华北板块北缘东段早前寒武纪稀土元素演化特征

通过对区内早太古宙深变质地体、晚太古宙花岗岩-绿岩地体,晚太古-早元古宙优地槽和火山岛弧各类变质岩稀土元素的研究,三个时期的稀土元素具大致相似的演化特征,不同时期相同的岩石类型的稀土配分型式也大致相似,反映了它们有着相同源岩。但是,它们又在稀土丰度、Eu异常和轻、重稀土分离程度方面表现出某些差异,表明本区在早前寒武纪的不同时期、不同构造环境中地壳成分的不均一性。不同岩石类型稀土配分的多样性,说明岩浆源不同,至少有超镁铁质、镁铁质和安山质或英云闪长岩-奥长花岗岩三种岩浆源。

The Evolutionary Characteristics of Rare Earth Elements of the Early Pre-Cambrian in the East Section of the North Margin of the North China Platform

Through the study of the rare earth elements in the high metamorphosed massif of the early Archaean, the granite-greenstone massif of the late Archaean and various metamorphic rocks in the eugeosyncline and volcano-island arc of the late Archaean-early Proterozoic in the east section of the north margin of the North China Platform, the authors conclude that the rare-earth elements in the above three geological periods possess approximately similar evolutionary characteristics and that the partition patterns of the rare-earth elements in similar rock types in different geological periods are about the same, indicating that they were derived from the same source rocks(genesis). However, there are some differences in abundance, Eu-anormaly and degree of fractionation of light and heavy rare earth elements, indicating the heterogeneity of the crustal composition in different geological periods and structural environments in the early Pre-cambrian in the area. The variety of the partition pattern of the rare earth elements in different rock types suggests that there are at least three different magmatic sources, namely, the ultramafic, mafic and the andesitic or the tonalitic-trondhjemitic magmatic sources.