Huang Yongsheng, Nakatani Takayuki, Nakamura Michihiko, McCammon Catherine
Department of Earth Science, Graduate School of Science, Tohoku University, Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578, Japan.
Bayerisches Geoinstitut, University of Bayreuth, 95440, Bayreuth, Germany.
Nat Commun. 2019 Dec 5;10(1):5557. doi: 10.1038/s41467-019-13513-7.
Recently, high electrical conductors have been detected beneath some fore-arcs and are believed to store voluminous slab-derived fluids. This implies that the for-arc mantle wedge is permeable for aqueous fluids. Here, we precisely determine the dihedral (wetting) angle in an olivine-NaCl-HO system at fore-arc mantle conditions to assess the effect of salinity of subduction-zone fluids on the fluid connectivity. We find that NaCl significantly decreases the dihedral angle to below 60° in all investigated conditions at concentrations above 5 wt% and, importantly, even at 1 wt% at 2 GPa. Our results show that slab-released fluid forms an interconnected network at relatively shallow depths of ~80 km and can partly reach the fore-arc crust without causing wet-melting and serpentinization of the mantle. Fluid transport through this permeable window of mantle wedge accounts for the location of the high electrical conductivity anomalies detected in fore-arc regions.
最近，在一些弧前区域下方检测到高电导率物质，据信这些物质储存了大量来自板块的流体。这意味着弧前地幔楔对含水流体是可渗透的。在此，我们精确测定了弧前地幔条件下橄榄石 - 氯化钠 - 水体系中的二面角（润湿性角），以评估俯冲带流体盐度对流体连通性的影响。我们发现，在所有研究条件下，当氯化钠浓度高于5 wt%时，二面角会显著降低至60°以下，重要的是，在2 GPa压力下，即使浓度为1 wt%时也是如此。我们的结果表明，板块释放的流体在约80千米的相对浅深度处形成了一个相互连通的网络，并且可以部分到达弧前地壳，而不会导致地幔的湿熔融和蛇纹石化。通过地幔楔这个可渗透窗口的流体传输解释了在弧前区域检测到的高电导率异常的位置。
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