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| Titel |
The influence of hydrogen on the transition from power-law creep to low-temperature plasticity of olivine at lithospheric temperatures |
| VerfasserIn |
Jacob Tielke, Mark Zimmerman, David Kohlstedt |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101173
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| Publikation (Nr.) |
 EGU/EGU2015-275.pdf |
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| Zusammenfassung |
| At high-temperature (asthenospheric) conditions, strain rate of olivine-rich mantle rocks
follows a power-law dependence on stress. At lower-temperature (lithospheric) conditions,
strain rate exhibits an exponential dependence on stress. However, the influence of water
(hydrogen) on the transition from high-temperature to low-temperature behavior is poorly
constrained. To investigate the influence of water on the transition in flow regimes at
lithospheric conditions, deformation experiments on single crystals of San Carlos olivine
under both wet (hydrogen-rich) and dry (hydrogen-poor) conditions were carried out.
Crystals were oriented relative to the applied load to exert the maximum shear stress on the
(100)[001] and (001)[100] dislocation slip systems, which are the dominate (weakest) slip
systems at both low temperatures and under wet conditions. Experiments were carried out
using a gas-medium apparatus with high resolution in stress (±2 MPa) and temperature
(±2°C). For the wet experiments, hydrogen was supplied to the crystals using talc sealed in
nickel jackets. Deformation experiments were carried out in either triaxial compression or
direct shear geometries at 1000-1300°C, differential stresses of 120 to 670 MPa, and
resultant strain rates of 6 x 10-6 to 4 x 10-4 s-1. At high-temperature, under dry
conditions, strain rate is a power-law function of stress with a stress exponent of 3.5 and
an Arrhenius function of temperature with an activation energy of 520 kJ/mol.
At low-temperature and high-stress conditions, under dry conditions, strain rate
increases exponentially with increasing stress with an activation energy of 360
kJ/mol. These observations are consistent with a transition from a climb-controlled
dislocation mechanism at higher temperatures to a glide-controlled dislocation
mechanism at lower temperatures for hydrogen-poor olivine crystals. Under wet
conditions, the strain rate dependence on stress follows a power-law relationship
with a stress exponent of 3.5 and an activation energy of 330 kJ/mol and does not
transition to an exponential dependence on stress. Post-deformation electron-backscatter
diffraction analyses indicate development of low-angle boundaries with rotation about
the [010] axis, consistent with deformation resulting from glide of dislocations
on the (100)[001] and (001)[100] slip systems. Water concentrations in crystals
from wet experiments determined using Fourier transform infrared spectroscopy
were 157 to 190 ppm H/Si, similar to values obtained from xenoliths derived from
the lithospheric mantle. These analyses indicate that the presence of water in the
lithospheric mantle results in considerable weakening and that power-law flow
behavior of mantle rocks may operate at shallower depths than previously thought. |
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