Subductability of continental lithosphere

Multiple lines of evidence from geological and geophysical observations indicate the deep subduction of continental lithosphere; however, the potential and driving forces of (self-sustained) continental subduction remain unclear. Here, systematic thermal-petrological models were conducted to quantitatively evaluate the subductability of continental lithosphere by analyzing its density structure and slab-pull evolution during subduction. The results indicate that the metamorphic densification of deeply subducted continental lithosphere (upper, middle, lower crust and lithospheric mantle) could provide considerable driving force for continental deep subduction. The numerical models further indicate that, if a Phanerozoic or Proterozoic continental lithosphere is dragged to a large depth of >300 km, then the continental slab pull overcomes the overall resistance force. Consequently, the continental subduction occurs self-consistently without any drag from the preceding oceanic slab. For Archean continental lithosphere, it is more difficult for self-sustained subduction to occur, due to the highly depleted mantle composition. In addition, we also systematically quantified the effects of multiple factors, including the scraping of continental crust, subduction velocity, subduction angle, and variable bulk-rock compositions of continental crust. Finally, a representative case study of the Himalayan orogen revealed that the slab pull of presently subducting Indian continental lithosphere ranges from 13 TN/m to 29 TN/m, providing a major contribution for the ongoing India-Asia collision.