There have always been academic debates regarding the timing and geodynamics of the superimposition and transformation between the Paleo-Pacific Ocean and the Paleo-Asian Ocean. To resolve the relevant issues over this debate, the authors selected the Jilin–Heilongjiang high-pressure metamorphic belt (Ji–Hei HP Belt) between the Jiamusi–Khanka Block and the Songliao Block in NE China as the study area. This area preserves important records of the superimposition and transformation between these two tectonic domains. This study aims to address this issue through geochemical and zircon U–Pb dating analyses of the Yilan blueschist of Heilongjiang Complex exposed in the Ji–Hei HP Belt. In the geochemical analysis, it has been discovered that the protoliths of the blueschist in the Yilan area consist of subalkaline basalt, which displays geochemical characteristics of Ocean Island Basalt that indicated an oceanic island setting. The LA–ICP–MS zircon U–Pb analysis yields ages of 248±4 Ma and 259±2 Ma from the magma zircons of the blueschists, indicating that the basalt protolith was formed in Late Permian to Early Triassic (259–248 Ma). Based on the results of this study and the regional data, it is proposed that the Jilin–Heilongjiang Ocean opened during Late Permian to Early Triassic (259–248 Ma). This period marks a crucial stage from the closure of the Paleo-Asian Ocean to the initiation of Paleo-Pacific oceanic subduction.