Orthopyroxene was analyzed as a proxy for water supra‐subduction‐zone peridotite by polarized infrared radiation. Samples from Conical and Torishima seamounts, Mariana‐Izu‐Bonin forearc (ODP‐Leg 125), have very similar average H₂O contents of 215 ppm (range: 122–363 ppm; Conical) and 191 ppm (range: 116–292 ppm; Torishima). Conical peridotite equilibrated at lower temperature (760°C) and oxygen fugacity (ΔlogFMQ −0.65) than samples from Torishima (830°C; ΔlogFMQ +0.33). The degree of partial melting is almost identical for the two sites (18% and 20%). The H₂O concentrations are considerably higher compared to samples from the Bismarck forearc (31–92 ppm; Tollan and Hermann, 2019). Instead, the average values resemble those of peridotitic orthopyroxene from MOR settings. The measured H₂O contents by far exceed values expected for residual peridotite. This implies that secondary uptake of water must have occurred after melt‐extraction but prior to exhumation to shallow crustal levels. Most likely, re‐equilibration took place at c. 50 km depth. As indicated by elemental correlations and/or enhanced contents, the secondary fluid(s) must have been enriched in B, K, Li, and Sr. The boron contents of orthopyroxene are c. 10 times higher those in MOR samples. These findings suggest that peridotite from Conical and Torishima seamounts was presumably infiltrated by fluid generated by dehydration reactions in a subducting plate. The elemental spectrum points to two source lithologies: (i) serpentinite (liberation of B) and metasediments (liberation of K, Li, and Sr). The varying H₂O contents point to heterogeneous fluid supply suggesting that fluid infiltration was not pervasive.

中文翻译：

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Mariana-Izu-Bonin前臂的超俯冲带地幔中的水：橄榄石化邻苯二酚的约束

通过偏振红外辐射分析了邻二甲苯作为水超俯冲带橄榄岩的替代物。圆锥形和鸟岛海山（Mariana-Izu-Bonin前臂（ODP-腿125））的样品中H ₂ O含量非常相似，分别为215 ppm（范围：122–363 ppm；圆锥形）和191 ppm（范围：116–292） ppm；鸟岛）。圆锥形橄榄岩在比鸟岛（830°C;ΔlogFMQ+0.33）的样品更低的温度（760°C）和氧逸度（ΔlogFMQ-0.65）下达到平衡。两个位置的部分熔化程度几乎相同（18％和20％）。与from斯麦前臂的样品相比，H ₂ O的浓度要高得多（31-92 ppm； Tollan和Hermann，2019年）。取而代之的是，平均值类似于MOR设置中的橄榄石邻苯二甲酚的平均值。测得的H₂ O含量远远超过残余橄榄岩的预期值。这意味着在熔体抽提之后但在掘出到浅层地壳之前必须发生二次吸水。最可能的是，重新平衡发生在c。深度50公里。正如元素相关性和/或含量增加所表明的，次要流体必须富含B，K，Li和Sr。MOR样品中的含量高10倍。这些发现表明，圆锥形和鸟岛海山的橄榄岩可能被俯冲板中脱水反应产生的流体渗透。元素谱指向两种源岩性：（i）蛇纹岩（解放了B）和沉积物（解放了K，Li和Sr）。变化的H ₂O含量表明流体供应不均一，表明流体渗透并不普遍。