Geochronology and Zircon Hf Isotope of the Paleoproterozoic Gaixian Formation in the Southeastern Liaodong Peninsula: Implication for the Tectonic Evolution of the Jiao-Liao-Ji Belt.

The Jiao-Liao-Ji belt (JLJB), in the Eastern Block of the North China Craton, is a major Paleoproterozoic orogen and underwent a complicated tectonic evolution during 2.2–1.8 Ga. The Liaohe Group, an important stratigraphic unit in the JLJB, is key to understanding the complex evolution of this belt. In this paper, we present new detrital zircon U–Pb ages and Hf isotope data for meta-sedimentary rocks from the Gaixian Formation in different areas of the JLJB, in addition to compiled data for other formations of the Liaohe Group, to establish the depositional age and source of detrital materials of the group. U–Pb age results show that the age ranges of zircons from the different samples are broadly similar. The youngest zircon group is ca. 2.06 Ga, and the youngest single-grain age is ca. 2.0 Ga, constraining the depositional age of the Gaixian Formation to between 2.0 Ga and the metamorphic age of ca. 1.9 Ga. The zircon age data indicate that the provenance was primarily Archaean basement of the Nangrim Block and Paleoproterozoic volcanic rocks of the Li'eryu Formation. On the basis of the new geochronological data and results from previous studies, it is inferred that the JLJB underwent a successive process of rifting–subduction–collision, with the different formations of the Liaohe Group being deposited in different stages from rift to passive continental margin and then to active continental margin. Zircon Hf isotope data from the JLJB and adjoining Longgang and Nangrim blocks indicate that a major crustal growth event occurred at 2.9–2.5 Ga, followed by crustal growth and intense recycling of ancient crust at ca. 2.2 Ga. [ABSTRACT FROM AUTHOR]