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| Titel |
Mechanisms for lithospheric shear localization and the generation of plate tectonics by two-phase grain-damage and pinning |
| VerfasserIn |
D. Bercovici, Y. Ricard |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069676
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| Zusammenfassung |
| Shear localization in the lithosphere is an essential ingredient for understanding how and
whether plate tectonics is generated from mantle convection on terrestrial planets. We present
a new theoretical model for the mechanism of lithospheric shear-localization and hence plate
generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline)
lithospheric rocks. Grain size evolves through the competition of coarsening, which drives
grain-growth, with damage, which drives grain reduction. However, in a two-phase medium
the interface between phases induces Zener pinning, which impedes grain growth and
facilitates damage. The size of the pinning surfaces is given by the roughness of the
interface, and damage to the interface causes smaller pinning surfaces, which in
turn drive down the grain-size, forcing the rheology into the grain-size-dependent
diffusion creep regime. This process allows damage and rheological weakening to
co-exist, which is normally considered impossible in single phase assemblages.
Pinning also greatly inhibits grain-growth and shear-zone healing, which is much
faster in single phase materials. Hence, the resulting shear-localization is rapid (less
than 1Myr), but the healing time for a dormant weak zone is very slow (greater
than 100Myrs). These effects therefore permit rapidly forming and long-lived plate
boundaries, in both simple shear cases as well as two-dimensional source-sink
flows that generate plate-like toroidal motion. The model therefore provides a key
ingredient and predictive theory for the generation of plate tectonics on Earth and other
planets. |
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