阿拉善地块下插河西走廊的发现及其构造意义

Discovery of the Alashan Block Thrusting beneath the Hexi Corridor and Its Tectonic implications

通过天然地震层析成象技术,反演了河西走廊中部地区的三维速度结构.基于横断北祁连、民乐盆地、龙首山及阿拉善地块南缘的速度结构剖面分析发现,在上地壳内,阿拉善地块以低速体“铲状”形式插入河西走廊之下.围绕这一深部地质结构现象、成因及相关依据进行了简单的辨析、论证.初步认为,龙首山既是逆冲断裂构造带或巨型推覆体,也是柴达木—祁连块体与阿拉善块体“碰撞造山”的结果,至少在河西走廊中部是青藏板块与华北板块的分界带.

A 3-D velocity structure thrusting beneath the central part of Hexi Corridor is obtained by using seismic tomography inversion. By analyzing the velocity distribution of the profile crossing Northern Qilianshan, Minle basin, Longshoushan and south margin of Alashan block, we find, in the upper crust, Alashan block with a low-velocity subduction slab of shovel shape is obviously thrusting beneath the Hexi Corridor. Concerning this geologic, phenomenon and its origin and causes of the low-velocity layer, we try to discriminate between facts and give out our opinions. Preliminary results show that the Longshoushan is not only a thrust fault zone or huge nappe structure, but also a collisional orogenic zone between Alashan and Chaidamu-Qilianshan blocks, and the central part of Hexi Corridor is at least a boundary of collision combination between North China and Qinghai-Tibetan plates.