中国阿尔泰造山带南缘晚古生代花岗岩脉年代学特征及构造意义  

Late Paleozoic Granite Veins in the Southern Chinese Altai: Structural Characteristics, Geochronology and Tectonic Implications

作　　者：徐扛 舒坦 孔令竹 李智勇 汪晟 蒋映德[1] XU Kang;SHU Tan;KONG Lingzhu;LI Zhiyong;WANG Sheng;JIANG Yingde(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049

出　　处：《大地构造与成矿学》2021年第3期444-462,共19页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41672056);中国科学院国际伙伴计划项目(132744KYSB20190039)联合资助。

摘　　要：中国阿尔泰造山带南缘晚古生代A型花岗岩体被认为是该区域处于伸展构造的重要岩石学证据,但是现有工作多集中在利用其地球化学特征对大地构造背景的追索,而对于其构造变形特征却鲜有深入研究。为探索阿尔泰南缘晚古生代花岗岩体产出的大地构造背景,本文对玛因鄂博岩体、喀拉苏岩体及其围岩开展了详细的野外地质观测和年代学研究。结果显示研究区普遍经历了一期近S-N向地壳缩短事件(D2),区域上形成平行于造山带走向的紧闭褶皱(F2)和近直立的轴面劈理(S2)。玛因鄂博岩体和喀拉苏岩体在野外露头虽没有展示出明显的变形特征,但是从其衍生的花岗岩脉体展示出与D2同构造变形特征。对玛因鄂博岩体的两条同构造变形花岗岩脉进行了独居石U-Pb测年,获得其年龄分别为273±3 Ma、266±2 Ma;对喀拉苏岩体的一条同构造变形花岗岩脉进行了锆石U-Pb测年,获得其年龄为282±10 Ma,均代表了同构造花岗岩脉的形成时代。结合构造观测和定年结果,表明青河地区和喀拉苏地区在二叠纪早期处于强烈的构造挤压环境。因此,中国阿尔泰造山带南缘在早‒中二叠世仍处于挤压而非伸展的大地构造环境。The Late Paleozoic A-type granites in the southern Chinese Altai have been traditionally taken as an indicator for a post-orogenic extensional environment after the amalgamation between the Chinese Altai and the southern Junggar arc domain.However,this conception was established merely based on the geochemical characteristics of the granites,and deformational patterns of these granites have rarely been investigated by using modern petro-structural methods.Moreover,this notion is at odds with the notion that the southern Chinese Altai is featured by contractional structures.In order to clarifying the regional tectonic setting during the emplacement of the late Paleozoic granites in the southern Chinese Altai,deformational characteristics as well as zircon and monazite U-Pb geochronology of the granite veins in the Qinghe(Mayinebo pluton)and Kalasu(Kalasu pluton)areas were investigated.Field observations indicate that these two areas are characterized by a major NNE-SSE-direction compression that resulted in the formation of tight folds and penetrative NWW-SEE foliation S2.Oval-shape granite intrusions in these regions lack apparent deformation.In contrast,abundant granite veins evolved from these intrusions are orthogonal to the regional main foliation S2 and followed by their tight folding,indicating their syntectonic emplacement.Monazite U-Pb dating yielded 273±3 Ma and 266±2 Ma for two deformed granite veins from the Mayinebo area.Zircon U-Pb dating yielded 282±10 Ma for a deformed granite vein from the Kalasu area.Collectively,these features suggest that these Early to Middle Permian granite veins were emplaced under a contraction environment.Combined with the available regional data,we suggest that the southern Chinese Altai was under a compressional tectonic setting which was probably responsible for the on-going amalgamation between the Chinese Altai and the Junggar arc domain during Early-to-Middle Permian.

关 键 词：中国阿尔泰 二叠纪 同构造花岗岩脉 U-PB年代学 大地构造环境 

分 类 号：P597[天文地球—地球化学] P542[天文地球—地质学]