Zircon evidence for the Eoarchean (∼3.7 Ga) crustal remnant in the Sulu Orogen, eastern China

Zircon provides one of the best records of the formation and reworking of continental crust in the early Earth. However, Hadean to Eoarchean zircons are relatively scarce worldwide. Here we present the first report of relict Eoarchean magmatic zircons in granitic gneisses from the Sulu Orogen, eastern China. Based on internal structures, trace element contents, and U-Pb ages, we identified four groups of zircon domains with U-Pb ages of similar to 3.7 Ga (Group I), similar to 2.1 Ga (Group II), similar to 790 Ma (Group III), and similar to 720 Ma (Group IV). Group I domains exhibit variable Th/U ratios, steep HREE patterns, and negative Eu anomalies. They yield lower intercept U-Pb ages of 1.82-1.95 Ga and discordia upper intercept ages of 3.65-3.69 Ga that are similar to the oldest concordant spot age of 3680 +/- 29 Ma. This indicates their growth from an Eoarchean magma and reworking during the Paleoproterozoic. The oldest Eoarchean domains with U-Pb ages of 3606 +/- 28 to 3680 +/- 29 Ma have low P contents of 216-563 ppm and high (Y + REE)/P molar ratios of 1.13-3.34, consistent with an igneous source. They show epsilon(Hf)(t) values of -2.8 to -0.9 at 3.67 Ga and T-CHUR2 ages of 3.7-4.0 Ga, suggesting the growth of juvenile crust during the early Eoarchean. Group II to IV domains have consistent T-DM2 ages of 2.6-3.0 Ga, suggesting that they grew during multiple reworkings of the Archean crust. Group II domains have variable Th/U ratios and steep to flattened HREE patterns that suggest growth during Paleoproterozoic crustal anatexis. Groups III and IV zircon domains have Th/U ratios and trace element contents that indicate growth from magmas that formed during Neoproterozoic continental rifting. In view of the unique feature of Neoproterozoic rifting magmatism in South China, the relict Eoarchean magmatic zircons would have originated in the Yangtze Craton and then undergone multiple phases of reworking during the Paleoproterozoic and Neoproterozoic. The results indicate the presence of similar to 3.7 Ga relict magmatic zircons in the Sulu Orogen, and they represent the oldest remnants of crustal material in the Yangtze Craton.