| This thesis studies the regional geological background, depositional environment and sedimentary facies, and tracks the tectonic environment of the sediment sources, evolution of magmatite-structure, structural form, deformation feature, and structural feature of the foreland thrust belt in the transitional zone from southeast margin of Simao basin to Ailaoshan orogenic belt. Accordingly, the coupling process and geological evolution of Simao basin and Ailaoshan orogenic belt have been discussed. The scientific research progress and new achievement possess great theoretical and practical significance in the aspect of Ailaoshan orogen in "Sanjiang" Region, the formation and evolution of the Tethys Ocean, and the uplifting process and associated mineralization of Tibet Plateau.Through the indoor and outdoor studies of lithology and lithologic associations of stratigraphic units occurred in the studied area, combined with the research of sedimentary structure, basic sequence and laboratory investigation on geochemical characteristics of radiolarian silicalite and pelite, possible sedimentary environment and facies of these stratigraphic units have been analyzed, also their possible basin prototypes have been recovered as follows:The Shuiqing Formation and Manbo Formation are interplatform basin facies; the top and bottom of Luohong Formation is interplatform basin facies, its middle part is plateau facies; Dazhongzai Formation is neritic shelf facies; Longbie Formation is blocking gulf facies; Xiamidi Formation is coastal swamp facies; Xianrendong Formation is broad plateau facies; Baliu Formation in Dahei mountains area is turbidity current deposit, silicalite mainly formed in continental margin; Dafengyakou area is back arc-basin deposit or broad ocean deposit; Yangbazhai Formation is coastal swamp facies; Sanhedong Formation is plateau facies; Waluba Formation is fan-delta front subfacies; Maichuqing Formation is delta plain subfacies; Yangjiang, Huakaizuo and Bazhulu Formations are main lacustrine deposits mixed with fluvial facies; Jingxing and Nanxing Formations both are fluvial facies.Comprehensive analysis of lithological combination, sedimentary structures, space distribution feature and clasolite resources of the Waigucun Formation in different localities reveals that the depositional period of Waigucun Formation is the development period of foreland basin with main sedimentary types of delta facies, rudaceous-sandy braided plain facies and fluvial plain facies. Their provenance dominatingly comes from the metamorphic rocks and volcanic arc in the eastern orogenic belt.The detrital zircons from key formations (Shuiqing, Yangbazhai, Waigucun and Maichuqing Formations) are analyzed systematically by LA-ICP-MS dating techniques, to determine the stratigraphic sequence of provenance in different periods and the uplift history of adjacent orogenic belt. It is showed that distinct provenance transition occurred in Permian and late Triassic, which are sedimentary response to the westward subduction of ancient Ailaoshan oceanic crust and continent-continent collision, thereout, two disappeared volcanic arcs, early Permian volcanic arc and early-middle Triassic volcanic arc, are recovered.A large number of detrital zircons of 281 Ma to 298Ma from sandstone of the Yangbazhai Formation and acid and basic igneous rocks of 260Ma to 266Ma with volcanic arc properties indicate that the westward subduction of oceanic crust has begun from the late Early Permian. Orogenic acidic magmatic activity occurred mainly in the Variscan Period (Late Permian), and formed a volcanic arc belt along the leading edge or trailing edge of subduction and collision zone. The granite gravels of turbidite fan in Baliu Formation further confirmed the presence of the volcanic arc and verified the collision before the deposition of Baliu Formation of Permian. In addition, the mafic magmatic activity of intracontinental rift character occurred in the Himalayan (Paleogene) Period.Tectonic environments of magmatic rock bodies in the studied area have been preliminary distinguished based on their outcropping morphology, petrochemistry and geochemical characteristics. It shows that Variscan acidic magma (Guangfeng Combination) is formed in continental arc setting in the collision period, in intracontinental environment (Zuobo Combination, Niukong Combination) in the post collision period, while the mafic magma in the Himalayan Period is formed in intracontinental extensional environment.The recognition of tectonic attribute and classification of tectonic units in the studied area indicate that the transition zone of Ailaoshan orogenic belt and Simao Basin is a typical basin-mountain coupling location. Ailaoshan Orogen is characteristic of compound orogenic belt. Initially, subduction-collision orogeny occurred in the Hercynian Period, then thrusting, strike-slip and extensional orogeny occurred in the Indo-Himalayan Period. Tectonic framework was finalized in Indosinian-Himalayan period. Ailaoshan nappe structures can be divided, from west to east, into foreland basin deformation zones, foreland fault-thrust belts, front thrust belt, the central thrust belt and trailing edge extension. Studied area is located in the foreland fault-thrust belts, which can be further divided into seven thrust sheets. Overthrust faults and thrust sheets overall inclined to NE with steep dipping angles, forming imbricate structures.The attribute of prototype basins of different periods is determined and the coupling relationship between basin and mountain is established on the basis of the basin sedimentary response to tectonic movement and the tectonic background.4 stages have been classified for the geological evolution in the studied area:① Extension rifting stage(S-D1), forming Jinsajiang-Ailaoshan oceanic basin; ②Main collision and subduction (P12-P3), forming back arc basin coupling stage; ③ Post-collision and formation of foreland basin (T3-K2); ④Intracontinental thrust and uplift, thrust nappe (64Ma-22.5Ma), strike-slip and formation of plateau (4.8-5Ma). |
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