We present the results of an experimental investigation of the influence of oxygen fugacity on the deformation of a partially molten spinel lherzolite using a 0.1MPa gas-media creep rig under temperatures of 1160-1190°C, stresses of 4-74MPa and well-controlled oxygen fugacities of 10-7 to 10-11MPa. The partially molten spinel lherzolite was deformed by a dislocation-mediated creep process such as dislocation creep or dislocation-accommodated grain boundary sliding (DGBS) (n=3.5±0.3) as well as in the diffusion creep regime (n=1.2±0.2). The average oxygen fugacity exponent of lherzolite is 0.04±0.02, which is significantly smaller than the values measured for olivine single crystals (0.10-0.36) and dunite rocks (0.20) deformed by dislocation creep. We attribute the low oxygen fugacity exponent of partially molten lherzolite samples either to the operation of grain boundary sliding, if DGBS dominates the deformation, or to the presence of pyroxenes whose deformation has a weak or no dependency on oxygen fugacity, if dislocation creep dominates the deformation. In the latter case, the oxygen fugacity exponent decreases rapidly with decreasing volume fraction of olivine. The low oxygen fugacity exponent for our partially molten lherzolite samples implies that dislocation creep or DGBS of mantle peridotite will most likely be insensitive to variations of oxygen fugacity in the upper mantle.
Bibliographical noteFunding Information:
Wang thanks Dr. Quan Bai and Michael Naumann for their kind help in teaching him to operate the 0.1 MPa creep rig. Shuyan Jin and Haijun Xu are thanked for assistance with the microfabric analysis. This work was sponsored by grants from the National Natural Science Foundation of China (grant nos.: 40702034 , 90714005 , 41172070 ), the Ministry of Education of China and the State Administration of Foreign Expert Affairs of China (grant nos.: B07039 , 2007B25 and NCET-11-0726 ) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) ( CUG120121 ). DLK acknowledges support from NSF grant EAR-0910687 .
- Oxygen fugacity
- Partial melting
- Spinel lherzolite