Metamorphic development of cordierite-bearing layered schist and mica schist in the vicinity of Savonranta, eastern Finland

• Main Authors: N.M. Halden, D.R. Bowes
• Format: Article
• Language: English
• Published: Geological Society of Finland 1984-12-01
• Series: Bulletin of the Geological Society of Finland
• Subjects: Metamorphism; Svecokarelides; deformation
• Online Access: http://www.geologinenseura.fi/bulletin/Volume56/sgs_bt_056_pages_003_023.pdf
• ISSN: 0367-5211; 1799-4632

The sequential development of minerals in polyphase deformed schists of the Savonranta district can be demonstrated in a limited number of lithologies. Cordierite- bearing and micaceous schists are used to established a polymetamorphic history within an area where field mapping and structural studies have provided a basis for the erection of temporal relations of metamorphic fabric elements. Coexisting phases whose relative times of development have been established were selected for microprobe analysis and their compositions used in a quantitative thermodynamic study to determine temperatures and pressures of successive metamorphic events. Conditions deduced for the phase of metamorphism (M1) associated with the D1 deformational phase are c. 550°C and 3 kb. The peak of metamorphism, during M2‒D2 was at c. 700°C and 7.5 kb. Conditions for an M3 metamorphic event of c. 300°C and 2‒3 kb are estimated from mineral assemblages in P‒T space, not from mineral compositions. A late thermal event (ML') is related to the emplacement of porphyritic granite: c. 600°C and 4kb are estimated from mineral assemblages in P‒T space. A single outcrop of a layered schist, which is unique to the district, is interpreted as a tectonic slice from a deeper crustal level. It provides evidence of a low P, high T granulite facies metamorphic event (MEARLY) pre-dating M1‒D1.