Crystal-melt differential behaviour during magma ascent in dykes: insights from 2-D numerical modelling

Yamato, P.; Tartèse, R.; Hallot, E.; Boulvais, P.; Poujol, M. and Gallagher, K. (2010). Crystal-melt differential behaviour during magma ascent in dykes: insights from 2-D numerical modelling. In: GeoMod 2010 - Modelling in Geosciences, 27-29 Sep 2010, Lisbon, Portugal.

URL: http://geomod2010.fc.ul.pt/abstracts/Yamato%20et%2...

Abstract

We
 present
 the
 results
 of
 2D
 numerical
 models
 of
 flow
 in
 a
 two-phase
 medium,
 composed
 by
 crystals
 carried
 by
 a
 viscous
 melt,
 subject
 to
 a
 vertical
 pressure gradient condition.
These simulations of magma migration in a vertical
 dyke
 show
 that
 presence
 of
 crystals
 and
 their
 proportion
 perturb
 the
 flow
 velocity.
As shown in previous analytical studies,
the presence of crystals leads to
 a
 significant
 drop
 in
 vertical
 velocity.
 However
 in
 our
 case,
 this
 global
 displacement
 is
 accompanied
 neither
 by
 obvious
 crystal
 rotation
 nor
 by
 a
 significant
 horizontal
 displacement
 of
 crystals
 towards
 the
 dyke
 centre.
 Moreover,
 our
 results
 show
 that
 separation
 between
 crystal
 and
 melt
 occurs
 under
 certain
 conditions,
 which
 can
 lead
 to
 geochemical
 differentiation
 of
 magmas
 during
 their
 ascent.
 We
 provide,
 through
 a
 quantitative
 parametric
 study,
the
 range
 of 
values 
leading 
to
 crystal-melt 
segregation
 and
 compare 
the
 obtained differentiation rates to natural observations.
 Consequently, our results
 have
 fundamental
 implications
 regarding
 the
 causes
 of
 geochemical
 heterogeneities
 in
 magmatic
 suites.
 They
 provide
 constrains
 on
 differentiation
 processes
 during
 ascent,
 which
 is
 often
 neglected
 in
 comparison
 with
 the
 two
 classical
 end-members
 (i.e.,
 source-related
 processes
 vs.
 emplacement-related processes differentiation.

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