Structure and in Situ Stress Analysis of the Tazhong Uplift, NW China: Implications for Fault Reactivation

Abstract

The Tarim Basin in northwest China is an intracratonic, poly-phase basin with a subsurface structure that records a protracted tectonic history associated with crustal accretion and amalgamation. Currently, the basin is bounded by actively deforming mountain belts but displays little evidence of active deformation within the basin. Here, detailed interpretation of 3D seismic reflection data and analysis of drilling-induced deformation in deep boreholes (e.g. borehole breakouts) are used to resolve uncertainties about the timing and distribution of past deformation, the effect of pre-existing structures on subsequent deformation, and the current in situ stress state in the Tazhong Uplift of the Central Tarim Basin. The geometry and kinematics of Ordovician thrust faults and folds, Silurian-Permian strike-slip faults, and Triassic igneous bodies and normal faults, along with stratigraphic relationships, suggest that creation of new faults, and reactivation of pre-existing faults occurred during tectonic events in the Paleozoic and Early Mesozoic; however, no evidence of faulting is observed in Late Mesozoic or Cenozoic strata in the Tazhong Uplift. The current in situ stress should favor extensional and strike-slip tectonics with maximum horizontal compression directed NE, which contrasts with past stress states in the basin inferred from Paleozoic and Mesozoic structures. In situ differential stress magnitude in the Tazhong Uplift (ranging from 94 to 170 MPa) is insufficient to reactivate the most optimally-oriented faults in the Central Tarim Basin, even though the basin is bounded by the active Tian Shan and Kunlun Shan thrust belts to the north- and south-west, and the left-lateral strike-slip Altyn Tagh fault to the south, all associated with the ongoing Himalayan-Tibetan orogeny. The low differential stress may be understood if the basin-bounding faults (particularly the Altyn Tagh fault) operate at low absolute shear stress, similar to continental transform faults such as the San Andreas fault, CA.