High-temperature creep of olivine crystals from four localities

Abstract

To compare the rheologies of olivine samples from various tectonic settings, an experimental investigation of the high-temperature creep behavior of crystals from China (Fo 89–91), Norway (Fo 93) and the Red Sea (Fo 90) was carried out. The results were examined in the context of the well-documented flow data for olivine from the USA (Fo 89–93). Both the major element and the minor element compositions differed depending on locality. Creep experiments were performed in an 1 atm deformation rig at temperatures from 1200 to 1500°C and compressive stresses from 15 to 175 MPa. Oxygen fugacity was varied over the full stability field of olivine. During deformation along three orientations, the samples remained in contact with orthopyroxene. The mechanical results for samples from all three localities can be summarized as follows: For the [110] c orientation, three rate-controlling creep mechanisms were observed; each can be described by a power-law relationship. Activation energies of 160 kJ mol −1, 1100 kJ mol −1 and 380 kJ mol −1 and oxygen fugacity exponents of 0.37, 0.04 and 0.13 were obtained for the low-, intermediate- and high-temperature creep regimes, respectively. For the [101] c orientation, activation energies of 270 kJ mol −1 and 660 kJ mol −1 and oxygen fugacity exponents of 0.30 and 0.05 were measured for the low- and high-oxygen fugacity creep regimes, respectively. For the [011] c orientation, an activation energy of 510 kJ mol −1 was obtained over the full range of oxygen fugacity; however, oxygen fugacity exponents of 0.02 and 0.31 were determined for the low- and high-oxygen fugacity creep regimes, respectively. The stress exponent is approximately 3.5 for all creep regimes. Within experimental error, the creep results for olivine from all three localities are the same as those reported for San Carlos olivine single crystals. Therefore, moderate differences in forsterite content (from Fo 89 to Fo 93) and in the concentrations of minor elements (such as Ni, Cr and Mn) do not significantly affect the creep behavior of olivine, Consequently, rheological data obtained for olivine samples from specific localities can be reasonably applied to model plastic deformation processes in the upper mantle.