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

English title Geodynamic modelling of intra-plate deformation guided by 3D electromagnetic imaging of the lithosphere below Mongolia
Applicant Kuvshinov Alexey
Number 189177
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2020 - 30.09.2023
Approved amount 305'018.00
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All Disciplines (2)

Discipline
Geophysics
Other disciplines of Earth Sciences

Keywords (11)

intra-continental uplift; Mongolia; lithosphere; delamination; new transfer functions; 4D thermo-mechanical modelling; magnetotellurics; astenosphere; upper mantle; inversion; 3D EM inversion

Lay Summary (German)

Lead
Prof. Dr. Alexey Kuvshinov, ETH Zurich
Lay summary
Das Hochplateau in der zentralen Mongolei wird aufgrund seiner geographischen Lage als natürliches Labor für die Untersuchung intrakontinentaler Hebungsprozesse angesehen. Im Rahmen eines früheren DACH-Antrags wurden von den Antragstellen magnetotellurische Messungen in der zentralen Mongolei durchgeführt. Die Untersuchungen zeigen unter dem Hochplateau eine Astenosphärenaufströmung, eine entsprechend ausgedünnte Lithosphäre und fluidführende Zonen in der Unterkruste. Aus diesen Ergebnissen ergeben sich neue wissenschaftliche Fragestellungen für die Mechanismen intrakontinentaler Deformationsprozesse im Allgemeinen und für die Mongolei im Speziellen. In diesem Vorhaben wollen wir thermo-mechanischer Modellstudien durchführen, mit dem Ziel die Mechanismen von interkontinentaler Hebung und Deformation besser zu verstehen – sowohl grundlagenorientiert als auch konkret für die Bedingungen in der Mongolei. Dazu wollen wir auch neue magnetotellurische Daten erheben, um einen breiteren tektonischen Kontext in das Modellgebiet einzubauen. Zur besseren Auflösung der tieferen Stockwerke der Astenosphäre soll zudem ein Stationsnetzwerk für langperiodischer Beobachtung elektrischer und magnetischer Variation für ein Jahr installiert werden. Ziel ist die Integration von Tagesvariationen mit magnetotellurischen Messungen.  Ziel sind insgesamt ein besseres Verständnis von intrakontinentalen Deformationsprozessen, und Fortschritte bei der Integration von EM Methoden der Tiefensondierung mit geodynamischen Modellszenarien.
Direct link to Lay Summary Last update: 18.08.2020

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Associated projects

Number Title Start Funding scheme
162660 Crust-mantle interactions beneath the Hangai Mountains in western Mongolia. Insights from 3D magnetotelluric studies and 4D thermo-mechanical modelling 01.04.2016 Project funding

Abstract

Deformation in the continental interior far from plate boundaries is poorly understood and the underlying mechanisms responsible are enigmatic and 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 that involved partnership between ETH-Zürich and WWU-Münster. The study detected a localized asthenospheric upwelling, and correspondingly thin lithosphere, below central Mongolia. This is supported by seismic studies and petrological analysis. In the lower crust, the MT study revealed unexpected fluid-rich domains, indicating a weak lower crust. These results raised many 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. In fact, 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 high-resolution 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 previously acquired 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 important 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 Hovsogol 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. This will involve significant new methodological developments, including the estimation of new transfer functions in the period range of daily variations and a new numerical tool for joint inversion with MT responses. The main challenges are that the inversion requires working in spherical geometry and the spatial complexity of the global source. Ultimately, this approach will ensure that the deep asthenospheric structure below Mongolia is well constrained. This will further help to discriminate crust-mantle processes responsible for the observed intra-plate uplift.
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