A set of the continental volcanic rocks has been recognized in the MoQinulla mountain of northeastern Junggar terrane,which angle unconformably overlies the Middle-Late Ordovician Miaoergou Formation.The volcanic rocks LA-ICP-MS zircon U-Pb dating yield trachytic andesite age of 434.4 ± 2.2Ma,which indicates that it formed in the Early Silurian.The volcanic rocks consist of tephrite,basaltic trachytic andesite,trachytic andesite and pyroclastic rock relatively,belonging to strong alkaline-alkaline series.The volcanic rocks have a SiOz ranging from 45.6％ to 54.4％,relatively high alkali (Na2O + K2O =6.75％ ～9.10％),high contents of TiO2 (0.85 ％ ～ 1.42％) and Al2O3 (17.75 ％ ～ 20.0％),low Mg# (25.1 ～ 55.6),high Rittmann index δ (3.63 ～ 9.68) and alkali feldspar and leucite appearing in the matrix.Rocks have a significant differentiation between the light rare earth element (LREE) and heavy rare earth element (HREE),(La/Yb)N number ranging from 4.22 to 6.29 and unconspicuous Eu negative anomaly.The rocks are all enriched with large ion lithophile elements (LILE),but are relatively depleted in high field strength elements (HFSE),and have a negligible negative Nb-Ta-Ti anomaly.The (87Sr/86Sr) i values of volcanic rocks are 0.7033 ～ 0.7046,with a low positive εNd (t) (+ 2.13 ～ +4.16),showing the depletion mantle source characteristics.But with high alkali,enrichment of LILE and the low (143Nd/144Nd) i values,the rocks reveal the enrichment of source characteristics which may arise from crustal recycling or hybridization of crust materials.Synthesized regional geology and Zr-Zr/Y,Ti/1000-V diagram,we speculate that the Early Silurian alkali basalt formed in the plate extensional setting after the collision between Junggar terrane and Altai-Mongolia terrane,which may represent the stage of Karamaili ocean intracontinental initial extension.It shows that Silurian is a key stage of structural transformation from collisional extrusion to extension in northeastern Junggar terrane.%在准噶尔地块东北缘莫钦乌拉山发现一套陆相火山岩,其与下伏中-上奥陶统庙尔沟组呈角度不整合接触,粗安岩LA-ICP-MS锆石U-Pb年龄为434.4±2.2Ma,表明其形成时代为早志留世.火山岩岩石组合为碱玄岩、玄武粗安岩、粗安岩和相应的火山碎屑岩,属于强碱性-碱性火山岩系列.SiO2含量在45.6％ ～ 54.4％之间,富碱(Na2O+ K2O=6.75％ ～9.10％),高的TiO2 (0.85％ ～ 1.42％)和Al2O3(17.75％～ 20.0％)含量,低Mg#(25.1 ～55.6),里特曼指数δ为3.63～ 9.68,玄武岩基质中出现碱性长石和白榴石.岩石轻重稀土分异明显,(La/Yb)N=4.22～6.09,Eu负异常不明显,富集LILE,亏损HFSE,具明显的Nb、Ta、Ti负异常.样品(87Sr/86Sr)i值为0.7033～0.7046,具低正εNd(t)值(+2.13 ～ +4.16)显示了来源于亏损地幔的特征,但在富碱、强烈富集LILE和低(143Nd/144Nd)i值(～0.5122)等方面又显示了源区富集的特征,富集原因可能为地壳再循环或上升过程遭受地壳混染.结合区域地质背景和Zr-Zr/Y、Ti/1000-V图解,推测早志留世碱性玄武岩形成的构造环境为准噶尔微陆块与北部阿尔泰-蒙古微陆块碰撞造山后的板内伸展环境,可能代表了北部卡拉麦里洋盆最初期的陆内拉张阶段,这表明志留纪是准噶尔地块东北缘碰撞挤压到伸展拉张的构造转换时期.
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