Provenance and metamorphism of the Mesoproterozoic Baoyintu Group: Implication for the interaction between the western Central Asian Orogenic Belt and the North China Craton

The deposition and metamorphism of the sedimentary rocks are closely related to the tectonic affinity and interactions among different terranes. The metasedimentary Baoyintu Group, which is distributed in the junctional area adjacent to the Alxa Block, the North China Craton (NCC), and the Central Asian Orogenic Belt (CAOB), is an ideal objective to investigate these issues. However, its depositional age, provenance, and metamorphism have not been well studied. To solve these problems, systematic detrital zircon and rutile dating, zircon Hf isotopic analysis, and phase equilibrium modeling were conducted. The youngest detrital zircon age of 1395 ± 32 Ma constrained the maximum depositional age of the Baoyintu Group younger than the Mesoproterozoic. The detrital zircon age pattern and the Hf isotopic data indicate it possessed a similar source to the Langshan Group from the NCC but in contrast to the Alxa Group in the Alxa Block. The peak metamorphic P-T conditions of the Baoyintu Group are 650–660 °C and 12.0–13.6 kbar, which are typical in the Barrovian-type metamorphic belt. Its metamorphic age is confirmed through the rutile dating analysis, which yielded a discordia age of 384 ± 58 Ma. Our synthesized data support the presumption that the Baoyintu Group is the sedimentary series draping on the margin of the northern NCC during the Mesoproterozoic. The metamorphism is involved with the subduction or orogenic process between the NCC and the Bainaimiao arc in the CAOB during the Devonian.