华北地块南缘花山、五丈山岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及成因

摘要

The Huashan granitoid pluton is located on the southern margin of the North China Block. Zircon LA-ICP-MS dating of the porphyritic monzogranites from the Huashan pluton yielded an age of 128 ± 1Ma. This pluton and its neighboring Wuzhang⁃shan pluton are of high K calc-alkaline series and belong to metaluminous to weak peraluminous rocks. They are enriched in large ion lithophile elements (LREE, Rb, Ba, K, Sr) and depleted in high-field strength elements (HREE, Zr, Hf, Ta, Nb, P, Ti), with in⁃significant Eu anomaly. These characteristics suggest that the granitoids have I-A type granite features. The zircon εHf(t) values and tDM2 values of the Huashan porphyritic monzogranites range from-25.8 to-19.6 and from 2.81Ga to 2.43Ga respectively, showing that their sources were mainly ancient crustal material with the addition of some juvenile components. The ages of gold, molybde⁃num deposits near the Huashan pluton are identical with those of the Huashan pluton, but are 20~25Ma younger than the age of Wu⁃zhangshan pluton. The formation of gold molybdenum deposits was close to the formation of Huashan granitoid pluton in time and space. This pluton might have provided a thermal source for the mineralization.%花山复式岩体位于华北地块南缘，采用LA-ICP-MS技术测得复式岩体中的中细粒似斑状黑云二长花岗岩的锆石U-Pb年龄为128±1Ma，此年龄被解释为成岩年龄。该岩体及邻近的五丈山岩体中花岗岩具有高硅、富碱特征，为准铝-弱过铝质高钾钙碱性系列；在稀土和微量元素上，富集LREE、Rb、Ba、K、Sr等大离子亲石元素，亏损HREE、Zr、Hf、Ta、Nb、P、Ti等高场强元素，总体上Eu异常不明显，显示出I-A过渡型花岗岩的特征。锆石Lu-Hf同位素组成表明，花山花岗岩的εHf(t)主要变化于-25.8~-19.6之间，tDM2为2.81~2.43Ga，显示源区物质以古老的壳源物质为主，有年轻组分的参与。与岩体外围多金属成矿年龄的对比分析发现，外围金、钼矿床与花山复式岩体的年龄一致，比五丈山岩体晚20~25Ma，表明金、钼矿的形成与花山岩体在时空上联系密切，该岩体可能为成矿提供了热源。