西准噶尔及邻区的岩石圈密度结构特征及其构造意义

对西准噶尔及周边地区壳幔结构的研究是揭示准噶尔盆地演化的重要基础.利用最新的卫星重力场模型, 通过计算得到西准噶尔及周边地区的布格重力异常, 进而采用三维反演技术, 对西准噶尔及周边地区的地壳与上地幔顶部进行密度成像, 得到了0~80 km深度范围的密度异常结构.地壳密度分布显示古准噶尔洋壳有可能向NE和NW分别俯冲于西伯利亚板块和西准噶尔地块之下.上地幔顶部密度变化表明: 阿尔泰褶皱带具有相对较低的密度, 可能为古大陆巨厚的硅铝层所致; 哈萨克斯坦-准噶尔盆地具有相对完整的高密度结构; 天山褶皱带区域的密度大幅度变化刻画了超岩石圈断裂对岩石圈的切割以及岩石圈形变与构造活动的痕迹. 

Characteristics and Tectonic Implications of Lithospheric Density Structures beneath Western Junggar and Its Surroundings

Structures in the crust and uppermost mantle beneath western Junggar and its surroundings, the key to better understanding of the tectonic evolution of the Junggar basin, are studied in this paper. Firstly, the Bouguer gravity anomaly is calculated from the satellite gravitational field model. Then 3D inversion technique is utilized, and the density imaging is operated in the crust and uppermost mantle beneath the western Junggar and its surroundings and finally the anomalous density structure at the depth range of 0-80 km is obtained. Crustal density distribution in the ancient oceanic crust of the Junggar indicates the possible subductions under the Siberian plate northeastwardly and the western Junggar northwestwardly. Density distribution in the uppermost mantle suggests that the relatively low density beneath Altay fold belt may have resulted from the thick sialic layer of the ancient continent, and Kazakhstan plate & Junggar basin are dominated by a relatively whole high-density structure while the significant density changes beneath the Tianshan fold belt describe the ultra-crustal deep faults and also the nicks of the tectonic activities and the lithospheric deformations.