Abstract
The Nyasyukka dike complex forms a NW-trending dike swarm in the Archean bedrock of the Murmansk Province adjacent to the Pechenga Complex. The dikes are mostly composed of two rock types, kaersutite-bearing peridotites and olivine gabbros. Also a rounded pyroxenite stock has been found in the area. The dikes were generated from ferropicritic parental magma which was similar to Pechenga ferropicrites though having a somewhat higher silica activity. A peridotite sample yielded an internal Sm-Nd isochron with an age of 1956 ± 19 Ma (MSWD = 0.7) and an initial 6 Nd value of +1.4 ± 0.4. This is consistent with the baddeleyite age of 1941 ± 3 Ma, showing that the Nyasyukka dikes are ca. 40 Ma younger than the Pechenga ferropicrites. The pyroxenite stock shows geochemical and Nd isotopic evidence for significant crustal contamination. We also present isotopic and geochemical data for olivine gabbro-norite from the Tuloma River area, supporting the earlier view that there exist dikes of the Nyasyukka type in this area.
Highlights
Several generations of mafic dike have been found in the Archean TTG gness bedrock in the area outside the northeastern margin of the Paleoproterozoic Pechenga Varzuga Belt in the Kola Peninsula [Smolkin, 1993, 1997; Fedotov, 1995; Arzamastsev et al, 2009] (Figs. 1, 2)
No apparent volcanic or deep seated, intrusive counterparts have been found for the first group, while close compositional analogues for the Paleoproterozoic dikes have been recognized among the volcanic and intrusive rocks occurring in the adjacent Pechenga Varzuga Belt
Among the dikes found in the Archean bedrock on the NE side of the Paleoproterozoic Pechenga Complex, there is a somewhat heterogeneous, but geochemically correlative group of mafic to ultramafic dikes, which have been assigned to the Nyasyukka dike complex
Summary
Several generations of mafic dike have been found in the Archean TTG (tonalite trondhjemite granodiorite) gness bedrock in the area outside the northeastern margin of the Paleoproterozoic Pechenga Varzuga Belt in the Kola Peninsula [Smolkin, 1993, 1997; Fedotov, 1995; Arzamastsev et al, 2009] (Figs. 1, 2). The last type includes kaersutite bearing peridotites and olivine gabbros of the Nyasyukka dike complex, which have earlier been regarded as comagmatic with the ore bearing gabbro wehrlite intrusions and ferropicritic volcanic rocks of the Pechenga Group [Fedotov et al, 1974; Fedotov, 1995; Smolkin, Borisova, 1995]. 100 km southeast of Pechenga, in the Tuloma River area southwest of Murmansk (see Fig. 1) Dikes of this affinity have been found in the Monchegorsk area close to the north western end of the Imandra Varzuga supracrustal belt where they penetrate Archean gneisses and a Paleoproterozoic mafic layered intrusion [Dokuchaeva et al, 1989]. Included was one olivine gabbro norite sample from the Tuloma area
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