SEDIMENTS OF THE ACTIVE RIFT-ZONE IN THE WESTERN WOODLARK BASIN AND THE DEVELOPMENT OF HYDROTHERMAL AND VOLCANIC ACTIVITY

In the western Woodlark Basin within the neovolcanic zone sediments fo rm ponds in fissures and between individual pillows and tubes. A conti nuous thin sediment cover appears only at the base of the neovolcanic zone. Its thickness increases with the distance from the zone. Data on the lithology, mineralogy and chemistry of sediment cores from the sp reading centre in the western Woodlark Basin and adjacent areas show t hat these calcareous sediments (avg. 44.1% CaCO3) contain significant amounts of terrigenous, are volcanic, hyaloclastic and hydrothermal ma terial, the latter constituting up to 15% of the non-carbonate fractio n. Two types of sedimentary sequences occur in the studied area. Those of the first type were formed by particle-by-particle sedimentation; horizons of redeposited sediments occur in sequences of the second typ e. Redeposition of sediments is widespread and is tentatively correlat ed with cycles of volcanic activity at swells along the spreading cent re. These alternate with hydrothermal cycles, which were determined by the presence of hydrothermal matter in sediments. Radiocarbon dating of sediments showed that both cycles are of similar duration, of the o rder of 10,000 years. They are not synchronous along the spreading axi s, each swell having a specific evolution. Based on these determinatio ns we can say that within the studied spreading centre only the Frankl in Seamount swell is prospective for contemporary hydrothermal activit y. (C) 1997 Elsevier Science B.V.