The transition from the Semail ophiolite mantle to the underlying metamorphic sole was drilled at ICDP OmanDP Hole BT1B. We analyzed the bulk major, volatile and trace element compositions of the mantle-derived listvenite series and metamorphic rocks, with the aim to constrain chemical transfers associated with peridotite carbonation along the ophiolite basal thrust. The listvenite series comprise variously carbonated serpentinites and (fuchsite-bearing) listvenites. They have high CO₂ (up to 43 wt.%) and variable H₂O (0–12 wt.%). Yet, they have compositions close to that of the basal banded peridotites for most major and lithophile trace elements, with fuchsite-bearing listvenites overlapping in composition with amphibole-bearing basal lherzolites (e.g., Al₂O₃ = 0.1–2.2 wt.%; Yb = 0.05–1 x CI-chondrite). The protolith of the listvenite series was likely similar in structure and composition to serpentinized banded peridotites which immediately overlie the metamorphic sole elsewhere in Oman. The listvenite series are enriched in fluid mobile elements (FME) compared to Semail peridotites (up to ∼10³–10⁴ x Primitive Mantle), with concentrations similar to the underthrusted metabasalts and/or metasediments for Cs, Sr and Ca and sometimes even higher for Pb, Li, As, and Sb (e.g., Li up to 130 μg/g; As up to 170 μg/g). We also observe a decoupling between Sr-Ca enrichments and other FME, indicating interactions with several batches of deep CO₂-rich fluids transported along the basal thrust. These results suggest that peridotite carbonation could represent one of the major trap-and-release mechanisms for carbon, water and FME along convergent margins.

中文翻译：

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Semail蛇绿岩基底大冲断层中Listvenite-变质转变的地球化学剖面：阿曼DP孔BT1B钻孔的结果

在 ICDP OmanDP Hole BT1B 钻探了从 Semail 蛇绿岩地幔到下伏变质底部的过渡。我们分析了地幔衍生的李斯特文岩系列和变质岩的主要、挥发性和微量元素组成，目的是限制与沿蛇绿岩基底逆冲断层的橄榄岩碳化作用相关的化学转移。listvenite 系列包括各种碳酸化蛇纹石和（含 fuchsite 的）listvenite。它们具有高 CO ₂（高达 43 wt.%）和可变 H ₂ O（0–12 wt.%）。然而，对于大多数主要和亲石微量元素，它们的成分接近于基底带状橄榄岩的成分，含菱镁矿的菱镁石在成分上与含闪石的基底橄榄岩重叠（例如，Al ₂O ₃  = 0.1–2.2 wt.%；Yb = 0.05–1 x CI-球粒陨石）。利斯特文岩系列的原岩在结构和成分上可能与蛇纹石化带状橄榄岩相似，后者立即覆盖在阿曼其他地方的变质底部。与 Semail 橄榄岩（高达 ∼10 ³ –10 ⁴ x 原始地幔）相比，listvenite 系列富含流体移动元素 (FME) ，其浓度与 Cs、Sr 和 Ca 的下冲变玄武岩和/或变质沉积物相似，有时甚至Pb、Li、As 和 Sb 的含量更高（例如，Li 高达 130 μg/g；As 高达 170 μg/g）。我们还观察到 Sr-Ca 富集与其他 FME 之间的解耦，表明与几批深 CO _{2 的}相互作用- 沿基底推力输送的丰富流体。这些结果表明橄榄岩碳酸盐化可能代表了沿收敛边缘的碳、水和 FME 的主要捕获和释放机制之一。