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The depositional environment and tectonic setting of the newly identified Ri-Qing-Wei Basin are the focus of controversy. In order to solve these questions, the geochemical characteristics of siltstones from Laiyang Group in Taolin area are analysed in detail. The siltstones present similar contents of SiO 2 and Al 2 O 3 compared with upper continental crust (UCC) and post-Archean Australian Shale (PAAS) and are classified as wacke on chemical classification plot of clastic rocks. The trace elements are characterized by the depletion of transition elements (Sc, V, Cr, Ni, and Cu). The chondrite-normalized REE patterns exhibit the enrichment of LREE and depletion of HREE, as well as significant negative Eu anomalies. Relative high Index of Compositional Variability (ICV) values suggest the siltstones are compositionally immature and the sediments of first-cycle. The low Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values of the samples indicate the weak source weathering condition. Moreover, the characteristics of A-CN-K plot suggest K-metasomatism occurred after burial. A series of palaeo-environment indexes imply that the Laiyang Group were deposited in a reducing marine environment with hot and arid climate. Major-and trace-based tectonic setting discriminant diagrams all indicate that the Ri-Qing-Wei Basin was formed in an active continental margin setting; this conclusion is also supported by the analysis of the coeval igneous rocks. Based on the investigations of the subduction of the Palaeo-Pacific plate and the development of Cretaceous basins on the eastern Eurasia, we propose that Ri-Qing-Wei Basin was formed in response to the delamination of the North China Craton and the subduction of Izanagi plate.

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems.