HR: 0800h
AN: T41B-0572    [Abstracts]
TI: Experimental Insights on Grain Growth Under Static Conditions Affected by Second Phases
AU: * Brodhag, S H
EM: brodhag@geo.unibe.ch
AF: Institute of Geological Sciences University of Berne, Baltzerstrasse 1+3, Bern, 3012, Switzerland
AU: Herwegh, M
EM: herwegh@geo.unibe.ch
AF: Institute of Geological Sciences University of Berne, Baltzerstrasse 1+3, Bern, 3012, Switzerland
AU: Berger, A
EM: berger@geo.unibe.ch
AF: Institute of Geological Sciences University of Berne, Baltzerstrasse 1+3, Bern, 3012, Switzerland
AU: Mettier, R
EM: mettier@geo.unibe.ch
AF: Institute of Geological Sciences University of Berne, Baltzerstrasse 1+3, Bern, 3012, Switzerland
AB: Mineral composition and grain size are two important parameters for the characterization of the microstructure of a rock and they both are closely linked to each other. Under static conditions, the grain size of the matrix phase is mainly controlled by the size, amount and dispersion of the second phases (Zener relation). In such polyphase systems, the second phases can pin or drag the migrating grain boundaries reducing the grain growth kinetics. Due to the fundamental influence of the interaction by different mineral phases and the fact that most natural rocks are of polymineralic composition, it is essential to understand the processes responsible for the formation of a rock's microstructure in such polymineralic systems. To gain new insights, we performed in-situ rock analogue experiments using rigid non-reacting phases (micro glass beads) as second phase to reduce on one hand the complex influence of a growing second phase, and on the other to focus on the behavior of the matrix grains. The second phase was added in different volume percentages (0-33vol%) to the matrix phase (norcamphor) to investigate the microstructural evolution and related growth kinetics in regard of different second phase contents. The results indicate that all mixtures undergo two main stages during the microstructural evolution: (a) a stage of continuous grain growth, which is followed by (b) a stage of stabilized grain sizes. With increasing amounts of second phases a well defined transition between (a) and (b) evolves, which increases with increasing second phase content. Furthermore, the amount of second phases is inversely proportional to the matrix grain size for all microstructural stages mentioned above. For continuous grain growth, this behavior can be expressed in form of a conventional grain growth law: Gⁿ - G₀ⁿ = k (t - t₀), where G is the main grain size at time t and G₀ the grain size at t=t₀. The grain growth exponent n, decreases from 4.6 to 2.8 for pure and impure (33vol% micro beads) samples, respectively, while the constants k show an increase with enhanced second phases contents. Based on these results, the second phase effect on grain growth of a matrix phase can be integrated into the grain growth law, allowing more realistic modeling of polymineralic systems in nature.
DE: 3625 Petrography, microstructures, and textures
DE: 3630 Experimental mineralogy and petrology
DE: 5112 Microstructure
SC: Tectonophysics [T]
MN: 2007 Fall Meeting