Whole-mantle convection and the transition-zone water filter

摘要: Because of their distinct chemical signatures, ocean-island and mid-ocean-ridge basalts are traditionally inferred to arise from separate, isolated reservoirs in the Earth's mantle. Such mantle reservoir models, however, typically satisfy geochemical constraints, but not geophysical observations. Here we propose an alternative hypothesis that, rather than being divided into reservoirs, is filtered at 410-km-deep discontinuity. We as ascending ambient (forced up by downward flux subducting slabs) rises out high-water-solubility transition zone (between 660 km 410 km discontinuities) low-solubility upper above 410 km, it undergoes dehydration-induced partial melting that filters incompatible elements. The filtered, dry depleted solid phase continues rise become source material for basalts. wet, enriched melt residue may be denser surrounding accordingly trapped boundary until slab entrainment returns deeper filter could suppressed both plumes (which therefore generate wetter more basalts) well hotter Archaean (thereby allowing early production continental crust). transition-zone water-filter model can explain many observations while avoiding major pitfalls invoking reservoirs.