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 g neisses and gneissic granites. The granitic gneisses had undergone the amph ibolite- to granulite-facies metamorphism of 500 Ma, and have the same gnei ssic structures as those of Mashan Group of basement. The gneissic granites are characterized by magmatic crystallized fabric and did not show any sig n of later stage metamorphism. Though these gneissic granites were thought formed in Neo-Proterozoic, our zircon SHRIMP U-Pb dating results suggest th at they were emplaced in Late Paleozoic of 270 similar to 254 Ma. The inher ited zircon grains or cores in some of these rocks support that they result ed mainly from the partial melting of the basement rocks of Mashan Group. T he mineral associations, chemical compositions of analyzed samples suggeste d that these granites were related to the suturing between the Jiamusi Mass if and surrounding micro-continents or terranes, or to the collision of ter ranes within the Jiamusi Massif.