Depositional age and provenance of the Anshan Group in the Gongchangling area, Liaoning Province: Constraints from detrital zircon U-Pb-Hf isotopic and rare earth element composition in the garnet-staurolite-mica-quartz schist

The Anshan Group, which has undergone greenschist to amphibolite facies metamorphism and polyphase deformation, is one of the most important banded iron formation(BIF)-bearing meta-supracrustal rocks in the Eastern Block of the North China Craton.Depositional age and provenance of the Anshan Group are vital for understanding the tectonic setting of the BIF in the North China Craton.In this study, LA-MC-ICP-MS(laser ablation inductively coupled plasma mass spectrometry) was employed to analyze detrital zircon U-Pb-Hf isotope and rare earth element compositions of garnet-staurolite-mica-quartz schist from the Anshan Group in the Gongchangling area.Based on the internal structure, and U-Pb ages of detrital zircons, the peak age of 2528 Ma recorded by the youngest group of detrital zircons is chosen as the maximal depositional age of the Anshan Group, coupled with the geological relationship which the Anshan Group was intruded by the ca.2500 Ma Qidashan K-rich granites and 2510~2470 Ma metamorphic age of the Anshan Group, suggest that the Anshan Group was deposited between 2528 Ma and 2510 Ma, late Neoarchean.The ²⁰⁷Pb/²⁰⁶Pb ages of the detrital zircons from the studied sample is between 2931 Ma and 2454 Ma, and detrital zircon age patterns of the studied sample is characterized by the major peak of 2528 Ma.Combined with the internal structure of the detrital zircons, our new U-Pb ages reveal that the main provenance of Anshan Group is the late Neoarchean acid magmatic rocks.The two-stage Hf model ages of the typical detrital zircons are 3532~2711 Ma with a peak age of 2830 Ma, which further reveals that the intensive crustal growth in the Anshan-Benxi area was concentrated in Late Middle Archean.Integrated with previous geochemical data from Anshan Group in the Anshan-Benxi area, it is speculated that the Gongchangling BIF-bearing meta-supracrustal rocks of Anshan Group were probably deposited in a back-arc basin on the ancient continental margin.