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    北淮阳东段杨家湾岩体地球化学特征、锆石U-Pb定年及地质意义

    Geochemical characteristics and zircon U-Pb dating of the Yangjiawan plutonin the eastern part of North Huaiyang and their geological significances

    • 摘要: 北淮阳东段杨家湾岩体为石英闪长岩,SiO2、Al2O3和碱质含量中等,Mg#小,具准铝质高钾钙碱性系列岩石特征。该岩体的稀土元素含量较低,(La/Yb)N和LREE/ HREE比值均较高,具较弱的Ce负异常,轻稀土分馏明显,重稀土较平坦,属轻稀土富集型; 富集大离子亲石元素(LILE)Rb、Ba、K及高场强元素(HFSE)Zr、Hf、Y-Nb、Ta、Ti、P、U呈低谷负异常,亏损HFSE,富集LILE。通过LA-ICP-MS锆石U-Pb定年,首次获得杨家湾岩体年龄为139.6±2.2Ma,属燕山中期,是早白垩世早期岩浆活动的产物,代表杨家湾岩体的成岩年龄。

       

      Abstract: The Yangjiawan pluton in the eastern part of North Huaiyang, which consists mainly of quartz diorite, contains medium contents of SiO2, Al2O3 and ALK, low Mg#, suggesting that the Yangjiawan pluton is characteristic of metaluminous high-k calc alkaline series rock. The pluton has low REE content, relatively high(La/Yb)N and LREE/HREE ratios and weak Ce negative anomaly, with strong fractionation between LREE and HREE, enrichment in large ion lithophile elements(Rb, Ba, K)and high field strength elements(Zr, Hf, Y). Low negative anomalies of Nb, Ta, Ti, P and U indicate depletion in HFSE and enrichment in LILE. LA-ICP-MS zircon U-Pb dating for the Yangjiawan pluton firstly yielded an age of 139.6±2.2 Ma, which belongs to middle Yanshanian period and can represent the rock-forming age of the Yangjiawan pluton. Our study shows that the Yangjiawan pluton should be the product of early Cretaceous magmatic activity.

       

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