ALKALINE ROCKS OF THE TURIY PENINSULA, RUSSIA, INCLUDING TYPE-LOCALITY TURJAITE AND TURJITE: A REVIEW

KEITH BELL and ELIZABETH ANN DUNWORTH
Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, Ottawa, Ontario K1S 5B6

ANDREI G. BULAKH
Department of Mineralogy, University of St. Petersburg, 7/9 University Emb., St. Petersburg, Russia 199034

VALERIY V. IVANIKOV
Department of Petrography, University of St. Petersburg, 7/9 University Emb., St. Petersburg, Russia 199034

Abstract

The Turiy Massif, emplaced during the late Devonian, forms part of the Kola Alkaline Province, in Russia. It consists of five magmatic centers, with three spatially related phases of dyke activity. Rock types range from pyroxenite to SiO2-undersaturated alkaline rocks, including melilitolite, late-stage carbonatite and phoscorite. The great diversity of rock types can be explained by crystal fractionation coupled with metasomatic activity. We present results of new electron-microprobe analyses of minerals from turjaite (a nepheline melilitolite) and turjite (an alkaline lamprophyre) from the type locality at Turiy. The turjaite contains Na-saturated and Fe3+-bearing melilite, phlogopite, nepheline or cancrinite, with lesser amounts of diopside, titanian andradite, calcite, apatite, magnetite, REE-rich perovskite and a number of accessory phases. Mineralogical and compositional changes in the mineral assemblages noted in two samples of turjaite are interpreted as the product of a differentiating magma body, with possible additional increase in Na and volatiles during the final stages of magmatic activity. Turjite is part of the syn-massif-emplacement stage of dyke activity and may relate, compositionally, to the reaction between a late-stage ijolite - urtite and carbonatite. The modal mineralogy of turjite includes phlogopite and biotite, garnet of the schorlomite - andradite series, primary calcite, interstitial analcime and cancrinite with lesser magnetite, apatite, perovskite and aegirine and possible relic nepheline. A more SiO2-rich sample also contains celsian, ilmenite and titanite.