Significance of Ultrahigh-P Talc-Bearing Eclogitic Assemblages

J. G. Liou and R. Y. Zhang
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA

Abstract: Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.

Keywords: talc • eclogite • phase equilibria • China

Mineralogical Magazine; March 1995 v. 59; no. 394; p. 93-102; DOI: 10.1180/minmag.1995.59.394.08
© 1995, The Mineralogical Society
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