BASAL DETACHMENT STRUCTURES AND OIL-GAS TERRITORY IN THE NORTHEAST OF TARIM BASIN

Basal detachment structure is a major structural style of intraplate deformation. At the end of Permian, Tarim plate drifted northward as a result of the opening and closing of Tethy; on the one hand, the closing of Haixi geosycline in Tianshan was advanced; on the other hand, the convergency and pressing after the collision continued, caused the deformation reconstru-ction with basal detachment as the major structural style in Palaeozoic basin of Tarim platform. Tabei (north Tarim) uplift in the northeast of Tarim basin is a nappe uplift belt, being developed on the upper hanging of Yanan ductile shear belt, has a southdipping listric nature. Furthermore, a series of slip fault and decollement structures with southdip bedding plane were formed along the "weak belts" of the Cambrian and Silurian bottom shales in Palaeozoic sedimentary cover.They may be subdivided into interlayer shear fracture cleavage, decollement folds, plastic flow belt, interlayer slip band and fault-slip front pressing belt. In the Palaeozoic strata in Tarim basin, there are the decollement folds of detachment faults, the dragging anticline on the upper hanging, and the relict on palaeo-erosion surface caused by late movement.They are the domi-nant structures for oil-gas accumulation in the study area.