Abstract: The Liaohe Group of Liaodong Peninsula, located in the northern segment of the JiaoLiaoJi Belt, is developed mainly of deformed sedimentary and volcanic successions and felsicmafic intrusions. In this study, we report a newly recognized metaacid volcanic rocks from the North Liaohe Group in the Helan area, on which we conducted a detailed petrological study through UPb zircon dating and wholerock geochemical and LuHf isotopic analyses to determine the rocks emplacement age, magma source and tectonic nature. Zircons from metaacid volcanic rocks were euhedralsubhedral in shape and displayed obvious oscillatory zoning, which indicate a magmatic origin, in accord with the Th/U ratios of 0.340.92 in the zircons. Zircon LAICPMS UPb ages show that the volcanic rocks were emplaced in the Paleoproterozoic 2153±11 Ma and comparable to the regional Paleoproterozoic Liaoji granitoids, suggesting the two rocks are from coeval magmatism. From geochemical analysis, high SiO2 contents (64.09%72.82%) and low Nb/Y ratios (0.240.42) indicate the rocks largely belong to the subalkalic volcanic rocks, and their high CaO, MgO and Fe2O3 contents are likely related to hydrothermal activities. LuHf isotopic analysis showed that REE patterns were rightleaned, and LREE/HREE, (La/Yb)N and δEu were 7.5711.13, 7.6011.53 and 0.140.22, respectively. Indeed, these rocks were relatively enriched in LILE (e.g., Rb, K), depleted in HFSE (e.g., Nb, Ta) and Ti and P, consistent with the geochemical characteristics of island arc magmatic rocks. In addition, insitu Hf isotopic analysis revealed that zircon εHf(t) values for metaacid volcanic rocks ranged between -12.00+6.88, with twostage Hf model ages (TDM2) varying from 3467 to 2310 Ma. These features suggest that the primary magma of metaacid volcanic rocks came from partial melting of a dominantly “old” MesoNeoarchaean crustal source possibly with significant addition of juvenile materials. Based on our overall analysis, together with previously reported data on igneous rocks and metamorphism, we propose that metaacid volcanic rocks from the North Liaohe Group were formed in an active continental margin setting presumably related to subduction of the paleooceanic plate beneath the south margin of the Longgang Block.

Key words: Paleoproterozoic, metaacid volcanic rock, zircon U-Pb dating, geochemistry, Jiao-Liao-Ji Belt