Metamorphism, migmatization and granites of the Mashan Complex in Heilongjiang Province, Northeast China
麻山杂岩的变质-混合岩化作用和花岗质岩浆活动

Both high-grade and middle-grade metamorphisms are developed in the Mashan Complex in the Jiamusi Block, Heilongjiang Province, Northeast China. In the high-grade area occurs the migmatization related with anatexis, while intensive injection migmatization prevails in the whole Mashan Complex. As the presence of euhedral plagioclase, albite rim along earlier plagioclase, the transformation textures of biotite to hornblende in the leucocratic granitic veins or bodies. It is deduced that the migmatization was predominantly derived from the magmatic injection from the deep, rather than in-situ anatexis after high-grade metamorphism. The anatexis was confined to granulite metamorphism area while the injection migmatization were widespread. With the age of ca. 500Ma, the injection migmatization was responsible for the amphibolite-facies metamorphism in the large area and retrograde grade metamorphism in the high-grade part. The middle-grade metamorphism was resulted from, not in, the injection migmatization. Although demonstrating some features of S-type granite, the synthetic analysis of mineral assemblages and geochemical characteristics show that the migmatization granite was basically I-type, or the KCG type of Barbarin (1999). The magmatism occurred in the transitional period from compression to extension. Both the metamorphism and migmatization features of the Mashan Complex suggest that some tectono-thermal activity similar to the Pan-african event in the Gondwana took place at the southern margin of the Siberian Craton, and the scale here may be smaller and there was a rapid shift of structural regime from metamorphism to tremendous magmatism activity.