Coupled Rapid Erosion and Foreland Sedimentation Control Orogenic Wedge Kinematics in the Himalayan Thrust Belt of Central Nepal
Coupled Rapid Erosion and Foreland Sedimentation Control Orogenic Wedge Kinematics in the Himalayan Thrust Belt of Central Nepal
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DOI：
10.1029/2020jb021256
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
P. DeCelles;B. Carrapa
中科院分区：
文献类型：
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作者：
P. DeCelles;B. Carrapa
上新世-全新世基岩快速折返、地形隆起的发育、季风降水的丰富、近端前陆盆地异常厚重的沉积、尼泊尔中部喜马拉雅造山楔两条最正面主要逆冲断裂上反极性凸起-折返对的发育之间的时空重合，为建立一个将这些不同现象联系起来并可在喜马拉雅前缘其他地区运行的模型提供了基础。纳拉亚尼河集水盆地的年轻(<；5 Ma)低温年代学年龄集中记录了基岩的快速侵蚀。在河流离开小喜马拉雅带的地方，主边界逆冲具有15公里的幅度折返性。在折返点的正南方坐落着∼50公里宽的奇特万楔顶盆地，它被主要前缘推力上的一个大凸起所限制。纳拉亚尼集水盆地的快速侵蚀和泥沙通量可能是由于尼泊尔中部这一地形凹陷地区异常强烈的季风降水造成的，导致前陆更大的挠曲沉降和表面沉积，这两者都增加了初始楔形锥度，使该地区更容易受到逆冲前锋异常向前传播的影响。对冲断带现代和后中新世锥度历史的分析表明，快速侵蚀阻碍了同时代主边界逆冲的向前传播，但同时在前陆产生了条件，最终将初始锥度提高到临界/超临界值，促进了主锋冲前的传播。这一分析对喜马拉雅地区破坏性较大的地震有一定的影响。
Spatial and temporal coincidence among rapid Pliocene‐Holocene bedrock exhumation, development of a topographic bight, abundant monsoonal precipitation, accumulation of anomalously thick proximal foreland basin deposits, and development of an opposite‐polarity salient‐reentrant couple on the two most frontal major thrust faults in the Himalayan orogenic wedge of central Nepal provide a basis for a model that links these diverse phenomena and could be operating in other parts of the frontal Himalaya. Rapid bedrock erosion is documented by a concentration of young (<5 Ma) low‐temperature thermochronologic ages in the Narayani River catchment basin. Where the river exits the Lesser Himalayan Zone, the Main Boundary thrust has a 15‐km‐amplitude reentrant. Directly south of the reentrant lies the ∼50 km wide Chitwan wedge‐top basin, which is confined by a large salient on the Main Frontal thrust. Rapid erosion and sediment flux out of the Narayani catchment basin, possibly due to anomalously intense monsoonal precipitation in this topographically depressed region of central Nepal, causes greater flexural subsidence and surface aggradation in the foreland, both of which increase initial wedge taper and render this region more susceptible to anomalous forward propagation of the thrust front. Analysis of the modern and post‐early Miocene taper history of the thrust belt suggests that rapid erosion hindered forward propagation of the contemporaneous Main Boundary thrust, but simultaneously produced conditions in the foreland that eventually elevated initial taper to a critical/supercritical value promoting forelandward propagation of the Main Frontal thrust. This analysis has implications for large damaging earthquakes in the Himalaya.