Abstract
Thirteen trace elements, Co, Sc, Ba, Th, Rb, Cs, La, Ce, Sm, Eu, Tb, Yb and Lu in the Tertiary igneous rocks from Cape of Ashizuri, Southwest Japan, were analyzed by the instrumental neutron activation technique and in part by X-ray fluorescence method. The obtained data exhibit a relatively good correspondence to those in the A-type granites after Loiselle and Wones (1979) and those from NE Australia (Collins et al., 1982), excluding some small differences. This confirms the previous results obtained on the major element geochemistry and also on the petrographic characters. The chondrite-normalized REE patterns of the rocks investigated show a marked enrichment in the light and middle rare earth elements in comparison with those on the granitic rocks from Chugoku area, Southwest Japan (Masuda et al., 1974). One of the investigated specimen, syenite porphyry, has a high enhancement also in the heavy rare earth elements. This seems to be due to the late crystallizing amphibole and other minerals from the liquids enriched in volatiles as discussed by Bowden and Whitney (1974). Distinct negative Eu anomaly which tends to become small with increase of quartz, is recognized in the most of the investigated rocks with the exception of gabbro, alkali dolerite and one specimen of syenitic rocks. This Eu-depletion is interpreted to be related to the fractionation of feldspars during magmatic differentiation or formation of magma (partial melting) from source rock. Some considerations on the cause of absence and very small magnitude of Eu-depletion are also described.
