Metamorphism, Magmatism/Igneous and Crustal Evolution

• Metamorphic  petrology, U-Pb  geochronology and  isotope tracing
  

This research has concentrated on understanding high-temperature processes involved in continental evolution through: a) obtaining geochronological and isotopic constraints on the evolution of high-grade, polymetamorphic terrains; b) petrological and mineral-scale geochemical studies of anatexis; c) understanding temporal relationships between anatexis and felsic magmatism in continental intra-plate settings; d) linking the trace element geochemistry of major silicate minerals in to those of accessory phases used to date metamorphism; e) the use of B- and Li- elemental and isotopic geochemistry to quantify HT metamorphic processes; f) the chemical, U/Pb geochronological and (Hf,Nd) isotopic evolution of S-type granites and their source regions; and g) development of U/Pb, Hf, Nd and O isotopic reference materials for high-spatial resolution geochronology and isotope tracing applied to metamorphic and igneous petrology.

 This research is partly field-work based and is heavily dependent on high-spatial resolution analytical techniques. It typically involves the use of SEM-EDS, EPMA, SIMS and LA-ICP-MS (quadrupole, sector field and multi-collector) instruments, as well as thermodynamic modelling involving software packages such as Theriak-Domino and Perplex. Application  of these techniques is currently being undertaken in a number of field areas, including the Damara Belt (Namibia), the West Coast Belt; Namaqua-Natal Metamorphic Belt; the Orange River Pegmatite Belt and the Limpopo Belt (South Africa); The Aravali-Delhi Orogenic Belt and the Kerala Khondalite Belt (India); and the Harts Range (central Australia).

 This research has been supported by grants from the Australian Research Council (ARC), the NRF; the Conselho Nacional de Desenvolvimento Científico e Techologíco (CNPq, Brazil; Programa Ciência Sem Fronteiras), and the CIMERA Centre of Excellence (a Wits/UJ/SU partnership). It has involved collaborations with scientists from South Africa (Stellenbosch University, University of the Witwatersrand, Council for Geosciences), Australia (Australian National University, Curtin University of Technology, Monash University), Japan (Niigata University, Okayama University), USA (Lehigh Univeraity, University of Maine), India (University of Rajasthan, Indian Institute of Technology, Kharagpur), Brazil (Federal University of Ouro Preto), Italy (University of Padova) and Spain (University of Grenada).

contact(s): Prof Ian Buick, buick at sun.ac.za

• Crustal evolution in the Namaqua Metamorphic Belt

This work is part of a large development project funded by the Namibian Geological Survey and managed by the Council for Geosciences. The work involves integrated petrology, geochemistry, radiogenics and geochronology to support the development of a new lithostratigraphic and tectonic framework for the Karas and Warmbad regions in southern Namibia which form part of the Namaqua Sector is the Namaqua Natal Metamorphic Belt. A particular focus of my work involves: (1) using radiogenic isotopes and geochronology to understand the lithostratigraphic framework and the relationships between different igneous and metamorphic rock suites; and (2) understanding the nature of terrane boundaries between different crustal components and the shear zones that define them. The work is conducted in collaboration with Dr Paul Macey from the Council for Geoscience and Dr Christie Rowe from McGill University in Canada. This work builds on similar work in northern Mozambique conducted with the same research team.

• Experimental petrology and partial melting of rocks

contact(s):

Prof Gary Stevens, gs at sun.ac.za

• Formation and emplacement of Large Igneous Provinces through space and time.

Large Igneous Provinces (LIPs) represent excessive volumes of predominantly basic/mafic (but occasionally also associated silicic/felsic) magmatism, which typically form during the break-up of a supercontinent. Phanerozoic examples (like the Jurassic Karoo and Cretaceous Etendeka across southern Africa) – related to the breakup of Pangaea (Gondwana) – are still preserved as remnants of continental flood basalts and associated feeder dykes, sills and layered mafic-ultramafic intrusions. Older LIP-examples, more tentatively related to the breakup of older supercontinents (e.g., Rodinia, Nuna-Columbia and the oldest Superia), are more deeply eroded and often only preserved as giant mafic feeder dyke systems. Precambrian mafic dykes, representing efficient magma transporting channel ways from a mantle source and up through the continental crust, therefore provide crucial outcrops that allow us to probe into these ancient LIPs. They allow us to do so in a number of ways: (1) Accessory crystal of baddeleyite (ZrO2) can be extracted and U-Pb dated, providing an age of magma crystallization; (2) Another mineral, magnetite, preserves the magnetic field during this crystallization and thereby allow paleomagnetists to orientate and position these dykes relative to a specific paleo-pole; (3) Dyke trends and swarm patterns relate to a paleo-stress field at the time of their emplacement, as well as the in-depth location of their mantle sources; (4) Last, but not least, a dyke’s bulk rock composition provides clues to the type of mantle source, as well as its degree and depth of partial melting. Combined, such multi-disciplinary research efforts into Precambrian mafic dykes thereby offer us with a wealth of information about how ancient LIPs formed, were emplaced, relate to supercontinental breakup and eventually got dispersed on their host fragments. Supercontinental reconstructions, in turn, provide an even larger group of geologists with a more complete geological puzzle picture to work on.

As part of a global, multi-disciplinary research programme (e.g., www.largeigneousprovinces.org and www.supercontinents.org), Stellenbosch contributes with the basic mapping, structural interpretation, sampling and petrological study of mafic dyke swarms across southern Africa, as well as Greenland’s North Atlantic Craton (NAC). This is done in close collaboration with (1) Prof Ulf Söderlund’s baddeleyite separation laboratory at Lund’s University (Sweden) and subsequent geochronological work at Stockholm’s TIMS-laboratory, (2) Prof Natasha Lubnina’s, Dr Michiel de Kock’s and Prof Dave Evan’s paleomagnetic laboratories at Moscow’s State University, the University of Johannesburg and Yale University, respectively, and (3) the Royal Geological Survey of Denmark and Greenland (GEUS), who has facilitated all sampling across the NAC. Since 2010, Stellenbosch’s Central Analytical Facilities (CAF) has generated XRF major and ICPMS-LA trace element data on bulk rock samples from (1) >300 dykes/sheets/sills from six major magmatic events affecting southern Africa since the Archaean (i.e., Pongola, Ventersdorp, Bushveld, Soutpansberg-Mashonaland, Umkondo and Karoo), financed by grants from Sweden’s Research Council and South Africa’s NRF, and (2) >400 dykes/sheets/sills from at least eight different swarms across NAC, financed by GEUS. Many of these results are currently being written up, while continued field work is being extended into the Greater Congo Craton, through support from South Africa’s NRF and collaboration with Central African Universities.