Coupled molybdenum and niobium depletion in continental basalts

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• 作者：Fitton ; J. Godfrey
• 刊名：Earth and Planetary Science Letters
• 出版年：1995
• 出版时间：December, 1995
• 年：1995
• 卷：136
• 期：3-4
• 页码：715-721
• 全文大小：477 K

文摘

Molybdenum concentrations have been determined for a suite of Late Cenozoic basalt lavas from the Basin and Range province of the western United States. Lavas older than about 5 Ma, which are thought to have had a lithospheric mantle source, are strongly depleted in Nb and Mo relative to La and Nd, respectively. Lavas younger than 5 Ma, which are chemically and isotopically similar to ocean island basalt, show no such depletion in either Nb or Mo. A close geochemical coherence between Nb and Mo is consistent with their similar ionic radii (Nb⁵⁺, 0.64; Mo⁴⁺, 0.65). Both elements are probably retained in residual rutile in a dehydrating subducted slab, while the overlying lithospheric mantle is enriched in large-ion lithophile elements (including light REE), contained in silica-rich hydrous fluids expelled from the slab.