西昆仑山库地北岩体的地球化学特征及构造意义

Geochemical characteristics and tectonic implications of North Kuda Pluton, West Kunlun Mountains

运用主元素、微量元素及同位素地球化学方法对西昆仑地区库地北岩体的地球化学特征、源区、构造意义 及成岩模式进行了系统的研究。研究表明，库地北岩体是一个高钾的Ⅰ型花岗岩岩体，其微量元素和同位素组成表 明，该岩体来源于陆壳岩石的部分熔融。其独特的微量元素分布特征以及与其共生的基性岩脉表明，该岩体形成于 加里东末期一引张的构造环境。该期引张构造的识别为研究西昆仑地区构造演化历史提供了新的依据。

Based on the major element, trace element and isotope compositions, study on the geochemical characteristics, source, tectonic implications and petrogenesis of the North Kuda Pluton (NKP), West Kunlun Moun- tains has been conducted. The NKP with an age of 404 Ma is enriched in K_2O (> 5. 4% ), and does not contain arfvedsonite. Its relatively high REE, LILE (e. g. Rb, Cs, U and Th) and HFSE (e. g. Nb and Zr) contents exhibit strong affinity to A-type granite, which makes it apparently different from most granitic intrusions in West Kunlun Mountains. Its heterogeneous Sr (^(87)Sr/^(86)Sr = 0. 7049 - 0. 7098) and Nd (εNd = - 1. 05 - 4. 04) isotope compositions preclude the possibility of a pure sedimentary or igneous source, rather, its geochemical compositions suggest that it may be derived from partial melting of a heterogeneous source, which contains both igneous and sedimentary rocks. Its within-plate characteristics, together with the coeval mafic dikes, indicate that it was generated in an extensional environment at the end of Caledonian. The recognition of the extensional event does not support a continuous subduction environment in West Kunlun Mountains; instead, the existence of the extensional environment provides new evidence for the two-phase island-arc model.