Provenance and tectonic setting of the Jiehekou Group in the Luliang Complex: Constraints from zircon U-Pb age and Hf isotopic studies

The Trans-North China Orogen (TNCO) is considered to be a continent-continent collisional belt, along which the Eastern and Western blocks collided. The Luliang Complex is located in the middle segment of the western margin of the TNCO, adjacent to the boundary between the Western Block and the TNCO. The Luliang Complex can be divided into the granitoid plutons and supracrustal rocks. The Chijianling gneisses in the former give LA-ICP-MS U-Pb zircon age of 2180Ma and epsilon(Hf) (t) values between + 0.52 and +4.30. The supracrustal rocks have been subdivided into the Jiehekou, Luliang and Yejishan groups, of which the Jiehekou Group is mainly composed of meta-siltstones, meta-pelitic rocks, marbles and minor amphibolites. Geochemistry and Nd isotopic data from the meta-sedimentary rocks indicated that the source rocks are felsic, probably from the Archean upper crust and newly-formed arc felsic rocks. Combined with the previous data, our data suggested that the youngest detrital zircon age peaks from samples of the Jiehekou Group are consistent within the errors and gave an age of similar to 2.0Ga, which is the maximum formation age of the group. On the other way, the similar isothermal decompression P-T path with other high-grade metamorphic rocks in the TNCO suggests that the Jiehekou Group also experienced the similar to 1.85Ga metamorphic event, which is the minimum formation age of the group. Furthermore, due to similarities of the Jiehekou Group with the khondalitic rocks from the Western Block and remarkable difference with the Yejishan Group in the Luliang Complex in the zircon U-Pb and Hf isotopic data, we suggest that the Jiehekou Group and the khondalitic rocks in the Western Block share a provenance. In a word, the Jiehekou Groups was formed between 2.0Ga and 1.85Ga on the eastern margin of the Western Blocks in a passive margin environment and was thrust eastward during the similar to 1.85Ga collision with the Eastern Block.