Geophysical and geological tests of tectonic models of the North China Craton

The geometry and timing of amalgamation of the North China Craton have been controversial, with three main models offering significantly different interpretations of regional structure, geochronology, and geological relationships. One model suggests that the Eastern and Western Blocks of the NCC formed separately in the Archean, and an active margin was developed on the Eastern Block between 2.5 and 1.85Ga, when the two blocks collided above an east-dipping subduction zone. A second presumes the Eastern Block rifted from an unknown larger continent at circa 2.7Ga, and experienced a collision with an arc (perhaps attached to the western block) above a west-dipping subduction zone at 2.5Ga, and the 1.85Ga metamorphism is related to a collision along the northern margin of the craton when the NCC joined the Columbia supercontinent. A third model suggests two collisions in the Central Orogenic Belt, at 2.1 and 1.88Ga, but recognizes an early undated deformation event. Recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models, showing that subduction beneath the Central Orogenic Belt was west-directed, and that there is a second, west-dipping paleosubduction zone located to the east of the COB dipping beneath the Western Block (Ordos Craton). The boundaries identified through geophysics do not correlate with the boundaries of the Trans-North China Orogen suggested in the first model, and the subduction polarity is opposite that predicted by that model. High-pressure granulite facies metamorphism at 1.85Ga is not restricted to the “TNCO” as suggested by the first model, but is documented across the NCC, as predicted by the second model, suggesting a major continent–continent collision along the north margin of the craton at 1.85Ga. Further, it has recently been shown that in the southern “TNCO”, there is no record of metamorphism at circa 1.85Ga, but only at 2.7–2.5Ga, showing that the “TNCO”, as defined as a circa 1.85Ga orogen, does not exist. This is further confirmed by recent Re–Os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern COB is late Archean in age, and that a province in the northern NCC is circa 1.8Ga, correlating with the proposed collision belt of the NCC with the Columbia supercontinent across the entire NCC. The COB is an Archean convergent belt, re-worked in the Paleoproterozoic, and the Paleoproterozoic tectonism is widespread across the NCC, as predicted by the model whereby the previously amalgamated Eastern and Western Blocks experienced a continental collision with Columbia at circa 1.85Ga, but uplift/exhumation rates are slow, necessitating a re-evaluation of the tectonic models of the NCC.