Mineralogy and Petrology

, Volume 108, Issue 4, pp 589–605 | Cite as

High-grade metamorphism of ironstones in the Mesoarchaean of southwest Swaziland

  • Péter Horváth
  • Jürgen ReinhardtEmail author
  • Axel Hofmann
Original Paper


A sequence of high-grade rocks collectively referred to as Mkhondo Valley Metamorphic Suite is exposed around the Nhlangano Gneiss Dome in southwest Swaziland and also less extensively further north. Meta-ironstones are part of this sequence and have been studied specifically with two main objectives in mind, firstly, to test the hypothesis of the high-grade metamorphic sequence correlating with lower-grade Pongola-age rocks nearby, and secondly, to assess the potential of these meta-ironstones for retrieving P-T conditions of metamorphism. The studied ironstones contain substantial Al due to terrigenous clastic input and also include Mn-rich varieties. Three compositional groups of meta-ironstones can be distinguished: garnet-orthopyroxene-bearing ones, garnet-bearing, orthopyroxene-free ones, and a garnet-poor to garnet-free type. A comparison of bulk rock compositions between these high-grade meta-ironstones and low-grade Mn-poor to Mn-rich ironstones from the Mozaan Group supports a stratigraphic correlation. Pseudosection modelling demonstrates that aluminous meta-ironstones provide useful P-T constraints at high peak temperatures as they do not tend to produce significant amounts of melt, if any. The presence of Al is critical for introducing garnet to amphibolite and granulite-facies assemblages, which also allows to apply conventional thermobarometers. The combination of pseudosection modelling and conventional thermobarometry yielded peak metamorphic conditions of 850–890 °C at 7 to 8 kbar. These data are compatible with the ones obtained from associated metapelitic gneisses, except that the latter indicate decompression to lower pressure granulite-facies conditions. The petrological, structural and geochronological data from southwest Swaziland confirm major orogenic activity in the eastern Kaapvaal Craton during the Neo-Archaean.


Magnetite Kaapvaal Craton Phase Diagram Calculation Transvaal Supergroup Peak Assemblage 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



P. Horváth acknowledges the support of an NRF postdoctoral scholarship. We would like to thank Noah Nhleko, Swaziland Geological Survey, for showing us the outcrops of low-grade Pongola Fe- and Mn-rich metasediments, Johann Diener for discussions on amphibole modelling, Thomas Fockenberg at the University of Bochum for performing the Fe2+ analytical tests to cross-check our own results, and the director and staff of the Geological Survey and Mines Department, Swaziland, for their hospitality and support. Armin Zeh and an anonymous reviewer are thanked for their critical comments that helped to improve the manuscript.


  1. Alexander BW, Bau M, Andersson P, Dulski P (2008) Continentally-derived solutes in shallow Archean seawater: rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa. Geochim Cosmochim Acta 72:378–394CrossRefGoogle Scholar
  2. Bekker A, Slack JF, Planavsky N, Krapez B, Hofmann A, Konhauser KO, Rouxel OJ (2010) Iron formation: the sedimentary product of a complex interplay among mantle, tectonic, oceanic, and biospheric processes. Econ Geol 105:467–508CrossRefGoogle Scholar
  3. Beukes NJ, Cairncross B (1991) A lithostratigraphic-sedimentological reference profile for the late Archaean Mozaan Group, Pongola sequence: application to sequence stratigraphy and correlation with the Witwatersrand Supergroup. S Afr J Geol 94:44–69Google Scholar
  4. Condie KC, Kröner A, Milisenda CC (1996) Geochemistry and geochronology of the Mkhondo suite, Swaziland: evidence for passive-margin deposition and granulite facies metamorphism in the late Archean of Southern Africa. J Afr Earth Sci 21:483–506CrossRefGoogle Scholar
  5. de Villiers J (1960) The manganese deposits of the Union of South Africa. Geological Survey of South Africa Handbook 2, Pretoria, Government Printer, 271 ppGoogle Scholar
  6. Diener JFA, Powell R, White RW, Holland TJB (2007) A new thermodynamic model for clino- and orthoamphiboles in Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O. J Metamorph Geol 25:631–656CrossRefGoogle Scholar
  7. Gold DJC (2006) The Pongola supergroup. In: Johnson MR, Anhaeusser CR, Thomas RJ (eds) The geology of South Africa. Geological Society of South Africa, Johannesburg/Council for Geoscience, Pretoria, pp 135–147Google Scholar
  8. González PD, Sato AM, Llambías EJ, Petronilho LA (2009) Petrology and geochemistry of the banded iron formation in the Eastern Sierras Pampeanas of San Luis (Argentina): implications for the evolution of the Nogolí metamorphic complex. J S Am Earth Sci 28:89–112CrossRefGoogle Scholar
  9. Holland TJB, Powell R (1998) An internally consistent thermodynamic dataset for phases of petrological interest. J Metamorph Geol 16:309–343CrossRefGoogle Scholar
  10. Holland TJB, Powell R (2003) Activity-composition relations for phases in petrological calculations: an asymmetric multicomponent formulation. Contrib Mineral Petrol 145:492–501CrossRefGoogle Scholar
  11. Holland TJB, Baker JM, Powell R (1998) Mixing properties and activity-composition relationships of chlorites in the system MgO-FeO-Al2O3-SiO2-H2O. Eur J Mineral 10:395–406Google Scholar
  12. Horstmann UE, Hälbich IW (1995) Chemical composition of banded iron-formations of the Griqualand West Sequence, Northern Cape Province, South Africa, in comparison with other Precambrian iron formations. Precambrian Res 72:109–145CrossRefGoogle Scholar
  13. Horváth P, Reinhardt J, Hofmann A, Nagy G (2010) Neoarchaean high-grade metamorphism of politic gneisses and ironstones in the Nhlangano area, SW Swaziland.20th General Meeting of the IMA, August 2010, Budapest, Hungary. Acta Mineralogica-Petrographica Abstract Series 6, p. 593Google Scholar
  14. Hunter DR (1970) The ancient gneiss complex in Swaziland. Trans Geol Soc S Afr 73:107–150Google Scholar
  15. Hunter DR, Barker F, Millard HT Jr (1978) The geochemical nature of the Archean Ancient Gneiss complex and granodiorite suite, Swaziland: a preliminary study. Precambrian Res 7:105–127CrossRefGoogle Scholar
  16. Klein C (2005) Some Precambrian banded iron-formations (BIFs) from around the world: their age, geologic setting, mineralogy, metamorphism, geochemistry, and origin. Am Mineral 90:1473–1499CrossRefGoogle Scholar
  17. Kröner A (2007) The ancient gneiss complex of Swaziland and environs: record of early Archean crustal evolution in Southern Africa. In: van Kranendonk MJ, Smithies RH, Bennett VC (eds) Earth’s oldest rocks. Developments in Precambrian Geology 15, Elsevier, pp 465–480Google Scholar
  18. Leake BE, Woolley AR, Arps CES, Birch WD, Gilbert MC, Grice JD, Hawthorne FC, Kato A, Kisch HJ, Krivovichev VG, Linthout K, Laird J, Mandarino J, Maresch WV, Nickel EH, Rock NMS, Schumacher JC, Smith DC, Stephenson NCN, Ungaretti L, Whitaker EJW, Youzhi G (1997) Nomenclature of amphiboles: report of the subcommittee on amphiboles of the international mineralogical association commission on new minerals and mineral names. Min Mag 61:295–321CrossRefGoogle Scholar
  19. Miyano T, Klein C (1989) Phase equilibria in the system K2O-FeO-MgO-Al2O3-SiO2-H2O and the stability limit of stilpnomelane in metamorphosed Precambrian iron-formations. Contrib Mineral Petrol 102:478–491CrossRefGoogle Scholar
  20. Mukasa SB, Wilson AH, Young KR (2013) Geochronological constraints on the magmatic and tectonic development of the Pongola Supergroup (Central Region), South Africa. Precambrian Res 224:268–286CrossRefGoogle Scholar
  21. Pattison DRM, Chacko T, Farquhar J, McFarlane CRM (2003) Temperatures of granulite-facies metamorphism: constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange. J Petrol 44:867–900CrossRefGoogle Scholar
  22. Potts PJ (1987) A handbook of silicate rock analysis. Blackie, Glasgow & London, 622 pCrossRefGoogle Scholar
  23. Powell R, Holland TJB (1999) Relating formulations of the thermodynamics of mineral solid solutions: activity modelling of pyroxenes, amphiboles and micas. Am Mineral 84:1–14Google Scholar
  24. Powell R, Holland TJB, Worley B (1998) Calculating phase diagrams involving solid solutions via non-linear equations, with examples using THERMOCALC. J Metamorph Geol 16:577–588CrossRefGoogle Scholar
  25. Taylor J, Stevens G, Armstrong R, Kisters AFM (2010) Granulite facies anatexis in the Ancient Gneiss Complex, Swaziland, at 2.73 Ga: mid-crustal metamorphic evidence for mantle heating of the Kaapvaal craton during Ventersdorp magmatism. Precambrian Res 177:88–102CrossRefGoogle Scholar
  26. Taylor J, Stevens G, Lana C (2012) Age and field relationships of Mahamba orthogneisses and Mkhondo Valley Metamorphic suite paragneisses from the Mkhondo River, Ancient Gneiss complex, Swaziland. S Afr J Geol 115:369–384CrossRefGoogle Scholar
  27. White RW, Powell R (2002) Melt loss and the preservation of granulite facies mineral assemblages. J Metamorph Geol 20:621–632Google Scholar
  28. White RW, Powell R, Holland TJB, Worley BA (2000) The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3. J Metamorph Geol 18:497–511CrossRefGoogle Scholar
  29. White RW, Powell R, Holland TJB (2007) Progress relating to calculation of partial melting equilibria for metapelites. J Metamorph Geol 25:511–527CrossRefGoogle Scholar
  30. Wilson AC (1980) Swaziland 1:50,000 geological series, sheets 2631CD, 2731AA and 2731AB, edition 1 (compiled by A.C. Wilson)Google Scholar
  31. Wilson AC, Jackson MPA (1988) Mantled gneiss domes in southern Swaziland and the concept of ‘stable’ Pongola cratonic cover. S Afr J Geol 91/3:404–414Google Scholar

Copyright information

© Springer-Verlag Wien 2013

Authors and Affiliations

  • Péter Horváth
    • 1
    • 2
  • Jürgen Reinhardt
    • 1
    Email author
  • Axel Hofmann
    • 1
    • 3
  1. 1.School of Agricultural, Earth & Environmental Sciences, Geological Sciences Div.University of KwaZulu-NatalDurbanSouth Africa
  2. 2.Department of GeologyRhodes UniversityGrahamstownSouth Africa
  3. 3.Department of GeologyUniversity of JohannesburgJohannesburgSouth Africa

Personalised recommendations