粤北长江地区花岗斑岩脉年代学、地球化学特征及其地质意义

Geochronological and Geochemical Characteristics and Geological Significances of Granite Porphyry Dykes From Changjiang Area in Northern Guangdong Province

粤北长江地区花岗斑岩脉呈近EW向分布于长江铀矿田中东部。通过对该花岗斑岩脉岩石学、锆石U-Pb年代学和地球化学特征开展研究,探讨了成岩年龄、岩石成因类型、物质来源、构造背景及与铀成矿的关系。长江地区花岗斑岩脉LA-ICP-MS锆石U-Pb年龄为151.8±0.7 Ma(MSWD=1.8),为燕山早期岩浆活动的产物。地球化学研究结果表明:其在主量元素方面具高w(SiO_(2))(平均为74.67%)、富w(Al_(2)O_(3))(平均为13.39%)、高w(K_(2)O)/w(Na_(2)O)值(平均为2.15)和高A/CNK值(平均为1.28)的特征,在微量元素方面具高w(Rb)/w(Sr)值(平均为9.93)和高w(Rb)/w(Nb)值(平均为20.03),Rb、Th和Hf富集,Ba、Sr、P和Ti亏损的特征,在稀土元素方面具Eu亏损明显(δEu平均为0.31)、轻稀土略富集右倾型配分曲线的特征,属于典型的壳源型花岗岩。综合研究认为:长江地区花岗斑岩脉主要形成于挤压造山向非造山转换的后造山拉张构造环境,由中-上地壳的泥质岩组分部分熔融形成。花岗斑岩脉的贯入,增加了含矿围岩结构的不均匀性,可能为铀成矿提供有利成矿空间。

The EW trending granite porphyry dyke mainly distributed in the central east of Changjiang uranium ore field of northern Guangdong province.With zircon U-Pb geochronological,petrological and geochemical research,the paper discussed the age,genetic type,magma sources,tectonic settings of the granite porphyry and their relations to uranium mineralization.LA-ICP-MS dating of Zircon in the granite porphyry got a concordant age of 151.8±0.7 Ma(MSWD=1.8),which means that the granite porphyry was the product of early Yanshanian magmatism.Geochemical characteristics indicated that granite porphyry was high in the contents of SiO_(2)(average 74.67%),Al_(2)O_(3)(average 13.39%),and high ratios of K_(2)O/Na_(2)O(average 2.15),A/CNK(average 1.28).The granite porphyry was found enriched in Rb,Th and Hf,but depleted in Ba,Sr,P and Ti,with high ratios of Rb/Sr(average 9.93)and Rb/Nb(average 20.03).The REE patterns are characterized by slight enrichment of light REE and right-inclining type,as well as obvious Eu depletion(average δEu of 0.31).These features indicate that the granite porphyry is a typical crustal derived type granite.Comprehensive results show the granite porphyry dyke from Changjiang area formed by partial melting of argillaceous rock in the middle-upper crust sources under the post-orogenic extensional environment during the transition from compressional orogeny to non-orogeny.The presence of the granite porphyry has increased the inhomogeneity of the pluton,which maybe provided a beneficial.mineralization space for the uranium mineralization.