The formation and evolution of the Jilin-Heilongjiang Ocean: Constraints from petrology and chronology of the Jilin-Heilongjiang high-pressure belt

There is considerable controversy over the formation and evolution process of the Jilin-Heilongjiang Ocean in Northeast China. This geological process is recorded by the Jilin-Heilongjiang high-pressure metamorphic belt located at the easternmost end of the Central Asian Orogenic Belt. To address this issue, we investigated the Heilongjiang Complex exposed in the Yilan and Luobei regions using geological and geochemical analyses combined with laser ablation inductively coupled plasma mass spectrometry zircon U-Pb isotopic dating. Our geochemical studies indicate that the protoliths of the Yilan blueschist consist of subalkaline basalt formed in an ocean island environment. The zircon U-Pb analyses yielded protolith ages of 251±2.7Ma and 268±2.5Ma for blueschist, and 260±12Ma and 251±4Ma for greenschist in the Yilan area. Additionally, protolith ages of 259±3.1Ma and 264±13Ma were obtained for amphibole schist and albite-amphibole schist in the Luobei area. After statistical analysis of the Ar-Ar ages of metamorphic single minerals in the Jilin-Heilongjiang high-pressure belt (Ji-Hei HP belt), it was found that metamorphic single muscovite has an isotopic age peak of 185Ma, representing the time of the blueschist-facies metamorphism in Heilongjiang. Our findings indicate that the opening of the Jilin-Heilongjiang Ocean occurred during Middle Permian to the Late Permian (268~251Ma) and its subduction occurred at Early Jurassic (~185Ma). The results of this study indicate that the opening of the Jilin-Heilongjiang Ocean, which developed between the Jiamusi and Songliao terranes, occurred during the Middle to Late Permian (268~251Ma) and closed during the Early Jurassic (peak age of 185Ma). The Jilin-Heilongjiang Ocean exhibits a trend of progressive closure and disappearance from west to east, which resulted in the formation and emplacement of the Zhangguangcai Range Complex (260~194Ma) earlier than the Heilongjiang Complex (256~185Ma).The Zhangguangcai Range Complex Belt was first located on the eastern edge of the Songliao Block during the Early Jurassic (194~185Ma), and after the Early and Middle Jurassic (~185Ma), the Heilongjiang Complex was located on the western edge of the Jiamusi Block. The Early Jurassic (194~185Ma) was the era of the formation and positioning of the Jilin-Heilongjiang high-pressure metamorphic belt, and also a crucial geological period when the Paleo-Asian Ocean closed and the Paleo-Pacific subduction was initiated, marking the superposition and transformation of the two major tectonic domains.