Mild-to-wild plasticity of Earth's upper mantle

Area of Science:

• Geophysics
• Materials Science
• Mineral Physics

Background:

• Earth's upper mantle flow is traditionally modeled as slow, continuous creep.
• High-resolution experiments reveal materials exhibit a spectrum of plastic behaviors, from mild to wild.

Purpose of the Study:

• To investigate the plastic behavior of olivine under varying conditions.
• To determine if olivine exhibits "wildness" in its plastic deformation.

Main Methods:

• Nanoindentation experiments on olivine single crystals at room temperature.
• Analysis of plastic strain rate fluctuations and displacement bursts.

Main Results:

• Olivine displays measurable "wildness" in plastic flow, even under mild conditions.
• Intermittent bursts of displacement, indicative of dislocation avalanches, account for ~8% of plastic strain.
• These bursts follow log-normal distributions, characteristic of avalanche phenomena.

Conclusions:

• The study demonstrates intermittent plasticity in olivine, challenging the continuous creep model for upper mantle flow.
• Mild-to-wild plasticity framework suggests increasing "wildness" with depth, impacting asthenosphere deformation.
• Findings provide new constraints on dislocation-mediated flow models and raise questions about transient instabilities like deep earthquakes and slow-slip events.