Fluid-rock interaction in retrograde granulites of the Southern Marginal Zone, Limpopo high grade terrain, South Africa

Huizenga, Jan Marten, van Reenen, Dirk, and Touret, Jacques (2014) Fluid-rock interaction in retrograde granulites of the Southern Marginal Zone, Limpopo high grade terrain, South Africa. Geoscience Frontiers, 5 (5). pp. 673-682.

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Abstract

Fluid infiltration into retrograde granulites of the Southern Marginal Zone (Limpopo high grade terrain) is exemplified by hydration reactions, shear zone hosted metasomatism, and lode gold mineralisation. Hydration reactions include the breakdown of cordierite and orthopyroxene to gedrite + kyanite, and anthophyllite, respectively. Metamorphic petrology, fluid inclusions, and field data indicate that a low H2O-activity carbon-saturated CO2-rich and a saline aqueous fluid infiltrated the Southern Marginal Zone during exhumation. The formation of anthophyllite after orthopyroxene established a regional retrograde anthophyllite-in isograd and occurred at P-T conditions of ∼6 kbar and 610 °C, which fixes the minimum mole fraction of H2O in the CO2-rich fluid phase at ∼0.1. The maximum H2O mole fraction is fixed by the lower temperature limit (∼800 °C) for partial melting at ∼0.3. C-O-H fluid calculations show that the CO2-rich fluid had an oxygen fugacity that was 0.6 log10 units higher than that of the fayalite-magnetite-quartz buffer and that the CO2/(CO2+CH4) mole ratio of this fluid was 1. The presence of dominantly relatively low density CO2-rich fluid inclusions in the hydrated granulites indicates that the fluid pressure was less than the lithostatic pressure. This can be explained by strike slip faulting and/or an increase of the rock permeability caused by hydration reactions.

Item ID: 34524
Item Type: Article (Research - C1)
ISSN: 1674-9871
Keywords: granulite; fluid; Limpopo; retrograde; Southern Marginal Zone
Additional Information:

This article is open access, funded by China University of Geosciences, under the Creative Commons Attribution-Non Commercial-No Derivatives 3.0 license: http://creativecommons.org/licenses/by-nc-nd/3.0/

Funders: National Research Foundation (NRF), South Africa, University of Johannesburg
Projects and Grants: NRF Grant No. IFR1202190048
Date Deposited: 14 Aug 2014 01:58
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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