Thermal and compositional lithospheric structure of the Sichuan-Yunnan region and its implication to lithospheric thinning

The Sichuan-Yunnan region is situated in the southwestern part of the Chinese mainland. The investigation of its lithospheric structure is essential for comprehending the tectonic evolution of the area. However, different research schemes have different focuses and limitations, which lead to disputes on the lithospheric structure and tectonic evolution process in the Sichuan-Yunnan region. Lithospheric thermal and compositional structure of these disputes. Based on thermodynamic simulation and probability density inversion, we studied the lithospheric thermal and compositional structure in the Sichuan-Yunnan region using the observed Rayleigh wave phase velocity dispersion curve, geoid height, topography and surface heat flow. The results show that the lithosphere in the Sichuan-Yunnan region is thinner in the south and thicker in the north. The thinner lithosphere of the IndoChina block is 60 similar to 80 km thick, with relatively small fluctuations; the lithosphere thickness in the Sichuan-Yunnan diamond block and the western edge of the Jiangnan orogenic belt increases from south (similar to 80 km) to north (similar to 200 km); the Songpan Garze block maintains thicker lithospheric roots (similar to 240 km). The lithospheric mantle of the IndoChina block and the western margin of the Jiangnan orogenic belt is mainly composed of transitional and refractory olivine, indicating the existence of some ancient refractory lithospheric mantle material. The lithospheric mantle of the Sichuan-Yunnan diamond block is mainly composed of fertile peridotite, indicating that the ancient refractory mantle lithospheric material has been replaced by new material. Through the study of the lithospheric thermal and compositional structure in the Sichuan-Yunnan region, this paper proposes that the southern Sichuan-Yunnan region is affected by the collision of the Indian plate and the Eurasian plate, resulting in the thickening and delamination of the lithosphere in this region, with ancient refractory lithospheric mantle materials still present. In the Sichuan-Yunnan diamond block, delamination led to the upwelling of hot asthenosphere materials, forming a new and fertile lithosphere. In other words, thermal erosion plays an important role in the process of lithospheric thinning of the Sichuan-Yunnan diamond block.