中文摘要：

利用青藏高原布格重力异常数据,通过均衡改正和二维密度结构拟合反演,获得了藏北钾质火山岩区下的区域剩余均衡重力异常特征以及二维密度结构特征.结果显示,藏北火山岩区下的地壳上地幔整体上处于密度亏损状态.结合已有的区域地质、构造和岩浆岩地球化学资料,地球物理资料,综合分析了藏北火山岩成因,即在印度板块持续北向俯冲作用下,使得亚洲岩石圈前缘发生断离,进而在新近纪藏北高原广泛地发生了钾质和高钾质的藏北火山喷发,同时也造成了藏北高原的快速隆升.

英文摘要：

This paper uses two techniques of isostatic correction and two-dimensional density fitting to analyze Bouguer gravity anomaly in Tibet,and obtains the regional and residual isostatic gravity anomaly in Tibet and two-dimensional density structure along 88.5°E.The results show that the crust and upper mantle beneath northern Tibet are in a deficit state with a lower density than other regions in Tibet.Based on the existing data of regional geology,tectonics,geophysics and geochemical characteristics of magmatic rocks in the northern Tibet,those great eruptions of potassic volcanoes in northern Tibet are the result of break-off of the front of lithosphere mantle of Asia under on-going northward subduction of the Indian lithosphere mantle since ～65Ma.