Collaborative Research: Differentiating Between Lithologic and Baselevel Controls on River Profiles: Canyons of the Colorado Plateau

合作研究：区分河流剖面的岩性和基准面控制：科罗拉多高原的峡谷

• 批准号: 1324627
• 负责人: Brian Clarke
• 金额: $ 2.55万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1324627&HistoricalAwards=false
• 关键词: Collaborative; Research; Differentiating; Between; Lithologic; Collaborative; Research; Differentiating; Between; Lithologic

The Grand Canyon is an iconic but enigmatic landform. For over a hundred years geologists have puzzled over the mystery of how and when the canyon was carved. Much new data has come to light recently, but the mystery has only deepened: some evidence points to a geologically recent canyon (carved in the last 6 million years) but some new evidence points to a much older history, with parts of the canyon dating back some 70 million years to when dinosaurs still walked the Earth. The debate has become intense and public interest is at an all-time high given the many visitors to the Grand Canyon National Park and the fact that most introductory Earth science classes from middle school through university involve some mention of the Grand Canyon. We bring a new, complementary, approach to this old problem. Dramatic, sharply defined canyons can result from either acceleration in river incision rate (the young canyon hypothesis) or river incision into stronger rocks (the old canyon hypothesis). Either is plausible given presently available data. Fortunately these alternative scenarios are dramatically different in one key regard: whereas in the young canyon hypothesis erosion rates within the canyon are much greater than in the surrounding landscape, in the old canyon hypothesis erosion rates in the canyon should be similar to, or even less than, erosion rates in the surroundings. We will use a relatively new method to measure erosion rates averaged over millennial timescales in key localities within and around the Grand Canyon: the concentration of isotopes produced by exposure of rocks to cosmic rays in river sediments and on river terraces provides a measure of how long rocks and sediment has spent at or near the Earth's surface, and thus allows a quantitative estimate of erosion rates. In addition we will study the strength of rock units within and surrounding the Grand Canyon to assess how much of the canyon's form can be explained by variations in rock strength alone. We anticipate that our results will be incorporated into materials at Grand Canyon National Park and into Earth science lesson plans across the country.We address three fundamental problems of broad interest to Geologists and Geomorphologists: (1) the role of lithology in river incision and landscape evolution in general, (2) how lithologic variability affects, and limits, our ability to interpret river incision history from study of landforms and (3) the controversial incision history of river canyons in the Colorado Plateau. Despite the fundamental, and long-recognized, importance of lithology in landscape evolution, it has received little attention in the quantitative studies of landscape evolution in recent decades. Partly this is because we have lacked the ability to quantitatively measure rock strength at the process scale and partly because until recently we lacked firm theory to relate rock properties to river incision processes; limitations that can now be overcome. We draw on and extend recent advances in using shallow seismic refraction surveys to estimate rock mass quality at the process scale, allowing us to account for the extent of rock fracture in estimates of erosional susceptibility. Thus we will contribute both to understanding of the controls on river incision into rock (which is at the heart of the interrelations among climate, tectonics, and topography) and to resolving the controversy over the age and origin of the Grand Canyon.

大峡谷是一个标志性但神秘的地形。一百多年来，地质学家一直困扰着峡谷的雕刻方式和何时雕刻的奥秘。最近有许多新数据已经曝光，但是这个谜团只加深了：一些证据表明，最近的峡谷（在过去600万年中雕刻），但一些新的证据表明，峡谷的一部分历史可以追溯到7000万年，直到恐龙仍在地球上行走。鉴于大峡谷国家公园的许多游客，辩论已经变得激烈，公众的兴趣处于历史最高水平，而且从中学到大学的大多数介绍性地球科学课程都提到了大峡谷。我们为这个旧问题带来了一种新的，互补的方法。巨大的，明确的峡谷可能是由于河流切口率（年轻的峡谷假设）或河流切口到更强的岩石（旧峡谷假设）而造成的。当前可用的数据给定数据是合理的。幸运的是，这些替代方案在一个关键方面截然不同：而在年轻的峡谷假设侵蚀率中，峡谷内的侵蚀速率远大于周围的景观中，而在旧的峡谷假设侵蚀速率中，峡谷中的假设侵蚀速率应与周围的损害率相似，甚至小于周围的侵蚀率。我们将使用一种相对较新的方法来测量大峡谷内部及其周围关键地区的千禧年时间标准的侵蚀率：通过暴露于岩石在河流沉积物中和河水露台上的宇宙射线产生的同位素的浓度，可以在地面上或在地面上花费多长时间的岩石和泥沙，从而允许数量率，并允许数量估算。此外，我们将研究大峡谷内外岩石单元的强度，以评估仅岩石强度的变化可以解释峡谷的多少。我们预计，我们的结果将被纳入大峡谷国家公园的材料中，并在全国范围内纳入地球科学课程。我们解决了三个基本兴趣的基本问题，地质学家和地貌学家：（1）岩性在河流切口和景观进化中的作用一般而言，（2）岩性可变性如何影响岩性的河流，研究河流的历史和研究历史（3）河流的历史（3）河流的历史（3）。科罗拉多高原的峡谷。尽管岩性在景观演化中的基本和长期认识的重要性，但在近几十年来，它在景观演化的定量研究中几乎没有关注。部分原因是我们缺乏在过程量表上定量测量岩石强度的能力，部分是因为直到最近我们还缺乏将岩石特性与河流切口过程联系起来的坚定理论。现在可以克服的局限性。我们利用并扩展了使用浅层地震折射调查在过程量表上估算岩石质量的最新进展，从而使我们可以考虑岩石骨折的程度，以估计侵蚀性易感性。因此，我们将既有助于理解河流切口的控制岩石的控制（这是气候，构造和地形之间相互关系的核心），并解决了大峡谷年龄和起源的争议。