赣东北地区瑶里花岗岩年代学、地球化学及其岩石成因

LA-ICP-MS zircon U-Pb age, geochemistry and petrogenesis of the Yaoli pluton in northeastern Jiangxi Province

瑶里花岗岩位于钦杭结合带赣东北地区,侵位于双桥山岩群和溪口岩群中,主要由石英、钾长石、斜长石、黑云母和少量白云母组成.LA-ICP-MS锆石U-Pb测年结果显示,该岩体形成年龄为132.0±1.9 Ma,获得的捕获锆石年龄表明该区在141.7±大于1.1,属于高钾钙碱性过铝质花岗岩.岩石富集大离子亲石元素,亏损Nb和Ti元素,具有明显的轻稀土元素富集特征,δEu值为0.30～0.86.通过与相邻岩体的对比,发现瑶里岩体与同时期的鹅湖和卧龙谷岩体的地球化学特征相似,均可能由地壳深处变质泥质岩发生部分熔融形成.但是,瑶里岩体与中侏罗世德兴铜厂花岗闪长斑岩岩石学特征和地球化学性质不同,表明中侏罗世至早白垩世,花岗岩的形成温度和压力降低,深度变浅,指示钦杭结合带赣东北地区中侏罗世至早白垩世为碰撞后的伸展环境.

Located in the northeast of Jiangxi Province along the Qinzhou-Hangzhou junction belt, the Yaoli granite intruded into the Shuangqiaoshan rock group and Xikou rock group. The granite is mainly composed of quartz, potash feldspar, plagioclase, biotite and minor muscovite. The LA-ICP-MS zircon U-Pb dating shows that the one-forming age of the Yaoli pluton is 132.0 ±1.9 Ma, with another age of 141.7 ± 2.6 Ma, suggest- ing that another magmatic activity occurred at 141.7 ±2.6 Ma. The Yaoli pluton is characterized by high K2O/ Na2O ratios and SiO2 content as well as low content of Al2O3, MgO, CaO and TiO2. The A/CNK ratios vary from 0.92 to 1.17, mostly higher than 1.1, implying that the Yaoli granite belongs to high-K calc-alkaline and peraluminous series. The Yaoli granite is also enriched in LILEs but depleted in HFSEs of Nb and Ti. The δEu values vary from 0.30 to 0.86. The granite is remarkably characterized by enrichment of LREE, which is simi- lar to things of Ehu pluton and Wolonggu pluton which were formed at the same time as the Yaoli granite. They were all generated by partial melting of metamorphosed argillaceous rock in the deep crust; nevertheless, the Yaoli granite is different from Tongchang granite, which formed in Middle Jurassic. These data show the de- crease of formation temperature and pressure of the granite from Middle Jurassic to Early Cretaceous, suggesting that the tectonic setting of the northeast of Jiangxi Province along the Qinzhou-Hangzhou junction belt was an extensional tectonic environment.