Abstract:

Jiandeng granite in the Zanhuang Complex is located in the northwestern Lincheng County, Hebei Province. The pluton consists mainly of Kfeldspar granite and monzogranite with few quartz diorite enclaves. SHRIMP dating of zircon from the granite yielded an age of (2490±13)Ma. The rocks have high contents of SiO2 (743%—754%), K2O (576%—937%) and alkali with K2O+Na2O=616%—951%, and low contents of CaO (014%—081%), TiO2(004%—015%), MgO (002%—049%) and total FeO(026%—105%), belonging to shoshonitic series with slightly peraluminous feature. They have lower REE contents((1207—16038)×10-6), with relative enrichment of the LREE and variational Eu anomaly (Eu/Eu*=046—197). The rocks are rich in largeion lithophile elements (LILE) Rb, Ba and Th, and poor in Sr, Zr, Nb, Y and Yb, with high Rb/Sr and Rb/Ba ratios. They have positive εNd (t) value ranging from 285 to 366, with TDM2 ages between 255 and 264 Ga. SHRIMP dating of zircon from the quartz diorite enclave yielded an age of （2506±13）Ma. The quartz diorite is high in Al2O3(1716%), Na2O(447%), CaO(434%) and TFeO (526%), and shows higher total REE content of 21282×10-6, with a small Eu anomaly (Eu/Eu*=083). This rock is rich in Rb, Sr and Zr, and has an εNd (t) value of 305 and a TDM2 age of 263 Ga. The geochemical data show that the Jiandeng granite is similar to the Stype granite formed by anatexis of the juvenile crust in a tectonic transition setting from compression to extension, and the quartz diorite may represent a residue of the source rock. The formation of Jiandeng granite marks a tectonomagmatic event resulting in stabilization of the North China Craton at the end of the Neoarchean.

Key words:  Jiandeng granite, Zanhuang Complex, Neoarchean, tectonic setting, North China Craton