U–Pb dating of baddeleyite and zircon from the Shizhaigou diorite in the southern margin of North China Craton: Constrains on the timing and tectonic setting of the Paleoproterozoic Xiongʹer group

The Xiongʹer volcanism marks an important thermal event in the southern margin of the North China Craton during the Paleoproterozoic. Precise U–Pb ages of zircon and baddeleyite from the Shizhaigou diorite which intruded the Majiahe formation of the upper part of the Xiongʹer Group were determined in this study by multi-collector SIMS. The mean 207Pb/206Pb ages are 1789 ± 3.5 Ma for baddeleyite and 1780 ± 11 Ma for zircon from Shizhaigou diorite, respectively. The major and trace elements and Sr–Nd isotopic compositions indicate an EM-I mantle type signature and crustal contamination features. Combining with previous chronological data, it is proposed that the age of the Xiongʹer volcanism is between 1770 Ma and 1800 Ma with a peak at 1780 Ma. Our result supports the view that the Xiongʹer volcanic rocks formed in an extensional rift environment.