鲁西沂南铜井闪长质岩体锆石U-Pb年龄、元素及同位素地球化学特征

Zircon U-Pb ages and geochemistry of elements and isotopes of the diorite from Tongjing,Yinan,western Shandong Province

对鲁西沂南铜井岩体的中生代闪长玢岩进行了主量元素、微量及稀土元素、Sr-Nd-Pb同位素以及锆石U-Pb年龄、Hf同位素研究,结果表明,铜井闪长玢岩SiO2含量为54.68%～63.01%,富Na,Na2O/K2O为0.93～4.46,Mg#较高,为55～66,为中钾-高钾钙碱性系列,TiO2含量较低,0.2%～0.71%。样品具有显著的LREE富集[(La/Yb)n=10～15]以及高场强元素Nb、Ta和Ti的负异常,Eu基本无异常,Sr、Ba含量高(分别为241×10-6～711×10-6和554×10-6～822×10-6)的特征。ISr和εNd(t)值分别为0.706473～0.708867和-15.13～-9.18,与鲁西方城玄武岩和前人所研究的沂南辉长岩结果有所差异,显示其源区具有多端员混合特征,除了富集岩石圈地幔外,亏损地幔和地壳物质的贡献也很重要,Pb同位素也显示其源区有扬子克拉通物质的贡献,佐证了华北克拉通中生代富集岩石圈地幔的形成与扬子克拉通的俯冲有关。闪长岩中锆石具有典型的岩浆锆石特征,U-Pb年龄为128～129Ma,锆石εHf(t)值主要在-13～-8(平均值为-10.3)范围内,暗示了岩浆来源于富集岩石圈地幔,但受到亏损地幔物质的混染。沂南铜井闪长玢岩岩浆源区的多元性以及亏损地幔物质参与程度的逐渐增强,说明该地区中生代岩石圈减薄已达到最大,岩浆源区的差异可能也是该地区与胶东地区成矿性差异的主要原因之一。

Zircon U-Pb age,major and trace elements,REE,Sr-Nd-Pb,and zircon Hf isotope compositions were discussed for the Mesozoic Tongjing diorite porphyry in Yinan area of western Shandong Province.The results show that the Tongjing diorite porphyry is characterized by high SiO2（54.68%63.01%）and Mg（Mg#=5566）and relatively low TiO2（0.2%0.71%）content,similar to high-Mg diorite distributed extensively in western Shandong Province.There is a strong enrichment of LREE [（La/Yb）n=1015] and HFSE（Nb,Ta,Ti）anomaly,with no Eu anomaly,and Sr（241×10-6711×10-6）and Ba（554×10-6822×10-6）content is high.The Sr-Nd isotope characteristics of rock resembling suggest that they have the same magma source.The ISr and εNd（t）values are respectively 0.706 4730.708 867 and-15.13-9.18,which are not consistent with the data of contemporaneous Yinan gabbro which had been studied by the former researchers.Available isotopic data of the Tongjing diorite porphyry reveal that the major magma sources were enriched lithospheric mantle.Besides,magma from the lower crust and depleted mantle is also important,and Pb isotope shows that the lower crust was formed by North China Craton and Yangtze Craton.Zircon U-Pb age is 128129 Ma,which is an embodiment of Mesozoic large-scale magmatic activities in east NCC,and the age is similar to that of Mesozoic intursive rock of Jiaodong area,indicating that the two areas might have the same background for magmatic activities.The εHf（t）values range mainly from-13 to-8 with a mean value of-10.3,also implying that the magma came from enriched lithospheric mantle mixed with depleted mantle.The variety of multiple magma sources and the progressive participation of depleted mantle components in response to the lithospheric thinning reached the max in late Mesozoic in the eastern part of North China Craton.The different sources of magma might have been the main factor responsible for mineralization between Jiaodong peninsula and western Shandong Province.