HYDROLOGICAL AND GEOCHEMICAL ANOMALIES ASSOCIATED WITH HYDROTHERMAL ACTIVITY IN SW PACIFIC MARGINAL AND BACK-ARC BASINS

Hydrological and geochemical anomalies were investigated in the Woodla rk, Lau and Manus basins, all regions of active spreading associated w ith island arcs of the southwest Pacific. The water column in all area s provides clear indications of hydrothermal activity. In the Woodlark Basin hydrothermal materials behave diffusely, with dissolved Mn conc entrations 2-4 x background and slightly elevated temperatures somewha t above the seabed, and also near-bottom plumes with dissolved Mn 4-6 x background and no changes in turbidity, derived from weak low-temper ature vents. In the eastern Lau Basin a plume with high turbidity and very high dissolved Mn (up to 2000 ng/l, about 50 x background) was di scovered. Strong plumes from high-temperature vents were encountered i n the eastern Manus Basin, and from grey smokers in the central Manus Basin, distinguished by turbidity, concentrations of dissolved Mn and suspended micro-elements. All plumes show positive temperature and sal inity anomalies. (C) 1997 Elsevier Science B.V.