Continental Deep Subduction Versus Subduction Cessation: The Fate of Collisional Orogens

The contrasting fates of collisional orogens, that is, continental deep subduction or subduction cessation, are widely recognized by petrological, paleomagnetic and geophysical observations. However, the mechanisms of such different collisional modes, especially the dynamics of continental deep subduction, are controversial. In this study, we integrate the phase transition-induced density evolutions into a thermo-mechanical numerical model. Combing the systematic petrological-thermo-mechanical models with force balance analysis, we find that the high metamorphic transformation degree, mildly depleted mantle composition of the subcontinental lithosphere, and a long preceding oceanic slab, increase the driving force for continental deep subduction. Additionally, the rheologically weak continental crust and asthenospheric mantle decrease the resistance force and promote deep subduction. Otherwise, the continental subduction cessation mode is favored. The calculations of slab negative buoyancy indicate that the phase transition-induced metamorphic densification of the subducted continental crust and the mildly to moderately depleted lithospheric mantle can provide a great slab pull force to sustain the continued continental deep subduction; however, the positive buoyancy of highly depleted Archean lithospheric mantle impedes deep subduction and causes subduction cessation. Based on systematic numerical models, we also evaluate the crustal mass balance or deficit in continental collisional system, which indicates that ∼12%–47% of pre-collisional felsic crust could be subducted deeply with the sinking slab in the regime of continental deep subduction. In contrast, the recycled felsic crust is negligible in the regime of subduction cessation. Thus, the different modes of continental collision play a crucial role in the global crustal recycling and related mantle heterogeneities. © 2023. American Geophysical Union. All Rights Reserved.