The trace-element characteristics of Aegean and Aeolian volcanic arc marine tephra
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High-silica volcanic ashes are found within deep-sea sediments throughout the Eastern Mediterranean. Although coring by Ocean Drilling Program has penetrated Lower Pliocene (similar to 4 Ma) sediments, few ashes older than 400 k.y. have been recovered, suggesting a young initiation to subaerial Aegean Are volcanism. Ashes derived from the Aegean volcanic front were cored south 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 found 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 element (LREE)-enriched pattern after normalizing against a chondrite standard. Aeolian Arc-derived ashes show greater enrichment than those from the Aegean area. Within the latter set, two groups are discernible, a mildly enriched. set similar to the volcanoes of the are volcanic front, and a more enriched group corresponding to lavas from the backarc region or possible from western Anatolia. Multi-element ‘spider diagrams’ also show a bimodal division of enriched and depleted Aegean ashes, possibly caused by source depletion due to melt extraction in the Aegean backarc followed by remelting under the volcanic front. Relative Nb depletion, a characteristic of are volcanism, is seen to be modest in Aegean and non-existent in Aeolian ashes. Using B/Be as a proxy for the flux of material from the subducting slab, this influence is seen to be low in the Aeolian Are but higher than at Vesuvius. B/Be is higher again in the Aegean Are. These differences may reflect the 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 Aegean backarc. (C) 1999 Elsevier Science B.V. All rights reserved.