GEOCHRONOLOGICAL AND GEOCHEMICAL STUDY ON THE METASEDIMENTARY ROCKS OF THE GAIXIAN REGION: NEW CONSTRAINTS ON THE PALEOPROTEROZOIC EVOLUTION OF THE JIAO-LIAO-JI BELT, NORTH CHINA CRATON

Jiao-Liao-Ji Belt (JLJB) is an important Paleoproterozoic mobile belt in the North China Craton. Although the study of JLJB was made considerable progress in the past decades, the tectonic evolution, whether it has experienced a rift-and-collision or an arc-continental event still remains controversial. The central segment of JLJB consists of Paleoproterozoic metasedimentary rocks (Liaohe Groups) and the uppermost of Liaohe Groups exposures Gaixian Formation, a representative clastic assemblage. In this study, new petrological, geochronological, geochemical, and Lu-Hf isotopic data of the Gaixian Formation from the Gaixian region, provided important constraints on the tectonic evolution of the JLJB. Detrital zircons of the Gaixian Formation have four U-Pb age populations at 2.2-2.1 Ga (major) and 2.1-2.0 Ga (minor), ~2.3 Ga (minor), ~2.5 Ga(minor), indicating that their provenances were dominated by 2.3-2.0 Ga igneous rock assemblage and Neoarchean basement rocks. The depositional age was constrained at 2.05-1.9 Ga and the metamorphic zircons yielded peak age of ~1.9 Ga. Regional geological and geochemical analyses indicated that the provenance of Gaixian Formation was most possibly deposited in an active continental margin setting. New Lu-Hf isotopic data also revealed that the continental crust probably existed on North China Craton before 4.1 Ga and the main crustal growth of this region was occurred between Mesoarchean and Neoarchean (3.0–2.5 Ga). Combined with the available data of the adjacent region, we suggest that the JLJB have experienced an intra-continental rifting stage since 2.2-2.05 Ga, followed by an active continental margin stage at 2.05-1.9 Ga, the peak collisional stage at ~1.9 Ga and the post-collisional extensional stage at 1.9-1.83 Ga, thus supporting that a rift-and-collision model is suitable for the tectonic evolution of JLJB.

This study was financially supported by the Nature Science Foundation of China [41772214], the 12^th Chinese 1000 Young Talents Program of the National Nature Science Foundation of China [2016-67, 32020002].