西藏南木林盆地林子宗群火山岩年代学和地球化学特征  

Geochronology and Geochemistry of the Linzizong Volcanic Succession,Namling Basin,Xizang

作　　者：黄永高 韩飞 康志强[1] 冯佐海[1] 李应栩 李光明 HuangYonggao;Han Fei;Kang Zhiqiang;Feng Zuohai;Li Yingxu;Li Guangming(Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources by the Province and Ministry,Guilin University of Technology,Guilin 541004,China;Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province&Sichuan Institute of Comprehensive Geological Survey,Chengdu 610081,China;Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China)

机构地区：[1]桂林理工大学有色金属矿产勘查与资源高效利用省部共建协同创新中心,广西桂林541004 [2]四川省综合地质调查研究所稀有稀土战略资源评价与利用四川省重点实验室,四川成都610081 [3]中国地质调查局成都地质调查中心(西南地质科技创新中心),四川成都610218

出　　处：《地球科学》2024年第3期822-836,共15页Earth Science

基　　金：国家自然科学基金项目(Nos.42173048,41863005);国家重点研发计划项目(No.2020YFA0714804);中国地质调查局项目(No.DD20160015-35);广西研究生教育创新计划项目(No.YCBZ2021065)。

摘　　要：为了更好地约束林子宗群火山岩的年龄格架、岩石成因及其演化历史,对拉萨地块中南部南木林盆地的林子宗群火山岩进行了详细的岩相学、锆石U-Pb年代学和全岩主微量元素地球化学研究.结果显示,南木林盆地林子宗群火山旋回时限依次为62.8~57.0 Ma、52.0~50.2 Ma、49.7 Ma.随着时间的演化,早期典中组以爆发相为主,年波组以喷发-沉积相为主,到晚期帕那组以喷溢相为主,且呈现出从中酸性向酸性演化,由钙碱性系列向高钾钙碱性系列再到钾玄岩系列逐渐过渡的趋势.其中,典中组英安质岩石为钙碱性系列,富集大离子亲石元素,亏损高场强元素,具有明显的Nb、Ta、Ti负异常,显示典型的弧火山岩特征;年波组和帕那组流纹质岩石为钙碱性-高钾钙碱性系列岩石,且有钾玄岩出现,富集大离子亲石元素,亏损高场强元素,除具有明显的Nb、Ta、Ti负异常外,还具有显著的Ba、Sr、P负异常,显示碰撞-碰撞后火山岩的特点.上述特征暗示典中组英安质岩石可能是新特提斯洋北向俯冲消减过程中岛弧区幔源岩浆底侵诱发上覆地壳部分熔融的产物,年波组和帕那组流纹质岩石则是印度-亚洲大陆碰撞初期阶段英安质岩石进一步分离结晶的产物.林子宗群火山岩是记录这种体制转换的重要载体.In order to better constrain the age framework,petrogenesis and evolution history of the Linzizong volcanic succession(LVS),this study focuses on the petrography,zircon U-Pb geochronology and whole-rock geochemical characteristics analyses of LVS in Namling basin in the central-southern Lhasa Terrane.Results show that the periods of eruptive cycles of LVS in Namling basin are 62.8 Ma to 57.0 Ma,52.0 Ma to 50.2 Ma and 49.7 Ma,respectively.With the evolution of time,the lithofacies have changed.Dianzhong Formation is dominated by the eruption facies,Nianbo Formation is dominated by the eruption-sedimentary facies,while Pana Formation is dominated by the eruption-overflow facies.Meanwhile,it shows the trend of evolution from andesitic to acidic,from calc-alkaline to high K calc-alkaline to shoshonite series.The dacite rocks of Dianzhong Formation are calc-alkaline series,which are enriched in LILE,depleted of HFSE,with obvious negative anomalies of Nb,Ta and Ti,showing typical arc volcanic characteristics.The rhyolite rocks of Nianbo Formation and Pana Formation are calc-alkaline to high K calcalkaline series with occurrence of shoshonite series,which are enriched in LILE,and depleted in HFSE.In addition to the obvious negative anomalies of Nb,Ta and Ti,there are also significant negative anomalies of Ba,Sr and P,showing the characteristics of collision to post-collision volcanic rocks.The above features suggest that the dacite rocks of Dianzhong Formation may be the product of partial melting of the overlying crust induced by the undercutting of mantle-derived magma in the arc region during the northward subduction of the Neo-Tethys Ocean.While,the rhyolite rocks of Nianbo Formation and Pana Formation are the products of further separation and crystallization of dacite rocks in the early stage of the Indian-Asian continental collision.In summary,LVS is an important archive for recording this system transformation from subduction to collision.

关 键 词：林子宗群火山岩 锆石U-PB年代学 地球化学 南木林 拉萨地块 岩石学 

分 类 号：P59[天文地球—地球化学]