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.
contact(s): Dr Jodie Miller, jmiller at sun.ac.za
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.
contact: Dr Martin Klausen, klausen at sun.ac.za