Since the Paleozoic, the tectonic evolutionary process of eastern Eurasia has been affected by at least three paleo-ocean regimes: the Paleo-Asian Ocean, the Mongol-Okhotsk Ocean, and the Paleo-Pacific Ocean. However, the tectonic transition among these ocean regimes is not well understood. Recently, the Heilongjiang Ocean was proposed to play an important role during the transition from the Paleo-Asian Ocean regime to the Mongol-Okhotsk Ocean (and later the Paleo-Pacific Ocean) regime. Here we report on a new combined study of petrological, geochemical, and geochronological data of biotite–plagioclase gneisses from the Qinglongcun Complex in the west Jiamusi-Khanka Block to better understand the tectonic evolution during this transition period. The results show that the protoliths of these biotite–plagioclase gneisses are medium-K calcalkaline rhyolites that were derived from a volcanic island arc environment related to paleo-oceanic subduction that occurred at ca. 260 Ma. Integrated with previous studies of the Permian arc-affinity rocks within the Jiamusi-Khanka Block, we identified two island arc magmatic belts with ages of ca. 290 Ma and ca. 260 Ma at the east and west margins of Jiamusi-Khanka Block, respectively. The east island arc magmatic belt was related to subduction of the Mongol-Okhotsk Ocean during the Early–middle Permian, which provided a driving force for the opening of the Heilongjiang Ocean. Subduction of the Heilongjiang Ocean during the middle–Late Permian resulted in the west arc island magmatic belt. These two belts provide key evidence for understanding the tectonic transition from the Paleo-Asian Ocean to the Mongol-Okhotsk Ocean to the Paleo-Pacific Ocean during the late Paleozoic to early Mesozoic.