摘要
同位素地质年代学是月球形成与演化研究的重要工具。目前对月岩和月球陨石的研究积累了大量的同位素年代学资料,其测试的主要方法包括K-Ar、Ar-Ar、Rb-Sr、Sm-Nd、Lu-Hf、Re-Os、Pb-Pb和U-Pb等。根据目前获得的资料,本文对月球上不同类型岩石的形成年龄进行了总结,发现月球高地岩石主要形成于45～38亿年,而月海玄武岩相对年轻,大致形成于38～31亿年。根据这一年代资料,结合对月岩样品进行的短半衰期Hf-W与Sm-Nd同位素体系的研究结果,认为月球大致形成于45亿年,其后开始由岩浆海导致的内部核-幔-壳的分异,岩浆结晶的低密度斜长岩构成最初的月壳,而密度大的岩石构成月幔,而此月幔则成为后来月海玄武岩的主要岩浆源区。同时指出了当前月岩同位素地质年代学存在的问题,并根据技术进展的情况,对未来月岩同位素年代学的发展趋势作了全面的分析。
Isotopic geochronology is one of the important tools to study formation and evolution of the Moon. The available dating techniques applied to the lunar rocks and meteorites include K-Ar, Ar-Ar, Rb-Sr, Sm-Nd, Lu-Hf, Re-Os, Pb-Pb and U-Pb, etc. According to the data obtained by these methods, the highland rocks were mostly formed during 4.5 - 3.8 Ca; whereas the mare basalts, mainly erupted in the period of 3.8 - 3.1 Ca, are a little younger than that of the highland rocks. This conclusion, combined with the data obtained from the short-lived Hf-W and Sm-Nd isotopic systematics, suggests that the Moon was initially accreted at 4.5 Ca, followed by de- velopment of the global lunar magma ocean （LMO） . The primary lunar crust is composed by ferroan anorthosite which was produced by flotation of plagioclase during cl^ystallization of the LMO. However, the marie minerals, coevally cl^ystallized with the plagioclase, sank to the base of the LMO due to their high density, and made up the main part of the lunar mantle, which served as the source during later mare basaltic magmatism. In addition, a comprehensive overview is given to the geochronologic study of the lunar rocks to date, and propose some key technical points which should be developed in the future.
出处
《地球化学》
CAS
CSCD
北大核心
2010年第1期37-49,共13页
Geochimica
