The role of fluid-induced partial melting in magmatic crystal mush in the origin of stratiform chromite deposits of the Bushveld Complex, South Africa
Final Report Abstract
This multidisciplinary research project combining field observations, mineralogical studies, experimental petrology and stable isotope analyses was aimed at testing the working hypothesis that chromitite layers in mafic-ultramafic layered intrusions, and specifically in the classical case of the Bushveld Complex in South Africa, can be formed by partial melting and replacement of silicate minerals by chromite due to additions of H2O and other volatile components to the resident magma at the contact with pre-existing, partly solidified cumulates. In general, the obtained results support the working hypothesis. Partial melting and replacement of orthopyroxene and plagioclase by chromite and olivine was reproduced in a series of experiments at 0.3 GPa and 1100–1300 °C by additions of variable amounts (2-6 wt.%) of H2O component to the model magma composition, which is believed to be parental for the lower mafic-ultramafic zones of the Bushveld complex. Triple-oxygen and hydrogen isotope ratios of interstitial, late-magmatic phlogopite from three localities of the UG2 chromitite layer imply two-stage contamination of the mantle-derived parental magma, first by as much as 30-40 wt.% of the lower and middle continental crust, and then by hydrous fluids (probably brines) derived from Transvaal sediments.
Publications
- (2018) Chemical and textural re-equilibration in the UG2 chromitite layer of the Bushveld Complex, South Africa. Journal of Petrology, 59, 1193–1216
Veksler I.V., Sedunova A.P., Darin A.V., Anosova M.O., Reid D.L., Kaufmann F., Hecht L., Trumbull R.B.
(See online at https://doi.org/10.1093/petrology/egy058) - (2018) How do chromitite layers form? 13th International Platinum Symposium, 30th June – 6th July 2018, Polokwane, South Africa
Veksler I.V.
- (2018) Small-scale Sr and O isotope variations through the UG2 in the eastern Bushveld Complex: the role of crustal fluids. Chemical Geology, 485, 100–112
Schannor M., Veksler I.V., Hecht L., Harris C., Romer R.L., Manyeruke T.D.
(See online at https://doi.org/10.1016/j.chemgeo.2018.03.040) - (2019). Variations in composition, texture, and platinum group element mineralization in the lower group and middle group chromitites of the Northwestern Bushveld Complex, South Africa. Economic Geology, 114(3), 569-590
Kaufmann, F.E., Hoffmann, M.C., Bachmann, K., Veksler, I. V., Trumbull, R.B., Hecht, L.
(See online at https://doi.org/10.5382/econgeo.4641) - (2020). Experimental study on the effects of H2O upon crystallization in the Lower and Critical Zones of the Bushveld Complex with an emphasis on chromitite formation. Contributions to Mineralogy and Petrology, 175(9), 1-17
Veksler, I.V., Hou, T.
(See online at https://doi.org/10.1007/s00410-020-01733-w) - (2021) Connate brine incorporation into the Bushveld magmas as evidenced by hydrogen and triple oxygen isotopes in phlogopite from the UG2 chromitite. Goldschmidt Conference 2021 (Virtual), 4-9 July 2021, Lyon, France
Zhou, H., Trumbull, R.B., Veksler, I.V., Bindeman, I.N., Glodny, J., Kaufmann, F.E., Rammlmair, D.
(See online at https://doi.org/10.7185/gold2021.6089) - (2021) Origin of chromitite layers in the Bushveld complex, South Africa, by hydration melting: an experimental study. 17th International Symposium on Experimental Mineralogy, Petrology and Geochemistry (EMPG-XVII), 1-3 March 2021, Potsdam, Germany
Veksler I.V., Wohlgemuth-Ueberwasser C., Hou T.
- (2021). Contamination of the Bushveld Complex (South Africa) magmas by basinal brines: Stable isotopes in phlogopite from the UG2 chromitite. Geology 49(11), 1272-1276
Zhou, H., Trumbull, R.B., Veksler, I.V., Bindeman, I.N., Glodny, J., Kaufmann, F.E., Rammlmair, D.
(See online at https://doi.org/10.1130/G49173.1)
