Interest in the mechanical properties of water ice under the conditions in which it exists in the outer solar system has motivated the development and use of a new high‐pressure, low‐temperature triaxial deformation apparatus. Constant displacement rate tests on 70 samples of pure polycrystalline water ice have been performed at temperatures 77≤T≤258 K, confining pressures 0.1≤P≤350 MPa, and strain rates 3.5×10−6≤ trueε˙ ≤3.5×10−4 s−1. In most cases, the ice polymorph tested was ice Ih. Both brittle and ductile behavior have been observed. Brittle behavior of ice, promoted by lower pressure, lower temperature, and higher strain rate, is analogous to that in rocks, with the important exception that brittle fracture strength becomes independent of confining pressure above 50 MPa pressure and the fracture angle is approximately 45° to the loading direction (i.e., the coefficient of internal friction is approximately zero). Ductile flow, the predominant behavior in our tests at T≥195 K, follows a law of form trueε˙ = Aσn exp (−H*/RT) (σ is stress; R is the gas constant; A, n, H* are material constants). Three sets of material constants are required to fit the data, with changes in sets (or mechanisms) occurring near 243 K and 195 K. The value of n remains near 4 throughout the measured ductile field, but H* drops from 91 to 61 to 31 kJ/mole as temperature decreases. The maximum brittle strength measured was 171 MPa; the maximum ductile strength measured was 91 MPa. At confining pressures near the phase transition pressure of ice Ih → ice II, the ductile strength is observed to drop dramatically. Some overlap with previous work occurs at higher temperatures and lower pressures. Agreement with present work is generally good, both quantitatively in the values of n and H*, and qualitatively in the mechanism of deformation. Although the ductile strengths measured here are somewhat higher than expected on the basis of extrapolations of previous work, the low value of H* at T<195 K indicates that the ice Ih layer on icy bodies in the solar system is much weaker than has generally been predicted.

More than 115 triaxial compression and extension experiments have been performed on the mechanically isotropic, homogeneous Solenhofen limestone to determine the transition from brittle fracture to ductile flow as a function of temperature, confining pressure, and interstitial fluid pressure. Temperature and confining pressures ranged from 25° to 700°C. and from 1 to 7500 atmospheres; interstitial fluids included water and carbon dioxide. Strain rates remained constant at 10~4/ second. Transitional behavior was arbitrarily defined as that point at which 3-5 per cent strain may be induced without notable loss in cohesion. In dry extension tests, the confining pressure required to induce transitional behavior decreased from 7300 atmospheres at 25°C. to about 700 atmospheres at 700°C. In dry compression tests, the pressure required for the transition was 1000 atmospheres at 25°C., decreasing to 1 atmosphere at 480°C. For transitional behavior in compression tests with interstitial fluids, with increasing confining pressure, the difference between confining pressure and interstitial pressure decreased almost exponentially from 1000 atmospheres at 25°C. and 850 atmospheres at 150°C. to nearly zero at 5000 atmospheres.Data for all stress-strain curves are summarized; most stress-strain curves are plotted and compared for a wide variety of test conditions. From these, plots of transition stress or ultimate stress at transition conditions, maximum and minimum principal stresses, and mean stress are derived and reported as a function of temperature.None of the various theories of strength examined were able to correlate results in compression and extension. The Mohr criterion predicted shear fracture angles within 4° at the brittle-ductile transition for dry compression tests and within 7° for extension tests at temperatures ranging from 25° to 400°C. By applying the Mohr theory, similar angles were predicted within 3° for transitional compression tests with interstitial water at both 25° and 150°C.The geological implications of these experiments are briefly discussed. Even though the experimental strain rate is vastly greater than tectonic strain rates, the qualitative difference observed between compression and extension would probably apply to naturally deformed limestones. The analogy of compression experiments to reverse faulting and of extension experiments to normal faulting is discussed. In the event that strain rate does not affect the brittle-ductile transition, these experiments predict normal faulting of dry limestone to a depth of 15 km and reverse faulting to a depth of 3.5 km. Interstitial fluid pressure would increase the depth to which faulting could occur. 193

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The coefficient of thermal linear expansion α, Young's modulus E, and bulk modulus K have been determined for the Westerly and Stripa granites to temperatures T of 350°C and pressures P to 55 MPa. Using conventional triaxial aparatus, displacement measurements were made on three samples from each of three orthogonal directions for both rocks. Comparison of the directional values at any P, T, and those from the nine‐sample population indicated that within our precision, both granites are isotropic in E, K, and α. Both E and K for both rocks decreased with T and increased with P in a nonlinear fashion. From 19° to 350°C, E decreased by as much as a factor of 2 and K decreased by 2 to 3 times, depending on P. From 6 to 55 MPa, E increased by factors of 3 to 6 and K increased by 3 to 5, depending on T. Values for α were neither constant nor a monotonic function of P or T. In both granites over the P range investigated, α typically increased from 6 to 12×10−6 °C−1 at 40°C to 10–15×10−6 °C−1 at 325°C. In both rocks over the T range investigated, increasing P from 6 to 55 MPa generally decreased α by 1–5 10−6 °C−1. Most measurements are consistent with microcracks controlling the thermoelastic response by cracks opening with increasing T and closing with increasing P. Changes in crack porosity ϕ due to bulk compressibility and thermal expansion have been calculated for both granites. Because K and α were nonlinear with P and T, ϕ was inferred to be a complex function of both. Assuming that all cracks affect fluid transport, changes in permeability κ with P and T have also been calculated from κ ∝ ϕ3. These changes have been compared as κ/κ0, where κ0 was the initial value at 0.1 MPa, 19°C. For example, κ/κ0 for Westerly granite was inferred to increase by a factor of 3 from 19° to 300°C at 8 MPa. In Stripa granite at 6 MPa, κ/κ0 decreased ∼25% with T at 19°–100°C, then increased approximately twofold by 350°C.

Electrical conductivity σ in the [100] direction has been determined for the Red Sea olivine (Fo 91) to 1440°C and 8 kbar in argon. No systematic variation of σ with pressure was observed. The effect of an 8‐kbar variation in pressure over the 1270°–1440°C range is equivalent to a temperature uncertainty of ±5°C. We have also determined σ on the same sample up to 1660°C with controlled oxygen fugacity ƒo2 at 1 bar of total pressure. By using published σ‐depth profiles and assuming olivine as the major phase in the earth's upper mantle with ƒ o 2 = 10 −6 ‐10 −3 bar, temperatures of the upper mantle are calculated as a function of depth. The temperature uncertainty due to possible pressure effects is 2–5 times smaller than that resulting from the ambiguity in published σ‐depth profiles.

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