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ReportsMetasomatized Lithosphere and the Origin of Alkaline LavasRecycled oceanic crust, with or without sediment, is often invoked as a source component of continental and oceanic alkaline magmas to account for their trace-element and isotopic characteristics. Alternatively, these features have been attributed to sources containing veined, metasomatized lithosphere. In melting experiments on natural amphibole-rich veins at 1.5 gigapascals, we found that partial melts of metasomatic veins can reproduce key major- and trace-element features of oceanic and continental alkaline magmas. Moreover, experiments with hornblendite plus lherzolite showed that reaction of melts of amphibole-rich veins with surrounding lherzolite can explain observed compositional trends from nephelinites to alkali olivine basalts. We conclude that melting of metasomatized lithosphere is a viable alternative to models of alkaline basalt formation by melting of recycled oceanic crust with or without sediment. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. * To whom correspondence should be addressed. E-mail: sebastien.pilet{at}unil.ch
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
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