Different gravity anomaly, crustal structure, and uplift mechanism of the eastern and western Qinling Orogen revealed by full coverage gravimetry

Exploring the crustal structure and uplift mechanism of the Qinling Orogen, China, contributes to a better understanding of the expansion of the northeast Tibetan Plateau. We conduct a gravity/GNSS survey comprising 649 stations across the Qinling Orogen. In situ measured gravity anomalies deviate from gravity model values in steep areas like the West Qinling, where the differences exceed 100 mGal, indicating the importance of the in situ measured data. Based on these data, significant divergences of gravity anomaly, crustal density structure, and isostatic flexure mechanisms between the West and East Qinling are found. The average free-air and Bouguer gravity anomalies of the West Qinling (- 20 mGal and - 220 mGal) are notably lower than those of East Qinling (70 mGal and - 160 mGal). According to flexure analysis, the surface, internal, and bottom loading ratios are 0.16, 0.47, and 0.37, respectively, for the West Qinling, while they are 0.08, 0.29, and 0.63 for the East Qinling. Combining the present outcomes with other tectonic and geophysical findings, we determine that for the West Qinling, the uplift is caused by lithospheric-scale vertical coherent deformation, with lower crustal flow being the most prominent factor. The East Qinling is characterized by layered deformation, with its upper, middle, and lower crust being affected by post-collisional extension, continental collision, and upwelling mantle material, respectively. We find that the elastic thickness of the Qinling Orogen is much smaller than those of the South China Block and North China Block, making it a possible channel for the extruded materials from the northeast Tibetan Plateau.