Prof. Lars Hansen (Department of Earth Sciences, University of Oxford, UK)

Size effects in geological materials: Resolving 40 years of debate on the strength of the lithosphere
When Nov 13, 2017
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283446
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Department of Earth Sciences, University of Oxford, UK

 

The strength of the lithosphere controls a wide variety of geodynamic phenomona, from the seismic cycle to the formation of new plate boundaries. Laboratory experiments over the last four decades have aimed to estimate the strength of the lithosphere by deforming aggregates of olivine under controlled conditions. Unfortunately, little consensus has been reached, with significant variability among results. Furthermore, most laboratory estimates of lithospheric strength are considerably larger than estimates from geophysical observations (e.g., lithospheric flexure) and geodynamic modelling. Here I present new experimental results using nanoindentation and synchrotron-based high-pressure experiments. These experiments reveal both an indentation size effect and a grain-size dependence of strength. This phenomenon resolves the discrepancy among previous laboratory-based studies, which were each conducted on aggregates with different grain sizes. Furthermore, extrapolation to grain sizes typcial of the lithospheric mantle indicate the lithosphere is much weaker than originally presumed, in better agreement with geophysical and geodynamic estimates.