Abstract The unique association of the epidote-group REE minerals, as well as the evolution of lanthanides and actinides, titanium and vanadium in their composition are described. Allanite-(Ce), often with a ferriallanite-(Ce) core, allanite-(Y) in an outer zone, and a rim of REE epidote forms pseudomorphs after chevkinite-(Ce) and perrierite-(Ce), as well as isolated crystals. They form intergrowths with biotite and are developed near it in quartz gabbronorite-dolerites and gabbronorite-diorites of the island-arc hypabyssal mafic Pervomaysk–Ayudag complex of the Middle Jurassic–Early Bajocian age in the Mountain Crimea. Zonal allanite-(Ce) of similar composition with REE epidote rims is widespread in the quartz diorites and plagiogranites of the same complex, where it is often developed in granophyric quartz–oligoclase intergrowths. Brown ferriallanite-(Ce) enriched in Ti (±Th) forms cores in brown allanite-(Ce) crystals enriched in Ti (±V) (up to 4.9 wt % TiO2). The Ti-rich (up to 3.5 wt % TiO2) allanite-(Ce) developed after ilmenite is extremely rich in vanadium (up to 4.5 wt % V2O3). Light colored low-titanium allanite-(Ce) has grown on the titanium-enriched allanite-(Ce). The distribution of REE and yttrium in the allanite-(Ce) and ferriallanite-(Ce) is as follows: Ce > La > Nd > Y > Pr > Sm ∼ Dy ∼ Gd > Er ∼ Tb. The outer zones of allanite-(Ce) crystals and REE epidote are relatively enriched in Nd, with Nd > La in some of them. The yttrium and REE show peculiar relations in allanite-(Y): Y <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11476_2025_11773_Article_IEq1.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\( \gg \)</EquationSource>  </InlineEquation> Ce ∼ Nd ∼ Dy ∼ Er > La ∼ Gd ∼ Yb. Allanite-(Ce) in the Crimean gabbroids is noticeably richer in La, Ti, V and poorer in Y, Sm, Gd in comparison with allanite-(Ce) in Crimean plagiogranitoids. The distribution of REE and yttrium in allanite-(Ce) of Crimean plagiogranitoids is close to that of common granites, differing in an increased proportion of Gd. The coloration reasons and sources of Crimean magmatic allanite are considered. Allanite was partially replaced by monazite-(Ce) during regional metamorphism under the prehnite-pumpellyite facies conditions.

Ti Ferriallanite-(Ce), Ti and Ti–V Allanite-(Ce), Allanite-(Ce), Allanite-(Y), and REE Epidote in Biotite-Bearing Quartz Gabbroids and Plagiogranitoids within the Island-Arc Pervomaysk-Ayudag Complex of the Mountain Crimea

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2025年8月1日

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E. M. Spiridonov,
G. N. Ovsyannikov,
S. V. Filimonov,
E. S. Koybagarova,
N. N. Korotaeva

摘要

Abstract

The unique association of the epidote-group REE minerals, as well as the evolution of lanthanides and actinides, titanium and vanadium in their composition are described. Allanite-(Ce), often with a ferriallanite-(Ce) core, allanite-(Y) in an outer zone, and a rim of REE epidote forms pseudomorphs after chevkinite-(Ce) and perrierite-(Ce), as well as isolated crystals. They form intergrowths with biotite and are developed near it in quartz gabbronorite-dolerites and gabbronorite-diorites of the island-arc hypabyssal mafic Pervomaysk–Ayudag complex of the Middle Jurassic–Early Bajocian age in the Mountain Crimea. Zonal allanite-(Ce) of similar composition with REE epidote rims is widespread in the quartz diorites and plagiogranites of the same complex, where it is often developed in granophyric quartz–oligoclase intergrowths. Brown ferriallanite-(Ce) enriched in Ti (±Th) forms cores in brown allanite-(Ce) crystals enriched in Ti (±V) (up to 4.9 wt % TiO₂). The Ti-rich (up to 3.5 wt % TiO₂) allanite-(Ce) developed after ilmenite is extremely rich in vanadium (up to 4.5 wt % V₂O₃). Light colored low-titanium allanite-(Ce) has grown on the titanium-enriched allanite-(Ce). The distribution of REE and yttrium in the allanite-(Ce) and ferriallanite-(Ce) is as follows: Ce > La > Nd > Y > Pr > Sm ∼ Dy ∼ Gd > Er ∼ Tb. The outer zones of allanite-(Ce) crystals and REE epidote are relatively enriched in Nd, with Nd > La in some of them. The yttrium and REE show peculiar relations in allanite-(Y): Y \( \gg \) Ce ∼ Nd ∼ Dy ∼ Er > La ∼ Gd ∼ Yb. Allanite-(Ce) in the Crimean gabbroids is noticeably richer in La, Ti, V and poorer in Y, Sm, Gd in comparison with allanite-(Ce) in Crimean plagiogranitoids. The distribution of REE and yttrium in allanite-(Ce) of Crimean plagiogranitoids is close to that of common granites, differing in an increased proportion of Gd. The coloration reasons and sources of Crimean magmatic allanite are considered. Allanite was partially replaced by monazite-(Ce) during regional metamorphism under the prehnite-pumpellyite facies conditions.