U-Pb and Hf isotopic study of detrital zircons from the Hutuo group in the Trans-North China Orogen and tectonic implications

There is a broad consensus that the North China Craton formed by the amalgamation of the Western and Eastern Blocks along the nearly N-S trending Trans-North China Orogen. However, it still remains controversial whether the Western and Eastern Blocks collided at ~2.5Ga or ~1.85Ga. U-Pb ages and Hf isotopic data of detrital zircons from foreland basins in the Trans-North China Orogen can place rigorous constraints on this controversial issue. One of such foreland basins is represented by the Hutuo Group in the Wutai Complex in the middle sector of the Trans-North China Orogen. The sequences of the Hutuo Group range from lower basal conglomerates and sandstones (Doucun Subgroup), through clastic sediments, dolomites and meta-basalts (Lower Dongye Subgroup), phyllites and dolomites (Upper Dongye Subgroup), to coarse-grained sandstones and conglomerates at the top (Guojiazhai Subgroup), most of which contain large amounts of detrital zircons. The detrital zircons from the Doucun, Lower Dongye, Upper Dongye and Guojiazhai Subgroups yield concordant ²⁰⁷Pb/²⁰⁶Pb ages of 2.11-3.88Ga, 2.01-2.84Ga, 1.88-2.72Ga and 1.92-2.65Ga respectively, the majority with Neoarchean to Paleoproterozoic ages. The presence of ~1.88Ga detrital zircons in the Upper Dongye and Guojiazhai Subgroups indicates that they deposited at some time after ~1.88Ga. This is in accordance with collision between the Eastern and Western Blocks along the Trans-North China Orogen to form the North China Craton at ~1.85Ga.