Abstract: The Fanjiatun Formation in central Jilin, situated on the northern margin of the North China craton, represents a key geological unit for constraining the closure of the eastern Paleo-Asian Ocean. Systematic petrography, detrital zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemical analyses were performed on its metasedimentary rocks. The youngest detrital zircon population yields a weighted mean age of （233.6±5.0) Ma (N = 11), constraining the maximum depositional age to not earlier than the Late Triassic. Whole-rock geochemistry (Al2O3/TiO2=24.65-63.69, avg. 37.84) and elemental ratios (La/Sc, Th/Sc, Cr/Th, Eu/Eu*) indicate felsic to intermediate upper-crustal sources. Detrital zircon age spectra and predominantly positive  εHf(t) values indicate provenance mainly from the Northeastern block and the northern margin of the North China craton. Tectonic discrimination parameters together with time-series variations in zircon trace elements reveal a transition from compressional orogenesis to extensional stabilization in the study area, and suggest that Paleozoic to Early Mesozoic crustal evolution was characterized by three episodes of thinning and two of thickening, closely coupled with the late subduction-closure regime of the eastern Paleo-Asian Ocean.

Key words: Fanjiatun Formation, detrital zircon, U-Pb ages, geochemistry, provenance analysis, closure of the Paleo-Asian Ocean