巴尔哲碱性花岗岩锆石稀土微量元素、U-Pb年龄及其成岩成矿指示  

Zircon REE,trace element characteristics and U-Pb chronology in the Baerzhe alkaline granite: Implications to the petrological genesis and mineralization

作　　者：丘志力[1] 梁冬云[2] 王艳芬[1,2,3] 孙媛[1] 李榴芬[1] 

机构地区：[1]中山大学地球科学系,广州510275 [2]广州有色金属研究院,广州510651 [3]江苏省有色金属华东地质勘查局,南京210007

出　　处：《岩石学报》2014年第6期1757-1768,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40073021);广东省科技计划项目(2007A050100030)联合资助

摘　　要：巴尓哲碱性花岗岩体是分布在我国东北兴蒙造山带中段的罕见超大型稀土、铌、铍、锆矿床。本文通过对碱性花岗岩东岩体(矿体)成矿期有关深色和浅色锆石进行阴极发光、电子探针成分和LA-ICP-MS的分析测试,利用锆石地球化学特征探讨了岩体成岩成矿作用的关系。岩体的锆石可分为浅色和深色两类,两类锆石阴极发光具有不同特征,浅色锆石可见较宽不连续振荡环带,部分锆石存在核幔分区;和浅色锆石相比,深色锆石边部或内部凹坑、裂纹处溶蚀结构更发育。两类锆石均富含Nb、U、Y和REE元素,但深色锆石具有更高的Fe含量。Ⅰ型浅色锆石轻稀土富集,重稀土分异明显,具有高Hf、Nb、Ta,低Y特征,Ⅱ型浅色锆石轻稀土亏损,重稀土分异不明显,其稀土元素球粒陨石分布模式具有明显的"M型"四分组效应,显示出熔体-流体结晶锆石的特征。深色锆石原生结晶部分稀土配分模式与浅色锆石Ⅱ型相似,轻稀土亏损,重稀土分异不明显,受流体改造部分∑REE无明显变化,但LREE和Nb、Ta、U、Th含量及Th/U比值降低。浅色锆石和深色锆石的206Pb/238U年龄相近,获得锆石U-Pb的结晶年龄为122.7±1.8Ma(MSWD=5.1),与前人用Rb-Sr法及U-Pb法测定的年龄值一致;上述结果显示,巴尓哲岩体成矿期锆石具有幔源花岗岩来源特征,大型稀有稀土金属成矿物质的富集可能和源区经历的近期富集交代及岩体在富含F,Cl等挥发分流体-水环境下作用下经历分离结晶两个因素叠加有关。可以认为,巴尓哲富稀土花岗岩成岩与成矿作用是近于同时完成的。The Barerzhe alkaline granite bearing a supergiant REE-Nb-Be-Zr deposit locates in the middle of the Xing＇ an-Mongolia orogenic belt of Northeast China. Using cathodoluminescence, electron microprobe and LA-ICP-MS analysis, nineteen grains of light- colored zircon and the dark-colored zircon from the East body （ore body） of the Baerzhe alkaline granite have been tested in this paper, and the relationship between petrological genesis and mineralization were discussed. The two type＇ s zircons of the light-colored zircon and the dark-colored zircon crystals present different CL characteristics. For the former, wide discontinuous oscillatory zoning can be present, and the core-mantle zoning zircon also can be found in some grains; The latter has more developed dissolution structures at its rim or internal pits and cracks than the former, indicating that the involvement of fluids in the formation of the dark-colored zircon is more obvious. Both two types of zircon are rich in Nb, U, Y and REE, but the dark-colored zircon has higher Fe content. The type I of Light-colored zircon has the features of LREE enrichment, clear I-IREE differentiation, high I-If, Nb, Ta content and the low Y content ; The type II of Light-colored zircon is poor in LREE with unobvious HREE differentiation, and its REE chondrite distribution pattern have obvious ＂M-type＂ tetrad effect, indicating that zircon crystallized in melt-fluid system. The primary region of dark-colored zircon shows similar REE patterns to the type ]I of Light-colored zircon with LREE poor and unobvious HREE differentiation. The EREE of altered part has no significant changes, but its LREE and Nb, Ta, U, Th content and Th/U ratio decreased. Both types have nearly the same 206b/23SU age and the calculated age is 122. 7 ± 1.8Ma （ MSWD = 5.1 ）, similar to the previous data by Rb-Sr and U- Pb isotope analyses. The above-mentioned results show that Baerzhe syn-minerogenic zircon has the characteristics of mantel source. The enrichment and metasomatism of the s

关 键 词：巴尔哲碱性花岗岩 锆石 稀土及微量元素 U-PB年代学 成岩成矿指示 

分 类 号：P578.941[天文地球—矿物学] P597.3[天文地球—地质学]