ORIGIN AND EVOLUTION OF THE HIGH-PRESSURE MAFIC META-IGNEOUS ASSEMBLAGE NEAR ST. MICHALIS, SYROS, GREECE

The island of Syros in the southern Aegean is a part of the lower unit in the Attic-Cycladic Crystalline Belt, which is inferred to have formed as the result of northward-directed subduction of the Apulian microplate beneath Eurasia (Okrusch & Brocker, 1990) during Alpine Orogeny in the late Cretaceous (Brocker & Enders, 1998). Syros is underlain primarily by meta-sedimentary rocks, including pelitic schists and marbles, but also contains some well-preserved meta-igneous rocks (Okrusch & Brocker, 1990).Flysch deposits are assumed to have been the protolith for the island's meta-sedimentary sequence (Dixon & Ridley, 1987), whereas its meta-igneous rocks presumably originated as ocean crust basalts or gabbros (Okrusch &Brocker, 1990). This study concentrates on the geochemistry and history of the diverse high-pressure, low-temperature, mafic, meta-igneous rocks located near the village of St. Michalis in the northeastern corner of Syros.

This meta-igneous assemblage includes glaucophanites, epidote-garnet-glaucophane blueschists, jadeitites, garnet-omphacite eclogites, mafic and calcareous meta-breccias, and metagabbros containing zoisite and either omphacite or glaucophane, depending on their Mg/Fe content. Some of these rocks occur as blocks in serpentinite melange zones; others appear to be parts of much larger meta-igneous bodies. One large metagabbro body is bounded on at least two sides by wide (up to 50 m?) zones of meta-breccia that contains blocks of many rock types found in the area. Chemical analyses of these rocks are underway in an attempt to constrain the origin and petrogenetic history of the St. Michalis assemblage and to explain how these diverse rocks are related to each other. Are these meta-igneous rocks genetically related or were they assembled from geographically separated protoliths during subduction? These data should also indicate whether the two areas of meta-breccia are igneous or tectonic in origin. In addition, mineral composition data are being gathered to constrain the metamorphic evolution of these meta-igneous rocks and, hopefully, learn more about subduction zone processes responsible for it.