Strikes of fault system in Bachu uplift

a secondary structural unit in Tarim basin

are mainly NNW

while those in the neighboring Kalpin thrust belt to the north

part of South Tianshan tectonic system

are nearly EW. These two fracture systems are nearly orthogonal in the plane view. Mesozoic and Cenozoic are absent in a large area in Bachu uplift

so it is difficult to determine the exact time of activity of the fracture system. Comparing the features of Cenozoic sequences and analysing their contact relations shows that the N-S fracture system in Bachu uplift began to come into being in Miocene and extended northward into Kalpin structural belt. The corresponding relations between the N-S fracture systems in the two structural units are studied in this paper.It is pointed out that the E-W fracture system in Kalpin area was active mainly after Pliocene(N

2

). The present N-S and E-W fracture systems in Kalpin structural belt are the results of superimposition of structures in different stages. Structural geologic models of Bachu and Kalpin fracture systems are also presented in this paper.