Late Quaternary and present‐day rates of slip along the Altyn Tagh Fault, northern margin of the Tibetan Plateau
Late Quaternary and present‐day rates of slip along the Altyn Tagh Fault, northern margin of the Tibetan Plateau
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DOI：
10.1029/2006tc002014
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发表时间：
2007-10
期刊：
影响因子：
4.2
通讯作者：
Peizhen Zhang;P. Molnar;Xi-wei Xu
中科院分区：
文献类型：
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作者：
Peizhen Zhang;P. Molnar;Xi-wei Xu
全球定位系统（GPS）的测量和晚第四纪断层的研究都与沿阿尔金断层中段沿着10 mm/年的滑动速率以及该速率向断层东端的系统性降低相一致。横向偏移阶地上方和下方的阶地的日期产生第四纪滑动速率的界限，范围从那些同意GPS测量的值快三倍。我们认为，受地形上游的保护，他们的错置阶地更密切的年龄比由较低的阶地的上部阶地。在某些情况下，断层上游的山谷被切割成基岩，山谷内几乎看不到阶地。这些溪流流入冲积的洪泛平原或扇，这些洪泛平原或扇可能在气候变化期间被切割，以形成阶地。阶地断层随后发生位移，使其位于断层上游基岩脊的下坡处，从而保护阶地断层不受进一步切割。在这种情况下，上层阶地的年代应该比下层阶地的年代更接近白垩纪的年代。这样的日期产生的滑动速率为100毫米/年的断层的中心部分和减少率向东。虽然我们不能肯定地排除较高的滑动率沿阿尔金山断层沿着，我们的分析确实表明，可行的解释与GPS测量一致的可能性更大，至少沿着断层的某些部分。这些速率不仅支持了青藏高原内部变形是由浅层脆性地壳中分布的断层网络上的滑动引起的，因此在深度上表现为连续体的观点，而且向东逐渐减小的速率也表明阿尔金断层并没有将两个有效刚性的岩石圈板块分开。相应地，相对较低的滑动速率和向东减小的滑动速率表明，阿尔金断裂并没有将印度和亚洲之间的大部分会聚转移到青藏高原的东北挤出。因此，在印度进入欧亚大陆的道路上，地壳物质的大规模挤压似乎主要限于青藏高原的范围。
Both Global Positioning System (GPS) measurements and studies of Late Quaternary faulting are consistent with a slip rate of ∼10 mm/yr along the central segment of the Altyn Tagh Fault and a systematic decrease in that rate toward the eastern end of the fault. Dates of terraces above and below laterally offset terrace risers yield bounds on Quaternary slip rates that range from those that agree with GPS measurements to values as much as three times faster. We argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace. In some cases, valleys upstream of the fault have been incised into bedrock, and few if any terrace risers can be seen within the valleys. Such streams debouch onto alluviated floodplains or fans that become incised, presumably during climate changes, to create terrace risers. The terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault, and thus the risers become protected from further incision. In such cases, dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces. Such dates yield slip rates of ∼10 mm/yr in the central segment of the fault and decreasing rates eastward. Although we cannot with certainty rule out the higher slip rates along the Altyn Tagh Fault, our analysis does show that viable interpretations consistent with GPS measurements are more likely, at least along some segments of the fault. Not only do these rates support the view that the Tibetan Plateau deforms internally by slip on a distributed network of faults in the shallow brittle crust, and hence behaves as a continuum at depth, but the gradual decrease toward the east also shows that the Altyn Tagh Fault does not separate two effectively rigid lithospheric plates. Correspondingly, the relatively low slip rate and the eastward decrease in slip rate suggest that the Altyn Tagh Fault does not transfer a significant portion of the convergence between India and Asia into northeastward extrusion of the Tibetan Plateau. Thus, large‐scale extrusion of crustal material in India's path into Eurasia seems to be limited largely to the confines of the Tibetan Plateau.