| Fangdoushan structure is located in the eastern margin of Sichuan Basin,and its structural subject is a long and narrow NE-NEE oblique anticline with southeast wing steep(50°-70°)and northwest wing gentle(45°-60°).Permian-Triassic strata are exposed in the core,and Jurassic strata are mainly exposed in both wings.East Sichuan is a favorable area for oil and gas exploration.Due to the poor quality of seismic data,chaotic in-phase axes and multiple tectonic movements,the structural characteristics can not be accurately implemented,the exploration work is limited.Therefore,this paper comprehensively studies and analyzes the geometric,kinematic and dynamic characteristics of Fangdoushan structure by combining the previous research results and regional geological data,drilling data and 2D seismic data,through detailed interpretation of seismic profile,analysis of profile evolution history and experimental study of structural physics simulation.The following understandings have been obtained:Fangdoushan structure is a curved structure protruding from the northwest,and the axial plane is inclined to the northwest.The anticline is divided into three sections: south,middle and north.Fenshuilin-Lijiaping is the southern segment of Fangdoushan,which is the main structure of Fangdoushan.Its strike is NE and converges with Shizhu syncline and southern Qiyueshan anticline;Lijiaping-Jinziping is the middle section of Fangdoushan.The axis turns from the North 40 ° east to the North 70 ° East,which is an arc protruding northwestward;The lower Triassic Jialingjiang formation is closed in the Yangziqian area;Jinziping to Yangziqian is the northern segment of Fangdoushan and converges with the northern segment of Qiyueshan;The lower Permian strata are exposed in the south core,and the lower Triassic Jialingjiang Formation strata are exposed in the north-middle core.Fangdoushan structure is mainly developed with two sets of main decollement layers: Gaotai Formation gypsum rock of Middle Cambrian and Jialingjiang gypsum rock of Lower Triassic,and a set of secondary decollement layers of Silurian shale.The structural characteristics of the upper and lower strata of the main decollement layer are obviously different,which can be divided into three structural deformation layers: upper,middle and lower.The lower structural layer is a deformation layer(Z-?1l)under the gypsum rock of Gaotai Formation of Middle Cambrian,and the basement is not involved in deformation,which is a wide and gentle fold formed under the compression background;The middle structural layer is a deformation layer(?2-3x-T1f)between the gypsum layer of Gaotai Formation of Middle Cambrian and the gypsum layer of Jialingjiang Formation of Lower Triassic.The deformation of this layer is the most complex,and thrust faults and related folds are mainly developed,showing complex fault fold belts,which is the result of multi-stage structural superposition;The upper structural layer is a deformation layer(T2l-J)above the gypsum layer of the lower Triassic Jialingjiang Formation.The structural features are mainly fold deformation,and faults rarely develop.The formation and evolution of Fangdoushan structure can be divided into four stages:(1)In Caledonian-Hercynian extension environment,synsedimentary normal faults developed;(2)During the Indosinian period,the differential uplifting and structural inversion occurred;(3)the late Yanshanian early Himalayan compression structure was formed;(4)In the late Himalayan period,the extrusion transformation and shaping was finalized.On the basis of structural geometry and kinematics,its dynamics is studied through physical simulation experiments.Through two sets of comparative simulation experiments,the structural physical simulation study on its dynamic source,boundary conditions affecting structural style and its evolution process reveals that Fangdoushan structure was formed in the late Yanshan period under the control of SE-NW compressive stress of Jiangnan-Xuefeng uplift and pre-existing faults. |
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