Exsolution of thortveitite, yttrialite, and xenotime during low-temperature recrystallization of zircon from New Caledonia, and their significance for trace element incorporation in zircon

摘要: Recrystallized zircon grains in a phengite-epidote-chlorite schist from north-eastern New Caledonia contain as inclusions mineral assemblage consisting of celadonite, kaolinite, quartz, Fe-oxy-hydroxide,smectite, chlorite, xenotime-(Y), thortveitite, yttrialite, and allanite-(Ce). This formed during low-temperature (<100 °C) seafloor alteration plagioclase-rich mafic rock represents the first documented evidence this event high-P belt northeastern Caledonia. The survival paragenesis that has undergone subsequent eclogite-facies metamorphism testifies to strength value container for inclusions. Thortveitite (Sc2Si2O7) yttrialite (Y2Si2O7) altered cores represent new occurrence these minerals suggest they may be more common than is currently recognized. The generally have lower trace-element contents than pristine igneous we xenotime-(Y) result expulsion recrystallization. Trace-element concentrations indicate trivalent cations (REE, Y, Sc) cannot charge-balanced by xenotime substitution alone. Pentavalent cation (Nb, As) are also insufficient charge balance. presence thortveitite suggests that might either monovalent anions substituting oxygen or small such H occurring interstitially lattice.