Effects of rheology on the dynamics and development of topography in 3D numerical simulations of continental collision, with an application to the India-Asia collision zone

Abstract:

The Himalayas and the adjacent Tibetan Plateau represent the largest region of elevated topography and anomalously thick crust on Earth. Understanding the formation and evolution of the region has been the focus of many tectonic and numerical models. While some of these models (i.e. thin sheet model) have successfully illustrated some of the basic physics of continental collision, none can simultaneously represent active processes such as subduction, underthrusting, channel flow or extrusion, for which fully 3D models are required.

Here, we employed the 3D code LaMEM to investigate the role that subduction, continental collision and indentation play on lithosphere dynamics at convergent margins, and the implications they have for the Asian tectonics. Our model setup resembles a simplified tectonic map of the India-Asia collision zone and we performed a large number of 3D simulations to analyse the dynamics and the conditions under which large topographic plateaus, such as the Tibetan Plateau can form in an integrated lithospheric and upper-mantle scale model.

Results of models with linear viscous rheologies show different modes between the oceanic subduction side (continuous subduction, trench retreat and slab roll-back) and the continental collision side (trench advance, slab detachment, topographic uplift and lateral extrusion of material). Despite the complex dynamics and the great variation in slab shape across the subduction-collision zone, which are consistent with tomographic observations, we note that slab-pull alone is insufficient to generate high topography in the upper plate.

Several studies suggested that external forces (i.e. ridge push, plume push or slab suction) must be important in order to sustain the on-going convergence of India towards Eurasia. We show that external forcing and the presence of strong blocks such as the Tarim Basin within the Asian lithosphere are necessary to create and shape anomalously high topographic fronts and plateaus, analogous to the Himalayas and the Tibetan Plateau.

Next, we present a few models with more complex (power-law viscous and plastic) rheologies and compare them with linear viscous models.

Funding was provided by the ERC under the European Community’s Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830.