Two metamorphism Mashan rocks and granite

Two types of metamorphism have been discerned from the Mashan Complex in the Jiamusi Block, Heilongjiang Province, northeastern China. The local earlier granulite facies metamorphism (M1) was accompanied by fluid-absent anatexis (> 530Ma). The subsequent widespread magmatism was responsible for the intensive migmatization (500Ma) and corresponding late amphibolite facies metamorphism (M2). The former is actually the high grade Mashan Group (s. s.) and the metamorphic rocks are dominated by residual massives or enclaves scattered in late migmatitic granites. The change from amphibolite to granulite facies is not transitional or progressive, suggesting the great difference of the two kinds of metamorphism. The migmatization was probably fluid-rich and made substantial retrograded alteration to the earlier "dry" metamorphics, accounting for the complicated textures of the rocks. In addition, the emplacement of the fluid-bearing granites may reset the U-Pb system of the zircons formed in earlier high-grade metamorphism and the real metamorphic ages could be hardly measured. For the metamorphism-granite sequence, the Mashan Complex is rather similar to that of the Prydz Bay belt of East Antarctica. In both areas the deformation-metamorphism were closely followed by granites. The difference is that the intensity of late granitization varies in the two areas. Along the southern margin of the Siberian Craton and some microcontinents in the Central Asian belt occurred some tectono-thermal-magmatic events similar to that around the Gondwana margin. That is to say, the Jiamusi Block and other analogues in the Central Asian belt are tectonically similar to the Pan-African belts in the Gondwana, though they may belong to different domains in ancient continent configuration.