A transition of Mongol-Okhotsk and Paleo-Pacific tectonic regimes in the Early Cretaceous: Evidence from sedimentary and volcanic events in the northern Great Xing’an Range (Northeast China)

The late Mesozoic evolution of Northeast China was dominantly controlled by the Mongol-Okhotsk and the Paleo-Pacific tectonic regimes. Their superposition during the Early Cretaceous profoundly influenced magmatic activity, volcanic assemblages, sedimentary basin development, and extensional structures, ultimately establishing the present-day tectonic framework of Northeast China. This comprehensive study focuses on the formation processes of sandstones and volcanic rocks of the northern Great Xing’an Range, highlighting the transitional processes between these two tectonic regimes in the Early Cretaceous. Geochemistry and framework analysis of sandstones, along with detrital zircon U-Pb ages and provenance studies, consistently suggest a transitional tectonic setting during the deposition of the Early Cretaceous Jiufengshan Formation. Comparative geochemical analysis of volcanic rocks and zircon Hf isotopes reveals a fundamental shift in magma generation processes for volcanic rocks formed before and after the Jiufengshan Formation. Zircon trace element systematics document two distinct episodes of crustal thickening and thinning during the Early Cretaceous, genetically linked to the final closure of the Mongol-Okhotsk Ocean followed by post-collisional extension, as well as low-angle subduction and subsequent slab rollback of the Paleo-Pacific plate. This paper demonstrates that the post-collisional extension of the Mongol-Okhotsk tectonic regime primarily governed the tectonic evolution recorded in the Baiyingaolao, Meiletu, Longjiang, and Guanghua formations, with its influence progressively diminishing during the deposition of Jiufengshan Formation. Synchronously, far-field effects induced by the low-angle subduction of the Paleo-Pacific plate had already propagated into the northern Great Xing’an Range, where subsequent slab rollback triggered the formation of bimodal volcanic rocks in the Ganhe and Gushanzhen formations. The transition between these two competing tectonic regimes is precisely constrained to the interval between 116 Ma and 111 Ma, based on integrated chronostratigraphic evidence.