P-T Constraints on the Metamorphic Evolution of the Paleoarchean Kromberg Type-Section, Barberton Greenstone Belt, South Africa

Low-grade metabasites and hydrothermally altered ultramafic rocks form most of the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. However, P-T constraints are sparse and the nature of the greenschist-facies metamorphism is poorly characterized. This study provides new P-T estimates an...

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Bibliographic Details
Published in:Journal of petrology 2012-03, Vol.53 (3), p.513-545
Main Authors: Grosch, E. G., Vidal, O., Abu-Alam, T., McLoughlin, N.
Format: Article
Language:English
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Summary:Low-grade metabasites and hydrothermally altered ultramafic rocks form most of the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. However, P-T constraints are sparse and the nature of the greenschist-facies metamorphism is poorly characterized. This study provides new P-T estimates and descriptions of the petrological characteristics of altered mafic-ultramafic rocks across the Kromberg type-section, Onverwacht Group, BGB, from both surface samples and fresh drill core. Application of a chlorite thermodynamic multi-equilibrium calculation and pseudosection modelling, in conjunction with petrographic observations, indicates a wide range in metamorphic conditions from sub-greenschist to the uppermost greenschist facies across the type-section. A central fuchsite-bearing zone containing strong mylonitic fabrics, referred to as the Kromberg Section Mylonites (KSM), records at least two metamorphic events: a high-T, low-P (420 +/- 30 degree C,
ISSN:0022-3530
1460-2415
DOI:10.1093/petrology/egr070