Pristine Moon rocks: A “large” felsite and a metal‐rich ferroan anorthosite
Pristine Moon rocks: A “large” felsite and a metal‐rich ferroan anorthosite
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原始月球岩石：“大”霏细岩和富含金属的铁斜长岩
DOI：
10.1029/jb092ib04p0e303
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发表时间：
1987
影响因子：
--
通讯作者：
G. Kallemeyn
中科院分区：
文献类型：
--
作者：
P. Warren;E. Jerde;G. Kallemeyn
我们报告新的化学分析和（在大多数情况下）描述19个月球岩石样本，包括5月海玄武岩从阿波罗15号和5个不常见的陨石从阿波罗17号。研究的两个样品是最不寻常的：一个是阿波罗12号的“大”（101克）长岩，另一个是阿波罗15号的原始铁斜长岩，它异常富含铁金属和微量亲铁元素。长石12033，507主要是钾长石和硅相的图形共生体，含有约6%的斜长石和1%的铁辉石、钛铁矿和铁橄榄石。这个结晶组合是纵横交错的，显然是侵入薄脉的褐色，长英质（平均SiO2 = 57重量%）玻璃。玻璃脉的成分远不均匀;显然，玻璃侵入后，它与结晶的长石发生了不同程度的反应。分散在玻璃脉网络中的明显节点处的深色球状物被解释为侵入玻璃中变化最小的。这些球状玻璃相对缺乏SiO2（平均值= 48重量%），但极其富含FeO（平均值= 36重量%）。它们可能是由于液体不可渗透性导致产生结晶长石的相同熔体分裂成富铁熔体（球状玻璃）加上贫铁、富硅熔体而形成的。根据这个模型，变形，很可能是由撞击引起的，然后把富含铁的熔体挤压到仍然在附近的，仍然很热的，结晶的Felsite中。铁斜长岩15363的铁金属含量在我们研究的薄片中为1.2wt%，但根据Co和Ni的质量平衡，在我们用于大块岩石分析的芯片中必须相当低。即便如此，测得的几个亲铁元素（Re，Os和Ir）的大块岩石浓度远远高于以前观察到的原始月球斜长岩。这些结果强调了与任何试图估计月球地壳中亲铁元素含量的尝试相关的巨大不确定性。在阿波罗17号的原始岩石中，位于Serenitatis盆地的边缘，铁斜长岩的数量仍然远远超过富镁岩石。
We report new chemical analyses and (in most cases) descriptions for 19 lunar rock samples, including 5 mare basalts from Apollo 15 and 5 uncommonly feldspathic rocklets from Apollo 17. Two of the samples studied are most extraordinary: a “large” (≈1 g) felsite from Apollo 12, and a pristine ferroan anorthosite from Apollo 15 that is unusually rich in Fe-metal and trace siderophile elements. The felsite, 12033,507, is mainly a graphic intergrowth of K-feldspar and a silica phase, with about 6% plagioclase and 1% each of ferroaugite, ilmenite, and fayalitic olivine. This crystalline assemblage is crisscrossed, and apparently intruded by thin veins of brownish, felsic (average SiO2 = 57 wt %) glass. The glass veins are far from uniform in composition; evidently after the glass was intruded it reacted, to varying extents, with the crystalline felsite. Dark globules scattered at apparent nodes in the network of glass veins are interpreted as the least altered of the intruded glasses. These globule glasses are relatively SiO2-poor (average = 48 wt %) but extremely FeO-rich (average = 36 wt %). They may have formed as liquid immiscibility caused the same melt that produced the crystalline felsite to split into Fe-rich melt (the globule glasses) plus Fe-poor, Si-rich melt. According to this model, deformation, most likely caused by an impact, then squeezed the Fe-rich melt into the still nearby, and still hot, crystalline felsite. The Fe-metal content of ferroan anorthosite 15363 is 1.2 wt % in the thin section we studied, but must have been, based on mass balance for Co and Ni, considerably lower in the chip we used for bulk-rock analysis. Even so, the measured bulk-rock concentrations for several siderophile elements (Re, Os, and Ir) are far higher than previously observed among pristine lunar anorthosites. These results underscore the huge uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon's crust. Among pristine rocks from the Apollo 17 site, located on the rim of the Serenitatis Basin, ferroan anorthosites continue to be far outnumbered by Mg-rich rocks.