VOLATILES IN MID-OCEANIC RIDGE AND OCEANIC ISLAND BASALTS (OR MY ADVENTURES WITH DAVID CLAGUE)

My collaboration with David Clague began in 1980 on a USGS cruise to the Juan de Fuca Ridge (JdF). After completing my masters with Dave in 1983, I moved on to Caltech to study volatiles in silicate melts with Ed Stolper and George Rossman, as well as with John Holloway at ASU. Using the emerging analytical technique of FTIR, combined with Dave’s talent for finding the right samples, we continued our collaboration on volatiles in MOR and ocean island basalts. Some of our greatest hits include: 1) Published the first detailed analysis of water and CO₂ along the JdF showing the LREE-like behavior of water during magmatic processes; 2) Showed that once a volcano breaches the sea surface (e.g., Kilauea), subaerially-degassed magmas may mix back into summit-chamber-stored magmas to be erupted along submarine rift zones (Puna Ridge); 3) Estimated water concentrations for Hawaiian magmas and mantle sources using glasses from the Kilauea (Puna Ridge, including high MgO glass sands), Loihi, Niihau, and marginal alkalic lavas; 4) Showed that the high volatile contents in marginal alkalic melts were consistent with extremely low percentages of partial melting of homogeneous source; 5) Showed that marginal alkalic magmas can be produced by melting of depleted mantle source that has been metasomatized by small amounts of low degree partial melts, both silicic and carbonatitic, derived from the Hawaiian plume (Dixon et al., 2008); 6) Showed that the various mantle components in Loihi magmas have distinct volatile characteristics. This body of work provides the foundation for new perpectives on the origin of normal and enriched MORB, relating the distinct volatile and stable isotopic compositions of EM and PREMA end-members to the composition of enriching metasomatic melts (sediment or crustal melts) derived from subducting slabs, thermal parameters of the slab, age of the metasomatism, and age of ocean basin rifting.