Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000, Clermont-Ferrand, France.
Department of Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA.
Nat Commun. 2017 Dec 19;8(1):2186. doi: 10.1038/s41467-017-02275-9.
The low-velocity layer (LVL) atop the 410-km discontinuity has been widely attributed to dehydration melting. In this study, we experimentally reproduced the wadsleyite-to-olivine phase transformation in the upwelling mantle across the 410-km discontinuity and investigated in situ the sound wave velocity during partial melting of hydrous peridotite. Our seismic velocity model indicates that the globally observed negative Vs anomaly (-4%) can be explained by a 0.7% melt fraction in peridotite at the base of the upper mantle. The produced melt is richer in FeO (33 wt.%) and HO (16.5 wt.%) and its density is determined to be 3.56-3.74 g cm. The water content of this gravitationally stable melt in the LVL corresponds to a total water content in the mantle transition zone of 0.22 ± 0.02 wt.%. Such values agree with estimations based on magneto-telluric observations.
低速层（LVL）位于 410-km 间断面之上，被广泛归因于脱水熔融。在这项研究中，我们在上升地幔中实验再现了跨越 410-km 间断面的蓝方石-橄榄石相变，并原位研究了含水橄榄岩部分熔融过程中的声波速度。我们的地震波速度模型表明，全球观测到的负 Vs 异常（-4%）可以用上地幔底部橄榄岩中 0.7%的熔体分数来解释。所产生的熔体富含 FeO（约 33wt.%）和 HO（约 16.5wt.%），其密度为 3.56-3.74g/cm。LVL 中这种重力稳定熔体的含水量相当于地幔过渡带总含水量的 0.22±0.02wt.%。这些值与基于大地电磁观测的估计值一致。
