Intrusive rocks in the ophiolitic melange of Crete - Witnesses to a Late Cretaceous thermal event of enigmatic geological position

The ophiolitic mi lange in the uppermost tectonic unit of the Cretan nappe pile contains crystalline slices which consist of a low-pressure/high-tempe rature metamorphic sequence and synmetamorphic intrusions, ranging in compo sition from diorite to granite. The plutonic rocks conform to two different igneous suites, dominated by diorites in eastern, and granites in central Crete, displaying I-type and A-type characters, respectively. Some of the g ranites from central Crete are classified as transitional I/S-type. They ar e closely associated with migmatitic paragneisses. Based on major and trace element, REE, Sr- and Nd-isotope geochemistry, the mafic members of both s uites are derived from a depleted mantle source. The higher concentrations of P and Ti in the mafic members of the igneous suite in central Crete and the deviant trend of the whole suite may be explained by a different mantle source or a lower degree of partial melting. In both suites, magmatic evol ution was governed by fractional crystallization of amphibole/clinopyroxene , plagioclase and minor phases. In addition, mixing or mingling of composit ionally different magmas is indicated for the intrusive suite of eastern Cr ete whereas in central Crete the magma composition was at least partially m odified through assimilation of (meta)pelites. The geochemical results sugg est that the plutonic rocks formed in a supra-subduction zone setting. Howe ver, a formation during continental lithospheric extension cannot be ruled out. Published and new Rb-Sr and K-Ar dates on amphiboles and biotites from intrusive rocks and their metamorphic country rocks show that the peak of the low-P/high-T metamorphism and the intrusion of the two igneous suites t estify to the same thermal event of Late Cretaceous age. A similar Late Cre taceous association of metamorphic and plutonic rocks has been described fr om the uppermost tectonic unit in the Attic-Cycladic Crystalline Complex. T ogether with the Cretan occurrences, they form a small sector radiating SSW along a distance of 300 km, across the general trend of the tectonic zones in the Hellenic orogen. This N-S alignment is regarded as a primary featur e which may delineate the frontier zone between the Hellenides and the Taur ides. The real paleogeographic position and geodynamic significance of the Late Cretaceous low-pressure/high-temperature belt, however, remains enigma tic.