BASEMENT DECOUPLING STRUCTURE IN JIANGNAN-XUEFENG——SERIES 1 OF THE SOUTHERN STRUCTURE STUDIES

The basement decoupling structure is the reaction in continent plate when the margin of continent plate is subducted,subdued,extruded and shortened.Extruded under horizontal effect,the earth crust is decoupled along such flabby zones as "low velocity zone" and "high conductivity formation".These huge flexile shear zones in metamorphic basement divide the lithosphere plate into several "thin sheets".Along the decoupling surface,great scale slide and nappe take place,resulting in the Jura-type fold and superimposition of sedimentary cover of the Paleozoic basin within plate.Interbed shear slide and distorted rebuilding and shortening from strong to weak take place so as to balance the middle and upper crusts.It is discussed in this paper the attribute of Jiangnan-Xuefeng uplift which is neither "thick-skinned structure" of orogenic belt nor "thin-skinned structure" of sedimentary cover fold but "intergradational basement decoupling structure".From Indosinian to early Yanshanian,decoupling and nappe take place from SE to NW(S to N,E to W at the meanwhile).It is the dynamic source and domination controlling deformation of Yangtze marine facies Meso-Paleozoic basins and at the same time it controls the generation and accumulation of marine facies petroleum.