100 years of migmatite - In Sederholms footsteps
Field guide (PDF 1.24 Mb)
Leaders: Olav Eklund (chief organizer: email@example.com) University of Turku; Peter Sorjonen-Ward, Geological Survey of Finland; Tapani Rämö, University of Helsinki; Carl Ehlers Åbo Akademi University; Pentti Hölttä Geological Survey of Finland; Markku Väisänen University of Turk; Matti Kurhila, University of Helsinki
Purpose: In 2007, 100 years will have passed since J.J. Sederholm published his paper "Om granit och gnejs, deras uppkomst, uppträdande och utbredning inom urberget i Fennoskandia " (On granite and gneiss, their origin, relations and occurrence in the Pre-Cambrian complex of Fenno-Scandia). This paper can be seen as the trigger of research in crustal melting processes. Sederholm''s contribution was remarkable because of its wide scope, from analysis of processes in outcrop, to the regional scale. We will arrange an excursion for 20 persons to Sederholm´s key localities, compare his 100 year old observations with the latest data from the same area. The excursion will focus on the regional evolution of the accretionary arc-complex of southern Finland. Particularly the formation of migmatites during the regional high grade metamorphism between 1840 and 1805 miljon years ago. The migmatites will be discussed from a number of view points:
- P-T regimes and melting processes
- Effect of protolith composition and changes in protolith composition by melt flux and loss
- Self-organizing differentiation processes
- Recognition and classification of migmatite structures and processes
- Strain patterns in relation to melt generation, segregation and extraction, and magma transfer and accumulation
- Fractal spatial analysis of magma transport
- What are migmatites? Residue? Transfer zones? Plutonic pathways? Aborted plutons?
- The crustal scale record of magmatic processes - the seismic view
- Magmatic processes at different crustal levels
The excursion will also visit classical sites where Sederholm classified four different granite generations in southern Finland.