Magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase: A new bulk silicate Moon model with sub-chondritic Ti/Ba, Sr/Ba, and Sr/Al ratios
Magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase: A new bulk silicate Moon model with sub-chondritic Ti/Ba, Sr/Ba, and Sr/Al ratios
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DOI：
10.1016/j.gca.2017.04.031
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发表时间：
2017-08
影响因子：
5
通讯作者：
S. Togashi;N. Kita;A. Tomiya;Y. Morishita
中科院分区：
文献类型：
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作者：
S. Togashi;N. Kita;A. Tomiya;Y. Morishita
通过对月球高地岩石中的斜长石进行二次离子质谱分析，估算了铁斜长石宿主岩浆（FAN 宿主岩浆）的成分。通过考虑基于 MELTS 算法的相关系并重新检查斜长石和熔体之间微量元素的分配系数，研究了岩浆的演化。采用Sc、Co含量相对原始的斜长石，选取受岩浆后作用影响较小的数据。 FAN 主体岩浆含有 90–174 ppm Sr、40–119 ppm Ba 和 0.5–1.3% TiO2，并且具有亚球粒状 Sr/Ba 和 Ti/Ba 比率。根据先前提出的块体硅酸盐月球模型的岩浆演化过程，很难解释 FAN 宿主岩浆的形成，并具有全球范围内难熔元素的球粒陨石比率。因此，FAN 岩浆的来源必定具有原始的亚球粒状 Sr/Ba 和 Ti/Ba 比率。 FAN 宿主岩浆的难熔元素与基于月球陨石的长石地壳估计的宿主镁铁质岩浆以及来自月球陨石的一些极低钛海岩一致。在这里，我们提出了另一种块状硅酸盐月球模型（cBSM模型），该模型相对于目前的整个地月系统，富含原体的地壳成分。
The compositions of host magmas of ferroan anorthosites (FAN-host magmas) were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks. The evolution of the magmas was investigated by considering phase relations based on the MELTS algorithm and by re-examining partition coefficients for trace elements between plagioclase and melts. Data little affected by post-magmatic processes were selected by using plagioclase with relatively primitive Sc and Co contents. The FAN-host magma contained 90–174 ppm Sr, 40–119 ppm Ba and 0.5–1.3% TiO2, and had sub-chondritic Sr/Ba and Ti/Ba ratios. It is difficult to account for the formation of FAN-host magma on the basis of magma evolution processes of previously proposed bulk silicate Moon models with chondritic ratios for refractory elements at global scale. Therefore, the source of the FAN-host magma must have had primordial sub-chondritic Sr/Ba and Ti/Ba ratios. The FAN-host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites, and some very-low-Ti mare rocks from lunar meteorites. Here, we propose an alternative bulk silicate Moon model (the cBSM model), which is enriched in crustal components of proto-bodies relative to the present whole Earth–Moon system.