Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Spandler, C. Articles by Rubatto, D. Search for Related Content GeoRef GeoRef Citation

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

¹ Department of Earth and Marine Sciences, Australian National University, Canberra, Australia 0200
² Research School of Earth Sciences, Australian National University, Canberra, Australia 0200

Correspondence: ^* E-mail: carl{at}ems.anu.edu.au

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

This article has been cited by other articles:

				M.A. FORSTER and G.S. LISTER Tectonic sequence diagrams and the structural evolution of schists and gneisses in multiply deformed terranes Journal of the Geological Society, September 1, 2008; 165(5): 923 - 939. [Abstract] [Full Text] [PDF]

				D. Rubatto and J. Hermann Zircon Behaviour in Deeply Subducted Rocks Elements, February 1, 2007; 3(1): 31 - 35. [Abstract] [Full Text] [PDF]

				T. Geisler, U. Schaltegger, and F. Tomaschek Re-equilibration of Zircon in Aqueous Fluids and Melts Elements, February 1, 2007; 3(1): 43 - 50. [Abstract] [Full Text] [PDF]