Structural deformation pattern within the NW Qaidam Basin in the Cenozoic era and its tectonic implications

• 5 right-step en echelon fold belts are recognized in the NW Qaidam Basin.
• Double fault systems are commonly observed within a single anticline.
• Accelerated deformation started at ca. 15 Ma and accelerated at ca. 8.2 Ma.
• The deformation is explained by a Riedel-P-Shear model.

The Qaidam Basin is located in the northeastern Tibetan Plateau and provides an excellent field laboratory in understanding the history and mechanism of the plateau growth. It deformed widely over the northwest during the Cenozoic but with little thrust loading along the margins, where no foreland depression is observed. Based on satellite images, seismic and borehole data, we investigated the structural deformation pattern (including the structural style and timing of deformation) and its formation mechanism within the northwestern Qaidam Basin during the Cenozoic era. Mapping of surface geology shows that the modern Qaidam Basin is characterized by five SE-trending anticlinal belts. Each belt consists of several right-step en echelon anticlines with plenty of normal and strike-slip faults crossing the crests. Those anticlines are generally dominated by double fault systems at different depths: an upper thrust fault system, controlling the anticlines identified on the surface and a lower dextral transpressional fault system characterized by typical flower structures. They are separated by weak layers in the upper Xiaganchaigou or the Shangganchaigou formations. The upper system yields shortening strain 2–5 times larger than that of the lower system and the additional strain is interpreted to be accommodated by hinge-parallel elongation in the upper system. Growth strata indicate that deformation within the Qaidam Basin initiated in the middle Miocene (~ 15 Ma) and accelerated in the late Miocene (~ 8 Ma). A simple Riedel-P-Shear model is used to explain the deformation mechanism within the northwestern Qaidam Basin.