Three-dimensional inversion of gravity and magnetic data and its application in the study on the characteristics of magmatic rocks in the Gangdise belt and adjacent areas, Tibetan Plateau

Magmatic rocks play an important role in research on continental dynamics in the Tibetan Plateau, which are records of tectonic evolution as well as the indications of major tectonic-magmatic-metallogenic belts. In this paper, we used large-scale ground gravity and aeromagnetic data to study the characteristics of magmatic rocks in the Gangdise belt and adjacent areas. To obtain the 3D density and susceptibility models of the study area, we carried out 2. 5D interactive inversion of gravity and magnetic data based on geological-geophysical prior information. The 2. 5D inversion results were then regarded as the reference model for the three-dimensional inversion. Integrating the inversion results with physical property statistics and geochemical data, we mapped the three-dimensional distribution of basic rocks, I type granites and S type granites in the study area. The resulting maps show that S type granites which are related to the Mesozoic collision are mainly distributed in the eastern Gangdise belt and the north of Gangdise back-arc fault uplift. No remarkable intrusive rocks are found west of northern Gangdise. While a large number of hidden basic rocks are present in the south and north sides of the northern Gangdise, and a few I type granites which are related to subduction are scattered there. In the southern Gangdise and Gangdise back-arc fault uplift, Mesozoic I type granites are widely distributed, but the large number of S type granites did not appear till the Cenozoic era. The above results provide important evidence to support the bi-directional scissors-style subduction model of the Mesozoic Bangong Co-Nujiang oceanic crust southward and the Neo-Tethys oceanic crust northward subduction. We consider that the Bangong Co-Nujiang oceanic crust may have subducted northward and southward subsequently in the west of the northern Gangdise in the range of 84 degrees E 88 degrees E. The oceanic crust subducted northward to the Qiangtang terrane and southward to the Gangdise terrane.