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This project is eligible for support from Cardiff Universtiy through the School of Earth & Ocean Sciences.

To apply, please visit the Cardiff University Postgraduate Research portal: http://www.cardiff.ac.uk/for/prospective/postgraduate/applying.html

Description

Rock fragmentation and transport at and below the Earth’s surface produces breccias (Fig. 1) consisting of clasts and chemically and mechanically formed matrix. Breccias may form from faulting (seismic or aseismic), solution and chemical alteration of rocks, volcanic eruption, igneous intrusion, meteorite impact, and several sedimentary processes.

Despite over two centuries of research, and their economic importance as ore deposit hosts, the origins of many breccias are highly controversial. This project aims to link the products of brecciating to the fragmentation and transport processes that formed them, by studying outstanding examples of breccias in the field and laboratory, combined with modelling.

A major difference between brecciation processes is the rates of fragmentation and transport. Aseismic faulting, solution and chemical alteration of rocks are slow compared to seismic faulting, fluid release in magmatic and some hydrothermal processes (e.g. Oliver et al., 2006), and meteorite impact. The rate of brecciation has a fundamental genetic significance. Examples of breccias formed at a wide range of strain rates will be analysed, including impact breccias, fault breccias, hydrothermal breccias and sedimentary breccias.

Breccias will be characterised in the field and by image analysis through fractal geometry, including properties such as clast size distribution, circularity, and anisotropy. These observations will be combined with theory, and used to constrain numerical modelling of brecciation by particle flow codes (e.g. Ord and Hobbs, 2010). The results will be applicable to understanding the origin of enigmatic breccias in the geological record, as well as having important implications for the genesis of many types of ore deposit, and for their exploration.

Breccia studied will come from the Lawn Hill Impact Structure, fault breccias, and hydrothermal breccias in the Mount Isa inlier, NE Queensland, which will be visited in the first year of the PhD, and the Triassic Wadi breccia of the Glamorgan coast, amoung others. Numerical modelling will be undertaken at the Universities of Western Australia and Bath, and 3D particle analysis at the University of Mainz.

Fig 1

Fig 1. Hydrothermal breccia in Mount Isa inlier, QLD, Australia.

Training

This PhD will combine training in field geology with laboratory analysis and numerical modelling, at four different institutions. The training will directly address four of the most wanted skills in postgraduates (NERC 2012): Modelling, Data Management, Numeracy and Fieldwork. The training will include advanced techniques in structural geology (field based; Mt Isa inlier, Australia), image analysis, optical and scanning electron microscopy (optical and electron microscopes available at Cardiff University), numerical modelling (particle flow codes available through University of Western Australia, University of Bath) and particle analysis (University of Mainz). Collaboration with the University of Bath involves an interdisciplinary interaction with the Department of Mechanical Engineering.

NERC 2012. MOST WANTED II: postgraduate and Professional Skills Needs in the Environment Sector. LWEC Report, NERC.

Background Reading

Oliver, N.H.S., Rubenach, M.J., Fu, B., Baker, T., Blenkinsop, T.G., Cleverley, J.S., Marshall, L.J., Ridd, P.J., 2006. Granite-related overpressure and volatile release in the mid crust: fluidized breccias from the Cloncurry District, Australia. Geofluids 6, 346–358.

Ord, A., Hobbs, B.E., 2010. Fracture pattern formation in frictional, cohesive, granular material. Philos. Trans. A. Math. Phys. Eng. Sci. 368, 95–118.

Contact Details

Professor Tom Blenkinsop – blenkinsopt@cardiff.ac.uk