Abstract
The NE Fennoscandian Shield comprises the Northern Belt in Finland and the Southern Belt in Karelia. They host mafic-ultramafic layered Cu-Ni-Cr and Pt-Pd-bearing intrusions. Precise U-Pb and Sm-Nd analyses indicate the 130-Ma evolution of these intrusions, with major events at 2.53, 2.50, 2.45, and 2.40 Ga. Barren phases were dated at 2.53 Ga for orthopyroxenites and olivine gabbro in the Fedorovo-Pansky massif. PGE-bearing phases of gabbronorites (Pechenga, Fedorovo-Pansky, Monchetundra massifs) and norites (Monchepluton) are 2.50 Ga old. Anorthosites of Mt. Generalskaya (Pechenga), the Fedorovo-Pansky, and Monchetundra massifs occurred at 2.45 Ga. This event produced layered PGE-bearing intrusions in Finland (Penikat, Kemi, Koitelainen) and mafic intrusions in Karelia. The Imandra lopolith dikes occurred at the final phase (2.40 Ga). Slightly negative εNd and ISr values (0.703–0.704) suggest that intrusions originated from an enriched mantle reservoir. Low 3He/4He ratios in accessory minerals (ilmenite and magnetite) indicate an upper mantle source. Large-scale correlations link the Fennoscandian Shield with the Superior and Wyoming cratons.
Highlights
The NE Fennoscandian (Baltic) Shield covers the Archaean crust formed at 3.5–2.7 Ga [1,2].The post-Archaean evolution is mainly reflected in rifting and emplacement of mafic-ultramafic complexes along NE-trending structures
FKB extends 350 km along the northern edge of the Karelian craton. It comprises Palaeoproterozoic mafic-ultramafic layered bodies in Finland (e.g., Penikat, Kemi) [4,5,6], Sweden (Tornio intrusion), and Russia (Olanga group) [7] that occurred in similar geodynamic settings [8]
This paper provides new data showing that magmatism in the Kola-Karelian Province correlates with the peak of mafic-ultramafic magmatism magmatism in the Kola-Karelian Province correlates with the peak of mafic-ultramafic magmatism in in the Superior and Wyoming provinces (2.45 Ga)
Summary
The NE Fennoscandian (Baltic) Shield covers the Archaean crust formed at 3.5–2.7 Ga [1,2].The post-Archaean evolution is mainly reflected in rifting and emplacement of mafic-ultramafic complexes along NE-trending structures. The NE Fennoscandian (Baltic) Shield covers the Archaean crust formed at 3.5–2.7 Ga [1,2]. The NE Baltic Shield hosts the Southern (Fenno-Karelian). Belt (FKB) and the Northern (Kola) Belt (KB) that we studied in detail in our profound research [3]. FKB extends 350 km along the northern edge of the Karelian craton. It comprises Palaeoproterozoic mafic-ultramafic layered bodies in Finland (e.g., Penikat, Kemi) [4,5,6], Sweden (Tornio intrusion), and Russia (Olanga group) [7] that occurred in similar geodynamic settings [8]. KB strikes northwestwards for over 500 km. It borders the SW edge of the Archaean Kola-Norwegian
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