High pressure and temperature deformation experiments in a liquid confining medium

To understand the ductile flow of rocks, experimental deformation studies must be performed at high temperature (to activate the appropriate mechanisms) and high pressure (to inhibit microcracking and cavitation). Such studies have been hampered by the inability to collect data of high quality at pressures greater than 500 MPa. We have developed a specimen assembly for the “solid-medium” apparatus that utilizes molten salt as the medium surrounding the specimen. Data collected with this liquid cell are much more accurate and precise than can be obtained with conventional solid-medium assemblies because an accurate measurement of friction is automatically made in each experiment. We have used this cell to conduct experiments on metals and silicates over a range of pressures from 0.1–3200 HPa at temperatures of 900–1700 K. Our measurements are in good agreement with gas-medium apparatus; they show that friction in the standard solid-medium cell can represent a large fraction of the apparent strength of the material. Currently, we can reliably measure strengths of less than about 10 MPa; we expect improvements in the near future to reduce this limit to a few MPa.