Chronology of the Jinan Gabbro in Western Shandong: Evidence from LA-ICP-MS Zircon U-Pb Dating

The zircons from Jinan gabbro show euhedral-subhedral shapes and striped absorption on their cathodoluminescence (CL) images. The Th/U ratios of zircons range from 0.44 to 1.46, indicating that they were formed by normal crystallization of magma. U-Pb dating of 30 zircons from Queshan, Huashan, and Yaoshan gabbros and of 11 zircons from Kuangshan gabbro was made on LA-ICP-MS. The results show that the data of 30 zircons cluster around the concordia of 124～142 Ma, yielding a weighted mean (~(206)Pb)/~(238)U age of 130.8±1.5 Ma, and that the data of 11 zircons yield a weighted mean ()~(206)Pb/~(238)U age of 127±2 Ma, which implies that the crystallization of the Jinan gabbro occurred in Early Cretaceous. It is held that the coexsitence of Early Cretaceous Jinan gabbro and synchronous granitoid characterizes bimodal magmatism in eastern North China craton and also implies the geodynamic background of a strong extension environment.