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 b een used to determine the detrital components of deep-sea sediments fr om the SW Pacific Ocean. Continental detritus derived mainly from the New Zealand landmass is characterised by high illite and chlorite cont ents, and Sr-87/Sr-86 ratios close to 0.7110. This material, eroded fr om the eastern margin of both islands, is transported into deeper wate r by turbidity currents and hemipelagic processes, and is carried nort hwards by the strong Western Boundary Current as far north as the Samo an Basin. Due to the great distance from source and unfavourable preva iling winds, the contribution of aeolian dust from the Australian dese rts to the sediment appears to be relatively small, particularly in th e northernmost part of the region. In the vicinity of the oceanic volc anic islands of Tonga, Samoa and the Cook Islands, volcaniclastic mate rial including heavy minerals (pyroxene and magnetite), pumice, glass shards (proximally) and smectite clays (distally) is dispersed into th e sediments by turbidity currents and airfall. In areas of very low se dimentation distant from landmasses, the sediments contain significant amounts of authigenic material (RSOs) characterised by high concentra tions of transition metals and rare earth elements. Strontium isotopes , together with trace element compositions, have proved particularly u seful in determining the relative proportions of the detrital types. T he contrasting Sr-87/Sr-86 ratios and Sr contents of the various sourc e rocks permit tile use of binary mixing relationships whch indicate t hat sediments less than 35 km from the Cook Islands contain 80% volcan ic detritus, and those more than 1200 km away contain up to 20% volcan ic detritus. (C) 1997 Elsevier Science B.V.