ARC Centre of Excellence for Core to Crust Fluid Systems

 

Fiona Foley

Credentials and Awards

BSc (Hons) Geology, University College Cork, Ireland; Thorley Sweetman Prize (2008); National University of Ireland Travelling Studentship in the Sciences (2008); MQRES Scholarship (2009).

 

Research Interests

My PhD research (begun March 2009) focuses on the Puysegur Subduction zone where the Australian Plate is currently subducting beneath the Pacific Plate. It is enigmatic in its almost complete lack of relict or active volcanism, save for the small Quaternary volcanic centres of Solander Island and associated seamounts, south of the South Island, New Zealand. Although it is tempting to assume that Solander andesites represent an island arc, there are significant problems in doing so. Seismicity patterns and the depth of large plate interface earthquakes in the subduction zone near Solander Island imply that the slab is both shallow and very shallowly dipping near Solander Island. The atypical setting, the adakitic geochemistry of the lavas, and their role as the sole volcanic expression of the Puysegur subduction make understanding the genesis of these volcanics critical.   

My research aims to contribute significantly to the determination of plate tectonic configurations in a complex collision zone. The expected outcome of this project is to differentiate between two models of crustal formation:
1) genesis of Solander Island lavas by melting in the presence of garnet along the exposed western edge of the subducting slab (Yogodzinski et al., 2001)
2) genesis of lavas by partial melting in garnet-bearing mafic rocks deep in the lower crust, probably similar to that which is exposed in Fiordland on the South Island, to the north.
Other outcomes include obtaining a more precise age for the Solander Island lavas.  The results will play an important role in deciphering genesis and evolution of the present-day subduction zone, as well as having significant impact on models for Archean and modern day continental crust genesis. 

Experimental Applications

I will be using experimental petrology to determine the equilibrium phase assemblages for Solander Island rocks. This will be performed on xenolithic and basaltic andesite lavas in order to establish whether primitive, hornblende-rich xenoliths on the island represent a suitable protolith for the lavas. Further to this, I will establish the most likely physical conditions of magma formation. Together with detailed geochemical investigations, I will be able to apply the results to geophysical models of the subduction zone to determine whether the subducting Australia Plate is melting or if upper mantle/lower crust is a more suitable protolith. Due to the young age of the Solander Island volcanics, I will also be able to study ¹⁰Be isotopes in order to establish contributions from the subducting plate to the magmas. On a broader scale, the experimental work performed here will give insights into melt segregation processes, chemistry of melts interacting with their hosts, and can further be applied to planetary formation mechanisms for both our own and other rocky planets.

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