摘要
大兴安岭北段嘎仙沟地区中侏罗世花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为172.7±1.1 Ma。全岩SiO_(2)含量为62.81%~68.78%,全碱(ALK)和Al_(2)O_(3)含量较高,FeO^(T)、MgO和TiO_(2)含量较低;里特曼指数σ=2.27~5.33,Na_(2)O/K_(2)O=1.19~3.57,Mg^(#)=38.0~49.0,属于中高钾钙碱性系列;铝饱和指数A/CNK=0.91~0.97,为准铝质岩石。稀土总量为(117.70~146.32)×10^(-6),(La/Yb)_(N)值为11.70~18.10,呈轻稀土富集、重稀土亏损的右倾型配分模式;具轻微的铕负异常(δEu=0.86~0.98),表明源区没有明显的斜长石残留或分离结晶;较高的Zr/Hf、Nb/Ta和Sr/Y值,低Y和Yb含量,富集大离子亲石元素Rb、Sr和Ba,亏损高场强元素Nb、Ta和Ti,指示源岩具有壳源特征。P_(2)O_(5)随SiO_(2)含量的增加而降低,T_(Zr)值为700.50~781.20℃,表明花岗闪长岩的成因类型为I型花岗岩,并具有C型埃达克岩特征。结合区域上的资料表明,中侏罗世花岗闪长岩形成于由碰撞向后碰撞过渡环境,蒙古-鄂霍茨克洋在中侏罗世的构造体系表现为由挤压向伸展、由地壳增厚向减薄的构造体制转换,与中侏罗世岩浆活动明显减弱相对应。
LA-ICP-MS zircon U-Pb age of the Middle Jurassic granodiorite is 172.7±1.1 Ma in Gaxiangou area,northern Great Xingan Range.The whole-rock SiO_(2)content ranges from 62.81%to 68.78%with higher whole-alkali(ALK)and Al_(2)O_(3)and lower FeO^(T),MgO and TiO_(2)tontents.Rittman index(σ)is from 2.27 to 5.33,Na_(2)O/K_(2)O=1.19-3.57,Mg^(#)values from 38.0 to 49.0,aluminum saturation index(A/CNK)=0.91-0.97,illustrating the granodiorite belongs to medium-high potassium calc-alkaline series and metaluminous rocks.TheΣREE=(117.70-146.32)×10^(-6),and(La/Yb)_(N)=11.70-18.10,show a right-leaning distribution pattern with enrichment in light rare earth elements and relative depletion in heavy rare earth elements.Slightly Eu negative anomaly(δEu=0.86-0.98)suggests that there is no significant plagioclase remains or fractional crystallization in the source region.The high Zr/Hf,Nb/Ta and Sr/Y ratios,low Y and Yb contents,enrichment of the large ionic lithophilic elements Rb,Sr and Ba,and depletion of the high-field-strength elements Nb,Ta and Ti indicate that the source rocks are crust-derived.P_(2)O_(5) decreases with increasing SiO_(2)content and T_(Zr) values range from 700.50 to 781.20℃.These indicate that the diagenetic type of this granodiorite is an I-type granite with C-type edakite characteristics.Combined with the regional data,the Middle Jurassic granodiorites were formed in the transition from collision to post-collision,and the Mongolian-Okhotsk Ocean tectonic system in the Middle Jurassic was characterized by a tectonic regime shift from extrusion to extension,and from crustal thickening to thinning,which is corresponding to the significant decrease of magmatic activity in the Middle Jurassic.
作者
孙靖尧
郑吉林
魏小勇
刘军帅
蔡艳龙
郭晓宇
王大可
杨志伟
SUN Jingyao;ZHENG Jilin;WEI Xiaoyong;LIU Junshuai;CAI Yanlong;GUO Xiaoyu;WANG Dake;YANG Zhiwei(Harbin Center for Integrated Natural Resources Survey,China Geological Survey,Harbin 150081,China)
出处
《桂林理工大学学报》
CAS
北大核心
2024年第1期1-10,共10页
Journal of Guilin University of Technology
基金
中国地质调查局项目(DD2016007807)。
