内蒙古敖汉旗克力代岩体锆石U-Pb年代及地球化学

通过LA-ICP-MS锆石U-Pb测年对内蒙古敖汉旗克力代岩体进行研究。结果表明,岩浆锆石的加权平均年龄为263±1 Ma,表明其结晶年龄为中二叠世。岩石地球化学分析表明,岩体具有高Si(SiO2=69.94%～72.56%),富ALK(Na2O+K2O=8.04%～9.23%),贫Fe(FeOT=1.50%～1.82%)、Mg(MgO=0.65%～0.86%)、Ti(TiO2=0.32%～0.35%)的特点;A/CNK值为0.87～0.93,为准铝质;A/NKC1.1,显示出I型花岗岩特征。固结指数(SI)为6.06～7.36,分异指数(DI)为88.82～91.82,说明岩体经历了较强的分异演化作用。稀土元素总量较低(ΣREE=91.76×10-6～143.16×10-6),轻稀土明显富集,重稀土相对亏损,LREE/HREE值平均为9.14,(La/Yb)N平均值为8.36,δEu平均值为0.58,为Eu亏损型。大离子亲石元素(LILE)Rb、K较富集,强烈亏损高场强元素(HFSE)Nb、Ti、Ta。因此,判定克力代岩体为高钾钙碱性I型花岗岩。结合测年结果和地球化学特征,判定该岩体为晚海西期华北板块和西伯利亚板块碰撞作用形成的同碰撞型花岗岩。

Zircon U-Pb dating and geochemistry of Kelidai pluton in Aohanqi,Inner Mongolia

LA-ICP-MS zircon U-Pb dating indicated that the ages of zircons from Kelidai pluton are （263 ±1） Ma,related to Middle Permian.The rocks are characterized by high Si （SiO2 =69.94％ ～ 72.56％）,high alkali （Na2O ＋ K2O =8.04％ ～ 9.23％）,low iron,magnesium and titanium （FeOT =1.50％ ～ 1.82％,MgO =0.65％ ～0.86％,TiO2=0.32％ ～0.35％）.A/CNK value was 0.87 ～0.93,A/NKC ＜ 1.1,belonging to quasi -aluminous Ⅰ-type granites.The rocks experienced a highly fractionated and evolving stage reflected from DI （88.82 ～ 91.82） and SI （6.06 ～ 7.36）.The rocks have low abundance of REE （∑REE =91.76 × 10-6 ～ 143.16 × 10-6）,with variable differentiation between LREE and HREE （LREE/HREE average as 9.14 and （La/ Yb） N average as 8.36）,revealling LREE enrichment and HREE depletionand with negative Eu anomalies （average δEu =0.58）,and enrichment in LILE （Rb,K） but depleted in HFSE （Nb,Ti,Ta）.In combination with the discrimination diagram,the Kelidai pluton belonged to high-potassium calc-alkaline Ⅰ-type granites.Considered the chronology results and geochemical characteristics,the rocks were syn-collisional granites formed in the collision between North China and Siberia plates in Late Hercynian.