冀东下营坊地区晚古生代富碱侵入岩锆石U-Pb年代学、岩石地球化学及其地质意义  

Zircon U-Pb Chronology and Geochemistry of Late Carboniferous Alkali-rich Intrusive Rocks in the Xiayingfang Area,Eastern Hebei Province,and Its Geological Significance

作　　者：邹滔[1] 王玉往[1] 王京彬[1] 张会琼[1] 赵路通[1] 石煜[1] 刘永振[2] 

机构地区：[1]北京矿产地质研究院,北京100012 [2]有色金属矿产地质调查中心,北京100012

出　　处：《地质学报》2017年第11期2423-2442,共20页Acta Geologica Sinica

基　　金：青年科学基金项目(编号41602098);国家自然科学基金项目(编号41030424);国家"973"计划项目(编号2014CB440803);中国地质调查局项目(编号12120113059800;DD20160072)联合资助的成果

摘　　要：富碱侵入岩具有重要的地质和矿产意义,倍受学者关注。冀东地区晚古生代钙碱性岩浆岩十分发育,而碱性岩少见,笔者首次在冀东下营坊地区识别出一批与金(铜铅锌银)多金属矿化有关的晚古生代中晚期的富碱侵入岩体。通过锆石LA-ICP-MS U-Pb测年,获得下营坊地区三处富碱侵入岩的侵位年龄分别为300.0±1.5Ma、299.3±2.1Ma、300.0±2.0Ma,侵位时间显示这些岩浆岩均为晚石炭世末—早二叠世的产物。岩石地球化学特征显示富碱(K2O+Na2O>8%),稀土元素含量较高,并强烈富集轻稀土,指示其具有富碱侵入岩的基本特征。下营坊富碱侵入岩富集大离子亲石元素,高La/Yb比,较高的La/Sm比值且变化范围大(>5),低Y,Eu异常不明显等特点,表明其源区可能与富集地幔有关,并可能受到俯冲板片脱水所释放流(熔)体的影响,在岩浆的侵位过程中可能受到地壳物质的混染。由成岩时代结合区域构造演化历史推断,该地区富碱侵入岩很可能与古生代期间古亚洲洋板块向华北板块俯冲有关,并形成于由俯冲板块后撤的伸展环境。Alkali-rich intrusions have been concerns of many scholars due to their geological significance and relation to mineralization.Late Carboniferous calc-alkaline magmatic rocks were widely developed in the northern part of Hebei province,but alkalic rocks are rare in this area and no related mineralization has been found.This study,however,for the first time recognized a bunch of the middle-late Late Paleozoic alkalia-rich intrusive rocks related to Au（Cu-Pb-Zn-Ag）polymetallic mineralization in the Xiayingfang area,eastern Hebei province.LA-ICP-MS zircon U-Pb dating yielded three emplacement ages of 300.0±1.5 Ma,299.3±2.1 Ma and 300.0±2.0 Ma respectively for three alkali-rich intrusions distributed in the Xiayingfang area and the results show that these magmas were the results of the late Carboniferous and early Permian.Petrological and geochemical data reflect that the rocks contain abundant alkaline minerals,such as nepheline,orthoclase,microcline,and so on,and are characterized by high Al2 O3（16.21% ~18.66%）,alkaline（（K2 O＋Na2 O）8%）,ΣREE（222.47×10-6~333.16×10-6）contents,indicating they belongs to alkali-rich intrusions.They exhibit highly fractionated rare earth element（REE）patterns,with no obvious Eu anomalies.Besides,they show characteristics of high Sr and Ba contents,high La/Y and La/Sm（5）ratios,low Y contents,enrichment in LILE and LREE and depletion of HFSE（e.g.,Nb,Ta）,P and Ti elements.These characters show that these alkali-rich intrusions were probably related to partial melting of the enriched lithosphere mantle,and might be affected by the fluids（melts）derived from the dehydration of subducted slab and contaminated by crustal material during magma emplacement process.Petrogenic age,combined with the evolution of regional geology,suggests that the alkali-rich intrusions in this area may have had genetic links with the southward subduction of the Paleo-Asian Ocean beneath the northern margin of the North China Craton,and formed in an extension setting due to s

关 键 词：富碱侵入岩 锆石U-PB定年 岩石成因 晚古生代 华北克拉通北缘 

分 类 号：P588.1[天文地球—岩石学] P597.3[天文地球—地质学]