Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard Margin west of Hornsund |
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| Authors: | Frode Ljones Asako Kuwano Rolf Mjelde Asbjrn Breivik Hideki Shimamura Yoshio Murai Yuichi Nishimura |
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| Institution: | a Department of Earth Science, Institute of Solid Earth Physics, University of Bergen, Allegt. 41, N-5007, Bergen, Norway;b Research Center for Prediction of Earth and Volcanic Eruptions, Tohoku University, Aramaki-aza Aoba, Aobaku, Sendai, Miyagi 980-8578, Japan;c Institute for Seismology and Volcanology, Hokkaido University, Sapporo 060, Japan |
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| Abstract: | The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic Vp and Vs models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. Vp is estimated to be 3.50–6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured Vp of 6.55–6.95 km/s for oceanic layer 3A and 7.10–7.25 km/s for layer 3B, both with a Vp/Vs ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10–40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (<10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone. |
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| Keywords: | Knipovich Ridge Crustal structure Oceanic crust Vp/Vs ratio Lithology Slow-spreading ridge |
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