| Abstract [eng] |
The Western Lithuanian Granulite Domain (WLG) is a crystalline basement structure occupying a large part of western Lithuania. The domain is composed of metamorphosed rocks. Felsic and intermediate metaigneous and metasedimentary rocks predominate. Granulites and other high-temperature rocks are important for the identification of geodynamic processes and are also useful for tectonic reconstructions. This work aims to investigate the metamorphism in Western Lithuania (Lauksargiai-1, Bliudžiai-150, and Pociai-3 drillings), to review a new material, to analyse the samples for bulk rock composition, to identify minerals, to (re)constrain peak metamorphism (P-T) parameters using phase equilibria modelling with “Perple_X”, to determine age of the peak conditions, and identify the type of metamorphism. Bulk rock analyses reveal that the investigated metasedimentary granulites (samples Lk1D, Pc3/6, and Bl150) are predominantly high-alumina, ferruginous pelites. Sample Lk1D records the evidence of both regional metamorphism at ~1.77 Ga and a subsequent thermal (contact) overprint at 1.60–1.70 Ga, the latter of which is clearly supported by phase equilibria modelling. Sample Bl150 has experienced a peak metamorphism followed by high-temperature thermal metamorphism at 1.62–1.63 Ga. Petrographic analysis and phase equilibria modelling defined the peak metamorphic assemblage: garnet, biotite, melt, K-feldspar, plagioclase, ilmenite, sillimanite, spinel, and quartz, indicating conditions consistent with partial melting. Sample Pc3/6 reveals a more complex metamorphic history, having undergone regional high-grade metamorphism at 1.76–1.79 Ga, followed by deformation and reheating between 1.53 and 1.57 Ga. During petrographic analysis and phase equilibria modelling the peak assemblage was revealed: garnet, biotite, K-feldspar, sillimanite, quartz, and rutile. To sum up, the studied samples illustrate the multi-stage metamorphic evolution of the Lithuanian crystalline basement, marked by a dominant regional high-grade metamorphism during the orogeny, followed by more localized high-temperature events during the Mesoproterozoic, driven by the intrusions. |
