The trace-element characteristics of Aegean and Aeolian volcanic arc marine tephra

High-silica volcanic ashes are found within deep-sea sediments throughout t he Eastern Mediterranean. Although coring by Ocean Drilling Program has pen etrated Lower Pliocene (similar to 4 Ma) sediments, few ashes older than 40 0 k.y. have been recovered, suggesting a young initiation to subaerial Aege an Are volcanism. Ashes derived from the Aegean volcanic front were cored s outh and east of the are, and are typified by medium-K, calc-alkaline major -element compositions, contrasting with high-K ashes from the Aeolian Are f ound in the Ionian Sea and as far east as Crete. Ion microprobe analysis of individual glass shards shows that all the ashes have a light rare earth e lement (LREE)-enriched pattern after normalizing against a chondrite standa rd. Aeolian Arc-derived ashes show greater enrichment than those from the A egean area. Within the latter set, two groups are discernible, a mildly enr iched. set similar to the volcanoes of the are volcanic front, and a more e nriched group corresponding to lavas from the backarc region or possible fr om western Anatolia. Multi-element 'spider diagrams' also show a bimodal di vision of enriched and depleted Aegean ashes, possibly caused by source dep letion due to melt extraction in the Aegean backarc followed by remelting u nder the volcanic front. Relative Nb depletion, a characteristic of are vol canism, is seen to be modest in Aegean and non-existent in Aeolian ashes. U sing B/Be as a proxy for the flux of material from the subducting slab, thi s influence is seen to be low in the Aeolian Are but higher than at Vesuviu s. B/Be is higher again in the Aegean Are. These differences may reflect th e rate of subduction in each system. Data suggest caution is required when correlating ashes solely on the basis of major elements, as alkaline ashes from the central part of the study may be derived from Italy or from the Ae gean backarc. (C) 1999 Elsevier Science B.V. All rights reserved.