| Title | Clark Volcano Dredged Samples, Kermadec Trench; Mineralogy, Fluid Inclusions and Preliminary S-Isotope Characterization |
|---|---|
| Authors | Marco A. Rubio R., Patrick R. L. Browne and Clemente Recio |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | Kermadec Ridge, Clark Volcano, Sr-barite, fluid inclusions, sulphur isotope, hydrothermal |
| Abstract | Clark Volcano is a recently discovered volcanic edifice located on the western side of the Kermadec Ridge. It represents just one of the multiple sites where submarine hydrothermal systems occur in this region. The study of samples dredged on the margin of this volcano shows both partial replacement and direct deposition textures, as layers (up to 10 cm thick) composed of sulphates, pyrite and lesser carbonates, arranged in rithmic, thin-layered (5 to 20 mm thick) barite/anhydrite pairs. Textures and mineralogical associations may be indicative of medium-high temperature hydrothermal fluids discharged from submarine vents. Several stages were recognized. Independent layers display both chemical and 34S isotopic variations, reflecting physico-chemical changes during deposition. Analyses by XRD indicates that pure anhydrite and Sr/Pb-rich barites are the dominant mineralogical phases. Silica forms are very rare and occur only in early paragenetic stages or associated to clay minerals. XRF analyses of sulphates suggest that Sr and Pb replace Ba in the barites, while both Ba and Sr may substitute for Ca into the anhydrite structure. Anomalous Zn and Sr contents appear to be preferentially associated with barite rather than anhydrite. Liquid-rich fluid inclusions are rare, whereas vapor-rich ones are more common. Homogeneization temperatures on primary liquid-rich fluid inclusions in anhydrite vary from 210 to 215?C and ice-melting temperatures range from -8.9 to -9.3?C. Preliminary sulphur isotopic data from individual layers indicate that sulphate minerals are depleted in the heavy isotope ( 34S = 14.5 to 19.2â) with respect to actual seawater. The largest 34S depletion was found on anhydrite at the anhydrite-pyrite interphase ( 34S = 5.0â). Late crusts and rims above early hydrothermal sulphates consist of very pure anhydrite, whose isotopic signature is almost identical to contemporaneous seawater ( 34S = 19.2 to 20.4â). The hydrothermal deposits of Clark volcano differ from other systems; its dominant anhydrite/barite layered products, low silica, and elevated Sr, Ba and Zn content could be indicative of high W/R ratios due to high permeability conditioned by the rock texture and the medium-temperature leaching effect K-rich lavas. |