Phase relations of peridotites under H2O-saturated conditions and ability of subducting plates for transportation of H2O
Phase relations of peridotites under H2O-saturated conditions and ability of subducting plates for transportation of H2O
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DOI：
10.1016/j.epsl.2004.08.013
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发表时间：
2004-10-30
影响因子：
5.3
通讯作者：
Iwamori, H
中科院分区：
文献类型：
--
作者：
Iwamori, H
根据MgO（-FeO）-SiO_2-H_2O、MgO-SiO_2-Al_2O_3-H_2O、CaO-MgO-Al_2O_3-SiO_2-H_2O和天然体系高压实验结果，阐明了28 GPa和2600 ℃饱和H_2O条件下橄榄岩的相关系。根据推导出的相组合和相的化学成分，使用质量平衡计算了两种岩石成分（二辉橄榄岩和方辉橄榄岩）的最大H2O含量。然后，结合俯冲带的相关系和热结构与俯冲板块年龄的关系，用简单的模型讨论了俯冲板块对H_2O的潜在输送能力，（15-130 Ma），俯冲速度u（0）（2.25-18 cm/年）和α角（30 °和60 °），以及地幔位温Tp（1300和1350 ℃）。结果证实了“阻塞点”的重要性（在6.2 GPa和550 T附近的尖点，在该尖点处，主要含水相的稳定性场在温度方面最小化），尽管具有0.4-0.7 wt.%的最大H2O含量的含镁菱锰矿组合超过了该阻塞点大约5-7 GPa和550-700 ℃。如果俯冲板块最冷部分的地温低于扼流点，则最大4.6 wt.% H2O可以消减，而H2O小于0.4-0.7重量%可以在阻塞点上方潜没当α = 30 ℃，Tp =1300 ℃时，α = 15 Ma，u（0）=9 cm/年，或α = 330 Ma，u（0）= 2.25cm/年为临界条件。如果α = 60度且T-p=1300摄氏度，或α = 30度且T-p=1350摄氏度，则临界条件略微向更老的年龄或更大的速度偏移（例如，α近似于30 Ma，u（0）=3.5 cm/年）。板坯的热参数（Au（0）sinx）是有用的预测大致的临界条件。然而，在较年轻的板块内，具有主要含水相的冷区域的空间范围较薄，因此较少的H2O被俯冲，即使具有相同的板片热参数。这表明板块的年龄和俯冲速度对俯冲板块的H2O输运能力有不同的影响。(C)2004 Elsevier B. V.保留所有权利。
Phase relations of peridotites under H2O-saturated conditions up to 28 GPa and 2600 degreesC have been clarified based on the high-pressure experimental results in the MgO(-FeO)-SiO2-H2O, MgO-SiO2-Al2O3-H2O, CaO-MgO-Al2O3-SiO2-H2O and natural systems. Based on the phase assemblages deduced and the chemical compositions of the phases, the maximum H2O contents for two bulk rock compositions (Iherzolite and harzburgite) have been calculated using mass balance. Then the potential ability of subducting plates for transportation of H2O is discussed by simple models combining the phase relations and the thermal structures of subduction zones as a function of the age of subducting plate a (15-130 Ma), the subduction velocity u(0) (2.25-18 cm/year) and angle alpha (30degrees and 60degrees), and the mantle potential temperature T-p (1300 and 1350 degreesC). The results confirm the importance of "choke point" (a cusp around 6.2 GPa and 550 T at which the stability field of major hydrous phases is minimized in terms of temperature), although the choke point is exceeded by the Mg-sursassite-bearing assemblage that has the maximum H2O content of 0.4-0.7 wt.% around 5-7 GPa and 550-700 degreesC. If the geotherm of the coldest part across the subducting plate passes below the choke point, maximum 4.6 wt.% H2O can subduct, whereas H2O less than 0.4-0.7 wt.% can subduct above the choke point. The critical conditions are clarified as follows: if alpha=30degrees and T-p=1300 degreesC, alphasimilar to15 Ma with u(0)=9 cm/year, or alphasimilar to330 Ma with u(0)=2.25 cm/year is the critical condition. If alpha=60degrees and T-p=1300 degreesC, or alpha=30degrees and T-p=1350 degreesC, the critical conditions slightly shift to an older age or a greater velocity (e.g., alphasimilar to30 Ma with u(0)=3.5 cm/year). The slab thermal parameter (au(0)sinx) is useful to predict roughly the critical condition. However, within the younger plate, the spatial extent of a cold region with major hydrous phases is thinner, hence less H2O is subducted, even with the same slab thermal parameter. This indicates that the age of the plate and the subduction velocity act differently on the H2O-transportation ability of subducting plates. (C) 2004 Elsevier B.V. All rights reserved.