Seminar

The Heilongjiang Complex represents a remnant of an oceanic plate suturing between the Jiamusi and Songliao blocks in NE China. Controversy has long surrounded the timing and origin of the complex, as well as its relationships between the Jiamusi and Songliao Blocks. We propose that the complex records evolution of an ocean between two blocks.

The ocean had been evolving from an intracontinental rifting since ~275Ma based on the geochemical and geochronological data of the mafic rocks in the complex. Progressively, the rifting developed into an ocean in which several oceanic islands were developed, as evidenced by the discovery of alkali rocks with OIB affinities and protolithic ages of 186±1Ma, 162±4Ma and142±1Ma. The subduction of the ocean took place in the Jurassic, resulting in formation of an active continental margin at the eastern margin of the Songliao blocks with large exhumation of I type granitoids and emergence of ~188 Ma andesitic rocks with arc features. Moreover, the blueschist-facies metamorphism of the complex that resulted from the subduction has been considered to take place in Middle-Early Jurassic according to new mineral Ar-Ar datings. The termination of this subduction between Jiamusi and Songliao blocks took place in Early Cretaceous.