Watt, Gordon R. (1995) High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions. Mineralogical Magazine, 59 (397) 735-743 doi:10.1180/minmag.1995.059.397.14
| Reference Type | Journal (article/letter/editorial) | ||
|---|---|---|---|
| Title | High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions | ||
| Journal | Mineralogical Magazine | ISSN | 0026-461X |
| Authors | Watt, Gordon R. | Author | |
| Year | 1995 (December) | Volume | 59 |
| Issue | 397 | ||
| Publisher | Mineralogical Society | ||
| Download URL | https://rruff.info/doclib/MinMag/Volume_59/59-397-735.pdf+ | ||
| DOI | doi:10.1180/minmag.1995.059.397.14Search in ResearchGate | ||
| Generate Citation Formats | |||
| Mindat Ref. ID | 2701 | Long-form Identifier | mindat:1:5:2701:8 |
| GUID | 0 | ||
| Full Reference | Watt, Gordon R. (1995) High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions. Mineralogical Magazine, 59 (397) 735-743 doi:10.1180/minmag.1995.059.397.14 | ||
| Plain Text | Watt, Gordon R. (1995) High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions. Mineralogical Magazine, 59 (397) 735-743 doi:10.1180/minmag.1995.059.397.14 | ||
| In | (1995, December) Mineralogical Magazine Vol. 59 (397) Mineralogical Society | ||
| Abstract/Notes | AbstractMonazite is a light rare-earth element (LREE)-bearing accessory phase common in felsic granitic rocks, and strongly influences LREE concentrations in granites and the chemistry of melts and residues formed during partial melting. Cheralite-rich (high-Th) monazite-(Ce) has been recorded as rims on partially dissolved cores in a suite of granulite-facies migmatites generated by disequilibrium melting. High-Th monazite has previously been recorded only in granitic-pegmatite occurrences. Subidiomorphic monazite-(Ce) from leucosome, melanosome and mesosome consists of complexly zoned cores (up to 300 µm in diameter) containing 5.17–9.87 wt.% ThO2, overgrown by essentially unzoned rims (containing up to 21.4 wt.% ThO2). Uranium contents are average for Th-rich monazite-(Ce) (0.22–3.17 wt.% UO2). Th enrichment (relative to LREE) in monazite-(Ce) rims is ascribed to the presence of fluorine-bearing melts (formed during the incongruent breakdown of biotite to produce a water-undersaturated melt), allowing the formation of REE-fluoride complexes in the melt, coupled with the increased charge balanced substitutions Th4+ + Si4+ ⇌ REE3+ + P5+ and Th4+ + Ca2+ ⇌ 2REE3+ into monazite-(Ce). Fractionation of Th and U (reflected by an increased in Th/U in rims relative to cores) may have occurred due to the removal by a CO2-rich fluid phase in the melt. These interpretations are consistent with elevated CO2 and F contents of granitic liquids produced during the water-undersaturated breakdown of biotite under granulite-facies conditions. Evidence for restricted monazite-(Ce)-melt equilibration and rapid melt removal is provided by the ubiquitous presence of partially embayed cores and unzoned rims. | ||
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