抄録
We present the result of precise determination of rare-earth elements (REE) in leucogranite from an Ocean Core Complex at the Central Indian Ridge. The sample was recovered by the deep-diving submersible SHINKAI 6500 during the YK05-16 Cruise. In order to obtain high precision REE data which is critically important to discuss lanthanite tetrad effect, a new method of ICP-MS analysis was developed using a combined acid treatment with Li2B4O7 fusion digestion. Reproducibility obtained from separate dissolutions and measurements of geochemical reference materials was generally better than 3%. REE abundances of the leucogranite are noticeably high, indicating that the rock is highly evolved. Chondrite-normalized REE pattern of the sample clearly shows M-type lanthanide tetrad effect with conspicuous negative Eu anomaly. However, the Eu anomaly is significantly smaller than other reported highly evolved granites such as Naegi granite in Central Japan. This may suggest different process of fluid-silicate interaction during evolution of granitic rocks in oceanic crust.
