摘要
长枪穹隆位于青藏高原北部松潘-甘孜地体之南端的木里地区,被东部的扬子板块和西部的羌塘地块所围绕。伏于三叠纪复理石地层之下的长枪穹隆由一套浅变质的沉积岩系组成,核部主要为里伍群二云石英片岩。为精确限定长枪穹隆核部里伍群的沉积时代和源区特征,本文运用LA-ICP-MS锆石U-Pb微区定年和原位Lu-Hf同位素分析技术,对里伍群变沉积岩系样品进行了锆石年代学、锆石微量元素和Lu-Hf同位素研究。结果显示,155颗碎屑年龄横跨早奥陶世-太古宙(476~3583Ma),碎屑锆石的Th/U比值均大于0. 1,大部分锆石具有明显的震荡环带,且锆石的稀土元素呈现明显的HREE富集、正Ce异常和负Eu异常的特点;上述特征指示该系列锆石为岩浆成因。碎屑锆石原位Hf同位素显示其εHf(t)值具有较宽泛的变化范围,介于-22^+14。锆石混合年龄谱能区分出四个明显的特征年龄峰值:~516Ma、~740Ma、~884Ma和~2. 5Ga。综合对比区域研究结果,我们认为476~560Ma的碎屑锆石可能来自于当时邻区冈瓦纳大陆北缘的泛非造山带,而715~1000Ma碎屑锆石可能来源于扬子板块西缘的新元古代的岩浆岩带和江南造山带。
The Changqiang dome,located in the Muli area at the south end of the triangled Sonpan-Ganzi terrane,Tibetan Plateau,sandwiched by the Qiangtang terrane to the west and the Yangtze block to the east.The Changqiang dome composes of low-grade metasedimentary core,the Liwu Group.In order to precisely constrain the protolith age of the Liwu Group and delineate its provenance characteristics,two low-grade metamorphic sedimentary samples collected from the Liwu Group were studied by zircon LA-ICP-MS UPb dating and in situ Lu-Hf isotope analyses.Zircon grains from two samples show high Th/U ratios,and distinct oscillatory zoning texture,as well as positive Ce anomalies,negative Eu anomalies,and HREE enrichments,indicating an igneous origin.Totally,155 zircon U-Pb ages were yielded for two samples,including four major age populations,e.g.476~675 Ma,715~812 Ma,820~1000 Ma and 2.4~2.6 Ga.Lu-Hf isotopes were analyzed on 137 corresponding zircon grains,yielding a wide range of Hf isotopic composition,withεHf(t)values of-22^+14.The detrital zircon age group of 476~560 Ma is probably related to the Pan-african events occurred along the northern margin of the Gondwana.Based on previous studies,we propose the 715~1000 Ma zircons were derived from the Neoproterozoic magmatisms within the Yangtze terrane and Jiangnan orogeny.In addition,Paleoproterozoic ages indicate the possibility of the growth of the continental crust event.
作者
刘晓佳
许志琴
郑艺龙
马泽良
LIU XiaoJia;XU ZhiQin;ZHENG YiLong;MA ZeLiang(MNR Key Laboratory of Deep-Earth Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences and Space Science,Peking University,Beijing 100087,China;School of Earth Sciences and Engineeri)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第6期1693-1716,共24页
Acta Petrologica Sinica
基金
中国地质调查局项目(1212010818094)资助
