摘要
内蒙古中部四子王旗北极各花岗岩基位于兴蒙造山带的二道井—查干乌拉—红格尔缝合带南缘,主要由正长花岗岩组成。为精确厘定该岩体的形成时代,对其进行了锆石LA-ICP-MS U-Pb定年,获得了（264.0±3.4）M a（MSWD=1.5）的^206Pb/^238U加权平均年龄,应代表其侵位年龄。岩石地球化学数据显示该岩体具相对富碱、富钾的特征,w（K2O＋Na2O）变化于8.0%～9.29%之间,w（K2O）/w（Na2O）比值为1.20～2.59,属于高钾钙碱性岩石系列;w（Rb）/w（Sr）值较低（2.4～4.2）,富集大离子亲石元素（LILE）,（La/Yb）N介于3.1～13.6之间,亏损高场强元素（HFSE）等特点显示其应为Ⅰ型花岗岩。岩石暗色矿物为黑云母,副矿物出现榍石而未见富铝矿物,富含暗色包体,与过铝质花岗岩相伴生,为较典型的KCG岩石组合,属于由俯冲作用向大陆碰撞演化过程中构造体制转换阶段的产物,而在构造环境判别图解中均落入同碰撞花岗岩区域。同位素定年和岩石地球化学特征表明北极各岩体形成于同碰撞环境,可能是大规模岩浆底侵作用导致地壳熔融的结果。
The Beijige pluton is located in the Siziwangqi area,Inner Mongolia,tectonically belongs to the Xing-Meng orogenic belt,lying on the southern margin of the Erdaojing-Chaganwula-Honggeer suture zone.It is predominantly composed of syenogranite.LA-ICP-MS U-Pb zircon dating and petrochemical analysis have been carried out in order to understand the formation age and natures of the pluton.As a result,zircons from syenogranite give a LA-ICP-MS mean U-Pb age of（264.0±3.4）Ma（MSWD =1.5）.Petrochemical data indicate that syenogranite belong to high-alkaline series（K2O＋Na2O=8.0%-9.29 %,K2O/Na2O=1.20-2.59）,low Rb/Sr ratios（2.4-4.2）,rich in LILE（（La/Yb）N =3.1-13.6）,deplete in HFSE show an affinity to I-type granite.The main dark mineral and accessory mineral of syenogranite are biotite and sphere,with abundant mafic microgranular enclaves,a common feature of KCG,which formed in the transition stage of continental subduction and collision.In the discrimination diagrams,all samples fall into the syn-collision area.Geochronological and petrochemical data imply that the Beijige pluton is related to a syn-collisional regime,maybe triggered by an extensive underplating.
出处
《现代地质》
CAS
CSCD
北大核心
2010年第1期112-119,150,共9页
Geoscience
基金
中国地质调查局华北地区基础地质及数据更新项目(1212010510506
1212010811001)
内蒙古自治区地勘基金项目(KD78)
国家自然科学基金项目(40772122)
