摘要
为了研究甘肃北山地区北山幅晚古生代岩浆岩的年代学特征和地球化学特征,利用Agilent7500 a ICP-MS的方法对研究区的花岗闪长岩进行全岩地球化学分析。结果表明:(1)岩石中Na_2O/K_2O<1,里特曼指数介于2.45~2.86,铝饱和指数A/CNK为1.48,总体显示过铝质、高钾钙碱质花岗岩类;(2)富集大离子亲石元素,如Rb,Ba和Sr,损失高场强元素如Ta,Ti和Hf;(3)δEu值为0.55~0.61,平均值为0.58,呈现负Eu异常,有一定的亏损,整体属于轻稀土富集类型。通过LA-ICP-MS方法对研究区的花岗闪长岩进行锆石~(206)Pb/~(238)U年龄测试,锆石~(206)Pb/~(238)U加权平均年龄为(400.1±2.3)Ma(MSWD=0.96),代表了花岗闪长岩的结晶年龄,即该期花岗闪长岩形成的地质时期为早泥盆世。
In order to study the chronological and geochemical characteristics of Late Paleozoic magmatic rocks in Beishan area,Gansu province,the whole-rock geochemical analysis of granodiorites in the study area was carried out by Agilent 7500 a ICP-MS method. The results show that:(1)Na_2O/K_2O < 1,ritman index is between 2.45 and 2.86,Al saturation index A/CNK is 1.48,showing peraluminous and high-potassium calc-alkaline granites;(2)Large ion lithophile elements such as Rb,Ba and Sr are enriched and high field strength elements such as Ta,Ti and Hf are depleted;(3)Delta Eu value is from 0.55 to 0.61,with an average of 0.58,showing negative Eu anomaly and a certain loss. The granodiorite belongs to the light rare earth enrichment type as a whole. Zircon ~(206)Pb/~(238)U ages of granodiorites in the study area were measured by LA-ICP-MS method.The weighted average age of zircon ~(206)Pb/~(238)U is(400.1±2.3) Ma(MSWD=0.96),which represents the crystallization age of granodiorite,i.e. the geological period of granodiorite formation is Early Devonian.
引文
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