The U-Pb ages and Hf isotopes of detrital zircons from Hainan Island, South China: implications for sediment provenance and the crustal evolution

摘要

In situ U-Pb dating and Hf isotopic of detrital zircons from beach sediments of Yalong Bay were analyzed to trace sedimentary provenance and reveal the crustal evolution of Hainan Island in South China. The grain size distribution of the sediments displays a clear single-peak feature, indicating the sediments were formed under the same condition of hydrodynamic force. The detrital zircons had Th/U ratios of greater than 0.1, and REE pattern displayed a positive Ce anomaly and a negative Eu anomaly, indicating that these zircons are predominantly of magmatic origin. The U-Pb spectrum of detrital zircons mainly peaked at the Yanshanian (96-185 Ma), Hercynian-Indosinian (222-345 Ma) and Caledonian (421-477 Ma). A portion of the detrital zircons were of Neoproterozoic origin (728-1,003 Ma), which revealed that the basement in the eastern region of Hainan Island was mainly of Neoproterozoic, with rare Archean materials. The positive ε_(Hf)(t) values (0 to +10.1) of the Neoproterozoic detrital zircons indicated that the juvenile crust grew in the southeastern Hainan Island mainly during the Neoproterozoic period. The Neoproterozoic orogeny in the southeastern part of the island (0.7-1.0 Ga) occurred later than in the northwestern region of the island (1.0-1.4 Ga). Importantly, the Grenvillian orogeny in the southeastern area of Hainan Island shared the same timing with that of the western Cathaysia Block; i.e., both areas concurrently underwent this orogenic event, thereby forming a part of the Rodinia supercontinent. Afterwards, the crust experienced remelting and reworking during the Caledonian Hercynian-Indosinianand Yanshanian accompanied by the growth of a small amount of juvenile crust.