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E411: Quantifying the anatomy of subduction zones in the Greek Cyclades (Lead Supervisor: Owen Weller, Earth Sciences)

Supervisors: Owen Weller (Earth Sciences) and Richard Taylor (Earth Sciences

Importance of the area of research:

Subduction zones are regions of intense multi-disciplinary interest, as they constitute conduits of direct geochemical exchange between the surface and mantle, are the foci of elevated seismic activity, and ultimately drive plate tectonic motions. However, fundamental questions remain regarding the anatomy of subduction zones, such as their precise thermal architecture [1] and extent of surface/mantle water recycling [2], which have implications throughout the Earth Sciences. This project will shed new light on these foundational issues through integrated structural, metamorphic and geochronological analysis of high-pressure metamorphic rocks that form in subduction zones.

Project summary:

This project will combine field and laboratory studies of blueschist- and eclogite-facies rocks from the Greek Cyclades in order to understand the thermal budget and hydration state of subduction zones. One of the major tools will be applying phase equilibria modelling to exhumed high-pressure rocks, in order to investigate prograde metamorphism in subduction zones. This modelling will take advantage of recent advances in activity-composition models appropriate for investigating high-pressure metamorphism, which allow for a more nuanced interrogation of metamorphic rocks and quantification of water budgets [3]. These natural data will then be compared with, and used to refine, existing tectonothermal models of subduction zones. A key feature of this work is using the Cyclades as a natural laboratory, given the exceptional preservation of high-pressure rock assemblages in this locality.

What the student will do:

The student will begin by conducting fieldwork on the island of Syros in the Greek Cyclades. We will characterise the tectonostratigraphic and structural setting of the high-pressure assemblages, and collect samples for dating and pressure-temperature calculations. State-of-the-art analytical techniques will be will be utilized to study the samples, including: electron microprobe analysis to determine mineral compositions, phase equilibria modelling to determine pressure-temperature conditions of formation, and laser ablation split stream geochronology to obtain temporal constraints and rates of metamorphism. The latter will be conducted using the world-class facilities at Curtin University in Western Australia. The student will integrate this analytical information with thermal modelling of subduction zones to gain new insight into subduction zone anatomy. The field-to-lab methodology will be initially developed in Greece, but there is scope to apply this to other regions with well-preserved high-pressure metamorphism, such as southern Spain.

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:

[1] Penniston-Dorland, S.C., Kohn, M. & Manning C.E. The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models. Earth and Planetary Science Letters, vol. 428, pp. 243-254, doi: 10.1016/j.ep

[2] Clarke, G.L., Powell, R. & Fitzherbert, J.A. 2006. The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling. Journal of Metamorphic Geology, vol. 24, pp. 715-725, doi: 10.1111/j.1525-1314.2006.00664.x.

[3] Weller, O.M., Wallis, S.R., Aoya, M. & Nagaya, T. Phase equilibria modelling of blueschist and eclogite from the Sanbagawa metamorphic belt of southwest Japan reveals along-strike consistency in tectonothermal architecture. 2015. Journal of Metamorphi

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