Fig. 7: Geodynamic reconstruction of subduction, mantle flow and Cenozoic volcanism in Tibet.
Conceptual geodynamic cross-sectional reconstruction to explain Cenozoic volcanism in Tibet based on this subduction modelling study compared with the location of Tibetan Cenozoic volcanism. a Pre-collisional stage before ~50 Ma during which subduction of Tethyan oceanic lithosphere drives large-scale poloidal flow in the mantle wedge, inducing a deep-seated mantle upwelling far away (570–760 km) from the trench. This deep-seated mantle upwelling triggers sub-lithospheric mantle melting below Asian lithosphere to produce the Qiantang Alkali basaltic volcanism dated 65–45 Ma. During this stage, the Linzizong arc volcanism is very active due to fast subduction. b Collisional stage (~50–0 Ma) during which long-lived rollover subduction of Tethyan lithosphere followed by Indian continental lithosphere drives large-scale mantle upwelling in the broader mantle wedge region. This broad mantle upwelling triggers mantle melting at the lithosphere-asthenosphere boundary and involves the thickened lithospheric mantle over a large area of Tibet, producing potassic volcanism in the Lhasa, Qiangtang and Songpan-Ganzi provinces in a domain located ~440–1000 km north of the Main Boundary Thrust (MBT). During this stage, the Linzizong arc volcanism becomes progressively extinct due to continental subduction and indentation, continuously thickening the Himalayan lithosphere and due to the slowdown of subduction, while potassic volcanism takes place instead slightly to the north from 25 Ma, possibly as a result of an upwelling following Tethyan slab breakoff. Position of volcanism in (b) is based on present-day location of Cenozoic volcanics from Ding et al. (2003). LM: lithospheric mantle. The low subduction angle of the Indian slab above 150 km and deeper angle below in (b) approximate the geometry found in seismic images84 and in a geodynamic numerical subduction-collision study85.
