Alkaline volcanism in the kola peninsula, Russia: Paleozoic Khibiny, Lovozero and Kontozero calderas

This paper presents the results of studying the Paleozoic volcanic series of the Kola Province, wide-spread in the areas of the Lovozero and Khibina massifs, the Kontozero caldera, and the Ivanovka volcano-plutonic complex. A distinctive feature of the volcanics is the presence of moderately alkaline basanites along with silica-undersaturated alkaline rock associations. All of the rocks are significantly enriched in incompatible elements: the contents of Rb, Ba, Sr, Nb, Zr and Y in the volcanics of the Lovozero and Kontozero formations. The Sm-Nd and Rb-Sr data suggest that the volcanics of the study area were derived from two different mantle sources: (1) superdepleted mantle material resulted from the multistage crustal growth over Archaean and Proterozoic time in the Kola-White Sea rift-collision zone and (2) a source that had properties of moderately enriched EMI-type mantle. It has been shown that the emplacement of the volcanics preceded the main pulse of alkaline magmatism in the region and can be referred to as the initial phase of the Paleozoic tectono-magmatic reactivation. According to geochronological data, the alkaline volcanic rocks were emplaced at least 20-30 m.y. before the intrusion of the alkaline plutonic rocks.