Syn-kinematic strata influence the structural evolution of emergent fold–thrust belts

Abstract

AbstractWhether thrusts are ramp-dominated and form imbricate fans or run out onto the syn-orogenic surface, forming ‘thrust-allochthons’, is governed by the activity of secondary ‘upper’ detachments along the syn-orogenic surface, activations of which are inhibited by syn-kinematic sedimentation at the thrust front. In the northern Apennines, where thrust systems are ramp-dominated and form an emergent imbricate fan, syn-kinematic sedimentation was abundant and accumulated ahead and above each thrust. In the southern Apennines, the far-travelled Lagronegro allochthon achieved its high displacements (>65 km) while the foredeep basin received little sediment. The imbricate fan at the front of the main Himalayan arc developed within a foredeep that experienced high rates of syn-kinematic sedimentation. In contrast, further west, the Salt Range Thrust emerged into a distal, weakly developed foredeep with significantly reduced rates of sediment accumulation. Displacements were strongly localized onto this thrust (c. 25 km displacement) which activated an upper detachment along the syn-orogenic surface. It is an arrested thrust-allochthon. Lateral variations into the adjacent, ramp-dominated but still salt-detached, Jhelum fold-belt are marked by increases in syn-kinematic sedimentation. As sedimentation styles can vary in space and time, individual thrusts and thrust systems can evolve from being allochthon prone to imbricate dominated.