Open Session - SWISS GEOSCIENCE MEETINGs

68
Symposium 1: Structural Geology, Tectonics and Geodynamics
and seismic anomalies in the CMB region and the transition zone. The numerical models treat the evolution of a planet over
billions of years, including self-consistent plate tectonics arising from plastic yielding, melting-induced differentiation, and
a parameterised model of core evolution based on heat extracted by mantle convection.
Figure 1. Example simulation with PERPLEX-calculated mineralogy and physical properties.
REFERENCES
Connolly, J. A. D., (2005), Earth Planet. Sci. Lett., 236, 524-541.
Irifune, T., and Ringwood, A. E., (1987), Earth. Planet. Sci. Lett., 86, 365-376.
Nakagawa T., and Tackley, P.J., (2006), Geophys. Res. Lett., 33, L12S11, doi:10.1029/2006GL025719.
Nakagawa, T., and Tackley, P. J., (2005), Proc. 3rd MIT conference.
Tackley, P. J., and Xie, S., (2003), Proc. 2nd MIT conference.
1. 6
The Availability of H 2 O for Deformation in Natural Quartz Single Crystal
Experiments
Thust Anja*, Tarantola Alexandre**, Heilbronner Renée*, Stünitz Holger***
*Department of Geosciences, University Basel, Bernoullistr. 32, CH-4056 Basel, Switzerland (anja.thust@unibas.ch, renee.heilbronner@unibas.ch)
** Institute of Geological Sciences, University of Bern, Baltzerstr. 3, CH-3012 Bern, Switzerland (alexandre.tarantola@geo.unibe.ch)
*** Institutt for geologi, Universitetet i Tromsø, Dramsveien 201, 9037 Tromsø, Norway (holger.stunitz@ig.uit.no)
H 2 O is very important for quartz deformation. Experimental studies on synthetic and natural quartz crystals demonstrated
that H 2 O dramatically reduces the strength of the material (e.g. Griggs & Blacic 1965). We have performed deformation experiments
in the solid medium Griggs apparatus on natural milky quartz single crystals in order to study the effect of H 2 O
weakening. The compression direction has been normal to the -axis and one of the prism planes.
The flow strength of the quartz crystal at 1 GPa confining pressure and 900 °C at a strain rate of 10 -6 s -1 is with 150 MPa low.
This strength is comparable to that of previous experiments on "wet" natural quartzites (Hirth & Tullis 1992) so that probably
H 2 O has been available in sufficient quantities to ensure weakening.