9:00am - 9:30amMEDAL LECTURE
Durham University, United Kingdom
The potential for the extraordinary island of Iceland to resolve seemingly intransigent problems in Earth Science has long been recognized. Alfred Wegener correctly surmised that his theory of continental drift could be tested there, and the necessary geodetic measurements were started as early as 1938. This, and other geophysical work often produced unexpected results. For example, observations reported before the acceptance of Wegener's hypothesis apparently supported it, while observations reported after its widespread acceptance seemed to contradict it. Iceland has always surprised us. In my presentation I shall report the most recent surprising findings. Long assumed to be one of very few places on Earth where sea-floor spreading can be observed on dry land, this model now requires modification. The convenience of studying oceanic crustal expansion on dry land apparently comes with a price. The crustal extension occurring in Iceland represents not classical seafloor spreading, with or without a mantle plume, but rather the process of continental volcanic margin formation–the process of continental breakup itself. I shall summarize the latest findings of an international group of collaborators of which I am privileged to be a member. I shall outline the rationale for our conclusion that Iceland, far from representing a simple oceanic spreading plate boundary on land, instead comprises magma-blanketed, extended continental crust. This theory is in need of evaluation through the collection of new, independent datasets that can test the predictions of the new model.
9:30am - 9:45am
Heterogeneous nucleation and transformation of ikaite (CaCO3 x 6H2O) on mineral surfaces
Department für Geo- und Umweltwissenschaften, Ludwig-Maximilians-Universität München, Germany
One of the most puzzling calcium carbonate minerals is ikaite (CaCO3 x 6H2O). Its formation is of particular importance, because anhydrous calcium carbonate minerals occur as pseudomorphs after ikaite. Consequently, ikaite may be an important and frequently forming precursor for more stable carbonate minerals especially in cold environments of Earth (Sánchez-Pastor et al. 2016). Despite the importance of ikaite, its formation conditions are not well constrained and knowledge about its decomposition and transformation is limited. Previous studies showed that cold temperatures and increased alkalinity promote ikaite formation and that dissolved Mg2+ and/or phosphate suppress a competing precipitation of calcite and/or vaterite (Purgstaller et al. 2017). However, these studies typically concern homogeneous ikaite formation. Therefore, it is still unknown whether mineral-water interfaces, which are ubiquitous in nature, affect both nucleation and transformation of ikaite.
Using cryo-mixed batch-reactor experiments (CMBR), we investigate which effects mineral surfaces exert on nucleation of ikaite, its subsequent transformation into more stable carbonates and the product phase selectivity. Besides ex-situ analyses of solution compositions and phase inventories of the reactor, in-situ monitoring of solution pH and Ca2+ concentrations gives insights into differences and similarities of ikaite behaviour in experiments with and without added minerals such as quartz and mica. Complementary to CMBR, in-situ flow-through cryo-atomic-force-microscopy (CAFM) can reveal the temporal evolution of the reactions on defined substrates in high spatial resolution. Initial results obtained by a newly developed CAFM will be presented.
9:45am - 10:00am
A profile through ancient fast-spreading oceanic crust in the Wadi Gideah, Oman ophiolite – reference frame for the crustal drillings within the ICDP Oman Drilling Project
1Leibniz University Hannover, Germany; 2University of Kiel, Germany
The Oman Ophiolite is the largest and best-investigated piece of ancient oceanic lithosphere on our planet. This ophiolite was target of the Oman Drilling Project (OmanDP) within the frame of ICDP (International Continental Scientific Drilling Program) which aimed to establish a comprehensive drilling program in order to understand essential processes related to the geodynamics of mid-ocean ridges, as magmatic formation, cooling/alteration by seawater-derived fluids, and the weathering with focus on the carbonatisation of peridotites.
Over two drilling seasons, the OmanDP has sampled the Samail Ophiolite sequence from crust to basal thrust. The total cumulative drilled length is 5458 m, with 3221 m of which was at 100% recovery. These cores were logged to IODP standards aboard the Japanese drilling vessel Chikyu during two description campaigns in summer 2017 and 2018.
Here we present the main results of the working groups of the Universities Hannover and Kiel, focusing on the magmatic accretion of the Oman paleoridge. During 5 field campaigns these groups established a 5 km long profile through the whole crust of the Oman ophiolite by systematic outcrop sampling, providing the reference frame for the 400 m long OmanDP drill cores.
The profile contains 463 samples from the mantle, through gabbros up to the dike/gabbro transition. Identical samples have been analyzed by several methods (bulk rock geochemistry, mineral analysis, Isotope geochemistry, EBSD analysis). The results allow implication on the accretion of fast-spreading lower oceanic crust as well as on the hydrothermal cooling of the deep crust.
10:00am - 10:15am
Mass movements in Germany - contributions to the landslide susceptibility modeling
Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover/Germany
The presentation provides an overview about the project “Mass Movements in Germany (MBiD)” jointly implemented by six State Geological Surveys and the Federal Institute for Geosciences and Natural Resources in the period from 2018 to 2020. The objective pursued in this intervention was to review the practical feasibility of the spatial assessment (modeling) of the landslide susceptibility in Germany both at regional and nationwide level. The chosen approach took into consideration the specific framework conditions with regard to the availability and application of official information to evaluate the spatial probability of this hazard in Germany. Focusing on both rotational and translational landslides as well as on rockfall, fourteen modeling case studies were performed in different natural environments to explore limits and possibilities. The methods applied representing state of the art assessment tools covering bi- and multivariate statistical, heuristic, physical and machine learning methods. The necessary model parameters were mainly deduced from nationwide thematic geoinformation layers that are featured by a high degree of consistency. Based on the case studies, conclusions on the applicability of the methods, the requirements for the recorded mass movement inventory, and the use of the selected parameters and parameter classes and their validity were drawn. The results of the case studies culminated in the development of practical solutions and recommendations (workflows), which include the selection of suitable methods according to requirements and the development of reproducible approaches for modeling the regional landslide susceptibility at different scales.
10:15am - 10:30am
Geothermal Reservoir Characterisation and Probability Analysis of Fractured Media at Grimsel Test Site, Switzerland
1RWTH AACHEN, Germany; 2ETH Zürich, Switzerland
Exploitation of deep geothermal energy is considered as one of the most efficient renewable energy applications. In this sense, reservoir stimulation is established to extract geothermal energy from EGS (Enhanced Geothermal System) which is highly dependent on its in-situ structural properties: damage/shear zones, faults, fractures, its statistics and characteristics. In more detail, damage zones may behave like a conduit providing preferential pathways for fluid flow in otherwise impermeable rock such as granite or gneiss. To improve the reservoirs’ characteristics frequently hydro-shearing or hydro-fracturing are used. It is imperative to account for the natural heterogeneities of the reservoir particularly with respect to the existing fracture network. In this study, we analyze the pre-stimulation fracture network of the EGS experiments conducted at the Grimsel Test Site, in the Swiss Alps. We use original data acquired at the tunnel wall and in boreholes to constrain a probabilistic 3D model further used for H-M simulations of the enhancement experiments. Fracture analysis include scanline mapping, cluster analysis of the spatial distribution and density plots.
Keywords: geostatistics, fracture analysis, DFN modeling, 3D geological modeling, geothermal energy