ARC Centre of Excellence for Core to Crust Fluid SystemsNicole McGowan
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PhD Student Contact DetailsAustralian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), GEMOC
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PhD
Thesis title: Messages from the Mantle: Geochemical Investigations of Ophiolitic Chromitites
Project:
Ophiolites are slices of oceanic crust and upper mantle, thrust onto the continents above subduction zones; they are direct evidence of the forces involved in plate tectonics. The mantle sections of these slices contain lenses of chromitites, rocks composed mostly of Cr-Al oxides. Small chromitite lenses represent the extraction of Cr from several cubic km of mantle, and its transport and deposition by large volumes of melts. Chromitite contains significant information about large-scale processes in Earth’s mantle, but their genesis is poorly understood.
My project uses several approaches to provide new kinds of geochemical data related to the origins and evolution of ophiolitic chromitites. A better understanding of processes involving large-scale fluid flow in the upper mantle; specifically how Cr is concentrated in one spot, and the sources/nature of fluids involved, is being investigated. The work will provide a clearer picture of the origins of “ophiolite” peridotites, addressing the problem of apparent old ages of some protoliths.
Techniques are being developed for in situ analysis of the stable isotopes of Mg and Fe, which will provide insight into intermineral isotopic fractionation during REDOX processes, and their role in the formation of chromitites. Laser-ablation and mass-spectrometric facilities in the Geochemical Analysis Unit (GAU) within the ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS)/GEMOC Key Centre (Department of Earth and Planetary Sciences) are being employed.
The GAU facilities are also being used to develop the analysis of radiogenic Sr, Nd (TIMS) and Hf isotopes (MC-ICP-MS) in chromitites and their associated host rocks, which will provide further constraints on source materials and mantle/fluid interactions to provide a basic picture of the chemical evolution of each locality. The low levels of each element will make this a challenging task. Previous Hf work on chromitite deposits has not been reported, and may prove to be a useful tool in chromitite genesis.
Three sampling locations have been selected to cover a range of deposit types. The first location includes the Luobusa and Dongqiao peridotite massif of SE Tibet. Luobusa chromitites have received a lot of attention because of reports of diamonds and other strange minerals. Dongqiao chromitites contain an older generation of PGMs, suggesting involvement of old (possibly continental) lithosphere. The second and third locations are the Antalya ophiolite complex in S. Turkey, and the Ojén Massif in S. Spain. Ojén neighbors the larger Ronda massif, which has chromitites that appear to be related to the intrusion of pyroxenites into the harzburgite massif.
My PhD project is linked to the ARC CoF CCFS Foundation Research Project 1 TARDIS-E: Tracing Ancient Residues Distributed in the Silicate Earth. This program includes the research of Dr. J. M. González-Jiménez, who is studying the detailed mineralogy and Os-isotope geochemistry of a large collection of ophiolite samples, and that of J. X. Huang, who is using Mg isotopes as tracers of fluid processes in the mantle. There is close collaboration with related research programs at China’s Tibetan Research Institute (Dr. R. Shi) and the Universities of Granada (Prof. F. Gervilla), Zaragosa (Prof. I. Fanlo) and Barcelona (Prof. J. Proenza).
Supervisors:
Professor William L. Griffin, A/Prof. Norman J Pearson, Professor Suzanne Y. O'Reilly
Publications
McGowan, N., Fowler, A. M., Parkinson, K., Bishop, D. P., Ganio, K., Doble, P. A., Booth D. J., Hare, D. J. (2014) Microchemical imaging: A new method for fine scale analysis of trace elements in fish otoliths during early life, Science of the Total Environment, 494-495, 177-186
Thomas, P. S., Stuart, B. H., McGowan, N., Guerbois, J. P., Berkahn, M., Daniel, V. (2011) A study of ochres from an Australian aboriginal bark painting using thermal methods, Journal of Thermal Analysis and Calorimetry, 104(2), 507-513
Background
Bachelor of Science (Honours, first class) in Applied Chemistry - University of Technology, Sydney, Australia
Project: Fish Migration by Analysis of Otoliths using Elemental Bio-Imaging LA-ICP-MS