An experimental investigation of F, Cl and H2O mineral-melt partitioning in a reduced, model lunar system
An experimental investigation of F, Cl and H2O mineral-melt partitioning in a reduced, model lunar system
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DOI：
10.1016/j.gca.2020.12.003
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发表时间：
2020-12
影响因子：
5
通讯作者：
N. Potts;G. Bromiley;R. Brooker
中科院分区：
文献类型：
--
作者：
N. Potts;G. Bromiley;R. Brooker
据认为，月球是在一个大的微行星与早期地球碰撞后形成的。在2004年的事件之后，月球受到的地质活动比地球少得多，可能提供了早期地月系统的过程和条件的更好记录。对月球物质中的H、F、Cl、S、C等岩浆挥发分的研究已经很多。然而，我们解释月球样品组中可变挥发性成分的能力取决于我们对月球系统中挥发性行为的理解。目前，这受到有限实验数据的限制。在这里，我们提出了第一个实验矿物熔体分配系数的F，Cl和H2O在一个模型月球系统在适当的条件下（日志fO2 IW-2.1，即氧逸度下降到2.1日志单位以下的Fe-FeO缓冲）。数据与月球地幔条件下硅酸盐熔体、橄榄石和辉石中F、Cl和OH −的结构结合一致。氧逸度对H2O形态的影响有限，而H2O，F和Cl的分配在很大程度上取决于矿物化学和熔体结构。分配系数大致一致的地幔源区的月球火山产品是显着亏损的F，Cl和H2O，亏损Cl相对于F和H2O，相比，陆地地幔。分区数据也被用来模拟月球岩浆海洋（LMO）结晶过程中的挥发分再分配。月球地幔累积的挥发分含量取决于LMO凝固过程中捕获液体的比例。然而，在矿物熔体分配LMO固化过程中的差异可能会导致显着富集F相对于Cl，和F相对于H2O，在累积相相对于原始LMO组合物。因此，月球火山产物中的氯耗尽可能部分是LMO固化的结果。
It is believed that the Moon formed following collision of a large planetesimal with the early Earth. Over the ∼4 Gyr since this event the Moon has been considerably less processed by geological activity than the Earth, and may provide a better record of processes and conditions in the early Earth-Moon system. There have been many studies of magmatic volatiles such as H, F, Cl, S and C in lunar materials. However, our ability to interpret variable volatile contents in the lunar sample suite is dependent on our understanding of volatile behaviour in lunar systems. This is currently constrained by limited experimental data. Here, we present the first experimental mineral-melt partitioning coefficients for F, Cl and H2O in a model lunar system under appropriately reduced conditions (log fO2to IW-2.1, i.e. oxygen fugacity down to 2.1 log units below the Fe-FeO buffer). Data are consistent with structural incorporation of F, Cl and OH−in silicate melt, olivine and pyroxene under conditions of the lunar mantle. Oxygen fugacity has a limited effect on H2O speciation, and partitioning of H2O, F and Cl is instead largely dependent on mineral chemistry and melt structure. Partition coefficients are broadly consistent with a mantle source region for lunar volcanic products that is significantly depleted in F, Cl and H2O, and depleted in Cl relative to F and H2O, compared to the terrestrial mantle. Partitioning data are also used to model volatile redistribution during lunar magma ocean (LMO) crystallisation. The volatile content of lunar mantle cumulates is dependent upon proportion of trapped liquid during LMO solidification. However, differences in mineral-melt partitioning during LMO solidification can result in significant enrichment on F relative to Cl, and F relative to H2O, in cumulate phases relative to original LMO composition. As such, Cl depletion in lunar volcanic products may in part be a result of LMO solidification.