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.
(
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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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