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LA‐ICPMS zircon U–Pb dating of the Heilongjiang Complex in the Luobei area: New constraints for the late Palaeozoic‐Mesozoic tectonic evolution of Jiamusi Block, NE China

The Heilongjiang Complex is a sequence of high‐pressure (HP) metamorphic rocks that are distributed along the N‐S suture zone between the Jiamusi and Songliao blocks in NE China. In this study, we investigated samples from Luobei in order to understand the geochronological and tectonic framework of the Heilongjiang Complex. The Heilongjiang Complex consists of two‐mica schist, muscovite‐albite schist, quartz schist, plagioclase gneiss, granitic gneiss, serpentinite, blueschist, greenschist, amphibolite, and marble. LA‐ICP‐MS dating of all samples shows a range of protolith ages from 435 to 210 Ma. These data, together with a 492 ± 6 Ma age from a granite gneiss sample in the Yilan area, indicate that the protoliths of the Heilongjiang Complex were formed over a protracted time span from ~490 to ~210 Ma. In addition, five zircon grains in two samples contain metamorphic rims that yield ages of 197 ± 2 Ma. These results, when combined with field evidence that the Heilongjiang Complex is overlain by Middle Jurassic strata, indicate it was metamorphosed between ~210 and 197 Ma and not in the Cretaceous as previously considered. This line of evidence, plus the occurrence of late Palaeozoic arc‐affinity volcanic rocks in the eastern margin of the Jiamusi Block and syn‐collisional Mesozoic volcanic rocks in the Zhangguangcai and Lesser Xing'an ranges, suggests the Heilongjiang Complex was a result of Panthalassa subduction during the late Palaeozoic and Paleo‐Pacific subduction during the Mesozoic.