西藏那曲地区早白垩世A型花岗岩成因及其构造意义  

Genesis and tectonic significance of Early Cretaceous A-type granites in the Naqu area,Tibet

作　　者：李金勇 翟庆国[1] 唐跃[1] 胡培远[1] 王伟[1,2] 刘一鸣[1] 杨宁 Li Jinyong;Zhai Qingguo;Tang Yue;Hu Peiyuan;Wang Wei;Liu Yiming;Yang Ning(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;College of Resources and Environmental Engineering,Key Laboratory of Karst Georesources and Environment,Ministry of Education,Guizhou University,Guiyang,Guizhou 550025,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]贵州大学资源与环境工程学院,喀斯特地质资源与环境教育部重点实验室,贵州贵阳550025

出　　处：《地质学报》2023年第5期1418-1433,共16页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42072268,42002069);第二次青藏高原综合科学考察项目(编号2019QZKK0703);国家重点研发计划(编号2021YFC2901901);中国地质科学院地质研究所基本科研业务经费(编号J2202);中国地质调查局地调项目(编号20221630)联合资助的成果。

摘　　要：班公湖-怒江缝合带及其两侧广泛分布早白垩世岩浆岩,它们是班公湖-怒江洋俯冲消减及拉萨地块与南羌塘地块碰撞过程的直接响应,为研究特提斯大洋演化、青藏高原早期陆块聚合提供了重要素材。本文报道了班公湖-怒江缝合带中段那曲地区黑云母二长花岗岩的锆石U-Pb定年、岩石地球化学和锆石Hf同位素分析结果。锆石LA-ICP-MS U-Pb定年结果表明,黑云母二长花岗岩形成于114~113 Ma(早白垩世晚期)。地球化学分析表明,岩石显示出高钾钙碱性—钾玄岩系列特征,同时具有高的Ga/Al×10000比值(介于2.02~3.15之间,平均为2.61)和Zr+Nb+Ce+Y含量(平均为524.87×10^(-6))。此外,锆饱和温度和锆石Ti温度计共同指示岩浆形成于高温的环境(>800℃),这些特征与典型的A型花岗岩相一致。黑云母二长花岗岩中锆石具有低的ε_(Hf)(t)值(10.1~6.4),对应的Hf同位素二阶段模式年龄(t_(DM2))为1852~1547 Ma,指示其岩浆可能源自安多微陆块中下地壳古老结晶基底的部分熔融。结合区域研究成果,认为那曲地区黑云母二长花岗岩可能形成于后碰撞伸展的构造背景,早白垩世晚期伴随着拉萨和南羌塘地块的拼合,班公湖-怒江中特提斯洋中段地区已经闭合。Cretaceous magmas are widely distributed within and on both sides of the Bangonghu-Nujiang suture zone.These magmatic rocks record the process of the subduction of the Bangonghu-Nujiang ocean and the collision between the Lhasa and Qiangtang terranes.In this study,we report new zircon U-Pb dating,petrogeochemistry,and zircon Hf isotopic analysis of biotite monzogranites from the Naqu area in the middle of the Bangong-Nujiang suture zone.Zircon LA-ICP-MS dating results show that biotite monzogranites were formed at the Early Cretaceous(114~113 Ma).All samples have high-K calc-alkaline or potassic basaltic affinities.They also show high Ga/Al×10000 ratios(in the range of 2.02~3.15,with an average of 2.61)and Zr+Nb+Ce+Y contents(with an average of 524.87×10^(-6),much higher than 350×10^(-6))with high zirconium saturation temperature and Ti-in-zircon thermometer(>800℃).These features suggest that these samples belong to the A-type granites.The zircons in the granites have lowε_(Hf)(t)values(-10.1~-6.4)and ancient two-stage Hf model ages(t_(DM2))(1852~1547 Ma),indicating that the magma was originated from anatexis of the middle-lower crustal crystallization basement of the Amdo microcontinent.Combined with previous works,we suggest that the Naqu biotite monzogranites may have been formed in post-collisional setting.At the late Early Cretaceous,the Bangong-Nujiang Meso-Tethyan ocean have been closed by the Lhasa and Southern Qiangtang collision.

关 键 词：班公湖-怒江缝合带 早白垩世 A型花岗岩 安多微陆块 后碰撞环境 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.121[天文地球—地质学]