Mineralogy and geochemistry of sediments in the Southwestern Pacific Basin: Tahiti – East Pacific Rise – New Zealand

Abstract

Considerable changes in colour, grain size, mineralogy, and chemical composition of marine sediments were observed on a Tahiti – East Pacific Rise (EPR) – New Zealand transect. Sediments collected on the traverse Tahiti – EPR flank are carbonate–rich silty clays dominated by smectite. The sediments have high transition element contents which suggests contributions from hydrothermal sources.

EPR crest sediments are foraminiferal oozes with varying amounts of amorphous ferromanganese hydroxides. No clay minerals were detected. The sediments are extremely enriched in Fe, Mn, Cu, and Zn, a consequence ofstrong hydrothermal input at the rise crest. The dispersal of hydrothermal exhalates to the west can be traced as far as 1450 km away.

On the transect from the EPR flank to New Zealand at 42°S, sediments change from calcareous silty clays to pelagic clays, according to water depth and distance from New Zealand. The Carbonate Compensation Depth lies at about 5050 m water depth. From east to west, the authigenic minerals (smectite, phillipsite, and barite) in the sediments

Keywords:

• Southwest Pacific
• marine sediments
• mineralogy
• geochemistry