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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L24607, doi:10.1029/2004GL021306, 2004

Absence of density crossover between basalt and peridotite in the cold slabs passing through 660 km discontinuity

Konstantin Litasov

Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, Japan


Eiji Ohtani

Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, Japan


Akio Suzuki

Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, Japan


Takaaki Kawazoe

Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, Japan


Kenichi Funakoshi

Spring-8, Japan Synchrotron Radiation Research Institute, Kouto, Hyogo, Japan


Abstract

Interaction between subducting slabs and surrounding mantle near 660 km discontinuity is one of the key issues in the dynamic of deep Earth. Distinguishing phase transformations occur in the both major parts of the slab: basaltic crust and underlying peridotite. Post-spinel transformation in peridotite takes place at 660 km, whereas post-garnet transformation in basalt is considered to occur at 720–800 km creating density crossover. In this paper we determined the post-garnet phase boundary in Mid-Ocean Ridge basalt (representative for oceanic crust) by in situ x-ray diffraction studies. The phase boundary can be expressed as P(GPa) = 0.0041 T(K) + 17.92. The present results imply that the basaltic component of the cold slab transformed to perovskite assembly at lower pressure than the surrounding mantle and provide direct evidence for penetration of the oceanic crust into the lower mantle without gravitational separation from the peridotite body of the slab.

Received 20 August 2004; accepted 10 November 2004; published 23 December 2004.

Index Terms: 1025 Geochemistry: Composition of the mantle; 3630 Mineralogy and Petrology: Experimental mineralogy and petrology; 3924 Mineral Physics: High-pressure behavior; 3954 Mineral Physics: X ray, neutron, and electron spectroscopy and diffraction; 8124 Tectonophysics: Earth's interior—composition and state.

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Citation: Litasov, K., E. Ohtani, A. Suzuki, T. Kawazoe, and K. Funakoshi (2004), Absence of density crossover between basalt and peridotite in the cold slabs passing through 660 km discontinuity, Geophys. Res. Lett., 31, L24607, doi:10.1029/2004GL021306.