Anders Plan
Doktorand
Metamorphic titanite-zircon pseudomorphs after igneous zirconolite
Författare
Summary, in English
The formation of metamorphic zircon after baddeleyite is a well-known reaction that can be used to date the metamorphism of igneous silica-undersaturated rocks. By contrast, metamorphic minerals formed after igneous zirconolite have rarely been reported. In this paper, we document metamorphic titanite + zircon pseudomorphs formed from the metamorphic breakdown of igneous zirconolite in syenodiorite and syenite, in the southeastern Sveconorwegian Province, Sweden. Water-rich fluid influx during tectonometamorphism in epidote-amphibolite-facies metamorphic conditions caused the release of silica during a metamorphic reaction involving igneous feldspar and pyroxene and the simultaneous breakdown of igneous Zr-bearing phases. Typical titanite + zircon intergrowths are elongated or platy titanite crystals speckled with tiny inclusions of zircon. Most intergrowths are smaller than 15 μm; some are subrounded in shape. Locally, bead-like grains of titanite and zircon are intergrown with silicate minerals. The precursor igneous zirconolite was found preserved only in a sample of near-pristine igneous syenodiorite, as remnant grains of mainly < 2 μm in size. Two somewhat larger crystals, 8 and 12 μm, allowed semiquantitative confirmation using microprobe analysis. Analogous with zircon pseudomorphs after baddeleyite, titanite + zircon pseudomorphs after zirconolite potentially offer dating of the metamorphic reaction, although the small size of the crystals makes dating with today's techniques challenging. The scarcity of reports of zirconolite and pseudomorphs reflects that they are either rare or possibly overlooked.
Avdelning/ar
- Berggrundsgeologi
Publiceringsår
2023-09-19
Språk
Engelska
Sidor
773-788
Publikation/Tidskrift/Serie
European Journal of Mineralogy
Volym
35
Issue
5
Dokumenttyp
Artikel i tidskrift
Förlag
Copernicus GmbH
Ämne
- Geology
Status
Published
ISBN/ISSN/Övrigt
- ISSN: 0935-1221