Yanshanian metamorphism of Jiaodong Peninsula: New evidence from zircon and titanite U-Pb dating of (garnet) amphibolites in the Rushan area, Sulu tectonic complex belt

The "Yanshanian Movement" generally refers to the large-scale tectonic movement of the eastern China in Jurassic-Cretaceous.Its related structural and magmatic events have been deeply studied by previous researchers.However, a few Yanshanian metamorphic ages were reported previously in the eastern China.In this study, LA-ICP-MS U-Pb dating of zircons and titanite from the(garnet) amphibolites in Rushan region indicates that: (1) the formation age of the Niantou garnet amphibolites was 1708 Ma, and the metamorphic age was 154 Ma; (2) the early metamorphic age of the Beizhuang amphibolite was 1840 Ma, and the late metamorphic age was 145 Ma.On the basis of the above new zircon and titanite age and the new magmatic-tectonic data of the Jiaodong Peninsula, it is suggested that the garnet amphibolites of the Rushan region have ever recorded the Yanshanian metamorphic event, and it is speculated that the metamorphic event occurred in a special period of regional tectonic transformation stage(from compression to extension), and the origin of the metamorphism may be related to the regional tectonic thickening during the Yanshanian orogeny in eastern China, but at present it cannot be ruled out that the metamorphism of this period is possibly related to the thermal drive of magmatism at the same time.