Growth and reworking of the Yangtze continental nucleus: evidence from zircon U-Pb ages and Hf isotopes
扬子陆核的生长和再造：锆石U-Pb年龄和Hf同位素研究

Abstract A combined study of zircon U-Pb and Hf-O isotopes was conducted on migmatite, gneiss and metpelite from the Kongling complex and the Liantuo sandstone at the Yangtze Gorge in Yichang. The results show great significance for growth and reworking of Yangtze continental nucleus. A detrital zircon as old as 3.8Ga was revealed by SHRIMP U-Pb dating for the Liantuo sandstone, implying the existence of crustal materials with this age in the Yangtze Block. Its Hf isotopes suggest growth of juvenile crust at 4.0Ga. Zircon U-Pb ages for the migmatite and gneiss from the Kongling complex suggest two episodes of magmatism at 3.2 ~ 3.3Ga and 2.9~ 3.0Ga, probably marking formation of Yangtze continental nucleus at Mesoarchean. Their Hf isotopes suggest extraction of protolith from the depleted mantle no later than 3.5Ga ago. Metamorphic event at 1.9 ~ 2. 0Ga is well recorded by the migmatite and metapelite, which may be the major episode for reworking of the nucleus and thus cratonization in the Yangtze Block. Neoproterozoic magmatism widely occurring in the periphery of the Yangtze Block caused not only remehing of Archean and Paleoproterozic ancient crust but also prompt reworking of juvenile crust.