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| Titel |
Transient subduction following upper plate acceleration/slow down |
| VerfasserIn |
Benjamin Guillaume, Solenn Hertgen, Nestor Cerpa, Joseph Martinod |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147985
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| Publikation (Nr.) |
 EGU/EGU2017-12209.pdf |
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| Zusammenfassung |
| Plate reorganization associated with mantle convection leads to changes in plate absolute
velocity over geological time scales. At the global scale, these accelerations/slow down
can reach values up to 2.5x10−23 m.s−2, i.e changes of up to 5 cm/yr over a 2
m.y. period (after Zahirovic et al., 2015). In this study, we aim at understanding
how such changes in the kinematics of the upper plate can influence subduction
dynamics and slab geometry. Are changes in the overriding plate tectonic regime
and in the slab geometry synchronous or delayed with respect to modifications
of plate kinematics? For this, we use an approach combining three-dimensional
analogue models and two-dimensional numerical models of subduction (ADELI
code).
In analogue models, we impose instantaneous changes of the upper plate velocity
during subduction and observe how the subduction system turns back to equilibrium
with the new boundary conditions. The adjustment times appear independent of the
imposed upper plate velocity and of the changes of upper plate velocity. Scaling of our
models show that this transient stage lasts ∼ 11±4 m.y. for the shallow (∼125 km
deep) dip of the slab, ∼16±2 m.y. for the deeper (∼330 km deep) part of the slab,
and ∼4±2 m.y. for bulk upper plate deformation. Using 2-D numerical models,
we explore the effect of different internal parameters (thickness and viscosity of
the slab, viscosity of the mantle) as well as external parameters (instantaneous vs.
progressive acceleration slow/down of the upper plate) on the duration of the transient
stage.
We also compare our modeling results with present-day subduction zones and their
evolution through the last 20 m.y. Data analysis suggests an adjustment time of ∼15 m.y. for
shallow slab dip and ∼20 m.y. for deep slab dip in Nature. Since only 1% and 9% of the 260
studied subduction transects exhibit a constant upper plate velocity over the last 20
m.y. and 15 m.y., respectively, most of subduction zones must be in a transient
stage at present-day. It may explain why the correlation observed in present-day
subduction zones between upper plate velocity on the one hand, slab geometry and
upper plate deformation on the other hand, is not as good in Nature as expected
from simple subduction models in which applied boundary are constant with time. |
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