青藏高原地壳密度变形带及构造分区

将区域重力场多尺度刻痕分析用于提取青藏高原地壳变形带的信息,可了解高原内地壳变形带从浅到深的变化和平面分布特征,并对青藏高原主要地体的空间分布定位,为岩石圈研究提供地表地质难以取得的新信息.多尺度脊形化系数的图像刻划不同深度平面上的地壳变形带.青藏高原地壳变形带从上到下由细密逐渐变为粗稀型,而且细密型变形区分布的范围逐渐缩小,到下地壳完全消失.从这种情况可以推测,以垂直地面方向上看,地壳变形带应该是树形的,下地壳粗稀型的变形带为树的主干,而中地壳粗稀型的变形带为树的分枝,上地壳的变形带为树枝的小枝杈.上地壳细密型变形分布区反映了与中新生代地壳缩短变形区的范围,下地壳清晰连续的变形带反映了青藏高原的构造骨架.多尺度边界刻痕系数的图像刻画不同深度平面上的地体边界,下地壳的刻痕边界系数与密度剧烈变化带位置吻合;因此,由多尺度刻痕分析划分地体时同时取得地体密度信息.青藏高原内密度较高的地体包括喜马拉雅地体、克什米亚地体、察隅河地体、柴达木地体、巴颜喀拉地体和羌塘地体.柴达木地体、巴颜喀拉地体和羌塘地体是青藏高原中有壳根的核,而密度最高的克什米亚和察隅河地体在大陆碰撞时不易碎裂,对东西两个构造结的形成起了关键作用.

Crustal density deformation zones of Qinghai-Tibet Plateau and their geological implications

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.#br#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.#br#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.#br#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.