浙江景宁岩体岩石地球化学特征与LA-ICP-MS锆石U-Pb年龄

Geochronological and geochemical characteristics of the Jingning Intrusion, Zhejiang Province

浙江景宁岩体位于中国东南沿海大陆边缘活动带，受丽水—余姚断裂控制，呈近南北向展布，主要岩石类型为二长花岗岩、花岗岩和闪长岩。对景宁岩体中的二长花岗岩和花岗岩进行了LA-ICP-MS锆石U-Pb测年及岩石地球化学分析。研究结果显示，二长花岗岩和花岗岩LA-ICP-MS锆石U-Pb年龄分别为121.3±0.3Ma和111.0±0.7Ma。岩体的岩石地球化学成分显示出富硅、富碱、低镁的特征，铝饱和指数介于1.01~1.09之间，分异指数为84.85~96.35，轻重稀土元素分馏显著，具有明显的负Eu异常，属于典型的弱过铝质高分异I型花岗岩。综合年代学和岩石地球化学特征，认为景宁岩体是早白垩世晚期岩石圈大规模伸展构造背景下地壳部分熔融的产物。

The Jingning Intrusion in Zhejiang Province is located on the active continental margin of southeast China and controlled by the Yuyao-Lishui faulted zone. The main rock types of the Jingning Intrusion distributed in S-N direction include monzonitic granite, granite, and diorite. In this paper, the authors conducted the LA-ICP-MS zircon U-Pb dating, obtained whole-rock geo-chemical data of the monzonitic granite and granite, and investigated lithologies of Jingning Intrusion, with the purpose of exploring the geochronology, petrogenesis, and tectonic implications. The results obtained show that the U-Pb zircon ages of the monzonitic granite and granite are 121.3 ± 0.3Ma and 111.0 ± 0.7Ma, respectively. The Jingning Intrusion samples are compositionally character-ized by high SiO2, Na2O＋K2O and low MgO. The A/CNK index ranges from 1.01 to 1.09, the fractionation between the light and heavy rare earth elements is obvious, the differentiation index varies from 84.85 to 96.35, and the Eu has an obvious negative anoma-ly. These geochemical features suggest that the Jingning Intrusion samples are slightly peraluminous and are of highly fractionated I-type granite. Based on the geochronological and geochemical data, the authors hold that the Jingning Intrusion was produced by the partial melting of the crust under the influence of wide lithospheric extension in the late Early Cretaceous.