Аннотация:Ibara dismembered ophiolite exposed in the western extension of the Maizuru Tectonic Belt is composed mainly of metabasalt and metagabbro. The Rb-Sr whole rock isochron of the ophiolite gives an age of 281±8 Ma which shows a magmatic one, and the initial Sr isotopic ratio is 0, 70359±04 which is slightly higher than those of modern MORE and marginal sea basalt. The high initial Sr isotopic ratio may result from the derivation of the marginal sea mantle previously contaminated by the subduction components having high Sr isotopic ratio. The magmatic age is almost identical with the metamorphic age (270-290Ma), This suggests that the Ibara ophiolite was metamorphosed soon after solidification of the magma.
