青藏高原及其邻区岩石层三维密度结构

THREE-DIMENSIONAL LITHOSPHERIC DENSITY STRUCTURE BENEATH QINGHAI-TIBET AND ITS ADJACENT AREA

搜集了青藏高原及其邻近区域的S波速度三维层析成像结果和2万多个实测重力点资料，将重力资料进行各种改正并网格化为30′×30′的布格重力异常．首先采用密度差与S波速度差之间的经验关系式，建立青藏地区岩石层密度的初始模型，再利用布格重力异常进行阻尼最小二乘法反演，得到青藏地区岩石层三维密度分布结果．反演结果表明：（1）青藏高原岩石层密度分布不仅在纵向上不均匀，而且在横向存在明显的不均匀．在深度10－70km范围内，高原整体呈低密度特性，在50－70km深度范围内低密度特征更加突出，与周缘地区存在0，1g／cm3的密度差．而在90－110km深度范围内，高原岩石层地幔显示密度高．（2）岩层密度分布与大地构造有明显相关的分区性，显示出青藏块体、巴颜喀拉块体、塔里木块体和印度块体．

We have abtained more than 20 000 practical gravity data and three-dimensional tomographic inversion results of shear velocity in Qinghai-Tibet (QT) region. Firstly, we made up initial model of lihospheric density of QT region using the empirical equation between the density difference and shear velocity difference. Then, inversion of 30'×30' Bouguer gravity anomaly by means of Marquardt-leverberg method yield a rather detailed density structural model. The results indieate as follows: (1) Lithospheric density distribution are inhomogeneous not only in vertical direction but aslo in horizontal direction, In the depth 10-70km ranges, QT plateau appears lower density. In the depth 50-70km ranges QT plateau more lower than its adjacent region,has 0.1g /cm3 density difference; In 90-110km depth ranges QT platean lithospheric mantle appears high density character. (2) the Lithospheric density distribution is relative with geotectonics, there are QT block, Bayancla block, Tarim biock and Indian block.