Zircons U-Pb and Lu-Hf isotopic and whole-rock geochemical constraints on the Gantaohe Group in the Zanhuang Complex: Implications for the tectonic evolution of the Trans-North China Orogen

Abstract

The Zanhuang complex is located at the eastern margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks collided to form the North China Craton. The complex has been divided into the Archean Zanhuang Group and the Paleoproterozoic Gantaohe and Dongjiao Groups. The Gantaohe Group is composed of meta-volcanic rocks, basal conglomerates, meta-tuffaceous siltstones, meta-sandstones, phyllites, slates and dolomites. Geochemistry of the meta-sedimentary rocks indicates that most of the source rocks are felsic, displaying continental island arc signature, whereas a few of them are mafic and have oceanic island arc feature. U-Pb ages of detrital zircons from the Gantaohe meta-sedimentary rocks yielded three age populations of 2600–2400Ma, 3010–2600Ma and 2400–1900Ma. The primary 2600–2400Ma detrital zircons were most probably sourced from the TTG gneisses in the Zanhuang and adjacent Fuping Complexes. The subordinate 3010–2600Ma detrital zircons were most likely directly or indirectly from the Meso- and Neo-Archean crust of the Eastern Block, and minor amounts of 2400–1900Ma detrital zircons may have derived from the Paleoproterozoic granitic rocks in the Fuping Complex. The crystallization age of 2088±8Ma of a phenocrystic rhyolite and the youngest detrital zircon age peak of 2077±37Ma of a quartzite from the Nansizhang Formation suggest that the sedimentation of the Gantaohe Group began at ~2.09Ga. In combination with the ~1850Ma major metamorphic episode in the Trans-North China Orogen, the depositional age of the group can be constrained between ~2.09 and ~1.85Ga. Taking into account the lithostratigraphic feature, provenance and depositional age, the Gantaohe Group is interpreted as having deposited in a back-arc basin, which is consistent with the model that the unique collision between the Eastern and Western Blocks to form the coherent basement of the North China Craton occurred at ~1.85Ga.