Geodynamic modelling of intra-plate deformation guided by 3D electromagnetic imaging of the lithosphere below Mongolia

Basic data for this project

Description

Deformation in the continental interior far from plate boundaries is poorly understood and the underlying mechanisms responsible are controversial. Due to its location, the high plateau of central Mongolia is an ideal natural laboratory for studying intra-plate uplift. A magnetotelluric (MT) study across central Mongolia was performed in the framework of a successful 2016-2019 DACH project of the applicants. The study detected a localized asthenospheric upwelling, and correspondingly thin lithosphere, below central Mongolia. This is supported by seismic studies and petrological analysis. The MT study also revealed unexpected fluid-rich domains, indicating a weak lower crust. These results raised new scientific questions for the evolution of this region. Intriguingly, independent conceptual numerical modelling studies determined that a weak lower crust promotes lithospheric delamination, which is significant because it is an appealing hypothesis for intra-plate uplift. Lithospheric delamination, driven by negative buoyancy, acts to thin or remove the lithosphere and prompts an asthenospheric upwelling, causing and supporting surface uplift. A careful comparison of requirements for delamination-induced uplift from numerical models and present-day and past geophysical and geological parameters in Mongolia reveals a close agreement. In this project, we propose to create geodynamic models, in the form of 4D thermo-mechanical numerical models, with the aim to understand the origin of intra-plate uplift and plateau-growth both fundamentally and as it applies to Mongolia. Numerical models provide the opportunity to test hypotheses for intra-plate uplift by predicting their spatial and temporal evolution. We will rely on 3D electromagnetic imaging, which can extract information about the physical properties at depth, to provide critical rheological input parameters and structural constraints. In turn, the model output will be evaluated against observational constraints, including geophysical and geological evidence. To do this we will combine previous electromagnetic data with new data covering a broader tectonic context. We propose to acquire new MT data across northern Mongolia, where currently the subsurface structure is comparatively unknown. This will give constraints on the lithospheric properties and architecture in the transition from the thin lithosphere, weak lower crust, and high plateau of central Mongolia to the thick lithosphere and strong crust of the Siberian Craton. Furthermore, the change in the style of crustal deformation, from compression to extension of the Hövsgöl rift, in this region is intriguing. To model the deep asthenospheric structure below Mongolia a new approach is required. To achieve this, a new network of dedicated year-long electromagnetic measurements across Mongolia is proposed, along with methodological advances to utilize solar quiet daily variations in combination with MT, and 3D inversion in a spherical geometry.