Decompaction weakening and channeling instability in ductile porous media: Implications for asthenospheric melt segregation

Détails

ID Serval
serval:BIB_86DF33660073
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
Decompaction weakening and channeling instability in ductile porous media: Implications for asthenospheric melt segregation
Périodique
Journal of Geophysical Research - Solid Earth
Auteur(s)
Connolly J.A.D., Podladchikov Y.Y.
ISSN-L
0148-0227
Statut éditorial
Publié
Date de publication
2007
Peer-reviewed
Oui
Volume
112
Pages
B10205
Langue
anglais
Résumé
We propose that a mechanical flow channeling instability, which arises
because of rock weakening at high fluid pressure, facilitates
segregation and transport of asthenospheric melts. To characterize the
weakening effect, the ratio of the matrix viscosity during decompaction
to that for compaction is treated as a free parameter R in the range 1
to 10(-6). Two-dimensional numerical simulations with this rheology
reveal that solitary, vertically elongated, porosity waves with spacing
on the compaction length scale delta initiate from miniscule porosity
perturbations. By analogy with viscous compaction models we infer that
in the absence of far-field stress, the three-dimensional expression of
the waves is as pipe-like structures of radius delta root R p, a
geometry that increases fluid fluxes by a factor of similar to 1/R. The
waves grow by draining fluid from the background porosity but leave a
wake of elevated porosity that localizes subsequent flow. Wave
amplitudes grow linearly with time, increasing by a factor of R(-3/8) in
the time required to drain the porosity a distance of similar to delta.
Dissipation of gravitational potential energy by the waves has the
capacity to enhance growth rates through melting. Maximum wave speeds
are similar to 40 times the speed of fluid flow through the unperturbed
matrix. Such waves may provoke the elastic response necessary to
nucleate, and localize the melt necessary to sustain, more effective
transport mechanisms. The formulation introduces no melting effects and
is applicable to fluid flow and localization problems in ductile porous
media in general.
Open Access
Oui
Création de la notice
09/10/2012 20:50
Dernière modification de la notice
08/05/2019 21:27
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