Collaborative Research: RUI: Continental-Scale Study of Jura-Cretaceous Basins and Melanges along the Backbone of the North American Cordillera-A Test of Mesozoic Subduction Models

形成北美科迪勒拉山脉的地质过程存在争议。科迪勒拉山脉是从墨西哥西部延伸到阿拉斯加的山脉。这些山脉和邻近的盆地(如加利福尼亚州的内华达山脉和大山谷盆地)传统上被解释为由于北美大陆西缘下方的大洋板块向东俯冲而形成的。最近的研究对这一模型提出了挑战，并提出科迪勒拉西部的大部分地区是在远离北美边缘的大洋板块向西俯冲的上方形成的一个群岛。在这个替代模型中，当北美大陆与群岛相撞时，群岛成为科迪勒拉的一部分。这项大陆范围的研究将沿着阿拉斯加中部、阿拉斯加东南部、不列颠哥伦比亚省和加利福尼亚州科迪勒拉西部的四个东西横断面测试这些模型。该项目将为四名PI提供支持，其中两名是女性，三名研究生的博士工作，以及每一名PI为本科生提供真实的实地和实验室经验的承诺。这些研究方法非常适合于训练本科生在实地观察和定量分析的背景下跨空间和时间尺度进行思考，本科生将受益于研究生的近乎同行的指导。研究人员还将带领美洲原住民学生进行为期数天的实地考察，重点是形成北美西部的地质过程与土著社区家园之间的联系。这项研究解决了沿古代会聚边缘确定俯冲极性的基本问题。该项目将把混杂岩带的研究与盆地地层结合起来，并沿着北美科迪勒拉盆地内假想的大陆规模的缝合线整合结果。该合作项目将评估1)混杂岩带的年龄和物源，2)盆地的构造和沉积学结构(包括内侧和外侧接触)，3)盆地形成和随后崩溃的时间，以及4)在东倾俯冲和西倾俯冲的背景下盆地和混杂岩源区的比较。利用碎屑锆石分析(U-Pb、Lu-Hf和微量元素地球化学)、砂岩岩相学、全岩Sm-ND同位素分析和微量元素地球化学对盆地地层和邻近的混杂岩带进行分析，将为所提出的模型提供大陆规模的测试，以更好地了解北美科迪勒拉的中生代发展。该项目还将改进在其他造山带中建立会聚边缘系统的几何和时间的方法，特别是在无法获得层析信息的前中生代系统。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The geologic processes that formed the North American Cordillera, mountains that extend from western Mexico to Alaska, are disputed. These mountain ranges and neighboring basins (such as the Sierra Nevada and Great Valley basin within California) are conventionally interpreted to have formed due to eastward subduction of an oceanic plate beneath the western margin of the North American continent. Recent studies challenge this model and propose that much of the western Cordillera formed as an archipelago above westward subduction of an oceanic plate far from the margin of North America. In this alternative model, the archipelago became part of the Cordillera when the North American continent collided with the archipelago. This continental-scale study will test these models along four east-west transects across the western Cordillera in central Alaska, SE Alaska, British Columbia, and California. The project will provide support for four PIs, two of whom are female, the PhD work of three graduate students, and each PI’s commitment to provide undergraduate students with authentic field and laboratory experiences. The research methods are ideal for training undergraduate students to think across a range of spatial and temporal scales in the context of field observations and quantitative analyses, and undergraduate students will benefit from near-peer mentoring by graduate students. The researchers will also lead a multi-day field trip for Native American students centered on the connections between geologic processes that formed western North America and the homelands of Indigenous communities. The research addresses the fundamental problem of determining subduction polarity along ancient convergent margins. This project will couple the study of mélange belts with basin strata, and integrate the results along the hypothesized continental-scale suture within the North American Cordillera. This collaborative project will evaluate 1) the age and provenance of mélange belts, 2) the basins’ structural and sedimentological configuration (including inboard and outboard contacts), 3) the timing of basin formation and subsequent collapse, and 4) basin and mélange provenance comparison in the context of east-dipping versus west-dipping subduction. Analysis of the basin strata and adjacent mélange belts using detrital zircon analysis (U-Pb, Lu-Hf, and trace element geochemistry), sandstone petrography, and whole-rock Sm-Nd isotopic analysis and trace-element geochemistry will provide a continental-scale test of proposed models to better understand the Mesozoic development of the North American Cordillera. This project will also refine methods for establishing the geometry and timing of convergent margin systems in other orogens, particularly pre-Mesozoic systems for which tomographic information is not available.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.