A Paradigm Shift: North China Craton's North Margin Orogen Is the Collisional Suture With the Columbia Supercontinent

In a new study, Wu, Wang, Zhou, Zhao, Haproff, et al. (2022, https://doi.org/10.1029/2022GC010662) present a comprehensive study of the North Margin Orogen of the North China Craton (NCC), showing that older accreted rocks in this belt preserve a record of active margin magmatism from 2.2 to 2.0 Ga, followed by collisional tectonics, marked by mélange and mylonitic shear zones, then granulite facies metamorphism at 1.9–1.8 Ga, marking the final collision of the NCC with the Columbia Supercontinent. The multidisciplinary studies presented in this work support earlier suggestions that the North China Craton amalgamated during accretionary orogenesis in the Neoarchean to earlier Paleoproterozoic, and that the late widespread 1.85 Ga high‐grade metamorphism is craton‐wide in scale, and not confined to a narrow orogen in the center of the craton. This new understanding creates new possibilities for refining reconstructions of one of Earth's earliest, best documented supercontinents, showing a globally linked plate network at 1.85 Ga, and suggests drastic new correlations and models for mineral resource exploration.

or West Africa suggest a new mineral exploration strategy for China When the supercontinent cycle started on Earth is an important question, as formation of the first supercontinent may reveal the time that earlier forms of plate tectonics were able to build continents of sufficient size to emerge above sea level, begin the Wilson Cycle, and begin subaerial weathering, fomenting major changes in numerous chemical and physical systems on our planet (Mitchell et al., 2021).Pre-supercontinent cycle tectonics were likely dominated by submergent intra-oceanic subduction and arc systems, numerous oceanic spreading ridges, and probably a much greater total plate boundary length with smaller overall plate sizes, with arc magmatism being the biggest contributor to continental growth (Windley et al., 2021).Determination of the configuration of the first supercontinent is plagued with difficulties in making reconstructions the further back in time one goes, with the loss of fossils, sea-floor spreading records, and reliable paleomagnetic results, so we must rely on classical geologic analysis and correlation for earlier times (e.g., Şengör et al., 2020).
For decades, a scientific debate has raged as to where is the collisional orogen responsible for the regional high-grade metamorphism of the North China Craton at 1.85 Ga, presumably related to the North China craton's amalgamation with the earliest well-documented supercontinent, Columbia, with Nuna at its core.One school of thought has argued that a north-south belt of uplifts that runs through the center of the craton is the collisional orogen between the Eastern and Western Blocks on either side as the blocks jumbled and joined the Columbia Supercontinent, and this proposed orogen was named the Trans-North China Orogen, or TNCO (Zhao et al., 2001(Zhao et al., , 2005(Zhao et al., , 2012)).In contrast, others have argued that the 1.85 Ga collisional orogen lies in an east-west belt along the north margin of the craton, marking the place where the North China Block joined the Columbia Supercontinent, after a long period of geographically wide Andean margin activity caused by subduction to the south under the craton.In this model, the 1.85 Ga continent/continent collision was Tibetanin-scale, affecting most of the craton, but stronger in the north (Kusky et al., 2016;Xiao et al., 2021).The paper by Chen Wu et al. ( 2022a) is a potential paradigm shifter, as it is the first to clearly, quantitively, and comprehensively describe the orogen on the north margin of the craton, and link it with other collisional orogens globally-related to the formation of the planet's first clearlydocumented supercontinent, Columbia.This has important implications, not only academically, but potentially economically.
The paper by Chen Wu and others (2022a) puts together a structural, geochronological, geochemical, and paleomagnetism-based plate reconstruction model that clearly documents the northern margin of the North China Craton as the 1.85 Ga collisional orogen, and the other belts (TNCO included) as zones of regional overprinting of older orogenic belts.Professor Chen Wu and his colleagues initially recognized a circa 1.9 Ga mélange along the north margin of the craton (Wu et al., 2018), then continued mapping and through detailed field studies (Wu et al., 2022a, b) have now documented many of the classical features of collisional orogens along the north margin of the craton, at 1.9-1.85(extending to 1.78 Ga for post collisional magmatism), using long-established indicators of collisional orogens.Specifically, Wu et al. (2022a) document the presence of an east-west striking belt of 2.2-2.0Ga continental margin magmatic arc rocks, an east-west striking 1.9-1.88Ga tectonic mélange and mylonitic shear zones, and lower Paleoproterozoic strata folded by N-S contraction, all metamorphosed to granulite facies at 1.9-1.8Ga.Analysis of a huge dataset of detrital zircons by Wu et al (2022a) is consistent with Neoarchean arc/continent collision in the older orogenic belt in the center of the craton, followed by active continental margin arc tectonics along the north margin of the craton from 2.2-1.85Ga forming the Bayan Obo subduction/accretion mélange, then ridge subduction at 1.92 Ga, followed by collision with Columbia Supercontinent at 1.93-1.80Ga, then post-collisional magmatism in the range of 1.87-1.80,with the final pulse of post-collisional lamprophyre dikes intruding at 1.78-1.77Ga.The North Margin Orogen was then intruded by 1.87-1.78plutons of the anorthosite -mangerite -charnockite -alkali feldspar granitoid suite (Peng et al., 2014), which are common in post-continental collisional settings such as the Rodinian Belts, including the Adirondacks the Grenville Province.
While the position of the North China Craton in the Columbia Supercontinent has been debated (Rogers and Santosh, 2002;Zhao et al., 2002;Meert, 2012), this is largely because most workers have been assuming the north-south striking TNCO in the center of the craton marked the collisional suture with Columbia.Since this turns out to not be true, confirmed by the new work reported by Wu et al. (2022a), one of the biggest reasons the NCC was so hard to fit into Columbia, was that these attempts were using the wrong orogen as the suture!The reconstruction of Kusky and Santosh (2009) used the North Margin Orogen to fit the NCC into Columbia, correlating this belt with the Trans-Amazonian of South America and Eburnian/Birimian orogens of West Africa.In a new greatly refined reconstruction of Columbia, Grenholm (2019) has fit together most cratons of Columbia into the "Atlantica" configuration, in which the North Margin Orogen of the NCC also correlates with the Birimian terrains amalgamated during the Eburnian orogeny (Fig. 1).Together, the North Margin Orogen of Wu et al. (2022a) and the Birimian terranes of West Africa as seen on this reconstruction to form a large 2.3-2.0Ga accretionary orogen, that collided with the other blocks of Columbia in the Atlantica configuration at 1.85 Ga.The importance of using the correct orogen to fit the NCC into the Columbia Supercontinent reconstruction is more than academic.Workers who have been using the TNCO as the collisional orogen, and the reconstructions based on that have faced the challenge of finding no associated orogenic gold deposits, or other economically significant mineral deposits associated with their proposed orogen.The Birimian, in contrast, has recently been recognized as the world's premier Paleoproterozoic gold province, with > 10,000 metric tons gold endowment known, so far (Masurel et al., 2022).In fact, the West African Craton constitutes an extensive Paleoproterozoic accretionary orogen which contain nu-merous orogenic gold deposits (Bierlein et al., 2009) formed around ca. 2.27-1.96 Ga (Para-Avila 2016;Şengör et al., 2021b).The orogenic gold deposits are typically located in metamorphosed fore-arc and back-arc regions, as well as in the arc (Goldfarb et al., 2015) and show a close spatial relationship to lamprophyres and associated felsic porphyry dikes and sills (Rock et al., 1987), similar to those of the North Margin Orogen of the NCC.Additionally, the Paleoproterozoic Birimian encompasses volcanic greenstone belts, and granitic intrusions related to the Eburnean orogeny, with ages between 2.2 to 1.8 Ga (Grenholm, 2019), similar to parts of the North Margin Orogen.The deformation period during Eburnean orogenesis is focused at about 2.1 Ga (Para-Avila, 2017), similar to the period when the north margin of the NCC was an active Andean-type accretionary orogen margin (Kusky et al., 2016;Wu et al., 2018Wu et al., , 2022a, b), b).
The recognition that the North Margin Orogen is an accretionary orogen correlated with the world's largest Paleoproterozoic gold province suggests the explorationists need to adopt a new geologic/tectonic model for exploration programs, and focus extra efforts on the North Margin Orogen of Wu et al. (2022a).If the erosion level of the North Margin Orogen is deeper than the typical greenschistamphibolite facies orogenic gold deposits, then perhaps the orogenic gold should be searched for in the retro-arc and foreland basins, much like the detrital gold of the Witwatersrand.The paper by Wu et al. (2022a) is indeed a paradigm shifter, with implications for global tectonic configurations, and economic mineral deposit exploration.