Creep behavior of Fe‐bearing olivine under hydrous conditions

Abstract

To understand the effect of iron content on the creep behavior of olivine, (MgxFe(1 − x))2SiO4, under hydrous conditions, we have conducted tri‐axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050° to 1200°C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas‐medium high‐pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53 ≤ x ≤ 0.90 in the dislocation creep regime: trueε˙=ε˙0.901−x0.11true/2exp[]226×1030.9−xRT. In this equation, the strain rate of San Carlos olivine, ε˙0.90, is a function of T, σ, and fH2normalO. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.

Evolution of the rheological and microstructural properties of olivine aggregates during dislocation creep under hydrous conditions

“…This conclusion is consistent with the experimental observations and detailed analyses of Mei and Kohlstedt [, ] and Hirth and Kohlstedt [] for Fo 90 olivine and Tasaka et al . [] for Fo 53 to Fo 90 olivine, all deformed under hydrous conditions.…”

“…Deformation experiments on polycrystalline olivine (both Fo 90 and Fo 50 ) under anhydrous conditions demonstrated clearly a grain size dependence with p ≈ 1 and n ≈ 3; this result was interpreted as indicating that creep occurred by dislocation‐accommodated grain boundary sliding [ Hirth and Kohlstedt , ; Wang et al ., ; Hansen et al ., , , , ]. In contrast, deformation experiments on polycrystalline olivine (Fo 90 ) under hydrous conditions lack a dependence of strain rate on grain size [ Mei and Kohlstedt , , ; Hirth and Kohlstedt , ; Tasaka et al ., ]. In these studies, the authors argued that dislocation climb was enhanced under hydrous conditions and replaced the need for grain boundary sliding present under anhydrous conditions, and therefore, dislocation climb contributes more strain than grain boundary sliding under hydrous conditions.…”

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due to Phase Mixing: 1. Mechanical Behavior

“…With these lower strength samples, deformation experiments could be conducted over a wider range of strain rates than possible with samples of Fo 90 , as demonstrated in previous torsion experiments on aggregates of Fo 50 (e.g., Hansen et al, , ; Tasaka et al, ). Since the effect of iron on the rheological properties of olivine has been determined for both hydrous and anhydrous environments (Tasaka et al, ; Zhao et al, ), the rheological behavior and texture development of Fo 50 can be scaled to that of Fo 90 , appropriate for Earth's upper mantle.…”

Precise and Accurate Doping of Nanoporous Silica Gel for the Synthesis of Trace Element Microanalytical Reference Materials

“…This study used the Paterson gas‐medium apparatus at the University of Minnesota to hot‐press three‐ and seven‐layer aggregates of doped silica gels at 1100 °C and 300 MPa for 1–3 h (following a procedure similar to Tasaka et al . ). Before the experiment, silica gel samples were calcined in a Pt crucible at 825 °C for 1 h, following the methods described by Luan and Paterson () and Nachlas and Hirth ().…”