REGIONAL GEOCHEMISTRY OF SEDIMENTS FROM THE HELLENIC VOLCANIC ARC IN REGARD TO SUBMARINE HYDROTHERMAL ACTIVITY

Some 600 surface sediment samples from the Hellenic Volcanic Are regio n have been analyzed by bulk and HCl selective leach geochemical techn iques. Geostatistical analysis, followed by further selective leaches on a number of samples, has been used in order to identify any regiona l hydrothermal influence on the sediments and/or any local hydrotherma l metal enrichments. The two main sediment components affecting the ge ochemical variability in the region are biogenic carbonate and volcani clastic/terrigenous detritus. Proximity to islands appeals to be the p rimary factor controlling the variability in these components. Sedimen ts from deeper water, to the south of the Hellenic Volcanic Are and in the Anydros Basin, exhibit some elevated levels of Mn, Co, and Cy pro bably of hydrogenous origin. No widespread hydrothermal Influence to t he sediments in the region is recognized, although this could in part be due to the high sedimentation rates in the region. Localized hydrot hermal inputs to sediments are, however, recognized proximal to Santor ini in particular within the northern part of the central caldera. The se are predominantly of Fe aad associated adsorbed/coprecipitated elem ents along with some Mn enrichment. Several samples proximal to Milos, just off the coast in the northern part of the central Miles embaymen t, also show enrichments of commonly hydrothermally associated element s, including Mn, Cu, Zn, and Pb. Data suggest that these enrichments c ould, ia part, be due to weathering of ''on-land'' mineralization as w ell as hydrothermal inputs.