Prof Gary Stevens

SARChI Professor in Experimental Petrology

Director Central Analytical Facilities

Ph (021) 808 3127, Fax (021) 808 3129

Email gs@sun.ac.za

Biography:

BSc (Hons) University of Johannesburg (RAU)
MSc University of Johannesburg (RAU)
PhD University of Manchester

Research Interests:

Experimental Petrology
Granite Petrogenesis
Archaean Metamorphism
Crustal Anatexis

Current Projects:
My current projects relate to several main themes that are generally interlinked through the concepts of the response of the crust to high temperature processes and the evolution of crustal melts. These are: 1. Studies of metamorphism, magmatism and partial melting in the rocks associated with the Barberton greenstone belt. These studies aim to better understand the geodynamic and chemical evolution of Earth’s young crust and the nature of the tectonic processes relevant to this crust. Papers 3, 4, 6, 7, 8, 9, 10, 11, 16 and 17 in the list below relate to this work. On my current students, Jeanne Taylor, Cynthia Sanchez-Garrido and Angelique Laure are involved in this work. Richard Armstrong (ANU), Alex Kisters, JF Moyen, John Clemens, Hervé Martin (Université Blaise Pascal) and Régis Doucelance (Université Blaise Pascal) are important collaborators. 2. S-type granite petrogenesis and the anatexis of metapelitic/psammitic rocks. These studies aim to better understand how the metasedimentary crust melts, how melts and magmas excape their anatectic source and how the resultant accumulations of granitic magma evolve. To date this work has focussed on the Damara belt in Namibia and the S-type granites of the Cape Granite suite. Rob Ward and Arnaud Villaros are current students involved in this work and papers 1, 5, 13 and 14 in the lists below give an insight into the nature of this research. There is a crossover between this theme and the one above in that the metasedimentary granulites of the ancient gneiss complex in Swaziland (Jeanne Taylor’s project) fit equally well in both areas. John Clemens, Ian Buick and Alex Kisters and important collaborators in this work. 3. Experimental investigations of the behaviour of sulphide minerals and melts during high temperature processes. These studies have focussed on the anatexis of Broken Hill type massive sulphide ores, the solubility of gold in S-bearing granitic magmas and the behaviour of gold and platinum group elements during partial melting of sulphide assemblages. Papers 12 and 15 in the lists below are relevant to this work. Each of these themes is fascinating provides wonderful opportunities for training. Whilst we have made very important advances in each area over the past few years, a huge amount remains to be done. Thus, my research activities for the next few years will be more or the same. Importantly, we are very close to critical breakthroughs in several projects and there are tremendous opportunities for students to involve themselves in truly exciting science. In the case of advanced students and post-doctoral researchers seeking academic careers, there are unique opportunities inherent to some of these projects currently available.

Publications:
Ward, R., Stevens, G. and Kisters, A.F.M. 2008. Fluid and deformation induced partial melting and melt volumes in low-temperature granulite-facies metasediments, Damara Belt, Namibia. LITHOS, doi 10.1016/j.lithos.2008.04.0 Fagereng,A., Harris, C., La Grange, M. and Stevens, G. 2008. Stable isotope study of the archaean rocks of the vredefort impact structure, central Kaapvaal craton, South Africa. Contributions to Mineralogy and Petrology, 155: 63-78. Stevens, G. and Moyen, J-F. (2007). Metamorphism in the Barberton granite greenstone terrain: a record of Paleoarchaean accretion. Developments in Precambrian Geology (Eds van Kranendonk M.J., Smithies, R.H. and Bennett, V.C. S Ed Condie K.C.). 15. Elsevier. Amsterdam. Moyen, J-F, Stevens, G., Kisters, A.F.M. and Belcher, R. (2007). TTG plutons of the Barberton granitoid-greenstone terrain, South Africa. Developments in Precambrian Geology (Eds van Kranendonk M.J., Smithies, R.H. and Bennett, V.C. S Ed Condie K.C.). 15. Elsevier. Amsterdam. Stevens G., Villaros, A. and Moyen, J-F. (2007). Experimental melt compositions as an aid to understanding S-type granite petrogenesis. GEOLOGY, 35: 9-12. Dziggel, A., Stevens, G., Poujol, M. and Armstrong, R. (2006). Contrasting source components of clastic metasedimentary rocks in the lowermost Formations of the Barberton greenstone belt. In: Reimold, W.U. and Gibson, R.L., eds., Processes on the Early Earth: Geological Society of America Special Paper, 405, 157-172. Moyen, J-F., Stevens, G. and Kisters, A.F.M. (2006). Record of an Archaean subduction zone: 3.2 Ga high-pressure, low-temperature metamorphism in the Barberton terrain, South Africa. Nature, 442: 559-562.

Clemens, J.D., Yearron, L.M. and Stevens, G. (2006). Barberton (South Africa) TTG magmas: Geochemical and experimental constraints on source-rock petrology, pressure of formation and tectonic setting. Precambrian Research, 151: 53-78.

Westraat, J., Kisters, A.F.M., Poujol, M. and Stevens, G. (2005). Transcurrent shearing, granite sheeting and the incremental construction of the tabular, 3.1 Ga Mpuluzi batholith, Barberton granite-greenstone terrain, South Africa. Journal of the Geological Society of London, 162, 373-388.

Diener, J.F.A., Stevens, G. Kisters, A.F.M., Poujol, M. (2005). Metamorphism and exhumation of the basal parts of the Barberton greenstone belt, South Africa: Constraining the rates of Mesoarchaean tectonism. Precambrian Research 143, 87-112 Diener, J.F.A., Stevens, G. Kisters, A.F.M. (2005). High-pressure low-temperature metamorphism in the southern Barberton granitoid greenstone terrain, South Africa: a record of overthickening and collapse of Mid-Archaean continental crust. American Geophysical Union Special Publication (in press). Stevens, G., Prins, S. and Rozendaal, A. 2005. Partial melting of the assemblage sphalerite + galena + pyrrhotite + chalcopyrite + sulfur: Implications for high-grade metamorphosed massive sulfide deposits. Economic Geology, 100: 106-110. Buick, I.S., Stevens, G. and Gibson, R.L. (2004). The role of water retention in the anatexis of metapelites in the Bushveld Complex aureole, South Africa: An experimental study. Journal of Petrology, 45: 1777-1797.

Spicer, E.M., Stevens, G. and Buick, I.S. (2004). The low-pressure partial-melting behavior of natural metapelites from the Mt Stafford area, Central Australia; including the role of boron as a possible melt fluxing agent. Contributions to Mineralogy and Petrology, 148: 131-152. Stevens, G., Przybylowicz, W.J. and Martin, L.E. (2004). Micro-PIXE studies of low-level gold solubility in natural magmas: Experiments on two felsic compositions. X-Ray Spectrometry, 33: 216-221.

Kisters, A.F.M., Stevens, G., Dziggel, A., Armstrong, R.A. (2003). Extensional detachment faulting and core-complex formation at the base of the Barberton greenstone belt: evidence for a 3.2 Ga orogenic collapse. Precambrian Research 127, 355-378.

Stevens, G., Droop, G.T.R., Armstrong, R.A., and Anhaeusser, C.R. 2002. The Schapenburg schist belt: Amphibolite facies Archaean metasediments of the Figtree Group, Barberton greenstone belt, South Africa. South African Journal of Geology, 105: To appear in December 2002 issue.

Preston, R.F., Stevens, G. and McCarthy, T.S. 2002. Fluid compositions in equilibrium with silica-undersaturated magmas in the system Na2O-Al2O3-SiO2-H2O: Clues to the composition of fenitizing fluids. Contributions to Mineralogy and Petrology, Manuscript: 0414. DOI: 10.1007/s00410-002-0414-1. Printed version to appear December 2002

Murphy, P.J., Stevens, G. and La Grange, M.S. 2000. Gold-chloride speciation in hydrothermal fluids: a Raman spectroscopic study at geologically relevant pressures and temperatures. Geochemica Cosmochemica Acta, 64: 479-494. Stevens, G., Clemens, J.D. and Droop, G.T.R. 1997. Migmatites, granites and granulites: The data from experiments on "primitive" metasedimentary protoliths. Contributions to Mineralogy and Petrology, 128: 352-370.