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(称为蛇纹岩化)是一个基本的地球过程，它影响物质的流变性，从而影响岩石如何变形、局部化应变和地震行为。此外，蛇纹岩作用影响了氢、碳、硫等关键元素的地球化学循环，从而影响了生命的演化。蛇纹岩化是一种广泛的过程，最常见的是在构造板块的边界。通过了解蛇纹岩化的条件(压力、温度、变形、流体来源)和时间，可以约束发生在板块边界的主要构造过程，如大陆裂谷、海底扩张、俯冲和沿走滑断层的应变局部化。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)历史一直是具有挑战性的；因此，该团队将确定与蛇纹岩有关的辉长岩的P-T-d-f-t历史，作为对蛇纹岩作用的时间和条件的限制的替代，以便解释板块边界的构造演化。这一多学科项目启用了从全职教授到助理教授再到研究生和本科生的分层导师结构。这项工作将通过部分资助研究生(博士和硕士)的多名学生来支持学生教育和科学培训。和本科水平，以及少数族裔学生暑期实习计划。研究小组将确定新西兰纳尔逊地区敦山蛇绿岩带的岩浆化(及相关蛇纹岩化)的条件和时间，以限制蛇绿岩的构造演化。尽管新西兰是沸石的典型产地，但有限的工作侧重于其形成的构造环境，从海底形成到陆上侵位后的解释，要么是因为地壳流体，要么是因为流体集中在晚期断层。该团队将验证这样的假设，即来自陡山蛇绿岩的沸石是在海底热液改造期间形成的，还是在中二叠世期间形成于上覆的弧前地幔楔体中。相反，来自伴生的蛇纹岩混杂岩系的橄榄岩是在俯冲和/或折返过程中通过与板块界面板岩衍生的流体相互作用而形成的，其年龄将略低。该团队将检验最小罗地尼化发生在就位后的假设。他们将利用相平衡模型确定蛇绿岩的P-T条件，并结合辉绿岩中安山岩石榴石的U-Pb年代学和钙、锶同位素组成的新技术，分别确定蛇绿岩的形成时间和流体来源，从而确定盾山蛇绿岩带的辉长化条件和时代。现场结构和显微构造数据将有助于评估岩浆化的时间，特别是与不同构造组构(例如，保存未变形的火成岩结构；岩浆岩和蛇纹岩中的穿透组构)有关的多代辉长岩。由于橄榄岩在U-Pb年代学和钙锶同位素组成方面的应用有限，该小组将首先从海底(快速扩张的海脊和被动的裂谷边缘)和西部阿尔卑斯山(折返的俯冲变质地体)的著名地点重建构造历史，以提供概念上的证据。然后，他们将确定盾山蛇绿岩带内的岩化发生的时间以及这些交代事件(S)如何记录盾山蛇绿岩带的构造历史。该项目的资金由美国国家科学基金会EAR构造和OCE海洋地质和地球物理项目提供。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智力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.