Reduced Viscosity of Mg2GeO4 with Minor MgGeO3 between 1000 and 1150 °C Suggests Solid-State Lubrication at the Lithosphere–Asthenosphere Boundary

Tectonic plates are thought to move above the asthenosphere due presence of accumulated melts or volatiles that result in a low-viscosity layer, known as lithosphere–asthenosphere boundary (LAB). Here, we report experiments suggesting may slide through solid-state mechanism. Ultrafine-grained aggregates Mg2GeO4 and minor MgGeO3 were synthetized using spark plasma sintering (SPS) deformed 1-atm deformation rig between 950 °C 1250 °C. For 1000 < T 1150 °C, derivative stress–strain relation material drops down zero once critical stress low 30–100 MPa is reached. This viscosity reduction followed by hardening. The curves consistent with what commonly observed steels during shear-induced transformation from austenite martensite, final being significantly harder. referred TRansformation-Induced Plasticity (TRIP), widely metal alloys (TRIP alloys). It should be noted such enhanced plasticity not necessarily phase transition, but could consist any kind transformation, including structural transformations. We suspect stress-induced grain-boundary destabilization. associated transient existence metastable forming vicinity grain boundaries However, no can recovered samples. Whatever its nature, rheological transition seems occur competition diffusional processes (i.e., thermally activated) displacive diffusionless). Consequently, would harder at 1200 than 1100 thanks diffusion strengthen thermodynamically stable phases structures. alternative scenario for LAB require volatiles. Instead, tectonic on layer which peridotite constantly adjusting via transformation.