Abstract The tectonic position of the Palaeozoic alkaline complexes containing phoscorites and carbonatites is determined by the combination of three factors. These are (1) the presence of rift systems; (2) the presence of deep fracture zones; (3) the powerful energetic excitement of lithosphere with an epicentre in the region of the Khibiny complex, i.e. the action of a mantle plume or ‘a hot spot’. The ages of alkaline magmatism in the eastern part of the Baltic Shield are in general synchronous with the manifestation of alkaline magmatism in the whole of the North Atlantic Alkaline Province. Early Palaeozoic alkaline magmatism on the Kola Peninsula is small-scale compared with that in western Fennoscandia. It consists of diatremes and dykes of olivine melilitite-alnöite-carbonatites. The formation of the carbonatitic ultramafite-foidolite complexes started in the early Palaeozoic. The peak of alkaline magmatism, of volcanic activity, large intrusions, and dykes, took place in the late Devonian, forming the Devonian Kola Alkaline Province (KAP). As a whole, the carbonatites in their various different forms and sizes are related to six petrogenetic types and varieties of alkaline complexes and dykes. They are: (1) Proterozoic complexes of ultramafic/mafic rocks-foidolites-foidosyenites; (2) dykes and diatremes of the early Palaeozoic series of the Kandalaksha Graben; (3) Kandagubian seriesdykes; (4) Turiy series dykes; (5) Palaeozoic plutons of alkaline-ultramafic rocks; (6) agpaite nepheline syenite complexes. A quantitative model proposed for the formation of the carbonatites involves liquid immiscibility from an evolved carbonated nepheline melilitite melt.

ABSTRACT The oldest alkaline silicate rocks known are Archaean (2700–2600 Ma) lamprophyres and alkali syenites. Several Proterozoic alkaline gabbroic intrusions which in part also contain carbonatites occur between 2000 and 1800 Ma. Intensive alkaline magmatic activity formed more than 20 complexes (Kola Alkaline Province, KAP) during the Palaeozoic between 410 and 362 Ma with the majority of ages being between 382 and 362 Ma. The data show no systematic geographical distribution of ages within the KAP so that timing of magmatic activity cannot be correlated to the major tectonic structures. A distinction of the intrusions into Caledonian and Hercynian groups is not supported. A lithologically controlled variation of ages within single complexes can neither be seen betweencarbonatites and associated alkali silicate rocks nor between carbonatites and phoscorites.