Zoning and sectoriality of monazite-(Ce) from granite pegmatites of the central and South Urals |
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Authors: | V I Popova E I Churin |
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Institution: | (1) Helmholz Centre Potsdam, German Research Centre for Geoscience GFZ, Telegrafenberg, Potsdam, Germany;(2) Department of Earth and Planetary Sciences, AMNH, Central Park West at 79th Street, New York, NY 10024-5192, USA;(3) ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, 7001, Australia; |
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Abstract: | Zonal and sectorial monazite-(Ce) crystals from ceramic granite pegmatites of the Adui pluton are enriched in Ce and La, whereas
monazite from the miarolitic gemstone pegmatites at the western contact of the pluton are enriched in Nd, Sm, Gd, and Y. This
difference is caused by earlier crystallization of ceramic pegmatites and higher temperatures of their formation (650–600°C
for ceramic pegmatites and 550–300°C for miarolitic pegmatites). Monazites from ceramic and miarolitic pegmatites of the Adui
pluton differ in La and Nd contents, but their compositional trend in La-Nd coordinates is similar to the variation in monazite
composition from the early to late granite pegmatites in the Ilmeny Mountains. It is suggested that decrease in temperature
is a factor controlling REE contents in monazite. Heterovalent P ↔ Si and REE ↔ Th, Ca isomorphism in the consecutive zones
of growth pyramids in monazite is both unidirectional and wave-like. Monazite from granite pegmatites of the Adui pluton and
Ilmeny Mountains crystallized mainly under slightly alkaline conditions. |
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