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

形成从墨西哥西部延伸到阿拉斯加的北美科迪勒拉山脉的地质过程是有争议的。这些山脉和邻近的盆地（如内华达山脉和加利福尼亚的大峡谷盆地）通常被解释为是由于北美大陆西部边缘下的海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，并提出西科迪勒拉的大部分地区是在远离北美边缘的海洋板块向西俯冲之上形成的群岛。在另一种模型中，当北美大陆与群岛相撞时，群岛成为科迪勒拉的一部分。这项大陆尺度的研究将沿着横跨阿拉斯加中部、阿拉斯加东南部、不列颠哥伦比亚省和加利福尼亚州西部科迪勒拉山脉的四条东西横断面测试这些模型。该项目将支持4名PI（其中2名为女性）、3名研究生的博士学位工作，以及每位PI为本科生提供真实的实地和实验室体验的承诺。这些研究方法非常适合培养本科生在实地观察和定量分析的背景下进行跨空间和时间尺度的思考，本科生将受益于研究生的近同伴指导。研究人员还将带领美国土著学生进行为期数天的实地考察，重点是形成北美西部和土著社区家园的地质过程之间的联系。研究解决了确定古辐合边缘俯冲极性的基本问题。本项目将把msamuange带的研究与盆地地层结合起来，并沿着北美科迪勒拉假定的大陆尺度缝合线整合研究结果。该合作项目将评估1)msamuange带的年龄和物源，2)盆地的构造和沉积构型（包括内侧和外侧接触），3)盆地形成和随后坍塌的时间，以及4)在东倾和西倾俯冲背景下盆地和msamuuange物源的比较。利用碎屑锆石分析（U-Pb、Lu-Hf和微量元素地球化学）、砂岩岩石学、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m<s:1>蓝格带进行分析，将为所提出的模型提供大陆尺度的检验，以更好地了解北美科迪勒拉中生代的发育。该项目还将改进在其他造山带，特别是无法获得层析成像资料的前中生代系统中建立收敛边缘系统的几何形状和时间的方法。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 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.