Structures on Lithospheric Density and Geomagnetism of the Tianshan Orogenic Belt and Their Geodynamic Implications

Abstract 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 both the Tarim basin and the Junggar basin under thrust 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 Tiansha 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 intensities. Some lowdensity 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 subduction of the Tarim block northward and that of the Junggar block southward to the Tianshan orogenic belt. During this process, the mass of the lower crust on the northern margin of the Tarim basin and the southern margin of the Junggar basin has been carried down to the top part of the upper mantle beneath the Tianshan orogenic belt. 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.