Crustal Density Inversion and Its Tectonic Structure in Badong-Zigui Area

  Objectives  The Badong-Zigui Basin is located in the west of the Three Gorges area, and it is surrounded by four different tectonic units: With the Xuefengshan thick-soil tectonic belt on the south, the Qinling orogenic belt on the north, the Huangling anticline on the east, and the eastern extension of the Sichuan Basin in the west. The Badong-Zigui basin is a north-south syncline structure, the sediments in the basin are dominated by Late Triassic-Late Turassic argillaceous rocks, and the special tectonic setting causes strong tectonic activities in the basin.

  Methods  Using a three-dimensional gravity inversion algorithm based on Lagrangian multiplier constraints, the local Bouguer gravity anomaly in Badong-Zigui area is inverted, and the underground three-dimensional density structure of Badong-Zigui and adjacent areas is obtained.

  Results  The inversion results show that the Zigui Basin is a low-density area compared with the surrounding area. The sedimentation thickness in the east is deeper than that in the west, and the sediment density is lower than that in the west. The small and medium earthquakes in the area are basically 4-12 km underground.

  Conclusions  The north-south and north-east ancient water flows in the northern edge of the Zigui Basin successively provide sources for the sedimentation and filling of the basin, forming a structure with lower material density and deeper deposits in the eastern part of the basin; low-density materials in the east are transported and accumulated to the west in the basin. At the same time, it is squeezed by the eastward extension of the Sichuan Basin, and it is speculated that there is a tendency of east-west movement and compression in the basin.