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| Titel |
Direct Shear of Olivine Single Crystals |
| VerfasserIn |
Jacob Tielke, Mark Zimmerman, David Kohlstedt |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127995
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| Publikation (Nr.) |
 EGU/EGU2016-7933.pdf |
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| Zusammenfassung |
| Knowledge of the strength of individual dislocation slip systems in olivine is fundamental to
understanding the flow behavior and the development of lattice-preferred orientation in
olivine-rich rocks. The most direct measurements of the strengths of individual slip systems
are from triaxial compression experiments on olivine single crystals. However, such
experiments only allow for determination of flow laws for two of the four dominate slip
systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip
systems independently, we performed deformation experiments on single crystals
of San Carlos olivine in a direct shear geometry. Experiments were carried out at
temperatures of 1000∘ to 1300∘C, a confining pressure of 300 MPa, shear stresses of 60
to 334 MPa, and resultant shear strain rates of 7.4 x 10−6 to 6.7 x 10−4 s−1. At
high-temperature (≥1200∘C) and low-stress (≤200 MPa) conditions, the strain rate of
crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system
follows a power law relationship with stress, whereas at lower temperatures and
higher stresses, strain rate depends exponentially on stress. The flow laws derived
from the mechanical data in this study are consistent with a transition from the
operation of a climb-controlled dislocation mechanism during power-law creep to the
operation of a glide-controlled dislocation mechanism during exponential creep. In the
climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker
than crystals orientated for shear on the (100)[001] slip system. In contrast, in the
glide-controlled regime the opposite is observed. Extrapolation of flow laws determined
for crystals sheared in orientations favorable for slip on these two slip systems
to upper mantle conditions reveals that the (001)[100] slip system is weaker at
temperatures and stresses that are typical of the asthenospheric mantle, whereas the
(100)[001] slip system is weaker at conditions typical of the lithospheric mantle. These
observations demonstrate that the relative strength of the dislocation slip systems in
olivine and, thus, the development of lattice-preferred orientation and anisotropic
viscosity in olivine-rich rocks are strongly dependent upon temperature and stress. |
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