Subduction and slab breakoff controls on Asian indentation tectonics and Himalayan western syntaxis formation

We test the link between large-scale Asian continent deformations and Indian slab subduction and breakoff during convergence by means of three-dimensional numerical models of the subducting-upper plates system. We find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the Indian motions, yet the upper plate deformation remains accommodated in a narrow belt along a straight margin. Comparable rates are measured when the subducting slab breakoff is modeled, although the convergent margin deforms and curves markedly, with large underplating contiguous to ongoing subduction, similar to what observed along the Himalayan range. The models support the interpretation of the Himalayan Western Syntaxis evolution, the progressive curvature of the Indian margin and the underthrusting as a consequence of the Indian slab breakoff. The modeled slab detachment is followed by short-lived large stresses in the upper plate interiors, propagating at large distance from the margin with a trend similar to several major Asian lithospheric faults. Such localized stress has likely provided the conditions for the formation of the Central Asian intracontinental faulting, the Bangong-Red River and the Altyn Tagh faults, that followed successive Indian slab breakoff episodes. Continent subduction and breakoff during India-Asia convergence offer an explanation for the different deformation mechanisms as the long-lived understhrusting and the episodic lithospheric faulting in the Asian continent and their link to deep processes.