Geology and zircon dating of trondhjemitic gneiss and amphibolite in the Tangezhuang area, eastern Shandong.

～2.5Ga and ～1.9Ga metamorphic events are widely recorded all over the North China Craton, being important for understanding the formation and evolution of the craton. Eastern Shandong is located in the eastern North China Craton and contains metamorphic rocks with ca. 2.5Ga and ca. 1.9Ga metamorphic zircon ages. For further constraining the Early Precambrian tectono-thermal events in the area, we carried out detailed field observation and SHRIMP U-Pb zircon dating in a road cutting section near Tangezhuang, Laixi County, eastern Shandong. The outcrop consists of interlayered and folded trondhjemitic gneisses and amphibolites. The foliation of the rocks is completely parallel to each other and shows thin interlayer in strong deformation domain, suggesting that thin interlayers of different components cannot be considered as a fact that the protoliths are sedimentary in origin. SHRIMP U-Pb zircon dating yielded an age of 2496±10Ma (MSWD=0.45) for magmatic zircons from a trondhjemitic gneiss sample (S1105), with metamorphic rims having ages of ca. 2.5Ga and ca. 1.9Ga. Two amphibolite samples (S1238 and S0812) contain metamorphic zircons with ages of 1842±3Ma (MSWD=1.6) and 1833±13Ma (MSWD=1.0), respectively, but no magmatic zircons have been identified. Combining with previous researches, we suggest that the Late Neoarchean metamorphism widespread over the whole Jiaodong terrane, leading to anatexis and recycling of older crust material, and the Late Paleoproterozoic metamorphism shows a zonal feature as a result of orogenesis.