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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 >Phase equilibria in subducting basaltic crust: implications for H_2O release fro the slab
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Phase equilibria in subducting basaltic crust: implications for H_2O release fro the slab

机译：俯冲玄武岩壳中的相平衡：从板中释放H_2O的意义

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摘要

Fluids released from subducting slabs induce partial melting of he mantle wedge above the slab, which in turn is responsible for arc volcanism at the Earth's surface. The partially hydrated basaltic layer of the slab is a potential source of these fluids and a major reservoir for H_2O at depth. Constraining the stability domains of hydrous phases and the position of the dehydration reactions in this system in pressure-temperature (P-T) space is essential to were conducted in the ranges of 2.2-3.4 GPa and 625-750 ℃ to determine phases equilibria in an H_2O-saturated natural basalt at conditions relevant to subduction zones. The experimental duration was typically 1 month, although some experiments were replicated with a shorter run duration (1-2 weeks) in order to identify potentially metastable phases. A mixture of a natural mid-ocean ridge basalt (MORB) glass and mineral seeds was used as the starting material. Oxygen fugacity was buffered within ±1.3 log units of nickel-bunsenite (NiNiO). The results obtained show that a calcic amphibole (barrosiste) is stable from 2.2 to about 2.4 GPa. At 2.6 GPa, it is replaced by a sodic amphibole (near end-member glaucophane), which is stable up to 3 GPa at 625℃. This high-pressure assemblage constitutes a true analog of a natural amphibole-bearing eclogite and the first synthesis of glaucophane from a rock of basaltic composition. As opposed to the results of previous studies on basaltic compositions [A. R. Pawley, J. R. Holloway, Science 260 (1993) 664-667; S. Poli, Am. J. Sci. 293 (1993) 1061/1107; S. Poli, M. W. Schmidt, J. Geophys. Res. 100 (1995)22299-22314; M. W. Schmidt, S. Poli, Earth Planet. Sci. Lett. 163 (1998) 361-379], chloritoid is present only as a metastable phase in the pressure-temperature range investigated here. Metastability of chloritoid in earlier experiments, due to short run duration, is the most likely explanation for this difference, and suggests that chloritoid does not play an important role in the overall dehydration process of the basaltic layer in subduction zones. At pressures above the stability field of amphibole, zoisite/clinozoisite becomes the stable hydrous phase at temperatures above 645 ℃, whereas lawsonite is stable at lower temperatures. The positions of the zoisite-out and lawsonite-out reactions determined in this study indicate that, for an intermediate temperature subduction zone, the basaltic layer of the slab would be completely dehydrated between 90 and 1
机译：从俯冲平板释放的流体引起平板上方地幔楔的部分融化，这又导致了地球表面的弧形火山作用。平板的部分水合玄武岩层是这些流体的潜在来源，并且是深处H_2O的主要储层。限制水相的稳定性域和该系统在压力-温度（PT）空间中的脱水反应位置对于在2.2-3.4 GPa和625-750℃的范围内进行测定以确定H_2O中的相平衡至关重要-与俯冲带有关的条件下的饱和天然玄武岩。实验持续时间通常为1个月，尽管某些实验以较短的运行持续时间（1-2周）进行了重复，以发现潜在的亚稳相。天然中洋脊玄武岩（MORB）玻璃和矿物种子的混合物用作起始原料。氧逸散度被缓冲在镍-白锌矿（NiNiO）的±1.3 log单位内。所获得的结果表明钙闪石（barrosiste）在2.2至约2.4GPa之间是稳定的。在2.6 GPa时，它被钠闪石（近端葡聚糖）取代，在625℃时高达3 GPa是稳定的。这种高压组合物构成了天然闪石榴辉岩和由玄武岩组成的岩石首次合成葡甲环的真正类似物。与先前有关玄武岩成分研究的结果相反[A. R.Pawley，J.R.Holloway，Science 260（1993）664-667;和S. Poli，美国J.科学293（1993）1061/1107; S. Poli，M。W. Schmidt，J。Geophys。 Res。 100（1995）22299-22314; M. W. Schmidt，S。Poli，地球行星。科学来吧163（1998）361-379]，类胡萝卜素仅以亚稳相的形式存在于此处研究的压力-温度范围内。由于持续时间短，在较早的实验中类固醇的亚稳态是造成这种差异的最可能原因，这表明类固醇在俯冲带中玄武岩层的整个脱水过程中并不发挥重要作用。在高于闪石稳定场的压力下，硅沸石/斜硅沸石在645℃以上的温度下变成稳定的水相，而钙钠铝石在较低的温度下是稳定的。在这项研究中确定的黄铁矿出和褐铁矿出反应的位置表明，对于中间温度俯冲带，板坯的玄武岩层将在90和1之间完全脱水。

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