A SERVOHYDRAULICALLY-CONTROLLED DEFORMATION APPARATUS FOR ROCK DEFORMATION UNDER CONDITIONS OF ULTRA-HIGH PRESSURE METAMORPHISM

A deformation apparatus has been developed to study the mechanical beh aviour of high pressure and ultra-high pressure metamorphic rocks. II is based on the conventional Griggs design and the molten salt cell co ncept introduced by H. E. Green II. Both, the axial loading and the co nfining pressure are servohydraulically controlled. Alternatively, a s elf-made multilayer pressure Vessel or a commercial stripwound constru ction are used. The pressure cell is improved with respect to systems described previously by the use of different salt mixtures with low eu tectic temperatures, by a mechanically stable arrangement of the therm ocouples, and by an optimization of the frictional characteristics of the axial loading system. The apparatus has been successfully used in deformation experiments on cylindrical aragonite and coesite samples 3 to 4 mm in diameter and 6 to 10 mm in length at confining pressures u p to 3.7 GPa and temperatures up to 1170 degrees C.