Abstract
The Kola region hosts numerous Paleozoic massifs of ultrabasic alkaline rocks and carbonatites with deposits of commercially valuable metals, such as iron, tantalum, niobium, and rare earth elements. These magmatic complexes are characterized by high contents of alkaline elements at generally low contents of SiO2 and/or Al2O3. In this study, we examined the precursors to the formation of the unique Paleozoic alkaline province through studying the early Precambrian stages in the evolution of the Kola collision area, from where these unique features probably originated. We mathematically modeled the changes in the chemical composition of these rocks. The obtained data can be used for metallogenic forecasting, which indicated a number of Precambrian objects in the region, namely, the Lapland Granulite Belt of the Kola region and granulite belts in Eurasia. The mathematical modeling performed during this research depicted a linear trend that defined the style of the changes in the chemical composition at the transition from the metaultrabasic-basic rocks of the Lapland granulite belt to the group of belts in Eurasia. These differences are statistically significant with respect to the obtained trend (chemical composition projected on the trend), mainly manifested as increased SiO2 and Al2O3 contents with a decreasing total alkalis content, which is opposite to the indicated trends of the changing chemical composition in the Paleozoic alkaline rock units of the Kola region. We concluded that one of the reasons for the unique composition of the Paleozoic magmatism products could be a specific feature of the earlier Neoarchean stages of the tectonic-magmatic activity in the northeastern Baltic Shield, which implies a close relationship between later geological events and the early Precambrian history, at least in the study area.
Highlights
The Kola region ranks in the leading position among the Precambrian provinces with its giant and high-grade mineral reserves of apatite, apatite-magnetite, phlogopite, and vermiculite deposits; rare metal mineralization; and platinum group element (PGE) ores
Our findings do not settle this issue for all specific rock assemblages and related mineral resources; we only address the possible relationship between the processes related to the formation of the Kola alkaline province and the Precambrian history of the regional evolution
As we studied the formation of the Paleozoic Kola alkaline province, alkaline rocks typically contain highly alkaline indicator minerals, which are reflected in the increased contents of Na2 O and K2 O with commonly low contents of SiO2 and/or Al2 O3 in the rock compositions [5]
Summary
The Kola region ranks in the leading position among the Precambrian provinces with its giant and high-grade mineral reserves of apatite, apatite-magnetite, phlogopite, and vermiculite deposits; rare metal mineralization (yttrium, firstly); and platinum group element (PGE) ores. The researchers who studied this province in detail considered it unique and one of the largest alkaline provinces in the world in terms of the scope of its multi-stage alkaline magmatism [1,2,3,4,5]. These and other authors studied the genesis of alkaline complexes mainly within the framework of the Paleoproterozoic stage in the magmatic activation of the region, with no reference to its prehistory. Geosciences 2020, 10, 11 reviewing the precursors of the unique Paleozoic alkaline province formation by studying early stages in the evolution of the Kola collision area, from where such unique features could have originated.
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