江西宜春雅山花岗岩体的成因与演化及其对成矿的制约  

Petrogenesis and Magmatic Evolution of the Yashan Granite Pluton in Yichun,Jiangxi Province,and Their Constraints on Mineralization

作　　者：杨泽黎 邱检生[1] 邢光福[2] 余明刚[2] 赵姣龙[1] 

机构地区：[1]南京大学地球科学与工程学院,南京210023 [2]中国地质调查局南京地质矿产研究所,南京210016

出　　处：《地质学报》2014年第5期850-868,共19页Acta Geologica Sinica

基　　金：中国地质调查局科研项目"钦杭成矿带东段地质矿产调查评价成果集成"(编号12120113065200);国家重点基础研究发展计划"973"项目"华夏地块花岗岩成因与成矿能力"(编号2012CB416702)联合资助成果

摘　　要：雅山岩体位于钦杭成矿带东段萍乡-绍兴结合带西端,是华南地区最重要的钽铌矿化稀有金属花岗岩之一。该岩体为一经多阶段演化形成的复式花岗岩体,自早至晚主要可区分为黑鳞云母-白云母花岗岩—锂云母花岗岩—黄玉锂云母花岗岩等不同阶段。锆石LA-ICP-MS U-Pb定年表明,岩体成岩年龄约为150Ma,属晚侏罗世岩浆活动的产物。化学组成上,雅山岩体富硅,贫铁、镁,分异演化程度高,分异指数(DI)值普遍大于93,并具亚碱、强过铝特征,过碱指数(AKI值)多低于0.80,铝饱和指数(A/CNK值)均大于1.20。岩体富Cs、Rb、Th、U、Nb、Ta,亏损Ba、Sr,稀土总量低,并具显著的Eu负异常(δEu=0.04~0.25)。自早至晚,岩体的Na2O/K2O比值渐次增大,F含量逐渐增多,Ta/Nb比值增大,稀土总量急剧降低,Eu负异常和稀土元素四组分效应增强,成岩温度逐渐降低。岩体具有低的εNd(t)值(=-9.5^-10.7)和CaO/Na2O比值(<0.3),指示其应主要起源于基底地壳中变质泥质岩的部分熔融,但其锆石εHf(t)值变化范围较大(=0.7^-14.8),表明其成岩过程中也有地幔组分参与。综合分析表明,雅山岩体成因类型应属高分异的S型花岗岩,其成矿受到岩浆高程度分异演化和晚期流体-熔体相互作用的共同影响,但前者是导致Ta、Nb富集的主控因素。The Yashan pluton,located in the west end of Pingxiang-Shaoxing suture zone referred as the eastern section of Qin-Hang metallogenic belt,is one of the most important rare-metal granitic plutons with Ta-Nb mineralization in South China.It is a composite granitic pluton formed via multi-stage magmatic evolution,which can be roughly distinguished from early to late into protolithionite-muscovite granite,lepidolite granite and topaz-lepidolite granite.Zircon LA-ICP-MS U-Pb dating yields an age of about 150Ma,indicating it was generated in Late Jurassic.Geochemically,the Yashan granites are enriched in silica,depleted in magnesium and iron,thus are highly-fractionated with differentiation index（DI）values mostly larger than 93.They are also characterized by subalkaline and strongly peraluminous signatures with agpaitic index（AKI）values less than 0.80and aluminum saturation index（A/CNK）values over 1.20.With increasing degrees of fractionation,Na2O/K2O and Ta/Nb ratios,fluorine contents,Eu depletion and REE tetrad effect of the pluton increase,while the total REE abundances and the crystallization temperatures decrease.The Yashan granites have lowεNd（t）values（=-9.5^-10.7）and CaO/Na2O ratios（0.3）,indicating that they likely originated from partial melting of metamorphic pelitic rocks in crustal basement.However,the granites show highly variable zircon Hf isotopic compositions withεHf（t）values range from-14.8to 0.7,implying that some mantle materials might have contributed to magma genesis.Basing on a synthesis of petrology,geochronology,elemental and isotopic geochemistry,we suggest that the Yashan pluton should be ascribed to highly-fractionated S-type granites,and the Ta-Nb mineralization of the pluton was controlled jointly both by highly fractionation of the magma and by fluidmelt interaction during the late stage,while the former is likely the main mechanism for the enrichment of tantalum and niobium.

关 键 词：稀有金属花岗岩 锆石U-PB年龄 元素地球化学 Nd-Hf同位素组成 岩浆演化 江西雅山岩体 

分 类 号：P588.121[天文地球—岩石学]