2006 Volume 57 Issue 3-4 Pages 89-103
Three gabbroids and nine granitoids from the Miocene pluton at Ashizuri-misaki, Outer Zone of SW Japan were analyzed for major and trace elements. These plutonic rocks are composed of gabbroids and granitoids, which are alkaline in nature plotted in the shoshonite fields in the alkalisilica diagrams. The granitoids are high in Ba, Zr, Nb, and Zn; implying the rocks are of A-type affinity. The REE contents are the highest among the Japanese granitoids, having an average of REE+Y=453 ppm and LREE/HREE=11. The late Cretaceous granitoids (20 samples) from the Sanyo Belt were also studied in four areas where the highest levels of calc-alkaline ilmenite-series granitoids are exposed. The REE+Y contents are generally lower than 300 ppm, but are relatively high in the Naegi Granite (ave. 246 ppm) and Tanakami Granite (ave. 213 ppm); both are rich in HREE (LREE/HREE=2.8-2.4). These granites are high in F and well fractionated (according to the Rb/Sr ratios), which are considered the main reasons for the REE concentration. An anomaly with 1,804 ppm REE+Y was discovered in a mafic enclave of the Tanakami Granite of the Kinki district.
