Temperatures from triple-junction angles in sulfides

John Lusk, Brian O. E. Calder, Terry E. Freeman

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    7 Citations (Scopus)


    Experiments carried out between 280 and 980 °C demonstrate that dihedral angles for galena, θgn ,in sphalerite-galena-sphalerite triple-junctions decrease with increasing temperature, and that therate of change increases in the same direction. Similar behavior is evident for sphalerite, θsp, ingalena-sphalerite-galena triple-junctions, and also for pyrrhotite, θpo, in sphalerite-pyrrhotite-sphaleritetriple-junctions. Triple-junction thermometry (TJT) is therefore most sensitive at high to very hightemperatures where isotope thermometers are least sensitive. The method relies on the temperaturedependenceof competitive surface tensions between shared surfaces of intergrown minerals. Becausechemical interaction is not a prerequisite, the TJT method is potentially applicable to a varietyof mineral pairs found in regional metamorphic situations. The method requires a slightly modifiedmicroscope equipped with a precision X-Y stage. The application of θgn-T (temperature) and θpo-T calibrations to regionally metamorphosed sulfideores yields temperatures that compare reasonably with temperatures obtained from sulfur isotopesand other geothermometers. Maximum regional metamorphic temperatures of ~470–480, ~590,and ~700 °C were obtained for the Bathurst (New Brunswick = greenschist facies), Ruttan (Manitoba= amphibolite facies) and Broken Hill (N.S.W. = granulite facies) deposits, respectively. The θgn and θpo thermometers also reveal recrystallization effects in microfabrics.
    Original languageEnglish
    Pages (from-to)1390-1400
    Number of pages11
    JournalAmerican Mineralogist: an international journal of earth and planetary materials
    Issue number10
    Publication statusPublished - 2002


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