Provenances of the Paleozoic successions in the Okcheon FTB, Korea with implications for the Phanerozoic tectonic evolution of the Korean Peninsula along the East Asian continental margin

Detrital zircon geochronology and isotope analysis can be used for inferring the provenance of detrital sedimentary sources in general, and can provide useful information to establish the tectonic evolution of a sedimentary basin. In this respect, analyzed detrital zircon SHRIMP U-Pb ages and LA–(MC)–ICP MS Lu-Hf isotopes from the Paleozoic metasedimentary successions in the Okcheon fold-thrust belt (FTB), providing new insights into their provenance and evolution during the Phanerozoic orogenesis.

The Okcheon FTB has been considered a prominent belt between the two basements (viz. Gyeonggi and Yeongnam massifs) in the southern part of the Korean Peninsula, and subdivided the Okcheon Zone to the west and the Taebaeksan Zone to the east. The Taebaeksan Zone consists predominantly of the Paleozoic metasedimentary rocks comprising Early Paleozoic Joseon and the Late Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally. On the contrary, the Okcheon Zone exposed the post-Devonian to Permian clastic wedge on top of the Neoproterozoic bimodal volcanic rocks related to the intracontinental rifted settings.

Our results show that all Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso- to Neoproterozoic ones. Each zircon population shows the following notable results, allowing estimation of their sedimentary sources: (1) The Paleoproterozoic zircons (ca. 1.85 and 2.50 Ga) with similar ranges of εHf(t) values are most common in the basement rocks of the Korean Peninsula, thus can be sourced from both the Gyeonggi and Yeongnam massifs. (2) The Meso- to Neoproterozoic zircons, only preserved in the late Middle to Late Cambrian strata, probably reflected abrupt changes in source areas. (3) The youngest Paleozoic zircons of each formation, almost coincident with its deposition ages, suggest the presence of syndepositional magmatism. This means that detritus was supplied from proximal magmatic sources during the deposition (4) The Cambrian-Ordovician zircons from the Lower Paleozoic sequences, but rarely not included in the successive Upper Paleozoic sequences, suggest a provenance change after the hiatus between the two sedimentary successions. (5) The Permian zircons showing different εHf(t) values in each locality within the study area indicate that detrital sources were varied and localized.  

These integrated results of the detrital zircon U-Pb ages and Hf isotope data from the Paleozoic successions together with the existence of a post-Devonian to Permian clastic wedge in the Okcheon Zone might possibly be related to the subduction in relation to Okcheon Orogeny similar to the Allegany orogenic time span in Appalachian. The entire sedimentary sequences within the Okcheon Belt experienced deformation and metamorphism related to the subsequent (Permo-) Triassic collisional orogeny (viz. Songrim Orogeny) along the Korean collision belt, forming regional fold-dominated mountains of the Okcheon FTB. This suggests that the Okcheon FTB records important information for Paleozoic provenance changes linked to the tectonic evolution of the Korean Peninsula, which will further help to understand the spatial and temporal evolution of orogenic belts during the Phanerozoic along the East Asian continental margin.