Investigating Cenozoic Deformation in the Southeast Tarim Basin Using Seismic Reflection: Evidence Against Large Scale Thrusting Along the Northwest Tibetan Margin

Abstract:

Interpretation of seismic reflection surveys of the Southeast Tarim Basin, in northwestern China, show minimal evidence of significant Cenozoic deformation and large-scale structures in the southeast depression. Seismic reflection profiles bound on the south by the transpressional North Altyn Fault (NAF) and on the north by the strike-slip dominated transpressional Cherchen Fault, obtained in a grid of 20 km-spaced parallel and 10 km-spaced perpendicular lines to these two major structures. Among the major features apparent on the seismic sections are: 1) a southwest-northeast trending anticline bound on the north by a minor reverse fault, 2) a basal Cenozoic angular unconformity evident as a major reflective horizon and confirmed with borehole data from the RC1 well, also verifying the thickness of Cenozoic aged sediments at <3500 m throughout SE Tarim, 3) minor reverse faults with minimal (< 500 m) cumulative vertical offset in early Cenozoic strata, 4) depth to crystalline basement of ~3500 m, evident from the lack of seismic horizons (reflections) below Jurassic aged strata. Though identifiable structures are few within SE Tarim, reconstructions of the structures shown in seismic sections indicate that a maximum of 1.5 km of crustal shortening has occurred in the southeast Tarim Basin throughout the Cenozoic, less than that necessary for a major thrust system. Quantifying this shortening helps to characterize the deformation within the footwall block of the NAF, constraining the maximum vertical component of offset on the NAF as less than the maximum vertical thickness of Cenozoic sediments in SE Tarim of ~3500 m, observations that suggest minimal vertical offset (<3 km) on the NAF. 1 Seismic section that extends north of the Cherchen Fault shows that the pattern of minimal deformation in SE Tarim extends north of this major structure, further solidifying the results showing minimal deformation within the Tarim Basin.