High-resolution Geochemistry, Mineralogy and Growth History of MOR Sulfide Deposits: Case Study of the Endeavour ISS

J.W. Jamieson¹*, M.D. Hannington¹, D.S. Kelley², M.K. Tivey³ & J.F. Holden⁴

Corresponding author: john.jamieson@uottawa.ca
¹University of Ottawa, Department of Earth Sciences, Ottawa, ON, K1N 6N5 Canada
²School of Oceanography, University of Washington, Seattle, WA 98195 USA
³WHOI, Department of Marine Chemistry and Geochemistry, Woods Hole, MA, 02543 USA
⁴Department of Microbiology, University of Massachusetts, Amherst, MA, 01003 USA

Abstract:
A first "census" of marine minerals was conducted on behalf of the U.N. International Seabed Authority in 2002 (Hannington et al., 2002). As part of this project, a much larger database, encompassing virtually all sampled hydrothermal vents on the seafloor (more than 2900 samples) is being compiled as the first step in a global "resource" assessment. These data will provide the basis for the first comprehensive analysis of the geochemical and isotopic variability of seafloor sulfide deposits across the complete spectrum of volcanic and tectonic settings in the modern oceans. For example, general trends have already been noted for major elements such as Cu and Pb, having higher abundances in arc-related hydrothermal systems than on the mid-oceans ridges, but systematic differences in accumulation rates for most of the trace metals in different volcanic and tectonic settings have not been established.

Interpretation of the global database hinges on a number of case studies for which much more comprehensive datasets are available. These case studies will permit a careful assessment of local factors controlling mass accumulation of metals (e.g., temperature, pH, fO2, and short-lived temporal variability in hydrothermal conditions). A major case study is currently being carried out at the Endeavour ISS. A unique archive of more than 300 samples has been collected from the Endeavour field, and geochemical data for more than 65 elements have been consolidated into a single dataset, representing the most comprehensive documentation of a single hydrothermal field available in the oceans. As part of the current project, this dataset is being expanded with new samples collected in previously unmapped parts of the field and integrated into a high-resolution GIS model. The database is being analyzed to better understand the relationship between element concentrations and venting temperatures, including short-term temporal variability in the nature of the underlying heat sources (e.g., diking events) and heterogeneities in the source rocks. A selection of barite-rich samples will be dated using a novel Ra-226 dating technique, to establish the age and growth history of the Endeavour ISS, making it possible to develop a high-resolution model of the thermal history of the vent field that can be linked to the geochemical compositions of the deposited sulfides. With this model, it should be possible to more reliably interpret the evolution of other less-well explored systems from the chemistry of their deposits long after the system has shut down.

Contributions to Integration and Synthesis:
High resolution sampling of the Endeavour ISS, and the information extracted from the geochemical, mineralogical and radioisotope dating of these samples, will aid in the understanding of the underlying geology, including processes of mass transfer from the crust to the seafloor and into the water column, as well as spatial and temporal variations within a single vent field. These data can be correlated with the volcanic history of the vent field. The trace element geochemistry of the sulfides may also record biological processes occurring within the hydrothermal vents.