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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >The water-basalt system at 4 to 6 GPa: Phase relations and second critical endpoint in a K-free eclogite at 700 to 1400 degrees C
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The water-basalt system at 4 to 6 GPa: Phase relations and second critical endpoint in a K-free eclogite at 700 to 1400 degrees C

机译：4至6 GPa的水玄武岩系统：700至1400摄氏度下无钾榴辉岩中的相关系和第二关键终点

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The phase diagram of a K-free mid ocean ridge basalt-H2O system was determined between 4 and 6 GPa to constrain compositions of the liquid phases as liberated from an eclogite during deep subduction and to elucidate mass transfer processes at convergent plate margins. Diamond trap and conventional multi-anvil experiments were combined with a recently developed technique, in which the liquid phases, quenched from high-pressure, high-temperature conditions, are directly laser ablated in a frozen stage and analyzed by ICP-MS. Results show that at 4 GPa a fluid containing similar to 80 wt.% H2O coexists with residual eclogite up to 850 degrees C while a hydrous melt appears at 900 degrees C, indicating a solidus located between 850 and 900 degrees C. At 5 GPa the solidus lies between 1000 and 1050 T but terminates at a second critical endpoint between 5 and 6 GPa. At 6 GPa a supercritical liquid, with a solute content continuously increasing with temperature, forms the volatile bearing phase. Low-temperature H2O-rich fluids and supercritical liquids have a nepheline- to quartz-normative, peralkaline character due to incongruent dissolution of clinopyroxene. The hydrous melts and high-temperature supercritical liquids evolve from rhyolitic to trachytic/andesitic with increasing liquid fraction. The melting reaction at the solidus changes from eutectic (4 GPa) to peritectic (5 GPa) with garnet changing from the reactant to the product side. With increasing melt fraction, the system becomes cotectic with about equal amounts of clinopyroxene and garnet consumed, the residual mineralogy being dominated by garnet. Most P-T trajectories calculated for subduction zone environment do not cross the hydrous K-free MORB solidus, therefore, the liquid phase released from the igneous portion of the subducting oceanic crust will change from fluid to supercritical liquid around 6 GPa. This change, however, is most probably associated with the change from fluid-like to melt-like properties of the mobile phase, with important consequences on trace element partitioning that will also change from fluid- to melt-Re. (c) 2005 Elsevier B.V. All rights reserved.
机译：确定无钾中洋脊玄武岩-H2O系统的相图在4 GPa和6 GPa之间，以限制深俯冲过程中从榴辉岩中释放出的液相成分，并阐明收敛板块边缘的传质过程。金刚石阱和常规的多砧实验与一项最新开发的技术相结合，其中将在高压，高温条件下淬灭的液相在冷冻阶段直接激光烧蚀并通过ICP-MS分析。结果表明，在4 GPa时，含有大约80 wt。％H2O的流体与残留的榴辉岩共存，温度高达850℃，而含水熔体在900℃时出现，这表明固相线位于850至900℃之间。固相线位于1000至1050 T之间，但终止于5至6 GPa之间的第二个关键端点。在6 GPa时，溶质含量随温度不断增加的超临界液体形成了挥发性轴承相。低温富含H2O的流体和超临界液体由于斜向辉石的不溶溶解，具有霞石到石英的碱性，碱性碱性。含水的熔融物和高温超临界液体随着液体分数的增加而从流纹岩变成疏松/安山岩。固相线的熔融反应从共晶（4 GPa）变为包晶（5 GPa），而石榴石则从反应物变为产物侧。随着熔体分数的增加，该体系变成共晶，消耗了大约等量的扁桃体和石榴石，其余的矿物学则由石榴石控制。为俯冲带环境计算的大多数P-T轨迹都没有越过无水的MORB固相线，因此，从俯冲洋壳火成部分释放的液相将在6 GPa左右从流体变为超临界流体。但是，这种变化很可能与流动相从流体状转变为熔体状有关，这对痕量元素分配也产生了重要影响，痕量元素的分配也将从流体Re转变为熔体Re。 （c）2005 Elsevier B.V.保留所有权利。

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