西藏尕尔穷-嘎拉勒铜金矿集区火山岩年代学及地球化学

Zircon U-Pb Age and Geochemical Characteristics of Volcanic Rocks in Gaerqiong-Galale Cu-Au Ore District,Tibet

尕尔穷-嘎拉勒铜金矿集区是班-怒结合带南部的重要矿集区.矿集区内发育大面积火山岩，利用锆石 U-Pb 年代学方法，首次精确测定了研究区内不同地层中火山岩年龄，并结合其岩石地球化学特征探讨了其形成构造背景.研究表明，区内朗久组火山角砾岩成岩年龄为141.7.0±0.47 Ma（MSWD=0.43），多爱组流纹岩年龄为136.80±0.48 Ma（MSWD=0.79），形成时代为早白垩世初期，属于班公湖-怒江洋南向俯冲的岩浆作用响应；原定多爱组火山角砾岩（GE 火山角砾岩）年龄为85.20±0.53 Ma（MSWD=3.40），形成时代为晚白垩世，不属于早白垩世多爱组产物，属于洋盆消亡后羌塘陆块与冈底斯陆块汇聚阶段的火山作用产物，晚于尕尔穷铜金矿的成矿年龄（86.87±0.50 Ma）.岩石地球化学特征表明，区内火山岩均具有相对富集 Rb、Th、U 等大离子亲石元素（LILE），而亏损 Ta、Nb、Yb、Ti 等高场强元素（HFSE）的特征，显示出弧火山岩特性.结合区域已有火山岩研究资料表明，在班公湖-怒江洋南向俯冲过程中，从早白垩世初至中晚期均有比较连续的火山作用，持续时间约为30 Ma（140~110 Ma）；在班公湖-怒江洋盆消亡后的羌塘陆块与冈底斯陆块汇聚晚阶段，又伴随有晚白垩世火山作用的发生，该期火山作用与区内成矿岩体年龄相当，可能为同一岩浆系统的产物.

Located in the southern Bangong Co-Nujiang River suture zone,the Gaerqiong-Galale ore district is an important Cu-Au ore dense district with a large area of volcanics.This study firstly accurately determinates the ages of volcanics in different strata using U-Pb zircon geochronology method,then discusses the structural setting during formation combining the geochem-istry characteristics.The results show that volcanic breccia age of Langjiu Group is 141.70±0.47 Ma （MSWD=0.43）,rhyolite age of Duoai Group is 136.80±0.48 Ma （MSWD=0.79）,formation age is early Early Cretaceous,being attributed to volcanism of Bangong-Nujiang southward subduction;volcanic breccias age of Duoai Group （GE volcanic breccias）is 85.20 ± 0.53 Ma （MSWD=3.40）,formation age is Late Cretaceous and does not belong to the Early Cretaceous Duoai Group,which was the＆amp;nbsp;volcanism product of Qiangtang landmass and Gangdese landmass converging after ocean basin demise and was later than the mineralization age （86.87±0.50 Ma）of the Gaerqiong Cu-Au deposit.Geochemical characteristics indicate that volcanics are en-riched in LILE,e.g.Rb,Th,U and others,but depleted in Ta,Nb,Yb,Ti and other HFSE,and it exhibits arc volcanic rock characteristics.It is found that there was continuous volcanism from early to middle Early Cretaceous during Bangong-Nujiang southward subduction about 30 Ma （140-1 10 Ma）;it was also accompanied by volcanism of Late Cretaceous during Qiangtang landmass and Gangdese landmass converging after ocean basin demise;the age of this volcanism is similar to that of rock min-eralization in district,and they may belong to the same magma system.