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    广东新丰新坪花岗闪长岩(104 Ma)地球化学、锆石U-Pb年龄和Hf同位素研究

    Petrogeochemistry, zircon U-Pb age and Hf isotope of Xinping granodiorite(104Ma) in Xinfeng area, Guangdong Province

    • 摘要: 新坪铜钼矿化花岗闪长岩体位于佛冈复式岩体中北部,LA-ICP-MS锆石U-Pb年龄为(104.6±1.8)Ma(MSWD=1.2),侵位时间为早白垩世晚期。岩石呈中酸性(SiO2=63.43%~65.27%)、准铝质(ACNK=0.76~0.92)、中等碱含量(ALK=6.09%~7.63%)和富钾钙碱性特征,富集轻稀土,LREE/HREE=8.26~13.20,(La/Yb)N=8.17~16.64,轻微的铕亏损(δEu=0.73~0.87),富集Rb、U、Th和La,亏损Nb、Ta、Ti和P、Ba、Sr。锆石εHft)值为-3.0~0.2,Hf二阶段模式年龄tDM2=1.16~1.36Ga,镁指数(Mg#)=42.64~46.95,表明源岩主要为中元古代地壳物质,并有亏损地幔组分的参与。Nb/U和Nb/La比值分别为0.20~0.38和1.7~2.2,显示源区受古太平洋板块俯冲流体交代作用的影响。研究表明,新坪岩体成岩过程主要受部分熔融作用控制,形成于燕山晚期古太平洋板片俯冲消减作用下的伸展拉张环境,与玄武质岩浆底垫诱发中元古代结晶基底的部分熔融有关。早白垩世晚期为中国东南部晚中生代重要的Cu-Au-Mo成矿期,位于南岭中东段的新坪花岗闪长岩体与邻区闽西南紫金山铜多金属岩(矿)体形成时代一致、岩石地球化学特征较为相似,且野外能观察到明显的铜钼矿化,因此具有较好的铜钼找矿前景。

       

      Abstract: Located in the north-central part of the Fogang complex pluton, the Xinping Cu-Mo mineralization granodiorite pluton formed in late Early Cretaceous, and its LA-ICP-MS zircon U-Pb age is (104.6±1.8)Ma(MSWD=1.2). The granodiorite is characterized by medium acidity (SiO2=63.43%-65.27%), quasi-aluminium(ACNK=0.76-0.92), medium alkali(ALK=6.09%-7.63%) and high-K Calc-alkaline. It shows enrichment in light rare earth elements Rb, U, Th and La, and the ratio of LREE/HREE is 8.26-13.20 while (La/Yb)N is 8.17-16.64. Otherwise, it shows depletion in Nb, Ta, Ti, P, Ba and Sr, with minor loss of Eu (δEu=0.73-0.87). The εHf(t) range from -3.0 to +0.2, and the two-stage model age of Hf(tDM2) is 1.16-1.36Ga, and the index of Mg(Mg#) is 42.64-46.95. All of these indicate that the source rocks are mainly crustal materials formed in Mesoproterozoic, with the participation of deficient mantle components. The ratio of Nb/U and Nb/La is respectively 0.20-0.38 and 1.7-2.2, which indicates that the source area is affected by the fluid metasomatism in subduction of Paleo-Pacific Plate. This study shows that the Xinping granodiorite is dominated by partial melting in process of diageneesis. The Xinping pluton formed in the extensional setting under the subduction of the Paleo-Pacific plate in late Yanshanian period, which is related to the partial melting of the Mesoproterozoic crystalline basement induced by the basaltic magma. In late Early Cretaceous, it was an important Cu-Au-Mo mineralization period in late Mesozoic in southeastern China, while the Xinping granodiorite, located in the middle east of Nanling mountains, coincide with the diagenetic age of the Zijinshan copper polymetallic rocks or ores in the southwestern Fujian Province, with similar petrochemical characteristics. Also, the obvious copper-molybdenum mineralization can be observed in the field, so it will have a good prospecting prospect for copper-molybdenum deposits.

       

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