Mantle and crustal processes, and associated metallogenesis including kimberlites

Focus Area 1

Mineral deposit formation in the light of the evolution of mantle and crustal processes through time, particularly focusing on the oldest (i.e. Archaean) and deepest parts of the lithosphere, including the study of kimberlites and diamonds and metallogenic provinces.

Mineral deposit formation in the light of the evolution of mantle and crustal processes through time, particularly focusing on the oldest (i.e. Archaean) and deepest parts of the lithosphere, including the study of kimberlites and diamonds and metallogenic provinces.

 

The southern African lithosphere is home to a complex assemblage of crustal and mantle rocks and minerals that formed over more than 3.5 billion years of Earth history. It hosts some of the oldest rocks on Earth in the Kaapvaal Craton, an Archaean continental nucleus around which younger crust accreted during plate tectonic processes in the Proterozoic and Phanerozoic eons. Primarily owing to secular cooling, geological and tectonic processes, including lithosphere formation mechanisms, changed over this vast time span of Earth history. This also resulted in changes in the composition, mineralogy and lithological diversity of igneous rocks of the crust and mantle rocks brought to the surface as xenoliths.  Surface processes also changed through time as a result of changes in factors such as solar luminosity and the evolution of life, that resulted in major changes in ocean and atmospheric chemistry (e.g., the rise of atmospheric oxygen). The evolution of surface processes, the growth of continental crust, and the cooling, thickening and modification (through early melt depletion and later metasomatism) of the mantle through time is linked to changes in metallogenic processes. This DSI-NRF CIMERA research focus area investigates the link between mantle and crustal processes and metallogenesis over Earth history.

 

The metallogenesis of primary diamond deposits is a case in point, as they are largely restricted to thick Archaean cratonic lithosphere. Investigations of mantle-derived xenoliths, xenocrysts and diamonds, and geophysical studies of lithospheric structure are thus included in this focus area. It also comprises studies pertinent to the formation and evolution of volatile-rich magmas such as kimberlites and carbonatites, including their potential to modify cratonic mantle. Studies pertaining to kimberlite pipe emplacement and subsequent erosion histories, as well as those advancing diamond exploration are also conducted in this focus area. Also of relevance for this focus area are studies that investigate fundamental questions in economic geology research related to the evolution of surface conditions, tectonic processes, and continental growth through time. It thus includes research on metallogenic provinces.

 

Current Research:

  1. Volcanology, petrology and geochemistry of selected kimberlites from the Lulo kimberlite field, Angola
    Dr Geoffrey Howarth
  2. Impact of metasomatic melt-rock interaction on thermal and chemical properties of adjacent on- and off-craton lithosphere from Lesotho and East Griqualand (South Africa): Implications for diamond preservation
    Prof. Phil Janney
  3. Testing the use of olivine as a diamond indicator mineral and in defining kimberlite/orangeite sampling depth and craton margins
    Dr Geoffrey Howarth
  4. Age and origin of the lithospheric mantle below the Ancient Gneiss Complex (Eswatini)
    Dr Karen Smit