A weathering-related origin of widespread monazite in S-type granites

Wayne N. Sawka*, Jillian F. Banfield, Bruch W. Chappell

*Corresponding author for this work

    Research output: Contribution to journalArticle

    63 Citations (Scopus)

    Abstract

    The S-type granite suites comprising more than a quarter of the extensively developed granites in the Lachlan Fold Belt, Australia, contain monazite which may be related to the chemical weathering of the sedimentary source rocks. We report a process whereby chemical weathering fixes mobile rare-earth elements (REE) in hydrous phosphate phases such as florencite and rhabdophane. This material contains up to 50 wt% LREE and occurs as very small particles (~3μm). Dehydration of these hydrous REE phases during anatexis directly yields monazite. The low solubility of phosphorus in S-type granite melts inhibits dissolution of both monazite and apatite. Refractory monazite may be thus entrained and transported in S-type granites in a manner similar to processes resulting in inherited zircon. Since both Th and the light REE are major components in monazite, materials containing this minute phase may be of widespread geochemical significance in both granites and metamorphic rocks.

    Original languageEnglish
    Pages (from-to)171-175
    Number of pages5
    JournalGeochimica et Cosmochimica Acta
    Volume50
    Issue number1
    DOIs
    Publication statusPublished - 1986

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