Oblique Arc–Arc Collision During the Earliest Permian in the Northern Beishan Orogenic Collage, NW China: Constraints From Transpressional Deformation and Geochronological Data

Understanding the deformation history and mechanisms is important for inferring orogenic processes and dynamics. We present new structural and geochronological data from the Pengboshan area in the eastern part of the Heiyingshan–Hanshan Arc (HHA), northern Beishan Orogenic Collage (BOC), to constrain the Carboniferous–Permian deformation mechanisms and tectonic evolution of the island arc. Our results show that the pre‐Permian sequences in the eastern HHA underwent a phase of widespread ductile deformation at temperatures of 400–500°C. In the study area, the deformation produced five major WNW–ESE‐striking dextral ductile shear zones and intervening fold zones. The fold zones include oblique transpressional fold zones as well as parallel transpressional and pure shear fold zones. These structures resulted from dextral transpressional deformation with a high degree of strain partitioning and are consistent with simple‐shear‐dominated transpression that corresponds to a plate convergence angle of <20°. Zircon U–Pb dating constrains the timing of the dextral transpression to 298–289 Ma (earliest Permian). We suggest that the dextral transpressional deformation resulted from an oblique arc–arc collision between the HHA and the Mazongshan Arc to the south, which pre‐dated both the final closure of the Hongshishan Ocean to the north and terminal collision in the BOC. These results demonstrate that a short‐lived (<10 Myr) arc–arc collision, rather than long‐term oceanic subduction, was responsible for the widespread shortening deformation in the island arc, which occurred during a magmatic lull. An accretionary orogen can be affected by oblique arc–arc collision and transpressional deformation, similar to continent–continent collisional belts.