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

合作研究：RUI：奥乔科盆地的物源和古地磁分析：了解晚白垩世古地理的窗口

• 批准号: 1451035
• 负责人: Bernard Housen
• 金额: $ 9.75万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-01 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1451035&HistoricalAwards=false
• 关键词: Collaborative; Research; RUI; Provenance; Paleomagnetic

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.

由于中生代法拉隆板块倾斜俯冲到北美板块之下，北美大陆的西缘通过不同起源的不同构造地体的增生过程而发展起来。这一过程的结果是建议将增生的地体随着时间的推移向北移动到今天的位置。这一过程发生的程度以及拟议的转换时间和规模一直是地质学界多年来争论的焦点。这项研究的目标是利用独立技术的组合来解决这一长期存在的科学争议，其中包括使用同位素测年方法确定蓝山和俄勒冈州中东部相关地区晚白垩世沉积岩的来源，并结合分析这些岩石中包含的古地磁特征。来源分析将提供有关这些岩石与北美其他地方年龄相似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了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 名本科生和一名研究生，学习重要的 STEM 学科，并扩大地球科学领域代表性不足的群体的参与。学生将参与协作团队环境，这将帮助他们培养分析和解决问题的技能，使他们更有竞争力，并为在研究生课程和职业生涯中取得成功做好更好的准备；此类培训将有助于促进 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，主要研究人员及其学生将贡献信息，这些信息将与国家公园管理局约翰迪化石床国家纪念碑共享。研究结果将通过专业协会会议上的演讲和经过同行评审的科学文献进行传播；数据将被存档并通过基于网络的社区数据库提供。北美科迪勒拉边缘是通过整个中生代时期的地体增生而形成的，倾斜变形导致许多地体的右旋平移。关于拟议翻译的时间和规模的重大问题仍未解决，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。拟议的项目将通过研究俄勒冈州中东部蓝山的晚白垩世沉积岩，利用补充方法来解决其中一些问题。主要研究人员建议将详细的物源分析与对米切尔因利尔晚白垩世碎屑沉积岩和蓝山其他地方相关沉积岩的广泛古地磁分析相结合，以测试这些沉积岩是否是沉积在蓝山上的单一奥乔科盆地系统的一部分。山脉，或者如果米切尔内利尔是一个独立的弧前碎片，其构造历史与蓝山的其他部分和其他晚白垩世沉积物不同。如果在沉积过程中存在一个与蓝山相连的大型奥乔科盆地，那么我们对沉积岩的强大古地磁分析，结合详细的物源分析，将使用独立和互补的数据更好地限制奥乔科盆地和蓝山合并后的古纬度套。或者，我们的结果可能表明，米切尔内层和可能的较小沉积内层的子集在白垩纪时期与蓝山是分开的，要求米切尔和蓝山之间存在现在被覆盖的大规模断层系统，并且限制蓝山以东剪切带的右旋平移量。该研究将为这些白垩纪岩石的古纬度提供强有力的约束，并提供对现有构造模型的测试以及这些模型对 Ochoco 岩石、Hornbrook 组和其他白垩纪盆地之间潜在相关性的预测。该项目将通过结合层状沉积岩的物源和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学中关于地体平移的大小和时间的长期争论。蓝山地区的晚白垩世沉积岩提供了一个理想的机会，可以使用独立和互补的方法来测试针对蓝山和相关地体的古地理和构造亲和力提出的几种想法。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中的古地磁倾斜误差。最后，确定我们在这里提出的边缘盆地的良好约束的古地理将更好地使从给定盆地碎屑矿物热年代学中获得的隆起和剥蚀证据与北美科迪勒拉山脉内的特定位置联系起来，可能促进我们对北美科迪勒拉山脉的认识取得了重大进展。