Nature of three episodes of Paleoproterozoic magmatism (2180 Ma, 2115 Ma and 1890 Ma) in the Liaoji belt, North China with implications for tectonic evolution

Three episodes of Paleoproterozoic magmatism with distinctively different nature in the Liaoji belt of the Eastern North China Craton are discussed here: the 2200–2140 Ma Liaoji A-type granites, the 2160–2110 Ma Haicheng mafic sills and the ∼1890 Ma Qingchengzi I-type granites. The Mafeng monzogranitic pluton, representative of the Liaoji A-type granites, gives a SIMS U-Pb zircon age of 2181 ± 6 Ma (n = 20, MSWD = 4.3). The Qingchengzi plagiogranitic pluton, representative of the Qingchengzi I-type granites, gives a SIMS U-Pb zircon age of 1891 ± 10 Ma (n = 8, MSWD = 1.8). The Mafeng monzogranites are high in Fe, Ti, K but low in Mg, Al and Ca. They have high abundance of total REEs (ΣREE = 213–346 ppm). They are relatively depleted in feldspar-compatible elements (e.g., Eu and Sr) and HFSEs (e.g., Nb, Ta, P and Ti). They have high 10000 × Ga/Al ratios of 3.19–3.61 and Zr + Nb + Ce + Y concentrations of 472–656 ppm, which are typical for A-type granite. The Qingchengzi plagiogranites have relatively high Al, Ca, Na but low Fe, Ti and K contents. They have low abundance of total REEs (ΣREE = 17.6–21.6 ppm). They are enriched in LILEs (e.g., Ba, K and Sr) but depleted in HFSEs (e.g., Nb, Ta, P, Ti and Y). These features, combined with extremely high Sr/Y ratios (327–413), are comparable with those of typical modern adakites. The Liaoji A-type granites show a source same to that of the Haicheng mafic sills and they originated from the Archean subcontinental lithospheric mantle plus with contamination from the Archean granites. However, the Qingchengzi I-type granites are interpreted to originate from subducted oceanic crust with significant contributions from sediments. The Liaoji A-type granites and the coeval bimodal volcanism in the Liaohe Group as well as the Haicheng mafic sills may represent episodic magmatism which was related to a protracted intra-continental rifting caused by lithospheric extension. The ca. 1890 Ma Qingchengzi I-type granites and coexisting S-type granites as well as the coeval regional metamorphism are favored to represent an active continental magmatism linked to Paleoproterozoic subduction