【摘要】 西天山阿吾拉勒东南部艾肯达坂花岗岩和2752高地闪长玢岩浅成小岩体侵入于石炭系火山-沉积岩中,岩石无变形,呈均一块状,具斑状/似斑状结构,属准铝质到弱过铝质高钾钙碱性花岗岩类,富集Rb、Th、U、K和Pb等大离子亲石元素,贫Zr、Hf等高场强元素,显示中等到弱的负Eu异常,亏损Nb、Ta、P、Ti和Sr等元素,具壳源岛弧区岩浆作用的地球化学特征。这两个岩体锆石均为正εHf(t)值和新元古代Hf陆壳模式年龄,指示其主要源自新元古代陆壳物质的部分熔融,个别锆石εHf(t)值明显高表明岩体形成过程还有幔源岩浆物质的加入。LA-ICP-MS锆石U-Pb定年分别获得2752高地闪长玢岩307 Ma和艾肯达坂花岗岩282 Ma的形成年龄,与区域上同期小岩体一同对应于西天山大规模壳-幔花岗岩浆活动末期,证明在晚石炭世—中二叠世期间,伴随着西天山大规模花岗岩浆活动的减弱,出现一期重要的小规模中酸性岩浆活动。综合分析西天山晩石炭世—中二叠世各类岩浆作用,该时期中酸性小岩体为后碰撞向陆内伸展拉张过渡阶段岩浆活动的产物,指示西天山晚石炭世晚期深部动力学背景和构造环境发生了重要转折。更多还原

【Abstract】 Aikendaban granite and 2752 Gaodi dioritic porphyrite in the southeastern Awulale area of West Tianshan intrude into Carboniferous volcanic-sedimentary sequences, showing undeformed uniform massive structures and porphyric/porphyric-like textures.Geochemically,they are enriched in large ion lithophile elements(Rb,Th,U,K,Pb,etc.),poor in high fieldstrength elements(Zr,Hf,etc.),depleted in Nb,Ta,P,Ti,Sr,etc.,Eu anomalies are weakmedium negative,displaying the feature similar to those of crust-derived magmatism in island arc.The zircons from Aikendaban granite and 2752 Gaodi dioritic porphyrite have positiveεHf(t)and Neoproterozoic continental crust model age,suggesting that they result from the partial melting of Neoproterozoic continental crust materials;however,individual zircons have higherεHf(t),indicating the involvement of mantle-derived magmatic materials during the formation of granitic pluton.LA-ICP-MS zircon U-Pb ages of Aikendaban granite and 2752 Gaodi dioritic porphyrite are 282 Ma and 307 Ma,respectively;the ages correspond to the forming period of regional small plutons and the late period of large-scale crust-mantle granitic magmatism in West Tianshan,suggesting a small-scale intermediate-acid magmatism with the weakening of largescale granitic magmatism from Late Carboniferous to Middle Permian. Based on the comprehensive analysis of Late Carboniferous-Middle Permian magmatism,the occurrence of these small plutons indicates an intermediate-acid magmatism,implying a decreasing of largescale magmatism in the transitional stage from post-collision to intra-continental extension,and indicating an important turning point of the deep dynamical background and the tectonic environment in West Tianshan.更多还原