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Under the auspices of the International Decade of Ocean Exploration (IDOE) the Hawaii Institute of Geophysics, Oregon State University, and representatives of several South American countries are investigating relations between plate tectonics and metal deposition on the oceanic Nazca plate. Detailed studies are being focused on the margins of this plate because metalliferous sediments form extensive deposits on and near the East Pacific Rise on the west and because vast hydrothermal deposits of metals are localized in the Andean Cordillera of the adjoining continental plate on the east.
Metalliferous sediments of the Nazca plate are enriched in iron, manganese, copper, nickel, zinc, silver, molybdenum, and lead, and share chemical, mineralogic, and possibly genetic similarities to deposits cored elsewhere by the Deep Sea Drilling Project. These sediments are demarked especially by an extensive basin, the Bauer Deep, about 800 km east of the East Pacific Rise. Elemental and isotopic data, supported by geologic information from core and geophysical data, suggest that the metals enriched in these sediments originated by the interaction of volcanism and sea water, by precipitation from sea water alone, and possibly by deep-ocean physical processes acting on detritus transported either from the continents or from the basaltic East Pacific Rise.
Previous investigators have noted the coincidence of calc-alkaline magmatism and metallogeny at convergent-plate boundaries. Because the Andean Cordillera contains large reserves of copper, iron, lead, molybdenum, silver, tin, zinc, and other metals, an additional objective at the eastern margin of the Nazca plate is to relate metals of the oceanic sediments to those of the continental deposits via intermediate processes of subduction, anatexis, and remobilization. Evaluation of this hypothesis is based on the definition of important chemical parameters for sediments, igneous rocks, and ores. Preliminary results are conflicting, at best.
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