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Seismic evidence for silicate melt atop the 410-km mantle discontinuity

Nature

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DOI: 10.1038/369474a0

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Abstract

LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism and major-element mass balances, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine ??? ??- phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents and perhaps as the deep 'proto-source' of kimberlites. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Seismic evidence for silicate melt atop the 410-km mantle discontinuity
Series title:
Nature
DOI:
10.1038/369474a0
Volume
369
Issue:
6480
Year Published:
1994
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Nature
First page:
474
Last page:
476
Number of Pages:
3