天山造山带岩石圈密度与磁性结构研究及其动力学分析

库尔勒—吉木萨尔剖面横跨塔里木盆地北缘、天山造山带和准噶尔盆地南缘.沿剖面完成了重磁联合反演,获得了岩石圈二维密度结构与二维磁性结构.结果发现,塔里木盆地与准噶尔盆地向天山造山带对冲.在地壳范围内,塔里木盆地北缘与准噶尔盆地南缘的平均密度较高,天山造山带的地壳平均密度较低.天山造山带具有较高的磁化强度,尤其表现在准噶尔盆地南缘至天山造山带中部的整个地壳范围内,预示着天山南北可能具有不同的构造演化历史、构造运动方式以及构造运动强度.在塔里木盆地与天山造山带以及准噶尔盆地与天山造山带的接触部位的上地幔顶部分别发现了低密度体,推测在塔里木盆地由南而北向天山造山带“层间插入与俯冲消减”,以及准噶尔盆地由北而南向天山造山带俯冲的过程中塔里木盆地北缘和准噶尔盆地南缘下地壳物质被带进天山造山带上地幔顶部.库尔勒—吉木萨尔剖面岩石圈二维密度结构与磁性结构为天山造山带的构造分段提供了岩石圈尺度的依据.

Structure of lithospheric density and geomagnetism beneath the Tianshan orogenic belt and their geodynamic implications.

The geoscience transect from Korla to Jimsar runs through the northern margin of the Tarim basin, the Tianshan orogenic belt and the southern margin of the Junggar basin. Along the profile a joint inversion of gravity with geomagnetism has been carried out and 2-D density structure and 2-D geomagnetic structure have been obtained. The result shows that the Tarim basin and the Junggar basin underthrust to the Tianshan orogenic belt in opposite directions. In the crust, the average density of the northern margin of the Tarim basin and the southern margin of the Junggar basin is relatively high, while that of the Tianshan orogenic belt is relatively low. However, the Tianshan orogenic belt bears a high geomagnetic intensity, especially in the entire crust from the southern margin of the Junggar basin to the middle of the Tianshan orogenic belt. This indicates that the southern margin and the northern margin of the Tianshan orogenic belt may possess different tectonic evolution histories, different tectonic movement patterns and different tectonic motion intensities. Some low density bodies located at the top part of the upper mantle are found on the boundaries between the Tarim basin and the Tianshan orogenic belt and that between the Junggar basin and the Tianshan orogenic belt. This may be inferred as a result of mass of the lower crust of the northern margin of the Tarim basin and the southern margin of the Junggar basin which has been carried down to the top part of the upper mantle beneath the Tianshan orogenic belt during the northward subduction of the Tarim block and that of the Junggar block southward. The 2-D density structure and the 2-D geomagnetic structure of the geoscience transect from Korla to Jimsar provide some lithospheric evidence for the tectonic segmentation of the Tianshan orogenic belt.