THE EVOLUTION OF THE CYCLADIC SUBDUCTION COMPLEX: CONSTRAINING P-T-T PATH GEOMETRY FROM COMPOSITIONAL ZONING AND MINERAL INCLUSIONS WITHIN GARNET IN WHITE MICA SCHISTS FROM SYROS, CYCLADES, GREECE

The Aegean Island of Syros, located in the Eastern Mediterranean, lies within the blueschist belt of the Attic-Cycladic complex. The rocks on Syros have undergone prograde metamorphism resulting from the northward subduction of the African plate with respect to the overriding Eurasian plate commencing at ~80 Ma during the Alpine Orogeny (Bröcker and Enders, 1999). These rocks have mineral assemblages transitional between the eclogite and epidote-blueschist facies. Oligocene to Miocene retrograde greenschist facies overprint, found locally on Syros, but more extensively throughout the Cyclades may be related to exhumation of the blueschist domain (Okrusch and Bröcker, 1990).

The high-pressure metamorphic assemblages of Syros can be used to constrain the thermal/tectonic evolution of the Cycladic subduction complex. Analysis of compositional zoning and mineral inclusions in garnets from white mica schists on the island allows for greater precision in determining equilibration conditions and thus constrains P-T-t path geometry.

Extrapolating P-T-t histories from the compositional zoning of garnet requires low variance, three-phase NFM mineral assemblages. Two different three-phase assemblages occur in the white mica schists of Syros (+quartz, +phengite, +paragonite, +epidote): (1) garnet+jadeite+glaucophane±chlorite and (2) garnet+chloritoid+glaucophane±chlorite. Mineral inclusions in chemically zoned garnets constrain the P-T-t evolution of these rocks and thus provide a check on the calculated P-T-t paths.

Preliminary garnet x-ray maps show continuous radial zoning of calcium, iron, and manganese with iron and calcium concentrations increasing rimward, as manganese decreases (Breecker, 2001). The mapping of trace elements in one garnet yields a complex oscillatory zoning of titanium and yttrium and concentric zoning of scandium. Maps of the major elements in this same garnet show complex oscillatory zoning of calcium, manganese, and magnesium.