The influence of water on melting of mantle peridotite
The influence of water on melting of mantle peridotite
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DOI：
10.1007/s004100050396
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发表时间：
1998-05-01
影响因子：
3.5
通讯作者：
Grove, TL
中科院分区：
文献类型：
--
作者：
Gaetani, GA;Grove, TL
本实验研究了不同浓度的溶解H2O对硅酸盐熔体组成及其共存的橄榄石+斜方辉石+/-单斜辉石+/-尖晶石+/-石榴石矿物组合的影响。实验是在1.2至2.0 Gpa的压力和1100至1345摄氏度的温度下进行的，液体中溶解的H2O高达12wt%。增加溶解H2O浓度对尖晶石二辉橄榄石矿物组合平衡熔体主要元素组成的影响是降低了SiO_2、FeO、MgO和CaO的浓度。Al(2)O(3)的浓度不受影响。水合熔体中SiO_2含量较低的原因是SiO_2的活度系数随溶解H2O的增加而增大。FeO和MgO浓度较低的原因是与无水熔体相比，含水熔体与地幔矿物共存的温度较低。这些成分变化导致含水橄榄岩部分熔体中的SiO_2/(MgO+FeO)比值升高，与无挥发基础上的无水熔体相比，它们相对富含SiO_2。含水橄榄岩熔融反应主要受下沉的地幔固相线影响。温度引起的共存辉石的组成变化降低了进入熔体的单斜辉石相对于斜辉石的比例。等压批量熔融计算表明，流体不饱和橄榄岩熔融的熔体生产率明显低于无水橄榄岩熔融，俯冲带橄榄岩熔融过程受从俯冲板带入地幔楔体的富H2O组分组成的强烈影响。
This experimental study examines the effects of variable concentrations of dissolved H2O on the compositions of silicate melts and their coexisting mineral assemblage of olivine + orthopyroxene +/- clinopyroxene +/- spinel +/- garnet. Experiments were performed at pressures of 1.2 to 2.0 GPa and temperatures of 1100 to 1345 degrees C, with up to similar to 12 wt% H2O dissolved in the liquid. The effects of increasing the concentration of dissolved H2O on the major element compositions of melts in equilibrium with a spinel Iherzolite mineral assemblage are to decrease the concentrations of SiO2, FeO, MgO, and CaO. The concentration of A1(2)O(3) is unaffected. The lower SiO2 contents of the hydrous melts result from an increase in the activity coefficient for SiO2 with increasing dissolved H2O. The lower concentrations of FeO and MgO result from the lower temperatures at which H2O-bearing melts coexist with mantle minerals as compared to anhydrous melts. These compositional changes produce an elevated SiO2/ (MgO + FeO) ratio in hydrous peridotite partial melts, making them relatively SiO2 rich when compared to anhydrous melts on a volatile-free basis. Hydrous peridotite melting reactions are affected primarily by the lowered mantle solidus. Temperature-induced compositional variations in coexisting pyroxenes lower the proportion of clinopyroxene entering the melt relative to orthopyroxene. Isobaric batch melting calculations indicate that fluid-undersaturated peridotite melting is characterized by significantly lower melt productivity than anhydrous peridotite melting, and that the peridotite melting process in subduction zones is strongly influenced by the composition of the H2O-rich component introduced into the mantle wedge from the subducted slab.