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| Titel |
Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age |
| VerfasserIn |
D. Arcay |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 3, no. 2 ; Nr. 3, no. 2 (2012-12-21), S.467-488 |
| Datensatznummer |
250001001
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| Publikation (Nr.) |
 copernicus.org/se-3-467-2012.pdf |
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| Zusammenfassung |
| The properties of the subduction interplate domain are likely to affect not
only the seismogenic potential of the subduction area but also the overall
subduction process, as it influences its viability. Numerical simulations are
performed to model the long-term equilibrium state of the subduction
interplate when the diving lithosphere interacts with both the overriding
plate and the surrounding convective mantle. The thermomechanical model
combines a non-Newtonian viscous rheology and a pseudo-brittle
rheology. Rock strength here depends on depth, temperature and stress, for
both oceanic crust and mantle rocks. I study the evolution through time of,
on one hand, the brittle-ductile transition (BDT) depth, zBDT, and,
on the other hand, of the kinematic decoupling depth, zdec,
simulated along the subduction interplate. The results show that both a high
friction and a low ductile strength at the asthenospheric wedge tip shallow
zBDT. The influence of the weak material activation energy is of
second order but not negligible. zBDT becomes dependent on the
ductile strength increase with depth (activation volume) if the BDT occurs at
the interplate decoupling depth. Regarding the interplate decoupling depth,
it is shallowed (1) significantly if mantle viscosity at asthenospheric wedge
tip is low, (2) if the difference in mantle and interplate activation energy
is weak, and (3) if the activation volume is increased. Very low friction
coefficients and/or low asthenospheric viscosities promote zBDT = zdec. I then present how the subducting lithosphere age affects
the brittle-ductile transition depth and the kinematic decoupling depth in
this model. Simulations show that a rheological model in which the respective
activation energies of mantle and interplate material are too close hinders
the mechanical decoupling at the down-dip extent of the interplate, and
eventually jams the subduction process during incipient subduction of a young
(20-Myr-old) and soft lithosphere under a thick upper plate. Finally, both
the BDT depth and the decoupling depth are a function of the subducting plate
age, but are not influenced in the same fashion: cool and old subducting
plates deepen the BDT but shallow the interplate decoupling depth. Even if
BDT and kinematic decoupling are intrinsically related to different
mechanisms of deformation, this work shows that they are able to interact
closely. Comparison between modelling results and observations suggests a
minimum friction coefficient of 0.045 for the interplate plane, even 0.069 in
some cases, to model realistic BDT depths. The modelled zdec is a
bit deeper than suggested by geophysical observations. Eventually, the better
way to improve the adjustment to observations may rely on a moderate to
strong asthenosphere viscosity reduction in the metasomatised mantle wedge. |
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