Chevkinite-(Ce) and perrierite-(Ce) of Island-Arc quartz gabbronorite-dolerites of the Ayu-Dag Intrusive, Crimean Mts

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Marco E. Ciriotti
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Chevkinite-(Ce) and perrierite-(Ce) of Island-Arc quartz gabbronorite-dolerites of the Ayu-Dag Intrusive, Crimean Mts

Messaggio da Marco E. Ciriotti » mer 07 ago, 2019 14:30

Prossima pubblicazione.

Referenza:
▪ Spiridinov, E.M., Filimonov, S.V., Semikolennyh, E.S., Korotaeva, N.N., Krivitskay, N.N. (2019): Chevkinite-(Ce) and perrierite-(Ce) of Island-Arc quartz gabbronorite-dolerites of the Ayu-Dag Intrusive, Crimean Mountains. Zapiski RMO, 148(4), (in press).

Abstract:
Сhevkinite-(Се) and perrierite-(Се) are the characteristic minerals of alkaline magmatic rocks and high-temperature alkaline metasomatites, as well as typical accessory minerals of island-arc gabbroids in mesozoides of the Mountain Crimea. Early magmatic mineral associations of these low-alkaline gabbroids of the Ayu-Dag intrusive include accessory Ti–Zr–LREE minerals undersaturated in silica: chevkinite-(Се), perrierite-(Се), zirconolite, baddeleyite. Сhevkinite and perrierite compose the isolated shortly prismatic crystals up to 0.1 mm and strongly corroded late-magmatic allanite-(Ce) inclusions in the center of late-magmatic allanite-(Ce) crystals. Both minerals are the main concentrators and carriers of lanthanides in Ayu-Dag gabbroids. The distribution of lanthanides in chevkinite and perrierite is Ce >> La > Nd >> Pr > Gd, Sm, Tb, Dy. The quantitative composition of lanthanides in chevkinite and perrierite is identical: Ce (54-58 % REE) – La (25-31 %) – Nd (12-20 %). The maintenance of Zr, Th, Y, Sc in both polymorphs of Ayu-Dag gabbroides is identical. Сhevkinite-(Ce) of the isolated crystals is magnesium prepotent; its structure is: [Cе1.5La0.8-0.9Nd0.3-0.4Pr0.1(Gd+Sm+Tb+Dy)0.1Y0.2Sc0.1Ca0.7-0.8Na0.1]4(Mg0.5Fe3+0.5)1(Fe3+1.1-1.2Ti0.4-0.7Zr0.1-0.2Al0.1-0.2)2Ti2[(Si3.7-4Al0.3-0)4O22]. Сhevkinite-(Ce) from allanite inclusions is poor in Mg, its structure is: [Cе1.5-1.7La0.6-0.9Nd0.5-0.6Pr0.1(Gd+Sm)0.1Y0.1-0.2Sc0.1Ca0.6-0.8Na0.1]4(Fe2+0.6-1Mg0-0.1Fe3+0-0.4)1(Ti0.8-0.9Fe3+0.3-0.7Al0.2-0.4Zr0-0.2)2Ti2[(Si3.9-4Al0.1-0)4O22]. Perrierite-(Ce) composing idiomorphic crystals is magnesium prepotent, its structure is: [Cе1.2-1.6La0.6-0.8Nd0.3-0.4Pr0.1(Gd+Sm+Tb+Dy)0.1Y0.1Sc0.1Ca1.0-1.1Sr0-0.1Na0.1]4(Mg0.9-1Fe3+0.1-0)1 (Fe3+1.0-1.2Al0.2-0.7Ti0.3-0.5Zr0-0.2)2Ti2[(Si3.9-4Al0.1-0)4(O21.3-21.5OH0.7-0.5)22]. Perrierite-(Ce) in allanite is poor in Mg, its structure is: [Cе1.3-1.5La0.7-0.8Nd0.3-0.5Pr0.1(Gd+Sm)0.1Y0.1Sc0.1Ca1.1-1.3Na0.1]4(Fe2+0.4-0.5Fe3+0.2-0.4Mg0.2)1(Al0.5-0.7Ti0.3-0.8Fe3+0.3-0.9Zr0.1-0.3)2Ti2[(Si3.9-4Al0.1-0)4(O21.4-22OH0.6-0)22].
Perhaps, the presence of chevkinite and perrierite, as well as zirconolite in unusual geochemical settings can be explained by poor development of late-magmatic processes in near-surface intrusives of the Mountain Crimea mesozoids.
Marco E. Ciriotti

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