Ree and Sr-Nd Isotope Compositions of Clinopyroxenites, Phoscorites and Carbonatites of the Seblyavr Massif, Kola Peninsula, Russia

Elena Balaganskaya,Daniel Demaiffe,Hilary Downes

doi:10.2478/v10002-007-0017-6

Elena Balaganskaya, Daniel Demaiffe + Show 1 more

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https://doi.org/10.2478/v10002-007-0017-6

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Abstract

Ree and Sr-Nd Isotope Compositions of Clinopyroxenites, Phoscorites and Carbonatites of the Seblyavr Massif, Kola Peninsula, RussiaClinopyroxenites, phoscorites and carbonatites from the Devonian Seblyavr intrusion (Kola Peninsula, Russia) have petrographic characteristics indicating that they are accumulative in origin. Their geochemical (major and rare earth elements) compositions can be accounted for by mixtures of their major rock-forming minerals and accessory phases, i.e. they reflect the record of mineral accumulation. All of the analysed Seblyavr rocks are strongly LREE-enriched with (La/Yb)Nmostly ranging from 38 to 189. However, a dolomite carbonatite with hydrothermal LREE-Sr mineralization has an extreme (La/Yb)Nvalue of 1659. Such late-stage dolomite carbonatites were formed by hydrothermal (rather than magmatic) processes. Whole-rock samples of representative magmatic lithologies from Seblyavr have initial87Sr/86Sr and εNdthat fall in a very narrow range from 0.7031 to 0.7033 and +4.9 to +5.9, respectively. We therefore conclude that clinopyroxenites, phoscorites and carbonatites were formed by differentiation and crystallization of a single batch of melt. The parental melt was derived from a depleted upper mantle source that had been meta-somatised prior to melting.

Highlights

Studies of carbonatites and coeval silicate rocks can provide insights into the processes that produce their contrasting magma types
To extend our understanding of the petrogenesis of coexisting alkaline and carbonatitic magmas, we undertook a study of Seblyavr, the northernmost intrusive complex in the Kola Alkaline Carbonatite Province (KACP) (Fig. 1)
This paper presents the results of a study on the mineralogy and geochemistry of the main types of intrusive silicate rocks and phoscorite-carbonatites of Seblyavr

Summary

Introduction

Studies of carbonatites and coeval silicate rocks can provide insights into the processes that produce their contrasting magma types. The Kola Alkaline Carbonatite Province (KACP) is a region of Devonian magmatism in NW Russia where both alkaline-ultramafic and carbonatitic magmatism was well developed (Woolley 1989; Kogarko et al 1995; Downes et al 2005). More than 20 massifs composed of alkaline and ultramafic rocks occur in the KACP, and sixteen of them contain carbonatites (Fig. 1). To extend our understanding of the petrogenesis of coexisting alkaline and carbonatitic magmas, we undertook a study of Seblyavr, the northernmost intrusive complex in the KACP (Fig. 1). This paper presents the results of a study on the mineralogy and geochemistry (major elements, REE, Sr and Nd isotopes) of the main types of intrusive silicate rocks and phoscorite-carbonatites of Seblyavr.

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