PECULIARITIES IN COMPOSITION OF MINERALS FROM PLUTONS OF THE PON'GOMA-VILLAGE REGION, DUE TO THEIR POLIMETAMORPHISM (BELOMORSKY-LAPLANDIAN BELT)

摘要

Garnets, pyroxenes, hornblendes, biotites and feldspars appeared consequently within enderbites, crystal-line schists, granodiorites, mafic dykes of several generations, while the polymetamorphism, during 1 billion years. There are four periods of granulite fades metamorphism events revealed for enderbites by the connected structural transformations. Among them, the first one was related to the II stage, and the last three - to the Ill-rd stage of the whole development. Granitoids was the younger rocks formed under amphibolite facies. But they reflect no lesser than two episodes related also to the III stage and influencing enderbites too. Transformations of the low-temperature amphibolite facies overexposed upon both plutons and dykes (the IV stage). In accordance to decrease of pressure and temperature, the above mentioned minerals become more ferruginous, with the higher Mn content, but with decrease of Ti and, in some eases, Ca. Wide variations in composition of each mineral within limits of one and the same sample testify to the absence of equilibrium during the studied transformations. It has been revealed that, while the polimetamorphism, the fluid components of rocks was the most unstable, so as plagioclases and zircons appear to be the most stable minerals.