Wedge-Shaped Structure and Its Implications for the Haiyuan-Liupan Shan Arcuate Tectonic Belt Revealed by High-Resolution Ambient Noise Tomography

The Haiyuan-Liupan Shan (HY-LPS) arcuate tectonic belt, located at the junction of the growth front of the Tibetan Plateau and the North China Craton, serves as a natural laboratory for investigating continental collision. Investigating the fine structure and dynamic processes in this area not only deepens our understanding of the debated growth and deformation patterns of the plateau, but also clarifies the interactions between the plateau and the adjacent craton. In this study, we establish a high-resolution three-dimensional crustal shear-wave velocity structure surrounding the HY-LPS arcuate tectonic belt using the surface wave imaging technique, utilizing ambient noise data from 219 broadband stations. The shear-wave velocity structure in this region exhibits a strong correlation with geological tectonics, consistent with the transformation of boundary faults from strike-slip to thrust. Low-velocity bodies are extensively distributed in the middle crust of the Longxi block, which is located at the northeastern margin of the Tibetan Plateau. The formation of these low-velocity anomalies may result from multifactorial interactions. Our results indicate that the upper and lower crusts in the Longxi block are decoupled, and the mid-crustal low-velocity bodies act as a detachment layer. This decoupling mechanism facilitates the growth of the plateau margin by enabling the upper crust to overthrust onto the craton, thereby contributing to the formation of the Liupan Shan. Furthermore, the lower crust of the Longxi block is found thickened due to the obstruction imposed by the North China Craton and intruded into the cratonic lower crust. The cratonic crust has been compromised due to the combined effects of tectonic compression and thermal erosion associated with the northeastward expansion of the Tibetan Plateau, which has facilitated the development of wedge tectonics.