EPMA Th-U-Pb Monazite Dating of Zhongtiao and Lüliang Precambrian Metamorphic Complexes

Zhongtiao and Lüliang Precambrian metamorphic complexes are essential parts of the southern segment of Trans-North China Orogen (TNCO), the North China Craton (NCC). Their metamorphism and related granitic magmatism enable to better understand the nature and the evolution of the TNCO, the NCC, with great scientific significance. EPMA Th-U-Pb monazite dating of two monzogranitic rock samples from Yongji and Henglingguan intrusions in the Zhongtiao Precambrian complex yields two peak ages of 1884.7 Ma-1849.9 Ma, and 1743.5–1738.8 Ma, respectively. The former is interpreted as the main metamorphic ages and the latter as the ages of fluid activation. Five samples from the Lüliang Precambrian complex were dated by EPMA Th-U-Pb monazite dating method. The garnet two-mica schist and the granitoid gneiss recorded three age peaks or range of >1902 Ma, 1883.3 Ma-1865.6 Ma, and 1731.3 Ma, corresponding to early magmatic and anatectic events, peak metamorphism, and late fluid activation, respectively. The two samples of garnet granite yield the ages of 1882.8 Ma-1850.9 Ma, corresponding to the anatectic granitic magmatism, which simultaneously occurred with the peak metamorphism. The unmetamorphosed granite vein yields the age of 1742.6 Ma, which is interpreted as the forming age of the granite vein and together with the age of 1731.3 Ma shown by the garnet two-mica schist may imply important fluid-magmatic activation events. The above dating results reveal that the peak metamorphism occurred during 1885 Ma-1849 Ma in the Zhongtiao and the Lüliang Precambrian metamorphic complexes, accompanied by the S-type granitic magmatism. The age range of the peak metamorphism and cogenetic S-type granitic magmatism in the Zhongtiao and Lüliang Precambrian complexes are consistent with the metamorphic and the deformation events in the Hengshan–Wutai–Fuping complexes, further proving that the amalgamation between the Western and the Eastern continental blocks in the NCC occurred during late Paleoproterozoic.