Precambrian continental crust evolution of Hainan Island in South China: Constraints from detrital zircon Hf isotopes of metaclastic-sedimentary rocks in the Shilu Fe-Co-Cu ore district

Abstract

Combined with the previous detrital zircons U-Pb ages of the two Precambrian successions, i.e. the Shilu Group and the Shihuiding Formation in Hainan Island of South China, the in situ Lu-Hf isotopes of detrital zircons were performed to evaluate the growth and reworking of Hainan Island continental crust during Precambrian. The results of 171 Hf-isotopic analyses on zircon grains from the Shihuiding Formation yield 176Hf/177Hf ratios between 0.280786 and 0.281188, 176Lu/177Hf ratios between 0.000228 and 0.003388, Hf model ages (TDMC) between 3.8Ga and 1.2Ga, and εHf(t) values ranging from −12.5 to +10.6. The analyzed results of 272 Hf-isotopic data on zircon grains from the Shilu Group exhibit a wide range of 176Hf/177Hf ratios (0.280810–0.282512), 176Lu/177Hf ratios (0.000062–0.004060), TDMC ages (3.7Ga–1.1Ga), and εHf(t) values (−20.5 to +12.3).The continental crust of Hainan Island maybe appeared firstly at ca. 4.0–3.8Ga and then was reworked. The 91.8% of detrital zircon grains from the Shihuiding Formation and 93.8% of the ones from the Shilu Group have crustal incubation time larger than 300Ma, indicating an involvement of reworked materials into the sedimentation of both the successions. Unambiguously, the crustal basement rocks in Hainan Island were formed mainly through reworking the previous continental components with minor input of juvenile materials. The generation of juvenile curst in Hainan Island predominantly occurred at ca. 2.7Ga and ca. 1.5–1.0Ga, which are consistent with that for the assembly of the Kenorland, and the Columbia breakup and subsequent amalgamation of the Rodinia, respectively. The present study further reveals that the crustal growths in Hainan Island are present at 2.7Ga, 2.3Ga and 2.1–1.8Ga, which is more favorable to the episodic growth mode. Moreover, a rough trend of decreasing maximum crustal incubation time of Hainan Island demonstrates that the incubation time of the juvenile crust is shorter when compared with that of the Cathaysia Block in the late Mesoproterozoic. Link to the previously reported geological works, we consider that Hainan Island did not share the same evolution history with the Cathaysia Block of South China during Precambrian.