Rheology of Earth Materials :

Closing the gap between timescales in the laboratory and in the mantle

8 March 2020: Publication in JGR on deformation of antigorite, in situ, in a transmission electron microscope

Serpentines play a major role as water carrier during subduction. Their rheological properties are also very important since serpentines have a strong influence on deformation partitioning and seismicity in subduction zones. Despite this importance, the rheology of serpentines is still a matter of questions.

In this work, we succeeded in performing the first in situ deformation experiments of antigorite in the Transmission Electron Microscope. This has been made possible by using the latest developments of in situ nanomechanical testing since the specimen scales to a bacteria.

No dislocation activity has been observed in our tests, even though the engineering tensile stress went up to 700 MPa. We suppose that this is due to high lattice friction opposed to dislocation glide on the corrugated planes. We show also that antigorite does not exhibit a purely elastic-brittle behavior since, despite the presence of defects, the specimens accumulate permanent deformation and did not fail within the elastic regime.

Instead, we observe that strain localizes at grain boundaries which, on figure below appear brighter with increasing strain (due to sliding). The specimen being very thin, one of those sliding boundary eventually leads to rupture.

Our observations show that under these experimental conditions, grain boundary sliding is the dominant deformation mechanism.

 

To learn more, the publication is here:

H. Idrissi, V. Samaee, G. Lumbeeck, T. van der Werf, T. Pardoen, D. Schryvers & P. Cordier (2020) In Situ Quantitative Tensile Testing of Antigorite in a Transmission Electron Microscope. Journal of Geophysical Research: Solid Earth, 125, e2019JB018383. https://doi.org/10.1029/2019JB018383