Collaborative Research: Rodingites as Recorders of Tectonic Processes from the Seafloor to Convergence: A case study of the Dun Mountain Ophiolite Belt

超镁铁质岩石的水化作用（称为蛇纹石化作用）是地球的一个基本过程，它影响材料的流变学，从而影响岩石的变形、局部应变和地震行为。此外，蛇纹石化影响了氢、碳、硫等关键元素的地球化学循环，从而影响了生命的演化。蛇纹石化是一个广泛存在的过程，在构造板块的边界上最为常见。通过了解蛇纹岩化的条件（压力、温度、变形、流体来源）和时间，人们可以对板块边界发生的主要构造过程（如大陆裂谷、海底扩张、俯冲和沿走滑断层的应变定位）进行限制。不幸的是，确定蛇纹岩本身的压力-温度-变形-流体-时间（P-T-d-f-t）历史一直是一个挑战；因此，该团队将确定与蛇纹岩相关的岩石的P-T-d-f-t历史，作为对蛇纹岩化时间和条件的限制的代理，以解释板块边界的构造演化。这个多学科项目采用了从正教授到助理教授再到研究生和本科生的分层指导结构。这项工作将通过部分资助研究生（博士和硕士）和本科生以及少数民族学生暑期实习计划来支持学生教育和科学培训。研究小组将确定新西兰纳尔逊地区敦山蛇绿岩带的蛇绿岩岩化（以及伴随的蛇纹岩化）的条件和时间，以限制蛇绿岩的构造演化。尽管新西兰是罗丁岩的典型地区，但有限的工作集中在其形成的构造环境上，解释范围从海底形成到陆地就位后，由于地壳流体或流体集中在晚期断层上。研究小组将验证一种假设，即来自盾山蛇绿岩的岩石形成于海底热液蚀变或上覆的弧前地幔楔在二叠纪中期。相比之下，在俯冲和（或）挖掘过程中，与板块界面上的板块衍生流体相互作用形成的伴生蛇纹岩的岩质岩年龄略小。该团队将测试一个假设，即在安置后发生了最小程度的污染。利用相平衡模拟确定蛇绿岩带成矿的P-T条件，并结合U-Pb年代学新技术和蛇绿岩中赤铁矿石榴石的Ca、Sr同位素组成，分别确定蛇绿岩带成矿的时间和流体来源，确定蛇绿岩带成矿的条件和时间。现场构造和微观构造数据将有助于评价岩石化的时间，特别是与不同构造结构（例如，保存未变形的火成岩结构；岩石和主蛇纹岩内的穿透结构）有关的多代岩石。由于U-Pb年代学和Ca、Sr同位素组成在岩石中的应用有限，该团队将首先从海底（快速扩张脊和被动裂陷边缘）和西阿尔卑斯山（发掘出的俯冲变质地体）的知名位置重建构造历史，以提供概念证明。然后，他们将确定盾山蛇绿岩带内岩化作用发生的时间，以及这些交代事件如何记录盾山蛇绿岩带的构造历史。本项目资金由NSF EAR构造学和OCE海洋地质与地球物理项目提供。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The hydration of ultramafic rock (called serpentinization) is a fundamental Earth process that influences the rheology of materials and thus how rocks deform, localize strain, and behave seismically. In addition, serpentinization affects geochemical cycling of key elements such as hydrogen, carbon, and sulfur and therefore influenced the evolution of life. Serpentinization is a widespread process most common at the boundaries of tectonic plates. By understanding the conditions (pressure, temperature, deformation, fluid source) and timing of serpentinization, one can place constraints on major tectonic processes occurring at plate boundaries, such as continental rifting, seafloor spreading, subduction, and strain-localization along strike-slip faults. Unfortunately, determining the pressure-temperature-deformation-fluid-time (P-T-d-f-t) histories of serpentinites themselves has long been challenging; therefore the team will determine the P-T-d-f-t histories of rodingites, rocks associated with serpentinites, as a proxy to place constraints on the timing and conditions of serpentinization in order to interpret the tectonic evolution of plate boundaries. This multi-disciplinary project invokes a tiered mentorship structure from full professors to assistant professors to graduate and undergraduate students. This work will support student education and scientific training by partial funding of multiple students at the graduate (Ph.D. and M.S.) and undergraduate levels, as well as a minority student summer internship program. The research team will determine the conditions and timing of rodingitization (and associated serpentinization) of the Dun Mountain Ophiolite Belt in the Nelson region of New Zealand to place constraints on the tectonic evolution of the ophiolite. Despite New Zealand being the type locality of rodingites, limited work has focused on their tectonic setting of formation with interpretations ranging from formation on the seafloor to post-emplacement on land due to either crustal fluids or fluid focusing along late faults. The team will test the hypothesis that the rodingites from the Dun Mountain Ophiolite formed during seafloor hydrothermal alteration or in the overlying forearc mantle wedge during the mid-Permian. In contrast, the rodingites from associated serpentinite mélanges formed during subduction and/or exhumation via interaction with slab-derived fluids along the plate interface and will be of slightly younger age. The team will test the hypothesis that minimal rodingitization occurred post-emplacement. They will determine the conditions and timing of rodingitization of the Dun Mountain Ophiolite Belt by using phase equilibria modeling to determine the P-T conditions of rodingitization, combined with the new and novel techniques of U-Pb geochronology and Ca and Sr isotope composition of andradite garnet in the rodingites to determine the timing of and fluid source responsible for rodingitization, respectively. Field structural and microstructural data will help in evaluation of timing of rodingitization, particularly with multiple generations of rodingites related to different tectonic fabrics (e.g., preservation of undeformed igneous textures; penetrating fabric within both the rodingite and host serpentinite). As the applications to U-Pb geochronology and Ca and Sr isotope composition to rodingites are limited, the team will first reconstruct the tectonic histories from well-known localities on the seafloor (fast-spreading ridge and passive rifted margin) and in the Western Alps (exhumed subducted metamorphic terrane) to provide proof of concept. They will then determine when rodingitization within the Dun Mountain Ophiolite Belt occurred and how these metasomatic event(s) record the tectonic history of the Dun Mountain Ophiolite Belt.Funding for this project is provided by NSF EAR Tectonics and OCE Marine Geology and Geophysics Programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.