A strontium isotope study on the Neu granitic pluton and its mafic inclusion, San'in zone, southwest Japan.

Abstract

Rb-Sr analyses were made on mafic inclusions and the host granites of the Neu granitic pluton, yielding an isochron age of 65.0 + or - 0.3 m.y., with an initial ratio of 0.70475 + or - 0.00001. The latter is lower than values for other Cretaceous to Palaeogene intrusive rocks in the San'in zone (<0.706), suggesting that the Neu magma was derived from upper mantle or lower crust, without much contamination of the upper crustal materials. A cognate origin for the granite and the mafic inclusion is supported by geological, petrographical and isotopic evidence.-M.Ak.