Modification of Primary Magma Composition Through Reaction With Lower Crust: Insights from Icelandic Glass Bearing Crustal Xenoliths

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"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit: Partial melting in the Earth's mantle and subsequent melt transport contribute to the formation of a new oceanic and continental crust, affect low-temperature surface processes and have significant impact on chemistry of the atmosphere. Compositions of primitive basaltic magmas ideally provide the most direct information about magma generation at depth, but they may be modified by melt-rock interaction during transport to the surface. To evaluate how extensively chemical compositions of primary magmas may be modified during migration through crustal rocks, this project will investigate compositions of crustal partial melts as represented by glasses in crustal xenoliths from Icelandic volcanics. Iceland provides an ideal setting for the proposed study because it has an anomalously thick crust situated on a mid-ocean ridge where, otherwise, normal MORB-like initial primitive melt compositions are expected to rise from mantle depths. This work will involve systematic study of major and trace element compositions of minerals and glasses and determination of temperature, pressure, redox conditions. Boron isotopes in quenched glasses associated with crustal xenoliths and their transporting magmas will be used as an independent proxy for magma contamination. Special attention will be given to U-Pb geochronology and Ti-geothermometry of zircons, which are abundant in leucocratic xenoliths; the aim is to determine the age of parent plutonic bodies and temperature range of their formation, thereby constraining time scales of the consequent melt/rock reaction processes. A combination of petrographic methods, conventional whole rock analytical and microanalytical techniques i.e., Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS), Electron Probe Microanalysis (EMPA) and Secondary Ion Mass Spectrometry (SIMS or Ion Microprobe) will be used to achieve the goals.Broader Impacts: The proposal will provide a basis for professional development of the PI who is a new NENIMF manager and also a new NSF PI. The project will help revitalize interest of the scientific community in using the WHOI ion probe facility, which was seriously damaged in a fire in October 2002. Finally, the project will foster international collaboration between Woods Hole Oceanographic Institution (A. Gurenko) and South Iceland Nature Center (Ingvar A. Sigurdsson).