Clouds Nappe Tectonic Features And Dynamic Analysis

Xiangyun locates in the middle part of the southwestern Three River Orogenic Belt—Yangtze Para-platform and Tanggula-Changdu-Lanping-Simao fold system which two are the interface level of the first-order tectonic units, so its geological structure is more complex.There are a large number of geological evidences in the general survey project of land and resources—1:50000 regional geological survey of Midu, Xiangyun, Weishan and Juli Country, reflecting between Midu basin and Xiangyun basin existing a nappe body. The formation from the northwestern Ordovician to the southeastern Devonian is not the original terrain, but the external terrain from the northwest nappe.Xiangyun nappe overall was a "tongue-shaped" and was limited by the Xiangyun and Midu basin which are the same trend and approximate parallel. It is a total distance of about 30 km from the northwest of Beiyun in Midu to the southeastern part of the Xiangyun Shuimu Mountain. This nappe is considered Shuimu Mountain fault as the main nappe slip plane, developing a series of secondary thrust fault along its North West-South East nappe direction which are all North East trend, North West tendency. These faults constitute the imbricate thrust faults of Xiangyun nappe structure.According to the characteristics of nappe development, this paper divides Xiangyun nappe into the forward extrusion belt, the middle imbricate pre-show belt and the root development belt which are three main belts. The forward outcropped in Xiangyun Baitutian-Shuimu Mountain, about 6 km long. This forward belt is considered Shuimu Mountain-Hedong village fault as nappe fault plane. The limestone and siliceous of Devonian-Carboniferous-Permian and Emei Mountain basalt nappe are above (feldspar) quartz sandstone and silty mudstone of Triassic-Jurassic footwall. This belt is considered developing a large number of overturned and recumbent folds as the main characteristics. Various types of mechanical analysis of deformation structures all showed the compressive stress of E—W direction and the nappe direction of NW—SE. The middle imbricate belt is 20 km long from Midu Jixiangzhuang to Xiangyun Baitutian. It is considered developing a group of thrust faults which are approximate parallel and North west tendency as characteristics. It happened the imbricate pre-show nappe during the different formation or the inner of the same formation. This belt also developed a series of oblique and overturned folds. The bit-state and deformation mechanism of the fold anastomosed with the whole nappe. The root belt exposed at the northwest of Beiyun and the northern region of the study area. It mainly sees the Ordovician quartz sandstone and sandy shale nappeing above the limestone of the Silurian Gallery Group.The paper discussed the Dynamic Mechanism and the tectonic evolution model of Xiangyun nappe, which are based on the geometry and kinematics characteristics analysis of the forward extrusion belt, the middle imbricate pre-show belt and the root belt of Xiangyun nappe, with the research results of predecessors about the regional tectonic settings. This paper proposed that Xiangyun nappe was formed at the regional tectonic settings of the Paleogene India-Eurasian plate subduction, collision resulted in the Jinsha River-Red River fault zone and Chenghai fault zone strike-slip movement. Since the beginning of the two-plate subduction and collision, the regional tectonic stress appeared as the main east-west pressure, and Indo-China blocked out of the south east, then the Red River began to sinistral strike-slip, while Chenghai fault belt occurred dextral movement and formed a group of north-east towards the sub-faults. In this tectonic setting, the Red River fault zone along the north-east set a series of rock tend to the North West Department of thrust fault occurred since the North West-South East thrust. Accordingly, the clouds of nappe formation and development is divided into three stages and three stages with the formation of India-Eurasian plate subduction, collision of three tectonic movement stage is the corresponding coordinate.