 |
| Titel |
Numerical models on thermal and rheological sensitivity of deformation pattern at the lithosphere-asthenosphere boundary |
| VerfasserIn |
Lukas Fuchs, Harro Schmeling, Hemin Koyi |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098453
|
| Publikation (Nr.) |
 EGU/EGU2014-14133.pdf |
|
|
|
|
|
| Zusammenfassung |
| Understanding the interaction between the oceanic lithosphere and the upper mantle
is a crucial part in understanding plate tectonics/kinematic, especially along the
lithosphere-asthenosphere boundary (LAB).
In this study, we analyzed finite deformation (f = log(a
b) , where a and b are the major
and minor axis of the strain ellipse, respectively) integrated over time, within the
upper 400 km of the mantle. The velocity field was numerically calculated within a
two-dimensional channel of certain depth and length with a constant plate velocity on
top (Couette flow), with no slip bottom boundary and open side boundaries. The
viscosity is described by a composite rheology (dislocation and diffusion creep)
which is given by a temperature field based on a half-space cooling model for an
oceanic lithospheric plate using variable thermal parameters. A constant pressure was
applied at the left boundary of the channel to obtain a faster flowing asthenosphere
(additional Poiseuille flow). The depth of the LAB is assumed to be mechanically
defined and corresponds to the depth at which no additional strain is accumulated
on the downstream side, separating the high-viscous non-deforming lithosphere
from the low-viscous asthenosphere. Model results show that the lower part of
the lithosphere defined in this way is characterized by large inherited strains (f
~2).
Due to the applied kinematic boundary conditions for a Couette-flow model and the
lateral viscosity variations within the channel a minor induced Poiseuille-flow component is
obtained within the model. Thus, the stresses vary significantly in comparison to the 1D
solution of a Couette-flow.
Preliminary results show that deformation along the LAB is strongly governed by the
temperature and the plate velocity. The maximum depth of the lithosphere defined in the
above way is 120 km, and correlates with the 1230 °C temperature contour line. Moreover,
assuming steady state, the finite deformation will always increase with depth due to the
slower moving material at the lower part of in the channel. Thus, the maximum deformation
does not correlate with the base of the lithosphere. Besides, an additional pressure leads to a
faster flowing asthenospheric material and thus to a shift in polarization of the deformation.
The numerical simulations show that finite strains above and below the LAB are
predicted to be large and subhorizontal, but may shift in shear sense within the
asthenosphere. |
|
|
|
|
|
|