Deep structures and surface boundaries among Proto-Tethyan micro-blocks: Constraints from seismic tomography and aeromagnetic anomalies in the Central China Orogen

Abstract

The Qinling–Qilian orogen preserves the records of Early Paleozoic convergence among the Proto-Tethyan micro-blocks. In this study, we analyze the seismic velocity structure and the aeromagnetic anomalies in the Qinling–Qilian orogen and its adjacent areas, showing that the northernmost boundaries of these Proto-Tethyan micro-blocks are defined by the Guyuan–Longshoushan Fault in the Qilian orogen and by the Luonan–Luanchuan Fault in the Qinling orogen, respectively. The lithosphere north of the Qinling–Qilian orogen subducted southward under the Qinling–Qilian orogen. The boundaries of the micro-blocks in the Qinling–Qilian orogen of the Proto-Tethys domain are mostly EW- or NE-trending. Combined with Early Paleozoic geological records, our results indicate that the south-dipping low-velocity anomaly under the Alxa block and the south-dipping high-velocity ones under the North Qilian orogen and the North China block might indicate that the Alxa block, the North Qilian Oceanic slab and the North China block subducted southward. The south-dipping high-velocity anomaly under the North Qilian orogen is interpreted as the remnant of the Proto-Tethys Ocean in that area. However, the north-dipping low-velocity anomaly under the South Qinling and the North Qinling orogens, the Qaidam block and the north-dipping high-velocity one under the Yangtze and the Bikou blocks suggest that the South Qinling and the North Qinling orogens, the Qaidam, the Yangtze and the Bikou blocks subducted northward. The present spatial framework of the Qinling–Qilian orogen is related to Early Paleozoic convergence among the Proto-Tethyan micro-blocks.