H. Kujala’s scientific contributions

The~1.88 Ga VaasaVaasa 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 Al2 O3 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.

This report consists of results of bedrock mapping in Pohjanmaa covering three 1:100 000 map sheets: Oravainen (1334), Lapua (2311) and Alahärmä (2312). The fieldwork was carried out during 2002-2006 by the staff of GTK. In addition, most of the mapping in the Alahärmä map sheet area was carried out by University of Turku in 2004. The map area is part of the Palaeoproterozoic Pohjanmaa schist belt, and the bedrock is clearly divided into two main parts. The main rock type in the region is a heterogeneous rock called Vaasa granite. It has formed from mica gneisses through melting to various degrees and re-crystallization. Eastern and southern parts of the mapped area form part of the Evijärvi schist belt where the dominant rock types are psammitic and pelitic metasediments. Chemical compositions indicate that the Vaasa granite has evolved from Evijärvi-type metagreywackes almost isochemically. In terms of mineralogical and chemical composition Vaasa granite is mainly granodioritic, but granitic areas also exist. The appearance of the rocks is very variable, but can roughly be divided into even-grained and porphyritic types. Garnet and quartz aggregates are common, though not present throughout the Vaasa granite. Locally, there is also orthopyroxene. In the Lapua-Alahärmä region, the main rock type is unoriented and its appearance is similar to intrusive rock. In the more western Oravainen and Vöyri-Maksamaa regions, the rocks are more heterogeneous and include abundant mica gneiss remnants melted to variable degrees, biotite-rich restites and skarn concretions. In these areas, the rock is commonly ductilely deformed and in places migmatitic. Inside the domain of heterogeneous granodiorite, there are several localities of homogeneous, even-grained to porphyritic granites which in this report are given the common name of Vöyri-type granites. On the basis of age determination from the Isomäki granite, at Vöyri-Maksamaa, they belong to the granites of the 1.88 Ga age group. Ultramafic Ni-critical intrusions have been discovered on the bottom of the Bay of Oravainen in diamond drilling by exploration companies. Metasedimentary rocks in the Evijärvi schist belt, in eastern and southern parts of the map area, are migmatitic. They are mainly psammitic and pelitic mica gneisses with graphite-sulphide interbeds. Metacherts, graphite-sulphide schists and banded metavolcanic rocks dominate in the Simpsiö area and its surroundings. The schist belt also contains several small tonalitic and granitic intrusions and minor volcanic-sedimentary interbeds. Metamorphic grade in the schist area is mainly at amphibolite facies, though in the Kauhava-Kortesjärvi region it has in places increased to granulite facies. Vaasa granite has developed from sedimentary rocks by gradual melting under PT conditions varying between amphibolite and granulite facies. Large volumes of bedrock aggregate are used in the map area to replace glacial gravel as building material. Hence, there are numerous aggregate quarries. The local aggregates are, at best, of moderate quality but still suitable for normal building. High-quality bedrock aggregates have not been detected from the area. The Punakari granite has been quarried for building material outside the mapping area. In addition, small volumes of porphyritic Vaasa granite have been used in building house bases and facades. There are no metal mines, historic or recent, in the area. The nickel deposit under the Bay of Oravainen is the most intensely investigated metal deposit in the map area. The text is in Finnish, with figure and table captions and conclusions in English.

This report gives results of lithological, geochemical, metamorphic and structural studies as well as radiometric age determinations and ore potential of the South Ostrobothnian schist belt, part of the Palaeoproterozoic Svecofennian schist belt, Western Finland. The fieldwork was carried out from 1994 to 2000. A geological map at scale 1: 200 000 is presented. Distinctive lithological assemblages, geochemical characteristics and geophysical features can be used to divide the study area into two schist areas. The eastern schist area is composed of mica gneiss and veined gneiss, calc-alkaline metavolcanics, silicate and oxide facies iron formation and dolomite-dominated carbonate rock. The western schist area is characterised by mica gneiss, veined gneiss, metatexite and diatexite together with tholeiitic metavolcanite associated with graphite sulphide schist and metachert containing iron oxide, iron sulphide and manganese silicate. The generally north-south trending contact of the two schist areas swings towards the east in the north. The mostly gradational contact is sheared in places or may even be fault-bounded. Most of the airborne geophysical conductivity anomalies occur in the western schist area, signifying occurrences of graphite-sulphide schists. The metasedimentary rocks of both schist are as are chiefly metaturbidites. Depending on the grade of metamorphism the rocks are classified as mica schists, mica gneisses, metatexites or diatexites. The most extensive diatexite covers an area known as the Vaasa granite. Besides this terrain, east of Vaasa, diatexites form extensive areas also along the coastal strip between the town of Vaasa and the county of Merikarvia. The metavolcanic rocks are divided into five units. The Laa kavuori Unit is situated within the eastern schist area and is composed of predominantly pyroclastic rocks ranging from calc-alkaline basalt to rhyolite although intermediate compositions prevail. Geochemically the Laakavuori Unit resembles the basalts of modern continental island arc settings. The Vittinki, Lerviken and Solax Units, all within the western schist area, are tholeiitic and are geochemically close to basalts and andesites of modern oceanic tectonic settings. Komatiitic and picritic metavolcanites of the Orrmossen Unit are exposed along the contact zone of the two schist areas in the middle part of the study area. They are characterised by aluminium undepleted chemistry and a mantle plume model for their genesis is proposed. The stratigraphic relation of the two schist areas was not possible to solve in the field, but correlation with neighbouring areas implies a younger deposition age of the eastern schist area. Contemporaneous deposition of different sedimentation facies environment cannot be ruled out, however. Svecofennian synkinematic 1.89-1.88 Ga tonalites and granodiorites intrude both schist areas. Some 1.88-1.87 Ga postkinematic pyroxene granitoids and postkinematic granites are common in the southern and south-eastern part of the area whereas post orogenic granites and ca. 1.80 Ga granitic dikes occur in the north near Vaasa. Near the coast anorogenic rapakivi granites (1.56-1.57 Ga) at Siipyy and Böle cover 10-20 km2. Further inland, two small intrusions (Orisberg and Käräjävuori) are classified as rapakivi-type due to their chemistry and texture. Svecofennian orogenic metadiabases cut supracrustal rocks as narrow deformed dikes. Anorogenic, linear Subjotnian diabases, both fine grained and coarse grained, intrude the country rock in two principal directions, N-S and E-W. Post-Jotnian olivine diabases occur only in the archipelago. Metamorphic grade in the South Ostrobothnian schist belt varies from lower amphibolite to granulite facies, with a facies series of andalusite-sillimanite type. The area has undergone polyphase deformation including both plastic and rigid phases. Potential economic minerals in the study area are nickel and copper sulphides, calcite, dolomite, graphite, ilmenite, apatite and gold. Favourable nickel potential, for example, is shown by the abundance of mafic magma in the crust manifested as small discrete gabbro and peridotite intrusions scattered especially throughout the western schist area. Sulphur, an important element for the enrichment of nickel sulphides, is also available especially in the western schist area. Also, encouraging is the correlation of the nickel bearing Pirkanmaa belt with the western schist area. However, the amount of peridotite cumulates critical for nickel are rare, possibly partly due to poor and selective exposure conditions.