Metamorphic history of the Central Pyrenees
Part II,
Valle de Arán, Sheet 4
Zwart
H.J.
Abstract
The structural
mica-schists
slates
and
with
major
numerous
The rocks
schists
cleavage
date
blasts. A
and
third
E-W
The
and
a
a
first;
These
of
then
last
of
each
than
of the
lower
this
grade
is
the
rocks
in
the
Granite
most
and
granites
or
phase
are
larger
Chemical
both
pegmatite
abundant
after the first
smaller
Valle
de Arán
limestones;
Silurian
dome
with
axial
shown
folds
the
ones,
so
vertical
with
finally
N-S foldaxes
planes
and
regard
in NW-SE
microfolds
of four
is
metamorphic
The
higher
zones
cordierite-sillimanite-zone
to
only.
porphyroblasts
to
andalusite-cordierite-zone
an
sillimanite.
beginning
with
rotated porphyro-
axial
minor
establishment
the
Cambro-Ordovician.
phase
increasing grade.
that
Garonne
numerous
by
aluminium-silicate
and
at the
the
to
by
with
mainly
in
the
and later
characterized
with
first
Ordovician
bytownite, grossularite, diopside
The
and
is
regard
second
as
order
andalusite, cordierite
the
with
crystallize
Before
of sillimanite
sillimanite
crystallization
have
has
the
increasing
started
to
andalusite
unstable.
Cale-silicate
but
are
This resulted
in
in
of Cambro-Ordovician
Devonian accompanied by
orogeny
the
with
A
microstructures
form, staurolite was already unstable;
became
in
staurolite-andalusite-cordierite-zone;
a
complex history. Staurolite
temperature,
phase.
phases
application.
biotite-zone;
folds
deformationhave
investigating
its
Hercynian
E-W direction
three
cordierite-sillimanite-zone;
passed through
most
fourth phase
method
discussed
zones:
and
direction.
the
from the main
in
area
consist
area
limestones.
Large steep
laminar flow
accompanied by
was
this
pegmatite bodies, phyllites
folded disharmonically
are
Both kinds of structures
in
exposed
and
from
dating
essentially horizontal schistosity.
plane slaty
and
granite
Devonian
structure
of the Bosost
metamorphic petrology
is discussed.
and
schists
The
and
geology
(Central Pyrenees)
rock
the
until
in
the
cordierite-sillimanite-zone contain
and
sills
occur
in
all
the
aluminium-silicate
bearing
cordierite-sillimanite-zone. Their emplacement lasted
of
composed
culminating point
albite, quartz,
and
lies
around
muscovite;
the
from
the fourth
zones,
shortly
phase.
pegmatites
carry
amounts of microcline.
analyses
groups
bodies
limestone
vesuvianite.
after the fourth. The
mainly
is
potassium decrease.
potassium.
in
and
of
phyllites
essentially
The
the
granites
and
same.
have
high
mica-schists
With
alcali
have
increasing
shown
silicium
percentages
with
that
the
content,
sodium
composition
aluminium
of
and
predominatingover
Contents
Page
1.
Introduction
323
2.
Stratigraphy
323
2.1
Cambro-Ordovician
323
2.11
Phyllites
323
2.12
Mica-schists
2.13
Limestones and
2.2
Silurian
326
2.3
Devonian
327
3.
Structural
3.1
Major
structures
327
3.2
Minor
structures
328
3.21
First
3.22
Second
3.23
Third
3.24
Fourth
3.3
Microstructures
334
3.31
Method of
334
3.32
Metamorphic
3.321
Biotite-zone
338
3.322
Staurolite-andalusite-cordierite-zone
339
3.323
Andalusite-cordierite-zone
352
3.324
Cordierite-sillimanite-zone
358
4.
Calc-silicate rocks
363
5.
Granites and
363
5.1
Occurrence
363
5.2
Petrography
366
6.
Petrochemistry
367
6.1
Phyllites
367
6.2
Mica-schists
368
6.3
Granites
373
325
marbles
geology
326
327
329
phase
331
phase
phase
332
phase
332
investigation
zones
pegmatites
338
INTRODUCTION
1.
The
Aran around Bosost
part of the Valle de
western
of the
river
Pique
of micaschists
consisting
The first
of the
area
done
the
to
reports
van
of
amount
to
As
shown
situated with
outside
portion
Silurian and
SW
phyllites
boundaries
the
1962)
Bosost
are
oblique
to
number of
large
the mica-schists.
tially they
of
are
They
are:
bearing
zoning
with
zone
that
distinguished
and
that
at
A
all
1
the
and
the
dome,
dome is
of the
part
along
Garonne
its
willingness
eccentrically
Garonne
dome
phyllites
for its
dome is
bounded
metamorphic dome,
a
phyllites
and
related
southern
boundary
Consequently
limits and the schists
the
near
lies
in
by
the
mica-schists
grade
into
metamorphic
Bosost
are
the
north of it.
pegmatites
the
to
1960.
to
up
whose
large
a
here.
Bosost
It forms
sides
Bosost
stratigraphie
granites
are
zones
least
occurs
regional
metamorphism
as
sills
or
bodies in
irregular
and
metamorphism
three
or
times
be
the
with
detected;
and
four
successive
stages
contemporaneous with
between
these
phases
a
mica-schists.
than apparent in the field.
complexity mainly
large part
can
andalusite-zone
andalusite in
complex
proceeded
the
during
of
biotite-zone,
without
or
more
which
continuous. The
depth.
the
of the
chlorite-zone,
is however,
indicated
fig.
and
the
revising
collecting
summer
Boschma
was
at
least par-
replacement origin.
In the field several
these
Dr. D.
of the remainder of the Garonne dome.
stratigraphie equivalents
A
The
time
small
a
who all submitted
author started
few weeks every
a
by
area
area.
dome
the Silurian. North of the Bosost dome the schists
to
way up
On
area.
Kapel,
same
an
mapped
Bosost
consists of Cambro-Ordovician
which
structure
major
for
of the
parts
the
at
area,
structures.
major
Devonian rocks.
of this
portion
reach all the
the
Zwart,
of other
in
Bosost
or
Geology Department
Francken
gratefully acknowledged
map, sheet 4,
the
to
B.
located
dome
students of the
by
and the headwaters
are
Bosost
as
1956 the present
area
is
samples
to
when R.
accompanied
was
with
the
on
regard
Sitter and
(De
he
season
heavy packs
is
In
of the
He visited the
specimens.
Spain
in
Franche
der Meer Mohr and A.
van
completed mapping
the last
carry
H. E. C.
Loon,
area
1951
mapping
Geology Department.
material and
During
Subsequent
in
referred
in the Bosost
of Leiden started in
Bosost itself.
M.
by
Luchon
granites,
and
investigations
University
near
de
Bagnères
near
of
of
increasing
The
metamorphic
evidence
Microscopic
metamorphism
kind
some
folding,
depth
granite-pegmatite
of
can
be
deformation,
metamorphism
was
arises from the interrelations between time and
of this paper will
be
devoted
to
the
deciphering
of the
meta-
morphic history.
2.
2.1
STRATIGRAPHY
CAMBRO-ORDOVICIAN
2.11
The
Phyllites
Cambro-Ordovician sediments outside the
monotonous
series
of dark
coloured slates
north side of the
quartzite
bands. On the
quartzite
than usual and there
typical
and
Bosost
'schistes
Bosost
phyllites,
dome
dome consist of
sandy
they
are
rubanés', thinly
phyllites
a
rather
and
thin
somewhat richer in
laminated alternations
324
H.
J.
Zwart:
Metamorphic history of
the Central
Pyrenees
zoning.
metamorphic
and
struct re
showing
area,
Bosost
of
map
Geol gical
1.
Fig.
325
Stratigraphy
of
and
quartzite
phyllite
The
crosscutting cleavage.
although
exudation
locality
small outcrop
a
of
are
with
parallels bedding
usually
widespread
the
phyllites
lenses
and
of
near
the
of
few
quite
are
with
a
these
rocks
flattened
cleavage
recumbent folds
of Bosost itself are less
village
of quartz
pods
conglomerate
a
In
occurrence.
only exception
of
the
At
frequent.
pebbles
few
a
with
quartzitic,
latter
size
cm.
has been found.
The
close
in
cleavage
the
Microscopically
with minor
but
ped,
the
phyllites
has
and
ore
the
dip although
The
mica-schists
appearance due
four different
of the
types
be
can
The
is
cleavage
Bosost
differences in
to
strike is
mostly
distinguished,
(2)
staurolite-andalusite-cordierite-schists,
(3)
where much
outside
more
or
restricted
each
same
well develo-
occurring
where
places
large
a
variation in
megascopic
mineralogical composition. Roughly
be
to
to
the
dome,
of the
parts
granites
of
amount
large
a
both
Bosost
and
feldspathic schists, occurring
banded mica-schists
transitional
localities. These
specific
at
found in
often
unoriented,
exposed, (4)
are
usually
in the northern half of the Bosost
at
peg-
in the
Lès.
near
and
phyllites
they
present
all mica-schists of the Bosost
Originally, however,
occurrence.
have been of the
is
granite
The biotite-schists
those
less
show
and
biotite-schists, mainly outcropping
occur,
main constituents
as
is
common.
very
dome
structure
(1)
dome, but mainly
sericite
slaty cleavage
Mica schists
are
matites
and
quartz
graphite.
crenulation
secondary
a
consist of
phyllites
iron
chlorite,
2.12
area
variable
a
E-W.
to
are
dome
of
must
has obliterated
kind; subsequent higher grade metamorphism
character.
part of their original
Most
muscovite
besides
biotite-schists
are
readily
good schistosity
a
E-W direction. The
varies
between
When obvious
and
Dykes
or
schistosity
with
sedimentary
schistosity
are
the
occur,
or
granite
large part
a
silicates
they
site and
Southern
high
as
As
elliptic
a
not
are
at
long
axis of the
|
cm
are
size.
are
oriented
to
to
to
diameter of 1
a
and
era
dome andalusite-schists
slates,
but
near
cordierite
schistosity
crystals
Almost
Bosost and
occur
usually
lies in the
all
size
|
the
dip
banded;
several
to
a
to
cm.
They
are
stratigraphically
occur
the
be
up
to
1
mm
small mica
rounded
equant
twins.
as
occurs
with
as
into
porphyroblasts.
but in that
short
penetration
expressed by
they grade
crystals
around
as
cm.
be found. In the
north of it
found
biotite
can
to
occur
of andalu-
of several
length
are
aluminous
outcrops
amount
of schistosity,
be
of the
best
large
elongate
as
curves
plane
crystals
the lineation
and
are
andalusite-schists,
as
fairly large
andalusite-cordierite-schists
the biotite-schists.
parallel
thickness of
a
studded with
distributed. Staurolite is
in
of
the field. Some of the
in
of mica-flakes with
phyllites
mica-schists
referred
the
to
staurolite-andalusite-cordierite-schists
crystals compared
they
the
section;
random
exceeding
these
Bosost
Andalusite and
cross
rule the
they
of the
Silurian black
a
Most
and
show,
absent in the biotite-schists.
often
dome. Due
with
developed
than in the
2).
biotite
parallel.
are
where the schists
crystals
well
portion
the
biotite-schists.
or
mine,
cordierite
East of Lés also
Bosost
readily recognized
are
the Victoria
near
of the
eye.
which
of these schists
quartzite intercalations, it appears that
like
nearly always
pegmatite
(fig.
in
Most
by elongation
mica-poor layers
Staurolite-andalusite-cordierite-schists,
form
naked
less steep
dips
40—50°
beds
rocks
mediumgrained
to
with
often
and
alternating
sills of
fine-
lineation determined
a
horizontal
mica-rich bands
bedding
are
recognized
In many
somewhat
long
plane
prisms
and
crystals.
of
larger
usually
326
H.
Folds of the
several
schists;
to
mostly they
several
m.
Luchon.
due
types
dierite
fibrolite
are
often
Banded mica-schists
the
presence of
of
ness
occurrence
schists
enclosing
the
frequently;
long
to
in these
1
cm
is rather
of the
axes
quite
of the
parts
less
biotite
vague
into
and
are
Similar schists also
specimens.
de
described
crystals.
for
Locally,
quartzofeldspathic
of andalusite and
absent.
altogether
large
ères
usually present.
common.
Large porphyroblasts
rare.
staurolite is
the
as
is
with
migmatites
Bagn
muscovite
schistosity
andalusite-schists
grade
dome where
oriented fabric
oriented
or
Bosost
NE of Bosost and E of
Bluish-grey
occur as
cor-
of
mats
inclusions in the
bodies.
granite
by
frequent
with the
perfectly
a
more
schists
in the
seen
a
schistose
and
common,
of
in thickness from less than
occurs
example
randomly
but
is
rocktype
less
are
of
and
Pyrenees
in size from microfolds up
vary
are
varying
those
for
show such
not
these
Bosost,
in
occur,
lacking
linear
to
near
but this
bands,
do
sills
pegmatites
occur
presence
often
are
Transitions
example
the
to
Lineations
Pegmatites
or
Central
NW-SE directions.
granite
These schists
and
pegmatites together
or
schists
bodies of crosscutting
common
are
size.
of the
N-S
mainly
oriented
Badly
of the
boudinage
have
boudings
metres
small bodies
are
Folding
Also
common.
of
tens
the
Metamorphic history of
schistosity plane
or
metres
Zwart:
J.
1
approximately
but contrary
elongated
instead of E-W.
sections
it
schistosity
common
(fig.
(fig.
mm
or
seen
24). Very
even
is
that the
3). Large
the
near
village
of biotite and
less.
The
visible
banding
of Lés and
in the
in
crystals
area
often makes
a
small
and
are
in
axes are
are
E-W
with the
oblique angle
cordierite
of andalusite and
thick-
a
schists
have N-S lineations
they
isoclinal recumbent folds with N-S
sharp,
porphyroblasts
with
these
schistosity planes
the
across
characterized
are
quartz-rich layers
biotite
other mica-schists
to most
banding
The
be
can
mainly
occur
peculiar banding
a
rather
frequently
observed in these schists.
2.13 Limestone and marble
Between Mina Victoria and
ness
occurs
overlain
schists.
large
near
by
the
top
of
amount
the limestone is
pelitic
diopside
It
is
a
material
probably
Guarbes, although
rather
limestone horizon of 20—30
by
a
marmorized,
it
contains
thin
locality
layer
a
coarsely
part
of the
the
same
here it does
limestone forms
not
occur
limestone
recrystallized
The
at
directly
its
base
Silurian slates and
and
often
staining.
slates often
are
the
schists, forming
aluminium content and
dant andalusite. The
altered
strongly
to
as
presence
Where
a
of
result
a
or
like
the
highest ridge
of the
underneath the Silurian.
intercalated
as
a
with
flatlying
an
important
near
or
of
and
have
They
metamorphism they
to
outside the
their
metamorphic
high plasticty.
chiastolite-schists. Good
Arres
marker bed in
a
slate
horizon
on
the
In
examples
the
often contain abun-
area
the
they
Bosost
very black
are
a
few
black
dome
of such rocks
Trona mountain. At
area,
remarkably
few percent of carbon makes the rock
occurring
contorted due
andalusite
Pique valley,
small
a
minerals,
SILURIAN
derived from black carbonaceous shales in euxinic facies.
high
thick-
Garonne dome.
2.2
are
m
immediately
contains
calc-silicate
and chert bands. At the Sierra de Guarbes the limestone occurs
forming
is
of Cambro-Ordovician
but when it
various
it
and clinozoisite.
Another outcrop of
Sierra de
a
the Silurian black slates; elsewhere
When pure,
grossularite,
la Bordeta
of the Cambro-Ordovician. At this
they
occur
places
in
small
Structural
sills and
pegmatite
They
and Arres.
schists
found.
are
bodies
may be
boudins
have
occur
in these schists.
of the
The
be
but
seen,
folded
severely
The
careful
Silurian is
zero
surface.
It
may be
when
impure.
slates
(Kleinsmiede
dark
usually
by
but
(1960),
it
is
of
Their
with
bluish
near
black.
or
the
overlain
They
of Las
village
fairly large portion
a
as
a
presence
Bordas.
of
mm
to
up
1
the rock
gives
small
of the
is
usually
stratigraphy
I refer
3.
to
The
larger
Bosost
dome is
Garonne dome
Ordovician rocks.
In
not
domeshaped; structurally
Bosost
it
simple
structure.
dome, phyllites
Bedding
in
example
shown
Guarbes,
and outside the Bosost
by
the
is
area
headwaters of the
Lez
of
there where the
bedding
occur,
Silurian and
The
cleavage
can
be
and Orle
no
are
and
strongly
Kleinsmiede
due
to
rounded
or
with
varying
a
large
in
size
shortly elongate.
schists.
A few peg-
Arro. For further details of the
(1960).
GEOLOGY
unit,
but it is
and
schists,
places
are
near
eastern
Only
and
on
large
characterized
La
has
their apparent
gentle
Bordeta,
on
no
The
structures.
by
are
there is
apparently
the
or
of Cambro-
boundaries which
metamorphic
horizontal
limestone
in the
part of the much
a
1962), consisting entirely
metamorphism
rivers.
schists
dips,
the
for
as
Sierra
de
part of the Garonne dome in the
north and
south sides steeper
Cambro-Ordovician is in steep
contact
dips
with the
Devonian.
bedding is, however,
or
are
to
cordierite,
the Garonne dome and
most
Ordovician
by
apparently
found in these
structural
Zwart
to
regional
converted
near
dome it is the
belongs
direct relation between the
rocks of the Garonne
separate
a
slates
sandstones
STRUCTURES
MAJOR
Sitter and
(De
the
Kleinsmiede
STRUCTURAL
3.1
Entecada
look. A lineation in ESE direction
be
to
matite sills have been observed in the Devonian
Devonian
the
thickness of this
This is
map.
crystals
peculiar spotted
a
slates,
maximum
m
andalusite and
Most of the
corrugations
of
wheathering
calc-silicate rocks
cleavage folding.
staurolite,
cm.
The
450
at
Bosost dome this series of slates is
porphyroblasts
series
a
white
to
or
interbedded with
are
estimated
small,
result of
by
limestone
intercalations of limestones. These
covers
thickening
as
some
so-called basal
bluish limestone with
rather
from less than 1
and visible
limestone
a
can
stratigraphie horizons,
slate. Its thickness varies from
marble when pure,
probably
South of the
amount
it is
basal
quartzites, especially
considerable
plane
has revealed.
the
horizon,
sandstone and
chert,
to
1960),
different
Alphen ( 1956)
limestone
a
Usually
m.
coloured,
folded series is
detachment
a
concerned consists of an
we are
two
one or
Van
mapping by
metamorphosed
The
commonly
Small folds
DEVONIAN
probably only
overlain
150
to
up
and sometimes
uncommon
as
Trona
with the
rocks and limestones. On the map several limestone bands
which contains intercalations of
almost
the
near
contacts
on.
represent
as
not
pebbles.
of the Devonian with which
portion
pelitic
they
of
behaviour of the Silurian
peculiar
2.3
The lower
sills is
string
a
instance
locally crosscutting
pegmatite
the appearance of
will be described further
alternation of
Silurian schists for
few dm. thick and
Boudinage
these
in the
occur
a
327
geology
schistosity
doubt
that
everywhere accompanied
and is with the
this
exception of a few
flatlying attitude of bedding
by
a
well
developed
cases
parallel
and
cleavage
to
slaty
it. There
dates
from
328
H.
early phase
an
and
all
with
regional
is shown
phism
that the
The
with
a
of the
vertical axial
type is
Devonian
itself to the flat
structures,
stone
east
as
plane
slaty
between
La
the
on a
takes
2.
by
place
Section
the
by
the
cutting
in the
Silurian,
Bosost
through
metamor-
possible
the Aston-
and
slope
scale. No
dissected in
two
halves
This
the
Cambro-Ordovician
adapts
area.
top
of the
the
strongly
is
rather
a
the Devonian
to
folded
Devonian
case
of dis-
nature
of
Bosost fault with
an
very
high angle
(see fig. 2,1).
Ordovician lime-
unique
metamorphic
the
by
are
folds
outside
the bottom of which
doubt it results from the
of the
tight
bedding.
Pyrenees
flat
position
Mina Victoria
large
the
all sides
of
Silurian in the Devonian anticlines
almost horizontal
and
on
occurrence
across
between the
visible in the mountain
plastic
front.
northern block.
3.2
Minor
structures
which
lineations, schistosities,
of such
(fig. 4—9).
these
and
described in
have
a
been observed
one
outcrop
directions of lineations have
on
the
field include small
combined with
are
only
microscopic
schistosity
data it
in the Bosost
in
the
appeared
dome.
is
present,
Bosost
dome.
that
They
evidence for their relative age will also be
microstructures.
folds,
measure-
assembled in stereograms
one
been observed
of deformation have been active
part
in
boudins and mullions. Several hundred
rule in any
chronological order;
next
STRUCTURES
have been made and the results
as
observations,
phases
MINOR
cleavages,
structures
Although
several kinds
in the
dome like
gneiss
Paleozoic of the
extremely high position
The Bosost dome is
or
a
the
here
characterized
and it is
the Garonne dome
often
the
transition
pinched
Bordeta
the Silurian and the
different
by
since
display
fact that
are
occur,
surface of the Cambro-Ordovician and the
by
section,
harmonie folding
From
rocks
higher grade
cleavage,
The
areas.
map this is visible
upthrown
dome
usually
Major
Pyrenees,
connection exists with regional
characterized
throughout
structures
upper
shown
of it. This
ments
some
Devonian, surrounding
Fig.
On the
which
lowgrade phyllites,
structures are
common
metamorphic
steep
in the
unique
massif.
structures
structural
and
remarkable structure
a
mountain chain.
Aston-Hospitalet gneiss
the Bosost dome where
different. These
regional
Pyrenees
Garonne dome arises from the
That
plane cleavage.
by
in this
not
however,
whole of the Garonne dome is underlain
Hospitalet
entirely
elsewhere
the
of the
in
structures occur
vertical axial
are,
domes like
peculiarity
the Central
such the Garonne dome is
phyllites
flatlying schistosity
metamorphic
metamorphic
by
of deformation. As
feature. The
same
Metamorphic history of
different from the
strongly
structures
Zwart:
J.
four
will
given
be
here
Structural
3.21
The first
area
the
phase,
has left its
far
first phase
structures
as
almost
structures
major
cleavages
as
traces
are
concerned the
everywhere. During
with
together
number
a
and certain lineations have been
in
a
eastern
side and
stereogram
of
west
It is
the
cleavage
very
3.
Isoclinal
to
probable
give.
on
the
In
recumbent
that the steep
any
case
of deformation. Although
the
Garonne
it
dome had
Variations from horizontal
steeper than 45°
as
are
rare
for instance shown
by
In many outcrops
with
micaceous
one
in the
phase,
schistosities,
as
of foldaxes
folds
by
Foldaxes and
to
plunge gently
with
of the Bosost
east
resul-
folding,
cleavage
side of the Bosost dome.
the
Fig.
east
4
near
suddenly
on
gives
dome. The
by flatlying schistosity,
N-S axis;
it steepens rather
area
structures
plane cleavage.
characterized
have
but
Lés.
that it
so
grades
both
ones;
can
s-planes
a
to
be
simultaneously,
into
angle
its
this
occur,
This variation is
Boschma
turn
due
is
the
at
a
cleavage
present
but in
to
proof
is
porphyroblastic growth
is older than
originally
attitude,
almost vertical
(fig. 5).
the
later
second
and
no
phase
schistosity
longer
Bosost schists
folding
of the
true.
dips
s-planes
(1963).
the mica-schists
the
at
that
schistosity
actual
although
older than the
are
proved
low
in the Devonian and the flat
cleavage
formed
of staurolite, andalusite and cordierite which
in
deformed
western
are
important
also called main
of the Devonian.
Cambro-Ordovician
difficult
of minor
vertical axial
measurements
the southside of the Bosost
the steep
in
the
Cambro-Ordovician
Fig.
on
to
number of
a
of the
structures
a
most
phase,
intersections have E-W direction and
cleavage-bedding
the
folds with
strongly compressed
this
produced.
The Devonian and part of the Silurian is
ting
329
geology
banding
are
is in
banded
most
rocks,
cases
siliceous
parallel
to
layers alternating
the
schistosity.
This
330
H.
J.
Fig.
Zwart:
Metamorphic history of
4-5-6-7-8-9.
Contours:
D:
A:
Stereograms;
4-10-20-40%;
1-2-4-10-15%;
E:
B:
for
the Central
explanation
1-2-4-10%;
2-4-10-25%;
F:
C:
Pyrenees
see
text.
2-4-8-12%
1-3-6%.
Structural
is
banding
often
of
observed
several
in few
E-W
are
this
localities,
in the
places
the formation of the
recumbent fclds
asymmetry has
of the
elongate shape
by
the
the
same
in
present
are
mica flakes
the
by
and muscovite
the
to
the
which
at
shows the
between
not
the
fig.
not
6
a
show
E-W
structures
and
not
which will be dealt with
In the
in the
with
be
to
later,
probably
eastern
western
occur,
movement.
schistosity
the
by
deter-
are
is
the
to
must
which
the
Devonian
an
the
the
no
date from the
other way.
to
boundary
the
meta-
doubt that
same
Microscopic
may
6),
due
incompetent
with
approximately
boundaries. Since there is
some
(fig.
above the Silu-
consequently
metamorphics
in
in the
Evidently
folds
that this difference is
indicates that this deviation
folding
evidence,
be the result of later
feature of these schists.
original
lineations
most
in agreement with the
west
aligned
are
metamorphosed Devonian,
stratigraphie
at
the smaller biotite
being separated by
lineations coincides
explained
not
have been formed
dome this lineation is accentuated
suggested
both
part of the Bosost dome
part
move-
produced
are
lineations and
direction like
that also the
and ESE
this deviation has
and
direction of
they
deviation of lineation direction and
E-W foldaxes
movements
small isoclinal-
shearing
determine whether the
lattice orientation like
a
the Devonian folds and the lineations in the
phase,
of
number of lineations has been assembled.
in
occur
however,
same
morphic boundary
to
is the
and
and both
schistosity
the SE with i 25°. It has been
Silurian. It is true,
rian,
In
crystals.
but deviates
contemporaneous with
plane
a
larger biotite-porphyroblasts
but which do
maximum does
level
that both
so
mica-schists of the Bosost
many
of somewhat
presence
direction,
same
mica-schists
that
both
schistosity,
and orientation of these micas. Therefore this kind of lineation is
shape
time. In
same
and which
sense
most
connected with the formation of the
the
is
schistosity
at
folds
mica-schists, indicating
few of such folds have been found
too
Foldaxes of such
and is
it
has been
mine SW of Bosost and
area.
character of these
asymmetric
that
evident
bedding
of lineation and
Hercynian folding,
indicates that the
probably
Bosost
development
folds. The
of such
folding
the Victoria
near
it is
places
some
the lineations in the
to
of the
phase
everywhere
Lineations
mined
parallel
major
Unfortunately
ment.
example
is connected with the
from the main
dating
for
at
isoclinal
Tight
Garonne dome outside the
WNW-ESE
to
tight folding
but
metamorphic origin,
represents the sedimentary bedding.
331
geology
plunge gently
general plunge
the
to
east,
of the dome in
both directions.
3.22
in
most
the
large
Although
except
occur
near
near
Lès
in the
parts
of the Bosost
granite bodies,
p.
326.
elongated
E-W
section is
lineations
In
in N-S
N-S lineations and
in the Bosost
with
In
N-S
in
some
must
have
are
these N-S
near
have
is
schistosity
with axial
the
an
N-S
direction.
of the mica-schists described
folds
Lés
these
have been
phyllites
been observed.
dome N-S folds
probably
they
conspicuous
are
different direction
a
are
related
schistosity
microfolds
are
parallel
plane
the
to
schistosity
to
plane
in
and
banding
itself shows
connected with
the
have formed rather late. At several localities elsewhere
Cambro-Ordovician
axes
axes
that
the
tight folding
Evidently
dome also N-S folds
the
bands with
of the schists
direction.
Here
area.
particular banding
outcrops
indicating
they
border of the Bosost
with N-S
and
visible,
(fig. 3).
minute folds
open.
a
The intersection of these
mica flakes
dome the ESE lineations
similar lineations with
northern half of this
Connected with these lineations is
on
Second phase
In
the
are not
found,
near
some
rather
Sierra de
Devonian limestones
uncommon
connected with
this
phase
others
more
cleavage
folds
tight,
Guarbes
near
the
southern
either. Boudins of pegmatites
of
folding.
332
H.
In
has
7
fig.
been
J.
Zwart:
number of
a
assembled.
variation in
certained
are
the
Although
in
is
phase
of the
In
first
the
chapter
on
ESE
present
second
microstructures
tosity
preserved
was
of the
either
phase
as
a
a
new
planar
it
planar
will be
shown
A
third
1959, Zwart,
Third
deformation is
where
1960)
the first
in the Bosost
dome;
that both NW and NE
directions
obvious
also
that
was
considered
are
the
directions
main
as
deformation,
schis-
the scale
on
as
a
flatlying
can
this
during
On
sheet and
hundred
with
ceptional
in
the
Bosost
between the Sierra
rather
cleavage
gentle
rarely
often present.
together
related
this
be
no
de
and
of
period
on
top
a
occurs
in
less
these
ones
enclosing
A fourth
on
fig.
NW-SE
the
but in slates
and
folding,
stereo-
and
exactly
separated
by
a
related. The folds
not
and
tight
very
Guarbes,
Ordovician limestone
Locally
of
size
a
the slates and
of
many
for
places,
schists
flatlying
a new
phyllites
such
to
two
are
ex-
one
limb. Folds of this size
at
to
8 it is
have been
the Sierra de
In mica-schists
are
objections
6 and
are
usually
Monteludo. In
sills in the mica-schists
no
From the
not
are
in folds
occur
symmetrical.
folds,
are
NE
gentle
It is obvious
coincide
phases
de Guarbes
axes
the
1958).
not
for instance
left its
only weakly developed.
of mica-schists.
about NW-SE
SW and
or
folding
as
the Sierra
Guarbes and the
more
A number
8.
fig.
investigation they
they
in
predominant.
(Zwart
doubt that
example
most
folds
crenulation
cleavage
is
often folded in the NW direction
mica-schists and boudins with NW-SE
axes
are
probably
phase.
3.24 Fourth
later than the
of
that
one
has
Comparing fig.
early stages
dome but smaller
Pegmatite
with the
to
steep
a
in NW and
one
and is shown in
dome.
massif
In
folding phase
direction is
folding phase
occurs
been refolded
meters
same
schistosity
crossfolding.
as
and that the latter is
occur
of the
being pene-contemporaneous and
same
there
limestones have
occurs
folded
on.
was
during
old
Aston-Hospitalet
to
difference in direction. Since both
produced
were
the
to
folds visible in thin section.
are
the
or
folding
it becomes evident that both maxima do
slight
a
of N-S
occurs
the
lineations almost coincide with
folding
due
The
in schists
mainly
in size from several hundreds of meters,
vary
to
for
been referred
here also the the NW
regarded
being
as
there is
which
it has
observed in the field. In the
however,
grams,
phase
only gently
or
responsible
have been found in the Bosost
hypothesis
that
phase
phase
being predominant.
one
of foldaxes has been measured
as
further
second
produced,
pene-contemporaneous directions have been found,
two
traces
of
period
direction,
this
not
E-W lineation
explained
the
as-
lineations
It should be noted that
was
A similar deformation has been described from the
(Lapré,
Both
and
structure
N-S
of deformation.
phase
that
be
not
outcrop.
planes.
NE
axis.
the
original
will be
as
schistosity
3.23
area
to
linea-
folding
could
folding
another
to
direction
connected with internal rotation about the N-S
this
due
lineations,
doubt that
no
due
are
of
phases
for the deviation of the
responsible
their
to
the
the ESE maximum of the first
to
lineations and
also
probably
of
spreading
some
evidence left
field, microscopic
phase
is
time relations between both
than the E-W
younger
This
the
right angles
at
Pyrenees
it is obvious that the maximum lies about 15—25°
schistosity,
E of north and almost
tion.
there
Central
of lineations and foldaxes in this direction
measurements
Although
of the
dip
Metamorphic history of the
phase
phase
of deformation with folds in E-W direction is
NW-phase.
As
in E-W direction. Folds
shown in the stereogram of
belonging
to
this
phase
vary
fig.
in
9
size,
a
considered
sharp
to
be
maximum
like the NW
phase,
Structural
from
microscopic
occur
at
folds is
usually
(fig.
by
more
are
often
this
phase.
shows
was
which
An
The
In
As
both
a
directions.
refolded
axis
and
making
E-W
E-W
10.
Folded
pegmatite
E-W
a
folding
is the
younger
in
of the
younger age of the E-W
to more
southerly
the direction of this
phases
not
In the
does
one
St.
The N-S
Barthélémy
been
can
and
western
part
emplacement
this
least
at
vertical
one
steep
plunges.
The
could
not
be
established
in
only rarely
occur
pegmatite
also
are
one
too
outcrop.
in favour of a
indicative for
are
a
valley.
the
Aston-Hospitalet massif,
outcrop, it has been demonstrated
Also Boschma
in the
phyllites
original
departure
recognized
probably
the
in mica-schists but in
occur
and
(1963)
has
supporting
north of the Bosost
area.
E-W lineations of the main
be older than the NW-SE
show any
phase
its
the
by
peculiar shape
made
folds with
in Barrados
two.
phase
must
not
of deformation have
lineations in the
do
directions
phase
succession.
after
be
may
pegmatite
axes.
Pyrenees especially
frequently
rather
are
north of this
has been folded both
NW axis
folding
It should be noted that the deviation of the
they
a
of the
plane
Barrados
a
They
more.
mica-schists
acquired
shortly
about
phyllites
in
folding. Microscopic relationships
deformations occur
evidence for
same
has
the fact that both
to
sills
pegmatite
pegmatite
gently plunging
From other
of the
parts
younger age.
All
even
minor folds
so-called
the relations between the folds of the Barrados
where both
the
is the
Originally,
about E-W
Fig.
the
This
the
slates and
Pegmatite
probably flatlying. Folding
younger age for the E-W
phase
probably
schists
flatlying
valley.
result this
relations between NW
age
the
asymmetric.
in the Bosost dome due
However,
that
and
meters
outstanding example
flank is refolded with
gentle
easily
is
strongly
phase.
in
foldaxes
pegmatite
flank
of
less open, but in the steep
or
in the Barrados
10) occurring
NW and the E-W
vertical.
to
steep
and
they
folded
hundreds
various localities in the Bosost dome as well north of it. The axial
symmetric
area
several
to
333
geology
since
crossfolding
from its usual direction.
elsewhere in the
Pyrenees
with
be correlated with N-S folds and
Castillon
massifs, although
in these
areas
high grade gneisses.
of the Aston massif N-S folds in mica-schists
occur
at
several
places.
From
the
study
morphism
started
phase
came
and
to
of
an
large
a
during
number of thin sections
the first
end
shortly
phase,
it became
continued throughout
after the E-W
folding.
clear that
meta-
the second and third
334
H.
In the
phase
the
late
E-W
(syn)
showed
N-S
between
which
during
between the four
III.
first
two
folding
and
Evidence based
the fourth
either
and
phases early,
the last
continued.
Metamorphism
they
phase
of the rocks
quiescence
first
such
during
episodes
numbered
are
is
four
postkinematic
could
phase
be
not
MICROSTRUCTURES
of the
description
deal with the
to
distinguished;
phase
dome.
3.31
Before the
be
earlier than the
metamorphism,
Bosost
3.3
it is necessary
to
are
later than deformation of the fourth
as
phases
two
of tectonic
episodes
to
of the
microscopic study
on
of deformation
phases
metamorphism
Prekinematic
(or static).
Method
of investigation
of the rocks
structures
under the
as seen
microscope,
involved in the determinationof the
principles
sequence
events.
The
mutual
minerals in
This
holds
are
profound
specimen
rather
with
well
as
other
to
the
areas
the
deciphering
of
been
of the
show
The
existing schistosity.
show all
kinds
relations
the
minerals is of
been
discuss
in
Ramberg (1952)
is made
or
to
of this
where these
area
asks for
a
thin
sections of this
specimens,
and
together
of the
fairly complete picture
on
its
turn
related
to
that of
an
internal
can
one
the
be
in many schists.
principles
with the external
checked
1958,
the
to
have made
are
1960,
and
se
pre-
room
the
Most of these
inherited from
schistosity (se).
field data.
or
the
Besides
an
They
these
replacement
of
Part of these criteria have
1961).
it is
involved, (1)
replacement
superfluous
(si)
schistosity
metamorphic history.
crystals
been made of the
mineral around another
(Zwart,
papers
has
use
of
primary importance
while
growing.
chemical
According
replacement
necessary space
and
to
to
(2)
for the mineral
elements from the future site of the
and
crystal
necessary elements.
room
cretionary growth
to
consideration.
Aran,
andalusite, staurolite, cordierite,
large quantities
is
simply
made
by
chemical
transport
very little mechanical disturbance of the
transported
a
much
of biotite,
compared
In chemical
the
under-
the scale of the outcrop the hand-
sequence is
relations between si
main
two
in
of
which
in which
growth.
the
Thus the
no
the
by removing
introducing
be
unraveling
previous
process
concretionary
can
in
Pyrenees.
occur
of rims of
in
use
considering
the
si
under
In total about 600
have lead
dome. This
presence
of relations
growth
published
In
the
on
history
of
crystallization
importance
area
from oriented
many
poikiloblasts
garnet and sillimanite which
porphyroblasts
investigation
they
the
unraveling
metamorphic history
and
porphyroblasts
and
rocks
primary
of the
history
thin section.
area
of
are
for the schists of the Valle de
made,
of events in the Bosost
metamorphic
In
sence
have
visists
repeated
area
interwoven that
that of the
as
area
deformation of
structural
true
and detailed structural
small
sequence
and
especially
strongly
so
between
metamorphic
metamorphic
statement
relations
relations
regional
any
the
standing
is
NW-SE
referred
in E-W direction;
folding
contemporaneous with
of deformation
phases
Metamorphism
demonstrated in the
of
three the
for the
Pyrenees
is called interkinematic and is of a static kind. Three interkinematic
episodes
to
the
is the main
phase
Metamorphism
synkinematic;
the Central
of deformation will be
phases
the first
or
kinematic has been used.
that
occurred
I
one
folding, phase
folding.
is called
phases
late
four; phase
is the
two
phase
Metamorphic history of
pages these four
following
to
one
Zwart:
J.
a
crystal
this site and
starts to
space
grow
at
is made
a
rock
on a
small scale and there
outside
the
crystal.
In
con-
certain spot, all necessary elements
by bodily pushing
aside the
are
surrounding
Structural
rock
that
so
bedding
to
According
or
combinationof both
existing
an
around
curve
rocks
metamorphic
the
probably
crystal.
by
grow
a
and that of concretiona-
replacement
growth.
ry
Careful
of the
study
fabric of
only,
at
without
least
the
disturbing
minor feature
a
does
As has been remarked many
ting
internal
an
and is
continuous into
but the
of
pattern
ment, and
the
absence
schist and
nection with
from other
in
two
the
in
depicted
cases a
the
fig.
could be
and
that
pattern
older than the
of
when the
only
has
chemical
the
has
occurred
to
the
both
the
principles
borders
of the
and
show
the
same
after
the
folded
curving
case
of
where it
no
contains microfolds.
since
crystals
around
completely
flow of the schist around the
plastic
C that
replace-
produced,
was
concretionary growth,
se
11
as
most
has grown
crystal
or
internal
flattening
as
any
porphyroblast
not
fig.
be
inter-
crystal
chemical
time
can
an
and in
rarely
very
con-
interpreted
growth
In
conclusive. In
the
by
planar
at
of
rocks
some
be
can
combined with
not
case
without any
crystal
established fact.
the
si,
no
replace-
extreme
been found in
observed
grows
matrix
was
to
crystal
is inherited from the
Moreover the pattern t>f
growth
crystal
an
in
been
pattern is
schistosity
a
is
curved
conclusive for
not
connection due
any
a
schist
matrix
formation of
without
such
1 IB is
fig.
have
movement
no
In
schistosity
around the
pattern
according
be
is present.
se
surrounding
a
a
the
contain
porphyroblasts
concern.
since
replacement
concretionary
produced
no
the contrary,
to
rocks.
for the existence of concretionary
must
crystals
curved
a
whether the
independent
Such
grows
but
consequently
proved
deformation of
crystal
crystal
C. Such
11
also be
can
proof
planar,
characteristic of
matrix,
Also the
the
be
si with
planar
should be
ment,
where
of
produced,
not
of inclusions constitu-
rows
indicative of pure
are
is
cases
does
replacement
straight through
runs
but it should be mentioned that it
Pyrenees
whereas chemical
cannot
cases
completely
curve
Therefore little
case,
schistosity
be
cannot
should
se
contain
other
of si
presence
si
in
A);
crystal (fig. IIB).
brought forward,
mediate
or
an
of the
parts
ways.
11
however,
chemical
by
metamorphic
all in
this si
cases
rocks,
grow
Concretionary growth,
at
porphyroblasts
many
(fig.
se
rock.
not occur
is similar. Both
se
concretionary growth
original
In
schistosity.
all, crystals
not
surrounding
or
metamorphic
many
support this conclusion and most, if
is
in
that of chemical
principles,
should
schistosity
minerals
most
Ramberg
335
geology
the
existing
crystal.
the evidence it
Summarizing
process
in which
disturb the
rock
is
can
be stated that chemical
metamorphic
rock
surrounding
surrounding
in
crystals
by
a
it
deformed,
rocks
grow;
so-called force of
be
must
the
that
minerals do
and
crystallization,
result of
is the main
replacement
growing
not
that if the
deformation
subsequent
by
tectonic action.
Deformation of rocks
(1)
the
s-plane
is
a
plane
thrown in microfolds.
for the
responsible
is
produced.
of si and
fig.
se
11 C is
of the
shown in
example
crystal.
The
occurs
as
(2)
development
exists.
fig.
movement
and
If
schistosity
a
it is
occur
may
of
mineral
a
produced, showing
slip
a
flattening, (2)
a
may be
plane
of three
of slip
simultaneous and
takes
schistosity itself, (3)
11
se
is
E;
continuous in
the
usually
si
is
garnets
during flattening
grows
planar
along s-planes
snowball
is
a
the
si,
but also
results
s-shaped.
This
described
accompanied
of
si in the center, and
by
of
a
a
is
from several
flattening,
well
a
schistosity
different pattern
the
pattern
around the
of
also
crystal.
crystallization
known
regions.
se
after
schist,
contemporaneous
pattern
may be
may in part be
curved si in the borders
partially
curves
s-planes
they
place
a
different kinds:
the
(3)
For any of these three different kinds of deformation
crystal.
When
(1)
displaying
of
in
Since
curves
is
garnets, for
this
kind
around
of
the
336
H.
Fig.
J.
11.
Zwart:
Metamorphic history of
Relations
between
the Central
porphyroblasts
and
Pyrenees
schistmatrix.
Structural
When the
11
(fig.
the
F)
inclusions in
inclusions
have
plane
in
the
as
result
a
the rim.
total
rotation is
folding
but since the
in
porphyroblasts.
the
causes
of
amount
does
usually
The four described patterns
Ramberg's
and
with
Another
folded
concentric
the
folds
schistosity
resulting again
rotate
in such folds is
relatively
of
sense
have been found in
cases
the
and
In this
produced.
11
H).
by
around
and
an
Also transitional stages in
11
si, but
of the rocks.
history
B which look similar
first
a
completely
a
which is
an se
which the second
special
also
case
connected with
not
also may
crystals
without
porphyroblast
a
formed after
deformation
shows
crystal
it
have
crystals
subsequent
the
case
It shows
growth.
the
to
show the pattern of fig.
curving
when
develops
when
may
contemporaneous
this
after. In
or
definite clues
give
concretionary
completely
se
which
crystallization
understandable that
that is before
schistosity
of
principle
pattern
produced
(fig.
develop,
se
for
diagnostic
are
deformation,
older than any
Crystals
it
of
independently
patterns ofsi and
si,
and stronger
when
to
case
folded
exceed 45°. Moreover the
not
with the described kinds of deformation. It is
to
crystals
one
weakly
Slip along
movement
limbs of the folds. Both
opposite
of
presence
the
crystal,
part of
develop
In
develop.
may
the
by
mica-schists.
Pyrenean
grow
patterns
pattern may
than the
of rotation
angle
the oldest
size
of concentric
opposite
different
two
A second
larger
s-shaped inclusions,
small the
which is
centre
towards
folded
shows the evolution of folding
crystal
considerably
a
is
schistosity
337
geology
the
crystal.
schistosity
was
is
schistosity
new
connected with
not
is
schistosity
not
fully
yet
have been found.
developed
Crystals
later than
a
and after
schistosity
had
movement
show the
ceased,
pattern
of fig. 11 A which is indicative ofpure chemical replacement and static metamorphism.
Se
is
the
s-plane
continuous
is
flattened
may be
si in the
with
crumpled
or
porphyroblast.
these folds
by
the
of this
usually
is
study
Besides the described
help
mineral
Bosost
other,
The
features
Also
interfere,
to
the
a
various
time
the rim
case
between
schistosity
are
in
one
and
is
and
biotite-schists and
a
are
shown: the
added,
a
staurolite
any
or
se
or
there
the
different rock
On
pegmatites
andalusite
these
types
interfering
fact
space.
fronts
with
granites
more
which
or
less
are
so
descended
not
parallel
different mineral
between
occur.
lies
on.
two
other. The
or
are
that
Both
from the
the coloured map
isograd,
are
in
boundary
and
one
replacement
of
fronts ascended
moreover
produced.
other features
of rims of
the
the
by
separately
metamorphic
aforementioned boundaries. These three lines
or
growth
folding.
will be described later
succession
treated
of de-
in the aluminium-silicates of
rendered difficult
be
are
growth
younger,
active
renewed
internal schistosities
epi-mesozonal
line within which
be
helpful. They
since
are
are
frequently
time and the
cannot
different histories
must
the
very
boundaries several
boundaries
could be
phases
These
dome. One
kind
straight extinction, although
by continuing
sequence.
cases occur
relations
folding
show
planar
a
schistosity
11 K.
folds, fig.
growing during
crystals
the matrix
of the
folding
shown in the inclusions. After the
in which
that the
stratigraphie
assemblages
dary
porphyroblasts
arises from the fact that certain
the
morphic
or
I. The main feature is
relations between si and
possible
the succession
strongly interwoven,
during
be rotated
later then
when
However,
schistosity.
may
so-called helicitic
as
of microstructures
description
difficulty
that
another. Both
by
dome.
and the external
crystals
D,
are
may be deformed
determine
to
mineral around the
one
crystal
11
fig.
crystals
crystal
clearly
crystal, however, they
which may
the
when
deformedand the
are not
the record of deformation is
of
the
of these patterns have been observed in schists of the Bosost
further result
of the
shown in
as
the
out
bowing
movements
Finally
inherited
are
Many
formation
without
si,
used for renewed
two
meta-
phyllites
between the
parallel
and
A third bountwo
and suggest
a
338
H.
rather
and
a
belonging
third
After
a
be
biotite
there
done,
for
isograd
would
second
a
phase
would
front.
Similarly
the
unraveling
is
however,
of the
periods
biotite
the first biotite
not
com-
metamorphic
for
isograd
whereas the
second andalusite
a
of the whole
history
certain group of minerals
could take
stable
was
the
andalusite
first
isograd
due
isograd,
isograd
the
to
from
dating
zones
or
facies
a
by
certain
a
for the rock
not
In other words all
present.
be
as
given
any
be
may
only
can
at
but that
time,
third and
a
mineral facies
or
of the rock and
are
it became clear that
area
during
followed
eventually
over,
history
of the
portion
succeeding
picture,
one
phase,
cut across
Consequently metamorphic zoning
certain
be
Pyrenees
could be constructed.
assemblage
one.
This
zoning.
drawn for different
this second
phase
place
metamorphic
metamorphic
to
rise of the
should
new
the Central
Metamorphic history of
could be
isograds
If this
history.
phase
Zwart:
simple progressive
since such
plete
J.
second
a
fourth
a
applied
for
a
whole since several
a
these rocks
are
polymeta-
morphic.
it
Although
sequence,
this
description
preferable
to
with the
so
start
gradually proceed
be treated in
a
be
might
dealing
logical
strongly
Four
with the
2)
more
but in
be
and
schists,
in
the
Devonian, 3)
The
comprising
forming
The
a core
same
zone
fourth
belong partly
It should be
described
for
one
phic
and
by
zone
zones
one
zone
to
fall in
the
added
the
that
the
and the rocks
are
mineral
compares
as
zones
considered
zones
at
have gone
to
one
be
4)
a
andalusite-cordierite-zone and
chapter
a
on
The
zone.
zone
lower part of the
zone
stratigraphy;
banded
three
the
whereas the
schists
near
(See fig. 1).
here
shows
zone
are
defined
not
one
phase
zones
contains
as
those
is characteristic
assemblage
In the
of
metamor-
metamorphism
show several successive
at
assemblages.
biotite-,
has
the
monometamorphic.
remaining
the
dome,
cordierite-sillimanitezone
the lowered numbered
through
biotite-
shell below the second
a
as
mineral
zone
least four different
passed through
with the
half of the
with the andalusite-zone,
proposed
the second
example
to
not
1).
the third
to
zones
but the
assemblage,
least two, the third
In
ones.
principle
the
at
higher
Thus the cordierite-
the staurolite-andalusite-cordierite-
complex
and
longlasting
history (see
fig. 22).
3.321
Biotite-zone.
Schists
the northern halfof the Bosost
of this
area
is quartz, muscovite and biotite
clase
(fig.
of the Bosost dome only the biotite
sillimanite zone has
table
Silurian and
occurring
granite-bearing
Barrow. In the Barrovian
least three and the fourth
and
the
second, partly
mineral associations. For
numbered
the northern
described in the
as
and then
the schists will
coinciding
zone,
in
the Silurian and Devonian rocks and
staurolite-andalusite-cordierite-zone
Lés
and
also the
comprising
is the
history
reason
disrupt
it seemed
in the northern half underlying the biotite-
zone,
underneath the third
reason
zones
biotite
a
andalusite-cordieritezone,
bioti te-zone
third and
1)
Bosost
near
chronological
zonal order.
metamorphic
distinguished:
occurring
southern half
an
a
this
complex
a
this would
order,
For
unintelligible.
intricate fabrics. For this
staurolite-andalusite-cordierite
a
not
can
zones
it
with those rocks which have the least
stratigraphical
(p. 325)
ifthe minerals in such
make
to
as
3.32
schists
describe the microstructures in
to
properties
(sodic oligoclase)
amounts
of
as
are
near
occur
as
already
Bosost. Their
main constituents with
and accessory
quartz and micas
zone,
and
apatite, zircon,
mentioned,
mainly
in
mineralogical composition
occasionally
tourmaline and
quite variable, depending mainly
ore.
on
some
plagio-
The relative
the chemical
Structural
of the schists.
composition
cm
thickness
and
aligned
the
to
quartz
little
they
crystals
occurs
the
to
present
the
fig.
folded
are
by
that
entirely postcrystalline, indicating
mm
to
amounts
perpendicular
2
to
3.
or
The
in the direction of the lineation. When
12
two
linear mica-schist
a
and
parallel
width
to
few
a
perfectly parallel
are
embedded between the
are
of mosaic. In
lineation of such
length
elongated
crystals
Where biotite-schists
is
of
of
quartz-rich layers
different in size in sections
the relation
a sort
banded,
micaceous bands. The micas
small and often
it forms
often
are
more
markedly
Usually
are
is
quartz
quartz
cular
are
lineation.
They
with
alternating
339
geology
are
the third
or
when much
micas;
sections, parallel
and
perpendi-
shown.
fourth
metamorphism
this deformation
phase,
had ceased before the third
phase.
3.322
in
the
of the
upper part
Fig.
schists
are
located
near
Cambro-Ordovician
12.
Two
part
is
belonging
and above
pegmatite bearing-zone
of Cambro-Ordovician age,
are
Schists
Slaurolite-andalusite-cordierite-zone.
of Silurian and
sections
through
linear
it.
a
narrow
band of
this
zone
Devonian age.
occur
The
latter
mica-schist.
the south side of the Bosost dome and
by
to
Part of these schists
andalusite-bearing
are
from the
separated
black Silurian schists.
The Devonian and Silurian schists will be treated later and first the Cambro-Ordovician
will be
described. The
muscovite-schists
lineation and
set
of
garnet. Andalusite and
plane
as
of
short
\—l
schistosity,
cordierite
they
1
produced
twins. The
mm
by
in
the
are
of
at
a
biotite
length.
They
elongated
the
a
occur
as
length
same
cm.
grain
\
cm,
always
porphyroblasts
show
small
a
are
crystals.
similar
size. In this matrix
biotite and
with
this
a
rounded
parallel
cleavages,
cross
in the
occurs
generally showing
much smaller and
Their
are
occasionally
Staurolite
plane.
idioblastic and
linear arrangement
mica
biotite-
a
Although usually lying
random distributed in
size of
minerals with
elongated crystals
of I—4
with the
comparable
same
staurolite, andalusite, cordierite,
diameter and
prismatic crystals
penetration
exceed
cm
is
contain the
They
and ofapproximately
schistosity
large porphyroblasts
section of
matrix of these schists
described above.
usually
to
the
do
not
lineation
however,
are
not
340
H.
Fig.
13.
J.
Zwart:
Biotite
Fig.
14.
Metamorphic history of the
porphyroblasts rotated
Biotite
porphyroblast
in
Central
Pyrenees
si
oblique
schistosity;
with
si
oblique
to
se.
to
se.
Structural
parallel
the
to
13,
(fig.
schistosity
Garnet
14).
Almost all
in
this
clusions
of
usually
runs
straight
The
visible
regard
si is
to
all
to
crystals
the
explained
in
an
15.
curved;
not
very
all
rotation, and
cular
to
to
the
the lineation
schistosity.
Since
crystals
schistosity
a
to
remains
se
may
16.
crystals. Long
show
of
crystal
contain
itself which
an
at
rotation
certain
a
across
are
to
a
with
itself existed
included
its
turn
must
all but
to
can
be
15 but
exception,
in
participated
to
crystals
(fig.
17).
the
plane
of
but
the
plane
of
in
they invariably
schistosity.
Since
the si is
before it started
attributed
the
of rotation is
rotated in
above,
must
cut
rotated.
crystals lying perpendi-
crystals
the
the
long
a
fig.
as
angle
16)
can
of rotation is
staurolite
have been the result
schistosity, they
slip
without any
of rotation
are
nearly
(fig.
andalusite and cordierite
at
As described
already
In sections
relationships
specimen
lineation;
prismatic crystals
of rotation, it
flattening only.
porphyroblast
amount
biotite
schistosity
regard
the
present.
result of
The
Hardly
and
amount
the
short
position
same sense
not
no
ESE lineation
These
Same
parallel
garnet
as
occur.
exceed 90—100".
of the
of the
position
the
be followed into si
can
the si
trend.
different inasmuch the si of
random orientation of these
of their
and
that the
porphyroblasts
shape
the
on
cases
curved
a
of in-
rows
most
si has
strongly
always
Fig.
staurolite,
the
have rotated
rotation
In
graphite.
porphyroblasts.
se
not
of
the staurolites
have the
schistosity plane
indicating
does
always
in
irrespective
the
lineation.
originally lying
resulting
se
orientation
smaller.
or
biotite and garnet
curved around
strongly
crystals
flattening
size
number of andalusites and cordierites. The
on
schistosity,
all
around
lattice
a
mm
perpendicular
but nevertheless
the lineation may show
Long crystals
rotation
se,
planar si;
usually
large
largely dependent
lying parallel
to
porphyroblasts
a
depends
se
the situation is
ways, either the
with
and
and
or
examples
some
matrix is
curves
perpendicular to
large
however,
with
angle
due
or
Staurolite
section
si
however,
always
two
schistosity plane
Fig.
between
in
not
1
determined by
schistosity
the lineation. In sections
lineation,
makes
but
but
of appr.
of micas
occasionally
crystal
form
andalusite, cordierite,
internal
connection between si and
a
The schist matrix
be
to
an
a
crystals
of staurolite,
but the schist
se
15) although
parallel
the
through
relationship
parallel
and
have
they
idioblastic
presence of
quartz
section with
(fig.
as
porphyroblasts
show the
zone
that
so
occurs
341
geology
to
of
show
a
moreover
slip
on
the
usually planar
rotate.
Since
all
have formed later than the
the
first
phase
of
folding.
H.
342
Moreover
J.
Zwart:
crystals
no
are
Metamorphic history of the
influenced
rotation about E-W
axes.
in the
hence the
and
s-plane,
schists also shows their
it
safe
seems
to
deformation
In several
the
si
is
crystals
17.
of staurolite,
17),
I
In
the
with
of
(fig.
in
inclusions
Summarizing
tectonic
the
characterized
first
fig.
18).
of any
porphyroblasts
lineation of the
the
first
were
main
or
that
its
outlasted
mica-
phase
of
cordierite,
parallel
it
can
be
After
the
s-shaped
over
inclusions
formation had
lies
crystal
took
and
on
new
that
second
crystals
had
place resulting
porphyroblasts
growth.
crystallization
of staurolite,
during
deformation
a
phase,
period
which
of
is
preexisting s-planes.
always
ceased
From the abundant presence of
growth
the
interkinematic
of the
many
schistosity
went
stated
the
porphyroblastic
Round
garnet started after the main phase
during
and
not.
occurred.
on
crystal
be concluded
during
E-W lineation.
to
of the
can
garnet and
and continued
long crystal
biotite, however,
crystallization
this evidence it
Crystallization
movements
that the culmination of its
has
and
growth
produced indicating synkinematic
evidence
by gliding
and
movements
phase
growth
and continued
Staurolite with
indicating
absence
and ESE lineations. Therefore
postdates
From
movements
crystals.
cordierite and
quiescence
18).
section
static, unoriented,
rotation of these
s-shaped
that
staurolite, andalusite,
sometime after the
Cordierite crystals
when
andalusite,
the
to
schistosity
movement
cases
many
completed crystallization gliding
in
the
by
cordierite, andalusite, garnet
indicating
rotated;
period
shown
as
parallelism
porphyroblastesis
rotation occurred
started
Fig.
absence of
later than the
origin
(fig.
crystallization
biotite,
phase
Furthermore the random orientation of the
conclude that
s-shaped
postcrystalline
that
this
Pyrenees
(fig. 22).
simultaneous.
were
by
Central
shows
before
crystals
the
with
some
end
planar
before the second
Postkinematic rotation of andalusite often does
post-crystalline rotation,
of the
second
si it
can
phase
(see
be concluded
phase.
not occur
and
consequently
this
Structural
mineral will
in
growing
The
have formed
the
schists
holds
same
up
the end of the second
to
indicate its
for
true
343
geology
continued
phase.
crystallization
for
cordierite, especially
A few
crystals quietly
after the
second
phase.
later than the second
crystals
phase.
The
biotite
crystals
elongate
form but
with
of
a
their
(fig.
13)
so
orientation,
axis
longest
si which
the relative
in
lattice
no
in
of si with
position
that
the
their
now
the direction of the
often
regard
longest
lineation
18.
Fig.
these
crystals
to
crystals
biotite
their
makes
crystals
an
the
have
the
This
cross
a
across
schistosity
and hence its
not
must
been
origin
curves
(fig.
around
andalusite and
pushing
aside
similar biotite
It
is
be
to
(fig.
angle
and also
crystals. Restoring
continued
remarked that
60°
with the
14).
Originally
si in
the
many
present schistosity,
these
they possessed
of i
a
60° with the
correlate this feature with
these
force
with
planar si, crystals
date from the second
porphyroblasts
cordierite. This is
by
have rotated
crystals
schistosity plane
crystals
any
as
must
form orientation
present schistosity.
phase
of
kind of deformation
remains obscure.
19); they
all
presence
the lineation
to
have formed after the first but before the second
to
a
lying
backward rotation shows that almost all of
apparently
an
the
showing
parallel
smaller mica
s-shaped si;
sections
but
showing
eye-shaped,
crystallization.
approximately
making
possible
Besides biotites with
observed
with
after
by
in the
strongly
lattice and form
perfect
shows that the
again
the
thin
schistosity
cross-schistosity
It has
folding.
of
In sections
defined
as
schistosity.
angle
in several
grown
se
are
types of biotite
larger crystals
lineation and
se.
they
two
deformed and
lying
Staurolite
has been observed
indicating
to
with
original position by
across
grew
less
or
dimension is
rotation
these
more
angle
an
a
another group of
direction of the
makes
frequently
2)
since
has been described
without si with
crystals
orientation and linear arrangement
mention
special
biotites. As
generation
small
1)
occur:
deserve
porphyroblasts
different from the first
of
again
in
due
crystallization.
porphyroblasts occurring
in
a
a
curved
phase
similar
to
manner
flattening
This
large
is
s-shaped
si have also been
of deformation. The
as
of the
corroborated
cordierite
around
matrix,
by
crystals.
the
schistosity
staurolite,
rather than
presence
of
Here the biotites
344
H.
J.
Fig.
Fig.
20.
Biotite
Zwart:
19.
Melamorphic history of
Biotite with
porphyroblasts
in
the Central
s-shaped si, dating from
large
cordierite
Pyrenees
second
crystal; si
phase.
in cordierite not
curved.
Structural
have been
and
position
s
t
shielded
matrix
of the
relation
-planes apparently
biotite
micas and
different
and
field
in
main
of
in
Since
20).
direction and
the
by
the
the
Both
phase.
crosscutting
biotite
Iineations
In
to
order
crystals,
a
evaluate
sections have been
than 300 rotated
sense
cates
ments
and
crystals
from
movement
sections
some
occurring
this
of
amount
of rotation
together containing
cases
A rotation of
d
ness
of
a
where
d
but
and it
sequence,
attached
is
walls,
and the
of the
crystal.
they
here
concerns
d.
X
relative
of
not
seem
distributed
of about 600
m
The direction of
and
folds
will
with
compared
to
the
direction of
second
be estimated
a
ball
as
a
1.6
to
to
has been present
stress
during
As
of the
first,
during
be
no
that
but
it is
and
it
with E-W
is
to
are
two
the diameter
slip
has
account.
in
total
a
is, however,
not
ESE lineations
that
probable
are
despite
this
phase
kind of
an
hence it contrasted
stress
to
to
prove
prove
definitely
are
field
during
E-W directed main
strongly
the
approximately
relationship they
determine the
differential
possible
the second
some
between
resulting
during
to
whole
crystals
be taken into
possible
difficult
without
the
that the
neither has it been
doubt that
time,
It
phase.
crystals;
movements
Although
can
the first
to
this
stress
the N-S main
phase.
staurolite, andalusite, cordierite, garnet
similar evidence of
phase
The
those
there
this
preferential
schist.
m
phase
direction and
X
so
in all
As
zones
moving
factor 2,
of the matrix has
the first
during
N-S
absence of rotated
independent.
phase,
in
place during
movement.
perpendicular
later and
movement
be
to
degree
crystal.
of thick-
layer
throughout
has exceeded
present thickness of 100
been
have taken
movements
this due
have
a
a
crystal.
affine deformation. Since the
Further, flattening
over
of the
with
place alternating
deduced from the si-se relations this adds another factor of 2,
slip
where the
in
movement
there do
slip certainly
can
the
diameter of the
X
equally
be
cannot
effect
braking
a
1.6
have taken
are
and
shape
rotation,
typical
a
amount
necessary
3.2
to
of
movements
apparently
This
90° indicates
to
degree
some
of the
the
to
approximately
the rock, rotation
to
amounted
crystal
which
show
most
movements,
As
round
7i
crystals
sections
zones
£
attributed
of
crystals
the whole series of schists, from the
position
be
of
move-
angle
90° and
near
of rotation is less
can
sense
The
distributed overthrust
Lower Devonian well into the Cambro-Ordovician. In many
it
amount
be calculated from the
this rotation is
cases
large
a
opposite
an
area,
and indi-
same
porphyroblasts.
amounts to a
can
throughout
occur
have
more
the entire
is the
sense
crystals
40 rotated
as
movement
In many
porphyroblasts.
amount
section
much
rotated
the
by
throughout
this
cases
the total thickness of schists
over
indicated
as
from localities
single
as
rotation of
produced by
Further it has been observed in
east.
no
containing
size. The
rotation of the
to
that in
a
has been collected from which oriented
specimens
originating
west
specimens
fairly large
showing
direction of
of rotation has been determined. In all
of unoriented
rotation,
the
a
in
growth
to
a-
elongated
direction.
In sections of 52 different samples
cut.
movement
a
in that
number of oriented
large
due
the
an
but have
subparallel,
are
by
is
biotites
fastest in the direction of least resistance —in this
grow
porphyroblasts
demonstrated
as
the
on
dimension of the
porphyroblastic
The B-lineation is
nature.
original
movements
largest
B-lineation as determined by the small
different
curving
nor
these biotites the
direction of movement,
existing
the micas
whereby
the
(fig.
seen
same
lineation caused
on an
are
the
and
the direction of the foldaxis—whereas the a-lineation is
case
of
lies
from the
dating
origin
in
occurred
has
be
can
se
the
rotation,
lineation, superposed
the
to
cordierite and neither rotation
surrounding
biotites
were
porphyroblasts
direction of
stress
the
by
around the
345
geology
growth during
of deformationand
during
and
the interkinematic
the second
phase,
biotite
phase
porphyroblasts
all show
between first and second
this mineral
assemblage
must
have
346
H.
formed
simultaneously
in
curs
Zwart:
J.
other
Hospitalet
and
is
metamorphic
essentially
stable
a
of the
areas
there also
massifs and
the Central
Metamorphic history of
evidence
good
The
one.
for
Pyrenees
for it
to
grow
first,
since it may be included in
relation does
The staurolite
ment
is involved
observed that
both
being
inclusions
and is
an
core
with
are
an
not
Idioblastic
overlap
cordierite with
staurolite
in
morphism
andalusite and
staurolite
zone,
zone,
cordierite
seems
to
be
similar relation exists
kyanite
temperature
in the biotite
a
lower
zone.
This
as
a
grade
both minerals
has
a
not
have
be included in
crystallize
oc-
and
assemblage
is
started
where
as
the
after the first
to
together
For these
of
rising
occur
been established,
means
that the
meta-
temperature. Hence
cordierite. A
zone
One
together.
envelop
it looks
and somewhat later
andalusite and
probably
cordierite,
reasons
synkinematic
where the staurolite
frequently
phase
Consequently
andalusite and
phase
result of further
zones,
and
s-shaped
of the second
crystallize
mineral than
which
rotated
replace-
it has been
(Devonian schist).
(fig. 22).
staurolite zone should
cordierite,
before the latter.
no
cases
inclusions.
staurolite-andalusite-cordieritezone overtook the staurolite
site may
Aston
which
cordierite,
movements
staurolite,
first staurolite started
probably
in view of these relations that
cordierite
rose
in the Barrovian
although
stable
a
mineral
idioblastic and
planar
andalusite
in time of the formation of
that when the
the
On the other hand staurolite with
but staurolite is the earliest mineral of the three
probable
are
andalusite rim
phase.
than andalusite and
21.
in
unstable. In several
have formed simultaneous with the
must
Fig.
ihere is
thus relations
(fig. 21)
antedate the second
younger
the
garnet or
in andalusite and cordierite
cores
association also
exist.
not
staurolite
a
obviously
andalusite,
same
example
present. Nevertheless there is evidence that staurolite is
reverse
Pyrenees
precedes
the
might expect,
the andalusite-staurolite
since
zone.
the
On its
higher
turn
grade
andalu-
former mineral started
to
Structural
Fig.
22.
Table
showing
relations
347
geology
between metamorphic
zones,
time
and
depth.
348
H.
In many
is
phase
thin
steep. Also
are
sections
characterized
scale. The
copic
Zwart:
J.
Metamorphic history of the
the
direction of
fourth
a
effect
by folding
the fold
to
As far
the
micas
NE and
or
is
folding
visible.
often
the axial
with E-W directed folds of s-planes
on
a
This
micros-
of the folds
planes
in this
occurs
is of course best visible in sections
phases
concerned all folds in the
are
bent in the fold
being
of aluminium-silicates in
NW-SE
or
blastesis
continued
E-W
this
with
blastesis took
place
the second
third
the
to
regard
been
area.
perpendicu-
phase.
third and
in the interkinematic
phase
of
nor
porphyroblasts
included helicitic folds in
other indications that
Therefore in
this
fourth
of
phase
porphyro-
crystallization
zone
and
folding,
between first and second
episode
but has ceased before the
deformation,
postcrystalline
are
for the
true
with
crystals
found,
directions
two
holds
same
Neither
zone.
the
during
The
hinges.
direction have
prekinematic
during
of
phase
axes.
the micas
as
third
Pyrenees
existing schistosity planes,
is NW
folding
phase
The effects of these deformation
lar
of the
of the
Central
is
porphyrophase
and
phase
had
third
started.
the
Summarizing
that
in
the first
during
the biotite
schists with
of this
then
the
the
Biotite
caused
these
porphyroblasts
orientation and
almost
second
andalusite,
NE
On
or
the
as
E-W
ced
similar
a
found
their
to
be
sericite
even
a
content.
large
is
due
of
graphite. Anyway
lying
rocks
The
have
matrix
of
quantity
No
J
metamorphic grade.
the
After this main
cm
grew
staurolite,
certainly
in
due
these
the
been noted in other
In several
rotated about
schists.
or
In
a
composition
metamorphic
axis
to
6
%
are
have
same
about
bounded
experien-
This has indeed
shows
in chemical
to
due
which
analysis
the
might
to
fine
besides
finegrained
be attributed
that the absence of biotite
effect
hampering
is
schistosity
of andalusite
some
of
postcrystalline.
appearance
schists
are
this
through
schistosity
zone are
different
Silurian
few sections
lattice
lineations
on
crystallization
different from the
is due
or
to
the
same
chiastolite up
crosscutting
under-
folding
to
biotite
a
size
occurs.
The absence of these minerals is
garnet has been found.
chemical
NNE
of the
No biotite similar
a
WNW
direction.
Crystallization
that these schists
Silurian schists
of
from
without
continued
has been found which
or
planar
NNE
described micaschists
possible, however,
development
areas
sections it is evident
a
up
opaque.
phase porphyroblasts
cordierite
to
the
of the
composition
matrix of the
although
in
a-lineation.
strongly
a
of
a
trends of inclusions with the
assume
graphite,
It is also
unsuitable chemical
mica-schists
phase.
of
to
to
the
s-planes
linear fabric
folding
and
porphyroblasts
lineations. Both
garnet
zone
mesozone),
showing
described Cambro-Ordovician schists.
the
biotite in the Cambro-Ordovician schists
lower
a
some
s-shaped
the
on
an
Subsequent
logical
the thinnest section almost
to
and
dome
Bosost
seems
the
as
although
carbon
high
grained
makes
history
true
show
of the
garnet, all
about small folds which in this
side of the
It
form
to
second
biotite
crystals.
the staurolite
to
rotation axis
a
earlier E-W
the
B,
a
They
earlier
brought
axes
the south
is
cordierite,
black Silurian schists.
by
first
of deformation.
phase
of rotation
NW,
the
with
as
so
the
on
minor
movements
rotate
rotated
were
superposed
but
parallel,
staurolite,
axis
are
to
first
(warmer portion
number of unoriented
shearing
minerals
stated
became biotite-muscovite-
and
slowly,
rose
large
a
be
can
metamorphosed
were
lineation in ESE direction. After the end
cordierite and
schistosity. Subsequent
ESE
to
of
andalusite,
the rocks
mesozone)
and
metamorphism
development
biotite, staurolite,
internal
of
of the
schistosity
staurolite-andalusite-cordierite zone
in
resulting
grade
Cambro-Ordovician schists it
Hercynian folding
portion
pronounced
the
phase
to
of the
(upper
zone
a
of' these
history
phase
like
in
that
the
of these schists
of the
the
and
the
same
feature has
Pyrenees.
andalusite
or
chiastolite
Cambro-Ordovician schists
crystals
and
also in
have
this
Structural
case
rotation does
exceed 90°. In
many
not
folded, mainly about NW
as
shown
the
by
it
schists
and structural
morphic
The
lowest
is
different from
dotted
Devonian
due
mainly
difference lies
schists
rocks.
were
fact that
epizonal
phyllites
these rocks
causes
section.
Lineations
Ordovician schists
which in this
tions
case
to
due
the
minute
indicating
that
locally metamorphism just
first
In
A
of small
amount
the
along
dust in
containing graphite
these
but also
eyelets
of the
sumably part
a
Devonian schists
is
content
of
phase
must
be
phase.
A
biotite
are,
eyelets
older than this
Similar
in
of
the
have
not
Bosost
cordierite
are
£
cm.
This
in
somewhat
not
larger,
porphyroblasts
is
mainly consisting
certain
with
to
this
of quartz
or
regard
to
Staurolite,
some
most
growth
be
deduced from the
due
|
to
by
graphite
of
chemical
during
the
from diffe-
show
large
a
less around
or
which
pre-
of three
analyses
since
dates
andalusite
is
the
from
sodium
the
main
corraborated
crystals
and
shortly
after
by
therefore
the
first
a
the
to
of
presence
the
size of
the
Mostly
mm;
planar
are
the rotation of
three
to
preventing
more
or
of these
schistosity,
are,
however,
schists,
mainly
be discussed.
aluminium-silicates shows
and second
si rotated
less
invariably
many
internal
There
schistosity.
at
andalusite and
and is almost
Cambro-Ordovician
(main)
outlook.
smaller and
graphite,
1
crystals
shape
again
and external
the
knotted
definitely
is
relations between the
the first
cordierite and also
particular
few times. Their orientation is
a
exceed
Devonian and
a
sec-
found
was
in the formation of
possibility,
structure
them
cm.
the
abundant of
presence
lineation
few thin
nearly always
more
staurolite, andalusite,
giving
usually
up
between
Cambro-
a
is unknown but
its formation
the aluminium silicates which need
the
a
They
resulting
developed,
the ESE lineation
visible
differences between the
evidence of either
as
parallel
clearly
In
mm,
curves
The
round except for staurolite which shows its idioblastic
twinned. In sections
the
show
orientation
structure
this
to
started
of
schists,
may
Staurolite does
in
do
dome.
random like in the Cambro-Ordovician schists but their size
crystallization.
and rather dark in
like
of 0,8 —0,15
in sodium
Further garnet and chloritoid have been observed
seldom exceeds
grained
present. The latter
been encountered in Cambro-Ordovician schists.
porphyroblasts
the Devonian
Besides fine
s-planes.
parallel
of these
most
Cambro-Ordovician
specimen
crystals
of the
of this
that
relicts
the
usually
is
schistosity
schistosity
as
the
red
a
appearance. The main
specimens
porphyroblasts.
probable
occur
the
size
a
contradictory
is
area
as
map with
in several Devonian schists
origin
mineral which
structures
number of
large
occur
It
which
folding during
these
oligoclase
Bosost
biotite is absent.
The
center.
however,
low.
of
meta-
history
reached mesozonal conditions
Devonian is rather rich
extremely
the fact that
the
of
of the
oligoclase
into it. The
runs
of small
amount
large
southern border
of sodic
eyelets
the hand
observed
was
the
on
recognizable.
folding
such
however,
like
graphite
biotite with
greenish
microstructure
peculiar
localities
rent
sections,
most
of
although
grained,
phase.
often
similar
a
of deformation
phase
length
fine
some
their
side of the
blackish
more
black in
unequal
to
shown
are
main
amount
be
south
biotite-schists
not
found
due
mainly
the
which show
matrix is still well
to
hardly
were
is
and
certain
a
Cambro-Ordovician,
at
They
size and
during
phyllitic
quartz and
some
constituent
thin
grain
in the
microfolded matrix.
a
mineralogical composition
look different from the Cambro-Ordovician
field the rocks
smaller
to
In thin section the
sericite,
Silurian schists.
In the
ornament.
schists,
entirely postcrystalline
in
is similar.
history
and
the
the
consists of staurolite-andalusite-cordieriteschists
Cambro-Ordovician
si
planar
a
is
folding
case
that, although
part of the
pelitic
the Silurian schists have been micro-
cases
in this
again
be stated
can
Silurian black
and
of andalusite with
occurrence
Summarizing
these
axes
349
geology
with
phase
regard
to
clear
of deformation
se,
or
during
the
350
H.
second
phase
Crystals
inclusions.
cian
and
a
shape
not
without
staurolite appears
this
case
as
rotation
be corroded and
to
that
staurolite
in the
or
both
zed
Rotated
and
the second
phase
first
cordierite
commonly
simultaneous
The main
during
a
core
of
with
of
be
to
planar
of the
crystalliztion
Devonian
or
an
however,
andalusite
formed.
together
In
re-
other
and hence
schist.
crystalli-
the last
ofthe interkinematic
part
staurolite formed
planar
a
with the second
si
and
took
a
simultaneously
si rotated with
at
phase.
place during
indicates
an
with
regard
s-shaped
is
si
are
slightly
rather
different from
the interkinematic
that the
somewhat later than that of the first
phase.
formation of the
one,
se,
but
although
its
(fig. 23). Crystals
the end of the interkinematic
This
to
s-shape clearly indicating
of deformation
phase
rim with
then falls
second
of staurolite in andalusite also
generally
presence
crystallization
the first part
whose main
during
it includes trends of inclusions with
development
phase
the
cases
stable and unstable
From the fact that staurolite also
phase,
rows
(fig. 22).
Andalusite also shows the
containing
phase.
in
cases,
cordierite
by
cases,
mineral
crystals
it is evident that
the first part of the second
andalusite and
more
andalusite
be older than the second
must
during
phase
23.
s-shaped
interkinematic
cordierite. In
many
partially replaced
the
crystals.
trends of
and the included staurolite has
the host mineral. In other
by
was
rim with
a
sections it is evident that host and included minerals have rotated
Fig.
the earlier
Like in the Cambro-Ordovi-
phase.
be unstable. Both
must
to
stage of growth
the second
corroded
being
parallel
si and
planar
first
a
show unstable relationships
the relations
indicate
lationships
with
core
interpreted
a
abundant than those with curved
staurolite is often included in andalusite
mutual relations do
and in
is
si with
more
continuing growth during
schists,
euhedral
show
crystals
which
much
are
the Central Pyrenees
Metamorphic history of
by s-shaped
si
planar
Other
of inclusions
phase
shown
as
with
Zwart:
J.
there
common.
phase
and
staurolite
The inclusion
latter mineral is
can
be
no
doubt
Structural
that simultaneous
of staurolite
ment
lasted
by
Cordierite shows
evidence
of
prolonged
more
indicate without any
phase.
second
phase.
Other
In
show
it
cases
of cordierite have rotated
an
In
one
si
growth
staurolite
a
vade the matrix of the schists
have
must
grown after
consequently
show
they
the
ce
tion in the
manner
The
a
similar age
Chloritoid
chloritoid is
definitely
Summarizing
metamorphosed
the first main
to
regard
it is older than the
as
one
a
the
second
lower
the
history
mainly
phase
andalusite
also
of the
of the
Thus
cordierite
shows
in the
cian
zone
in
one
other
grade
had
ceased and
andalusites
three
of cordierite
ofsi
of folding but the eviden-
phase
with
the
near
a
form orienta-
biotites
in the
they
Consequently
between first and
the Trona
second
same
rotated
are
of the
most
phase.
mountain;
thin
section
minerals
small
as
could
be
not
mineral than staurolite it
of the Devonian schists it
Hercynian
its relation-
crosscutting
crystals.
but since
established,
may
orogeny.
phase
of
to
can
locally
to
be assumed that
After the end of this
deformation,
had
comprising
ceased
and
rocks
uniformity.
units.
mainly
time.
first
stauro-
but first staurolite then andalu-
the
the
some
became
same
third
history
of
the
Cambro-Ordovician,
The
Going
phase
were
during
time after the
partially replaced
time
as
phase
staurolite and
of deformation
(fig. 22).
structural
of
at
During
they
Formation of these minerals
crystallize.
end of formation of staurolite it
stratigraphie
be stated that
mesozonal schists
whereas cordierite remained stable for
metamorphic
into the
and
phyllites
dates from this
remarkable
schists
and is
the
crystallization
the
in-
A few
incipient folding
some
around
curves
episode
cordierite. Biotite formed
garnet probably
most
age
After
or
seem to
These cordierites
crystallization
elongate crystals
as
thin section
epizonal
to
crystallization
phase.
of deforma-
latter.
continued well into the second
by
or
than andalusite and cordierite started
site ceased
of
the aluminium-silicates.
discovered
was
relation with
lite,
phase.
like in the Cambro-Ordovician schists.
cases
Garnet has been found in
Its
the
cases
the third
often
schistosity
from the interkinematic
indicate
phase
observed,
and without
schistosity
around the aluminium-silicates. Included si shows that
as
biotite dates
ships
during
few
a
this
to
hence
never,
crosscutting crystals
schistosity.
number of
a
as
occurs
phase
crystals
schistosity planes
regard
minerals. In
cordierites grew
the
along
with
staurolite
two
been
(fig. 22).
is rather scanty
Biotite
in
some
movements
but
outlasted that of the other
indicates that
small staurolite
disturbance of the
any
postkinematic
are
relations,
similar
including
the included staurolites have been rotated.
rotation, although
any
often
without
planar
a
of cordieriteoutlasted that of staurolite. There
crystallization
large porphyroblasts
the
rim
a
formation of
the second
during
is evidence that cordierite continued crystallization after the second
tion. Some
as
cordierite has also
by
has
core
interpreted
the
during
of staurolite and
a core
a
Nevertheless
mineral started before
be
to
with
Crystals
scarce.
indicative of
of cordierite
of staurolite
rather
are
thin section
of andalusite
relationships.
crystallization.
but
si which is
and
phase
replacement
that the
s-shaped
an
s-shaped
staurolite in the interkinematic
again indicating
occur
has been observed that
together.
and the rim of cordierite
deformation. Partial
infrequent partial replacecrystallization
doubt that formation of this
crystals
few
a
not
that the
in unstable
resulting
si like in staurolite and andalusite do
second
si
also. The
andalusite then indicates
than that of staurolite
longer
planar
they
occurred
crystallization
351
geology
same
sequence
of
events
downward from the
andalusite-cordierite
zone
the
staurolite-andalusite-
Silurian
can
upper
and
be
Devonian
determined
Cambro-Ordovi-
history
becomes
belong
to
more
complex
longer lasting.
The banded schists with N-S lineations near Les
the second and
partly
352
H.
the
to
third
Zwart:
J.
Melamorphic history of
Under the
zone.
this
through
segregation
parallel
to
to
a new
but
a
this
this
from
to
the
at
phase
may
be
Staurolite,
and cordierite
are
24.
are
the
rocks.
A
of the old
metamorphic
will
have been
transposed
was
banding
preserved,
was
banding parallel
new
has
banding
been
to
ob-
3.
have been found
included
as
mica-schist
postdate
of rotation. Microfolds in
N-S
the
near
second
direction
Lés;
near
Les, but andalusite
E-W section.
phase
dating
second
Fibrolite
phase.
demonstrated
as
from
helicitic folds in the cordierite and
younger than the
certainly
are
the old
whereby
fig.
aggregates
Banded
Most of these minerals
phase
schistosity
with
obliquely
common.
Fig.
sence
the first
on
cuts
of
phase
produced (fig. 24). Folding
neither shimmer
result
schistosity
axes
served in several outcrops and is shown in
the
clear
quite
time the
crosscutting schistosity imposed
schistosity
is
banding
is
schistosity
which
the second
about N-S
folding
character
The
alternating (fig. 24).
presumably
the main
banding. During
due
one
new
and
banding
dating
the banded
microscope
biotite- and muscovite rich bands
the Central Pyrenees
the end
consequently
mats
by
the
of the
these
have been
ab-
second
crystals
found in
a
few of these banded schists.
3.323 Andalusite-cordierite
morphism
in
the
metamorphic
Bosost
history
zone.
is
area
From
the
foregoing
it is evident
of the
stratigraphy
independent
is encountered in the
upper portion
of the
the Silurian and the Devonian. Below the described zone II
site-cordierite
are
similar
until the
part
to
zone
111
occurs,
end of the second
of the
transitional
those of zone I and II and
metamorphic
phase
no
to
the
lower
appreciable
of deformation. In
history
is
well
the
and
a
meta-
similar
Cambro-Ordovician,
intermediate andalu-
zone
IV.
The first
stages
differences have been found
zone
preserved,
an
that
111 the record
contrary
to
zone
of the
IV
early
where
Structural
Fig.
25.
Staurolite remnants
Fig.
3
26.
Partly
353
geology
in cordierite
muscovitized
(in cordierite-sillimanitezone).
and
rotated
staurolite.
354
H.
J.
Zwart:
continuing crystallization
first stages
has
characterized
small
can
be
by
the
bodies. The
with
to
to
and
or
Fig.
and is
cases
27.
zone
occur
The muscovite
and
the
muscovite
covites
regard
are
to
crystals
and
zone
lite
intact,
to
phase.
arrangement
is restricted
to
until
only
although
the
whereas in
a
a
the
and
this
since
the
portion
are
also
the
fully
and its
prolonged
partially replaced
was
andalusite-cordierite
after second
is
or
and
only partial
cordierite like in the
borders
small relic
decussate
a
or
and
even
consequently
they
are
replacement
of the
only
crystals
small
process
to
at
grow
(fig.
26).
in
of
some
zone.
attacks
all is left.
crystals
with
The
postkinematic
and leaves
fragments
upper
of several
tendency
crystals
cores
In
gradually
nothing
intergrowth
strong
zone,
phase.
The rotation of the staurolite is often
lower
these
occurs
muscovite-biotite aggregates.
there is
fringes
and
gradual
porphyroblasts
many
zone
unstable and
border of the staurolite
outer
is
zones
of this mineral and
from the
starts
of the micas. This
the
schists
replacement
or
andalusite
undeformed and
generally
the second
this
to
always
three
groundmass,
unstable in
muscovite. This
minor biotite forms
perpendicular
the
is
zone
sills and
as
(fig. 22).
locally
in
different orientations
the
to
by
granites mostly
number of thin sections.
instability
definitely
record of the
andalusite-cordierite
and
andalusite; crystallization
The muscovitization
cleavages
the
II became
is
Static
the interior part of the
shape
are
staurolite has been altered
(fig. 25).
with
II
Pyrenees
evidence and the
The
Staurolite in
zone.
upper
cordierite,
usually replaced
always
of the
between
large
their relations
zone
Staurolite which in
staurolite
transition
a
the Central
pegmatites
many
of andalusite and cordierite
crystallization
andalusite
of
the aid of
those of the
main difference with
by
most
been retained.
be said about the matrix of the
of aluminium silicates
comparable
destroyed
occurrence
mapped
Little has
has
only sporadically
crosscutting
only
Metamorphic history of
the
mus-
with
still visible in the
the
most
of the
upper part
of the
of
stauro-
older mineral
Structural
are
this
is much less
process
rolite is
almost
andalusite and
Although occasionally
left.
surrounded
a
rim
of cordierite for
muscovitized whereas
completely
that the muscovitization is related
both
becoming
It is
more
difficult
is
more
less
or
28.
Fig.
the
similar
irregularly (fig. 27)
by long
or
with
Cordierita porphyroblast
very
When
in
mimetically
grown
the
slightly
schists
deformed in
the
are
fold
mineral is older
the
curved
than this
altered
partially
rotated staurolite
This
andalusite
to
together
phase
of
staurolite,
to
contains
apparently
is
mineral
and
stau-
may
no
be
doubt
pegmatites
and thin
the
the
In
curved
has
zone,
upper
of the
of
this
schists
apparently
margin
outside
phase
not
one
this
the
have
crystal;
is
crystals
both often
se,
being
not
or
planar.
of deformation andalusite is
enclosing
often
schist
occurs
replace
section
schistosity
later than
the
which
towards
Andalusite
but does
end.
phase.
third
folding.
an
groundmass
crystals
schistosity
with
its main
undoubtedly
to
in
as
the
folds
steeper
The
but
of deformation. In thin sections
invade
of third
muscovite.
the
first
granites
come
conformable with
si is
folded due
staurolite or muscovitized
may be
schistosity.
and
hinges
began,
characteristics
phase
which
crystals
folding
only
of the
emplacement
after the second
ill-bounded
by
muscovite,
to
latter is unaltered. There is
after all deformation had
late,
showing
crystallization
illustrated
to
the
the
instance,
tell when the muscovitization
besides
Andalusite,
continued
to
altered
are
in the cordierite-sillimanite zone.
pronounced
falls rather
development
cordierite
than the muscovitization of staurolite. When
common
by
355
geology
an
it.
as
that
this
rims around
Locally
andalusite
andalusite rim around
without
curving,
indicating
also
itself
hence
being
a
deformed.
later than
phase
II
(fig. 22).
Cordierite
tated with
occurs
regard
to
either
se,
as
bowing
rounded
out
the
or
elongate crystals
schistosity
and
with
planar
si and
consequently dating
ro-
from the
356
H.
interkinematic
static
lier
postdate
The
the
Crystals
or
developed
in
rim of the
grew
to
ging
are
and in
the third
later
distinctly
as
case
any
Besides
phase.
show the presence of
contains
a
a
from
period
of
this
larger part
cases
crystal
competent
staurolite
both
at
a
the
as
29.
a
result of
must
but cordierite
crystal
whereby
not
the
show
time
in
are
they
phase.
show
the
steeper toward
of
this
cordierites
some
helicitic folds.
true
history.
fig.
before
grow
NW direction belon-
phase
example
For
the
at
one
such
crystals
cordierite
of the
lips
In
crystal.
28.
the
third
and
phase
had another
cordierite grows
the
as
included
close
grew
any
with
in
a
rim
around
staurolite. In
phase.
curved
at
certain
a
around
during
the
the second
In other
cordierite shows
sign
is curved.
schistosity
together
and rotation
second
si
as
deformed cordierite and the extinction of the
cases
a
regard
to
phase.
the second
phase.
In this
cordierite rim
case
less
competent
more
strong curving
of deformation. In this
Apparently
time. The
case
occurs
although
the
staurolite is pre-,
Both
cases
have been
specimen (fig. 30—31).
When all this evidence is
long
folding
plane
has uniform extinction. Some
as
deformed and
the
post-kinematic
one
this
as
ear-
the NW third
by
schistosity
and helicitic folds
Same
strongly
flattening
predate
cordierite itself does
a
to
amount
staurolite
around staurolite
observed in
same
cordierite became
crystals
after
or
and
they rotated,
are
folds in
are
occurrence
portion
conditions arise when
cordierite and
andalusites
after it.
this rim consists of
rotates
the
of the described
cordierite started
growth
Special
some
of the
helicitic folds which
as
deformed and
not
Fig.
Evidently
part
deformed
of the
the inherited folds
si in its central
planar
during
folding
schistosity
nor
are
being contemporaneous to
evident
the cordierite itself is
cases
Pyrenees
28 —29). Several of such cordierites have been observed
crystal (fig.
thin sections
them
by
even
the
during
record of folding in the internal
the
disturbed
not
like
or,
Some of these cordierites
phase.
actually
phase,
Central
but have less clear boundaries than the
fairly large
is
cordierites
of the
which
Melamorphic history of the
from the second
schistosity
second
Part
phase.
I
phase
which may be
crystals
crystals.
Zwart:
J.
assembled,
it
appears
that cordierite
the andalusite-cordierite zone. It started its
crystallized during
development
in the inter-
Structural
Fig.
Fig.
31.
Same
30.
as
Cordierite
fig.
30
rim
but with
undeformed;
357
geology
around muscovitized
crossed
later
nicols;
than
cordierite
second
staurolite;
has
phase.
curved
si but
is
H.
358
val
first
between
Zwart:
J.
and
second
deformation and ended
the
to
fourth E-W
but
occurrence,
Like
rotated
third
In
schists.
schists
it
with
Fig.
minerals will be
is of
more
The
on
ceased
crystallization
third
the
portion
of the
replaces biotite,
and
without
in
the
hinges,
32.
Unoriented
in the
given
part
relationships
zone
phase.
grows
fibrolite
in andalusite
from
latest mineral
forming
in
some
cordierite. It
More
details
micaoccurs
about
these
zone.
about the cordierite-sillimanite zone where it
on
hand and muscovite
one
and
the
to
crystallize
as
based
abundant
This
occurrence
zone
is
characterized
of sillimanite,
mainly
Further the fabric of the rock may be different from that of the
record of the
different in
first
phases
has for
the fact that the
developed
mainly
disappearance
two
aluminium
observations in the
on
(fig. 22).
3.324 The cordierite-sillimanite zone.
and the
micas
occurs
or
cordierite-sillimanite
between andalusite and cordierite
cordierite-sillimanitezone
well
not
Some folds of the
importance.
silicates. In fact it is the
is
its erratic
time.
in the intermediate zone
the other indicate that the latter mineral is later than either of the
staurolite
to
that
recrystallized
aluminium-silicates.
mica-schist
next
at
third
regard
Crosscutting crystals,
second
but
and
frequently.
intermediate
but also
other
phase.
later than the
are
due
certainty
and
partly through
second
Relations with
crystallization
biotite has continued its
deformed micas
lower
Usually
phase.
established with
have been observed rather
arcs
the
be
not
Pyrenees
throughout
end of the third
cordierite had
existing schistosity
show
phase
polygonal
in
second
in the
could
phase
the Central
continued
deformation,
after the
only
probably
cordierite,
the
through
Metamorphic history of
due
to
of the
a
large part disappeared.
schistosity although
the
growth
perfect
of
in
most
most
the
its
higher
absence of
fibrous form.
zones
and the
The fabric of these schists
cross-cutting
orientation of
by
in
rocks
still
present,
is less
biotites and muscovites
of the micas
(fig. 32).
Structural
staurolite
Although
muscovite
aggregates,
those of the
higher
two
covite. In several
previous
has
only
the
specimens
N-S
than in the
axes
later
it
was
has been
as
found
small
as
almost
replaced
as
completely by
of shimmer aggregates is
occurrence
in
remnants
in these schists
widespread
in
mus-
of its
suggestive
presence.
Andalusite and cordierite
dantly
that
but it
zones,
been
occasionally
it is assumed
359
geology
do
than
upper
occur,
the
but rather
second
are
found in many of these rocks
and intermediate
zone.
of deformation and
phase
minerals
they
also in
occur
which
directionand like in the intermediate zone
in these
predate
33.
Fig.
E-W
fold
this
folding
with
(fourth phase)
On
phase.
the
polygonal
the
replace
rocks
of refolding in NW
folds and
less abun-
rotated
are
about
Much of the andalusite and cordierite is
exceptionally.
mechanical disturbance. Both
although
which
Crystals
they
may
other hand
arcs
schist
show
effects
be deformed
some
of muscovite
without
the
cordierites
crystals
(recrystallized fold)
showing
the
of helicitic folds
presence
of the
later. No andalusite with well
crystallized
has been found and hence the
third
developed
and
phase
fourth
of andalusite
cordierite which
by
In the folds of the
of micas
arcs
than
E-W
folding.
phase
have
third
also
Polygonal
and
phase
observed,
arcs
of micas
crystallization
has
micas
been
must
been
are
occur
witnessed
often bent in
indicating
have
has
of cordierite outlasts that of andalusite,
crystallization
like in the andalusite-cordierite zone. This relation is also ascertained
ment
phase
E-W direction
helicitic folds in
that
also in
in
the
a
by
few
hinges
but
belonging
continued until
after
replace-
polygonal
lasted
crystallization
folds
the
thin sections.
to
the
the
end
longer
fourth
of this
phase (fig. 22, 33).
Both,
andalusite
muscovite flakes
this
process
in
a
and
cordierite
similar fashion
has seldom
gone
to
are
as
sometimes
the
completion.
shimmer
partially
replaced
aggregates
The decussate
by
coarse
after staurolite but
intergrowth
and
unde-
360
H.
J.
Fig.
Fig.
Zwart:
34.
35.
Metamorphic history of
Fibrolite
mat
in
the Central
Pyrenees
cordierite-sillimanite
Andalusite partially
replaced by
schist.
fibrolite.
Structural
formed
of the
nature
361
geology
muscovite indicate that
this
took
process
under static
place
circumstances.
Fibrolite which started
found in
biotite and
bundles
of the schists
most
or
muscovite
mats
lying
well
as
in the
fibrolite
that
late
be
to
fibrolite grows
minerals
are
at
(fig 35).
not
is
than the
since in several
but
of
this
is
synkinematic
in
other
at
its
biotite and
due
(fig.
paper
It
34).
this
also
stated
I
(1958)
aluminium-silicates,
linear
mimetic
to
be
cannot
thin sections it has been observed that
new
andalusite in
turn
forms
replaces
these
partially replaces
replaced
thin sections it has been observed that staurolite is
some
be
original
origin
previous
a
to
the expense
undoubtedly
the expense of cordierite and andalusite and
In
is
zone
carry quartz,
at
When it
neighbouring quartz.
of the
only
it has grown
cases
considerably larger
Although
any
which
with other aluminium-silicates. It
and in many
proof
no
in schists
occurs
elongate,
biotite.
replace
correct
and
by andalusite,
often
also
certainly
cross-cutting
fibrolite does
considered
mats
and
crystallization
are
It
in schists
as
have grown out in the
apparently they
replaces
present in the andalusite-cordierite
zone.
schistosity
ofbiotite. The fibrolite mats
biotite the
be
to
of this
also staurolite-cordierite-fibrolite
fibrolite,
and andalusite-cordierite-fibrolite
alterations have been noticed. This is in agreement
with
the
trend of the
general
cordierite
or
belonging
This
the
well
the
same
fibrolite could have started
in the rotation about N-S
partook
and
does it disturb
period
of
this
the
In few
phase.
through
the
may bow
outlasts
reverse
mats.
time
seems
this late muscovite is
that this
It
has continued
certainly
considered
as
to
important
There is
related
to
a
separate
this
in
no
the
deformed
On its
probably
that it had
second
to
third
phase
a
very
to
deformed
or
the
even
For these
phase.
replace
may
turn
reasons
continues
phase,
then
true
short time and
develop
the
former,
that
folding phase
before
or
Polygonal
arcs
so
during
and after this
In
by
few
that it
can
that
phase.
phase
the
a
(fig. 22).
sequence
but
replaced
fibrolite may be
lies after the fourth
zone.
started
not
had ceased. If this is
entirely postkinematic
phase.
The main
and could be
of micas in microfolds
or
static
metamorphism
region.
doubt that
some
the
formation of both
of the
granites
importance during
From the described relations between
minerals the
that fibro-
clear that the formation of fibrolite
crystallization throughout
fifth muscovite
to
no
of staurolite,
than the
age
before the third
folding
the fourth E-W
by
since
easy
however,
fibrolite is
the fourth
to start
It is
muscovite started
emplacement
action has been of
Much of the
latter mineral
indicate that
phase
this
seems
(see fig. 22).
of the late muscovitization
belonging
was
late
less
porphyroblasts
of later
be the last mineral in the whole
to
be assumed
period
evident,
be
must
deformed by
been observed.
never
It is
like the
that of andalusite for
overlaps
phase.
Therefore
early.
that fibrolite is folded in NW-SE microfolds
end before all
that of cordierite since the
relation has
muscovite and
cases
longer
a
not
this is
and may be later than the
of fibrolite
the second
postdating
formation rather
schistosity, clearly indicating
fibrolite is
and does
its
axes
phase (fig. 35).
schistosity
cases
formation of fibrolite
of cordierite for
appeared
the
third
crystallization
phase
it
out
before the
already
fourth
the
thin sections
some
further it
grow
nor
In
minerals
Unfortunately
andalusite, cordieriteand biotite and hence it
phase.
replace
Sillimanite may
for the other aluminium-silicates have
applied
is present in the fibrolite
schistosity
never
ages;
as
viz. staurolite-andalusite-
overlap.
it attacks rotated andalusite and cordierite
determine the age of the fibrolite.
to
included
lite
that
as
criteria which have been
same
be used
early crystals
minerals,
fields
stability
andalusite of different
to
means
formation of the
their
cordierite-fibrolite, although
following
conclusions
can
and
fibrolite and
pegmatites
and
late muscovite
that
is
metasomatic
this time.
structures
be drawn. It
and the
appears
development
that the
of various
metamorphic
362
H.
first
zone
the
passed through
for
has
instance,
a
The
muscovitization,
probably
indication of
only
which
some
apparently
andalusite;
andalusite and
From the
diagram
the
biotite,
36.
of
kyanite,
stability
became
site
together
only
only
but with
then
various authors
tions of low
area
take
sillimanite,
place
the
at
the
phase
can
the
a
be
shows
a
various mineral
seen
in the
introduction of
and
cordierite;
fibrolite
late
water
biotite,
borders.
only
sillimanite have
This is in agreement with the
since simultaneous
phase boundary
rising temperature
both
boundary
a
phase
crystallization
lines which
of
separate
first andalu-
minerals
temperature andalusite became
crystallized
unstable and
crystallize.
paragenesis
(Miyashiro, Zwart)
pressure.
where the
by
andalusite
with
crystallization.
passing
A few remarks about this
by
garnet,
staurolite
further increase in
sillimanite could
development
doubt that the
sequence
temperature the following mineral
fields of the three minerals. Hence with
stable,
no
the
cordierite and sillimanite.
andalusite and
can
area
22 it is clear that andalusite and
of
staurolite-andalusite-
there is
temperature
increasing
Muscovitized
diagram fig.
the
accompanied
staurolite,
overlapping period
of these minerals
two
the
in the
higher grade
The cordierite-sillimanite-
muscovite; biotite and staurolite; biotite, staurolite,
cordierite; biotite,
Fig.
very short
in
decreasing
was
With
potassium.
one
Pyrenees
that every
sense
zones.
biotite-zone,
highest grade
associations appear: biotite and
garnet,
the
through
grade
slowly rising temperature, resulting
associations.
and
lower
andalusite-cordierite-zone. Since
cordierite-sillimanite-zoneis the
record of
in the
complex history
preceding
gone
cordierite-zone and the
the Central
Metamorphic history of
described here have
zones as
zone
Zwart:
J.
This
is
stratigraphie
value of about 2000—2500
seem
that
in
place
here.
indeed in agreement with the
thickness of the
m.
(1000
m.
It has been concluded
this association is formed under
beds above
situation in
the
condiBosost
the biotite-zone reached
for the Dvonian and
1000—1500
m.
a
for the
Structural
For
Carboniferous).
has
be
to
which
be
can
geothermal
in
of
estimated
considerable
The
of about
gradient
described
area
the
temperature
15°
C
C/100
the
corresponding
m.
the
This
1957).
been
top
to a
gives
approximately
is
these relations it
had
biotite-zone
thickness alone will have
thickness
of the
confining
of the staurolite-andalusite-cordierite-
which
From
gradient.
For
thickening.
(Winkler
m
tectonic
Hercynian folding
been
small
too
times
larger
that
probable
seems
installed.
is
the
result
the
Apparently
maintain
to
steep
very
a
5
staurolite-andalusite-cordierite-paragenesis
temperature after
rising
stratigraphie
tectonic
of 3500—4000
figure
500—530°
at
the main
metamorphism postdates
at a
normal continental
a
the
arrives
of 950—1100 bars.
pressure
than
one
staurolite-andalusite-cordierite-zone the
for
responsible
was
staurolite-zone
zone
the
since this
calculated,
363
geology
sufficiently
high
the first tectonic phase.
temperatures for the formation of aluminium-silicates during
After
of the
thickening
allow
to
enough
4.
the
by
sequence
CALC-SILICATE
cleavage
ROCKS
AND
It is of
rocks
some
of the
interest
metamorphic
The
zoning.
the
cordierite-zone;
discuss
to
From the
a
Ordovician
ones
The
mineral
In the
of
are
Devonian the
plagioclase
lusite-cordierite
in
these
content
metamorphism.
This
metamorphism.
The
to
the
not
therefore
they
are
not
contain such
mainly
due
to
relation with the deformation
indicates, however,
that
succeeding
calcite,
diopside,
biotite, quartz, potassium feldspar,
determined),
sphene
and
muscovite.
probably belong
determinable
no
of interest since
near
to
of
it is
known
diopside, however,
La Bordeta in
has
to
the
plagioclase
that
was
plagioclase
areas
with
indicates condi-
facies and
the cordierite-sillimanite-zone
been found. Here
clinozoisite or
the
following
calcite and tremolite.
prehnite.
This association
formed simultaneous with
GRANITES AND
5.1
but
do
This is
minerals
Diopside
and
clearly belongs
cordierite-sillimanite
the
in the schistose rocks.
5.
Especially
a
but the other minerals
occurrence
assemblage
may be altered
metamorphism
dant,
features
grossularite, idocrase, diopside, bytownite,
amphibolite
the
to
facies.
amphibolite
distinctly higher grade
grossularite
regard
An-content is stable under relative low
in
temperatures
In the Ordovician limestone
occur:
that these rocks
the micaschists.
Unfortunately
would be
high
a
with
staurolite-andalusite-
which then will be contemporenaous with the staurolite-anda-
rocks.
the
as
which excludes
secondary,
low pressure
to
the
the cordierite-sillimanite-zone along
tremolitic amphibole,
with relative
tions close
mainly
to
minerals have been observed:
following
often is
primary paragenesis,
found
to
belong
appeared
replacement
(anorthite
Epidote-clinozoisite
partly
all
present in these rocks.
zoisite, epidote-clinozoisite,
sodic
Ordovician,
metamorphic history
occurrence
assemblages
CAMBRO-ORDOVICIAN
area.
the absence of s-planes in these rocks
phases.
rise
the mineral associations in the calcareous
Upper
of thin sections it
study
clear record of their
IN
Devonian rocks
the southern border of the Bosost
could
temperature
DEVONIAN
briefly
Devonian and
Lower
the
folding
of aluminium-silicates.
crystallization
in the
occur
to
PEGMATITES
OCCURRENCE
cordierite-sillimanite-zone granites
and
pegmatites
are
abun-
also in the staurolite- and andalusite-zones. Most of these rocks
be found in the
Cambro-Ordovician,
but
along
the southside of the
364
H.
Bosost
a
few
area
sills
as
or
in the
masses
that
where the
pegmatites
occur
to
contain
small discordant bodies in the mica-schists
The
They
of
has
relationship
trusive but of
granites
may show
and
certain
these
by
lead
the
to
pegmatites
grade,
can
age
regard
emplaced
to
the
during
deformation
37.
and
is
the
the
late E-W
Barrados
between the
they
are
would
in
to
the
phase
are
not
in
imposed
a
grade
the
In the
main
structural
a
completely
and
perpendi-
pegmatites
detailed survey
the
neighbouring
(fig. 38, 39).
sense
of these bodies
are
not
A
few
for
10)
area
nor
elsewhere in the
aid of structural
area
of the
is
no
sills
by
they
are
on
Pyrenees
are,
folded
by
folding phases
the
both
are
later than the first
these rocks.
pegmatites
orogeny.
or
or
This
were
can
flattened
be
by
however, influenced
boudins
throughout
is folded
or
sheared
folded,
pegmatite
common
rocks of
of these rocks
analysis
granites
Herynian
Pegmatites
which
to
mat.
instance,
direction.
concerned,
in-
these
rocks.
of these rocks
bodies and the
that
being
staurolite-andalusite-cordierite-zone
Bosost
phase
shown,
schistosity
A
nor
their occurrence is
the
the described
rather
(fig.
one
muscovite-
are
usually
by
with
the
area.
N-S axis
third
A
phases.
good example
The relations
contacts
second
and
NW-SE
less obvious. In
less concordant, but in detail many discordant
This indicates
have
same
They
and
mica-schist.
or
Folded fibrolite
phase.
as
as
case
in lower
none
this
phase,
pegmatite
or
the
fact that
larger granite
more
observed.
before
belonging
pegmatites
occur
least
far
be determined with
the, N-S, second
folded
as
this
in
folding phases.
or
deduced from the
by
inclusions
at
largest
which is in accordance with the fact that all
Nowhere in
zones.
muscovite-granites
Their
with
the
grained. Both, granites
conclusion that many
limited
are
metamorphic
size
grain
and
irregular patches
larger bodies,
neither these inclusions
bodies,
replacement origin,
higher grade
similar
or as
pegmatites
orientation of muscovite flakes
some
to coarse
larger
or
Fig.
or
intermediate
medium
are
smaller
frequently
wall rock is influenced
This
form
granites usually
pegmatites
the walls.
Devonian,
thin sills and boudins in these formations. Most
as
of these bodies has shown that
one
Pyrenees
the eastside of the Garonne river between Lés and Bosost.
on
cular
the Central
fronts have risen into the Silurian and
metamorphic
occur
granites.
unoriented. The
a
Metamorphic history of
muscovite-biotite-granites
or
of
Zwart:
J.
general
have been
phase,
Moreover many NW-SE
as
these
folds
are
Granites and
pegmatites
365
granite.
the
by
schists
of
disturbance
no
Bosost;
of
south
mica-shit
in
pegmatie
of
map
Geol gical
38.
Fig.
366
H.
off
cut
by
the
corroborated
folds.
Zwart:
J.
granites
E-W folds
that
so
the
by
fact
at
that
also
are
Metamorphic history of
least
off
cut
they
this direction
(fig. 40). Consequently
falls
around and
probably
partly
to
be rather
with
the
The whole
crystallization.
long
and
granites
sidered
as
a
pegmatites
contact
and
the
in
metamorphism
the
of the
there
culminating point
until after the
is
clear
a
Garonne dome and
of sillima-
it
any
be
cannot
but
con-
metamorphism
the Bosost
especially
more
biotite-zone started before
seems
fourth,
connection between
character of the
regional
granites
pegmatite emplacement
phase
these
and is contemporaneous
higher grade metamorphism,
since the
metamorphism,
This is
phase.
contain
seldom contain folds in
emplacement
phase
the
and
often
granites
or
area
pegmatites
emplaced.
were
Fig.
39.
Stereogram showing
in schist in
Most
of the
granites
biotite. Accessories
varieties
finegrained
rocks
which
Most
sericite
The
is
The
structure
rather
characterized
graphic
by
occur
into
of the
large
(
rock
in these
is
biotite
10—20
with
and
foldaxes
38.
fig.
fine
as
grained
is
only
may
be
a
feldspar crystals
some
important
more
to
a
albites
quartz,
also
zircon. In
the
coarser
and may
occur
trondjemitic composition.
tend
to
a
hypidiomorphic
unoriented. Alteration of albite
chloritzed.
feldspar
mica,
and
of
specimens
minor component, but in the
it is
potassium
Plumose
and consist
garnet, fibrolite and
therefore tend
but
rocks
main constituents. Some
completely
cm)
quartz.
of
pegmatites
xenomorphic,
are
lineations
sometimes
rocks
finegrained
common;
intergrowth
quartz may
apatite,
potassium feldspar
of the minerals
shape.
are
gradually change
large crystals.
to
and muscovite
albite, potassium feldspar
carry
medium
are
area
PETROGRAPHY
5.2
as
and
granite
intensity. Although
is evident for the whole of the
where
of
period
and extends from before the second
gradually increasing
granites
the main time of
after the fourth E-W
with the cordierite-sillimanite metamorphism
nite
in the
but included schists
locally
Pyrenees
in part younger than this
are
inclusions
schist
the Central
an
The
pegmatites
crystals
intergrowth
probably
is
a
which
are
may
to
often
show
of muscovite and
replacement
product
367
Petrochemistry
of it.
is
In
quite
muscovite
folded
and
crystals
then
occurs
as
the
typical
with
contacts
small
has
beryll
near
pegmatites
the
along
cordierite
pegmatites
some
common
contacts
petrochemical
area
been
phyllites,
made
executed
120,
by
198,
from
Mrs.
Dr.
129 which
40.
Fig.
C.
In order
for the
Ordovician
of
ten
to
phyllites
specimens
Lés
Bosost
along
situated
locality
itself
the
on
five
have
and
on
5
on
the
Miss H.
composition
analyses
been
east
M.
the
near
the
Tourmaline
cm.
sills
pegmatite
the
the wall. In
to
The
hinges.
schists
this mineral
tourmalinized;
thickness.
some cm.
rocks
cut
Two of these
road
from
the
village
one
samples
are
is
made
in the
and
collected
Bonaigua
of Alos in
samples
locality, usually
river,
were
the
118,
the initial material
constituting
localities
Garonne
samples
been
off by pegmatite dyke.
of composite
of the
at
have
have
They
PHYLLITES
rocks
made. Each
been conti-
Analyses
except for the numbers 117,
102—106)
Two
of sheet 3 has
surroundings.
I. Bik.
phase,
of the
(no.
side of the
river.
along
sheet 4
the
muscovite-granites.
Sitter-Koomans,
by
of fourth E-W
long.
metres
on
of
CAMBRO-ORDOVICIAN
Garonne
sheet
is also
started
which have been collected
of about hundred
near
de
done
know the
metamorphics,
was
mica-schists
Microfolds
6.1
in
occur
strongly
zone
size of 1
perpendicular
few other localities in the
a
M.
were
a
a
times. In
PETROCHEMISTRY
work which
and
nued for the Bosost
often
are
abundant in
crystals
few
a
muscovites
fan-shaped
of
crystals
as
often oriented
are
pegmatites
6.
The
occurs
been found
the
of Cambro-
of
a
along
Bosost
north of the
near
pass
upper
to
Esterri
Esterri.
Pallaresa
mixture
a
section
area,
viz.
village
de
of
Aneu
The
valley.
fifth
368
H.
The
analyses
in
percentages,
In the
analyses
and lower Al
This
has the
values.
ones
show
analyses
Bosost
percentages
and the
1959).
41.
Variation
it
not
content
becomes
vary
In
composition
very
any
larger
a
case,
obey.
high
are
similarities
as
in
phyllites
there
has
are
aluminium and
higher
and
circle
of the
be
Si
potassium
area
are
sample (102)
these values
to
are
high
those
and
from
published
of these
five
new
the
mica-schists.
phyllites.
of the Bosost
average
remarked
certain
low
Bosost
Alos
Si
east.
considerable difference lies in
analyses
to
the
The
analyses
phyllites
with
new
that
(fig. 41, 42).
from Esterri show intermediate
variation than shown in the
mainly
been recalculated.
similar and show
Pyrenees.
only
composition
it
and then in cation
rules
area.
that
analyses
of the
analyses
which
to
percentages
From these
Cambro-Ordovician
are
of
single
composite
the variation in
accompanied
by
percentages. The other elements
little variation.
Twenty analyses
higher
the
the
analyses
of
dots
in the
the
however,
There
quite
is rather similar
analyses
6.2
executed
since
diagram
higher
have
content; connected with
mica-schists;
clear that
well
as
average of these six
much, although
very
sodium and
show
which is
will show
specimens
are
3
of the Cambro-Ordovician farther
analyses
Al
highest
Pyrenees
shown.
are
in almost
every respect similar. The
magnesium
samples.
106)
than elsewhere in
Also the
Dots
analyses
are
and low sodium percentages. Both
Fig.
low
(105,
than the
quartzitic
of sheet
certain differences
area
the Central
weight percentages
analyses
already anticipated,
was
more
(Zwart,
are
does
the
The variation of these five
3
sheet
in the usual
as
way
also the cation percentages
lowest Si
potassium
Metamorphic history of
given
same
of the
difference
somewhat
first
are
the
diagrams
These five
Both
Zwart:
J.
(no.
than
of
single samples
107—126).
the
MICA-SCHISTS
These 20
of mica-schists
specimens
chlorite-zone. Further
one
are
of the
from all
analyses
of
a
Bosost
zones
area
have
been
of metamorphism
composite
sample
of 20
369
Petrochemistry
1
table
Si0
Weight percentages
2
102
103
104
105
106
55.24
58.95
59.42
63.95
63.45
1.19
1.09
0.82
0.98
0.87
0.20
0.17
0.17
0.23
0.28
0.21
16.90
19.51
Ti0
Average
60.20
0.99
2
p
2
o
A1
6
0
2
19.80
23.62
3
19.80
0.92
2.28
4.14
4.95
4.26
0.06
0.02
0.05
0.04
2.48
2.72
2.30
1.75
2.32
0.78
0.98
0.74
1.23
1.52
1.05
1.55
2.09
1.92
1.95
2.30
1.96
0
4.12
3.28
3.19
3.45
3.34
3.47
0
4.30
4.08
4.02
2.89
3.50
3.75
100.20
100.15
99.90
100.30
99.83
102
103
104
105
106
Average
Fe 0
2.58
2.81
3.41
FeO
4.22
4.38
3.63
MnO
0.04
0.04
MgO
2.36
CaO
2
Na
K
2
H
17.44
3
0
1.72
2
2
Cation
percentages
54.0
57.8
58.3
62.1
62.3
58.9
Ti
0.9
0.8
0.6
0.7
0.6
0.7
P
0.2
0.2
0.2
0.2
0.2
0.2
27.2
22.8
22.9
19.9
19.5
22.4
Si
Al
Fe"'
Fe"
1.9
2.1
2.5
1.2
0.6
1.7
3.5
3.6
3.0
3.3
4.1
3.5
2.5
3.4
Mg
3.5
3.6
4.0
3.4
Ca
0.8
1.0
0.8
1.3
1.6
1.1
Na
2.9
4.0
3.7
3.7
4.4
3.8
K
5.1
4.1
4.0
4.2
4.2
4.3
100.0
100.0
100.0
100.0
100.0
102 —106:
Analyses
102
near
103
near
104
near
105
near
106
near
Alos
composite samples (each
the
Esterri
higher.
In
fig.
of Cambro-Ordovician
phyllites.
(Pallaresa valley)
Esterri
Lés
(Bosost area)
Bosost.
two
analyses
specimens)
(Pallaresa valley)
mica-schists has been made
to
10
100.0
phyllite
(no. 127).
analyses
shows somewhat lower
Consequently
42
where
the
the
This latter
of the Bosost
area
versus
the
shows remarkable similarity
(105 —106).
Si percentage and
variations fall into
potassium
analysis
the
again
same
sodium
The average of the
Na is
lower and Al and
category
content
is
as
the
shown,
20
K
phyllites.
the
phyllite
127
Ave- rage
64.15 0.93 0.20 17.80 1.14 4.55 0.02 2.32
1.31 1.92 3.28 2.11
18.49 2.94 4.50 0.34 2.68
1.14 2.04 3.85 2.14
61.04
0.95 0.18
99.73
1.85 1.05 1.12 3.48 1.83
126
65.45 0.84
0.07
17.38 2.87 3.89 0.04
125
65.45 0.92
0.12
15.92 2.56 4.31 0.05 2.70 0.94
124
64.52 0.94
0.12
16.80 3.23 3.32 0.04 2.44
123
63.35 0.99
0.16
122
64.60 0.80
121
63.50
120
62.95 0.83
119
118
99.87
1.95 2.70 2.14
99.76
1.05 1.90 3.64 2.12
10 .12
17.30 4.23 3.39
0.05 3.45 0.68 0.85 3.18 2.38
10 .01
0.12
17.60 2.07 3.62
tr.
2.48 1.18 2.94 3.08 1.81
10 .30
1.10 0.34
17.95 2.44 3.52
tr.
2.58 1.16 1.00 4.90 2.00
10 .49
0.23
17.76 3.15 4.23
tr.
2.77 0.52 1.55 3.35 1.84
99.18
63.65 0.87
0.21
16.70 2.17 5.54 0.03
3.33 0.66 1.85 3.40 1.68
10 .09
62.15 0.95
0.26
17.78 2.94 4.10 0.01 2.38 0.74
1.63 3.65 2.54
=0.38 99.51
C
117
63.85
1.00 0.15
16.65 3.10
4.25 0.04 2.48 1.50 2.68 3.18 1.13 0.49
10 .50 0.12 10 .38
—
=
0
2
perc ntages
weight
3.58 0.04 2.54 1.65 3.00 2.88 1.76
116
62.98 0.89 0.15 17.32 3.28
61.43
0.84 0.16
17.10 2.72 4.84 0.04
1.90 1.74 2.91 3.27 2.49
115
114
62.10
0.97 0.48
17.42 2.04 6.28
2.95 1.18 1.70 3.52 1.66
113
59.98
1.05 0.16
19.65 2.72
112
60.25
0.97 0.10
18.70 2.33
5.12
111
58.60
0.99 0.12
C=0.12
10 .07
99.56
—
10 .30
5.75 0.05 2.93 0.63 1.28 3.80 2.08
—
10 .08
2.88 0.93 2.15 4.85 1.68
—
99.96
19.20 3.88
4.11 0.05 2.24 1.60 3.01 2.97 3.15
—
99.92
110
58.65 0.77 0.09 19.96 3.32
4.98 0.07 2.88 0.61 2.32 3.75 2.80
—
10 .20
109
56.80
1.04 0.25
19.60 1.05 6.79 0.04 2.34 2.16 2.32 5.25 2.54
—
10 .18
108
57.05
0.74 0.23
21.40 1.18 4.98 0.04
2.23 1.82 2.84 5.15 2.63
—
10 .29
107
43.42
1.47 0.14
27.52 7.46
3.40 0.07 4.25 1.09 1.74 7.00 2.45
—
10 .01
tr.
—
2
3
table
—
S
2
2
Si0 Ti0
5
o
2
p
3
0
0 0
2
2
A1 Fe
FeO
MnO MgO CaO
2
Na
0 0
2
2
K H
127
62.1
0.6 0.2
20.3 0.8
3.7 3.3 1.3 3.6 4.1
100.0
Ave- rage
58.9
0.7 0.2
21.0 2.1
3.6 3.8 1.2 3.8 4.7
100.0
126
63.8
0.6 0.1
20.0 2.1
3.2 2.7 1.1 2.1 4.3
100.0
125
63.6 0.7
1.9 3.5 3.9 1.0 3.7 3.4
100.0
124
62.3
0.7 0.1
19.2 2.3
2.7 3.5 1.1 3.6 4.5
100.0
123
62.1
0.7 0.1
19.9 3.1
2.8 5.0 0.7 1.6 4.0
100.0
122
61.3
0.6 0.1
19.7
1.5 2.9 3.5 1.2 5.4 3.8
100.0
121
61.3 0.8 0.2 20.4
1.7 2.8 3.7 1.2 1.9 6.0
120
61,3 0.6
119
0.1
18.2
20.5
2.3 3.5 4.0 0.5 2.9 4.2
100.0
61.2
0.6 0.2
18.9
1.6 4.4 4.7 0.7 3.5 4.2
100.0
118
61.2
0.7 0.2
20.6
2.1 3.4 3.5 0.7 2.1 4.5
100.0
117
61.0
0.7 0.1
18.7 2.2
3.4 3.5 1.5 5.0 3.9
100.0
116
60.2
0.6 0.1
19.5
2.3 2.9 3.6 1.7 5.6 3.5
100.0
115
59.7
0.6 0.2
19.6 2.0
114
59.7
0.7 0.4
19.8
113
58.0
0.8 0.1
22.4 2.0
112
57.4
0.7 0.1
111
3.9 2.7 1.8 5.4 4.1
1.4 5.1 4.2 1.2 3.2 4.3
area.
cordierte, sil manite silmanite sil manite silmanite cordierte, Bosost
staurolite, silmanite andalusite, sil manite cordiert , cordierte, cordiert , andalusite, mica-shits
muscovite, muscovite muscovite, muscovite, muscovite muscovite, muscovite, muscovite, muscovite, muscovite,
100.0
0.2
100.0
100.0
bioti e, bioti e, bioti e, bioti e, bioti e, bioti e, bioti e, bioti e, bioti e, bioti e,
perc ntages
100.0
21.0
1.7 4.1 4.1 1.0 4.0 5.9
100.0
56.8
0.7 0.1
22.0
2.8 3.3 3.2 1.7 5.7 3.7
100.0
110
56.6
0.6 0.1
22.7
2.4 4.0 4.1 0.6 4.3 4.6
100.0
109
54.3
0.7 0.2
22.5
0.7 5.4 3.3 2.2 4.3 6.4
100.0
108
54.2
0.5 0.2
23.9
0.8 4.0 3.2 1.8 5.2 6.2
100.0
41.3
1.0 0.1
30.8
5.3 2.7 6.0 1.1 3.2 8.5
Ti
Al
Fe'" Fe"
Cation
sample
:
117: 118: 119: 120: 12 122: 123: 124: 125: 126: 127:
1
area.
Bosost
garnet. cordiert
of
107—26:
mica-shits silmanite cordierte, andalusite, andlusite cordiert
acesories)
Cambro-Odvican
(without
silmanite
cordiert , staurolite, staurolite, cordierte, andalusite, silmanite oligoclase silmanite cordierte, silmanite
muscovite, muscovite, muscovite, muscovite, muscovite, muscovite, muscovite, muscovite, muscovite, muscovite,
composit n biotie, biotie, biotie, biotie, biotie, biotie, biotie, biotie, biotie, biotie,
MAnalyses ineralogical quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz,
:
107
2
table
20
of
quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz, quartz,composite
:
4.7 4.2 0.7 2.4 4.7
sil manite
silmanite
Si
P
Mtr
Ca Na
K
100.0
107: 108: 109: 110:
1
11
112: 113: 114: 115: 116:
372
H.
field lies
and
series.
phyllite
and
variation of these schists
Na percentages.
whole
Metamorphic
The
apparently
it
be
can
mica-schist the
to
no
the
again
remaining
Consequently
and shale
companied
the
history of
Central
within that of the mica-schists. With the
wholly
107 the
Zwart:
J.
introduction
or
shows the
stated
that
exception
same
elements show
removal
of the first
relations between
little variation
the
during
in chemical
changes
Pyrenees
analysis
Si, Al,
throughout
transition of shale
composition
of elements other
K
the
to
négligeable
are
than water,
has
ac-
metamorphism.
This conclusion is different from that drawn for rocks of sheet 3. There it looked
that
probable
Fig.
42.
if
in
in
a
different
which
of
certain,
granites
the
also.
but
exception
percentages
Fig.
phyllites.
though
The
of
one
It should be
to
chemical
mica-schists
like
of the
those of the
small outcrop
near
than
that
schists
diagram
of
(explanation of
These
Bosost
changes
area
Ariège region
place
may
contain
are
and
see
mica-
fig. 42)
by migmatitic
have taken
changes
phyllites
symbols
that the schists of sheet 3
underlain
are
mica-schists
not
during
rocks
their
have affected
the
muscovite-
many
exposed
there with
Bosost.
is
sillimanite-schists
without
Al-Si
noted, however,
migmatite.
mineralogical composition
evident
43.
situation since these
small,
introduced in the
were
schists;
geological
migmatites
When the
it becomes
magnesium
phyllites
transformation from sediment
mica-schists
and
mica-schists.
with the
compared
are
diagram
Na-K
and
potassium
some
compared
with the chemical
generally
show
sillimanite but
with
higher
other
Si
composition
and
lower Al
aluminium-silicates.
373
Petrochemistry
Exceptions
content
schists show
as
have
we
this rule
to
carries
exist,
sillimanite.
certain position
a
seen,
sodium
the
due
Na-K
analysed
three
analyses
show
to
no.
42)
107 with
also
Si
three
rocks,
are
very
low Si
sillimanite-
most
Devonian
staurolite-schists;
percentage and
Cambro-Ordocivian
significance
have
specimens
the third is
and
some
doubtful whether
has any
consequently
schists
since
quite logical
those of silicon. Furthermore
to
mineralogical composition
Two of those
rather low
a
Contrasted
percentages.
(fig.
field and therefore it is
phyllite
Cambro-Ordovician
218 —130).
(no.
linked
are
this correlation between chemical and
the
analysis
diagram
low sodium content, but this is
to
percentages
of the sillimanite-schists fall in the
Besides
for instance
however;
In
a
Al
high
been
slate. All
and K
of similar
phyllites
3
TABLE
weight percentages
128
SiO
cation
129
130
percentages
128
129
130
55.9
52.03
51.20
57.90
50.8
51.2
Ti0 2
1.06
1.08
1.47
0.7
0.7
p,o 5
0.26
0.24
0.2
0.2
?
AU)
—
1.1
—
25.37
25.67
23.70
29.2
30.3
Fe„0 3
3.27
3.77
5.76
2.4
2.8
FeO
5.94
5.06
4.8
4.2
MnO
0.08
0.04
3.9
2.9
MgO
2.67
1.96
1.64
CaO
2.96
1.40
1.51
1.0
1.1
1.1
Na
0.53
0.60
0.60
3.9
5.1
6.7
3.15
4.00
5.42
2.45
4.74
n.d.
2
;1
0
K 0
—
—
3.1
27.0
4.2
—
2.4
1.5
1.6
2
H 20
C=
99.77
Analyses
schist
129:
schist
130:
slate
with
with
with
composition,
higher
Devonian schists and slate of
quartz, muscovite,
staurolite
muscovite,
staurolite
quartz,
mainly
the
Ordovician rocks
kind
of sediment
percentages.
in the
and
Six
analyses
—136)
pegmatites
their
large
of
a
Bosost
area
remarkable low sodium
Therefore
they
the result
possibly
THE
muscovite-granites
of
more
mature
have
been
executed.
composition,
although
would have
composition.
These have
a
different
Since
the
they
are
chemical
a
even
Cambrodifferent
weathering.
GRANITES
show little variation in
grainsize.
with
content
fall outside the field of the
diagrams (fig. 42, 43). Consequently
6.3
131
100.0
sericite.
Devonian rocks show
aluminium
100.0
98.24
99.76
128—130:
128:
100.0
0.24
microscopic
it is
examination
These
not
not
analyses
(no.
inconceivable that
been
proved
analysed
that
due
to
pegmatites
374
H.
Zwart:
J.
Fig.
44.
Metamorphic history of
Variation
lines
Fig.
are
45.
richer in
Na-K
diagram
microcline,
it is
of
of
diagram
data
represent
that
Central
Pyrenees
muscovite-granites;
of sheet
Muscovite-granites
probable
the
they
3
Bosost
are
dashed
Ariege.
area
richer in
and
Ariege (sheet 3)
potassium
and poorer in
sodium.
for
Except
predominates
albite and
low
replacement
Si, Al,
over
of
Na and K all elements show low percentages
potassium,
in
potassium feldspar
mica-schists,
the
mineralogical
contents.
fairly large
composition
If indeed
changes
in
these rocks
chemical
(fig. 44).
resulting
are
Sodium
in
high
produced
composition
are
by
in-
375
Petrochemistry
table
weight percentages
4
131
132
Si0 2
71.50
71.82
Ti0
tr.
tr.
2
p
2
o
A1
2
133
134
73.00
73.05
74.62
74.40
tr.
tr.
tr.
tr.
135
136
Average
73.06
—
5
0.27
0.13
0.13
0.14
0.15
0
14.99
15.90
14.30
13.88
13.80
0.87
0.54
0.40
1.31
0.48
0.53
0.68
0.46
0.07
0.53
0.32
0.65
0.52
0.18
0.24
0.64
0.17
0.21
0.14
0.26
1.13
0.83
1.14
0.98
0.80
0.63
0.91
5.02
5.60
5.18
4.58
5.00
5.11
5.08
4.38
3.98
4.68
4.92
3.82
3.75
4.25
0.67
0.59
0.45
0.78
0.89
0.63
0.66
100.10
100.09
99.99
100.34
100.09
100.33
131
132
133
134
135
Fe 0
2
3
3
FeO
1.09
0.25
0.17
14.24
14.51
MnO
MgO
CaO
Na
0
2
K 0
2
H
2
0
Cation
percentages
130
67.2
66.1
66.5
Si
68.1
Average
69.0
69.5
67.7
Ti
P
0.1
0.1
17.2
15.5
15.2
15.2
15.5
15.9
0.2
0.1
16.4
Al
0.1
0.1
0.1
Fe'"
0.6
0.4
0.3
0.9
0.3
0.4
0.5
Fe"
0.8
0.4
0.1
0.4
0.3
0.5
0.4
Mg
0.2
0.3
0.9
0.2
0.3
0.2
0.4
Ca
1.1
0.8
1.1
1.0
0.8
0.6
0.9
Na
9.0
10.0
9.3
8.3
9.0
9.2
9.1
K
5.2
4.7
5.5
5.8
4.5
4.4
5.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
Analyses
All
rocks
volved.
131—136:
contain
Granites
from Bosost
Silicon and sodium should have
Ti would be
unlikely
in view of the
tion of the schists
is
scale
chemical
changes
With
rocks
are
For the
in
regard
to
different
rest
they
so
by
in
neighbouring schists,
composition
similar
the
are
be introduced and
to
AI, Fe,
Mg,
Ca
and
The destination of these removed elements remains uncertain.
expelled.
That aluminium would be fixed
seems
area,
muscovite.
quartz, albite,
to
that of the
composition
quite
high
similar
phyllites,
have
muscovite-granites
their
like
previously
supposed,
of the sillimanite-schists. Also the
sodium
taken
that it is excluded
place
from sheet 3
content
(fig. 45).
and
during
(Ariège)
low
composi-
that
large
metamorphism.
the Valle de
potassium
Aran
percentage.
376
H.
Zwart:
J.
Metamorphic history of
the
Central
Pyrenees
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