[S-MP46_28PM2] Deformed rocks, Metamorphic rocks and Tectonics

[SMP46-P06_PG] Stress and strain history during the microboudinage for granite intrusion: Mt. Edger granite complex, East Pilbara

3-min talk in an oral session

*Taroujirou MATUMURA¹, Nozomi KIMURA², Atsushi OKAMOTO³, Toshiaki MASUDA² (1.Graduate school of science and Technology, Shizuoka University, 2.Institute of Geoscience, Shizuoka University, 3.Graduate school of Environmental studies, Tohoku University)

Keywords:microboudin structure, stress, strain, granite complex, Archean

Stress and strain analysis is essential to improving the understanding of deformation process. Microboudinaged columnar minerals can be used as an indicator of stress and strain during the microboudinage for quartzose and calcareous metamorphic tectonites. In this presentation, we discuss the stress and strain history during the microboudinage deduced by the microboudin method with a collaboration of the strain reversal method.We collected samples of metachert from the Archean Warrawoona greenstone belt around Mt. Edger granite complex, East Pilbara, Western Australia, and identified microboudinaged tourmaline grains embedded within quartz matrix in 10 samples. The result revealed that the samples experienced extensional strain at least -0.56 and differential stress in the range from 3.9 to 11.9 MPa. We obtained stress-strain curves which show increase in differential stress with increasing inverse natural strain (ε_inv). The frequency distribution of interboudine gaps between separated grains with respect to ε_inv for boudinaged tourmaline grains shows that end of microboudinage occurred immediately after the peak frequency of fracturing. This occurrence commonly appeared in all the 10 samples. These results provided us with keys to discuss a stress-strain history during the microboudinage in relation to evolution of the granite complex. The spectacular implication would be a drop or relaxation in increased differential stress at the end of the microboudinage.