Geochemical features of the drusite massifs, the central part of the Belomorian mobile belt: I. Distribution of major and trace elements in the rocks

Abstract

The comparative-geochemical study was first conducted for the ultrabasic-basic massifs of the central part of the Belomorian mobile belt, which were previously ascribed to the drusite complex on the basis of the presence of coronal textures. The studied magmatic bodies are geochemically heterogeneous and can be subdivided into three groups: (1) high-Mg rocks (MgO > 20 wt %) with elevated Cr content, enriched trace element patterns, and deep negative Ta-Nb anomaly (Sorkajoki Massif). Intrusions of this group are geochemically close to the layered plutons of Northern and Eastern Karelia (Kivakka, Burakovsky) and to the intrusions of the Kola Peninsula (Monchepluton and others); (2) low-Mg intrusions (MgO < 10 wt %) with elevated contents of Fe, Ti, and P (403-m Height Massif). The rocks composing these intrusions are characterized by subhorizontal trace element patterns and weak Ta-Nb anomaly; (3) intrusions with intermediate MgO contents (10–20 wt %), flat, occasionally depleted REE patterns, and lack of Ta-Nb anomaly (Mt. Grob Tundra). The identified geochemical differences do not depend on the degree of metamorphic transformations, but were presumably caused by differences in phase and chemical composition of parental magmas, as well as by conditions of their crystallization. It was substantiated that ultrabasic-basic massifs presently united into the drusite complex are genetically diverse and acquired similar textural appearance due to regional metamorphism. Thus, the presence of coronal textures is insufficient to ascribe the intrusions to the drusite complex, their mineralogical and geochemical composition should be taken into account.