A 3D lithosphere-scale model of the Barents Sea and Kara Sea region

• Main Author: Klitzke, Peter
• Format: Thesis
• Language: English
• Published: RWTH Aachen University 2020
• Subjects: Barents Sea; 3D Gravity Modelling; 3D Modelling; Lithosphere; Arctic; Arctic Ocean; Svalbard; Kara Sea; Vestbakken; Novaya Zemlya
• Online Access: https://dx.doi.org/10.18154/rwth-2020-11440; https://publications.rwth-aachen.de/record/807554

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2020). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020 : The Barents Sea and Kara Sea encompass one of the wide shelf margins of the Arctic Ocean. Since the 70-ies, scientific and economic studies contributed to a comparatively broad geological and geophysical database with regard to the remaining Arctic. A dense grid of seismic reflection profiles and few deep seismic refraction profiles clearly image that subregions experienced fundamentally different modes of basin formation. Extrapolation of structural geological information from onshore geology implies the presence of different tectonic provinces as a result from Precambrian to Paleozoic basement amalgamation. The deep crustal and lithospheric structure is only insufficiently imaged by seismic data across the Barents Sea and Kara Sea and the spatial extent of orogenic provinces and their potential influence on different stages of basin evolution from Paleozoic to early Cenozoic times remains only poorly understood. Therefore, the scope of this PhD thesis is to develop a 3D lithospheric model that captures first-order structural, compositional and thermal information on the sediments, the crystalline crust and the lithospheric mantle to understand the main factors controlling the evolution of these basins. Published datasets on the structural configuration, on physical properties and the temperature distribution are available but heterogeneously distributed across the study area. Therefore, a 3D modelling workflow is established. In a first step, all available geological and geophysical data, including interpreted seismic refraction and reflection data, seismological data, geological maps and previously published 3D models are integrated into one consistent model. This approach provides several advantages. The geological model can be constrained in more detail for regions where different types of observations exist such as for the top basement. In addition, the interpretation of coarsely scattered data can essentially be improved by applying physical principles in the frame of 3D gravity modelling in underexplored regions. In this context, 3D gravity modelling was used to constrain the configuration of the continental upper and lower crust. The final model resolves four major megasequence boundaries (earliest Eocene, mid-Cretaceous, mid-Jurassic and mid-Permian), the top crystalline crust, the top of the lower continental crust, the Moho and a newly calculated lithosphere–asthenosphere boundary. In addition, the 3D gravity modelling approach provides the base for a lithology-controlled parameterization of the crust (with mechanical and thermal properties) to allow for 3D calculations of the conductive thermal field and strength of the lithosphere. The structural and physical configuration of the lithosphere correlates with the orogenic and subsidence history of the Barents Sea and Kara Sea region. The southwestern Barents Sea is underlain by a thinned lithosphere (80 km) and high geothermal gradients as the result of multiple Phanerozoic rifting episodes. Thereby, rifting followed predominantly the Caledonian grain and culminated in the opening of the NE Atlantic from Paleocene/Eocene times on. Net horizontal forces exerted by the mid-oceanic ridge are high enough in Miocene times to overcome the lithospheric strength and could explain compressional deformation along the Vestbakken margin and at the Bjørnøyrenna Fault Complex in the western Barents Sea as observed in seismic lines. Thinnest continental lithosphere is present below northwestern Barents Sea including Svalbard (60 km), where late Cenozoic uplift was most pronounced. The East Barents Basin is assumed to encompass Timanian basement. The lithosphere thickens in two major steps to 150 km and follows the curvature of Novaya Zemlya. This correlation indicates that the lithosphere was possibly reworked during the Uralian collision. Elevated mantle densities as observed below the eastern Barents Sea seem to isostatically compensate thicknesses of the less dense sediments. This spatial relationship further exposes mantle density variations as a driving force for significant late Permian–earliest Triassic subsidence. Similar lithospheric thicknesses are found in the northern Kara Sea, which is also probably underlain by Timanian basement. Thickest lithosphere (200 km) and elevated upper mantle velocities distinguish the South Kara Basin from the surrounding regions. The positive mantle velocity anomaly may indicate a different upper mantle composition and support the affinity to the Siberian Craton. Beyond the discussion of the basin history, the shallow thermal and pressure configuration of the sediments was extracted to calculate the potential gas hydrate distribution at present-day and future alterations with regard to ocean warming. The modelling results show that thickest potential gas hydrates at present-day occur along the western Svalbard continental margin where their existence was revealed by numerous bottom-simulating reflectors in seismic profiles. Considering moderate ocean warming models, the gas hydrate stability zones along the continental margin will thin by several tens of meters within the next 100 years. In summary, this thesis demonstrates that the 3D lithospheric model is consistent with geological and geophysical data and reproduces independent observables including the gravity and thermal fields. The model is the first one to link the deep and shallow lithospheric structural and physical configuration with tectonic processes both onshore and offshore across the Barents Sea and Kara Sea region. The derived thermal field and rheological configuration could potentially serve as boundary condition for new projects covering different spatial scales including plate tectonic models as well as high-resolution basin models and geothermal projects. : Published by RWTH Aachen University, Aachen