ZIRCON LA-ICP-MS U-Pb GEOCHRONOLOGY OF THE DIABASE DIKES IN AOHAN QI, INNER MONGOLIA: Indication for the Activity of Chifeng-Kaiyuan Deep Fault

Diabase dikes, which are derived from the mantle, can be used as an indicator of deep fault activities. During the 1:50000 geology survey in Aohan Qi area, Inner Mogolia, the authors identified near east-west extended diabase dikes in the Paleoproterozoic Baoyintu group in Xingjiawopu. The zircon U-Pb LA-ICP-MS dating of the diabase dikes show five age groups:603-521 Ma, 450 Ma, 259-262 Ma, 237 Ma and 167.4±3.0 Ma. The youngest age (167.4±3.0 Ma) represents the cooling age of the dikes, indicating the activation of Chifeng-Kaiyuan deep fracture in Middle Jurassic. The other ages are also corresponding to the magmatic activities of different periods in Chifeng area. The formation and evolution of the Chifeng-Kaiyuan deep fault are summarized by combination with previous literatures.