摘要
对西藏亚东地区前寒武纪结晶基底岩系59个岩石样品的地球化学特征的研究发现,亚东岩群和聂拉木岩群不仅岩石组合特征不同,而且两者的岩石地球化学特征也存在很大的差异:(1)亚东岩群过渡族元素V、Cr的含量远大于聂拉木岩群的,而亚东岩群的Rb、Sr、Ba、Mo的含量远小于聂拉木岩群的,这与上、下地壳中这些元素的平均含量的变化趋势相一致。在亲氧元素族特征上,表现为亚东岩群的w(Th)/w(U)值远大于聂拉木岩群的。(2)在稀土元素特征上,亚东岩群和聂拉木岩群均表现为LREE富集、HREE亏损,但(La/Yb)N值和δEu值均为亚东岩群的小于聂拉木岩群的。因此,认为亚东岩群的埋深要大于聂拉木岩群,亚东岩群的变质程度和构造层次要深于聂拉木岩群,二者的原岩物源区不同或沉积区大地构造背景存在着差异,为构造地层划分提供了有力的的证据。从岩石地球化学这一角度证明了将亚东地区结晶岩系划分为亚东岩群和聂拉木岩群是合理的,它为研究喜马拉雅结晶基底的构造演化提供了资料。
A great difference in trace and rare earth elements between the Yadong and Nyalam groups has been found by studying their 59 samples. Trace elements' character exhibits that the tectonic horizon of the Yadong Group is lower than that of the Nyalam Group. The contents of V and Cr in the Yadong Group are larger than those in the Nyalam Group, and the contents of Rb,Sr,Ba and Mo in the Yadong Group are lower than those in the Nyalam Group. This accords with the characters in the lower and upper crusts. The level of metamorphism of the Yadong Group is deeper than that of the Nyalam Group by studying the ratio of Th to U. The distribution patterns of rare earth elements of the Yadong Group differ obviously from those in the Nyalam Group.The values of (La/Yb)N and δEu of the Yadong Group are smaller than those of the Nyalam Group. It is concluded that the Yadong and Nyalam groups are apparently different in provenance and tectonic background. This is a proof for dividing tectonicstratigraphic units of crystalline rocks in the Yadong area, and an information for studying the tectonic evolution of Himalaya crystal basement.
出处
《现代地质》
CAS
CSCD
2003年第3期237-242,共6页
Geoscience
基金
中国地质调查局"西藏1:25万江孜县幅
亚东县幅区域地质调查项目"(20001300009111)。
关键词
前寒武系
岩石地球化学
亚东地区
西藏
trace elements
rare earth elements
Precambrian
the Yadong area
Tibet
