<p> In the past decade, sites of hydrothermal activity along the Juan de Fuca Ridge have gained a growing amount of attention. Increased sampling has provided the materials for more detailed studies, including those collected from Axial Seamount, a large shield volcano on the central portion of the ridge. Axial Seamount is host to at least three active vent sites, one of which, along the northwest caldera wall, consists of recently active eruptive-fissures and nearby chimney-like spires. A sampled spire from this location and samples from other vent areas are described using reflected and transmitted light techniques. They have been
found to consist of the sulphide phases sphalerite, wurtzite, pyrite, marcasite, chalcopyrite, isocubanite, and galena. Jordanite and tetrahedrite-tennanite are also known to
precipitate at these vent sites, but were not observed here. The most dominant non-sulphide minerals are amorphous silica and barite. Native sulfur, Fe and Mn oxides and a variety of
sulfosalts may also be present. The complex textures in these samples reflect precipitation and growth from higher temperature fluids that are mixing with local ambient seawater. Fluid inclusions in sphalerite have revealed salinities in the 5.6 to 7.0 weight % NaCl range, with
homogenization temperatures ranging from 214.8°C to 269.4°C. Temperatures of homogenization require pressure-corrections between approximately 9.0°C and 13.0°C, to set-up a range of trapping temperatures that lie between 211.8°C and 279.4°C. Fluid inclusions are also found in wurtzite, barite, and amorphous silica however, these would yield no data. Middle Valley is a sedimented rift valley that lies at the extreme north end of the Juan de Fuca Ridge. A number of hydrothermal sulphide mounds that lie atop the sediment pile have been sampled. The mineralogy is similar to that at Axial Seamount; however, the dominant sulphide phase at Middle Valley is pyrrhotite. Textural differences between the two
sites are significant, a result of the traversing of hydrothermal fluids through a thick package of hemepelagic sediment at Middle Valley. Samples from Middle Valley are found to contain no measurable fluid inclusions in the sections available for study. Mineralogical and fluid inclusion studies are important methods that can be used to help solve the complex growth history of sulfides that are and have been accumulating at mid-ocean ridge vent sites.</p> / Thesis / Bachelor of Science (BSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19463 |
| Date | 26 April 1990 |
| Creators | Meecham, Randy John |
| Contributors | Crocket, J. H., Geology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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