Geochemistry and zircon U–Pb–Hf isotopic data for Permo-Carboniferous sediments in the Solonker Zone, Inner Mongolia, China: Constraints on depositional age, provenance and tectonic setting

The Permo-Carboniferous tectonic setting of the SE Central Asian Orogenic Belt is poorly understood, especially with regard to the development of the Solonker (Suture) Zone. New stratigraphic, geochemical and detrital zircon analyses for Permo-Carboniferous sediments have been undertaken to resolve this problem. In the Mandula area, the Baotege Formation and former Amushan Formation were deposited in the early Permian. An unstable alluvial–proluvial fan to a stable shallow marine environment has been proposed. In the NE Sonid Youqi area, late Carboniferous to middle Permian carbonate–clastic rocks were deposited in a relatively stable shallow sea with a series of transgressions. Upper continental crust-like geochemical features, magmatic zircons and petrography show that the clastic rocks have a felsic source ranging from granites to tonalite– trondhjemite–granodiorite. Detrital zircons with prominent age groupings at c. 280–330 Ma, c. 350–370 Ma and/or c. 400–500 Ma with some Precambrian ages, together with zircon Hf isotopic data, indicate that the sediments were dominantly sourced from the orogenic belt itself and microcontinents. Basin analysis shows a transition from restricted basins in the late Carboniferous–early Permian to wider and deeper basins in the middle Permian. Accordingly, an extensional stage has been proposed, at least before the final closure of the Solonker Zone.