Abstract
The syenites of the Cape of Ashizuri are fine to coarse-grained, and composed mainly of albite to oligoclase, highly sodic orthoclase, ferropargasitic amphibole, and green biotite. They are transitional to the older biotite granite and intruded by the younger biotite granite. From field evidences and petrographic characters, it is considered that the syenites have been derived from the older granites by the metasomatic action of alkali solution, originated probably from the younger granite magma. The addition of Al2O3, Fe2O3+FeO, CaO and Na2O to the original rock is accompanied by the subtraction of SiO2 and K2O, slight increase in oxidation ratio, and high decrease in Or content in potash feldspars. The syenites of the Cape of Ashizuri are considered to have been formed at comparatively higher temperature and lower oxygen pressure than some syenitic rocks in southwestern Japan.
