REE mobility due to alteration of Indian Ocean basalt

Abstract

Indian Ocean basalts from DSDP site 249 on the Mozambique Ridge exhibit a progressive up-hole increase in alteration and Fe2O3/FeO and decrease in MgO and density over the approximately 3.5 m of recovered core. Abrupt increases in H2O+ and K2O and a decrease in CaO relative to lower basalt samples occur in the uppermost sample. These up-hole changes are accompanied by increasing REE and LREE/HREE and the development of a pronounced negative Ce anomaly. A rough estimate of the magnitude of chemical change is obtained by holding our most immobile element (Lu) constant.