Testing Models for Incision and Neotectonics of the Grand Canyon Region: Field Studies, Ar-Ar Dating of Neogene Basalts, and Detrital Zircon and Monazite

确定大峡谷的准确切割历史可以为理解科罗拉多高原新构造隆起的规模提供关键的缺失元素。这项研究项目正在验证这样的假设，即在过去的600万年里，通过新构造正断层的运动，东部大峡谷地块相对于科罗拉多河下游地块上升了约700-900米。关于大峡谷雕刻的百年争议通过两个方面来解决。项目的第一部分旨在验证第四系切割断层阻尼型模型，在该模型中，大峡谷离散河段观测到的差异切割是由正断层系统隔开的区域地块的相对垂直运动解释的。对玄武岩流动进行定年的战略活动，结合确定日期的流动和未确定日期的流动之间的地球化学对比，将验证东部、西部和科罗拉多河下游地块的假设一致的块体行为，以及分隔它们的断层的滑动速率和位移历史。断层历史的恢复，结合准确的切割速率，将允许建立古河流剖面，以现代和550万年前的古海平面作为参考层位来评估地表抬升的程度。该项目的第二部分使用碎屑锆石和独居石测年来了解石英岩鹅卵石的来源。石英岩鹅卵石是该地区河流砾石中普遍存在的成分；它们将被指纹识别，并与其来源地形联系起来，使用以下方法：1)碎屑锆石年龄谱，2)碎屑独居石组成，3)碎屑独居石年龄谱，4)变质组合，5)痕量相地球化学特征。由于对美国西部元古界石英岩领域的认识不断增加，而落基山脉源区中石英岩露头地区的数量有限，因此应该有可能严格限制许多石英岩的源区。该项目将确定熔岩流下面的砾石是否代表古科罗拉多河沉积。自近140年前约翰·韦斯利·鲍威尔首次探险科罗拉多河以来，大峡谷的切割和科罗拉多高原的隆起一直引起地球科学家和公众的兴趣。尽管进行了近一个世纪的研究，但人们对这些问题仍然知之甚少，也仍然存在争议。这个项目提供了一个新的模型来解释大峡谷的切割，如果成功，有可能解决关于这个非常受欢迎的旅游目的地的长期争论。研究团队将继续努力，通过大峡谷国家公园的时间之路推广计划，教育公众了解大峡谷的地质历史。

Defining an accurate incision history for Grand Canyon can provide the critical missing element for understanding the magnitude of neotectonic uplift of the Colorado Plateau. This research project is testing the hypothesis that the eastern Grand Canyon block has been uplifted approximately 700-900 meters relative to the lower Colorado River block in the last 6 million years through movement on neotectonic normal faults. The century-old controversy about carving of Grand Canyon is addressed through a two-fold approach. The first part of the project aims to verify the fault-dampened model for Quaternary incision in which the observed differential incision in discrete river reaches of Grand Canyon is explained by relative vertical movement of regional blocks, separated by normal fault systems. A strategic campaign of dating of basalt flows, combined with geochemical correlations between dated flows and undated flows will verify the hypothesized coherent block behavior of eastern, western, and lower Colorado River blocks as well as the slip rates and displacement history of the faults that separate them. Restoration of faulting history, combined with accurate incision rates, will allow paleo river profiles to be constructed to evaluate the extent of surface uplift, using present and 5.5 million year old paleo-sea level as reference horizons. The second part of the project uses detrital zircon and monazite dating of quartzite cobbles to understand provenance. Quartzite cobbles are ubiquitous components of river gravels in this region; they will be fingerprinted and linked to their source terrain using: 1) detrital zircon age spectra, 2) compositions of detrital monazite, 3) detrital monazite age spectra, 4) metamorphic assemblages, and 5) trace phase geochemical characteristics. Because of the increasing knowledge of Proterozoic quartzite domains in the western U.S., and the limited number of quartzite outcrop areas in the Rocky Mountain provenance terrains, it should be possible to tightly constrain the source regions of many. The project will establish whether the gravels beneath dated lava flows represent paleo-Colorado River deposits.The incision of the Grand Canyon and the uplift of the Colorado Plateau have been of interest to earth scientists and the public ever since John Wesley Powell's first expedition of the Colorado River almost 140 years ago. Despite nearly a century of research, these are still poorly understood and remain controversial. This project poses a new model to explain the incision of the Grand Canyon and, if successful, has the potential to resolve long-standing debates about this very popular tourist destination. The research team will continue efforts to educate the public about the geological history of the Grand Canyon through the Trail of Time outreach program at the Grand Canyon National Park.