粤北大宝山北部九曲岭花岗岩锆石U-Pb年龄和Hf同位素特征

采用LA-MC-ICP-MS锆石U-Pb年龄和Hf同位素测定技术,对大宝山北部九曲岭花岗岩进行测定。结果显示来自九曲岭岩体的三个花岗岩样品的U-Pb谐和年龄分别为169.0±1.9 Ma,171.3±1.4 Ma,450.2±2.9 Ma,表明九曲岭花岗岩体为一复式岩体,主体为燕山期花岗岩,但局部有加里东期花岗岩。锆石Lu-Hf同位素组成测定显示:燕山期岩体的锆石具有低的负εHf(t)值(分别为–12.19~–8.51和–19.47~–8.63),二阶段模式年龄(tDM2)为1.45~1.63 Ga,与华南燕山期花岗岩特征一致,表明其主要是下地壳重熔的产物;加里东期岩体的锆石具有高的εHf(t)值(8.89~12.06),tDM2为0.62~0.78 Ga,表明其源区有新生地壳物质的贡献,暗示早古生代加里东期大宝山区域处于伸展环境。

Zircon U-Pb Ages and Hf Isotopic Compositions of Jiuquling Granite in Dabaoshan Region,Northern Guangdong Province

The intrusions in the Dabaoshan region,the center of Nanling Metallogenic Belt,consists mainly of the Dabaoshan dacite-porphyry,granitic diorite-porphyry and the Chuandu granitic diorite,the Xuwu intrusion in the Southeast,the Qiuba intrusion in the East and the Jiuquling granite in the North.LA-ICP-MS zircon U-Pb dating for three representative samples from the Jiuquling granite yielded the weighted mean ages of 169.0±1.9 Ma,171.3±1.4 Ma,and 450.2±2.9 Ma,respectively.This suggests that the Jiuquling granite is a multiphase pluton which is predominately emplaced in the Yanshanian and minor in the Early Paleozoic.LA-MC-ICP-MS Hf isotopic compositions of zircons from the two Yanshanian granite samples have low negative εHf(t) values (-12.19--8.51,and-19.47--8.63) and two stage model ages of 1.45-1.63 Ga,while the zircons from the Caledonian granite have high positive εHf(t) values (8.89-12.06,average 10.33) and two stage model ages of 0.62 Ga to 0.78 Ga.The low negative εHf(t) values of the Yanshanian granites are similar to those of the other granites in South China.The high positive εHf(t) values and young model ages of the Caledonian granite suggest that the granite was most likely derived from partial melting of juvenile crust,which may emplaced in an extensional tectonic setting in the Dabaoshan region during Early Paleozoic.