北天山四棵树岩体地球化学特征及地质意义

Geological Significance and Geochemical Characteristics of the Sikeshu Pluton in North Tianshan,Xinjiang

四棵树岩体侵入于北天山蛇绿混杂岩带巴音沟蛇绿岩,属“钉合岩体”.通过对四棵树岩体进行详细的地球化学分析,该岩体主要组成为闪长岩、花岗闪长岩及二长花岗岩,SiO2含量为63.3%-68.9%,富碱,铁、镁、钙,钛含量较低,贫磷,具有偏铝质I 型花岗岩特征.相对富集轻稀土而亏损重稀土,具明显铕负异常（δEu=0.4~0.7）,富集大离子亲石元素K,Rb,Ba 及Th,亏损高场强元素Nb,Ta,Zr 及Hf.四棵树岩体可能来源于由洋壳和岛弧建造组成的年轻地壳,结合区域地质背景,认为该岩体形成的构造背景为后碰撞构造环境.

Sikeshu pluton intruded into the Bayingou ophiolite of the North Tianshan ophiolite mélange belt,with stitch-ing pluton tectonic significance.Through detailed geochemical analyses, the Sikeshu pluton is mainly composed of dio-rite,granodiorite and monzonitic granite.SiO2 content is 63.3%~68.9%,enrichment in alkali and low abundances of FeO, MgO,CaO,TiO2 and P2O5.The granites have a metaluminous I-type affinity.Moreover,the pluton enrichment in light rare earth element (LREE) and large ion lithophile element (LILE,such as K,Rb,Ba and Th),but depletion in heavy rare earth element (HREE) and high field strength element (HFSE, such as Nb,Ta,Zr and Hf),showing pronounced negative Eu anomaly (δEu=0.4~0.7).The Sikeshu pluton may be derived from young crust which is composed of oceanic crust and arc material.Combined with the regional geologic background,it is inferred that the pluton emplaced in post-collision set-ting.