9:00am - 9:30amSession Keynote
Cenozoic evolution of the Icelandic Plume and its influence upon the topographic evolution of Northwest Europe
University of Cambridge, United Kingdom
The Icelandic mantle plume is probably the largest convective upwelling on Earth. It is generally agreed that its growth and evolution have had a significant influence on the geologic and oceanographic evolution of both the North Atlantic Ocean and Northwest Europe during Cenozoic times. At the present day, three significant observations testify to the existence and size of this plume.
First, residual depth anomalies prevail in the oceanic lithosphere surrounding Iceland. These anomalies show that the oceanic plates are 1-2 km shallower than expected in a region that stretches from Baffin Bay to the coast of Norway, and from Svalbard to Newfoundland.
Secondly, an irregular-shaped long wavelength free-air gravity anomaly with an amplitude of 30-50 mGal is centred upon Iceland.
Thirdly, full-waveform tomographic imaging of the North Atlantic region shows that the planform of the Icelandic plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100-200 km. Distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. It has been suggested that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. For radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the Péclet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. Shear wave velocity estimates have been combined with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plates. These calculations yield mobility ratios, Péclet numbers, and asthenospheric channel thicknesses that are compatible with Saffman-Taylor fingering. A useful rule of thumb is that the wavelength of fingering is ~5 times the thickness of the horizontal layer. Across the Northwest European shelf, the pattern of mapped residual topography and subsidence anomalies is remarkably consistent with the planform of asthenospheric fingering. In conclusion, a combination of disparate observations supports the notion that Cenozoic dynamic topography of Northwest Europe is generated by fast, irregular horizontal flow within thin, but rapidly evolving, asthenospheric fingers of the Icelandic plume.
9:30am - 9:45am
Timing and mechanisms of Late Mesozoic to Early Cenozoic exhumation and uplift in Central Europe
University of Göttingen, Geoscience Center, Germany
Widespread exhumation and uplift affected Central Europe in Late Cretaceous to Paleogene time (e.g. Kley and Voigt, 2008, Geology, 36, 839-842). The area involved includes thrust-related basement uplifts and inverted Mesozoic basins and extends at least from the Rhenish Massif to the Bohemian Massif and from the Black Forest/Vosges to the North German Basin. Exhumation and basin inversion started at approx. 95 Ma based on stratigraphic constraints (Voigt et al. 2021, Solid Earth, https://se.copernicus.org/preprints/se-2020-188), well in line with ZHe cooling data (e.g. von Eynatten et al. 2019, International Journal of Earth Sciences, 108, 2097-2111). Late Cretaceous SW-NE directed basement thrusting (e.g. Harz Mountains, Thuringian Forest, Flechtingen High) peaked around 85 to 70 Ma. Thermochronological data (AFT, AHe) from the Triassic uplands between the basement highs reveal km-scale exhumation of a wider region, at least 250-300 km across, suggesting long-wavelength domal uplift (von Eynatten et al. 2021, Solid Earth, 12, 935-958). This domal uplift is dated slightly later at 75 to 55 Ma and calls for a separate mechanism superimposed on the Late Cretaceous compressional event. Based on timing, spatial extent of the doming area and thickness of eroded strata (3-4 km), possible mechanisms are evaluated for their contribution to exhumation and uplift. While shortening and crustal thickening may explain 50% of the domal uplift at most, upwelling asthenosphere driving dynamic topography appears capable of producing uplift and erosion of the required magnitude, wavelength and rate.
9:45am - 10:00am
On Mesozoic uplifts along the SW edge of the East European Craton – new insight from regional onshore (PolandSPAN) and offshore (BalTec) seismic reflection data from Poland
1Institute of Geological Sciences, Polish Academy of Sciences, Poland; 2Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland; 3Institute of Geophysics, University of Hamburg, Hamburg, Germany; 4Polish Geological Institute, Gdańsk, Poland; 5Federal Institute for Geosciences and Resources (BGR), Berlin, Germany
East European Craton (EEC) in Poland has been recently studied by onshore PolandSPAN and offshore BalTec regional seismic surveys. PolandSPAN data imaged earliest Late Jurassic, earliest Late Cretaceous and mid-Late Cretaceous laterally extensive unconformities that document hitherto unknown substantial uplifts of the SW edge of the EEC. Cretaceous unconformities might have been formed as a result of inversion-induced buckling of the cratonic edge. BalTec offshore survey was acquired within the transition zone between the Paleozoic Platform and EEC. SW part of BalTec data imaged offshore segment of the Mid-Polish Swell formed due to inversion of the axial part of the Polish Basin. NE from the MPS, within the Bornholm–Darłowo Fault Zone, system of Late Cretaceous strike-slip syn-depositional faults was documented. E part of the BalTec survey is located above the EEC basement overlain by Cambro-Silurian sedimentary cover that is dissected by a system of steep, mostly reverse faults, regarded so far as having been formed as a result of the Caledonian orogeny. BalTec seismic data proved that at least some of these deeply-rooted faults were active as a reverse faults in latest Cretaceous. This suggests that large Paleozoic blocks might have been uplifted during the widespread Late Cretaceous inversion. Erosion of these blocks might have provided sediments that formed Upper Cretaceous progradational wedges within the onshore Baltic Basin imaged by PolandSPAN data.
This study was funded by NCN grants UMO-2017/27/B/ST10/02316 and UMO-2015/17/B/ST10/03411. ION Geophysical is thanked for providing PolandSPAN seismic data, and Kingdom IHS for providing seismic interpretation software.
10:00am - 10:15am
Evidence for time-variable thickness of the Phanerozoic continental lithosphere in Central Europe
1Kiel University, Germany; 2National Research Institute of Astronomy and Geophysics, Cairo, Egypt; 3Dublin Institute for Advanced Studies, Dublin, Ireland; 4Institute of Geosciences (CSIC,UCM), Plazade Ciencias, 3, ES-28040 Madrid, Spain; 5GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
The Phanerozoic lithosphere in Central Europe was formed due to the Caledonian and Variscan Orogenies. It then probably underwent modification and thinning associated with widespread and intense Permian volcanism. Since the Permian, the evolution of the Central Europe lithosphere is characterized by various phases of moderate extension and inversion tectonics caused by external forces. Sedimentation and intra-plate volcanism yield evidence for additional intra-plate processes related to variable lithsopheric thickness and deformation. Whereas its crustal structure has been extensively studied by Deep Seismic Soundings, properties of the subcontinental mantle lithosphere including its thickness are less well known. Surface waves are well suited to study the lithosphere and the sub-lithospheric structure, being mainly sensitive to the S-wave velocity structure at those depths. Here we present results of high-resolution surface-wave tomography, down to ~250 km depth, from automated broad-band inter-station Rayleigh phase velocities. The thickness of Central Europe lithosphere shows a remarkable variability. Thick lithosphere is found beneath the Paris Basin, whereas the lithosphere in the area of the North German Basin and the Bohemian Massive shows moderate thickness. Thinner lithosphere is found in the area of the Cenozoic intra-plate volcanism. Comparison to the distribution of Permian and Jurassic volcanic rocks provides evidence for a time variable thickness of the continental lithosphere in Central Europe. We relate subsidence and sedimentation without substantial extension to lithospheric cooling and thickening. In contrast, uplift and volcanism without compression indicate thermal thinning of the lithosphere. Conceptual models for the lithopsheric evolution in the area are discussed.