Abstract:

Karamay overthrust belt is located at the front of the compresso-shear beltin west Junggar.It is on the active boundary of the convergent transforma-tion type and has special mechanical model:1.With a nappe as the main part,the three subbelts of the overthrus tbelt developed into two divergent brush structures in reverse directions onboth sides of each nappe.The whole form of the overthrust belt looks likethree S-shaped or reversed S-shaped structures.2.The stronger the compressed stress that each subbelt underwent,thesmaller the curvature of arc faults in divergence parts was.The stronger the shear,the larger the curvature.3.On the starting end of the shear stress of each subbelt,the structure developed stronger,and it is known as“strong head”;the other end maybe called“weak tail”.The fracture of the“strong head”divergens towards mountain,and that of the“weak tail”divergens towards the basin.4.The fault blocks on the overthrust belt can be divided into four kindsaccording to their mechanical properties:echelon fault block;flank faultblock;λ-type fault block and branch reclosing fault block.5.The fault belt consists of many faults stacked by different mechanical properties during different geological times.The more the number of paleofaultsstacked,the better the fractures developed.The relationship between mechanical model and hydrocarbon accumulationon the fault belt are shown in follwing:1.In planar and vertical hydrocarbon distribution,the“strong head”hasan advantage over“weak tail”,2.The high production rate of echelon fault block is greater than that offlank fault block,that of the flank fault block is greater than that of λ-typefault block,the one of λ-type fault block is greater than that of fault block.3.All the fault blocks mentioned above which formed under rotation stress and the places where most paleofaults stacked are favourable for the explo-ration of high production hydrocarbon.