EFFECTS OF GAMMA RADIATION ON THE EXPERIMENTAL DEFORMATION OF CALCITE AND CERTAIN ROCKS

Abstract

Calcite single crystals, Yule marble, and certain other rocks were deformed dry at room temperature under constant confining pressures of 2000 or 2750 bars at a strain rate of 1 per cent per minute. Uniaxial compression and extension experiments were made; for the marble, parallel and normal to c v fabric maximum; for the single crystals, parallel to c v and normal to m {1010}. Yule marble exposed to 17 megaroentgens of gamma radiation before deformation turned from white to bright blue when deformed. Intensity of color varied with orientation and amount of strain. Irradiated single crystals changed from amber to ultramarine blue when the greatest principal stress paralleled c v . No color change occurred when the least principal stress paralleled c v . Irradiation resulted in small reductions in yield stress of most of the rocks, but not of the single crystals. Petrographic studies of the single crystals revealed that established principal deformation mechanisms, twin gliding on e {0112} and translation gliding on r {1011}, were still operative and confirmed that blue color was associated with translation gliding only. In Yule marble blue grains had deformed by translation, clear grains by twinning. Thermoluminescence studies indicated that compression along c v yielded a new peak in the glow curves (at 280°), not present in undeformed irradiated calcite. Extension along c v increased the magnitude of the glow curve at about 240° but gave rise to no new peaks.