Provenance of the detrital component of deep-sea sediments from the SW Pacific Ocean based on mineralogy, geochemistry and Sr isotopic composition

Clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep-sea sediments from the SW Pacific Ocean. Continental detritus derived mainly from the New Zealand landmass is characterised by high illite and chlorite contents, and 87Sr/ 86Sr ratios close to 0.7110. This material, eroded from the eastern margin of both islands, is transported into deeper water by turbidity currents and hemipelagic processes, and is carried northwards by the strong Western Boundary Current as far north as the Samoan Basin. Due to the great distance from source and unfavourable prevailing winds, the contribution of aeolian dust from the Australian deserts to the sediment appears to be relatively small, particularly in the northernmost part of the region. In the vicinity of the oceanic volcanic islands of Tonga, Samoa and the Cook Islands, volcaniclastic material including heavy minerals (pyroxene and magnetite), pumice, glass shards (proximally) and smectite clays (distally) is dispersed into the sediments by turbidity currents and airfall. In areas of very low sedimentation distant from landmasses, the sediments contain significant amounts of authigenic material (RSOs) characterised by high concentrations of transition metals and rare earth elements. Strontium isotopes, together with trace element compositions, have proved particularly useful in determining the relative proportions of the detrital types. The contrasting 87Sr/ 86Sr ratios and Sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the Cook Islands contain 80% volcanic detritus, and those more than 1200 km away contain up to 20% volcanic detritus.