【摘要】 南阿尔金造山带是中国西北地区重要的俯冲—碰撞杂岩带。笔者等对茫崖地区出露的闪长岩开展岩石学、地球化学、锆石U-Pb年代学和Lu—Hf同位素地球化学研究，探讨其岩石成因和成岩时的构造环境。研究表明，茫崖闪长岩亏损Nb、Ta、Ti、P、Th、U、HREEs、Ba、Sr等元素，富集Rb等大离子亲石元素及LREEs,显示与俯冲相关岛弧岩浆岩相似的地球化学特征。样品的锆石U-Pb年龄为494～461 Ma,ε_Hf （t）为0.01～3.90,t_DM2为1496～1447 Ma,少量ε_Hf （t）为负值（-2.22～-0.03）,t_DM2为1453～1254 Ma,指示其物质来源以中元古代（1453～1254 Ma）新生地壳物质为主，混合少量中元古代（1496～1447 Ma）古老地壳物质。综上，该期岩浆活动是幔源岩浆的底侵作用导致下地壳熔融的产物，指示南阿尔金造山带在<494 Ma进入深俯冲陆壳断离—折返阶段，同时伴随着大规模幔源岩浆的底侵作用，茫崖闪长岩是深俯冲陆壳断离后折返作用的岩浆活动响应。更多还原

【Abstract】 The South Altun orogenic belt is an important subduction—collision complex belt in northwest China. In this paper, we study the petrological, geochemical, zircon U-Pb and Lu—Hf isotopic characteristics of the Manya diorites, to discuss its petrogenesis and tectonic environment. Based on our research, the Manya diorites are depleted in Nb, Ta, Ti, P, Th, U, HREEs, Ba and Sr, while enriched in LREEs and Rb, indicating geochemical characteristics of subduction-related island arc magmatic rocks. The zircon U-Pb ages are in the range of 494 Ma to 461 Ma, and the ε _Hf （t） are in the range of 0.01 to 3.90, with t_DM2 ranging from 1496 Ma to 1447 Ma, and some negative values ranging from-2.22 to-0.03(t_DM2 =1453～1254 Ma) are also included, indicating that the diorites were derived from Mesoproterozoic（1453～1254 Ma） juvenile crustal materials, mixed with small amount of Mesoproterozoic（1496～1447 Ma） ancient crustal materials, triggered by underplating of mantle magma. Thus, the Southern Altyn orogenic belt was in break off and exhumation stage of the deep～subduction continental crust in <494 Ma, accompanied by underplating of large-scale mantle-derived magma, and the Manya diorites were magmatic response to the exhumation of the deep-subduction continental crust.更多还原