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《Acta Geologica Sinica》 2017-11
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Zircon U-Pb Chronology and Geochemistry of Late Carboniferous Alkali-rich Intrusive Rocks in the Xiayingfang Area,Eastern Hebei Province,and Its Geological Significance

ZOU Tao;WANG Yuwang;WANG Jingbin;ZHANG Huiqiong;ZHAO Lutong;SHI Yu;LIU Yongzhen;Beijing Institute of Geology for Mineral Resources;China Non-ferrous Metal Resources Geological Survey;  
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 slab roll-back in late Carboniferous.
【Fund】: 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
【CateGory Index】: P588.1;P597.3
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