Quantifying the impact of mechanical layering and underthrusting on the dynamics of the modern India‐Asia collisional system with 3‐D numerical models

Abstract

The impact of mechanical layering and the strength of the Indian lower crust on the dynamics of the modern India-Asia collisional system are studied using 3-D thermomechanical modeling. The model includes an Indian oceanic domain, Indian continental domain, and an Asian continental domain. Each domain consists of four layers: upper/lower crust, and upper/lower lithospheric mantle. The Tarim and Sichuan Basins are modeled as effectively rigid blocks and the Quetta-Chaman and Sagaing strike-slip faults as vertical weak zones. The geometry, densities, and viscosities are constrained by geophysical data sets (CRUST2.0, gravity, and seismology). Both static (no horizontal movement of model boundaries) and dynamic scenarios (indentation) are modeled. It is demonstrated that 3-D viscosity distributions resulting from typical creep flow laws and temperature fields generate realistic surface velocities. Lateral variations in the gravitational potential energy cause locally significant tectonic overpressure (i.e., difference between pressure and lithostatic pressure) in a mechanically strong Indian lower crust (up to~500 MPa for the static scenario and~800 MPa for the dynamic scenario). Different density distributions in the lithosphere as well as different viscosities (3 orders of magnitude) in the Indian lower crust cause only minor differences in the surface velocity field. This result suggests that

The Mechanism and Dynamics of N‐S Rifting in Southern Tibet: Insight From 3‐D Thermomechanical Modeling

“…Over 40 million random Lagrangian markers are deployed evenly in the Eulerian cells. Table 1 ( Jiménez-Munt et al, 2008;Lechmann et al, 2014;Priestley et al, 2008;Xu et al, 2015;Yuan et al, 1997;Zhao et al, 1993). One extra sticky air layer (20 km thick) is imposed in the top of the model domain, approximating the crustal surface as an internal free surface (Schmeling, 2008).…”

Impact of Lithospheric Strength Distribution on India‐Eurasia Deformation From 3‐D Geodynamic Models

“…Previous authors have used 3‐D thermos‐mechanical simulations that derive viscosity structure from laboratory flow laws and/or assumed temperature profiles to investigate the role of the subducted Indian plate, lateral crustal strength variations within Asia, and preexisting strong lithospheric blocks in the development of topography within the IN‐EU collision zone (Capitanio & Replumaz, ; Chen et al, ; Chen & Gerya, ; Cook & Royden, ; Lechmann et al, , ; Püsök & Kaus, ; Yang & Liu, , ). These results highlighted the need for variable variations in both vertical and lateral strength in order to reproduce observed topography.…”

Limitations on Inferring 3D Architecture and Dynamics From Surface Velocities in the India‐Eurasia Collision Zone

“…The primary result of the modeling exercise is to demonstrate that a simple vertically homogeneous TVS with kinematic boundary conditions determined from relative plate velocities, body forces set by the distribution of GPE, an approximate representation of crustal faults using lateral variations in effective viscosity, and realistic coupling of the Pamir and Tibet fits the full GPS surface velocity field within uncertainties for the entire Indo-Asian collision from Afghanistan to SE Asia. Quantitative comparisons of the best TVS solution to fully 3D forward models that incorporate additional structural and dynamic complexity based on a priori additional knowledge of the region, such as stresses applied by a coherent lithospheric slab in the Pamir, the development of very weak lower crust in Tibet (Royden et al, 2008), sublithospheric tractions (Ghosh et al, 2006), or the introduction of 3D architecture (Lechmann et al, 2014;Yang & Liu, 2013), demonstrate that increased complexity does little better than our minimally complex formulation in reproducing the observed surface velocities, and therefore violates an information criterion of model efficiency. On the other hand, simpler models than the TVS, such as a three-block elastic formulation (Avouac & Tapponnier, 1993) or a homogeneous Newtonian sheet (England & McKenzie, 1982), perform so poorly at matching the high spatial resolution of available surface velocities and topography that they also violate the information criterion.…”

“…Geophysical Research Letters 10.1002/2017GL076503 conditions in westernmost Tibet that preclude westward advection of mass (i.e., strike-slip only) (e.g., Flesch et al, 2001;Lechmann et al, 2014;Vergnolle et al, 2007;Yang & Liu, 2013) with continuity across the northern Karakorum Fault (e.g., Robinson, 2009), shortening in the Pamir (Ischuk et al, 2013), and westward extension into the Tajik Depression (Ischuk et al, 2013). This version of the forward model also includes a more highly spatially resolved effective viscosity and GPE distribution.…”