Experimental research on rheology and seismic wave velocity properties of partially molten lower crustal rocks

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In order to estimate the effect of melt and water on the rheological behavior of the lower crust, high pressure and temperature deformation experiments were conducted using Griggs type solid medium apparatus. Increases in the melt content decreases flow strengths under the presence of water. The flow stress decreases with increasing the water content added to the sample and decreasing strain rate. This indicates that the flow strength of anorthite aggregates is determined by the amount of water contents introduced into the aggregate. The water content required to cause weakening was consistent with the lower bound of water contents in the lower crust estimated by geophysical observations. The water contents left in the weakened samples measured after deformation experiments are consistent with naturally deformed feldspars. This indicates that the amount of water in the lower crust controls the rheological behavior of lower crustal rocks.