Editorial handling: Joonas Virtasalo The ~1.88 Ga Vaasa Batholith in western Finland is a large granitoid area (8 000 km 2) with gradational contacts against the garnet-and cordierite-bearing diatexite and metatexite migmatites of the Pohjanmaa Belt. It is located in the middle part of the Fennoscandian Shield and was formed during the Svecofennian orogeny (1.9-1.8 Ga). The Batholith area consists of porphyritic and even-grained granodiorite with smaller proportions of granite and pyroxene granitoid. The various phases in the Vaasa Batholith mainly grade into each other and usually contain relicts of Ca concretions and schists, biotite and garnet, locally resembling uniform diatexites. All the phases are peraluminous in composition. The Mg# of biotite in the granodiorites and pyroxene tonalites is high (50-60), in contrast to lower values in the granite (20-35). Orthopyroxene in the tonalite has an elevated Mg# value and Al 2 O 3 concentration. In Harker diagrams, bulk composition of the tonalites, granodiorites and granites of the Vaasa Batholith evolves along the same path, but the metatexites are beyond or cutting the path. The textural, mineralogical and chemical continuity between the granodiorites of the Vaasa Batholith and the adjacent diatexites indicate that the Vaasa Batholith represents a magma layer formed by extensive in situ melting of the crust. The diatexites are mainly from the inhomogeneous magma, although they texturally grade to the metatexites. The Vaasa Batholith and adjacent diatexites are separated from the metatexites of the Pohjanmaa Belt by 'magma interface' (MI). The metatexites formed in a conduction heat flow zone above the MI. The Vaasa Batholith is an exceptional type example of the voluminous and diverse granitoids in Finland.
Extensive biotite diatexites resembling S-type granitoids occur in the eastern part of the Vaasa Migmatite Complex (VMC, 1.89 Ga, 6000 km 2 ) at Kauhava, western Finland. These rocks have undergone a textural homogenization that has destroyed the primary bedding. Pre-migmatization structures are preserved only in inclusions. The diatexites are clearly peraluminous and have relatively high concentrations of TiO 2 (0.7-0.9 wt%), CaO (2.4-3.0 wt%) and total of Fe 2 O 3 tot + MgO (6.6-8.8 wt%). The contact of the diatexites against pelitic metatexites is usually a gradual zone, 1-200 m wide, but locally a boundary limiting places of higher melt fraction. The contacts indicate that the anatectic melt formed, with residual solids, has not ascended greatly; the VMC forms the most voluminous in situ melted rocks with granitoid appearance in Finland.The study area also includes peraluminous orthopyroxene-bearing rocks, granitic in texture, which are hornblende free and have relatively high TiO 2 (1.0-1.2 wt%) and MgO (2.1-2.5 wt%) contents. They gradually change to biotite diatexites and also suggest fusion of metasedimentary rocks at reduced a H2O . The chemical composition of minerals in the orthopyroxene-biotite diatexite indicates crystallization conditions of high-grade metamorphism; X Mg in garnet is 0.23, orthopyroxene has 3 wt% Al 2 O 3 and biotite contains over 5 wt% TiO 2 .
The Palaeoproterozoic Svecofennian bedrock of the Seinäjoki-Ilmajoki area, western Finland, is largely composed of porphyroblastic metapelites. In the area, the regional metamorphic grade increases towards the southwest. Over a distance of 15 km, andalusite mica schists gradually grade into migmatitic garnetcordierite-sillimanite mica gneisses with a facies-series of the andalusite-sillimanite type. Five regional metamorphic zones are present: andalusite, sillimanite-muscovite, sillimanite-K-feldspar, cordierite-K-feldspar and garnet-cordierite-K-feldspar. The primary layering (S 0) of the mica schists is deformed by an isoclinal fold phase (F 2), which is synchronous with the main metamorphic phase and the growth of micas. S, is very weak and subject to interpretation. The S 2 schistosity is deformed by intense late-metamorphic F 3 and F 3b folds, which have formed under slightly different metamorphic conditions: practically no metamorphic micas have grown parallel to axial planes while within F 3b folds there are a few granitic veins parallel to these planes. The F 3 and F 3b folds probably belong to one phase. S 2 dominates in the mica schists while S 3 and S 3b dominate in the mica gneisses. The metapelites are also deformed by younger minor fold phases (F 4 and F 5). A composite schistosity (S C j±S,±S 2 ±S, or S 3b) commonly occurs in the metapelites. The peak of regional metamorphism has been associated with the intrusion of 1.89-1.88 Ga old tonalite plutons. Geothermometric estimates for regional metamorphism are c. 730 °C at an assumed pressure of 5 kbar. Neosomes in the high-grade mica gneisses occur as patches rather than as elongated, narrow veins. Garnet coexists with cordierite, but the minerals are rarely in equilibrium. Muscovitization and the formation of retrogressive andalusite did not occur in the high-grade mica gneisses, but there is minor kyanite indicating that the crust probably underwent near-isobaric cooling. The area of highest-grade regional metamorphic conditions contains a post-kinematic mangeritic quartz monzonite (1.87 Ga), which has a narrow granulite-grade contact aureole. The chemical composition of biotites in the metapelites varies as a function of metamorphic zoning, but the chemical composition of metapelites remains mostly unchanged.
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