Dynamics of the Tengchong Volcanic Region in the Southeastern Tibetan Plateau: A Numerical Study

The constraints of surface heat flow and lithospheric structure were used to investigate the dynamics of the Tengchong volcanic region based on thermal–mechanical modeling. Three different boundary conditions representing three types of tectonic movements were modeled to discuss the thermal state and lithospheric deformation. The compressive model shows that the subduction of the Indian plate causes the upwelling of asthenosphere beneath the Tengchong block. In this process, upwelling of the asthenosphere causes thinning of the lithosphere beneath the Tengchong block. However, the surface heat flow of this model is not consistent with the observations. The regional extension model shows that, under the extension, the asthenosphere upwells along the preexisting weak suture zone in the southeastern Tibetan plateau. The thickness of lithosphere is the thinnest along the suture zone, and the surface heat flow is the highest. However, the extension time was found to generally need 10–15Myr to conform to the surface heat flow, however, this is not consistent with accepted geochronological data. When a boundary condition from compression to extension is imposed, both the surface heat flow and the lithospheric structure fit well with the observations. The results show that the subduction of the Indian plate leads to the upwelling of the asthenosphere which causes a thinned lithosphere beneath the Tengchong block. Since the late Miocene (8–5Ma), the extension or extrusion has been predominant. The thermal erosion of the lithosphere caused by upwelling of the asthenosphere renders the lithosphere even thinner along the Bangong–Nujiang suture zone. The upwelling of the asthenosphere provides an upward driving force and high-temperature environment for the Tengchong volcanic region. These findings suggest that the origin of the Tengchong volcanic region is caused by both the subduction of the Indian plate and regional extension across the Bangong–Nujiang suture zone.