GRÖKORT Project

In 1988 the passive continental margin of East Greenland in the region of the Scoresby Sund was investigated by deep seismic sounding and gravity measurements with RV POLARSTERN. A long continent (Scoresby Sund) ocean transition profile was observed by seismic landstations (Univ. of Kiel, E. Flüh) and ocean bottom seismographs (Univ. of Hamburg, W.Weigel). This 400 km long profile ended on the west flank of the Kolbeinsey Ridge, where another refraction profile along the 5 my isochron was observed. Seismic energy was generated by explosives and a 32 ltr.-airgun lent from the Pacific Geoscience Center, Canada. Project GRÖKORT was performed in cooperation of IFG Hamburg (coordination), IFG Kiel, Alfred-Wegener-Inst. (Bremerhaven) and the Greenland Geological Survay (GGU). The area of the Greenland margin off the Scoresby Sund was selected, because east of the Liverpool Land the Jan Mayen Ridge has been separated from Greenland and because a crustal development from young (Kolbeinsey Ridge) to old continental Paleozoic crust could be studied in a relative small area. First results show a clear oceanic crust (~10 my old) with a relative low p-velocity of layer 3a (6.0 km/s), and a Moho depth of 11.7 km.

Greenland-Scotland Ridge

In 1988 a ridge related joint project between the Geological Institute (P. Stoffers, F. Werner), the Geophysical Institute (R. Meißner), the Institute of Applied Physics (P. Koske) (University of Kiel) and GEOMAR (J.Thiede) began to investigate the geology of the Kolbeinsey Ridge north of Iceland. This project, called "The Greenland-Scotland Ridge: modern geodynamics of the world's ocean most important hot spot system", was funded by the German Ministry of Research and Technology (BMFT).

Scientific interest was focused on the aseismic Iceland-Faeroe-Ridge and on the active mid-ocean ridge segment between Iceland and Jan-Mayen (Kolbeinsey Ridge). An essential aim was to explore the deep structure of the ridge and to locate magma chambers using seismic analyses and to investigate the petrology of the MOR rocks and their chemical relation to the Iceland hot spot. Investigations of the hydrothermal site near Kolbeinsey Island include analyses of hydrothermal precipitates, biological studies, and hydrocast seafloor observations with the submersible GEO. Another aim of this project was to investigate the sediment composition and distribution in the vicinity of the Kolbeinsey Ridge. Of pronounced interest were the relations between volcanic, hydrothermal, detritic and biogenic particle input and the resulting sedimentary deposits. Dating and correlation of sediment layers allowed us to reconstruct changing depositional processes in space and time. Geochemical investigations have been used to elucidate elements or element groups suitable for characterizing these different depositional processes.
Investigations in the target area performed during five expeditions led to a better understanding of depositional processes near the ridge crest. The combination of processes leading to deposition, redeposition and overprinting of sediments makes the reconstruction of the depositional environment difficult. The geotectonic-structural character of the mid-ocean ridge as well as the oceanographic and climatic processes are highly important inter-regional factors influencing the depositional processes. Of more local importance are the morphological structure, depth and volcano-tectonic activities of ridge segments. In detail, ridge crest morphology and small-scale current systems which depend on this morphology play an important role by controling sediment distribution patterns, sediment transport and the maintenance of ecological niches for sessile benthos (foraminifers, sponges). In the southernmost part of the Kolbeinsey Ridge, explosive volcanic activity, the appearance of which is highly dependent on water depth, provides the most important contribution to sedimentary deposition. North of the Spar Fracture Zone, deposition is mainly of pelagic character. The Spar Fracture Zone itself is characterized locally by typical sediments due to its extreme morphology. Recent low-temperature hydrothermal activity near Kolbeinsey Island leads to Fe-rich precipitates in this area (D. Stüben and P. Stoffers, pers. comm.).
Sediments sampled in regions distant from the ridge crest exhibit an increasing clay content occuring parallel to a color change from gray-black to olive-gray.
Between Iceland and ca. 68°ree;N sediment cores located west of the ridge axis exhibit a primarily pelagic succession of sandy-silty clays to sandy silts with typical dark-brown colors. East of the ridge crest, sediments are more olive-gray, which is related to higher portions of volcanic material. Obviously, north of ca. 68°ree;N the volcanic material is distributed less homogeneously over the ridge area, but is locally more concentrated on the western side. This is probably due to the complex hydrodynamic and oceanographic situation in this area.

Lackschewitz, K., Nürnberg, D. & Wallrabe-Adams, H.-J. (1989). Sedimentological characteristics of young deposits of the southern Kolbeinsey ridge. TERRA Abstracts, 1, 31.

Lackschewitz, K. S., Dehn, J. & Wallrabe-Adams, H.-J. (1994). Volcaniclastic sediments from mid-oceanic Kolbeinsey Ridge, north of Iceland: Evidence for submarine volcanic fragmentation processes. Geology, 22, 975-978.

Lackschewitz, K. S., Wallrabe-Adams, H.-J. & Garbe-Schönberg, D. (1994). Geochemistry of surface sediments from the mid-oceanic Kolbeinsey Ridge, north of Iceland. Mar. Geol., 121, 105-119.

Lackschewitz, K. & Wallrabe-Adams, H.-J. (1991). Composition and origin of sediments on the mid oceanic Kolbeinsey Ridge. Marine Geol., 101, 71-82.

Oehmig, R. & Wallrabe-Adams, H.-J. (1993.). Hydrodynamic properties and grain-size characteristics of volcaniclastic deposits on the mid-atlantic ridge north of Iceland (Kolbeinsey Ridge). J. Sed. Petrol. 63 (1), 140-151.

Wallrabe-Adams, H.-J., Lackschewitz, K. S. & Thiede, J. (1992). Sedimentary processes on the Kolbeinsey Ridge. InterRidge News, 1, 5-6.