Timing the closure of the Jilin−Heilongjiang Ocean: Constraints from zircon, apatite, and titanite U-Pb dating of the Heilongjiang Complex, Northeast China

The timing of the Paleo-Asian Ocean closure, the onset of Paleo-Pacific Ocean subduction, and the transition between these events remains highly controversial. The Jilin−Heilongjiang high-pressure metamorphic belt, Northeast China, which formed following the closure of the Jilin−Heilongjiang Ocean, provides well-preserved evidence of this transitional tectonic process. We present whole-rock geochemical data and multi-mineral U-Pb geochronology for the Yilan blueschists within the Jilin−Heilongjiang high-pressure metamorphic belt. Whole-rock major and trace elements indicate that the protoliths of the Yilan blueschists were alkaline basalts formed in an ocean-island setting. The youngest concordant zircon U-Pb ages from the Yilan blueschists are 262 ± 3 Ma, constraining their protolith to the Late Permian. Based on their occurrence and composition, two generations of apatite were identified: Ap-I yielded a U-Pb age of 185 ± 13 Ma, recording prograde subduction to peak blueschist-facies conditions in the Early Jurassic; Ap-II yielded a U-Pb age of 165 ± 10 Ma, reflecting retrograde metamorphism during exhumation in the Middle Jurassic. Integrating these results with published chronological data from the Jilin−Heilongjiang high-pressure metamorphic belt indicates that the Jilin−Heilongjiang Ocean opened during the Early to Middle Permian (288−260 Ma), with subduction initiating in the Late Permian to Early Triassic (260−230 Ma). Driven by westward subduction of the Paleo-Pacific plate, further subduction of the Jilin−Heilongjiang Ocean occurred from the Early Triassic to Early Jurassic (230−185 Ma), culminating in the amalgamation of the Jiamusi−Khanka Block with the Songliao Block.