Zircon SHRIMP U-Pb ages of gneissic granites in Jiamusi massif, northeastern China.

The Jiamusi massif in northeastern China is characterized by the widespread granitic intrusions, which can be divided into two major types, granitic gneisses and gneissic granites. The granitic gneisses had undergone the amphibolite to granulite facies metamorphism of 500 Ma, and have the same gneissic structures as those of Mashan Group of basement. The gneissic granites are characterized by magmatic crystallized fabric and did not show any sign of later stage metamorphism. Though these gneissic granites were thought formed in Neo Proterozoic, our zircon SHRIMP U Pb dating results suggest that they were emplaced in Late Paleozoic of 270～254 Ma. The inherited zircon grains or cores in some of these rocks support that they resulted mainly from the partial melting of the basement rocks of Mashan Group. The mineral associations, chemical compositions of analyzed samples suggested that these granites were related to the suturing between the Jiamusi Massif and surrounding micro continents or terranes, or to the collision of terranes within the Jiamusi Massif.