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

大峡谷地区切割和新构造运动测试模型：现场研究、新近纪玄武岩 Ar-Ar 测年、碎屑锆石和独居石

• 批准号: 0711546
• 负责人: Karl Karlstrom
• 金额: $ 16万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-15 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711546&HistoricalAwards=false
• 关键词: Testing; Models; Incision; Neotectonics; Grand

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.

定义大峡谷准确的切割历史可以为了解科罗拉多高原新构造隆升的幅度提供关键的缺失元素。该研究项目正在测试以下假设：在过去 600 万年中，通过新构造正断层的运动，大峡谷东部地块相对于科罗拉多河下游地块抬升了约 700-900 米。关于大峡谷雕刻的百年争议通过两个方面得到解决。该项目的第一部分旨在验证第四纪切口的断层阻尼模型，其中观察到的大峡谷离散河段的差异切口是通过由正常断层系统分隔的区域块体的相对垂直运动来解释的。对玄武岩流进行测年的战略活动，结合已测年流和未测年流之间的地球化学相关性，将验证科罗拉多河东部、西部和下游地块的假设相干块体行为，以及分隔它们的断层的滑移率和位移历史。恢复断层历史，结合准确的切割率，将能够使用现在和 550 万年前的古海平面作为参考层位，构建古河流剖面来评估地表隆起的程度。该项目的第二部分使用碎屑锆石和独居石对石英岩卵石进行测年来了解来源。石英石鹅卵石是该地区河流砾石中普遍存在的成分；将使用以下方法对它们进行指纹识别并与其来源地形联系起来：1）碎屑锆石年龄光谱，2）碎屑独居石成分，3）碎屑独居石年龄光谱，4）变质组合，以及5）痕量相地球化学特征。由于对美国西部元古代石英岩领域的了解不断增加，并且落基山物源地形中石英岩露头区域的数量有限，因此应该可以严格限制许多石英岩的来源区域。该项目将确定测年熔岩流下的砾石是否代表古科罗拉多河沉积物。自从约翰·韦斯利·鲍威尔 (John Wesley Powell) 大约 140 年前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。尽管经过近一个世纪的研究，人们对这些仍然知之甚少，并且仍然存在争议。该项目提出了一个新模型来解释大峡谷的切口，如果成功，有可能解决有关这个非常受欢迎的旅游目的地的长期争论。研究小组将继续努力通过大峡谷国家公园的“时间之痕”外展计划向公众宣传大峡谷的地质历史。