Abstract
The maflc inclusions and the host granites of the Neu granitic pluton were studied mainly from a view point of Sr isotopes. All of the analysed data are plotted on a definite isochron, yielding as age of 65.0±0.3 Ma with an initial ratio of 0.70475±0.00001. The Neu pluton has the lowest initial ratio among Cretaceous to Paleogene intrusive rocks in the San'in zone, which usually have the ratios lower than 0.706. The result is consistent with an interpretation that the magma for the Neu pluton was derived from upper mantle or lower crust without much contamination with the upper crustal materials. A cognate origin for the granite and the mafic inclusion is suggested by geological, petrographical and isotopic evidences.
