Poster Abstract
The driving force behind the break-up of continents has been hugely debated during the past years: is it caused by hot upwellings in the Earth’s interior or processes acting upon the Earth’s surface? Getting to know the temperature just below the Earth’s outermost layer, in the upper mantle at the time the separation of the continents happened could provide clues as to which process is responsible. We used a method, the Hc-Vp, to estimate this temperature from seismic wave-speed measurements carried out on more than 40 3-400 km long lines in the North Atlantic Ocean between 55°N and 75°N latitudes.
Our results show more than 300°C variation between the lowest and highest temperatures: the areas with the highest temperature are the Northeast Greenland margin and the Greenland-Iceland-Faroes Ridge with over 1500°C, while the lowest temperatures are found in the oceanic basin just north of Iceland with less than 1250°C. This variation corresponds to more than. 20% of the average mantle temperature of 1300°C. Generally closer to the continents’ edge, higher mantle temperatures prevail, while in the middle of ocean basins the temperature evens out with a value close to the average mantle temperature. This indicates the disappearance of the initial thermal anomaly through the opening of the North Atlantic Ocean. We attempt to locate the centre of this anomaly from the temperature distribution by assuming a symmetrically shaped initial anomaly. By locating the centre of the anomaly and tracking it through the evolution of the opening North Atlantic Ocean, we prove that a hot upwelling primarily influenced the separation of Greenland from Europe.
Plain text summary
There are some high bathymetry areas in the North Atlantic region, most notably the Greenland-Iceland-Faroes Ridge and the continental margins. The continental margins are a result of continental break-up between Greenland and Europe and are characterised by voluminous magmatism. The question is whether continental break-up is initiated by external forces acting upon the plates of the Earth (Plate model) or by internal forces, like mantle upwellings originating deep inside the Earth (Plume model) that weaken the crust and eventually lead to continental break-up. In order distinguish between these two models mantle temperature and active upwelling distribution is estimated. We expect a margin parallel temperature anomaly if external forces dominate while a circular pattern if internal forces do. A melting model provides connection between mantle properties such as mantle temperature and active upwelling ratio and physical observables such as crustal thickness and p-wave velocity. This enables us to estimate mantle temperature and active upwelling directly from seismic profiles. A map of mantle temperature and active upwelling is created to compare with our expectations from the Plate and Plume models. High mantle temperature was found at high bathymetry areas, like the Greenland-Iceland-Faroes Ridge and the continental margins. Low temperatures dominate the middle of the North Atlantic Ocean. The high temperature anomaly disappears 10 million years post-break-up when temperatures reach a steady value. This indicates the disappearance of the initial thermal anomaly. High active upwelling values characterise the Greenland-Iceland-Faroes Ridge, offshore Northeast Greenland and offshore the UK. Everywhere else passive upwelling dominates. Original temperature distribution at the location of the seismic profiles was reconstructed back in time to 40, 45 and 50 million years. A 2000 km wide synthetic anomaly was created to model a mantle plume. A grid search was carried out to determine whether the centre of the anomaly exists and if it does then where it would be based on the original data. Root mean square error was calculated for each possible centre position with the minimum eventually pointing out the best-fit position. The anomaly centre was located at the Greenland margin shortly after break-up happened between Greenland and Europe. In the next 5 million years its amplitude decreased and by 40 million years ago it moved inside the Greenland from the margin. The observed mantle temperatures prove that high values were dominant at the time of continental break-up. The good fit between a synthetic circular anomaly and the observed temperatures and the location of this anomaly at the margin shortly after break-up indicates that internal forces in the form of a mantle plume influenced continental break-up in the North Atlantic
Poster Title
Mantle temperature distribution and its implications during the opening of the North Atlantic Ocean
