Fe-Smectite-Glauconite Transition in Hydrothermal Green Clays from the Galapagos Spreading Center

Martine Buatier, Jose Honnorez and Gabrielle Ehret
Centre de Sédimentologie et de Géochimie de la Surface, CNRS, 1 rue Blessig, 67084 Strasbourg, France

Abstract: X-ray powder diffraction (XRD) and energy-dispersive X-ray analyses (EDX) of individual clay particles from hydrothermal mounds in the Galapagos spreading center (GSC) (Deep Sea Drilling Project, hole 509B) and high-resolution transmission electron microscopy (HRTEM) of the <2-µm size fraction of these sediments were carried out to document the mineralogy, geochemistry, and evolution of their clay horizons. The hydrothermal clay minerals of the GSC mounds were found to be intercalated with pelagic sediments and occurred as irregular interstratified illite/smectite according to X-ray powder diffraction analyses. On the basis of TEM, HRTEM, and EDX data, two types of clays appeared to coexist; these types differed in morphology, potassium content, and mode of stacking sequence. Lath-shaped particles having regular 10-Å, spacings were identified as glauconite, and filmy or veil-like particles, having curly edges and variable 10-13-Å spacings were identified as Fe-smectite (nontronite and Fe-montmorillonite). The absence of lattice fringes between Fe-smectite and glauconite crystallites was observed by HRTEM in clay aggregates. This structural discontinuity between Fe-smectite and glauconite layers suggests that a dissolution-recrystallization mechanism was responsible for the textural and chemical transition from the filmy Fe-smectite to the lath-like glauconite.

Key Words: Deep-sea hydrothermal clay • Glauconite • Smectite • Transmission electron microscopy • X-ray powder diffraction

Clays and Clay Minerals; December 1989 v. 37; no. 6; p. 532-541; DOI: 10.1346/CCMN.1989.0370605
© 1989, The Clay Minerals Society
Clay Minerals Society (www.clays.org)