0000000000122299
AUTHOR
Taras Gerya
Numerical modeling of eastern Tibetan-type margin: Influences of surface processes, lithospheric structure and crustal rheology
The eastern Tibetan margin is characterized by a steep topographic gradient and remarkably lateral variations in crustal/lithospheric structure and thermal state. GPS measurements show that the surface convergence rate in this area is strikingly low. How can such a mountain range grow without significant upper crustal shortening? In order to investigate the formation mechanism of the eastern Tibetan-type margins, we conducted 2D numerical simulations based on finite difference and marker-in-cell techniques. The numerical models were constrained with geological and geophysical observations in the eastern Tibetan margin. Several major parameters responsible for topography building, such as th…
Numerical modelling of PT-paths related to rapid exhumation of high-pressure rocks from the crustal root in the Variscan Erzgebirge Dome (Saxony/Germany)
Abstract The Bohemian Massif in the Central European Variscides contains many crustal slices with (ultra-)high-pressure rocks related to continent-continent collision. After closure of pre-existing oceans during the Devonian, excess crustal thickness was maintained for about 50 Ma until at around 340 Ma large volumes of high-pressure rocks from the crustal root were exhumed within a few million years. We relate this event to delamination and complete detachment of the lithospheric mantle, causing a crustal-scale isostatic instability. In the Erzgebirge dome, a model region in the northern part of the massif, an array of interrelated PTtd-paths with “decompression/cooling” and “decompression…
Thermomechanical modeling of slab eduction
[1] Plate eduction is a geodynamic process characterized by normal-sense coherent motion of previously subducted continental plate. This mechanism may occur after slab detachment has separated the negatively buoyant oceanic plate from the positively buoyant orogenic root. Eduction may therefore be partly responsible for exhumation of high pressure rocks and late orogenic extension. We used two-dimensional thermomechanical modeling to investigate the main features of the plate eduction model. The results show that eduction can lead to the quasi adiabatic decompression of the subducted crust (≈2 GPa) in a timespan of 5 My, large localized extensional strain in the former subduction channel, f…
A free plate surface and weak oceanic crust produce single-sided subduction on Earth
[1] Earth’s lithosphere is characterized by the relative movement of almost rigid plates as part of global mantle convection. Subduction zones on present-day Earth are strongly asymmetric features composed of an overriding plate above a subducting plate that sinks into the mantle. While global self-consistent numerical models of mantle convection have reproduced some aspects of plate tectonics, the assumptions behind these models do not allow for realistic single-sided subduction. Here we demonstrate that the asymmetry of subduction results from two major features of terrestrial plates: (1) the presence of a free deformable upper surface and (2) the presence of weak hydrated crust atop subd…
A comparison of numerical surface topography calculations in geodynamic modelling: an evaluation of the ‘sticky air’ method
SUMMARY Calculating surface topography in geodynamic models is a common numerical problem. Besides other approaches, the so-called ‘sticky air’ approach has gained interest as a free-surface proxy at the top boundary. The often used free slip condition is thereby vertically extended by introducing a low density, low viscosityfluid layer. This allows the air/crust interface to behave in a similar manner to a true free surface. We present here a theoretical analysis that provides the physical conditions under which the sticky air approach is a valid approximation of a true free surface. Two cases are evaluated that characterize the evolution of topography on different timescales: (1) isostati…