a pic in San Francisco - AGU 2006                Athena statue in Vienna - EGU 2007



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     "ΓΝΩΘΙ ΣEΑΥΤΟN"
               Socrate



        updated: 21 Sept. 2014



My past and present research

0. Cu and Mo ores in Ireland

I am supervising three projects hinging on definition of mineralisation across Ireland:

    1) Hydrothermal Cu ore in SW Ireland and Irish Midlands;

    2) Vein-hosted Cu ore in the volcanic-sedimentary sequence of Waterford Copper Coast;

    3) Mo-prorphyry mineralisation in Connemara granites.

pyrite

1. Origin of pallasite meteorites

Pallasites are a fairly misterious type of meteorite. They belong to the stony-irons group and are made essentially of olivine, Fe(Ni) and FeS. To define the formation conditions of pallasites I have used annealing experiments of olivine + Fe-S mixtures and image analyses of synthetic and natural samples.

pallasite synthetic



2. Properties and ordering of water-bearing silicate liquids, and silicate-bearing supercritical fluids

Starting September 2010 I studied the structure of hydrous granite melts and silicate-rich fluids using high energy X-Ray Diffraction (XRD) and I will try to enlighten the local structure of metals in hydrous melts and silicate-rich fluids by mean of X-ray Absorption Spectroscopy (XAS).
The main topics related with these investigations are the complexation of transition metals and High Field Strenght Elements (HFSE) in water-bearing melts (granites) and in the closely realted pegmatitic and hydrothermal fluids, often advisable as "intermediate" fluids, with both characters of a hydrous-melt and a high-solute-rich fluid.
The tools that I will use are: 1. Hydrothermal Diamond Anvil Cell (HDAC)   2. Synchrotron XRD, X-Ray Fluorescence (XRF) and XAS operated in-situ (i.e. at elevated T-P).
Synchrotron analyses/experiments will be performed at the Advanced Photon Source (APS), belonging to the Argonne National Laboratory (Chicago, USA), whereas standard (well not really!) HDAC runs will be made in the hydrothermal laboratory of Prof. Alan J. Anderson, at St. F.X. Univesity, Antigonish, NS, Canada.

hy-melt and solute-rich fluid             light saber ?

Left: snapshot of an experiment, where hy-melt (droplets) and solute-rich fluid coexist at 720 C and 160 MPa.
Right: snapshot of gasketless experiment with the x-ray beam crossing through the top (fluorescent) diamond anvil (room temperature).

Another topic of my current research is determination of thermal reduction temperature and dissolution of various metal oxides (e.g. MoO3, Cr2O3) in water domintaed fluids at sub- and supercritical conditions. The following video illustrate examples of visual dissolution of MoO3 (run name: moly-0.25M-GS-4)and thermal reduction of the same phase into MoO2 (little opaque prisms - run name: moly-0,1M-GS-2).


video of dissolution & thermal reduction



3. Core formation in terrestrial bodies

I am involved in the debate over the feasibility of percolative core formation in accreting planets and planetesimals. The key points of this controversy are: the finding of a percolation threshold for Fe-S melt in a peridotite matrix, which would tell us how much metalis left in a silicate mantle separated from metal melt through gravitational percolation, and the measurement of the segregation velocity of the melt, in order to compute the actual separation time of metal from silicates and compare it with isotopical ages and modelled times for core formation in terrestrial bodies. Yoshino et al. (2004) and Roberts et al. (2007) measured interconnectivity threshold of 4-6 vol% for a solid peridotitic aggregate, however, Walte et al. (2008), assert that, for any fraction of metal melt, the system will equilibrate forming isolated melt pockets surrounded by silicates, with enough time to reach textural maturation. Our data (Bagdassarov et al., 2009 a) seem to confirm the existence of a fairly higher threshold. Nevertheless, in my personal opinion, it would be necessary to run long duration experiments (i.e. weeks or better months), in order to understand how textural equilibration evolves in such systems. Moreover, there have been only few attempts to perform deformation experiments on such systems. Furthermore, the study of the only natural samples, which could be representative of this stage of the evolution of planets, such are Pallasite meteorites, have been so far, not taken into the appropiate account, while their study could bring interesting new insights within this topic. A different case is, when we are in presence of a partial silicate melt. We, for the first time, have performed metal segregation experiments, in partially molten peridotite aggregates (Bagdassarov et al., 2009 b), thanks to the usage of the newly developed ‘centrifuging piston cylinder’ (see Schmidt et al., 2006). Our results indicate that only for large fraction of silicate melt, segregation velocity of metal melt is large enough to accomplish for terrestrial bodies core formation times. The debate stays open regarding, how much metal could segregate, and how it would be possible to remove the metal remnants. Numerical modelling, seems nowadays, the best answer to solve the quarrel.
The project has been realized in collaboration with
Gregor Golabek and supervised by Prof. Max Schmidt and PD Dr. Nikolai Bagdassarov, who also collaborated to the experimental part.

percolation of Fe-S melt in partially molten peridotite            BSE image of olivine surrounded by Fe-S melt



4. Percolation of MORB melt in middle oceanic ridge areas

Gravitational segregation of basalt melt in Middle Oceanic Ridge areas is another topic in which I am deeply involved. The permeability of asthenospheric mantle controls the time scale for transport of MORB melt to the ocean bottom surface, thus it controls the timing for formation of Earths crust. Our experiments (Connolly et al., 2009), performed with the ‘centrifuging piston cylinder’ on olivine aggregates added with 4-14 vol% of basalt melt, allowed to calculate much larger permeabilities than previously accepted (e.g. Richardson and McKenzie, 1994 and Wark et al., 2003). Such large permeabilities accomplish for dramatically higher transportation velocities of basalt melt via percolation.
The project has been supervised by:
Prof. Max Schmidt, PD Dr. Nikolai Bagdassarov and Prof. James Connolly

BSE image of olivine surrounded by MORB melt



5. Cumulates formation in mafic layred intrusions

The problematic of the formation of cumulate layer is very interesting for people studying Mafic Layred Intrusions. In fact, there exist cumulus layers containing up to 80-90 vol% of solid grains, but it is still poorly understood whether they form by simple gravitational settling and mechanical compaction, or if chemical compaction is required, and how long do these processes extend. In our experiments, we have observed that pure gravitational settling of olivine grains can generate a layer with a residual melt fraction slightly larger than 50 vol% (preventive results were presented at EMPG XII conference EMPG XII ). At this stage, grains are in mutual contact and chemical compaction starts to play a role in addition to mechanical gravitational one. A theoretical 100 vol% solid grain aggregate could then form. We have computed formation times, for olivine cumulates, with 20-30 vol% residual porosity (typical for mafic intrusions sub-metric layers), spanning over a few months to a few years. However it his crucial to understand wheter grain boundary diffusion or dissolution-precipitation is the dominating process during chemical compaction. 
The project has been supervised by: Prof. Max Schmidt, PD Dr. Nikolai Bagdassarov and is part of the current Ph.D. project of M. Forien.
 
cumulus layer formation over time - series of BSE images
The numers in figure could be read as: e.g. '3 h 200g'  means that sample ZOB-6 was kept at T, P, and
an acceleration of 200 times g, for 3 hours.



6. Slab penetration at '660' discontinuity

The subject of my master thesis, consisted in the individuation of phase assemblages in subducting oceanic crust at depths of the transition zones of the mantle. The subject has been widely treated in the last 5 years; however, there is at list one point, which has not been fully cleared yet. Tackley (1993), pointed out that if density contrast between the subducting oceanic crust and the surrounding mantle is larger than 8-9%, then, single mantle convection is promoted, however, this seems not to overcome 2-3%. The individuation of the abundances of different phases (e.g. majoritic_ garnet, stishovite, K-hollandite, Fe-Ti-oxide, etc.) at 660 km depth is critical for calculating the density contrast, thus, it would be important to further investigate this subject. Furthermore, we can nowadays compute density of single mineral phases at the desired temperature and pressure through series of databases and codes, which allows for more meaningful calculations.
The project has been supervised by: Prof. Stefano Poli and Dr. Kazuaki Okamoto.



References:

Bagdassarov, N., Golabek, G., Solferino, G., Schmidt, M.W. Constraints on the Fe-S melt connectivity in mantle silicates from electrical impedance measurements. Physics of the Earth and Planetary Interior,
vol. 177, pag. 139-146, 2009.
doi:10.1016/j.pepi.2009.08.003

Bagdassarov, N., Solferino, G., Golabek, G., Schmidt, M.W. Centrifuge assisted percolation of Fe-S melts in partially molten peridotite: Time constraints for planetary core accretion. Earth and Planetary Science Letters, vol. 288, pag. 84-95, 2009. doi:10.1016/j.epsl.2009.09.010

Connolly, J.A.D., Schmidt, M.W., Solferino, G., Bagdassarov, N.  Permeability of asthenospheric mantle and melt extraction rates at mid-ocean ridges. Nature, vol. 462, pag. 209-212, 2009. doi:10.1038/nature08517.

Roberts J. J., Kinney J. H., Siebert J., Ryerson, F.J., 2007. Fe-Ni-S melt permeability in olivine: Implication for planetary core formation. Geophys. Res. Lett. 34, L14306, doi: 10.1029/2007GL030497.

Richardson, C. and McKenzie, D., 1994. Radioactive disequilibria from 2d models of melt generation by plumes and ridges. Earth and Planetary Science Letters, 128: 425-437.

Schmidt M. W., Connolly, J.A.D., D. Gunther, D., Bogaerts, M., 2006. Element Partitioning: The Role of Melt Structure and Composition, Science 312, 1646 – 1650.

Tackley, P.J., Stevenson, D.J., Glatzmaier, G.A., Schubert, G. Effects of an endothermic phase transition at 670 km depth in a spherical model of convection in the Earth’s mantle. Nature, 361, 699-704.

Walte N. P., Becker J. K., Bons P. D., Rubie D. C., Frost D. J., 2007. Liquid-distribution and attainment of textural equilibrium in a partially-molten crystalline system with a high-dihedral-angle liquid phase. Earth Planet. Sci. Lett. 262, 517-532, doi: 10.1016/j.epsl.2007.08.003.

Wark, D.A., Williams, C.A., Watson, E.B., 2003. Reassessment of pore shapes in microstructurally equilibrated rocks, with implications for permeability of the upper mantle. Journal of Geophysical Research – Solid Earth, 108: 18,320-18,338.

Yoshino T., Walter M. J., Katsura, T., 2004. Connectivity of molten Fe alloy in peridotite based on in situ electrical conductivity measurements: implications for core formation in terrestrial planets. Earth Planet. Sci. Lett. 222, 625-643.