Seismic structure of the crust and upper mantle in central-eastern Greenland

• Main Author: Kraft, Helene Anja
• Format: Book
• Language: Danish
• Published: Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen 2016
• Subjects: Greenland; Scoresby; Scoresby Sund; Sund; Ice Sheet; Iceland; North Atlantic
• Online Access: https://curis.ku.dk/portal/da/publications/seismic-structure-of-the-crust-and-upper-mantle-in-centraleastern-greenland(94f9141d-2ef9-4d11-99c9-453361a9bf58).html; https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122260407405763

Geophysical and geological knowledge of the interior of Greenland is very limited. The lack of knowledge arises mainly due to the logistical challenges related to conducting geophysical fieldwork on the up to 3400 m thick ice sheet, which covers around 80% of the land area. This PhD thesis is based on the very first regional passive seismic study in central-Eastern Greenland, focusing on the area between Scoresby Sund and Summit. The study aims to image the structure of subsurface Greenland starting from the crust and down to the mantle transition zone. Furthermore, the thesis links these observations with topographic features, the recent uplift history of the North Atlantic region, break-up related processes, and the possible track of the Iceland hotspot. The core of this study are P to S- and S to P- receiver functions, which image the difference in arrival time between not-converted and converted phases. The receiver functions were jointly inverted for the velocity structure of the crust and delay times, and shapes of signals originating at the mantle transition zone discontinuities, P410s and P660s, were analysed. The crustal models show a deepening of the Moho from east to west from less than 20 km depth at the east coast to 50 km in central Greenland. The observed crustal thicknesses indicate that the high topography in eastern Greenland of up to 3700 m cannot be explained by Airy type isostatic equilibrium alone. Major parts of the mantle transition zone below central-eastern Greenland are substantially thinned with up to 25 km thinner than standard. The delay times of P410s and P660s furthermore imply that the average upper mantle velocities are below IASP91-velocities. These two observations together indicate a significant heating of the region that probably cannot be explained by the passage of the Iceland hotspot alone, but requires an additional process. Analysis of the shape of the P410s signal suggests a low velocity layer below the 410-km discontinuity inside the mantle transition zone. Plans for further work include proceeding with closing the gap between the crust and the mantle transition zone and constructing seismic models for the entire upper mantle.