REMNANTS OF THE ARABIAN-NUBIAN SHIELD IN PERMOTRIASSIC SEDIMENTS OF CRETE: CONSTRAINTS FROM U-PB ZIRCON AGES OF PROTEROZOIC GRANITOIDS

The nappe stack of Crete is the result of southward accretion of basement and cover rocks during the Alpine orogenic cycle. The basement complexes of Crete provide not only insight concerning the Alpidic event, but also help to decipher Hercynian and Pan-African geodynamic evolution of the Mediterranean. A beachside outcrop east of Sitia in eastern Crete exposes an imposing felsic orthogneiss-olistolith suspended in meta-tuffites of the Permotriassic Chamezi Beds (Tyros Unit). Although the contact between the Tyros Unit and the underlying Pre-Alpine Basement Unit is tectonic, it is likely that andesitic magmas and pyroclastics of the Chamezi Beds were originally deposited atop the basement unit. U-Pb ID-TIMS analyses of zircon originating from the orthogneiss-olistolith deliver a protolith age of 600±7 Ma, as well as inherited ages at 674±17, 720±2.5, and 2038±28 Ma. 600±7 Ma is an age of great significance for eastern Mediterranean geology: it is the first Pan-African granitoid to be dated in Crete. Recent age constraints for granitoids of the Arabian-Nubian Shield in Aswan, SE Egypt fit perfectly with the analyses conducted. The Aswan Monumental Granite reveals a protolith age of 605.9 ± 2.2 Ma (U-Pb zircon, Finger et al., 2008). These ages pre-date the Cambrian basement of eastern Crete. Along with previous data concerning distribution of detrital and inherited zircons in eastern Mediterranean crystalline complexes, existing models of Mediterranean geodynamic evolution have been refined. The Neoproterozoic orthogneiss-olistolith presents the long sought proof that the Minoan Terranes not only once constituted a coherent unit with Gondwana, but have also not drifted far since then. The presence of Proterozoic basement in the Permotriassic Chamezi Beds proves that Gondwana and the Minoan Terrane Cimmeria were in contact during deposition.

FINGER, F., DÖRR, W, GERDES, A., GHARIB, M., DAWOUD, M., (2008) U-Pb zircon ages and geochemical data for the Monumental Granite and other granitoid rocks from Aswan, Egypt: implications for the geological evolution of the western margin of the Arabian Nubian Shield. – Mineral. Petrol., Springer.