The effects of magma replenishment processes on U-238-Th-230 disequilibrium

R D Hughes, Chris Hawkesworth

    Research output: Contribution to journalArticlepeer-review

    27 Citations (Scopus)

    Abstract

    Short lived isotope data are increasingly used to investigate magma chamber residence times. Are lavas have excellent potential as tracers of magma evolution because their magmas are often out of U-series isotope equilibrium, and some are magmas have yielded surprisingly;old pre-eruption U-series ages from mineral separates. A model is presented to examine the behaviour of U-Th isotopes for a range of conditions between closed system and steady-state magmatic systems. Magmas can be maintained out of secular equilibrium for long periods of time by periodic mixing events with new magma batches. The latter results in oscillations in (Th-230/Th-232) consistent with the relatively constant values observed in lavas of different ages from some centres. The effects of periodic reinjection of magma and mixing of old and young crystals on U-series mineral isochrons are also considered. Mixtures of crystals produced by either replenished or dosed system processes can readily result in linear arrays. In many cases it may be valid to interpret these as minimum average residence times for the crystals, whereas the liquid residence times calculated from U-series data for periodically replenished systems are maximum values. Copyright (C) 1999 Elsevier Science Ltd.

    Original languageEnglish
    Pages (from-to)4101-4110
    Number of pages10
    JournalGeochimica et Cosmochimica Acta
    Volume63
    Issue number23-24
    Publication statusPublished - Dec 1999

    Keywords

    • U-SERIES ISOTOPES
    • TRACE-ELEMENTS
    • RESIDENCE TIME
    • GEOCHEMICAL EVOLUTION
    • LESSER ANTILLES
    • RATES BENEATH
    • ISLAND-ARC
    • FLUX RATES
    • TH
    • SYSTEMATICS

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