Surface Expressions of Rayleigh-Taylor Instability in Continental Interiors

Abstract

Two-dimensional thermal-mechanical numerical models show that Rayleigh-Taylor-type (RT) gravitational removal of high-density lithosphere may produce significant surface deformation (vertical deflection >1000 m) in the interior of a continental plate. A reasonable range of crustal strengths and thicknesses, representing a variation from a stable continental interior to a hot orogen with a thick crust, is examined to study crustal deformation and the surface deflection in response to an RT instability. In general, three types of surface deflection are observed during the RT drip event: (1) subsidence and negative topography; (2) uplift and positive topography; (3) subsidence followed by uplift and inverted topography. One key factor that determines the surface expression is the crustal thickness. Models with a thin crust mainly show subsidence and develop a basin. In the thick crust models, surface expressions are more variable, depending on the crustal strength and depth of high-density anomaly. With weak crust and a deep high-density anomaly, the RT drip is decoupled from the overlying crust, and the surface exhibits uplift or little deflection, as the RT drip induces contraction and thickening of the overlying crust. In contrast, with a strong crust and shallow anomaly, the surface is more strongly coupled with the drip and undergoes subsidence, followed by uplift.