Contamination effect in Ôkueyama granite

Abstract

Ôkueyama granite, which is essentially granodiorite, situating in the border common to Miyazaki and Ôita Prefectures in Kyûshû will be able to be divided regionally and petrographically into two types, Shishigawa type and Hôrigawa type.
The granite mass includes epixenolith characterized by spinel, corundum etc. and basic hypoxenolith characterized by augite, hornblende and a diabasic texture in widespread.
The Ôkueyama granite, especially Hô"rigawa tyep, is high in alumina and potash, and its position on the AKF diagram suggests that it has an affinity with hornfels and pelitic xenolith. Namely, the formation of this granite has a close relation with pelitic or aluminous sediments, and its heterogeneity is mainly originated from the contamination effect by them.