桂东北苗儿山张家花岗岩LA-ICP-MS锆石U-Pb年龄与地球化学特征
Geological Bulletin of China(2018)
Abstract
对张家岩体乍古田矿床及张家矿床的2件赋矿围岩样品,开展LA-ICP-MS锆石U-Pb同位素定年,获得乍古田矿床赋矿围岩形成年龄为218.0±1.4Ma,张家矿床赋矿围岩形成年龄为226.8±5.7Ma.另外,对张家岩体8件样品的主量、微量元素及Sr-Nd同位素分析测试显示,张家花岗岩富硅(SiO2=74.35%~76.29%)、高铝(Al2O3=12.54%~ 14.03%)、高碱(Na2O+K2O=6.95%~9.17%)、低镁(MgO=0.34%~0.45%)、低钙(CaO=0.68%~1.03%)、低钛(TiO2=0.106%~0.18%),属高钾钙碱性花岗岩;富集Rb,亏损Ba、Sr,Rb/Sr值高,属于低Ba-Sr花岗岩;轻稀土元素富集,负Eu异常;富U(平均21.5×10-6),Th/U值低(平均1.63),有利于铀矿化;(87Sr/86Sr)i高(约0.7247),低εNa(t)值(平均--13.95),二阶段Nd模式年龄为2.07~2.19Ga.张家花岗岩属于强过铝质S型花岗岩,可能是华夏板块古元古代基底变泥质岩经部分熔融形成的.
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Key words
U-bearing granite,LA-ICP-MS zircon U-Pb age,geochemistry,Zhangjia granitic pluton
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