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Journal of Petrology Advance Access published online on January 7, 2009
Journal of Petrology, doi:10.1093/petrology/egn075
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© The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Chloritoid-Bearing Mineral Assemblages in High-Pressure Metapelites from the Bughea Complex, Leaota Massif (South Carpathians)

Elena Negulescu1,*, Gavril Sabau1 and Hans-Joachim Massonne2

1Geological Institute of Romania, 1 CaransebeS St., RO-012271 Bucharest 32, Romania
2Institut Für Mineralogie und Kristallchemie, Azenbergstr. 18, D-70174 Stuttgart, Germany

Received January 11, 2008; Revised typescript accepted December 3, 2008


  Abstract

High-Mg chloritoid (XMg = 0·40–0·47) and relatively high-Mg staurolite (XMg = 0·25–0·28) coexisting with kyanite and garnet were identified in a mica–garnet-rich rock associated with very high-pressure eclogites in the Bughea Complex of the Leaota Massif (South Carpathians). Major and trace element geochemical data for both fresh eclogites and associated rocks which represent a metasomatic or retrograde alteration rind of the eclogites, indicate a pelitic precursor. Magnesian chloritoid was found as inclusions in garnet as part of a chloritoid–kyanite–garnet assemblage which is indicative of high-pressure conditions. The host garnet shows a typically prograde chemical zoning pattern. The chloritoid-bearing assemblage is confined to the inner part of the garnet porphyroblasts, whereas the matrix assemblage in equilibrium with Mg-rich garnet rims has exceeded the thermal stability limit of chloritoid. Pressure–temperature pseudosections for simplified compositions approaching the rock bulk-chemistry show a high-pressure field for the identified chloritoid-bearing assemblage in good agreement with pressure–temperature estimates in the CFMASH and KCFMASH chemical subsystems using analysed mineral compositions. The derived pressure–temperature path is clockwise, indicating overprinting during exhumation from 1·8 GPa and 580°C to 1·15 GPa and 620°C, at a water activity approaching aH2O = 1. These conditions were attained in a subduction mélange indicating transient thermal perturbations of a subduction channel.

KEY WORDS: high-pressure metapelite; Mg-rich chloritoid; P–T path; P–T pseudosection; very high-pressure eclogite

*Corresponding author. Telephone: +40-21-3181328. Fax: +40-21-3181326. E-mail: elinegu{at}yahoo.com


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