Formation of the Grand Canyon 5 to 6 million years ago through integration of older palaeocanyons
Formation of the Grand Canyon 5 to 6 million years ago through integration of older palaeocanyons
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DOI：
10.1038/ngeo2065
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发表时间：
2014-03-01
影响因子：
18.3
通讯作者：
Shuster, David L.
中科院分区：
文献类型：
--
作者：
Karlstrom, Karl E.;Lee, John P.;Shuster, David L.
关于美国大峡谷形成的时间，人们一直争论不休。在一个视图中，大部分的峡谷是雕刻的科罗拉多河相对较近，在过去的5-6百万年。或者，大峡谷可能早在7000万至5500万年前就被同一地点的前体河流切割到其现代深度的200米以内。在这里，我们调查的形成时间的大峡谷的五个部分中的四个，使用磷灰石裂变径迹测年，径迹长度测量和磷灰石氦测年：如果任何部分是年轻的，旧的峡谷的假设是伪造的。我们重建了从现代峡谷基地和邻近的峡谷边缘1,500米以上的样品的热历史，以限制当岩石冷却作为峡谷切口的结果。我们发现三个中间部分中的两个，飓风部分和东部大峡谷，分别形成于7000万至5000万年前和2500万至1500万年前。然而，大理石峡谷和最西端的大峡谷这两个末端部分都很年轻，是在过去的500 - 600万年中雕刻出来的。因此，尽管峡谷的部分地区是古老的，我们的结论是，科罗拉多河通过更古老的古峡谷的整合雕刻了大峡谷，开始于5-6百万年前。
The timing of formation of the Grand Canyon, USA, is vigorously debated. In one view, most of the canyon was carved by the Colorado River relatively recently, in the past 5-6 million years. Alternatively, the Grand Canyon could have been cut by precursor rivers in the same location and to within about 200 m of its modern depth as early as 70-55 million years ago. Here we investigate the time of formation of four out of five segments of the Grand Canyon, using apatite fission-track dating, track-length measurements and apatite helium dating: if any segment is young, the old canyon hypothesis is falsified. We reconstruct the thermal histories of samples taken from the modern canyon base and the adjacent canyon rim 1,500 m above, to constrain when the rocks cooled as a result of canyon incision. We find that two of the three middle segments, the Hurricane segment and the Eastern Grand Canyon, formed between 70 and 50 million years ago and between 25 and 15 million years ago, respectively. However, the two end segments, the Marble Canyon and the Westernmost Grand Canyon, are both young and were carved in the past 5-6 million years. Thus, although parts of the canyon are old, we conclude that the integration of the Colorado River through older palaeocanyons carved the Grand Canyon, beginning 5-6 million years ago.