Zonal garnets in gneisses Lapland granulite belt as a result of repeated high temperature metamorphism

摘要

New data on Yavr and Lotta areas allow to assume that granulite metamorphism appeared in Lapland granulite belt (LGB) repeatedly. Moderate and low-pressure metamorphism took place in the north-east (upper) part of the LGB complex, the highly baric one - in the south-western (lower) its part. Along the west-ward direction areas of high-pressure granulites decreases, so as fields of low-pressure granulites become larger. It is unlikely that those low-pressure coarse- grained and intensively migmatized cordierite-bearing rocks are a product of migmatization of the high-pressure granulites. Most probably, they represent the earlier stage of the granulite metamorphism. In the south-west part of LGB (the front zone of slip-thrust), while the later high-pressure stage of granulite metamorphism these rocks were transformed into small-grained thin-banded blastomylonites differing by their paragenesis, composition of minerals, character of migmatization and some peculiarities of regressive alteration. The new data on composition of minerals and zoning of garnets just give the possibility to define a difference between peak thermodynamic conditions during low-pressure (750-950 deg C, 5-6 kbar) and high-pressure (750- 800 deg C, 8-9.5 kbar) stages of the granulite metamorphism.