Mantle superplasticity and its self-made demise.

Area of Science:

• Geophysics
• Materials Science
• Mineral Physics

Background:

• Superplasticity, the ability of solid materials to undergo large plastic deformation, is well-documented in metals and ceramics.
• Its occurrence in geological materials, like ice sheets and Earth's mantle, has been long speculated but experimentally unconfirmed.

Purpose of the Study:

• To experimentally demonstrate and characterize superplasticity in geomaterials relevant to Earth's mantle.
• To investigate the deformation mechanisms and associated microstructural evolution during superplastic flow in these analogues.

Main Methods:

• Experimental deformation of polycrystalline forsterite + periclase (9:1) and forsterite + enstatite + diopside (7:2.5:0.5) analogues under subsolidus conditions.
• Analysis of microstructural changes, including grain size evolution and deformation mechanisms (grain boundary sliding).

Main Results:

• Geomaterial analogues achieved homogeneous elongation up to 500% without failure, confirming superplasticity.
• Deformation was accompanied by strain hardening, attributed to grain growth via grain boundary sliding.
• An empirical strain-grain size-viscosity relationship was established.

Conclusions:

• Superplastic flow in Earth's mantle, particularly in shear zones and subducting slabs, is plausible.
• Mantle superplasticity inevitably leads to significant grain growth, increasing viscosity and eventually halting the flow.
• This microstructural evolution impacts mantle dynamics and rheology.