Transient Surface Tectonics Controlled by the Convective Thinning of the Lithosphere: Geodynamic Modeling perspective

Abstract:

Lithospheric instabilities may form in the terminal stage of the orogenic cycle and they can be responsible for various styles of surface displacements, deformation, and heating/magmatism of subduction, orogenic, and orogen-adjacent intraplate regions. Many geophysical, petrological and geological evidence suggest that orogenic plateaus such the Andes, Tibet and the Anatolian plateaus has experienced post-orogenic lithospheric removal and this removal event has a distinct spatial and temporal effect in the crust resulting in plateau uplift as well as distinct zones of shortening and extension. In this work, we use thermomechanical numerical experiments of Rayleigh-Taylor type convective instability models that are designed to investigate quantitatively the surface and crustal evolution of the removal process. Experimental results are presented for a range of models where the role of rheological characteristics of the lithosphere, imposed plate convergence velocity, pre-existing thicker crust/collapsing orogen and the strain weakening are tested to explore the transient surface tectonics. Our numerical results suggest that the initial phase of instability promotes local isostatic thickening of the crust and dynamic surface subsidence due to the downward forcing of the downwelling mantle lithosphere. Following this initial stage of instability, the sinking root thins and detaches while hot mantle lithosphere flows into the region vacated by the dripping mantle litosphere. This results in topographic inflection with surface uplift ( >1.5 km) mainly controlled by flow-induced dynamic topography and local crustal thickening above the drip. As the hot mantle ascends and comes into contact with the overlying crust, it creates significant crustal extension. Mantle dynamics can play a major role in the evolution of surface tectonics, such as shift from subsidence to uplift that develops in conjunction with the change in the tectonic style from contraction to extension. The crustal extension still occurs even with the imposed plate convergence and with previously thickened crust but such extension does not take place in the piecemeal-partial lithospheric removal models. The outcome of this work may have implications on the neotectonic evolution of the Central Anatolia and the Southern Puna plateaus.