乌拉特中旗二叠纪Ⅰ型花岗岩类地球化学特征及构造意义  

Geochemistry and Tectonic Implications of the Permian I-Type Granitoids from Urad Zhongqi,Inner Monglia

作　　者：罗红玲[1,2] 吴泰然[1] 赵磊[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871 [2]中国矿业大学地球科学与测绘工程学院,北京100083

出　　处：《北京大学学报（自然科学版）》2010年第5期805-820,共16页Acta Scientiarum Naturalium Universitatis Pekinensis

基　　金：国家自然科学基金(40902065,40672146);中央高等学校基本科研业务费资助

摘　　要：内蒙古乌拉特中旗的华北板块北缘中段发育了大量的花岗岩类,主要由石英闪长岩和花岗闪长岩组成。岩石具有钙碱性I型花岗岩类特征:暗色矿物以黑云母为主,A/CNK为0.77～1.04。多数岩体地球化学特征类似于埃达克岩:SiO2含量为55.70%～68.65%,Al2O3含量为15.32%～22.87%,Y和Yb含量分别为2.82～20.89μg/g和0.25～2.24μg/g;大离子亲石元素(LILE)和轻稀土元素(LREE)富集,如Ba含量为627～2124μg/g,Sr含量为327～968μg/g,Sr/Y为32.2～211,(La/Yb)N为5.83～81.1;Eu多为正异常(δEu=0.63～2.25)。它们形成于后碰撞抬升的背景,主要由增厚的下地壳部分熔融形成,可能与来自EM1型富集地幔的玄武质岩浆底侵作用有关。北七哥陶岩体、塔拉布基岩体、阿格如岩体和保尔汗图庙岩体中黑云母的40Ar/39Ar年龄分别为260±3,258±1,260±3和258±2Ma,表明它们的侵位时代均为晚二叠世。The Permian granitoids are widespread in Urad Zhongqi,Inner Mongolia,and are located on the middle segment of the northern margin of the North China Plate.The granitoids consist mainly of quartz diorite and granodiorite.They show a calc-alkaline I-type affinity and are characterized by dominant biotite in dark mineral,low A /CNK（0.771.04）.They have the geochemical characteristics similar to adakites by ≥56% SiO2（55.70%-68.65%）,≥15% Al2 O3（15.32%-22.87%）,low Y（2.82-20.89 μg/g） and Yb（0.25-2.24 μg/g）,enrichment of LILE（large-ion lithophile elements） and LREE（e.g.Ba = 627-2124 μg /g,Sr = 327-968 μg /g,Sr /Y = 32.2-211,（La /Yb） N = 5.83-81.1）,and mostly evidently positive Eu anomalies（δEu = 0.63-2.25）.They are interpreted as post-collisional calc-alkaline granitoids,formed mainly by partial melting of the overthickened continental lower crust due to underplating of EM1-type mantle-derived basaltic magma.Biotite 40Ar /39Ar ages of Beiqigetao Pluton,Talabuji Pluton,Ageru Pluton and Baoerhantumiao Pluton are respectively 260 ± 3,258 ± 1,260 ± 3 and 258 ± 2 Ma,which indicate they were emplaced during the Late Permian.

关 键 词：华北板块 内蒙古 后碰撞 埃达克岩 底侵作用 

分 类 号：P588.121[天文地球—岩石学]