Landscape Spatial-Temporal Evolution And Ecological

Longmen orogenic belt, known as the “Geological Bermuda" to the geologists,develop various nappes and klippe and attract attentions of geologists from all overthe world. After hard researches, remarkable fruits of Longmen mountain geologicalstructures were achieved. However, major geological problems were still in suspense,such as, the nature of Longmen mountain nappe structure, its genetic mechanism andevolution. Based on the detailed researches on the thrusting nappe structure geometrycharacteristics, propagation and evolution processes, and klippe structure in Sandui ofnorthern segment of Longmen Mountain, some new achievements are reached.Based on the geologic investigation, remote sensing image, geomorphic features,the nappes in Sandui Area can be divided into five types from northwest to southeast:(I)Lishuba ductile nappe rock slices,(II)Zhaojiagou-Chenjiashan brittle ductile napperock slices,(III)Qilixiang-Xiejiagou nappe,(IV)Shishanzi nappe rock slices and(VI)Longdongpo-Songlingpo nappe. After a detail investigation or measurement ofsliding face features, fault nature, inner geometry characteristics, compositions,deformation and metamorphic characteristics, microstructures and foliations, weconclude their kinematics and dynamics. According to their distributions and tectonicfeatures, three klippes were named:(一) Lianhuashi klippe group,(二)Sanmenyaklippe group,(三)Wujiaping klippe group. Internal textures, fault structures, stackedrelationships and the underlying systems of klippes were described, and theirmechanisms, evolution and formation time were analyzed.Nappes in Sandui Region propagate in direction of NE-SW, and their mainsliding surfaces are reverse faults inclining NW, in the way of laminated tiles. Theirformation strength decrease from NE to NE, changing from ductileâ†'brittle ductileâ†'brittle, and reverse closed folds in the nappes were changed to leniency upright folds. All of these suggested that deformation strength gradually decreased anddeformation level shoaled.The evolution processes of nappes in Sandui Region can be divided into threestages:â‘ i n early Indosinian, Longmen mountains is the"Piggyback Type" expansionand the central fault (F2) and the front range fault (F5) formed with a giant nappe slipsurface.â‘¡in late Indosinian, during the process of forward extrusion, the nappe frontwas stopped by the Jurassic clastic rock and front range fault (F5)formed(Longdongpo-Songlin fault).â‘¢in the Yanshan and Himalayan era, a series offolds and secondary imbricate thrust fault formed inner the giant nappet, andShizishanfault (F4) and Xiejiagou fault (F3) formed. Secondary nappes formed in heway of poststressed imbricate fan. In the late stage of nappe extrusion process, thecentral fault (F2) was reactivated and Chenjiashan fault (F2) formed. Finally, Lishubafault (F1) replaced Chenjiashan fault (F2) to be the central fault and are still active.Klippe formed during the nappe process from Northwest to southeast. Root ofthe lower klippe, composed of Cambrian strata, is located in Qilixiang-Songlinpothrust nappe. The lower klippe formed a much earlier than the upper klippe, may be inearly Himalayan. Root of the upper klippe, composed of Silurian strata, is covered byLishuaba thrust nappe. The upper klippe is synchronic to foreland molasse (Dayiconglomerate) accumulation, which is Pliocene-early Pleistocene.Based on the formation process of the nappe in Sandui Area of northernLongmen Mountian, it is clear that in the early stage, the nappe was Piggyback Type.In the later stage, the nappes front was blocked and its inner were deformed to befaults. The new nappe covered the old ones, exhibiting to be poststressed imbricatefan. The klippes provided strong evidence for the poststressed imbricate type.