The Relationship and Timing of Granitoid Evolution with respect to Felsic Volcanism in the Wutai Complex, North China Craton

摘要

The Wutai Complex is an Archaean greenstone sequence within the North China Craton, Located approximately 400 km west-southwest of Beijing. Felsic volcanism in the Middle Wutai Hongmenyan Formation has been dated at 2524 ± 8 Ma by U-Pb zircon SHRIMP techniques. This confirms its Archaean age and thus settles a major debate which has taken place in China in recent years. The Lanzhishan Granite has an age of ~ 2524 Ma and is older than the felsic volcanics of the Middle Wutai. However, the overlying metasediments may not belong to the Lower Wutai Banyukou Formation but to the overlying Hutou Group, and so its relation to the Wutai Complex is still unknown. Granitoids within the Longquanguan Shear Zone are identical in age to the Lanzhishan Granite, indicating that the two are closely related: both contain evidence of ~ 2700 Ma granitoid precursors in the form of inherited zircon cores. The Ekou Granite has an age of 2555 ± 6 Ma and is considered to intrude the Lower Wutai Complex. Unfortunately, no reliable age data are currently available on the Lower Wutai formations. New data presented here indicate that felsic volcanism and granitoid emplacement took place over a relatively short time span between 2500 and 2560 Ma ago. The post-tectonic Dawaliang Granite has an age of 2176 ± 12 Ma and provides a constraint on the timing of major deformation in the area.