Seismicity and structure of a magmatic accretionary centre at an ultraslow spreading ridge: The volcanic centre at 85°E/85°N, Gakkel Ridge

• Main Author: Korger, Edith I.M.
• Format: Thesis
• Language: unknown
• Published: 2013
• Subjects: Antarc*; Antarctica; Arctic Ocean
• Online Access: https://epic.awi.de/id/eprint/33348/; https://hdl.handle.net/10013/epic.42749

Mid-ocean ridges are divergent plate boundaries, where the seafloor spreads apart and new oceanic crust is formed. Yet, there are important differences between these individual ridges, which seem to be linked to the rate with which they spread apart. At full spreading rates of < 20 mm/yr, these ridges are called ’ultraslow’ spreading, and their appearance is drastically different from ridges which spread faster. Generally, ultraslow spreading ridges have a very rugged appearance, with steep rift flanks which contain numerous normal faults, and discontinuous volcanic activity in space and time at discrete volcanic centres. Magma supply is thought to be extremely limited, as mantle flow models infer a reduced melt production owing to the greater conductive cooling compared to faster spreading ridges. Crustal thickness as well is thought to be affected by the greater conductive heat loss of the ascending mantle, resulting in thick crust at volcanic centres, and only thin or absent crust in between. However, the processes which cause this are still only poorly understood. Ultraslow spreading ridges consist of alternating magmatic and amagmatic segments, each emphasizing a primary accretionary mode. Magmatic segments are robustly magmatic, with basalts exposed on the seafloor and axial volcanic ridges. In contrast, at amagmatic segments volcanic activity seems to be almost absent, and plate divergence is accommodated by the uplift of mantle horst blocks. Predominantly peridotites are dredged from the seafloor, interrupted by isolated centres of volcanic activity. Due to the remote locations of the two main representatives of this spreading class (Arctic Ridge System, Southwest Indian Ridge), only few surveys have so far been conducted. Gakkel Ridge, as part of the Arctic Ridge System, lies in the perennial ice covered Arctic Ocean far from any land, and the Southwest Indian Ridge is located between South Africa and Antarctica in latitudes with frequent storms. Both environmental conditions inhibit seismic surveys ...