamorphic Pressure-Temperature-time analysis, all tied to detailed mapping offers a unique opportunity to not only test the idea of isostatically induced flow, but to fully characterize the detailed geometries of the resulting structures, as well as the timescales and controls on flow.

就像许多山脉一样，北美西部的科迪勒拉山脉经历了水平拉伸，使地球变薄？的外壳。在太平洋西北部，减薄开始于大约5000万到5500万年前，紧接着造山运动结束，并且沿着沿着断层和剪切带高度局部化，这些断层和剪切带通常记录了数十公里的延伸。地壳深层对这种局部拉伸和变薄的反应方式目前仍有争议。目前流行的一种模型是，由于减薄区域的重力应力减小，地壳深部足够脆弱，以至于它从未延伸的区域流入局部减薄区域。这项研究将测试这个模型，并解决控制，确定是否发生这种类型的弱引力诱导流。本研究期间进行的研究将通过为重要的STEM（科学，技术，工程和数学）学科的研究生和本科生的培训提供支持，从而有助于发展具有全球竞争力的劳动力，从而为重要的社会成果做出贡献。该项目将为本科生提供参与研究的机会，包括根据他们的研究完成论文。该项目还包括通过佛罗里达大学为高中生举办的“佛罗里达未来科学家”暑期项目开展的重要外联和教育活动，研究生将通过在大学分析实验室协助这些“未来科学家”获得指导经验。因此，该项目有助于提高科学素养和公众对STEM的参与。该项目将使用新的和现有的NSF资助的分析设施在佛罗里达大学。因此，该项目的资金将确保这些设施积极用于地质研究，并为未来的NSF项目进行全面校准和运作，包括佛罗里达大学以外的合作。这些仪器的持续研究和教育使用对于维持研究基础设施至关重要。将通过在专业地球科学会议上的介绍和同行审查的科学文献，广泛传播这项研究所取得的技术成果。变质核杂岩的特征是高度局部化的伸展，这被认为是由于局部折返作用所引起的地形诱导的压力梯度，导致弱下地壳侧向流动进入伸展区域。虽然有显着的支持，从间接观测的均衡诱导流，直接现场的例子，这一过程中的核心复杂的下盘很少。在已经推断出这一过程的例子中，地质年代学通常不能明确地证明不同层次上应变的同步性。此外，一些经常引用的例子缺乏收敛流的证据，这是从流入预测。均衡诱导流的数值模型预测了与少量现场实例非常相似的特定收敛结构。然而，在自然环境中可能存在无法在数值模型中充分解决的控制。这些不同的特征可能导致一系列的结构，其全部范围尚待在现场确定。在先锋核心复杂（爱达荷州），我们已经确定了一个很好的暴露突然垂直过渡线理方向，可以解释为一个区的解耦均衡诱导流。重要的是，变形和未变形岩脉的广泛套件暴露在线理过渡的上方和下方。铀铅地质年代学应用于这些脉提供了一个难得的机会，以测试这些织物是否形成同步或顺序。这种地质年代学与详细的运动学分析、变质压力-温度-时间分析相结合，所有这些都与详细的绘图相关联，这提供了一个独特的机会，不仅可以测试均衡诱导流动的想法，而且可以充分表征由此产生的结构的详细几何形状，以及时间尺度和流动控制。