中天山尾亚杂岩体的铅同位素组成特征

CHARACTERISTICS OF LEAD ISOTOPIC COMPOSITIONS OF THE WEIYA GRANITIC COMPLEX IN MIDDLE TIANSHAN

对尾亚杂岩体钾长石铅同位素组成的详细研究发现,它们符合幔-壳二元混合模式。即地幔来源的铅和不同数量的地壳来源的铅的混合。经计算,其中约有25％—37％的铅来自上地幔,而63％—75％的铅来自地壳,该区陆壳平均年龄约2450Ma。本区岩石铅同位素组成与中国东部不同,显示贫钍富铀的特征。铅同位素的研究进一步证明尾亚杂岩体系幔-壳混合源的同熔系列花岗岩。

A detailed study of lead isotopic composions in K-feldspars from the Weiya complex indicates their consistence with the model for binary mixing,i.e. the mixing of mantle lead with variable amounts of radiogenic crustal lead. Calculations show that 25—37％ of lead in the magma derived from the upper mantle, and 63—75％ from the upper crust. The continental crust of this region has an average age of about 2450Ma. The isotopic compositions in the rock of this region is distinct from those in East China, displaying the feature of Th-poor and U-rich. The study of lead isotope has further p(?)ved that the Weiya granitic complex is syntexJs series derived from mixing source of the mantle and crust.