江西九瑞矿集区东雷湾矿区中酸性侵入岩及其铁镁质包体的成因:锆石U-Pb年代学、地球化学与Sr-Nd-Pb-Hf同位素制约

Petrogenesis of Intermediate-Felsic Intrusive Rocks and Mafic Microgranular Enclaves(MMEs)from Dongleiwan Deposit in Jiurui Ore District,Jiangxi Province:Evidence from Zircon U-Pb Geochronology,Geochemistry and Sr-Nd-Pb-Hf Isotopes

九瑞矿集区成矿与燕山期中酸性侵入岩体关系密切,但对该区东雷湾矿床的地质地球化学研究还相对较少,对东雷湾矿区中酸性侵入岩(花岗闪长斑岩、石英闪长玢岩)及其铁镁质包体进行了系统的锆石U-Pb年代学、矿物化学、岩石地球化学和SrNd-Pb-Hf同位素研究,探讨其岩石成因.锆石LA-ICP-MS U-Pb定年表明:东雷湾中酸性侵入岩的成岩年龄为144.3~148.7 Ma,铁镁质包体的年龄为146.4~147.1 Ma,与寄主侵入岩花岗闪长斑岩的年龄一致,东雷湾侵入岩属准铝质范围,岩石的Mg~#较高(42.5~68.0,平均56.0),并具有较高的相容元素含量,富集轻稀土,Eu异常不明显,富集大离子亲石元素,亏损高场强元素,暗色铁镁质包体呈细粒结构,常见针状磷灰石和钾长石斑晶.东雷湾样品的Sr-Nd同位素组成变化范围较小,初始~87Sr/~86Sr比值位于0.706 4~0.7079,ε_(Nd)(t)值变化于-5.80^-3.31,t_(2DM)(Nd)为1.2~1.4 Ga,锆石ε_(Hf)(t)值为-15.9^-3.6.样品的^(206)Pb/^(204)Pb(t)、^(207)Pb/^(204)Pb(t)、^(208)Pb/^(204)Pb(t)值分别变化于17.333 3~18.260 0、15.513 5~15.6210、37.404 1~38.395 4之间,详尽的元素和同位素地球化学特征表明,东雷湾铁镁质包体是由拆沉的加厚下地壳发生部分熔融,并在其上升过程中与地幔物质发生相互作用,进而与花岗质岩浆混合过冷结晶形成的.该区侵入岩的形成很可能是因为加厚下地壳拆沉入软流圈地幔后发生部分熔融,熔体与地幔橄榄岩相互作用后在上侵的过程分别形成了铁镁质岩石和花岗质岩石.

The intermediate-felsic intrusive rocks show a close relationship with mineralization in the Jiurui ore district,however,the studies of these rocks in the Dongleiwan deposit are relatively rare.In this study,we present a detailed study on zircon geochronology,mineral chemistry,whole rock geochemistry,and Sr-Nd-Pb-Hf isotopes of both the intermediate-felsic intrusive rocks and their mafic microgranular enclaves（MMEs）.LA-ICP-MS zircon U-Pb dating yields crystallization ages of 144.3-148.7 Ma for the felsic rocks and 146.4-147.1 Ma for the MMEs,indicating they are coeval.All the intrusive rocks from the Dongleiwan deposit are metaluminous with high Mg~#（42.5-68.0,with an average of 56.0） and high contents of compatible elements such as V,Cr,Co and Ni.The REE characteristics are LREE enriched and lack any significant Eu anomaly.The trace elements are characterized by enrichment of LILE and depletion of HFSE.The MMEs are characterized by microgranular texture,and contain acicular apatites and K-feldspar phenocrysts.The Dongleiwan rock samples have a narrow Sr-Nd isotopic ratio range with initial ^（87）Sr/^（86）Sr ratios from 0.706 4 to 0.707 9,ε_（Nd）（t） values from-5.80 to-3.31,and t_（2DM）（Nd）values from 1.2 to 1.4 Ga.The samples show radiogenic Pb isotopic ratios with values of ^（206）Pb/^（204）Pb（17.333 3-18.260 0）,^（207）pb/^（204）pb（15,513 5-15,621 0） and ^（208）Pb/^（204）Pb（37.404 1-38.395 4）.The zircon Hf isotope analysis shows emit） values of -15.9 to-3.6.These data suggest that the MMEs were probably produced by mixing of mafic and felsic magmas,and the mafic magma was derived from partial melting of delaminated lower crust and may have reacted with surrounded mantle peridotites during its ascent.While the felsic intrusive rocks of this area have been formed by the upwelling of magma which have experienced strong crust-mantle interaction after the delamination of lower crust into the asthenosphere.