Hf isotope compositions of northern Luzon arc lavas suggest involvement of pelagic sediments in their source

International audienceNew Hf isotopic compositions for island arc basalts from the Luzon arc (Philippines) define a remarkable sub-horizontal trend in Hf-Nd isotopic space with a small range of εHf (+5 to +17) associated with a large variation in εNd (-7 to +8). The data plot above and barely overlap the terrestrial array defined by oceanic basalts and continental crust. Mixing hyperbola passing through the data intersect fields for depleted mantle and pelagic sediments suggesting that these two components formed the source of the Luzon arc lavas. An exception is the Batan Island where the low εNd ratios are associated with low εHf values. A mixing hyperbola fitting the Batan samples suggests that their mantle source was modified by subducted material prior to contamination by terrigenous clays. The relationship between Nd and Hf isotopic compositions in the Luzon volcanics show that the type of sediment subducted under an island arc is a determining factor in the control of the two isotopic systems in island arc environments