Numerical and analogue modelling of tectonic processes
Numerical and analogue modelling has been applied to solve a range of geodynamic problems related to convergent tectonics in the Variscides, Tibetan-Himalayan system and Central Asian Orogenic Belt. Using numerical magmato-thermo-mechanical models we study the fate of the crust during continental subduction and collision. Our models capture different spatial scales of the collisional process: upper-mantle scale (trans-lithospheric flow of subducted material), crustal-scale (laterally-forced gravity-driven overturns in crust) and local (melt transfer through crust).
Numerical model of trans-lithospheric diapirism. The model is two-dimensional and simulates motion and thermal evolution of the earth's crust and upper mantle on a regional scale. It shows that the weak continental crust can be subducted to mantle depth and then either exhume back in a channel along the subduction zone or flow through the sub-lithospheric mantle and lithosphere into the upper-plate crust. The process is accompanied by melting of the subducted material and hydration and melting of the mantle. The model explains the occurrence of ultra-high-temperature ultra-high-pressure rocks in the European Variscides. [link] [link]
The Paleozoic Variscan orogen in Europe or the Mongol-Hingan orocline in the Central Asia are partly built-up of dome-like structures comprising migmatites and granulites and are surrounded by sedimentary units affected by Barrovian metamorphism. The arrays of such domes form by crustal-scale buckling, whereas the crust was heated during a precursory phase of extension or by emplacement of a hot relaminant below the lower crust. The development of these domes is associated with rapid ascent and cooling of their anatectic cores. [link]
Using the analog modeling, we aim to understand the dynamics of buckling of the crust containing an anatectic lower crust and role of melt in this process. The models are created in the Tectonic modeling laboratory at the institute of Geophysics. We use paraffin wax superposed by sand (+ low density cenosphere particles) to simulate the lower and upper crust, respectively. A thermal gradient is created by heating of the models from the bottom by a heating plate. A computer controlled step-motor is used to move the base plate against a backstop. We employ standard particle image velocimetry tools (Python OpenPIV, Matlab (PIVlab)) and also the state of the art deformation quantification system, the stereoscopic 3DStrainmaster from LaVision GmbH, based on digitial image correlation technique. [link] [link]
There are two currently running analog modeling projects related to the crustal scale buckling involving the anatectic lower crust. The first is a parametric study of dome shape development at different thermal gradients and tectonic shortening velocities. In the second one, we aim to understand and quantify the impact of changing indentor angle, simulating the progressively closing limb of an orocline, on the growth, deformation pattern and final shapes of the anatectic domes.
Left: Apparatus for a thin sheet contraction modelling and example of a progressing model of detachment folding. The device is capable of heating the model from top and bottom to create a stable thermal gradient in the vertical profile. The basal plate is pulled to the right by a computer controlled step-motor. This allows a deformation of the model multilayer by pushing against the back-stop wall on the right. Paraffin wax and granular materials (sand and cenosphere mixtures) are used to simulate the ductile anatectic lower crust and brittle upper crust, respectively.
Right: Experimental setup for simulating crustal-scale detachment folding with an anatectic lower crust, where deformation is captured in the plan view. The temperature of the bottom hot plate and the ‘heat box’ is set close to the melting point of the wax inside of the model. The model is preheated for 24 hours to attain an equilibrated thermal gradient and then horizontally shortened. In next series of models, the indentor angle will progressively change during the shortening to simulate the deformation conditions in the region confined in front of a closing orocline.