ZIRCON U-Pb CHRONOLOGY OF THE HEILONGJIANG COMPLEX IN MUDANJIANG AREA: Geological Implication

The Heilongjiang complex, mainly occurred in the western margin of Jiamusi massif along Mudanjiang fault, is a tectonic melange formed during the suturing of Jiamusi massif and Songnen massif. The complex is dominated by strongly deformed felsic mylonite, which contains a large number of ultrabasic rocks, metabasic lava (blueschist), meta-silicalite and marble blocks or slices with the nature of oceanic crust. The zircon LA-ICP-MS U-Pb dating of felsic mylonites in Mudanjiang area yields two groups of ²⁰⁶Pb/²³⁸U age data, with the weighted mean ages of 509.4±7.1 Ma (n=9, MSWD=1.3) and 269±1.9 Ma (n=22, MSWD=0.93). The zircons with the oldest ages of 2 420 and 2 459 Ma indicate that the complex contains ancient Paleoproterozoic materials. The age about 509 Ma is for advanced metamorphism and granitic magmatism of Mashan Group in Jiamusi massif. The age about 269 Ma suggests the deformed matrix of Heilongjiang complex be formed after Late Permian, which may be related to the closure of Paleo-Asian Ocean in Late Paleozoic.