Local distribution of oxygen isotopes and fluid exchange during genesis of the corundum-bearing rocks of Khitostrov Island

摘要

New data are presented on the distribution of oxygen isotopes and conditions of the local isotope equilibrium in high-Al rocks rocks of Khitostrov Island showing abnormally low delta O-18 values (below-25aEuro degrees). The temperatures of isotope equilibrium are within 400-475A degrees C. The minimum delta O-18 values have been registered in the in plagioclase, whereas the same phases in kyanite-bearing rocks lacking corundum demonstrate delta O-18 values usually 3-5aEuro degrees higher. The fluid delta O-18 value varies from-22 to-16aEuro degrees at 475 +/- 15A degrees C, from-18 to-23aEuro degrees at 425 +/- 25A degrees C, and from-17 to-22aEuro degrees at 380 +/- 15A degrees C. The results obtained do not require abnormal depletion of delta O-18 values owing to the infiltration of an external fluid under the Svecofennian transformations. The association of corundum-bearing rocks with the basic intrusions, the presence of zircon cores of older ages compared to these rocks, and the peculiarities of rock chemistry may be ascribed to the fact that lower crustal layers of ancient rocks depleted in delta O-18 before metamorphism were captured by basite melts.