Associate Professor Tracy Rushmer
Associate Professor (CoRE)
Office : E7A 423
A/Prof. Tracy Rushmer
B.Sc.: University of California at Berkeley, Diplom (Masters): University of Zurich; Ph.D.: ETH-Zurich (Geology and Petrology)
I am an experimentalist who works with both hydrostatic (piston-cylinders and other high pressure non-dynamic equipment) and deformation (mainly solid-media equipment, e.g. Griggs) to investigate mineral interactions under pressure and temperature. My research interests include partial melting processes in zones of active plate convergence; the chemical and physical interplay between deformation and fluid flow; extraction and migration of partial melt in different tectonic environments; core formation (metal-silicate separation) and dynamics at the core/mantle boundary. My work focuses on the evolution of planetary bodies, particularly on differentiation, which is the fundamental mechanism by which the terrestrial planets evolve through time. We know now that major differentiation between crust and mantle occurred much earlier in the Earth than previously thought. To understand fully the consequences of major differentiation events, I see the way forward is to integrate experimental, theoretical and numerical studies of partial melting, thermal evolution and geodynamic processes. Therefore I am most interested in this type of scientific approach.
Most recently we have begun developing fully collaborative experimental high pressure facilities between the Bragg Institute, Macquarie University and the Australian synchrotron. We are bringing a D-DIA (deformation mulit-anvil high pressure and temperature apparatus) to Australia to perform high-pressure, in-situ, experiments on the Melbourne-based synchrotron and 2) building a modified D-DIA style multi-anvil apparatus to ANSTO/OPAL facility in order to complement x-ray information with neutron scattering techniques, allowing light elements to be explored. This will see an increase in research productivity and educational possibilities in the community
A flavour of the work I have been involved in:
My work has explored differentiation of terrestrial bodies through a combination of phase equilibria studies, rock deformation experiments and numerical modelling (see Publications, below). The far-reaching applications of our research have been recognised with funding from NSF, NASA, and now here in Australia by the ARC. These kinds of integrated studies are time consuming, but key work and results over the past 20 years include the following:
• Some of the first combined experimental and thermal modelling on partial melting of oceanic crust, with the results constraining the conditions for melting in subduction zones (Peacock et al., 1994). Subsequently, a wealth of similar data from other research groups has significantly enhanced our understanding of solid/fluid/melt relationships in dynamic settings.
• Combining phase equilibria and rock deformation experiments on the same rock type which has provided chemical signatures of magmas in active tectonic environments (Rushmer, 1991; Rushmer, 1995).
• Investigation into the role of volume change in mineral melting and the development of crack networks during different melting reactions in the crust and estimates of permeability/porosity relationships (Rushmer, 2001, Holyoke & Rushmer, 2002; Rushmer and Miller, 2006).
• Using experimental partial melting experiments integrated with numerical modelling to investigate the generation of tonalite-trondhjemite granodiorite suites in different tectonic settings. The results are particularly significant to studies of the early Earth (Rushmer & Jackson, 2008; Getsinger et al., 2009).
• Integrating numerical modelling and deformation experiments performed on ordinary chondrite (Kernouve) to investigate core formation processes under dynamic conditions (Rushmer et al., 2000; Rushmer et al., 2005) and with applications to both planetesimals (Rushmer et al., 2005) and the core-mantle boundary (Petford et al., 2005; Petford et al., 2007).
Partial melting in natural metal-silicate and silicate systems: rheological and geochemical implications for the earth and other planets: Research in the laboratory, in addition to field work in New Zealand and in Tonga, is focused on the general process of differentiation. Differentiation is the separation of a melt or fluid from its host and is the fundamental mechanism by which the terrestrial planets have evolved both chemically and physically through time and central to how the crust has evolved from mantle, how metallic cores are formed from undifferentiated planetary bodies and how economic elements can be concentrated. Our projects tackle this primary process by using the true (observed) rock textures and compositions as templates uniquely constrained by experiment and field studies so the data (combined also with numerical modelling) can quantify flow processes and deformation regimes. It provides a basis for understanding fluid migration and chemical consequences in dynamically evolving environments. Specific projects are described below:
Tonalite-Trondhjemite-Granodiorite Petrogenesis: In coordination with Matt Jackson (Imperial College, UK), we are experimentally testing the Jackson et al. (2003; 2005) numerical model which shows that TTG arc crust formation is not only a function of partial melting of a mafic source region, but is also dependent on melt segregation processes. The numerical model describes melt migration and chemical reaction through a steep thermal gradient to predict pressure, temperature, and bulk composition. In our experimental investigation we have designed melt segregation equilibrium (MSE) experiments to reproduce the local changes in bulk composition that are predicted by the numerical model to occur in response to buoyancy-driven melt segregation along grain edges and associated compaction of the solid residue.
Faux amphibolite: Together with John Adam, we are working to establish the relationships between the oldest mafic rock found on the planet (4.28 Ga; O’Neil & Francis, 2008) and possible crustal compositions that may be derived from this. Is this the precursor for the widespread development of Hadean TTG crust? We are currently constructing phase equilibria diagrams for the faux amphibolite, and then we can establish the effects of differing pressure, temperature and H2O on the composition of melts derived from this type of protolith.
Solander Island: Together with PhD student Fiona Foley and RA Beverley Coldwell, we are investigating the origin of a previously unstudied Quaternary volcano south of the South Island, New Zealand. Its position above the subducting Australia Plate raises questions over the origin of the magmas supplying the volcano, which in turn supply information on the geometry of the subducting Australia Plate. We are using a multi-pronged approach, combining fieldwork, experimental petrology on xenoliths recovered from Solander Island, geochemical interpretation and isotope studies to fully document the island, and to assess origins and relative contributions to magmas from different sources.
Fonualei Volcano in Tonga: Fonualei is unique in that it erupts extremely silicic lavas for its intra-oceanic setting, which makes it ideal for investigating the genesis of evolved 'continental' crust at island arcs. The project with PhD student James Cowlyn is characterising the generation and evolution of the Fonualei magmas from source through to the erupted products, through a combination of geochemical and experimental studies. Direct measurement of lava viscosity through high temperature and pressure using the state-of-the-art laboratory at the University of Munich provides a unique opportunity to test the relationships between viscosity and the observed flow morphologies of different compositions of highly silicous lavas.
Mindanao, Philippines: Together with Beverley Coldwell, John Adam and Colin Macpherson (Durham University, UK) we are working to document the melt phases and compositions which may be generated at an island arc by simple differentiation. The margin has generated adakitic rocks, whose origins are controversial. We are testing samples at mantle pressures and temperatures in piston cylinder apparatus, producing melt phase equilibrium diagrams for each sample and for the sample suite. This work fits into a NERC supported project Colin Macpherson is heading at Durham.
Rushmer, T. and Petford, N. (2011) Micro-segregation rates of liquid Fe-Ni-S metal in natural silicate-metal systems: a combined experimental and numerical study Geochemistry, Geophysics, Geosystems, (G3), in press.
Coldwell, B., Adam, J. Rushmer, T., Macpherson, C. (2011). Evolution of the East Philippine Arc: Experimental constraints on magmatic phase relations and adakitic melt formation, Contributions to Mineralogy and Petrologyin press
Martin, L., Turner, S., Wood, B., Rushmer, T. (2011) Experimental Measurements Of Trace Element Partitioning Between Lawsonite, Zoisite And Fluid And Their Implication For The Composition Of Arc Magmas, Journal of Petrology, in press.
Rushmer, T. and Knesel, K., (2010). Defining geochemical signatures and timescales of melting processes in the crust: An experimental tale of melt segregation, migration and emplacement. In: Dosseto, A., Turner, S. and Van Orman, J. (eds.) Timescales of magmatic processes: from core to atmosphere. Blackwell, pgs. 181-211.
Getsinger, A., Rushmer, T., Jackson, M.J., Baker, D. 2009. “Generating high Mg numbers and chemical diversity in TTG magmas during melt segregation” Journal of Petrology (in press).
Rushmer, T., 2008. Distribution of Pt, Os, Ir during liquid metal segregation under extremely reducing conditions. Geochimica et Cosmochimica Acta, 72(12), A813-A813.
Rushmer, T., Jackson, M., 2008 (for 2006). Impact of melt segregation on tonalite-trondhjemite-granodiorite (TTG) petrogenesis. Transactions of the Royal Society of Edinburgh-Earth Sciences, 97, 325-336.
Petford, N., Rushmer, T. and Yuen, D., 2007. Deformation-induced instabilities at the core-mantle boundary. In “Post-perovskite: The Last Phase Transition”, AGU Geophys. Mono. Series 174, pgs. 271-287.
Brown, M., Rushmer, T., 2006. Evolution and Differentiation of the Continental Crust. Cambridge University Press, UK, 562p.
Rushmer, T., Gestinger, A., Jackson, M.D., 2006. Generating large volumes of TTG arc crust: An experimental study. Geochimica et Cosmochimica Acta, 70(18), A546-A546.
Rushmer, T., Petford, N., Humayun, M., 2006. Deformation-assisted core formation. Geochimica et Cosmochimica Acta, 70(18), A547-A547.
Rushmer, T., Petford, N., Humayun, M., Campbel, A.J., 2005. Fe-liquid segregation in deforming planetesimals: Coupling Core-Forming compositions with transport phenomena. Earth and Planetary Science Letters, 239(3-4), 185-202.
Rushmer, T., Humayun, M., Campbel, A.J., 2002. Siderophile elements in dynamically segregated metallic liquids . Geochimica et Cosmochimica Acta, 66(15A), A656-A656, Supp. 1.
Holyoke, C.W., Rushmer, T., 2002. An experimental study of grain scale melt segregation mechanisms in two common crustal rock types. Journal of Metamorphic Geology, 20(5), 493-512.
Rushmer, T., 2001. Volume change during partial melting reactions: implications for melt extraction, melt geochemistry and crustal rheology. Tectonophysics, Special Issue 342(3-4), 389-405.
Rushmer, T., 1995. An experimental deformation study of partially molten amphibolite – application to low-melt fraction segregation. Journal of Geophysical Research-Solid Earth, 100(B8), 15681-15695.
Peacock, S.M., Rushmer, T., Thompson, A.B., 1994. Partial melting of subducting oceanic-crust. Earth and Planetary Science Letters, 121(1-2), 227-244.
Rushmer, T., 1993. Experimental high-pressure granulites – some applications to natural mafic xenolith suites and Archean granulite terranes. Geology, 21(5), 411-414.
Rushmer, T., 1991. Partial melting of 2 amphibolitea – contrsting experimental results under fluid-absent conditions. Contributions to Mineralogy and Petrology, 107(1), 41-59.
Evolution and Differentiation of the Continental Crust. Cambridge University Press, M. Brown and T. Rushmer (Editors).