Geochemical and geochronological study on the Paleoproterozoic rock assemblage of the Xiuyan region: New constraints on an integrated rift-and-collision tectonic process involving the evolution of the Jiao-Liao-Ji Belt, North China Craton
Abstract The tectonic evolution of the Jiao-Liao-Ji Belt (JLJB) has been a hot topic into understanding the Precambrian geology of the North China Craton. Although there is a broad consensus that the JLJB is a Paleoproterozoic mobile belt, whether it has experienced a rift-and-collision or a simply arc-continental collision event still remains controversial. The Central JLJB preserves excellent rock exposures of variable ages and therefore represents the most promising area to tackle the above controversy. This study present new field mapping results, U–Pb zircon ages, and geochemistry of the Paleoproterozoic rock sequence (i.e. volcano-sedimentary rocks and gneissic granites) from the Xiuyan area of the Central JLJB. Field investigation reveals that the Paleoproterozoic rocks are mainly in tectonic contact with one other. The zircon U–Pb dating results show that these meta-volcanic rocks and gneissic granites have the similar formation age of 2.2–2.0 Ga. Geochemical data indicate that these 2.2–2.0 Ga rocks show a typical A-type granite signature. Associated with the co-existing bimodal volcanic sequences, these data suggest an intra-continental rift setting of the region. By contrast, detrital and metamorphic zircon ages from the meta-sedimentary rocks further constrain the depositional age to be at 2.0–1.9 Ga, and could have been derived from the 2.2–2.0 Ga rift-related igneous rock assemblage and the ∼2.5 Ga Neoarchean basement of the Longgang Block. Geochemical data show that these 2.0–1.9 Ga meta-sedimentary rocks were mostly developed at an active continental margin. Combined with available geochronological, geochemical and metamorphic data of the adjacent area, the JLJB most likely experienced an integrated introversion tectonic process that was initiated from a 2.2–2.0 Ga intra-continental rifting event, transited into the active continental margin at 2.0–1.9 Ga, and followed by the significant arc-continental collision at ∼1.9 Ga and the post-collisional extension at 1.9–1.8 Ga. A rift-and-collision model is mostly workable for the Paleoproterozoic tectonic evolution of the JLJB.