The Crust of Qinghai-Tibet Plateau is the product of collision between the Eurasia and India plates. Though some geophysical profiles have been performed to reveal the lithospheric structures, but very few work on deep plane mapping of whole plateau have been done. We study 3D crustal density disturbance of the plateau and present corresponding deformation belt maps for the upper, middle and lower crust respectively. We apply a method called the multi-scale scratch analysis to Qinghai-Tibet Plateau for delineation of deformation belts and division of continental tectonic units. The method of regional gravity data processing have been developed by our group, combining theories based on multi-scale wavelet analysis, spectral analysis of potential fields, geophysical inversion, and surface scratch analysis. The multi-scale wavelet analysis, spectral analysis of potential fields and inversion produce density disturbance maps on planes of different depth, which are used as input for scratch analysis to compute the ridge coefficient images. The ridge coefficient images for each equivalent layer indicate the crustal deformation belts at certain depth in the crust. The sharp edges in the ridge-coefficient images reflect the boundaries between different secondary structural units. The ridge coefficient images show the variation of the deformation belts in Qinghai-Tibet Plateau from the upper crust to the lower, as well as the geometry of main crustal terrans exist in the plateau. The deformation belts are very dense and thin in the upper crust, but become coarse and thick in the lower crust, demonstrating the vertical variation modes of the deformation belt similar to a tree that has a coarse and thick trunk in its lower part and dense and thin branches in its top. The dense and thin deformation areas in the upper correspond to crustal shortening areas in the plateau. The thick and continuous deformation belts in the lower crust indicate structural framework of the plateau. The ridge-edge coefficient images show terrane boundaries at different depth in the crust and coincide with sharp varying zones of the density disturbance, therefore presenting the tectonic division of lower-crust units. The divided high-density terrans in the plateau include Himalaya, Kashmir, Chayuhe, Qiangtang, Qaidam and Baryanhar. Among them the Qiangtang, Qaidam and Baryanhar terrans have the crust roots of high density in the lower crust. As Kashmir and Chayuhe terrans are solid and of very high density, they were not easy to be crashed during the collision between the India and Eurasia Plates, playing the special effect in formation of the western and eastern structural knots, respectively. The method of multi-scale scratch analysis has been successfully applied to Qinghai-Tibet Plateau for delineation of crustal deformation belts and division of secondary tectonic units, providing some new evidences for understanding the deep structures in the plateau.
