Thermal-rheological structure of lithosphere beneath the northern flank of Tarim Basin, western China: Implications for geodynamics

摘要

Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equation, the thermal structure of the lithosphere under this region is determined. Our results show that the average surface heat flow of the northern flank of the Tarim Basin is 45 mW/m~2, and the mantle heat flow is between 20 and 23 mW/m~2; the temperature at crust-mantle boundary (Moho) ranges from 514℃ to 603℃ and the thermal lithosphere where the heat conduction dominates is 138—182 km thick. Furthermore, in combination with the P wave velocity structure resulting from the deep seismic sounding profile across this region and rheological modeling, we have studied the local composition of the lithosphere and its rheological profile, as well as the strength distribution. We find that the rheological stratification of the lithosphere in this region is apparent. The lowermost of the lower crust is ductile; however, the uppermost of the mantle and the upper and middle parts of the crust are both brittle layers, which is typically the so-called sandwich-like structure. Lithospheric strength is also characterized by the lateral variation, and the uplift region is stronger than the depression region. The lithospheric strength of the northern flank of the Tarim Basin decreases gradually from south to north; the Kuqa Depression has the lowest strength and the south of the Tabei Uplift is strongest. The total lithospheric strength of this region is 4.77 x 10~(12)—5.03 x 10~(13) N/m under extension, and 6.5X10~(12)—9.4X10~(13) N/m under compression. The lithospheric brittle-ductile transition depth is between 20 km and 33 km. In conclusion, the lithosphere of the northern flank of the Tarim Basin is relatively cold with higher strength, so it behaves rigidly and deforms as a whole, which is also supported by the seismic activity in this region. This rigidity of the Tarim lithosphere makes it little deform interior, but only into flexure under the sedimentation and tectonic loading associated with the rapid uplift of the Tianshan at its northern margin during the Indian-Eurasian continental collision following the Late Eocene. Finally, the influences of factors, such as heat flow, temperature, crustal thickness, and especially basin sediment thickness, on the lithospheric strength are discussed here.