Colliding Channels and Double Domes in Metamorphic Core Complexes

造山运动涉及大陆地壳增厚，通常伴随着伸展性坍塌和以混合岩穹丘（曾经部分熔融的岩石）为核心的变质核杂岩的形成。该项目检验了这样一种假设，即上地壳的伸展触发了两条部分熔融的地壳通道，它们在伸展带下方汇合。这些“碰撞通道”产生收缩结构和地壳深部向上流动进入两个亚穹（“双穹”），这两个亚穹被陡峭的高应变区隔开。这项研究结合了构造地质学、变质岩石学、地质年代学和数值模拟来检验碰撞通道解释了片麻岩/混合岩穹丘的许多特征的假设，例如穹丘相对于地幔岩所显示的复杂内部几何形状，“推覆体状”结构的常见现象，这些结构可能被错误地解释为在伸展之前收缩，以及作为深度的函数的穹丘中的应变变化，其中在深度处的收缩可能与在较浅水平处的延伸同时发生。基于实地的研究部分侧重于Montagne Noire（法国中央地块）双圆顶，在那里圆顶岩石和覆盖单元的压力-温度-时间-变形历史进行了评估。建模（2D和3D）探索有利于、修改或限制碰撞通道和双圆顶的条件;建模还量化了双圆顶结构所有点的压力-温度路径，以便与基于场的数据进行比较。3D建模研究了上地壳伸展的连续性和地壳成分/厚度的横向变化如何影响碰撞通道和双圆顶的发展。该项目研究了在山带崩塌过程中，深层岩石如何向地球表面挖掘，在高温下结晶的部分熔融岩石如何与非变质岩并置，以及部分熔融地壳的横向和垂直流动如何适应大陆地壳中的物质和热量转移。该方法集成了构造和变质地质学、地球物理学、地质年代学和地球动力学建模等领域。该项目探讨了片麻岩/混合岩穹丘的内部动力学，并提出了地壳变形的新概念，其中深部的收缩结构与浅部地壳的伸展结构相同。这项工作有可能调和内部和周围的片麻岩圆顶的神秘关系，并提供一个新的三维分析的过程，挖掘地壳深部。除了该项目的智力价值外，它还促进了美国研究人员之间的国际合作，澳大利亚和法国，并正在为一名博士的培训和指导做出贡献。学生和明尼苏达大学的本科生。研究结果将在专业协会会议和同行评议的文献上发表，也将作为地球科学专业人员建模短期课程的一部分。这项研究得到了NSF地质构造计划和NSF国际科学与工程办公室的支持。

Mountain building involves thickening of continental crust and is typically followed by extensional collapse and the formation of metamorphic core complexes that are cored by migmatite domes (rocks that were once partially molten). This project tests the hypothesis that extension in the upper crust triggers two channels of partially molten crust that converge beneath the zone of extension. These "colliding channels" generate contraction structures and upward flow of deep crust into two subdomes ("double dome") that are separated by a steep high strain zone. This study combines structural geology, metamorphic petrology, geochronology, and numerical modeling to test the hypothesis that colliding channels explain many features of gneiss/migmatite domes, such as the complex internal geometries displayed by domes relative to mantling rocks, the common occurrence of "nappe-like" structures that may be erroneously interpreted to indicate contraction prior to extension, and strain variations in domes as a function of depth, where contraction at depth may be coeval with extension at shallower levels. The field-based research component focuses on the Montagne Noire (Massif Central, France) double dome, where pressure-temperature-time-deformation history of dome rocks and overlying units are evaluated. Modeling (2D and 3D) explores the conditions that favor, modify, or limit colliding channels and double domes; modeling also quantifies pressure-temperature paths at all points of double domes structures for comparison with field-based data. Modeling in 3D examines how the obliquity of upper crustal extension and the lateral changes in crustal composition/thickness affect the development of colliding channels and double domes. This project addresses how deep-seated rocks are exhumed toward the Earth's surface during the collapse of mountain belts, how partially molten rocks that crystallize at high temperature are juxtaposed with non-metamorphic rocks, and how lateral and vertical flow of partially molten crust accommodates mass and heat transfer in the continental crust. The methodology integrates the fields of structural and metamorphic geology, geophysics, geochronology, and geodynamic modeling. This project explores the internal dynamics of gneiss/migmatite domes and offers a new concept of crustal deformation in which contraction structures at depth are coeval with extension structures in the shallow crust. This work has the potential to reconcile enigmatic relations within and around gneiss domes and to provide a new three-dimensional analysis of the processes that exhume the deep crust. In addition to the intellectual merit of the project, it is fostering international collaboration between researchers in the U.S., Australia, and France and is contributing to the training and mentoring of a Ph.D. student and an undergraduate student at the University of Minnesota. Results of the research will be presented at professional society meetings and the peer-reviewed literature and will also be presented as part of a modeling short course for geoscience professionals. The research is supported by the NSF EAR Tectonics Program and by the NSF Office of International Science and Engineering.