辽宁－吉林东部地区超镁铁质岩包体的微量元素地球化学特征

Trace geochemical elemental characteristics of ultramafic inclusions in eastern part of Liaoning-Jilin district, China

发展了预浓集中子活化分析方法，结合仪器中子活化分析对辽宁—吉林东部地区新生代火山岩中尖晶石二辉橄榄岩包体的稀土元素（ＲＥＥ）及其他微量元素进行了测定。它们的过渡金属元素中不相容元素Ｔｉ以及适度相容元素Ｖ和Ｓｃ相对于原始地慢（ＰＭ）均具亏损的特征；而相容元素Ｃｏ、Ｎｉ和Ｃｒ含量略高或类似于ＰＭ，反映了它们应为经历了部分熔融后的残余地幔。依据ＲＥＥ特征尖晶石二辉橄榄岩可分为两类：第一类包体的ＲＥＥ含量和ＲＥＥ分配型式与ＰＭ相比呈现明显的亏损，提供了它们是残余地慢岩的又一证据。第二类包体的重稀土元素（ＨＲＥＥ）比前者低，但轻稀土元素（ＬＲＥＥ）比前者明显的高，揭示了它们在地幔源岩经历了部分熔融，使ＲＥＥ发生了亏损之后又遭受了ＬＲＥＥ富集，即地幔交代作用。

The cenozoic volcanic rocks in eastern part of Liaoning-Jinn district consist mainly of basaltS which contain abundant mantle-derived xenoliths. The rocks of ultramafic inclusions are composed mostly of spinel lherzolites and a small amount of websterites. It order to study the origin of xenoliths, the concentrations of several trace elements (REE, Rb,Sr, Ba, Th, U, Hf, Sc, Cr, Fe, Co and Ni) have been studied by NAA. According to geochemical characteristics of REE and other trace elements,there are two types of spinel lherzolite inclusions. The first type is refractory residues left after partial melting of the upper mantle and the second type is metasomatizing refractory residues. It applies that even within a small volume beneath the area studied the upper mantle is inhomogeneous. But websterites inclusions are formed by segregation of basaltic melt derived from high degree of melting of mantle source rocks.