Quantifying crustal stacking contribution to thickening of the eastern Northern Himalayan belt

The Indian continental crust beneath the Himalayan orogenic belt exhibits remarkable thickness (up to 78 km), approximately twice the global average for continental crust. However, its deep crustal structure and deformation mechanisms, such as distributed ductile flow versus high-intensity stacking, remain debated. This study deployed a 130 km-long, dense nodal array of short-period seismometers to investigate the crustal architecture of the eastern Northern Himalayan Belt. We applied the P-wave receiver function Common Conversion Point (CCP) stacking method to image fine crustal structures. Furthermore, we developed a neighborhood algorithm-based velocity inversion method that integrates the receiver functions with crustal H-κ parameters to derive the velocity structure. Our results reveal that the high-velocity Yardoi Dome within the mid-upper crust exhibits a short-wavelength, antiformal stacking style. The Main Himalayan Thrust (MHT) acts as a décollement, effectively decoupling the upper stacking system from the vertically thickening lower crust. We propose a hybrid crustal thickening model wherein mid-upper crustal thrust stacking dominantly contributes (approximately 70 %) to the total thickness. This is attributed to long-term thermal weakening along the Indian crustal front, where sustained high temperatures facilitated localized ductile shearing and upward crustal stacking. Critically, persistent orogenic thermal conditions preserve this ultra-thickened crust, offering a paradigm for continental thickening in collisional systems.