Monazite-(Ce)-Huttonite Solid Solutions in Granulite-Facies Metabasites from the Ivrea-Verbano Zone, Italy

H.-J. Förster and D. E. Harlov
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany

Abstract: Composite populations of monazite-group minerals of both metamorphic and metasomatic origin have been discovered in thin layers of granulite-facies metabasites interlayered with metapelites, located in the Val Strona di Omegna region of the Ivrea-Verbano Zone, Italy. In addition to monazite-(Ce), which is uncommonly poor in Th and is probably formed by incongruent dissolution of apatite, these populations include members of the monazite-huttonite series. The latter minerals contain between 13 and 30.1 mol.% ThSiO4 [= huttonitic monazite-(Ce)], and are known from only half a dozen other occurrences worldwide. We propose that breakdown of primary monazite-(Ce) in the metapelites during granulite-facies metamorphism mobilized Th and the REEs, which were then transported by high-grade metamorphic fluids into the metabasite layers to form the Th-rich minerals of the monazitehuttonite series.

Keywords: monazite • huttonite • apatite • crystal-chemistry • granulite-facies metamorphism • metabasite • Ivrea-Verbano Zone

Mineralogical Magazine; August 1999 v. 63; no. 4; p. 587-594; DOI: 10.1180/002646199548637
© 1999, The Mineralogical Society
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