【作者】 王平；

【导师】 刘少峰；

【作者基本信息】 中国地质大学（北京） ， 资源与环境遥感， 2010， 博士

【摘要】 四川盆地东部现今的构造活动并不明显,然而新生代以来却遭受强烈的侵蚀/剥蚀,以至于几乎没有保留下任何新生代沉积地层。中生代时期来自雪峰山和大巴山两个方向的逆冲作用奠定了四川盆地东部的构造地貌基本格局。新生代时期长江及其庞大的支流水系构成了主要的河流侵蚀系统,直接决定了四川盆地东部的地貌演化。本论文首先分析了川东-雪峰褶皱逆冲带的弧形构造成因,而后转入对长江中游袭夺-反向和流域地貌演化的研究。与世界范围内弧形褶皱逆冲带6种基本的构造形迹样式相比较发现,川东-雪峰褶皱逆冲带北翼和南翼具有不对称的收敛样式,构造形迹几何样式和后缘典型的叠加褶皱暗示了川东-雪峰褶皱逆冲带存在两期构造变形。早期与南大巴山褶皱逆冲带构成了同时期不同方向的“双弧”联合构造体系。受南大巴山NE-SW向构造的限制作用,川东-雪峰弧形褶皱逆冲带在其北翼(开县至五峰一带)形成了大曲度的弧形褶皱。二维弹性有限元数值模拟进一步验证了这一联合构造变形样式。大约早白垩世晚期南大巴山逆冲作用逐渐停止,川东-雪峰褶皱逆冲带脱离了南大巴山的限制,在北翼后缘地区(齐岳山至五峰一带)形成了小曲度的弧形褶皱,并叠加于早期大曲度弧形褶皱之上。与此同时川东-雪峰褶皱逆冲带前缘则继续向盆地内部扩展,在华蓥山一带形成了直线型褶皱。四川盆地东部的地形起伏度分析表明长江中游(川江)水系的河流侵蚀作用控制了区域地形起伏度的变化。地形条带剖面和河道缓冲区剖面反映了川江干流重庆-宜昌河段流向与区域地形梯度之间的逆向关系。通过计算川江干流上游汇水盆地面积、河道距离和支流汇入角度,并依据河流发育的基本规律,进一步判断并揭示了川江在四川盆地东部的袭夺-反向过程。古长江西支为E→W流向,古长江东支W→E流向,二者的分水岭位于奉节(齐岳山)一带。新生代江汉-洞庭盆地的快速沉降促使古长江东支向源扩张并逐渐向西开始袭夺奉节以西的古长江西支。由于侵蚀速率和基准面的差异,原本E→W流向的古长江西支通过分水岭迁移的方式逐渐反向,同时袭夺了四川盆地内部的支流水系。对川江重庆-宜昌河段33个旁侧支流汇水盆地的地貌特征分析,揭示了汇水盆地侵蚀程度的空间分布规律。对比川江上段(重庆-涪陵)、中段(涪陵-奉节)和下段(奉节-宜昌)5个汇水盆地的河道纵剖面,并结合河道剖面演化数值模拟分析了裂点迁移模式和暂时地貌状态的成因。结果表明川江干流的袭夺-反向过程造就了其旁侧支流汇水盆地不同形式的河流侵蚀地貌。干流河道的侵蚀脉冲造成局部基准面下降,迫使支流河道向着新的平衡状态调整或直接袭夺了支流水系。川江下段支流汇水盆地最先调整,现今河道剖面已经调整到新的平衡稳定状态。川江中段和上段支流水系先后以被袭夺的方式进入川江干流,汇水盆地内河道均处于暂时地貌调整状态,岩性结构决定了裂点波形的样式和分布规律。更多还原

【Abstract】 The landscape in eastern Sichuan Basin does not show tectonically active, but theMesozoic bedrock suffered from intensive erosion/denudation, and very few Cenozoicdeposit remained even in low-relief area. Two Mesozoic arc-shape fold thrust belts,Western Xuefengshan and Southern Dabashan, build the original margins of easternSichuan Basin. Modern river system, made up of Yangtze river and its large tributaries,dominate the landscape evolution as erosion agency. This thesis focus on the two sub-jects, one is the formation of the western Xuefengshan salient, the other is the captureand reversal of the Middle Yangtze river and the ?uvial landscape evolution in easternSichuan Basin.Compared with classical trend-line patterns of the salients worldwide, the westernXuefengshan salient shows asymmetry of the two limbs. The northern limb includelarge-scale NE-trending curved folds and converge with the SE-trending curved fold ofthe southern Dabashan. While the southern limb protrude further than the northern limbwithout large-scale curved folds. Also in the northern limb zone are many superposedfolds, which indicate the at least two phase compression of the western Xuefengshansalient. In Phase I (properly from Middle or Late Jurassic to Early Cretaceous), thethrusts of both western Xuefengshan and southern Dabashan compose a conjunct struc-tural system with large-scale arc-shape folds. The conjunct structural process is alsosupported by 2D elastic finite element model using ABAQUSTM. In Phase II (properlyin late Early Cretaceous or Late Cretaceous), the southern Dabashan became tectonicquiescence while the western Xuefengshan still propagated westwardly. Subsequentthrusting lead to straight folds near HuaYing Shan and small-scale curved folds super-posing on the first deformation west of QiYue Shan.The local relief of the eastern Sichuan Basin are mostly controlled by bedrock ero-sion of the Middle Yangtze river system. Lithology and original tectonic topographyalso in?uence the distribution of the local relief. From Chongqing to Yichang, revealedby swath profiles and river buffer profile, the Middle Yangtze stem ?ow reversely to thetopography gradient. Based on Hack’s law, the logarithm relationship of the drainage area and distance suggests the continuous capture events in Middle Yangtze stem. Thecon?uence angle of the tributaries also suggests the main stem was captured and re-versed in upper reach of the Middle Yangtze river. The Paleo-Yangtze river had twobranches divide by QiYue Shan near Fengjie, the west branch ?owing westwardly andthe east branch ?owing eastwardly. Driving by the increased rate of distal base-level fallof the Jianghan-Dongting basin, the east branch grew headward and captured the westbranch gradually. The mean normal steepness index (ksn), minimal erosion volume inunit area (Rva) and mean slope angle ( Sˉ) are calculated in 33 side-tributary basins ofthe Middle Yangtze River. The three parameters quantitatively re?ect that the erosionincrease gradually along the Middle Yangtze stem from Chongqing to Yichang. Thelongitude profiles in five side-tributary basins with Jurassic substrate are also extractedand analyzed using detachment-limited erosion model. Most profiles are characterizedby knickpoints in side-tributary basins of the upper and middle reaches of the MiddleYangtze river. However, in side-tributary basins of the lower reach the profiles show noknickpoints. As the reversal of the Middle Yangtze stem caused by the incision pulsefrom distal base-level fall, the tributaries will also respond to the base-level fall in themain stem. Thus the tributaries will adjust toward a new equilibrium state, or be cap-tured to the main stem. The tributaries in the middle and upper reaches were capturedsuccessively, and now in the transient state adjusting to the new base-level. The stylesof the knickpoints mainly depend on the structure of the substrate and lithologies.更多还原