Geochemical variations along the Kolbeinsey Ridge : the behaviour of the sub-axial magmatic system on a slow-spreading ridge

• Main Author: Wieneke, Martin
• Format: Thesis
• Language: English
• Published: 1998
• Subjects: Jan Mayen; Jan Mayen Fracture Zone; Kolbeinsey; Kolbeinsey Ridge; Tjörnes; Iceland; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/59621/; https://oceanrep.geomar.de/id/eprint/59621/1/Diss_Wieneke_M_1998.pdf

The Kolbeinsey Ridge is situated directly north of Iceland and is part of the global midocean ridge system with a total length of over 50 OOO km of presently active sea-floor spreading. It is the world's shallowest ridge segment and represents a very slow-spreading ridge with a half-spreading rate of 1 cm/a. The Kolbeinsey Ridge extends about 500 km from the Tjörnes Fracture Zone in the south to the Jan Mayen Fracture Zone (JMFZ) in the north. It is subdivided into three major segments called the South, Middle and North Kolbeinsey Ridge (SKR, MKR and NKR), which are separated by non-transform overlapping spreading centres, namely the Spar offset (~69 N)and the Eggvin offset (~70 45'N). During two cruises of the "R.V. POSEIDON" closely spaced (< 2 km) samples were recovered by dredging the neovolcanic zones of the SKR, MKR and NKR. Major element, trace element, and isotope compositions of selected samples have been analysed in order to investigate magmatic processes beneath the Kolbeinsey Ridge and the nature and composition of mantle sources. This study focusses on mantle melting processes and the magma supply system feeding the presently active spreading axes and their respective implications for along-axis geochemical variations. Moreover, the context of the Kolbeinsey Ridge in the North Atlantic ridge framework and the relationship to the Iceland plume are examined in terms of differing mantle sources and domains. The samples are generally both basaltic pillows and sheet flow fragments, mostly with well preserved glass rims. Geochemical compositions show clear changes occuring at the ridge offsets. The lavas from the MKR are highly depleted N-MORB, those from the SKR show enrichments in some elements relative to the MKR. The largest compositional change occurs at the Eggvin offset where incompatible element ratios jump from very low values on the MKR to higher and generally much more variable values in the highly enriched NKR lavas. Fractionational crystallization of olivine, clinopyroxene, and plagioclase ...