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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B4, 2209, doi:10.1029/2002JB002048, 2003

Origin of ocean island basalts: A new perspective from petrology, geochemistry, and mineral physics considerations

Yaoling Niu

Department of Earth Sciences, Cardiff University, Cardiff, UK


Michael J. O'Hara

Department of Earth Sciences, Cardiff University, Cardiff, UK


Abstract

Consideration of petrology, geochemistry, and mineral physics suggests that ancient subducted oceanic crusts cannot be the source materials supplying ocean island basalts (OIB). Melting of oceanic crusts cannot produce high-magnesian OIB lavas. Ancient oceanic crusts (>1 Ga) are isotopically too depleted to meet the required values of most OIB. Subducted oceanic crusts that have passed through subduction zone dehydration are likely to be depleted in water-soluble incompatible elements (e.g., Ba, Rb, Cs, U, K, Sr, Pb) relative to water-insoluble incompatible elements (e.g., Nb, Ta, Zr, Hf, Ti). Melting of residual crusts with such trace element composition cannot produce OIB. Oceanic crusts, if subducted into the lower mantle, will be >2% denser than the ambient mantle at shallow lower mantle depths. This negative buoyancy will impede return of the subducted oceanic crusts into the upper mantle. If subducted oceanic crusts melt at the base of the mantle, the resultant melts are even denser than the ambient peridotitic mantle, perhaps by as much as ∼15%. Neither in the solid state nor in melt form can bulk oceanic crusts subducted into the lower mantle return to upper mantle source regions of oceanic basalts. Deep portions of recycled oceanic lithosphere are important geochemical reservoirs hosting volatiles and incompatible elements as a result of metasomatism taking place at the interface between the low-velocity zone and the cooling and thickening oceanic lithosphere. These metasomatized and recycled deep portions of oceanic lithosphere are the most likely candidates for OIB sources in terms of petrology, geochemistry and mineral physics.

Published 19 April 2003.

Index Terms: 1025 Geochemistry: Composition of the mantle; 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 8121 Tectonophysics: Dynamics, convection currents and mantle plumes; 8124 Tectonophysics: Earth's interior—composition and state; 8125 Tectonophysics: Evolution of the Earth.

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Citation: Niu, Y., and M. J. O'Hara (2003), Origin of ocean island basalts: A new perspective from petrology, geochemistry, and mineral physics considerations, J. Geophys. Res., 108(B4), 2209, doi:10.1029/2002JB002048.