| 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. |
| Genre: | Article |
| ProdID: | 70017042 |
| Citation Author: | Revenaugh, J.; Sipkin, S. A. |
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| Citation End Page: | 476 |
| Citation Issue: | 6480 |
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| Citation Language: | English |
| Citation Larger Work Title: | Nature |
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| Citation Number Of Pages: | 3 |
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| Citation Search Results Text: | Seismic evidence for silicate melt atop the 410-km mantle discontinuity; 1994; Article; Journal; Nature; Revenaugh, J.; Sipkin, S. A. |
| Citation Start Page: | 474 |
| Citation Volume: | 369 |
| Citation Year: | 1994 |
| Type: | citation/reference |
| Text: | Seismic evidence for silicate melt atop the 410-km mantle discontinuity; 1994; Article; Journal; Nature; Revenaugh, J.; Sipkin, S. A. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1038/369474a0 |
| Date Other: | Sat, 1 Jan 1994 00:00 -0600 |
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