Meliphanite and Leucophanite from the Sakharjok Alkaline Massif, Kola Peninsula

Abstract The North Qôroq centre comprises a series of concentric nepheline syenite intrusions and forms part of the Igaliko Nepheline Syenite Complex, in the rift-related Gardar Province of South Greenland. The North Qôroq syenites range from mildly undersaturated augite syenite to strongly peralkaline agpaitic nepheline syenite. Extensive in situ fractional crystallization has been postulated for the chemical variation both within units and throughout the centre. Many of the rocks have been affected by metasomatic fluids associated with the emplacement of younger syenite units, and this complicates their interpretation. In this study, the trends and compositions exhibited by pyroxene and amphibole from North Qôroq are examined and related to either primary crystallization or metasomatic activity (e.g. controls of f O2 , peralkalinity). Implications thus drawn are used to interpret the chemical processes inherent in the chemical and fluid evolution of alkaline magmas, and, in particular, the transition from miaskitic to agpaitic magmatism. In general, the major phases of the North Qôroq syenites records the increasing evolution of the units by crystal fractionation, towards peralkaline compositions. The composition of olivine, in the least evolved syenites, also points to a relatively high state of fractionation of the parent magma, whilst pyroxene and amphibole record an overall decrease in Mg/Mg+Fe), and a general increase in Fe 3+ and alkali content, with increased fractionation. The increasing peralkalinity of the magma also governs the evolution of pyroxene and, to a lesser degree, amphibole towards higher Zr and Ti contents in the more Na-rich compositions. The trends for pyroxene from metasomatized syenite show similar patterns, but lower Fe 2+ enrichment, suggesting the source of the metasomatic fluids is similar to the evolving syenites. The presence of amphiboles in metasomatic rocks, and high F contents attest to the F-rich nature of the metasomatic fluids, which is in agreement with results previously reported for metasomatic fluorapatite.

Peralkaline rock

Nepheline

Nepheline syenite

Amphibole

Pyroxene

Metasomatism

Alkali feldspar

Fractional crystallization (geology)

Carbonatite

10.1180/0026461036750149

Cite

Citations (28)

Compositional variation of loparite from the Lovozero alkaline complex, Russia

The Canadian Mineralogist (1996)

Roger H. Mitchell Anton R. Chakhmouradian

Perovskite-group minerals from the Lovozero peralkaline complex, on the Kola Peninsula, Russia, are primarily loparite-rich members of the perovskite-lueshite-loparite-(Ce) solid-solution series. From early-forming poikilitic nepheline syenite to late eudialyte lujavrite, loparite compositions evolve by enrichment in Na, Sr, and Nb, and depletion in Ca, Ti and light rare-earth elements. The evolutionary trend is from calcian niobian loparite-(Ce) in the poikilitic nepheline syenite and rocks of the differentiated complex through niobian calcian loparite-(Ce) in the differentiated complex and eudialyte lujavrite to cerian lueshite in eudialyte lujavrite. This trend coincides with the proposed order of crystallization of the major intrusive series of the massif. Intra- and intergrain compositional variation and diverse patterns of core-to-rim zonation exhibited by loparite grains from the same sample are characteristic of most parageneses and may result from a combination of re-equilibration phenomena and late-stage metasomatic processes.

Nepheline syenite

Peralkaline rock

Nepheline

Kola peninsula

Massif

Pegmatite

Metasomatism

Source

Cite

Citations (25)

Paragenesis and decomposition assemblage of a Mn-rich eudialyte from the Sushina peralkaline nepheline syenite gneiss, Paschim Banga, India

Lithos (2012)

Roger H. Mitchell Aniket Chakrabarty

Peralkaline rock

Aegirine

Nepheline

Nepheline syenite

Carbonatite

10.1016/j.lithos.2012.02.003

Cite

Citations (15)

Evolution of peralkaline calcite carbonatite magma in the Fen complex, southeast Norway

Lithos (1988)

Tom Andersen

Nepheline

Nepheline syenite

Carbonatite

Peralkaline rock

Pyroxene

Alkali feldspar

Aegirine

Trachyte

10.1016/0024-4937(88)90019-9

Cite

Citations (56)

The miaskitic-to-agpaitic transition in peralkaline nepheline syenite (white foyaite) from the Pilanesberg Complex, South Africa

Chemical Geology (2016)

Tom Andersen Marlina Elburg Muriel Erambert

Peralkaline rock

Nepheline syenite

Nepheline

10.1016/j.chemgeo.2016.08.020

Cite

Citations (32)

Naujakasite from the Ilímaussaq alkaline complex, South Greenland, and the Lovozero alkaline complex, Kola Peninsula, Russia: a comparison

Geology of Greenland Survey Bulletin (2001)

A. P. Khomyakov Henning Sørensen Ole V. Petersen J.C. Bailey

Naujakasite, Na6(Fe,Mn)Al4Si8O26, long known from the Ilímaussaq alkaline complex, South Greenland, was not reported until 1999 from other occurrences of alkaline rocks in spite of the fact that the mineral is composed of common elements. In 1999, a variety of naujakasite rich in Mn was found in the Lovozero alkaline complex in the Kola Peninsula, Russia. This variety has been approved by the IMA as a new mineral, manganonaujakasite, Na6(Mn0.53Fe2+ 0.47)Al4Si8O26. At Ilímaussaq naujakasite is a rock-forming mineral in the highly evolved rock naujakasite lujavrite in which it may make up more than 75 vol.%; at Lovozero manganonaujakasite is a very rare constituent in mineralised lovozerite–lomonosovite lujavrite. Naujakasite appears to take the place of nepheline in hyper-agpaitic nepheline syenites characterised by exceptionally high Na/K ratios. The nepheline syenites at Ilímaussaq have an average Na/K (atomic) ratio of 3.08, and the naujakasite lujavrites have the extreme ratio 4.56. The nepheline syenites of the Khibina and Lovozero complexes are characterised by lower Na/K ratios, 1.27 for Khibina and 1.67 for Lovozero, and thus nepheline is stable in the hyper-agpaitic rocks and naujakasite occurs only in pegmatites.

Nepheline

Kola peninsula

Nepheline syenite

Pegmatite

10.34194/ggub.v190.5178

Cite

Citations (8)

Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia

Minerals (2022)

Julia A. Mikhailova Yakov A. Pakhomovsky L. М. Lyalina Е. А. Селиванова

The 360-370-Ma-old Lovozero peralkaline massif (NW Russia) is a layered nepheline syenitic–foidolitic pluton. In the rocks of the massif, late-stage (auto)metasomatic alterations of rock-forming minerals are quite intense. We studied the products of the alteration of nepheline and sodalite via microtextural, microprobe, and spectroscopic methods. We found that these minerals are extensively replaced by the association between natrolite + nordstrandite ± böhmite ± paranatrolite in accordance with the following reactions: 3Nph + 4H2O → Ntr + Nsd + NaOH; 6Nph + 9H2O → Ntr + Pntr + 2Nsd + 2NaOH; Sdl + 4H2O → Ntr + Nsd + NaOH + NaCl, where Nph is nepheline, Ntr is natrolite, Nsd is nordstrandite, Pntr is paranatrolite, and Sdl is sodalite. As a result, about one-third of the sodium from nepheline (and sodalite) is set free and passes into the fluid. This leads to an increase in the Na/Cl ratio and, hence, the pH of the fluid. An increase in pH stabilizes hyperagpaitic minerals (e.g., ussingite, villiaumite, thermonatrite, and trona), which can crystallize in close proximity to pseudomorphized nepheline and sodalite. Thus, the alteration of feldspathoids increases the pH of late-magmatic fluids, which in turn can lead to the crystallization of hyperagpaitic minerals.

Nepheline

Peralkaline rock

Sodalite

Massif

Nepheline syenite

Aegirine

Metasomatism

10.3390/min13010039

Cite

Citations (2)

Minerals of zirconolite group from fenitized xenoliths in nepheline syenites of Khibiny and Lovozero plutons, Kola Peninsula

Geology of Ore Deposits (2015)