U-Pb dating and composition of inclusions in zircon from ophiolitic gabbro of the Klyuchevsk massif (Middle Urals): Results and geological interpretation.

The U-Pb (SHRIMP) dating of zircon from the layered complex of ophiolitic gabbro in the Klyuchevsk massif yielded an age of 456 ± 6 Ma corresponding within the limits of error to zircon dates obtained for other petrographic varieties from this massif. The investigation of the composition of silicate inclusions in dated zircon grains revealed that they are represented by typical metamorphic minerals: albite, zoisite, and secondary amphiboles. The data indicate that zircon was crystallized during metamorphic transformations of gabbroids and its U-Pb age (Late Ordovician-Silurian) is characteristic of all rocks in the ophiolite association of the Klyuchevsk massif indicating the age of metamorphism, not their formation time. [ABSTRACT FROM AUTHOR]