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陈伟,陈斌,孙克克. 2018. 江西大湖塘矿集区茅公洞钨矿有关的高分异花岗岩成因研究. 岩石学报, 34(6): 1704-1724
江西大湖塘矿集区茅公洞钨矿有关的高分异花岗岩成因研究
作者单位E-mail
陈伟 造山带与地壳演化教育部重点实验室, 北京大学, 北京 100871  
陈斌 南方科技大学地球与空间科学系, 深圳 518055 binchen@pku.edu.cn 
孙克克 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083  
基金项目:本文受合肥工业大学高层次人才引进项目和国家自然科学基金项目(41272067)联合资助.
摘要:
      江西省大湖塘钨(铜、钼、锡)矿集区位于江南造山带中段九岭山脉,是世界级钨矿。茅公洞岩体位于大湖塘矿集区南部,由花岗斑岩和白云母花岗岩组成,后者有显著钨矿化。本文对此岩体进行详细的锆石U-Pb年代学、云母-长石矿物化学、全岩主微量元素及Nd同位素研究。LA-ICP-MS锆石U-Pb定年结果表明花岗斑岩的成岩年龄为133±2Ma,野外穿切关系表明含矿白云母花岗岩侵位稍晚。岩相学和岩石地球化学表明白云母花岗岩属于高分异花岗岩,与花岗斑岩相比,具有高硅,富碱,过铝质,较低的Ga/Al值,高Rb/Sr, Eu负异常明显,稀土四分组效应和异常的微量元素特征(non-CHARAC性质),以及较高的εNd值。基于以上特征,我们提出高分异的白云母花岗岩的形成模式:双桥山群变质沉积岩经部分熔融形成花岗斑岩之后留下麻粒岩相残余体,后者在幔源高温玄武岩底侵交代作用下再次发生深熔作用而形成白云母花岗岩;玄武质岩浆的底侵不仅为麻粒岩相残余的部分熔融带来高温,同时也带来挥发份F、B等,以及少量幔源物质的添加(导致白云母花岗岩具有较高εNd值)。F、B的加入改变了岩浆体系的物理化学性质,显著降低了岩浆的粘度、密度和固相线温度,这导致岩浆体系分离结晶过程的延长和高度的分离结晶;延长的岩浆演化过程活化了围岩中的水,导致强烈的熔-流体相互作用,形成白云母花岗岩的稀土四分组效应。同时,围岩流体的活化也萃取围岩中的成矿物质,加剧成矿物质的富集。而较还原的岩浆体系阻止了钨的分离结晶,为成矿提供了必要的条件。
英文摘要:
      The Dahutang tungsten (molybdenum, copper, tin) ore fields are located in the middle segment of the Jiangnan orogen, northern part of Jiuling batholith, which is the largest tungsten mine in the world. The Maogongdong granite pluton occurs in the southern part of the Dahutang tungsten ore field, composed of porphyritic granite and muscovite granite with tungsten mineralization. In this paper, we reported detailed studies on the LA-ICP-MS zircon U-Pb dating, major and trace elements, in-situ mica LA-ICPMS trace elements and the whole-rock Nd isotopic compositions of the two rock types. The results show that zircon U-Pb dating of the porphyritic granite yields an age of 132.5±1.8Ma, and the muscovite granite was emplaced later according to the field investigation. Petrography and geochemical data indicate that muscovite granite is a highly evolved in comparison with the porphyritic granite, and is characterized by high silica and alkalis, low Ga/Al ratios, high Rb/Sr, weak LREE/HREE fractionation, pronounced negative Eu anomalies, REE tetrad effect, and modified behavior of trace elements (non-CHARAC). The muscovite granite has εNd values (-5.4~+2.5) higher than the porphyritic granite (-7.5~-5.9). We suggest that the porphyritic granite was derived from melting of the Shuangqiaoshan Group meta-sediments, leaving behind in the lower crust a granulitic residue, and the highly differentiated muscovite granite formed by re-melting of the residue, triggered by the underplating of a new pulse of basaltic magma. Underplating of basaltic magma provides not only the high temperature required for melting the residue but also the volatile (fluorine, boron) in the source of the granite. Addition of fluorine and boron lowered the solidus temperature and the viscosity of granite magma, and thus prolonged the process the magma evolution. This appears to have resulted in extreme fractional crystallization and intense interaction between melt and circulating waters from country rocks, forming the unusual geochemical features of the granite and subsequently extract ore-forming metal from the country rocks, forming the polymetallic deposits.
关键词:高分异花岗岩  Nd同位素  地球化学  稀土四分组效应  江西大湖塘钨矿集区
投稿时间:2017-06-04  修订日期:2018-01-14
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