第94回ジオダイナミクスセミナー
　 　Geodynamics　Seminar

要　旨
　Geophysical and geochemical evidence suggest that crustal rocks, formed at Earth's surface,are recycled into the deep mantle in subduction zones. These materials, including oceanic crust and mixtures of terrigenous and pelagic sediments, which are highly enriched in incompatible, lithophile elements, introduce extreme chemical and isotopic heterogeneity into the deeper mantle. Deeply subducted sediments have been implicated in the origin of plume-related ocean island basalts (e.g., EM-I type OIB) and in the petrogenesis of some rare, ultrapotassic intraplate lavas (e.g., diamondiferous lamproites and some kimberlites) believed to originate from the mantle transition zone. We have conducted a series of phase-equilibira experiments on natural sediment lithologies in the multi-anvil apparatus at 15-24 GPa, looking at the distribution and fractionation of incompatible elements in the high-pressure mineral assemblages that are formed. The most important repository of heat-producing (e.g., K, U, Th) and lithophile elements in deeply subducted sedimentary materials appears to be K-hollandite (KalSi3O8). Geochemical evidence suggests that breakdown of K-hollandite in the mantle transition zone may be linked to the origin of EM-I type OIBs and some lamproites.







　　　　　　　　問い合わせ先：山崎　大輔 　TEL　　　（089）927-8408
　　　 　　　　　　　　　　　　　　　　E-mail　　yamazaki@sci.ehime-u.ac.jp