Dissected Hydrologic System at Grand Canyon: Interaction Between Upper and Lower World Waters in Modern Springs and Ancient Travertines

大峡谷水文系统剖析：现代泉水和古代石灰华中上层和下层世界水域之间的相互作用

• 批准号: 0310323
• 负责人: Laura Crossey
• 金额: $ 13.77万
• 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: 2003
• 资助国家: 美国
• 起止时间: 2003-09-01 至 2007-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310323&HistoricalAwards=false
• 关键词: Dissected; Hydrologic; System; Grand; Canyon

Crossy0310323 The spectacular landscape at Grand Canyon provides a unique view of a deeply dissected (1-2 km deep) aquifer system. Active springs and Quaternary travertines provide key data for understanding the hydrochemistry of the Colorado Plateau, as well as a record for understanding how this system has evolved and interacted with Quaternary canyon incision. Our preliminary data suggest the modern and ancient travertine-depositing springs, and the Colorado River itself, record a "tale of two waters": a mixing of deeply-circulated waters rising along faults with surface- and groundwaters of the plateau. We propose to combine mapping, water and gas analysis, and travertine geochemistry to test this model. Travertine occurs where major spring-producing horizons (such as the Muav Limestone-Bright Angel Shale contact) intersect Laramide and Precambrian basement-penetrating faults. We suggest on the basis of a pilot study of spring water chemistry and gas analysis that large volumes of travertine are produced from deep saline waters that are rich in CO2 and higher in 87Sr/86Sr than waters derived from the plateau aquifers. Spring waters in two travertine-forming localities record high He/Ar and He/N2, and 3He/4He ratios of 0.15 Ra suggesting contributions of mantle-derived He and its carrier gas CO2 potentially from nearby coeval volcanic fields. 87Sr/86Sr in central Grand Canyon springs ranges from 0.710 to 0.735 and we will test whether radiogenic Sr contributed by deeply-circulated waters can account for previously observed increases in Colorado River 87Sr/86Sr between Lee's Ferry and Lake Mead. Broader scientific impacts of the work extend to the longer-term (Plio-Pleistocene) record of the Colorado Plateau: we propose that the radiogenic Hualapai Limestone (~5 Ma) in the Grand Wash trough was formed by spring waters similar to those seen in today's travertine localities (87Sr/86Sr of Grand Canyon travertine is comparable to values reported for the Hualapai Ls.). Rapid travertine deposition in selected localities has also caused pervasive cementation and preservation of Quaternary terrace sequences and this allows direct U-series dating of aggradation events and calculation of incision rates. Dating so far suggests that major pulses of travertine accumulation occurred over the last 350 ka. Previous workers suggested that travertine growth episodes correspond with glacial events/ regional wetness. However, modern spring discharge variations correspond to microseismicity, suggesting that seismicity/volcanism influence the movements of deep water up faults. The travertine record, combined with spring water chemistry and geochemical analysis will provide a quantitative understanding of both the Quaternary history and evolving hydrologic system of the region.

在大峡谷的壮观景观提供了一个深刻的解剖（1-2公里深）含水层系统的独特看法。活跃的泉水和第四纪古岩溶为了解科罗拉多高原的水化学提供了关键数据，也为了解该系统如何演变和与第四纪峡谷切口相互作用提供了记录。我们的初步数据表明，现代和古代的沉积有白藜芦醇的泉水，以及科罗拉多河本身，记录了一个“两种沃茨的故事”：沿着断层上升的深层循环沃茨与高原的地表和地下沃茨混合。建议将联合收割机填图、水和气分析、岩石地球化学等方法结合起来进行验证。 钙华出现在主要产泉层（如Muav石灰岩-Bright Angel页岩接触）与Laramide和前寒武纪基底穿透断层相交的地方。 我们建议的基础上的泉水化学和气体分析的试点研究，大量的钙钛矿产生于深盐水沃茨，富含CO2和更高的87 Sr/86 Sr比沃茨来自高原含水层。在两个榴辉岩形成地点的泉水沃茨记录高的He/Ar和He/N2，和3 He/4 He比值为0.15 Ra，这表明幔源He及其载气CO2的贡献可能来自附近的同时代火山场。大峡谷中部泉水中的87 Sr/86 Sr的范围从0.710到0.735，我们将测试深层循环的沃茨所贡献的放射性Sr是否可以解释先前观察到的科罗拉多河87 Sr/86 Sr在李氏渡口和米德湖之间的增加。 更广泛的科学影响的工作延伸到长期（上新世-更新世）记录的科罗拉多高原：我们建议，放射性华拉派石灰岩（~5马）在大洗槽形成的泉水沃茨类似于今天看到的古陆地区（87 Sr/86 Sr的大峡谷古陆是报告的值为华拉派Ls。）。在选定的地区，快速的钙钛矿沉积也引起了广泛的胶结作用和第四纪阶地序列的保存，这使得直接的U系列定年的加积事件和计算切割率。 迄今为止的测年表明，主要脉冲的钙钛矿积累发生在过去的350 ka。以前的工作者认为，南极洲的生长事件与冰川事件/区域湿度相对应。然而，现代泉水流量变化对应于微震活动，这表明地震/火山活动影响深水断层的运动。结合泉水化学和地球化学分析，第四纪记录将为该地区的第四纪历史和水文系统的演变提供定量的了解。