河北汉诺坝玄武岩中麻粒岩类和辉石岩类捕虏体Sr、Nd、Pb同位素特征及其地质意义

Sr, Nd and Pb Isotopic Characteristics of Granulite andPyroxenite Xenoliths in Hannuoba Basalts, Hebei Province,and Their Implications for Geologic Processes

系统研究了河北汉诺坝玄武岩中二辉麻粒岩和辉石岩捕虏体的Ｓｒ、Ｎｄ、Ｐｂ同位素特征。虽然未确定捕虏体的形成时代，但同位素特征显示它们可能为较近期（中生代以来）形成。低的Ｒｂ／Ｓｒ与高的８７Ｓｒ／８６Ｓｒ比值的解耦表明捕虏体的形成经历了较强的混合作用。在二元同位素相关图上，三类具不同矿物组成的辉石岩与二辉麻粒岩有密切关系，即二辉麻粒岩投点位置是三类辉石岩的共同端点。综合考虑捕虏体的空间分布及其在Ｓｒ、Ｎｄ、Ｐｂ同位素协变图上的关系，可以认为层离作用可较好地解释这些现象。

RbSr, SmNd and Pb isotopic systematics are reported for granulite and pyroxenite xenoliths in Hannuoba basalts, Hebei Province. The isotopic characteristics of xenoliths suggest that they might have formed recently, although there is no strict constraint on the precise age. The decoupling of low Rb/Sr and high 87Sr/86Sr ratios implies the multistage evolution history and strong mixing processes. There are close ties between granulite and pyroxenites with different mineral assemblages on the SrNd, PbSr and PbNd correlation figures. The granulite is the common endmember of the three kinds of pyroxenite. Combined with the distribution of the xenoliths in space and their isotopic relationships, It is proposed that delamination can be well used to explain the ties.