Garnet amphibolite in the internal Eastern Segment, Sveconorwegian Province : monitors of metamorphic recrystallization at high temperature and pressure during Sveconorwegian orogeny

Abstract: The analyzed area exposes a deep underthrusting lower plate of the Sveconorwegian orogen and facilitates studying of an elsewhere hidden portion of the Earth. Petrographic and structural studies of different metamorphic rock types within the southern Eastern Segment, Sveconorwegian Province, Sweden, were carried out to better understand the regional metamorphism and deformation history. The analyzed rock types are migmatitic garnet amphibolite, migmatitic garnet poor amphibolite, quartz feldspar rich gneisses and metagranites, leucocratic granitic gneiss and coronitic metagabbro. Analyzed microtextures within the metagabbroic rock include coronitic textures. Such textures reveal the metamorphic history of the rocks and implies solid-state reactions forming such prominent coronites. Furthermore, penetrative coronitic texture together with a preserved igneous texture in metagabbroic rocks is an indicator of high-grade metamorphism in dry conditions, reaching granulite facies. Previous studies imply that the coronitic metagabbro and the migmatitic garnet amphibolite have an identical protholith, and that such can be traced throughout the Eastern Segment. The relict igneous texture of the coronitic metagabbro confirms dry conditions within the rock complex. Fluids did not percolate the system and the reactions where therefore inhibited and did not run to completion. Additionally, a regional scale fold within the garnet amphibolite, with the coronitic metagabbro located in the hinge zone, is suggested to cause a lack of fluid percolation due to deformational differences. Differences in deformation and metamorphism may be affected by folding as the hinge zone can be less deformed than the limbs of the fold. Conclusively, the coronitic metagabbro with its peculiar texture has been of substantial importance to monitor the metamorphic conditions and recrystallization processes. It supports previous studies within the region, that the rocks experienced high-grade metamorphism and deformation.