龙木错—双湖古特提斯洋俯冲记录——羌塘中部日湾茶卡早石炭世岛弧火山岩  

Early Carboniferous subduction of Lungmu Co-Shuanghu Paleo-Tethys Ocean: Evidence from island arc volcanic rocks in Riwanchaka, Central Qiangtang

作　　者：刘函[1,2] 王保弟[1,2] 陈莉[1,2] 李小波[1,2] 王立全[1,2] 

机构地区：[1]中国地质调查局成都地质调查中心 [2]中国地质调查局青藏高原地质研究中心,四川成都610081

出　　处：《地质通报》2015年第2期274-282,共9页Geological Bulletin of China

基　　金：国家自然科学青年基金项目(批准号:41303028);四川省基金项目(编号:2014JQ0025);中国地质调查局项目(编号:12120114020601;1212011121262)

摘　　要：尽管龙木错—双湖结合带经历早古生代—三叠纪的长期演化过程，但已有资料显示羌塘中部沿该带的岩浆活动主要与碰撞作用有关，仍缺乏与俯冲相关火成岩的报道。报道龙木错—双湖结合带西段日湾茶卡东的一套那底岗日组火山岩中安山岩的年龄、岩石及地球化学特征，利用LA-ICP-MS方法测得安山岩锆石U-Pb年龄为330.6±2.8Ma，表明火山活动的时间为早石炭世。该套岩石因遭受硅质流体交代，SiO2含量变化较大（54.84%~72.84%），在Nb/Y-Zr/TiO2×0.00001图解中全部落入安山岩区，属于低—中钾钙碱性系列；微量元素蛛网图明显富集Rb、Th、U等大离子亲石元素，亏损Nb、Ta、Ti等高场强元素，具火山岛弧特征。日湾茶卡安山岩是在羌塘中部发现的早石炭世岛弧型火山岩，为龙木错—双湖古特提斯洋盆晚古生代俯冲作用提供直接的年代学和岩石学证据。Though Lungmu Co-Shuanghu suture experienced the evolution process from early Paleozoic to Triassic, the existing da-ta only show that there are numerous collision-related volcanic rocks along this suture in central Qiangtang, whereas information about subduction-related volcanic rocks is very insufficient. To tackle this problem, the authors report the zircon LA-ICPMS U-Pb dating results as well as petrological and whole-rcok geochemical data for andesites from the east side of Riwanchaka in the west part of the Lungmu Co-Shuanghu suture. One sample was dated at 330.6±2.8Ma, suggesting that the Riwanchaka andesites were formed in Early Carboniferous. Volcanic rocks were replaced by silicic fluid and display unstable SiO2 content （54.84%~72.84%） , but all the samples fall in the andesite field in the Nb/Y-Zr/TiO2×0.00001 diagram. Riwanchaka andesites belong to the low to medium-K calc-alkaline series in SiO2-K2O diagram. They are enriched in large-ion lithophile elements such as Rb, Th, U and K, and depleted in high field strength elements such as Nb, Ta and Ti, which are comparable with the characteristics of volcanic arc-related rocks. The Riwanchaka Early Carboniferous andesites in central Qiangtang were eventually emplaced at an island arc setting. The results ob-tained by the authors provide geochronologic and petrological evidence for early stage subduction process of Lungmu Co-Shuanghu paleo-Tethys Ocean.

关 键 词：岛弧火山岩 早石炭世 龙木错-双湖结合带 日湾茶卡 羌塘中部 LA-ICP-MS锆石U-PB年龄 

分 类 号：P542[天文地球—构造地质学] P534.45[天文地球—地质学]