Zircon U–Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China

Abstract

Four populations of zircons are recognized by U–Pb analyses of the Neoproterozoic Liantuo Formation in the northern part of the Yangtze Block, South China. They are grains of detrital zircon older than 3.0 Ga, ca. 2.95 Ga, ca. 1.95 Ga and 820–750 Ma, respectively. The oldest zircon has a U–Pb age of 3802±8 Ma with a εHf(t) value of −0.8 and model Hf ages of 3.96 Ga (TDM1) and 4.00 Ga (TDM2). This demonstrates the existence of 3.8 Ga old crustal remnants in South China, with possible crustal growth as early as 4.0 Ga. A series of 3.3 Ga zircons have positive εHf(t) values as high as 4.2, providing compelling evidence for growth of juvenile crust from a depleted mantle reservoir at Paleoarchean. All the zircons have Archean Hf model ages, with prominent peaks at 3.2 to 3.6 Ga, indicating an important period of crustal growth in this period. The other three zircon populations at ∼2.95 Ga, ∼1.95 Ga and 820–750 Ma have negative εHf(t) values and consistent Archean Hf model ages, suggesting multi-stage episodic reworking of Archean crustal materials. The youngest zircons have U–Pb ages of ∼750 Ma, very close to the deposition time of the Liantuo Formation. This indicates rapid recycling of supracrustal materials in a rift basin, possibly in association with breakup of the supercontinent Rodinia at that time.