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Publications (15)
The Orijärvi area within the Paleoproterozoic Uusimaa belt contains volcanic and minorsedimentary formations, providing valuable insights into the oldest Svecofennian crust insouthern Finland. Previously, felsic volcanic rocks from the Orijärvi, Kisko and Toija formationshave been dated at 1895 ± 3, 1878 ± 4 and 1878 ± 4 Ma, respectively. In the pr...
The E-MORB type Haveri basalt differs from the volcanic arc type rocks in the Tampere
belt showing no subduction signature. It is considered to have formed in a marginal
basin prior to the volcanic arc. We present here zircon U-Pb dating on two samples. The
basalt and the felsic dyke yielded 207Pb/206Pb ages of 1902 ± 5 Ma and 1891 ± 2 Ma,
respecti...
We characterise the geochemistry, zircon Lu-Hf composition, age and the structure of the Uunimäki gabbro (UGB) in south-western Finland to improve the understanding of i) the early Svecofennian (1.92–1.89 Ga) crustal evolution of the central Fennoscandian Shield, ii) the potential role of rift-related magmatism for the build-up of the Paleoproteroz...
The bedrock of the Salo area in SW Finland is mainly occupied by granitoids. We dated five granitoids and two mafic volcanic rocks with single zircon method. The granitoids fall in two age groups, 1.86-1.85 and 1.83-1.82 Ga. Mafic plutonic rocks occur in both age groups. The volcanic rocks are 1.90 and 1.89 Ga in age. Further, the samples display t...
Arclogites, i.e., lower crustal garnet-pyroxenite cumulates, are suggested to play an important role in controlling magma differentiation in modern continental arcs. Until now, arclogite-related magmatism has only been described from the Phanerozoic Era. The Svecofennian orogen in the central Fennoscandian Shield hosts a rare association of 1.86 Ga...
The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of...
The Mawat ophiolite, NE Iraq, is one of the Neo-Tethyan ophiolites within the Iraqi Zagros orogen. It consists of many metre-to kilometre-sized tectonic slices of serpentinized dunite, peridotite, gabbro, basaltic rocks and associated oceanic metasediments. Felsic intrusions crosscut the ophiolite. We present U-Pb zircon and monazite ages and Hf zi...
The earliest Svecofennian magmatism in southern Finland has been dated at 1.90-1.88Ga. As an example of this, the Orijärvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. Here, we report geochemical and Sm-Nd isotope data from int...
High Field Strength Element ratios, in particular Nb/Ta and Zr/Hf (~17,5 and 36, respectively; Sun & McDonough 1989), in the unfractionated Earth are assumed to follow those of the chondrites. However, the Nb/Ta ratio of the Earth’s crust and mantle show subchondritic values (~ 12-15) which have led to so-called “Nb/Ta paradox” and searching for a...
We describe here a newly discovered cross-cutting mafic dyke in the vicinity of Lohja, southern Finland. The dyke is E-W trending and about 6 m in width. Only a few zircons were recovered from the dyke despite the high Zr contents and they all were inherited. Therefore, the crystallisation age remains uncertain. The dyke is shoshonitic in compositi...
The geochemical composition of seven post-kinematic mafic dykes in southern part of Central Svecofennia have been studied. Two dykes have been selected for in situ zircon U-Pb geochronology and one for in situ zircon Lu--Hf isotope analysis. These c. 1.86 Ga dykes can be divided into two subgroups by their geochemical characteristics: i) an enriche...
The Svecofennian bedrock in the Salo area in SW Finland comprises granitoids and migmatised metasedimentary and metavolcanic rocks, metamorphosed in higher amphibolite and granulite facies conditions. The area is characterised by subhorizontal structures in large areas. We performed U-Pb zircon and monazite age determinations on two granites using...
