月海玄武岩与月球演化

发布时间：2017-12-26 22:09

本文关键词：月海玄武岩与月球演化　出处：《地球化学》2010年01期 　论文类型：期刊论文

【摘要】：月海玄武岩主要产于月球近边的盆地中,覆盖面积为月球表面的1%,其形成年龄多在39～31亿年之间,是各类月岩中最年轻的。与地球玄武岩相似,月海玄武岩由斜长石、辉石和橄榄石组成,但它们比地球玄武岩具有更低的Mg#、Al2O3、K和Na含量,高的FeO含量(大于16%)和变化范围大的TiO2含量(小于1%到大于13%)。根据TiO2含量的变化,月海玄武岩分成高Ti(6%),低Ti(1.5%TiO26%)以及极低Ti(1.5%)三类。所有月海玄武岩都具有Eu负异常,并亏损挥发性元素和亲铁元素。月海玄武岩的同位素特征指示其至少为三个组分混合的产物:(1)高238U/204Pb、高87Sr/86Sr和负εNd组分,可能是岩浆海分异的残余岩浆即KREEP;(2)低238U/204Pb、低87Sr/86Sr和正εNd组分,来源于原始月幔,其熔融产物为低Ti玄武岩;(3)中等87Sr/86Sr和εNd组分,位于月幔的顶部,经历了岩浆海(洋)过程中形成的堆晶物质的再熔融,还可能受到了陨击事件的影响,其熔融产物是高Ti玄武岩。月海玄武岩的元素和同位素地球化学性质支持岩浆海的假说,其源区的形成与岩浆海的分异密切相关,并经历了三个阶段:(a)岩浆海阶段,通过岩浆海的结晶分异形成顶部为斜长岩月壳,中间为高Ti、富钛铁矿层,底部为巨厚的硅酸盐低Ti层的三层壳幔结构;(b)富钛铁矿堆晶岩(携带少量残余熔体)因密度大而下沉至下部的硅酸盐月幔(400km以下);(c)月幔中这些不同源区的岩石发生减压熔融。早期由较浅的低熔点组分熔融形成低K高Ti玄武岩,之后形成来源较深的高Ti玄武岩和低Ti玄武岩。
[Abstract]:Mare basalts occur in the near side of the moon, covering an area of 1% of the lunar surface, its formation at the age of 39 to 3 billion 100 million years, is the youngest of all kinds of rocks. Similar to the earth basalts, the moon sea basalt is composed of plagioclase, pyroxene and olivine, but they have lower Mg#, Al2O3, K and Na contents than the earth basalt. The TiO2 content of the high FeO content (greater than 16%) and the wide range of variation (less than 1% to 13%). According to the changes of TiO2 content, mare basalt divided into high Ti (6%), low Ti (1.5%TiO26%) and low Ti (1.5%) three. All have the mare basalts negative Eu anomaly, and loss of volatile elements and siderophile elements. The isotopic characteristics of mare basalts indicate the product of at least three mixed components: (1) high 238U/204Pb, high 87Sr/86Sr and negative epsilon Nd components may be residual magma differentiation of the magma ocean is KREEP; (2) low 238U/204Pb, low 87Sr/86Sr and positive epsilon Nd components, from the primitive mantle the product is low, the melting of Ti basalt; (3) medium 87Sr/86Sr and epsilon Nd component, at the top of the mantle, magma experienced sea (Ocean) re melting cumulate material formed in the process, may also be affected by the meteorite strike event, its product is high Ti basalt melt. Mare basalts of elemental and isotopic geochemistry of support magma ocean hypothesis, the source region of the formation and differentiation of the magma ocean are closely related, and has experienced three stages: (a) magma sea stage, through the crystallization of magma sea differentiation at the top of the anorthosite in the lunar crust, high Ti, the titanium rich iron ore layer, the bottom three layer of crust mantle structure of thick Portland low Ti layer; (b) rich ilmenite cumulates (to carry a small amount of residual melt) because of the density of large and sink to the lower part of silicate mantle (400km); (c) the homologous decompressional melting of the rocks the mantle. In the early period, the low K high Ti basalt was formed by melting the shallow low melting point components, and then the high Ti basalt and low Ti basalt were formed.
【作者单位】：中国科学院同位素年代学和地球化学重点实验室中国科学院广州地球化学研究所;
【基金】：国家自然科学基金(40721063) 中国科学院知识创新工程方向性项目(KZCX2-YW-T004)
【分类号】：P184.1
【正文快照】： 1月海玄武岩的基本特征、分布和年代学1.1分布特征0引言美国于1969-1972年间实施的Apollo探月计划是人类对月球及其演化的认识的转折点。其中最重要的原因是美国6次Apollo载人探月计划和俄罗斯3次非载人计划向地球返回了近地球一侧9个点的380kg月球样品(Apollo11、12、15、17

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