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首页> 外文期刊>Journal of Petrology >The High P–T Stability of Hydroxyl-apatite in Natural and Simplified MORB—an Experimental Study to 15 GPa with Implications for Transport and Storage of Phosphorus and Halogens in Subduction Zones
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The High P–T Stability of Hydroxyl-apatite in Natural and Simplified MORB—an Experimental Study to 15 GPa with Implications for Transport and Storage of Phosphorus and Halogens in Subduction Zones

机译：天然磷灰石和简化MORB中羟磷灰石的高PT稳定性-对15 GPa的实验研究，对俯冲带中磷和卤素的运输和储存具有重要意义

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摘要

Experiments have been conducted in the range 3–15 GPa and 850–1800°C to investigate the P–T stability field of OH-apatite in an average mid-ocean ridge basalt (MORB) and a model Mg-basalt, to study the compositional evolution of apatite and its breakdown products and the partitioning of P between phosphates and silicates. In the bulk compositions investigated OH-apatite is stable to 7·5 GPa at 950°C in a typical eclogite assemblage garnet + omphacite + SiO2 + TiO2. This is ∼5 GPa below the breakdown P of pure OH-apatite. The high-P breakdown product is tuite [γ-Ca3(PO4)2]. Both apatite and tuite are stable in a wide range of subduction zone T regimes but not along an average mantle adiabat. This precludes apatite or tuite stability in the asthenospheric mantle. Apatite may be stable in cold continental lithosphere (40 mW/m2) but is restricted to P ∼4–5 GPa. The apatite breakdown reaction is an important limit for the crust–mantle transport of Cl in subduction zones and can contribute to the Cl depletion of subducted cust. Both apatite and tuite are important storage sites for large ion lithophile elements (LILE) and rare earth elements (REE), therefore apatite breakdown does not greatly affect LILE or REE transport in subduction zones. In an eclogite assemblage only garnet can accommodate significant P. In the presence of apatite or tuite, P2O5 contents in garnet range from ∼0·2 to 0·6 wt % between 3 and 11 GPa and increase to ∼0·8 wt % at 15 GPa in the absence of a detectable phosphate phase. The P-storage capacity of clinopyroxene is limited to ∼250 ppm. Because of the extreme preference of P for the garnet structure, virtually the entire P budget of subducted MORB will be locked up in garnet well into the lower mantle provided fO2 is high enough to prevent the stability of a metal phase.
机译：已经在3–15 GPa和850–1800°C的温度范围内进行了实验，以研究平均洋中脊玄武岩（MORB）和Mg玄武岩模型中OH-磷灰石的P–T稳定性场。磷灰石及其分解产物的组成演变以及磷在磷酸盐和硅酸盐之间的分配在所研究的整体组成中，OH-磷灰石在典型的榴辉岩组合石榴石+绿榴石+ SiO 2 + TiO 2 中在950°C稳定至<7·5 GPa。这比纯OH-磷灰石的击穿P低约5 GPa。高P击穿产物是[ite] [γ-Ca 3 （PO 4 ） 2 ]。磷灰石和土特石都在很宽的俯冲带T型区域稳定，但在平均地幔绝热层中却不稳定。这排除了软流圈地幔中磷灰石或土石的稳定性。磷灰石在寒冷的大陆岩石圈中可能是稳定的（40 mW / m 2 ），但仅限于P <〜4-5 GPa。磷灰石分解反应是对俯冲带中Cl的壳幔运输的重要限制，它可能有助于俯冲带的Cl耗竭。磷灰石和土石都是重要的离子锂亲石元素（LILE）和稀土元素（REE）的重要储存场所，因此磷灰石的分解不会对俯冲带的LILE或REE传输产生很大影响。在榴辉岩组合中，只有石榴石可以容纳大量的P。在磷灰石或tuite的存在下，石榴石中P 2 O 5 的含量范围为〜0·2至0·6重量百分比介于3和11 GPa之间，并且在15 GPa的情况下，在没有可检测的磷酸盐相的情况下增加到〜0·8重量％。亚油基吡咯烷酮的P储存量限制为〜250 ppm。由于P对石榴石结构的极度偏爱，因此只要fO 2 足够高，可以防止石榴石结构的整个P预算都被石榴石锁定在较低的地幔中。金属相。

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    《Journal of Petrology》 |2009年第11期|p.2043-2062|共20页
  • 作者

    Jürgen Konzett1* and Daniel J. Frost2;

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    1Institut Für MINERALOGIE Und Petrographie, Universität Innsbruck, Innrain 52, A-6020 Innsbruck, Austria 2Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany;

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