Mid-Miocene lithospheric mantle delamination and rejuvenation of Himalayan orogenesis

Continuous Cenozoic India-Asia convergence and collision has formed the Himalayan orogen with complex multiphase structural deformation, magmatism and metamorphism, preserving critical records for unraveling the Himalayan orogenic process and collisional orogeny. Following the intense shortening and thickening, the exhumation of the orogenic core (the Greater Himalayan Crystalline, GHC) and related stretching activities along the South Tibetan Detachment System (STDS) have occurred since the Oligocene. By the mid-Miocene, activities along the STDS ceased, while the N-S contractional structures, such as the Main Central Thrust (MCT), Gyirong-Kangma thrust (GKT), and Main Boundary Thrust (MBT), (re-) activated. Concurrently, extensive anatexis at multiple depths, diverse magmatism involving contributions from the Tethyan Himalayan Sequence (THS), GHC, Lesser Himalayan Sequence (LHS), Indian thickened lower crust, and lithospheric mantle, ultrahigh-temperature metamorphism, and the rapid uplift of the orogen occurred. The mid-Miocene deep processes, relationships among these tectono-anatexis-magmatic-metamorphic events, as well as implications for the Himalayan orogenesis remain poorly constrained. This paper reviews the records of tectonics, anatexis, magmatism, metamorphism and uplift history of typical localities in the orogen, with a focus on the mid-Miocene geological processes. It is concluded that the delamination of Indian lithospheric mantle triggered the (ultra-) high temperature anatexis-magmatic-metamorphic events and rapid uplift of the orogen in the mid-Miocene. The removal of the orogenic root reduced the resistance to underthrusting, induced the (re-) activation of the thrusts, and rejuvenated the Himalayan orogenesis, with its influence in Tibet and its adjacent regions. Undoubtedly, the continuous convergence between continents serves as the fundamental driving mechanism of the Himalayan orogenic rejuvenation.