Delamination of the lower crust or lithospheric mantle is one explanation for the surface uplift observed in areas of mountain building. This process describes the removal of the lower part of the tectonic plate and can occur in various ways. Different styles of delamination typically have in common that the upper material (e.g., lowermost crust or lithospheric mantle) is denser than the underlying material (e.g., asthenosphere) and therefore sinks. It has been proposed that the higher density can be caused by the formation of eclogite. In this study we apply a thermomechanical model featuring a density increase within the lithosphere by a phase transition. The model setup is designed to investigate surface uplift and mountain building in an intracontinental setting. Specifically, the model is arranged to closely resemble central Mongolia. The models give insights into the dynamically evolving flow field with respect to the style of removal, therefore the general outcome is also applicable to other orogenic regions. In addition to a systematic study on the phase transition, we also investigate the influence of convergent motion and of the rheology of the crust. Our results reveal that for the absence of a dense (eclogite) layer, delamination initially occurs as a stationary Rayleigh-Taylor instability which appears as a late and short-lived event. In comparison, for a strong density contrast an early, long-lived peeling-off removal style with a stationary slab results. The subsequent asthenospheric upwelling causes further peeling-off events for all density contrasts. For this removal style a retreating slab is observed that occasionally breaks off giving way to a periodic behaviour. The findings confirm that a strong convergence and low viscosity of the crust promote delamination. In addition, the asthenospheric upwelling yields a wide and flat surface uplift. Such dome-like features are observed to be more pronounced for high density contrasts (i.e., strong eclogitisation). ... Read more

Thermo-mechanical numerical modeling can provide valuable insights by simulating the temporal evolution of dynamic processes. The simulation model can be evaluated against the available observational evidence and physically plausible mechanisms can be further explored. To better understand the evolution of the lithosphere, multi-disciplinary results can be integrated into the geodynamic modeling, creating more realistic and reliable models. What’s more, such modeling offers an excellent opportunity to test various hypotheses and to constrain the possible ranges of parameters. By systematically varying physical parameters, their influence and control on dynamic tectonic processes can be tested. Here we present work that uses Central Mongolia as a case study. This location is an ideal natural laboratory for studying surface deformation and intraplate uplift because of its high-elevation plateau in a location in the continental interior — far from tectonic plate boundaries. Intracontinental surface deformation is enigmatic, and the underlying mechanisms responsible are not fully understood. However, because deformation solely by means of tectonic plate motion is not possible in an intraplate setting, crust-mantle interactions (e.g., driven by mantle convection) are likely required to explain the origin and evolution of intracontinental deformation. Explanations for surface uplift in the continental interior include: 1. hot, buoyant, deep-rooted mantle plumes; 2. crustal thickening from mafic magmatic underplating; 3. broad-scale mantleflow and thermal convection processes that produce dynamic topography; and 4. small-scale asthenospheric upwelling prompted by isolated lithospheric removal. We use self-consistent thermo-mechanical numerical modeling to investigate a subset of the latter explanation: lithospheric removal by delamination or a Rayleigh-Taylor instability. We explore the conditions under which delamination can occur and investigate the timing and amplitude of the consequent surface deformation. ... Read more

The aim of this work is to develop a geodynamic model of our measured area in Mongolia using the knowledge from our magnetotelluric model and other fields, such as geology. In this geodynamically active region, where we observe volcanism and uplift, a thin lithosphere is determined by the magnetotelluric data. One possible process for lithosphere thinning is delamination, which is coupled to convective processes. It has been shown that features in magnetotelluric data can be linked to viscosity structures, and these can be investigated with geodynamic models. The combination of magnetotellurics and geodynamics is a new approach which we use to bring further insights into the geological history of Mongolia. ... Read more