U-Pb dating, oxygen and hafnium isotopic ratios of zircon from rocks of oceanic core complexes at Mid-Atlantic Ridge: evidence for an interaction of young and ancient crusts at spreading of the ocean floor

U-Pb age, oxygen and hafnium isotopic ratios in zircon from rocks of ocean core complexes at Mid-Atlantic Ridge have been studied using SHRIMP and MC-LA-ICP-MS techniques. U-Pb dating revealed four group of zircons: 1) 0,6-1,7 Ma, 2) 6,7-11,2 Ma, 3) 12,9-17,6 Ma, 4) 200 to 2044 Ma. The 18O values range from 4,74 to 7,2 and are distinct for zircon grains of different ages. Hafnium isotopic ratio for zircon aged from 0,6 to 17,6 Ma corresponds or...