Collaborative Research: RUI: Provenance and Paleomagnetic Analysis of the Ochoco Basin: A Window into Late Cretaceous Paleogeography

北美大陆西缘是在中生代法拉龙板块斜向俯冲到北美板块之下，形成不同起源的构造体的增生过程中发育起来的。这一过程的一个结果是，人们提出将增生的地形向北迁移到它们现在的位置。这一过程发生的程度以及拟议的翻译时间和规模一直是一个持续的争议，已经与地质界争论了多年。这项研究的目标是解决这一长期存在的科学争议，使用独立的技术组合，包括确定来自蓝山和俄勒冈中东部相关地区的晚白垩世沉积岩的来源，使用同位素测年方法，结合分析这些岩石中包含的古地磁特征。物源分析将提供有关这些岩石与北美其他地方类似年龄的岩石的潜在起源的信息，而古地磁特征将提供有关这些岩石形成的古纬度的信息。这些数据将有助于更好地理解北美西部板块边缘的地质演化。除了拟议研究的研究目标外，该项目还有助于培训来自两所大学的10名本科生和一名重要STEM学科的研究生，并扩大代表性不足的群体在地球科学领域的参与。学生们将参与到一个协作的团队环境中，这将帮助他们培养分析和解决问题的能力，这将使他们在研究生课程和职业生涯中更具竞争力，并为取得成功做好更好的准备；此类培训将有助于STEM研究和教育方面的重要国家优先事项。研究结果将用于课堂课程，主要研究者和他们的学生将提供信息，这些信息将与国家公园管理局约翰·戴化石床国家纪念碑共享。研究结果将通过在专业学会会议上的发言和通过同行评议的科学文献传播；这些数据将存档并通过基于网络的社区数据库提供。整个中生代北美洲科迪勒拉边缘是通过地体增生发育起来的，其斜向变形导致许多地体向右平移。关于提出的平移时间和幅度的重要问题仍未解决，这些不确定性阻碍了对该边缘白垩纪古地理和构造历史的进一步了解。拟议中的项目将利用互补的方法，通过研究俄勒冈州中东部蓝山的晚白垩纪沉积岩来解决其中的一些问题。主要研究人员建议将详细的物源分析与广泛的古地磁分析结合起来，对米切尔英利尔的晚白垩世碎屑沉积岩和蓝山其他地方的相关沉积岩进行分析，以测试这些沉积岩是沉积在蓝山上的单一奥乔科盆地系统的一部分，还是米切尔英利尔是一个单独的弧前银块。它的构造历史与蓝山其他地区和其他晚白垩纪沉积物截然不同。如果在沉积过程中存在一个与蓝山相关联的大型Ochoco盆地，那么我们对沉积岩进行的强大的古地磁分析，结合详细的物源分析，将更好地利用独立和互补的数据集约束Ochoco盆地和蓝山相结合的古纬度。另外，我们的研究结果可能表明，在白垩纪时期，米切尔河和可能的一小部分较小的沉积河与蓝山分离，这要求米切尔河和蓝山之间存在现已覆盖的大型断层系统，并限制了蓝山以东剪切带的右平移量。这项研究将为这些白垩纪岩石的古纬度提供强有力的约束，并为现有的构造模型和这些模型的预测提供测试，这些模型与Ochoco岩石、Hornbrook组和其他白垩纪盆地之间的潜在相关性有关。该项目将通过结合物源和层状沉积岩的古地磁分析来重建晚白垩世古地理，直接解决科迪勒拉构造中关于地层平移幅度和时间的长期争论。蓝山地区晚白垩世沉积岩提供了一个理想的机会，可以用独立和互补的方法来检验关于蓝山及其相关地体的古地理和构造亲和性的几种观点。此外，获得的大型古地磁数据集将允许应用三种独立的方法来评估和校正含磁铁矿碎屑沉积物的古地磁倾角误差。最后，确定边缘盆地的良好约束古地理，如我们在这里提出的，将更好地使从给定盆地的碎屑矿物的热年代学中获得的隆起和剥蚀证据与北美科迪勒拉的特定位置联系起来，潜在地促进我们对北美科迪勒拉的理解取得关键进展。

The western margin of the North American continent developed through the process of accretion of distinct tectonic terranes of diverse origin due to the oblique subduction of the Farallon plate beneath the North American plate during the Mesozoic. A consequence of this process has been the proposed translation of accreted terranes northward through time to their present-day locations. The extent to which this process has occurred and the proposed timing and magnitude of translation has been an ongoing controversy that has been debated with the geologic community for many years. The goal of this research is address this long-standing scientific controversy using a combination of independent techniques that involve determining the provenance of Late Cretaceous sedimentary rocks from the Blue Mountains and related areas in east-central Oregon using isotopic dating methods, combined with analysis of the paleomagnetic signature contained within those rocks. The provenance analysis will contribute information regarding the potential origin of those rocks with those of similar age elsewhere in North America and the paleomagnetic signature will contribute information regarding the paleolatitude at which these rocks formed. These data will contribute to a better understanding of the geologic evolution of the western North American plate margin. In addition to the research objectives of the proposed study, the project is contributing to the training of ten undergraduate students from two universities and a graduate student in an important STEM discipline and the broadening of participation of underrepresented groups in the earth sciences. The students will be involved in a collaborative team environment that will help them develop analytical and problem solving skills that will make them more competitive for and better prepared to succeed in graduate programs and careers; such training will contribute to important national priorities in terms of STEM research and education. Results of the research will be used in classroom curricula, and the principal investigators and their students will contribute information that will be shared with the National Park Service John Day Fossil Beds National Monument. Results of the research will be disseminated through presentations at professional society meetings and through the peer-reviewed scientific literature; the data will be archived and made available through web-based community databases.The North American Cordilleran margin developed through terrane accretion throughout Mesozoic time, with oblique deformation resulting in dextral translation of many terranes. Significant questions regarding the timing and magnitude of proposed translation remain unresolved, and these uncertainties hinder further understanding of the Cretaceous paleogeography and tectonic history of this margin. The proposed project will utilize complimentary approaches to address some of these questions through study of Late Cretaceous sedimentary rocks of the Blue Mountains in east-central Oregon. The principal investigators propose to integrate detailed provenance analysis with extensive paleomagnetic analysis of Late Cretaceous clastic sedimentary rocks of the Mitchell Inlier and related sedimentary rocks elsewhere in the Blue Mountains to test if these sedimentary rocks were part of a single Ochoco basin system deposited on the Blue Mountains, or if the Mitchell Inlier was a separate forearc sliver, with a tectonic history distinct from the rest of the Blue Mountains and other Late Cretaceous sediments. If there was one large Ochoco basin that was linked to the Blue Mountains during deposition, then our robust paleomagnetic analysis of sedimentary rocks, combined with detailed provenance analysis, will better constrain the paleolatitude of the combined Ochoco basin and Blue Mountains using independent and complimentary data sets. Alternatively, our results may suggest that the Mitchell Inlier and possibly a subset of smaller sedimentary inliers were separate from the Blue Mountains during Cretaceous time, requiring the presence of now-covered large-scale fault system(s) between Mitchell and the Blue Mountains and limiting the amount of dextral translation accommodated on shear zones east of the Blue Mountains. The study will provide robust constraints on the paleolatitude of these Cretaceous rocks, and also provide a test of existing tectonic models and the predictions of these models with respect to potential correlations between Ochoco rocks, the Hornbrook Formation, and other Cretaceous basins. The project will directly address a long-standing debate in Cordilleran tectonics regarding the magnitude and timing of terrane translation by combining provenance and paleomagnetic analysis of well-bedded sedimentary rocks to reconstruct Late Cretaceous paleogeography. The Late Cretaceous sedimentary rocks in the Blue Mountains region provide an ideal opportunity to test several ideas proposed for the paleogeography and tectonic affinity of the Blue Mountains and related terranes using independent and complimentary methods. Furthermore, the large paleomagnetic dataset obtained will allow the application of three independent methods for evaluation and correction for paleomagnetic inclination error in magnetite-bearing clastic sediments. Finally, determining the well-constrained paleogeography of marginal basins such as we propose here will better enable the evidence of uplift and denudation obtained from thermochronology of detrital minerals of a given basin to be tied to a specific location within the North American Cordillera, potentially fostering critical advances in our understanding of the North American Cordillera.