Activation volume for creep in the upper mantle.

Area of Science:

• Geophysics
• Mineral Physics
• Petrology

Background:

• Understanding the mechanical behavior of the Earth's mantle is crucial for geodynamic processes.
• Olivine is a primary mineral in the upper mantle, controlling its rheology.
• Creep deformation in mantle rocks is influenced by temperature, pressure, and mineral composition.

Purpose of the Study:

• To determine the activation volume for creep (V*) in olivine-rich rocks (dunite).
• To investigate the relationship between V* and oxygen ion self-diffusion.
• To estimate variations in mantle stress, strain rate, and viscosity with depth.

Main Methods:

• Pressure-differential creep experiments were conducted on dunite samples.
• Experiments were performed at high temperatures (1100–1350°C) and confining pressures (5–15 kbar).
• The activation volume for creep (V*) was calculated from experimental data.

Main Results:

• Measured V* values ranged from 10.6 to 15.4 cm³/mol.
• The mean V* was determined to be 13.4 cm³/mol.
• This mean value is close to that predicted for oxygen ion self-diffusion in olivine.

Conclusions:

• The activation volume for creep in dunite is consistent with oxygen ion diffusion mechanisms.
• Incorporating V* into flow equations, combined with xenolith data, allows for estimations of mantle rheology with depth.
• This research provides insights into the factors controlling mantle viscosity and deformation.