Occurrence of kaolinite and mixed-layer kaolinite/smectite in hydrothermal sediments of Grimsey Graben, Tjornes Fracture Zone (north of Iceland)

• Published in: Marine Geology
• Main Authors: Dekov, V. M., Scholten, J., Botz, R., Garbe-Schönberg, C. D., Thiry, M., Stoffers, Peter, Schmidt, Mark
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2005
• Subjects: Grimsey; Iceland
• Online Access: https://oceanrep.geomar.de/id/eprint/16046/; https://oceanrep.geomar.de/id/eprint/16046/1/Dekov.pdf; https://doi.org/10.1016/j.margeo.2004.12.004

The sediments at a site situated among high-temperature vents in the Grimsey Graben (Tjornes Fracture Zone, north of Iceland) exhibit features of strong hydrothermal alteration: (1) almost total dissolution of the volcaniclastic material composing the background sediment; (2) sulfate and sulfide precipitation; (3) kaolinitisation. Smectite, precipitated in the shallowest sediment, is gradually replaced downward by mixed-layer kaolinite/smectite and pure, well-crystallised kaolinite. The kaolinite/smectite is interstratified with up to 10% swelling smectitic layers. According to the oxygen isotope composition kaolinite/smectite mixed-layer mineral most likely formed at temperatures near 160 degrees C. The vertical sequence kaolinite -> kaolinite/smectite -> smectite as well as the distinct zonation across the kaolinitic veins (almost pure kaolinite in the central zone and kaolinite/smectite along the rim) suggest hydrothermal transformation of initially formed smectite -> kaolinite/smectite -> kaolinite. Most probably this conversion occurred in an evolving (from alkaline to slightly acidic) hydrothermal environment. (c) 2004 Elsevier B.V. All rights reserved.