PALEOZOIC VOLCANIC-ROCKS OF CHIOS, GREECE - RECORD OF A PALEOTETHYAN SUTURE

Hypabyssal intrusions and pyroclastics of basaltic andesite to rhyolit ic composition cut and overlie a Carboniferous accretionary wedge mela nge in northeast Chios. The igneous rocks are pre-Triassic; correspond ing rocks in Lesbos are overlain by Permian sediments. They are older than uppermost Permian rocks in Attika with which they have previously been correlated. The igneous rocks of Chios correlate with the early Permian granodiorites of the Kazdag-Uludag region of Anatolia, which f orm part of the Karakaya Complex. The volcanic rocks consist of low-K calc - alkaline basaltic andesites and dacites. Two types of basaltic andesite are distinguished by Ti and Nb content. A primitive low-Ti, l ow-Nb magma was derived from partial melting of downwelling hydrated l ithospheric mantle and a more fractionated high-Ti, high-Nb magma was derived from an asthenospheric OIB source. The co-existence of such ma gmas in a subduction zone suggests significant back-arc extension. The Chios igneous rocks record final subduction of a Paleotethyan oceanic region.