Collaborative Research: Resolving Conflicting Models for the Laramide Orogeny and the Flat-Slab Paradigm in the Southern California Batholith

了解落基山脉在美国西部是如何发展起来的是一个至关重要的问题，因为它们蕴藏着对我们的国民经济很重要的珍贵矿产资源，如金、铅、铜和银。这些经济资源中的许多都是沿着沿着大断层被带到地表的，这些断层形成于晚白垩世的一次造山运动中，被称为Laramide造山运动。一个关键的问题是，这一事件背后的驱动力的时间和起源以及落基山脉的形成是非常有争议的，并且对这些山脉形成的构造环境没有共识。研究人员假设，了解落基山脉和拉腊米山脉起源的答案在于加州南部的圣加布里埃尔山脉。这一区域包含两个重要特征，使其成为本研究的重点：（1）它们保存了Laramide造山带从最早期到其终止的完整时间历史，这对于重建事件背后的驱动力非常重要;（2）它们包含一个独特的地壳深部部分，包括一个在Laramide造山带开始时活动的主要韧性断层系统。这些功能的分析将提供关键的见解开始的Laramide orthodox，这将是必不可少的，在解决相互矛盾的假设。该项目的研究计划将包括在圣加布里埃尔和附近山区进行3个季节的实地工作和数据收集。从圣加布里埃尔山脉收集的岩石的实验室分析将包括地质年代学，地球化学和微观结构工作在加州州立大学北岭激光消融和LatinXellence在STEM实验室。该项目将通过创新的夏季研讨会和一个名为LA-ROCS的学术年辅导计划来推动社会成果，这两个项目都旨在为加州南部少数民族服务机构的代表性不足的学生提供研究经验。这些指导和本科生的研究机会将使他们接触到尖端的分析研究设施，并将有助于发展一个多样化的，具有全球竞争力的STEM劳动力。这项建议的目的是解决有争议的开始Laramide orthopathy通过测试有关的起源和构造影响Laramide造山作用的南加州岩基的演化在CA的相互矛盾的假设。 八千五百万到七千万年前。美国科迪勒拉山脉发展的这一关键时期通常与南加州下方的浅板俯冲有关，这被认为是推动了从薄皮（塞维尔式）到厚皮（拉腊米德式）变形的转变。平板模型的一个关键问题是，该团队的初步地质年代学数据显示，南加州的Laramide造山带的启动在空间和时间上与假设发生平板俯冲的同一地区的岩浆爆发事件有关。这一矛盾使得拉拉米造山带与其他板块俯冲的地区不同，包括现代阿根廷的Sierras Pampeanas，其特征是岩浆间隙。为了解决这个问题，研究人员提出了一个多尺度的方法，侧重于南加州岩基的根源，并结合实地工作与各种国家的最先进的分析技术（铀铅地质年代学，铪和锇同位素地球化学，电子背散射衍射（EBSD）和显微结构分析，结构分析沿着连续断面）。这些数据将使研究人员能够将南加州岩基的岩浆活动与中低地壳深度的变形和板块运动学信息联系起来，以解决与平板范例和Laramide orthodons.This开始相关的冲突模型。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Understanding how the Rocky Mountains developed in the western United States is a problem of vital importance because they host precious mineral resources such as gold, lead, copper, and silver, which are important for our national economy. Many of these economic resources were brought to the surface along large faults which formed in the Late Cretaceous during a mountain building event, termed the Laramide orogeny. A key problem is that the timing and origin of the driving force behind this event and the formation of the Rocky Mountains are highly controversial and there is no consensus on the tectonic setting in which these mountains formed. The investigators hypothesize that the answer to understanding the origin of the Rocky Mountains and the Laramide orogeny lies in the San Gabriel Mountains of southern California. This region contains two important features which make it the focus of this study: (1) they preserve a complete temporal history of the Laramide orogeny from the earliest phase until its termination, which is important in reconstructing the driving force behind the event, and (2) they contain a unique section of the deep crust including a major ductile fault system that was active during the beginning of the Laramide orogeny. Analysis of these features will offer critical insights on the beginning of the Laramide orogeny, which will be essential in resolving conflicting hypotheses. The research plan for this project will involve 3 seasons of field work and data collection in the San Gabriel and nearby mountains. Laboratory analyses of rocks collected from the San Gabriel Mountains will consist of geochronology, geochemistry and microstructural work at the California State University Northridge Laser Ablation and LatinXellence in STEM Laboratories. The project will advance societal outcomes through innovative summer workshops, and an academic-year mentoring program termed, LA-ROCS, both of which are aimed at providing research experiences to underrepresented students at minority-serving institutions in southern California. These mentorship and research opportunities for undergraduate students will expose them to cutting-edge analytical research facilities and will aid in developing a diverse, globally competitive STEM workforce. This proposal aims to resolve the controversial beginnings of the Laramide orogeny by testing conflicting hypotheses about the origin and tectonic effects of Laramide orogenesis on the evolution of the Southern California batholith at ca. 85-70 million years ago. This critical period in the development of the U.S. Cordillera is commonly associated with shallow-slab subduction beneath Southern California, which is thought to have driven the transition from thin-skin (Sevier-style) to thick-skin (Laramide-style) deformation. A key problem with the flat-slab model is that the team's preliminary geochronology data show that the initiation of the Laramide orogeny in Southern California is spatially and temporally linked to a magmatic flare-up event in the same region where flat-slab subduction is postulated to have occurred. This contradiction makes the Laramide orogeny distinct from other areas of flat-slab subduction, including the modern-day Sierras Pampeanas in Argentina, which is characterized by a magmatic gap. To resolve this problem, the investigators propose a multiscale approach that focuses on the roots of the Southern California batholith and combines field work with a variety of state-of-the art analytical techniques (Uranium-Lead geochronology, Hafnium- and Osmium-isotope geochemistry, electron backscatter diffraction (EBSD) and microstructural analysis, structural analyses along continuous transects). These data will allow the investigators to link magmatism in the Southern California batholith with deformation and plate-kinematic information at mid-lower crustal depths to resolve conflicting models associated with the flat-slab paradigm and the initiation of the Laramide orogeny.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.