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首页> 外文期刊>The American mineralogist >Crystal/melt partitioning of water and other volatiles during the near-solidus melting of mantle peridotite: Comparisons with non-volatile incompatible elements and implications for the generation of intraplate magmatism
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Crystal/melt partitioning of water and other volatiles during the near-solidus melting of mantle peridotite: Comparisons with non-volatile incompatible elements and implications for the generation of intraplate magmatism

机译：地幔橄榄岩近固相线融化过程中水和其他挥发物的晶体/熔体分配：与非挥发性不相容元素的比较及其对板内岩浆作用的影响

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Concentrations of H2O, F, Cl, C, P, and S have been-measured by secondary ion mass spectrometry (SIMS) in experimentally produced peridotite phases (including clinopyroxene, orthopyroxene, olivine, garnet, amphibole, and mica) and coexisting basanitic glasses. Because only two experiments produced glasses on quenching (with the melt phase in others reverting to felt-like crystallite masses) H2O concentrations in melts were also separately determined from mass-balance relationships and by assuming constant H2O/La in melts and starting materials. The resulting values were used to calculate mineral/melt partition coefficients (D values) for H2O [where D-H2O(crystal/melt) = (mass fraction of H2O in crystal)/(mass fraction of H2O in melt)] for conditions of 1025-1190 degrees C and 1.0-3.5 GPa. These gave 0.0064-0.0164 for clinopyroxene, 0.0046-0.0142 for orthopyroxene, 0.0015-0.0016 for olivine, and 0.0016-0.0022 for garnet. Although less information was obtained for the other volatiles, F was found to be significantly more compatible than H2O during peridotite melting, whereas Cl is significantly less compatible. S also has small but appreciable solubilities in amphiboles and micas, but not in pyroxenes or olivine. The solubility of C in silicate minerals appears to be negligible, although C was present in coexisting melts (similar to 0.5 wt% as CO2) and as residual graphite during experiments. The D values for H2O in clinopyroxene and orthopyroxene are positively correlated with Al-iv but negatively correlated with the H2O concentrations of melts (when considered as wt%). These relationships are consistent with the broad trends of previously published partitioning data. Although some of the concentration dependence can be related to cross-correlation between Al-iv in pyroxenes and H2O concentrations in melts (via the latter's control of liquidus temperatures) this relationship is too inconsistent to be a complete explanation. A concentration dependence for DriPraume" can also be independently predicted from speciation models for H2O in silicate melts. Thus it is likely that Dg(H2O)(pyx/melt) is influenced by both Al-iv and the absolute concentration of H2O in melts. D-H2O/D-ce for clinopyroxene is inversely correlated with M2 site radii. Because the latter decrease with increasing pressure and temperature, relatively hot and/or deeply derived melts should be enriched in Ce relative to H2O when compared to melts from cooler and shallower mantle sources. Conversely, melts from H2O-rich settings (e.g., subduction zones) should have higher H2O/Ce than their source rocks. When combined with previously obtained partitioning data for non-volatile elements (from the same experiments), our data are consistent with the enrichment of intraplate basalt sources in both volatile and non-volatile incompatible elements by small-degree melts derived from local mid-ocean ridge basalt sources. In this way, volatiles can be seen to play an active role (via their promotion of partial-melting and metasomatic processes) in the auto-regulation of incompatible element concentrations in the depleted upper mantle.
机译：已通过二次离子质谱仪（SIMS）测量了实验生成的橄榄岩相（包括斜长石，邻斜方石，橄榄石，石榴石，闪石和云母）和共存的玄武岩玻璃中H2O，F，Cl，C，P和S的浓度。因为只有两个实验在淬火时生产了玻璃（其他相中的熔体相恢复为毡状微晶质），所以熔体中的H2O浓度也可以通过质量平衡关系并假设熔体和起始原料中的H2O / La恒定来分别确定。在以下条件下，将所得值用于计算H2O的矿物/熔体分配系数（D值）[其中D-H2O（晶体/熔体）=（晶体中H2O的质量分数）/（熔体中H2O的质量分数）]。 1025-1190摄氏度和1.0-3.5 GPa。这些对克林吡rox烯为0.0064-0.0164，邻苯二酚为0.0046-0.0142，橄榄石为0.0015-0.0016，石榴石为0.0016-0.0022。尽管获得的其他挥发物信息较少，但是发现在橄榄岩熔融过程中，F与水的相容性明显高于水，而氯的相容性则较差。 S在闪石和云母中也有少量但可观的溶解度，但在辉石或橄榄石中却没有。 C在硅酸盐矿物中的溶解度似乎可以忽略不计，尽管在实验过程中共存的熔体中存在C（与CO2相似，为0.5 wt％）和残留的石墨。斜茂铁和邻茂铁中H2O的D值与Al-iv正相关，而与熔体的H2O浓度负相关（当以重量％计）。这些关系与以前发布的分区数据的广泛趋势一致。尽管某些浓度依赖性可能与辉石中的Al-iv与熔体中的H2O浓度（通过后者对液相线温度的控制）之间的互相关有关，但这种关系太不一致了，无法完全解释。 DriPraume的浓度依赖性也可以从硅酸盐熔体中H2O的形态模型中独立预测。因此Dg（H2O）（pyx / melt）可能受Al-iv和熔体中H2O绝对浓度的影响。 Clinopyroxene的D-H2O / D-ce与M2半径成反比，因为后者随着压力和温度的升高而降低，因此相对于H2O而言，相对较热和/或较深衍生的熔体应富集Ce，而不是来自较冷和高温的熔体。相反，来自富H2O环境（例如俯冲带）的熔体应具有比其源岩更高的H2O / Ce。当与先前获得的非挥发性元素分配数据（来自同一实验）结合使用时，我们的数据与局部洋中脊玄武岩源产生的小规模熔体丰富了板内玄武岩源在挥发性和非挥发性不相容元素中的含量。 en在耗尽的上地幔中不相容元素浓度的自动调节中起积极作用（通过促进部分熔融和交代过程）。

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