Major Element and Rare Earth Elements Investigation of Merapi Volcano, Central Java, Indonesia

Major element and rare earth element (REE) investigations of 2010 Merapi eruption are newly reported. Several samples from Merapi summit were analyzed. SiO2 and K2O contents range from 55.2 to 60.3 wt% and 1.99 to 2.99 wt%, respectively. The increase in silica and potassium contents newly obtained in this study indicates the diffe rence of magma composition compare to previous geochemical data. Chondrite normalized REE is characterized by enrichment of light rare earth element (LREE) and slightly depleted in heavy Rare Earth Element (HREE). This characteristic of the pattern commonly occurs in subduction bearing volcanic rocks with no Eu anomaly. Chondrite normalized La/Yb ratio ranges from 6.3 to 7.6 showing high potassium content. Increasing volatile components indicates degassing and subsequent saturation of the volatiles which may trigger such eruption. Positive correlation between La/Yb and SiO2 shows that garnet is rarely major fractionating phase, while negative correlation between Dy/Yb and SiO2 indicates amphibole fractionation. Therefore, amphibole fractionation with high concentration of water may lead fluid saturation which may trigger strong explosive eruptions.