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E438: The role of liquid immiscibility in creating Fe-Ti oxide deposits in mafic layered intrusions (Lead Supervisor: Marian Holness, Earth Sciences)

Supervisors: Marian Holness (Earth Sciences), Jens Andersen (University of Exeter) and Sam Weatherley (Geological Survey of Denmark and Greenland)

Importance of the area of research:

Much recent work on mafic layered intrusions has demonstrated the significance of the onset of liquid immiscibility as fractionation drives basaltic magma down its liquid line of descent. The different physical properties of the two immiscible conjugates means that the dense inviscid Fe-rich liquid can be effectively segregated from its buoyant viscous Si-rich conjugate, potentially leading to chamber-wide mass transport and fractionation. The concentration of economically important metals such as V, Pd and PGE in the Fe-rich liquid, means that this differential migration has enormous implications for the development of commercially important mineral deposits. The extent to which differential migration occurs in layered intrusions, both in the mushy layers on the intrusion’s roof and floor, and in the convecting bulk magma, is not currently well understood.

Project summary:

The project will focus on three intrusions. Geochemical and microstructural methods to detect the record of differential migration of immiscible liquid conjugates will be developed using observations of the two of these intrusions (the Skaergaard intrusion of East Greenland, and the Bushveld Intrusion of South Africa) that contain excellent evidence for immiscibility. These methods will then be applied to the Baima Intrusion of SW China, which contains notable thick layers of Fe-Ti oxides liquid for which there is currently no adequate hypothesis to explain their formation.

What the student will do:

The student will undertake a detailed petrologic investigation of examples of differential migration in the Skaergaard. Microstructural investigations involving quantifying the grain-scale distribution of oxides, reactive symplectites indicative of differential migration, and granophyre will be undertaken to constrain the role of wetting properties in controlling the movement of the immiscible conjugates through a crystal mush. The microstructures and geochemistry of highly oxide-rich layers in the Bushveld will be analysed to determine the extent to which they are built of discrete cumulus oxide grains compared to segregations of Fe-rich immiscible interstitial liquid. The understanding gained from study of these intrusions will be applied to the Baima intrusion, to determine whether it is possible to develop robust methods to distinguish the relative contributions of cumulus grains and differential migration of Fe-rich immiscible liquids in forming oxide-rich layers of economic importance.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Holness, M.B., Stripp, G., Humphreys, M.C.S., Veksler, I.V., Nielsen T.F.D. & Tegner C. 2011. Silicate liquid immiscibility within the crystal mush: late-stage magmatic microstructures in the Skaergaard Intrusion, East Greenland. Journal of Petrology, vol. 52, pp.175-222.

Fischer, L.A., Wang, M., Charlier, C., Namur, O., Roberts, R.J., Veksler, I.V., Cawthorn, R.G. & Holtz, F. 2016. Immiscible iron- and silica-rich liquids in the Upper Zone of the Bushveld Complex. Earth and Planetary Science Letters, vol. 443, pp. 108-117

Zhou, M., Chen, W.T., Wang, C.Y., Prevec, S.A., Liu, P.P. & Howarth, G.H. 2013. Two stages of immiscile liquid separation in the formation of Panzhihua-type Fe-Ti-V oxide deposits, SW China. Geoscience Frontiers, vol. 4, pp. 481-502

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Other projects available from the Lead Supervisor can be viewed here.

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