Structural position of Devonian alkaline occurrences in the Kola Peninsula

Terekhov E.N., Baluev A.S., and Przhiyalgovskii E.S.

Geological Institute of the Russian Academy of Sciences, Moscow, Russia

New information was obtained on the basis of modern geophysical investigations, carried out in the sea areas surrounding the Kola Peninsula (Zhuravlev, 2006.). It allows consider in a different way the geodynamic position of well investigated sites of alkaline magmatism in the northeastern part of the East European platform. The Kola Peninsula contains a lot of alkaline massifs and dykes. At present, the age of all massifs, dykes, and explosion pipes was dated as 380-360 Ma (Кramm, Kogarko, 1994). Though more ancient and younger age dating is also available, it is still believed that alkaline rock occurrences were mostly developed in the Kola Peninsula within this comparably short time interval. In addition, a great number of dikes of the basaltic composition occur along the Murmansk coast of the Kola Peninsula. In this case the age was also dated as Devonian (Arzamastsev et al., 2009).

Studies of aero- and satellite images allowed creation of a structural scheme of the region, while the data intended for interpretation of the geophysical materials on water area surrounding the Kola Peninsula, were used to perform the geodynamic analysis of this territory and to outline the main principles of alkaline rocks distribution (fig.1). We believe that two significant events controlled the development of the region: drifting of the Kola Peninsula in Baltia with elements of clockwise rotation (Baluev, 2006) and rifting generating the East-Barents Trough with its prolongation zone. The main structural elements of drifting were the fault zones bordering the Kola Peninsula, known as the Karpinskii Fault and Kovdoro-Gridin Zone. The identified S-shaped structure, proposed to be called Chupino-Svyatonos, is also an important element. A characteristic feature of the faulted drifting structures was the changing polarity of their inclination. The Kovdoro-Gridin Zone at its different segments has at times NE dipping, at others, SW dipping; places of changing polarity, the so-called accommodation zones, incorporate most abundant dyke magmatism, “clusters” of alkaline dykes (Baluev et al., 2009) . The eastern flank of the Chupino-Svyatonos zone is NW dipping, whereas its western flank with widespread massifs of ultramafic-alkaline complex dips towards the top of the Kandalaksha Bay. The bending and polarity change segment is abundant in kimberlitic explosion pipes of the Tersk coast.

Quite different alkaline rocks develop in the rifting Khibini-Contozero zone: these are nepheline syenites of the Khibini, Lovozero, of the Nivе and Contozero massifs, as well as numerous NE trending dykes. In the continuation of this zone, in the Barents Sea water area, geophysical data suggest the existence of massifs of the basic and intermediate composition. In the closing zone of this structure in northern Karelia, there are diamond finds (Polyakov, 1997), which seem to be related to dyke-type kimberlites, tuffisites and other rocks, rather than to usually kimberlite of explosion pipes. An analogous zonation, spanning from the oceanic rift across basalts and alkaline intrusions towards dyke-type kimberlites, is known in Western Africa (Haggerty, 1992).

Thus, crustal structures of the drift and rift types determined both the structural position of isolated occurrences of alkaline and kimberlite magmatism, and the differences in their lithological composition. At the same time, mantle heterogeneities, among them, the lithosphere “keel” or nuclear edge, controlled the very appearance of alkaline magmatism in this region.

This study was financially supported by RFBR grant 09-05-00812

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