大兴安岭北部漠河地区早奥陶世A型花岗岩锆石U-Pb年代学、地球化学及Hf同位素研究  

Geochronology,geochemistry and Hf isotopes of the Early Ordovician A-type granite in the Mohe Region,northeastern Da Hinggan Mountains

作　　者：吴琼 丰成友[2] 瞿泓滢[1] 钟世华[1] 刘建楠[1] 张明玉[1] WU Qiong;FENG Chengyou;QU Hongying;ZHONG Shihuan;LIU Jiannan;ZHANG Mingyu(MLR Key Laboratory of Metailogeny and Mineral Assessment,Insititute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing,100037;Xi'an Center of Geological Survey j China Geological Survey,Xi'an,710054)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质调查局西安地质调查中心,西安710054

出　　处：《地质学报》2019年第2期368-380,共13页Acta Geologica Sinica

基　　金：国家重点研发计划(课题编号2016YFC0600205)"南岭成矿带典型成矿系统的深部过程和成矿模式";项目资助的成果

摘　　要：大兴安岭北部漠河地区黑云母二长花岗岩中锆石自形程度较好,主要为长柱状,具有较为清晰的韵律环带结构,表明锆石岩浆成因。锆石LA-ICP-MS U-Pb年代学研究显示岩石形成时代为早奥陶世(481±5Ma)。岩石地球化学研究显示,岩石属于钙碱性、弱过铝质系列花岗岩,高硅(SiO_2=71.42%～72.57%)、富碱(ALK=8.11%～8.76%)、贫镁(MgO=0.52%～0.54%)。10000Ga/Al值为2.73～2.85,Zr+Nb+Ce+Y含量374×10^(-6)～495×10^(-6),岩浆形成温度801～897℃,判断岩石为A型花岗岩。岩石有中等的负Eu异常(δEu=0.24～0.35),Rb/Sr值为1.18～1.38、Ba/La值为8.7～12.4、Mg~#值为23.3～30.3,及低Ni(1.51×10^(-6)～5.59×10^(-6))、Cr(6.60×10^(-6)～13.4×10^(-6))、V(20.0×10^(-6)～21.6×10^(-6))含量。岩石的ε_(Hf)(t)值为-2.22～5.57,二阶段模式年龄(t_(DM2))变化于1021～1453Ma之间,主要源于中新元古代增生地壳。结合区域构造演化及构造判别,认为岩石形成于额尔古纳地块与西伯利亚板块拼合造山后的伸展背景。Zircons from the granites in the Mohe region,northeastern Da Hinggan Mountains are euhedral in shape and display oscillatory zoning in CL image,implying their magmatic origin.LA-ICP-MS zircon U-Pb dating results indicate that these rocks were formed in the Early Ordovician(481±5Ma).Lithogeochemcial analysis shows that these rocks belong to the calc-alkaline,slightly peraluminous series granitoids,characterized by high Si02 contents(71.42%?72.57%),high alkali contents(8.11%-8.76%)but low MgO contents(0.52%-0.54%).The 100000Ga/Al ratios in these rocks vary from 2.73 to 2.85,Zr+Nb+Ce+Y contents 374.495×10.6,and the temperature of magma formed is 801-897℃,all these characteristics indicate the rocks belong to aluminous A-type granite.The granites are characterized by the low Sr(150×10^-6-205×10^-6)and low Yb(0.89×10^-6-1.07×10^-6)and 3Eu values(0?24?0?35).The rocks have Rb/Sr ratios(1.18-1.38),Ba/La rations(8.7-12.4),Mg#rations(23.3-30.3)and low contents Ni(1.51×10^-6-5.59×10^-6),Cr(6.6×10^-6-13.4×10^-6),V(20.0×10^-6-21.6×10^-6).The in situ zircon value varies from-2.22 to 5.57 and the two-stage model age(TDM2)varies from 1021 to 1453 Ma,suggesting that the primary magma was derived from partial melting of juvenile crustal materials.It can be concluded from regional tectonic evolution and discrimination diagram of tectonic setting that the granites formed in the post-orogenic extension setting due to agglomeration of Siberia block and Erguna Massif.

关 键 词：锆石U-Pb年龄 岩石地球化学 兴华渡口群 A型花岗岩 大兴安岭 漠河地区 

分 类 号：P534.42[天文地球—古生物学与地层学] P588.121[天文地球—地质学] P597.3