摘要
嫦娥五号玄武岩采自月球风暴洋的月海玄武岩单元(EM4/P58),同位素定年显示它形成于20亿年前,是迄今为止人类采集的最年轻的月海玄武岩,对其开展岩石学和地球化学研究将揭示月球长时间火山活动之谜,从而帮助我们更深刻地认识月球的热演化历史。本文总结了嫦娥五号玄武岩的研究进展,综合分析了已发表的数据,并对其岩石地球化学特征和成因机制进行了探讨。嫦娥五号玄武岩的平均TiO_(2)含量为5.6%±1.7%,属低钛玄武岩,其橄榄石和斜长石的Ti含量变化也符合低钛玄武岩的演化趋势;辉石的Ti/(Ti+Cr)值落在阿波罗高钛玄武岩区域,系因其Cr_(2)O_(3)含量(0.12%±0.09%)显著低于阿波罗玄武岩的Cr_(2)O_(3)含量,导致辉石的Ti/(Ti+Cr)值也相应增大。尽管嫦娥五号玄武岩具有轻稀土富集的特征,但其Sr和Eu的负异常程度与克里普(KREEP)玄武岩显著不同,结合其具有非常低的初始^(87)Sr/^(86)Sr值(0.69934~0.69986)和亏损的εNd(t)值(7.9~9.3),指示其源区克里普物质的贡献非常有限。嫦娥五号玄武岩源区亏损挥发分,水含量为1×10^(-6)~5×10^(-6),S含量为1×10^(-6)~10×10^(-6),Cl含量为0.1×10^(-6)~1.5×10^(-6),F含量为0.6×10^(-6)~2.4×10^(-6),指示月幔挥发分分布不均一或源区经历过岩浆活动导致的挥发分抽取。嫦娥五号着陆区火山活动的诱发机制可能是~20%的单斜辉石-钛铁矿堆晶进入源区使其熔点降低(约80℃),但月球的冷却速率为何如此之慢,单斜辉石-钛铁矿堆晶如何进入源区并在20亿年前诱发熔融,仍是未解之谜。
The Chang’E-5(CE5)basalt was sampled from the lunar mare basalt unit(EM4/P58)in Oceanus Procellarum.Radiogenic dating indicates that it formed two billion years ago,making it the youngest mare basalt ever collected.The study of its petrological and geochemical characteristics will unravel the mystery of the long-term volcanic activity of the Moon and thus help us better understand the thermal evolution history of the Moon.In this paper,we summarize the recent research progress on the CE5 basalt,comprehensively analyze the published data and discuss the petrological and geochemical characteristics of the CE5 basalt and its origin.The average TiO_(2)content of the CE5 basalt is 5.6%±1.7%,which belongs to low-Ti basalts,and the variations of Ti contents of its olivine and plagioclase is also consistent with the evolution trend of low-Ti basalts.Although the Ti/(Ti+Cr)ratio of pyroxene falls in the Apollo high-Ti basalt field,it can be explained by the fact that Cr_(2)O_(3)content of the CE5 basalt(0.12%±0.09%)is significantly lower than that of Apollo basalts.The CE5 basalt exhibits an enrichment of light rare earth elements.However,the extent of negative anomalies in Sr and Eu is significantly distinct from that of KREEP basalts,which,combined with its very low initial^(87)Sr/^(86)Sr ratios(0.69934~0.69986)and depletedεNd(t)values(7.9~9.3),indicate that the contribution of KREEP material in its mantle source region must be very limited.The source of CE5 basalt is estimated to contain 1×10^(-6)~5×10^(-6)water,1×10^(-6)~10×10^(-6)S,0.1×10^(-6)~1.5×10^(-6)Cl,and 0.6×10^(-6)~2.4×10^(-6)F,which suggests that the volatile components in the lunar mantle are heterogeneous or the source region has experienced extraction of volatiles due to magmatic processes.A possible explanation for young volcanism at the CE5 landing site is the involvement of~20%ilmenite-clinopyroxene in the mantle source,which lowers the melting point by~80℃.What remains unknown,however,is why the cooling rate of the Moon is so slow and h
作者
杨蔚
田恒次
陈意
胡森
苏斌
林杨挺
李献华
YANG Wei;TIAN Heng-ci;CHEN Yi;HU Sen;SU Bin;LIN Yang-ting;LI Xian-hua(Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2023年第3期442-461,I0003,共21页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
国家自然科学基金资助项目(42241103)。
