Timing, Provenance, and Tectonic Implications of Ore-Hosting Metasedimentary Rocks in the Giant Liba Gold Deposit, West Qinling Belt, China

Abstract

The closure time of the Shangdan Ocean is critical for understanding the tectonic evolution of the Proto-Tethys Ocean. However, the proposed closure time was prolonged from Ordovician to Devonian. In the present study, detrital zircon from the metasedimentary rocks of the Liba Group in the West Qinling Belt was analyzed to constrain the closure time of the Shangdan Ocean. The three youngest grains from the Liba Group yield a maximum deposition age of 418 ± 13 Ma, indicating the Middle Devonian deposition. Detrital zircon grains show two main U–Pb age peaks of 810 Ma and 440 Ma with εHf(t) values spanning from −24.3 to +8.8 and −6.3 to +4.1, respectively, suggesting that the sediments of the Liba Group were derived from both the North and South Qinling Belts. The Lower Devonian in the South Qinling Belt shows similar provenance to the Liba Group, whereas sediments from the North Qinling Belt are absent in the Silurian strata of the South Qinling Belt. From Late Silurian to Early Devonian, the tectonic setting changed from subduction to collision. This evidence consistently suggests the disappearance of the Shangdan Ocean. The noticeable decrease in magmatism from 510–420 Ma to 420–390 Ma and the shrinking of εHf(t) values from −15.5–+12.8 to −8.4–+4.2 reveal that the Shangdan Ocean, as the eastmost embranchment of the Proto-Tethys Ocean, was closed at ca. 420 Ma.