Abstract:

Analogue modeling of the formation and evolution of Longmenshan belt and foreland basin system in western Sichuan Basin reveals a strong impact of tectonics, erosion, and sedimentation as well as of the interactions between the later two processes, especially those changing along the the strike of the system.The modeling shows a negative relationship between wedge geometry (i.e., length and height) and surface erosion magnitude.Heavier erosion makes it easier for faults at the back of the wedge to thrust in a random sequence and be reactivated, thus stopping the wedge from further forelandward propagating.While surface sedimentation, that adds to the layers overlying the thrusts and increases the possibility of fault locking, serves to faciliate the forelandward propagation of the wedge.Changing (e.g., increasing) erosion-sedimentation process along the strike of the wedge results in a direction shift of the strike of deep strata and steeper faults at the back of the wedge, some evidently shrinking forelandward faults with smaller dips and increasing backthrusting and the formation of oblique ramps in the foreland basin.We therefore conclude that it is this changing or differential erosion-sedimentation process in the Longmenshan belt and foreland basin system since the Late Triassic that controls the development of a rejuvenated foreland basin with a possible oblique ramp (Longquanshan fault) from the Late Cretaceous to Ceonozoic.

Key words: erosion-sedimentation, wedge, foreland basin, analogue modelling, Longmenshan, western Sichuan Basin