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Marine Geophysical Researches

, Volume 23, Issue 2, pp 123–145 | Cite as

Vp/Vs-ratios from the central Kolbeinsey Ridge to the Jan Mayen Basin, North Atlantic; implications for lithology, porosity and present-day stress field

  • Rolf Mjelde
  • Roar Aurvåg
  • Shuichi Kodaira
  • Hideki Shimamura
  • Karl Gunnarsson
  • Ayako Nakanishi
  • Hajime Shiobara
Article

Abstract

The horizontal components from twenty Ocean Bottom Seismometers deployed along three profiles near the Kolbeinsey Ridge, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. Two profiles were acquired parallel to the ridge, and the third profile extended eastwards across the continental Jan Mayen Basin. The modelling requires a thin (few 100 m) layer with very high Vp/Vs-ratio (3.5–9.5) at the sea-floor in the area lacking sedimentary cover. The obtained Vp/Vs-ratios for the remaining part of layer 2A, 2B, 3 and upper mantle, correspond to the following lithologies: pillow lavas, sheeted dykes, gabbro and peridotite, respectively. All crustal layers exhibit a decreasing trend in Vp/Vs-ratio away-from-the-axis, interpreted as decreasing porosity and/or crack density in that direction. A significant S-wave azimuthal anisotropy is observed within the thin uppermost layer of basalt near the ridge. The anisotropy is interpreted as being caused by fluid-filled microcracks aligned along the direction of present-day maximum compressive stress, and indicates crustal extension at the ridge itself and perpendicular-to-the-ridge compression 12 km off axis. Spreading along the Kolbeinsey Ridge has most likely been continuous since its initiation ca. 25 Ma: The data do not suggest the presence of an extinct spreading axis between the Kolbeinsey Ridge and the Aegir Ridge as has been proposed earlier. The Vp/Vs-ratios found in the Jan Mayen Basin are compatible with continental crust, overlain by a sedimentary section dominated by shale.

Keywords

Shale Lithology Continental Crust Crack Density Pillow Lava 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Rolf Mjelde
    • 1
  • Roar Aurvåg
    • 2
  • Shuichi Kodaira
    • 3
  • Hideki Shimamura
    • 4
  • Karl Gunnarsson
    • 5
  • Ayako Nakanishi
    • 6
  • Hajime Shiobara
    • 7
  1. 1.Institute of Solid Earth PhysicsUniv. of BergenBergenNorway
  2. 2.Institute of Solid Earth PhysicsUniv. of BergenBergenNorway
  3. 3.Institute of Seismology and VolcanologyHokkaido UniversitySapporoJapan
  4. 4.Institute of Seismology and Volcanology, Hokkaido UniversitySapporoJapan
  5. 5.National Energy AuthorityReykjavikIceland
  6. 6.Institute of Seismology and VolcanologyHokkaido UniversitySapporoJapan
  7. 7.Institute of Seismology and VolcanologyHokkaido UniversitySapporoJapan

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