Cambrian granitoids in pre-Alpine basement of Crete (Greece): evidence from U-Pb dating of zircon

摘要

The pre-Alpine basement of eastern Crete consists of at least three sub complexes which show differences in age and grade of pre-Alpine metamorphism. U-Pb analyses of zircons of two orthogneisses yielded upper intercepts in the concordia diagram at 511+/-16 Ma (Chamezi crystalline complex) and 514+/-14 Ma (Myrsini crystalline complex). These values are interpreted as protolith ages of the gneisses, suggesting that parts of the basement underwent Cadomian (Pan-African) imprints at the northern margin of Gondwana. The lower intercept ages are attributed to Alpine subduction which led to high-pressure/low-temperature metamorphism (T=ca. 300degreesC), brittle-ductile deformation, and hydrothermal fluid activity. Due to pervasive Alpine fluid migration, the zircons of the Chamezi crystalline complex display disturbed zonation and solution, resulting in 87% radiogenic Pb loss, Ca- and Al-gain, and Zr depletion.