Structural and magmatic evolution in the Loimaa area, southwestern Finland

U-Th-Pb zircon geochronology on igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: Constraints on the age of volcanism and metamorphism

“…These include 1.83 − 1.79 Ga metamorphic ages in Bergslagen in Sweden (Andersson et al, 2006b and references therein). In southwestern Finland there is zircon data on 1.85 Ga and 1.83 Ga metamorphism (Torvela et al, 2008), 1824 ± 5 Ma and 1804 ± 14 Ma leucosomes and c. 1830 Ma and younger monazite data from granites (Suominen, 1991;Nironen, 1999;Ehlers et al, 2004). From the West Uusimaa area there are from c. 1.85 Ga to 1813 ± 4 Ma granites (Kurhila et al, 2005;Skyttä & Mänttäri, 2008) and from 1832 ± 2 Ma to 1792 ± 5 Ma metamorphic ages (Mouri et al, 2005 and this study).…”

“…This marks the minimum age of the synvolcanic stage and the commencement of the synorogenic stage. In the Turku area, the latter magmatism is slightly younger, at around 1870 Ma (Nironen, 1999;.…”

“…Ages close to 1795 Ma are quite common in crustally derived plutonic rocks in SW Finland. In addition to several post-orogenic intrusions dated in Suominen (1991), monazite from the Oripää Granite in the Loimaa area has been dated at 1794 ± 10 Ma (Nironen, 1999), monazite in the Torsholma pegmatite yielded an age of 1795 ± 4 Ma and zircon in the Sottunga Granite, within the South Finland shear zone, yielded an age of 1790 ± 6 Ma (Ehlers et al, 2004). The 1790.6 ± 7.5 Ma zircon cores in the Åva granite are also interpreted to indicate the age of magma formation, although it was emplaced later at c. 1762 Ma (Eklund & Shebanov, 2005).…”

The Oripää granite, SW Finland: Characterization and significance in terms of Svecofennian crustal evolution

“…It is a small (~20 km 2 ) stock surrounded by metamorphic rocks (migmatite, horn- Nironen (1999). blende gneiss) and is petrographically quite heterogeneous with a coarse (pegmatitic) appearance and abundant inclusions of garnet-bearing biotite gneiss and hornblende gneiss (Nironen 1999). The U-Pb systematics of the Oripää granite are also heterogeneous with two distinct zircon populations that yielded upper intercept ages of 1850 ± 27 and 1860 ± 41 Ma (Nironen 1999). A concordant monazite has a 207 Pb/ 206 Pb age of 1794 ± 10 Ma.…”

“…We have studied the Oripää granite (Nironen 1999) in the western part of the southern arc complex in order to extend the isotopic data set on the granitoids of this terrane. In this report, we present elemental geochemical and Nd and Pb isotopic data on the Oripää granite and compare these to those of the granitoids of the CFGC region farther to the north.…”