Abstract
The Lovozero Alkaline Massif intruded through the Archean granite-gneiss and Devonian volcaniclastic rocks ca. 360 Ma ago and formed a large laccolith-type body. The lower part of the massif (the Layered complex) is composed of regularly repeating rhythms: melanocratic nepheline syenite (lujavrite, at the top), leucocratic nepheline syenite (foyaite), foidolite (urtite). The upper part of the massif (the Eudialyte complex) is indistinctly layered, and lujavrite enriched with eudialyte-group minerals (EGM) prevails there. In this article, we present the results of a study of the chemical composition and petrography of more than 400 samples of the EGM from the main types of rock of the Lovozero massif. In all types of rock, the EGM form at the late magmatic stage later than alkaline clinopyroxenes and amphiboles or simultaneously with it. When the crystallization of pyroxenes and EGM is simultaneous, the content of ferrous iron in the EGM composition increases. The Mn/Fe ratio in the EGM increases during fractional crystallization from lujavrite to foyaite and urtite. The same process leads to an increase in the modal content of EGM in the foyaite of the Layered complex and to the appearance of primary minerals of the lovozerite group in the foyaite of the Eudialyte complex.
Highlights
Zirconosilicate of sodium, calcium, and iron, “eudialyte” was described more than 200 years ago in samples from the Ilimaussaq alkaline massif in Greenland [1]
The Lovozero massif is composed of alkaline rocks, which are either foid syenites or foidolites
It is important to note that, in all types of rock of the layered complex and leucocratic rocks of the Eudialyte complex, there are no significant correlations between the compositions of pyroxenes and eudialyte-group minerals (EGM) (Figure 11)
Summary
Zirconosilicate of sodium, calcium, and iron, “eudialyte” was described more than 200 years ago in samples from the Ilimaussaq alkaline massif in Greenland [1]. Even this mineral, more precisely a group of minerals (eudialyte-group minerals, or EGM), is being actively studied and is a subject of debate. The EGM are indicator minerals of so-called agpaitic rocks [8,18,22,23] Such rocks are neglegible in volume of the earth’s crust, it is important to study conditions of their formation for mineralogy and material science, since agpaitic
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