粤北下庄矿田帽峰岩体的岩石地球化学特征

Lithogeochemical Character of Maofeng Pluton in Xiazhuang Ore Field of North Guangdong

从主元素、微量元素、稀土元素的四分组效应及结合已有的锶同位素比值等方面研究了帽峰岩体的岩石地球化学特征,研究结果表明:(1)帽峰岩体具有富铝、硅和碱,A/CNK平均值为1.2,A′为正值等主量元素特征,富含石榴石、白云母等过铝矿物,强烈的铕亏损(δEu=0.01～0.25)及基本上无轻重稀土分异的稀土元素配分特征等,表明帽峰岩体是强过铝花岗岩,其物质来源主要是壳源;与同区域其它岩体相比较低的锶同位素比值((87Sr/86Sr)i=0.7185)是伴随着区域伸展构造所带来的幔源流体成分叠加所导致的。(2)帽峰岩体具有较为典型的稀土元素四分组效应,较低的Y/Ho比值(<28)及Zr/Hf比值(7.52～24.75),岩体的锆石年龄老(207.6±3.2Ma),而白云母KAr年龄(141.2Ma)与区域地壳伸展年龄(140Ma)及铀矿体的形成时代(138Ma)相接近,且岩体中常见碳酸盐团块,因此帽峰岩体较为典型的稀土元素的四分组效应是伴随着区域伸展和铀成矿过程与重碳酸络合物有关的流体之间的相互作用形成的。

Major elements, minor and trace element, tetrad effects combined with the isotopic data are employed to study the lithogeochemical characteristic of Maofeng granite. It may concludes: (1) Aluminium, silica and alkaline enriched in Maofeng granite, average A/CNK equal to 1.2, A′>0, peraluminous minerals such as garnet and muscovite detect in it, Eu strongly deplete(δEu=0.01～0.25) and nearly no or slightly REE differentia pattern might infer that Maofeng pluto is strong peraluminous granite and crust-derived,(^(87)Sr/^(86)Sr)_i =0.719 slight lower than the granite of vicinage might interpret by the mantle fluid superprint accompanied by the regional crust extend. (2) Typical M type tetrad effect, Y/Ho<28, Zr/Hf value varies in 7.52～24.75, and the big time different between the petrogenesis age of U-Pb zircon (207.6±3.2 Ma) and the metallogenic ages , but the later is simultaneity with crust extend alteration age of granite, which is 138 Ma, 140 Ma and 141.2 Ma separately, M type tetrad effect inferres the interaction between granite and HCO^-_3 complex.