拉萨地块北部～90Ma斑岩型矿床年代学及成矿地质背景  

Geochronology and Ore-Forming Geological Background of ～90 Ma Porphyry Copper Deposit in the Lhasa Terrane,Tibet Plateau

作　　者：王保弟[1] 许继峰[2] 刘保民 陈建林[2] 王立全[1] 郭琳 王冬兵[1] 张万平[1] 

机构地区：[1]成都地质矿产研究所,成都610081 [2]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室,广州510640 [3]西藏地勘局区域地质调查大队,拉萨850000

出　　处：《地质学报》2013年第1期71-80,共10页Acta Geologica Sinica

基　　金：国家自然科学基金(编号41073033;40930316);国家重点基础研究发展规划项目(编号2009CB421003);中国地质调查局项目(编号1212011121259;1212011086039)联合资助的成果

摘　　要：近年来青藏高原多个大型—超大型斑岩Cu-Mo-Au矿床的发现已引起人们广泛的关注,现有研究显示这些含矿斑岩和斑岩型矿床的形成年龄主要集中在120～110Ma、～90Ma、54～45Ma和18～12Ma4个阶段,其中90Ma左右的斑岩型矿床的成矿地质背景仍存在很大争议。本文报道拉萨地块北部尼玛县拔拉扎斑岩型矿床含矿斑岩的LA-ICPMS锆石U-Pb定年以及辉钼矿Re-Os定年结果,并分析了该期的成矿地质背景。两件花岗闪长斑岩锆石206Pb/238U加权平均年龄分别为92.1±1.2Ma、93.8±1.2Ma,代表了岩浆的结晶时代;而辉钼矿Re-Os模式年龄为88.2～89.6Ma,代表了拔拉扎矿床的成矿年龄。依据区域地质资料,本文认为拉萨地块北部～90Ma岩浆活动和成矿作用既不可能是雅鲁藏布江结合带所代表的新特提斯洋平板俯冲或洋脊俯冲的产物,也不可能是班公湖-怒江洋盆南向俯冲消减直接的产物,而很可能是班公湖-怒江洋盆俯冲消减闭合之后碰撞过程的产物。因此本文认为拉萨地块中北部地区～90Ma的岩浆作用及其成矿作用是形成于碰撞的构造背景。A number of large-very large porphyry Cu-Mo-Au deposits have been discovered in the Tibetan plateau,which has caused widespread concern in recent years.Existing research results show that the formation ages of thse ore-bearing porphyries and porphyry deposits in the Tibetan Pleteau concentrate mainly on four stages：120~110 Ma,~90 Ma,54~45 Ma and 18~12 Ma,but the ore-forming geological background of porphyry deposits forming at the second stage（90Ma） is still controversial.This study reports the zircon LA-ICPMS U-Pb and molybdenites Re-Os ages of the porphyry Cu-Mo-Au deposits in the northern Lhasa terrane,along with analysis of ore-forming background.Two weighted average 206Pb/238U ages for two granodioritic porphyry samples are 92.1±1.2 Ma and 93.8±1.2 Ma,which probably record the age of magma crystallization,while the molybdenites Re-Os isotopic age of 88.2~89.6 Ma probably represents the age of mineralization of the Balazha porphyry deposits.Based on the regional geochemical data,this study suggests that the magmatism and mineralizaion at ~90 Ma in the northern Lhasa terrane was neither the prodcut of subduction of the Neo-Tethys ocean and oceanic ridge,which are represented by the Yarlung-zangbo suture,nor the direct result of subduction of the Bangongco-Nujiang Ocean,but likely the product of collision process after the subduction and closure of the Bangongco-Nujiang Ocean.

关 键 词：碰撞型矿床 90Ma成矿作用 斑岩矿床 拉萨地块 

分 类 号：P588.13[天文地球—岩石学]