The India-Eurasia convergence system: Late Oligocene to early Miocene passive roof thrusting driven by deep-rooted duplex stacking

Abstract

The Late Oligocene-Early Miocene epoch represents a critical stage in the collisional history of the India-Eurasia dominant collision zone. Within this timeframe, a set of tectonic events occurred simultaneously or progressively. However, the key responsible for triggering these nearly coeval events remains unclear. This study used an integrated analysis of both geological and geophysical data to document the tectonic interactions throughout the Himalayan Orogenic Belt from west to east. Deep seismic reflection profiles outline crustal geometry of a decoupled Indian subduction front, and the overlying sheets over the Main Himalayan Thrust (MHT) is evidenced with a sequence of detachment-associated ramp-anticlines. Meanwhile, regional magnetotelluric (MT) profiles document rheologic connections in the form of a highconductivity anomaly running top-to-the south between the southernmost Tibet and the areas beyond the Yarlung-Zangbo Suture Zone to the south. The overall architecture provides a complete picture of the complex deformation pattern beneath the tectonic convergence system. Together with previous studies in surface geological investigations, we propose that the enhanced duplex stacking of the underthrusting Indian crust increased crustal shortening of the convergence system. The consequent sudden exposure of the northern Himalayan domes released the accumulated stress to trigger the onset of a south-dipping passive roof thrusting through the convergence system to the southernmost Tibetan Plateau. Recognition of this exchange pattern from crustal duplex stacking to passive roof thrusting replenished an understanding of the tectonic interactions of the ongoing India-Eurasia collision.