The formation ages of the Langzishan and Lieryu Formations in Lianshanguan area, Benxi, Liaoning Province, and its geological significance.

A large area of the Paleoproterozoic Liaohe Group is exposed in Lianshanguan area, Benxi, Liaoning Province. Two layers of amphibolite and a set of felsic volcanic rocks have been identified in the Langzishanand Lieryu Formations of the Liaohe Group. The samples include two amphibolites and two rhyolites. Zircons from D020 for LA-ICP-MS U-Pb dating have black interior structure, unequal striation absorption and low Th/U ratios, indicating typical metamorphic origin. The age of 1934±45Ma represents the metamorphic age of the Langzishan Formation. Zircons from the other three samples for LA-ICP-MS U-Pb dating have oscillatory zoning and high Th/U ratios, indicating typical magmatic origin. The ages of 1952±38Ma and 2177±34Ma, 2208±12Ma represent the formation age of the Langzishan and Lieryu Formations respectively. In consideration of previous data, the authors hold that the formation age of the Liaohe Group is limited in the range of 2.20~1.95Ga, lasting about 250Ma. Field contact relations and chronological characteristics of volcanic rocks reveal that the Liaohe Group is a series of disordered and locally ordered structural strata, and there is no upper and lower relation between the rock groups. The Langzishan Formation is no longer suitable for being placed beneath the Lieryu Formation.