Is the Paleoproterozoic Jiao-Liao-Ji Belt (North China Craton) a rift?
As a typical example of the Paleoproterozoic crust in the Eastern Block of the North China Craton, the Paleoproterozoic Jiao-Liao-Ji Belt consists principally of the Liaohe Group (and its equivalents), Liaoji granites and mafic intrusions. Previous studies indicate that the evolution of the Jiao-Liao-Ji Belt has been mainly attributed to the opening and closing of an intracontinental rift along the eastern continental margin of the North China Craton. Here we synthesize the Paleoproterozoic magmatism, sedimentation, metamorphism and metallogeny against the rift model and propose a process of arc-continent collision between the northern Longgang and the southern Nangrim Blocks. This conclusion is consistent with the observations, including that (a) the 2.0- to 2.2-Ga magmatism shows a typical subalkaline series, rather than a bimodal distribution, since the mafic rocks mostly have arc affinities and the acidic–intermediate rocks belong to the calc-alkaline series; (b) the main source of the 1.9- to 2.0-Ga sedimentary rocks is the Paleoproterozoic arc materials, indicating a fore-arc or back-arc basin setting; (c) a couple of big borate deposits occur in the boron-rich volcanic rocks that were formed in convergent continental margins; (d) the North and South Liaohe Groups show different rock associations and metamorphic histories (P–T paths); and (e) the Nangrim and Longgang Blocks vary in lithological units, geochronology and metamorphic features. Thus, an arc-continent collision tectonic scenario for the Paleoproterozoic Jiao-Liao-Ji Belt is involved: (a) a southward subduction in the period 2.0–2.2 Ga; (b) sedimentation during the period 1.9–2.0 Ga; (c) arc-continent collision at ca. 1.9 Ga; and (d) post-collisional extension at 1.82–1.87 Ga, marking the end of the Paleoproterozoic tectonothermal event.