针对江西会昌富城岩体年代学的不同结论，对该岩体西部的细粒花岗岩进行了锆石U-Pb年代学研究，并分析了细粒花岗岩和粗粒花岗岩的岩石地球化学和锆石Hf同位素地球化学特征，探讨了该岩体的成因和构造背景。细粒花岗岩LA-ICP-MS锆石U-Pb定年结果表明，成岩年龄为219.1~221.5 Ma（平均220 Ma），为印支期岩浆活动产物；岩石地球化学组成上表现为高硅（SiO2=71.7%~78.2%）、富碱（K2O+Na2O=7.16%~8.13%，K2O/Na2O=2.00~3.53）、强过铝（A/CNK=1.11~1.26），贫Ca，Mg；稀土元素总量较低（ΣREE=72.9×10-6~203.0×10-6)，Eu负亏损强烈，富集Rb，Cs，K，Pb等大离子亲石元素和Th，U，Ta，Zr等高场强元素，贫Ba，Sr，P，Ti等元素；综合岩相学和岩石地球化学特征表明该岩体为S型花岗岩。粗粒花岗岩定年结果表明，成岩年龄为227 Ma，也为印支期岩浆活动的产物；岩石地球化学组成上同样表现为高硅（SiO2=75.1%~76.3%）、富碱（K2O+Na2O=7.39%~8.72%，K2O/Na2O=1.79~2.60）、弱过铝到强过铝（A/CNK=0.9~1.14），贫Ca， Mg。稀土元素总量较低（ΣREE=125.5×10-6~160.2×10-6），Eu负亏损强烈，富集Rb，Cs，K，Pb等大离子亲石元素和Th，U， Ta，Zr等高场强元素，贫Ba，Sr，P，Ti等元素；综合岩相学和岩石地球化学特征表明该岩体为S型花岗岩。同位素组成方面，富城细粒花岗岩体的εHf（t）值变化于-2.3~-10.8之间，平均为-7.5，两阶段模式年龄为1.4~1.96 Ga，粗粒花岗岩体的εHf（t）值变化于-5.0~-19.8之间，平均为-8.8，两阶段模式年龄为1.59~2.51 Ga，表明源岩为元古代壳源富泥质变质组分经过部分熔融，再经过分离结晶作用，在同碰撞构造背景下形成了富城细粒花岗岩和粗粒花岗岩。%In this paper, fine-grained granite in western part of the Fucheng pluton in Huichang county, Jiangxi Province, was selected for a detailed geochronological, whole-rock geochemical, and Hf isotopic geochemical study in order to elucidate its petrogenesis. LA-ICP-MS U-Pb zircon dating of the studied fine-grained granites yields ages of 219.1-221.5 Ma, with an mean value of 220 Ma, indicating that this pluton was generated during Indosinian stage. Chemically, this pluton is peraluminous (A/CNK=1.11-1.26) and shows high contents of silica (SiO2=71.7%-78.2%) and alkalis (K2O+Na2O=7.16%-8.13%, K2O/Na2O=2.00~3.53), low abundance of calcium, and magnesium. The rocks display low total REE contents (ΣREE=72.9× 10-6~203.0×10-6) with strongly negative Eu anomalies, and are enriched in LILEs such as Rb, Cs, K, Pb, and HFSEs such as Th, U, Ta, Zr, and depeted in Ba, Sr, P, Ti. Overall, the mineralogical and geochemical features suggest that the Fucheng fine-grained granite can be genetically grouped into S-type granite. LA-ICP-MS U-Pb zircon ages for the main coarse-grained granite of the Fucheng pluton are 227 Ma, indicating that this pluton was also generated during Indosinian stage. Chemically, the coarse-grained granites are weakly peraluminous to strong pereluminous (A/CNK=0.9~1.14) and show high contents of silica (SiO2=75.1%~76.3%) and alkalis (K2O+Na2O=7.392%~8.72%,K2O/Na2O=1.79~2.60), low abundance of calcium, magnesium. The rocks display low total REE contents (ΣREE=125.5×10-6~160.2×10-6) with strongly negative Eu anomalies, and enriched in LILEs such as Rb, Cs, K, Pb, and HFSEs such as Th, U, Ta, Zr and depeted in Ba, Sr, P, Ti. According to the petrographic and geochemical characteristics, the coarse-grained granite is also S-type. The zircon Hf isotopic compositions of the fine-grained granites show large variations, with εHf(t) values ranging from -2.3 to -10.8 (mean value of -7.5), and two stage model ages between 1.4 and 1.96Ga. The zircon Hf isotopes of the main coarse-grained granite also show large variations, with εHf(t) values varying between-5.0 and -19.8 (average of -8.8), and two stage model age between 1.59 and 2.51 Ga. In summary, the granite was formed from the magma generated by partial melting of metamorphic rocks of mainly pelite, and the magma then suffered fractional crystallization under a syn-collisional setting.
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