Zircon geochronology and trace element characteristics of the Woniushan granites in Taibus Ban-ner, Inner Mongolia, and their geological significance

The Woniushan granite in Taibus Banner of Inner Mongolia is located in the middle part of the Late Paleozoic-Early Me-sozoic magmatic belt on the northern margin of the North China plate. The weighted average age of ²⁰⁶Pb/²³⁸U by LA-ICP-MS of zircon from Woniushan pluton is 274.7±1.2Ma (MSWD=0.82), indicating that the pluton is not the Jurassic in age as previously con-sidered. TheΣREE values of zircon are 362.67×10^-6~1177.09×10^-6 with an average of 797.91×10^-6. The REE patterns of all zircon grains are highly consistent, characterized by enrichment of HREE, depletion of LREE, and obvious positive Ce and negative Eu anomalies. Through the analysis of REE characteristics, diagrams of tectonic setting, crystallization environment, and Ti thermometer in zircon, combined with regional geological setting and magmatic characteristics, the authors hold that the Woniushan granite, as the mixture of crust and mantle, was formed during the tectonic-magmatic activities of paleo-Asian Ocean subducting to the Northern North China plate, being the product of active continental margin, and the source and tectonic setting of the Woniushan granite were similar to those of the Permian magmatite in eastern and western parts of the Late Paleozoic-Early Mesozoic magmatic belt on the northern margin of the North China plate. The results confirm that, in late Hercynian period, the genetic relationship of the mag-matite of the middle part of the Late Paleozoic-Early Mesozoic magmatic belt on the northern margin of North China plate was the same as that of the eastern and western parts.