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Non-metamict zirconolite polytypes from the feldspathoid-bearing alkali-syenitic ejecta of the Vico volcano complex (Latium, Italy)

Fabio Bellatreccia, Giancarlo Della Ventura, C. Terry Williams, Gregory R. Lumpkin, Katherine L. Smith and Michael Colella
Non-metamict zirconolite polytypes from the feldspathoid-bearing alkali-syenitic ejecta of the Vico volcano complex (Latium, Italy)
European Journal of Mineralogy (August 2002) 14 (4): 809-820

Abstract

This paper presents the results of a combined electron microprobe and analytical TEM study that describes the chemical and structural characteristics of non-metamict zirconolite from a volcanic ejectum collected within a pyroclastic formation of the Vico volcanic complex, near Tre Croci Community, Latium (Italy). The host rock is a foid-bearing alkali-syenite and consists of potassium-feldspar and plagioclase, with minor biotite, titanite, clinopyroxene and magnetite. Sodalite occurs as well-faceted crystals inside miarolitic cavities between intersecting feldspars and it is variably altered to a kaolinite-like product. Accessory minerals include zircon, baddeleyite, stillwellite, hellandite, fluorite, apatite and monazite. Zirconolite occurs both as elongated acicular crystals of orthorhombic symmetry (zirconolite-3O), space group Acam, with (in Aa) a = 10.13(1), b = 14.16(1) and c = 7.288(2), and as pseudo-hexagonal platy crystals of trigonal symmetry (zirconolite-3T), space group P3 (sub 1) 2, with a = 7.279(2) and c = 16.89(2).TEM studies revealed additionally the presence of polytype zirconolite-2M in a subset of grains analyzed. Zirconolite displays pronounced compositional zoning, observed in backscattered electron images, resulting mainly from an antipathetic variation in the actinide elements (Th+U) and REE contents. Analytical TEM results indicate compositional differences exist between the zirconolite-3T and zirconolite-2M polytypes. Zirconolite, and associated accessory REE, Th, U minerals crystallized after the formation of the major rock-forming minerals of the ejectum, from metasomatic fluids rich in F and P.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 14
Serial Issue: 4
Title: Non-metamict zirconolite polytypes from the feldspathoid-bearing alkali-syenitic ejecta of the Vico volcano complex (Latium, Italy)
Affiliation: Universita di Roma La Sapienza, Museo di Mineralogia, Rome, Italy
Pages: 809-820
Published: 200208
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 40
Accession Number: 2002-064892
Categories: Mineralogy of non-silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N41°13'60" - N42°49'60", E11°30'00" - E14°00'00"
Secondary Affiliation: Universita della Calabria, ITA, ItalyNatural History Museum, GBR, United KingdomAustralian Nuclear Science and Technology Organisation, AUS, Australia
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200220
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