UNRAVELING THE TECTONOSTRATIGRAPHY OF A HP-LT METAMORPHIC BELT USING COMBINED DETRITAL ZIRCON U-PB AND TRACE ELEMENT ANALYSIS: AN EXAMPLE FROM THE CYCLADIC BLUESCHIST UNIT, CYCLADES, GREECE

Discerning stratigraphic relationships between packages of high-pressure low-temperature (HP-LT) metamorphic rocks is a historically difficult issue. Complex poly-metamorphic and multi-stage deformation histories obscure primary stratigraphic relationships and make regional scale correlation of units problematic. Detrital zircon U-Pb geochronology has been employed to great success in these environments as a tool to determine maximum depositional age of units, and therefore the tectonostratigraphy. The Cycladic Blueschist Unit (CBU) of Greece is a HP-LT metamorphic terrane in which the blueschist and eclogite facies history has largely been obscured by greenschist and amphibolite facies retrograde metamorphism and deformation. Under the P-T conditions experienced by the CBU, detrital zircons act not only as passive markers of maximum depositional age, but also as records of the metamorphic history. As a result, teasing out which age data represent the metamorphic history and which records the maximum depositional age requires trace element analysis of zircons. Depth profiling of zircons combined with laser ablation split stream (LASS) ICP-MS analysis allows for simultaneous determination of U-Pb age data and trace element compositions. We present detrital zircon data from metasediments and metavolcanics on the regional scale of the Cyclades and suggest correlations between packages of CBU exposed on mainland Greece in Attica and in the Western Cyclades based on maximum depositional ages. Within this region, the CBU can be subdivided into a late Mesozoic and early Mesozoic volcanic and sedimentary sequence which was deposited on Permian and Pennsylvanian igneous basement. Finally, we present new age data for high-pressure metamorphic conditions from the islands of Syros and Serifos based on LASS data.