Oxygen isotope evidence for chemical interaction of Kilauea magmas with basement rocks

David Green has shown us that the geochemistry of basaltic volcanoes is largely governed by mantle processes. However, Kilauea volcano, one of the most active volcanoes on Earth, also records interaction with its crustal rocks. Kilauea is built on a ~ 6 km thick crustal basement of ~100 Ma oceanic crust [1] overlain by 8-10 km of young lavas (<1 Ma) from the adjacent growing shield volcano, Mauna Loa. The contribution of these basaltic basement rocks on the geochemistry of Kilauea magma was thought to be negligible based on major, trace element and Pb, Nd and Sr isotope analyses of historical lavas from this volcano [2]. New oxygen isotope results provide evidence for extensive exchange between Kilauea magmas and the volcano’s basement. This exchange is documented by analyses of basalt matrix material and olivine-matrix pairs for historical lavas. The matrix oxygen isotope ratios are lower and the disequilibrium between olivine and matrix is greatest following summit explosions and collapses in 1790 and 1924. The source of this contamination is not likely to be shallow because blocks from the 1924 explosions (derived from depths