Lithospheric structure and thermal effect in the collisional orogen, Northeastern Tibetan Plateau

Lithospheric thermal structure and temperature field characteristics are essential for understanding the rheological properties and geothermal anomalies in the collisional orogen. In this study, we systematically modelled the lithospheric structure in light of the stratified crustal structure revealed by the seismic profiles in the Northeastern Tibetan Plateau (Maduo-Gonghe-Yabrai). Furthermore, using thermophysical data and CRUST 1.0 model, we calculated the thermal background to assess the lateral disparities in the thermal effect across the collisional orogen. The results reveal that, across the Haiyuan Fault, there are significant variations in the lithospheric thermal structure. On the orogen side, crustal thickness and heat flow ranges from 50 to 62 km and from 55 to 120 mW/m², respectively, which is primarily dominated by a higher temperature anomaly zone related to thickened crustal partial melting. Numerical simulation shows the partial melting temperatures could reach 650–700 °C at depths of approximately 20 km. In contrast, on the Alxa Block side, crustal thickness ranges from 45 to 47 km with heat flow values between 40 and 54 mW/m², and crustal heat flow contributes less. The study suggests that regional middle-crustal partial melting is the primary heat source for the regional geothermal anomalies in the Northeastern Tibetan Plateau. Additionally, the Cenozoic crustal extension by conjugate strike-slip faulting led to lithosphere uplift. This, in turn, promoted thermal upwelling and transferred heat to the upper crust and sedimentary layers, ultimately resulting in the formation of a regional geothermal anomaly.