ALKALINE VOLCANISM OF THE INITIAL PHASE OF PALEOZOIC TECTONOMAGMATIC REACTIVATION IN NORTHEASTERN FENNOSCANDIA - GEOCHEMICAL FEATURES AND PETROLOGIC CONSEQUENCES

This paper presents the results of studying the Paleozoic volcanic ser ies of the Kola Province, widespread in the areas of the Lovozero and Khibina massifs, the Kontozero caldera, and the Ivanovka volcanopluton ic complex. A distinctive feature of the volcanics is the presence of moderately alkaline basanites along with silica-undersaturated alkalin e rock associations. All of the rocks are significantly enriched in in compatible elements: the contents of Rb, Pa, Sr, Nh, Zr, and Y in the volcanics of the Lovozero and Kontozero formations are considerably hi gher than those in the alkaline basalts of continental associations fr om various provinces. The Sm-Nd and Ph-Sr data suggest that the volcan ics of the study area were derived from two different mantle sources: (1) superdepleted mantle material resulted from the multistage crustal growth over Archean and Proterozoic time in the Kola-White Sea rift-c ollision zone and (2) a source that had properties of moderately enric hed EMI-type mantle. It is shown that the emplacement of the volcanics preceded the main phase of alkaline magmatism in the region and can b e referred to as the initial phase of the Paleozoic tectono-magmatic r eactivation. According to geochronological data, the alkaline volcanic rocks were emplaced at least 20-30 m.y. before the intrusion of the a lkaline plutonic rocks. The Early Paleozoic volcanism of the Kola alka line province was coeval with the peak of tectonic activity at the nor thwestern boundary of the Fennoscandian Shield in the North Atlantic b elt of Caledonides and can be correlated with the collision maximum as sociated with the closure of the Iapetus Ocean.