Clays and Clay Minerals, Vol. 44, No. 1, 96-112. 1996.
D I A G E N E S I S A N D M E T A M O R P H I S M OF CLAY M I N E R A L S
IN THE HELVETIC ALPS OF E A S T E R N S W I T Z E R L A N D
HEJING WANG, 1,2 MARTIN FREY, 1 AND WILLEM B. STEr~N1
Mineralogisch-Petrographisches Institut der Universit~it, Bernoullistrasse 30, CH-4056 Basel, Switzerland
2 Present address: Department of Geology, Peking University, Beijing 100871, RR. China
Abstract--Helvetic sediments from the northern margin of the Alps in eastern Switzerland were studied
by clay mineralogical methods. Based on illite "crystallinity" (Ktibler index), the study area is divided
into diagenetic zone, anchizone and epizone. Data on the regional distribution of the following index
minerals are presented: smectite, kaolinite/smectite mixed-layer phase, kaolinite, pyrophyllite, paragonite,
chloritoid, glauconite and stilpnomelane. Isograds for kaolinite/pyrophyllite and glauconite/stilpnomelane
are consistent with illite "crystallinity" zones. Using the ordering of mixed-layer illite/smectite, the
diagenetic zone is subdivided into three zones. The illite domain size distribution was analyzed using the
Warren-Averbach technique. The average illite domain size does not change much within the diagenetic
zone, but shows a large increase within the anchizone and epizone. The average illite bo value indicates
conditions of an intermediate-pressure facies series.
The Helvetic nappes show a general increase in diagenetic/metamorphic grade from north to south,
and within the Helvetic nappe pile, grade increases from tectonically higher to lower units. However, a
discontinuous inverse diagenetic/metamorphic zonation was observed along the Glarus thrust, indicating
5-10 km of offset after metamorphism. In the study area, incipient metamorphism was a late syn- to
post-nappe-forming event.
Key W o r d s - - C l a y mineralogy, Diagenesis, Helvetic Alps, Incipient metamorphism, Switzerland.
INTRODUCTION
are o v e r l a i n b y the P e n n i n i c n a p p e system. T h e M e sozoic s e d i m e n t s m a k i n g up the largest part o f the Helvetic z o n e c o m p r i s e essentially a c a r b o n a t e s h e l f seq u e n c e o f the n o r t h e r n E u r o p e a n margin. In the c o u r s e
o f the A l p i n e collision the P e n n i n i c n a p p e s w e r e thrust
o n t o the H e l v e t i c zone. D u r i n g this process, the r o c k s
o f the H e l v e t i c zone were buried, d e f o r m e d a n d m e t a m o r p h o s e d up to l o w e r g r e e n s c h i s t facies conditions.
T h e H e l v e t i c z o n e o f the area i n v e s t i g a t e d is subd i v i d e d b y the G l a r u s thrust, w h i c h has a d i s p l a c e m e n t
o f up to 4 0 km, into the H e l v e t i c n a p p e s ( a b o v e ) a n d
the Infrahelvetic complex (below). The Helvetic
n a p p e s r e p r e s e n t classic d e t a c h m e n t tectonics, w h e r e a s
the I n f r a h e l v e t i c c o m p l e x is a t h i c k - s k i n n e d fold-andthrust belt, c o r e d b y the A a r m a s s i f b a s e m e n t uplift.
T h e stratigrapbic s e q u e n c e o f the H e l v e t i c z o n e includes P e r m i a n c o n g l o m e r a t e s , Triassic dolomites,
various t h i c k l i m e s t o n e s o f Jurassic a n d C r e t a c e o u s
age a n d Tertiary s a n d s t o n e s that are i n t e r b e d d e d w i t h
various shaly a n d m a r l y horizons. O n top o f the Helvetic S~intis nappe, S o u t h h e l v e t i c units a n d separated
b y the b a s a l P e n n i n i c thrust, several P e n n i n i c klippes
are f o u n d (Figure 1). T h e S o u t h h e l v e t i c units c o m p r i s e
m a i n l y l i m e s t o n e s a n d m a r l s o f U p p e r C r e t a c e o u s to
E o c e n e age. T h e P e n n i n i c klippes consist m a i n l y o f
C r e t a c e o u s N o r t h p e n n i n i c flysch. F o r m o r e detailed inf o r m a t i o n o n the g e o l o g i c e v o l u t i o n o f the H e l v e t i c
zone, the r e a d e r is r e f e r r e d to Trtimpy (1980), Pfiffner
(1986) a n d Pfiffner et al. (1990).
Very l o w - g r a d e m e t a m o r p h i s m o f the H e l v e t i c z o n e
o f eastern S w i t z e r l a n d has b e e n studied b y m a n y an-
D i a g e n e t i c and v e r y l o w - g r a d e m e t a m o r p h i c sedim e n t s are w i d e s p r e a d in external parts o f the Alps
(Frey 1986). Therefore, a n u n d e r s t a n d i n g o f i n c i p i e n t
m e t a m o r p h i s m is i m p o r t a n t to u n r a v e l the tectonot h e r m a l e v o l u t i o n o f such areas. C o n t r a s t i n g m e t h o d s
h a v e b e e n applied to q u a n t i f y the d e g r e e o f i n c i p i e n t
m e t a m o r p h i s m d u r i n g A l p i n e o r o g e n e s i s such as illite
" c r y s t a l l i n i t y , " i n d e x minerals, coal r a n k a n d fluid inclusion data. T h e a i m o f this study is to p r o v i d e n e w
i n f o r m a t i o n o n diagenesis a n d i n c i p i e n t m e t a m o r p h i s m
o f the Helvetic Alps o f eastern S w i t z e r l a n d b a s e d o n
clay m i n e r a l data. B e s i d e s the classical a p p r o a c h u s i n g
illite " c r y s t a l l i n i t y " a n d i n d e x minerals, additional inf o r m a t i o n was o b t a i n e d f r o m the o r d e r i n g o f illite/
smectite m i x e d - l a y e r m i n e r a l s a n d the d o m a i n size o f
illite. I n f o r m a t i o n o n coal rank, b a s e d o n vitrinite reflectance data u s i n g the s a m e s a m p l e s o f the p r e s e n t
study, is g i v e n b y E r d e l b r o c k (1994).
GEOLOGICAL SETTING
T h e study area is located in n o r t h e a s t S w i t z e r l a n d
a n d e x t e n d s f r o m A p p e n z e U in the n o r t h to C h u r in
the s o u t h (45 kin) a n d f r o m L a k e W a l e n in the west
to the R h i n e R i v e r in the east (30 k m ) (Figure 1).
Tectonically the study area b e l o n g s to the H e l v e t i c
zone a l o n g the n o r t h e r n m a r g i n o f the Alps. To the
north, n a p p e s o f the H e l v e t i c z o n e o v e r r i d e the Tertiary clastics o f the a d j o i n i n g M o l a s s e basin, a f o r e d e e p
w h i c h f o r m e d d u r i n g the later stages o f the A l p i n e
collision. To the s o u t h a n d east, the H e l v e t i c n a p p e s
Copyright 9 1996, The Clay Minerals Society
96
Vol. 44, No. 1, 1 9 9 6
Diagenesis and metamorphism of clay minerals in eastern Switzerland
97
Figure 1. Tectonic map of NE Switzerland, modified after Spicher (1980). Marginal numbers refer to the Swiss coordinate
network system. Fb = Flfischerberg, La = Landquart.
thors, using mainly the illite "crystallinity" technique
and index minerals, supplemented by a few virtrinite
reflectance and fluid inclusion data. Frey (1970) noted
a general increase of illite "crystallinity" from the
lower anchizone south of Lake Walen to the epizone
in the parautochthonous cover of the Aar massif. Frey
(1988) found epizonal illite "crystallinities" in the
Verrucano of the lower Helvetic nappes and mid-anchizonal values in the underlying flysch units of the
Infrahelvetic complex. The discontinuous inverse
metamorphic zonation was explained by post-meta-
morphic thrusting along the Glarus thrust. Frey et al.
(1973) and Frey (1987a) mapped index minerals in
glauconite-bearing limestones. A stilpnomelane-in isograd was located in the mid-anchizone and a biotitein isograd at the beginning of the epizone. Frey
(1987b) located the isograd kaolinite + quartz = pyrophyllite + H20, running in a WSW-ENE direction
close to the eastern end o f Lake Walen, and estimated
metamorphic conditions at the isograd from vitrinite
reflectance and fluid inclusion data to be 1.3-2.1 kbar
and 240-270~ at a water activity of 0.6-0.8. Recent-
98
Wang, Frey, and Stern
ly, Erdelbrock et al. (1993) presented a coalification
map of the study area, based on about 450 vitrinite
reflectance values. The thermal maturity was found to
increase from ca. 0.5% R~ in the Subalpine Molasse in
the north to R r ~ > 5 % in the south. Hunziker et at.
(1986) dated the main phase of Alpine metamorphism
at 30-35 Ma, based on concordant K-Ar, 4~
and
Rb-Sr illite ages, while a second age group between
20 and 25 Ma was attributed to movements along the
Glarus thrust.
METHODS
MATERIAL STUDIED. Some 386 samples were analyzed.
Lithologies included - 4 0 % shales and slates, --30%
sandstones, --20% marls and --10% limestones and
marbles. The location of the samples is given in Figure
2. Note the uneven sample density with few samples
west of Sargans and in the southernmost part of the
study area.
SAMPLE PREPARATION. Samples were cleaned with a
steel brush, crushed into small pieces with a hanuner
and - 7 0 g of sample were ground in a tungsten-carbide swing-mill for 30 sec. Carbonate was removed by
treating with 5% acetic acid and by washing with
deionized water. The < 2 ixm fraction was prepared
using differential settling tubes and millipore filters
with 0. I m m pore size. The clay fraction was then Casaturated with 2N CaC12. Oriented slides were prepared by pipetting suspensions onto glass slides (--5
mg/cm 2) and allowing it to air-dry. Glycolated mounts
(for 228 samples) were prepared in a glycol steam bath
at 60~ overnight. Heat-treated mounts (for 48 samples) were prepared in an oven at 375 or 500~ for 1
h. Randomly oriented samples were prepared using the
technique proposed by Handschin and Stern (1989)
and Stern (1991) needing only 20 mg o f material.
Measurements w e r e p e r formed with a Siemens D500 diffractometer, optimized for counting statistics and acceptable resolution
(Table 1).
X-RAY DIFFRACTION (XRD).
DOMAIN SIZE ANALYSIS.The method proposed by Warten and Averbach (1950) and the Scherrer equation
were used to investigate the domain size or the mean
domain thickness. Analyses were performed on XRD
patterns after deconvolution. For the Scherrer equation, the constant K was set at 1.84 for layer-minerals
according to Klug and Alexander (1974, p. 667).
The < 2 t~m fractions
of 41 samples were analyzed using a Guinier-de Wolff
camera for the " 0 6 0 " d-spacing analysis. Measuring
conditions were with FeKct 1 radiation at 36 kV, 20 m A
and with 16 h. exposure time. The films were transformed into diffractograms by use of a CR-650S densitometer.
GUINIER CAMERA X-RAY ANALYSIS.
Clays and Clay Minerals
RESULTS AA~D DISCUSSION
Incipient metamorphism in the study area will be
documented by use of several index minerals and various properties of illite, mixed-layer illite/smectite and
chlorite. Results from illite "crystallinity" will be presented frst, because it will serve as a reference frame
for other indicators of incipient metamorphism.
Illite "Crystallinity"
GENERAL.Illite "crystallinity" (IC) was measured from
X-ray diffractograms of air-dried preparates using the
technique o f Ktibler (1967, 1968). This IC index is
defined as the full width at half maximum intensity
(FWHM) of the first illite basal reflection at around 10
,~, expressed as a difference in 2 0 values. The numerical value of the Kiibler index decreases with improving "crystallinity." Since illite/smectite mixedlayer minerals are abundant in the study area, especially in the diagenetic zone (see below), the measurement
of the F W H M includes both illite and illite/smectite
basal reflections. For simplicity, however, the term IC
will be retained here.
RESULTS. I f was determined on 368 samples. In order
to avoid interfering basal reflections, paragonite- and
pyrophyllite bearing samples from the anchizone were
avoided, but some paragonite-bearing samples showing epizonal IC values were retained. F W H M values
range from 2.50 to 0.16 ~
The regional distribution of IC data is depicted in Figure 2, grouping the
data into four classes using an arbitrarily chosen value
of 0.80 ~
and the limiting IC values of 0.42 and
0.25 ~
for the anchizone. In general, IC improves
southward. The transition from the diagenetic zone to
the anchizone is shown as a 2-3 km broad band limited by two lines labelled 1 and 1'. Line 1 is defined
by the first anchizonal IC values going southward (neglecting three anchizonal values east of Appenzell),
and line 1' is defined by the disappearance of diagenetic IC values (neglecting four data points south of
Sargans). In a similar way, the transition from the anchizone to the epizone is shown as a 2-3 km broad
band limited by two lines labelled 2 and 2'. Line 2 is
defined by the first epizonal IC values going southward (neglecting four epizonal data points further
north, three from the Verrucano and one from the basal
part of the Axen nappe), and line 2' is defined by the
disappearance of anchizonal IC values.
The following tectonic units belong to the diagenetic zone (compare Figures 1 and 2): the Subalpine
Molasse, Penninic and Southhelvetic units as well as
the major part of the underlying Helvetic Santis nappe
(excluding a small area east of Alvier and the Fl~ischerberg east of Sargans). Localities with IC values
>0.8 and 0.8-0.43 ~
are intermixed in the diagenetic zone. The transition from the diagenetic zone to
the anchizone occurs mainly in the lower part of the
Vol. 44, No. 1, 1996
Diagenesis and metamorphism of clay minerals in eastern Switzerland
99
Figure 2. Illite "crystallinity" distribution map. Lines 1 and 1' indicate the transition from the diagenetic zone to the
anchizone. Lines 2 and 2' indicate the transition from the anchizone to the epizone. The two dashed lines 2 and 2' W of
Sargans indicate the transition from the anchizone to the epizone in the Verrucano.
A x e n n a p p e n o r t h e a s t o f the Seez Valley ( b e t w e e n
L a k e W a l e n a n d Sargans). T h i s area is c h a r a c t e r i z e d
b y a strong relief o f a l m o s t 2 km. F u r t h e r to the west,
this b o u n d a r y is located in the M i i r t s c h e n n a p p e southeast o f L a k e Walen. N o r t h - n o r t h e a s t o f Sargans, this
b o u n d a r y is cutting t h r o u g h the Santis thrust, separating S~intis a n d A x e n nappes. T h e f o l l o w i n g tectonic
units o f the study area b e l o n g to the anchizone" the
A x e n n a p p e a n d the V e r r u c a n o southeast o f the Seez
Valley ( F l u m s e r b e r g e ) , A x e n a n d S~ntis n a p p e o f the
Wang, Frey, and Stern
100
Clays and Clay Minerals
Table 1. Instrumental conditions and measurement procedure.
Equipment
Radiation
Slits
Goniometer
Computer
Software
Ka2
IC (Ktibler index)
d001J001of I/S
Domain size
bo
Diffractometer SIEMENS D 500
Cu, 40kV, 30mA, no primary filter
automatic divergence set at 3 ~, slits on primary side 3~ secondary
side 1~ 0.05 and 0.15 ram. Graphite monochromator
routine measurement
cell parameter
low angle
medium angle
high angle low to high angle
2-15~
15-42~
42-48~
5-65~
0.05 ~ increment
0.02 ~
0.02 ~
0.02 ~
30 sec.
1 sec.
10 sec.
10 sec.
Sicomp 32-20 80-386 with internal and external hard discs and CDrom for JCPDS-data
Diffrac AT Version 3.2 by Socabim/Siemens 1986, 1993, JCPDS data
bank system version 2.14. Sets 1-43, PDF-1, 2
not stripped
measured from the unresolved 10 A complex using single peak-op
tion in Diffrac AT
deconvoluted from the 10 A complex for glycolated samples
I/S and illite were deconvoluted using Pearson function for the 10 ,~
complex at air-dried state, the backgrounds were subtracted, no
smoothing operation. The deconvoluted profiles were then transferred to the WlN-CRYSIZE programme (version 1.03, Sigma-C.
1991-1994), from which the average domain size of US and illite,
and the domain size distributions were calculated using the W-A
method. Single crystal of muscovite was used as standard
The background was subtracted first, no smoothing operation, zoom
editing technique was used. At least 20 reflections of illite were
edited and transferred to the WIN-METRIC programme (version
2.0B, Sigma-C. 1991-1994), from which the cell parameters were
refined using the least square method assuming a 2M 1 polytype for
all investigated samples. The tolerances are 0.08-0.05~
rejected
reflections less than 10%
Fl~scherberg, a n d m a j o r parts o f the S a r d o n a flysch,
S o u t h H e l v e t i c units a n d N o r t h H e l v e t i c flysch. T h e
transition f r o m the a n c h i z o n e to the e p i z o n e is located
m a i n l y in the N o r t h H e l v e t i c flysch w e s t o f L a n d q u a r t ,
but further to the w e s t this transition takes place in the
S a r d o n a flysch. E p i z o n a l c o n d i t i o n s are e n c o u n t e r e d
in the p a r a u t o c h t h o n o u s o f the A a r massif, but also in
the V e r r u c a n o n o r t h o f Pizol a b o v e the G l a r u s thrust.
DISCUSSION. IC is d e p e n d e n t o n m a n y variables, including temperature, fluid c h e m i s t r y and pressure,
stress, d u r a t i o n of alteration, illite c h e m i s t r y , interfering basal reflections o f o t h e r p h a s e s and e x p e r i m e n t a l
c o n d i t i o n s (Frey 1987a; Yang a n d H e s s e 1991). Foll o w i n g Ktibler (1967, 1968) it is b e l i e v e d that temperature is the m o s t i m p o r t a n t v a r i a b l e affecting IC in
the study area, b e c a u s e t h e l o w e r a n d h i g h e r a n c h i z o n e
b o u n d a r i e s are subparallel to i s o r a n k lines d e t e r m i n e d
b y vitrinite reflectance ( E r d e l b r o c k 1994).
T h e f o l l o w i n g c o n c l u s i o n s c a n b e d r a w n f r o m the
IC distribution pattern o f F i g u r e 2: 1) P e n n i n i c klippes
in the n o r t h e r n part o f the study area s e e m to h a v e
r e a c h e d a similar stage o f diagenesis as the u n d e r l y i n g
S o u t h h e l v e t i c units a n d the Santis nappe; 2) T h e l o w e r
and h i g h e r a n c h i z o n e b o u n d a r i e s cut t h r o u g h important thrust planes. Therefore, i n c i p i e n t m e t a m o r p h i s m
o c c u r r e d after these t e c t o n i c m o v e m e n t s ; a n d 3) Epizonal c o n d i t i o n s were r e a c h e d in the Verrucano north-
w e s t o f Pizol a b o v e the Glarus t h r u s t b u t a n c h i z o n a l
c o n d i t i o n s exist in the flysch units b e l o w the G l a r u s
thrust. This d i s c o n t i n u o u s i n v e r s e m e t a m o r p h i c zonation is e x p l a i n e d by p o s t - m e t a m o r p h i c t h r u s t i n g a l o n g
the Glarus thrust. T h e s a m e p h e n o m e n o n was already
o b s e r v e d for a n identical tectonic situation 20 k m further to the w e s t (Frey 1988). T h e a m o u n t o f this postm e t a m o r p h i c t h r u s t i n g c a n b e e s t i m a t e d as 5 - 1 0 kin,
c o r r e s p o n d i n g to the d i s t a n c e b e t w e e n the a n c h i z o n e e p i z o n e b o u n d a r y in the V e r r u c a n o west of S a r g a n s
( d a s h e d lines in F i g u r e 2) and the same b o u n d a r y in
the I n f r a h e l v e t i c c o m p l e x . U s i n g vitrinite reflectance
data, E r d e l b r o c k (1994) d e d u c e d an a m o u n t o f 5.5 km.
Chlorite "Crystallinity"
GENERAL. C h l o r i t e 7 A p e a k w i d t h m e a s u r e d u n d e r the
s a m e e x p e r i m e n t a l c o n d i t i o n s as illite 10 * p e a k w i d t h
is u s e d to d e t e r m i n e chlorite " c r y s t a l l i n i t y " (CC). Arkai (1991) p r o p o s e d that C C " c a n b e applied as a reliable regional, statistical t e c h n i q u e c o m p l e m e n t a r y
with, or instead of, the illite crystallinity m e t h o d . "
RESULTS AND DISCUSSION. F i g u r e 3 s h o w s that chlorite
has an e n h a n c e d " c r y s t a l l i n i t y " c o m p a r e d to that o f
illite f r o m the same sample. D u e to the r a t h e r p o o r
correlation b e t w e e n IC a n d CC, the latter was not used
as an i n d i c a t o r o f incipient m e t a m o r p h i s m in this
study.
Vol. 44, No. 1, 1996
Diagenesis and metamorphism of clay minerals in eastern Switzerland
0.7 I
I
v
I
I
n
101
v
N = 105
0.6
"el
eLil
l,,.t
P,.l
eJml
0.5
%d +
=
0.4
I
0.3
o
9
t
~
9
" .'o:
....
0.2
0.1 V
0.1
,
0.2
,
0.3
,
0.4
,
0.5
IC, *A20 CttlK~ (Kiibler
Figure 3.
spection.
,
0.6
I
0.7
Index)
Illite "crystallinity" vs chlorite "crystallinity." The line of equal IC and CC values is indicated for visual in-
Regional Distribution of Index Minerals
SMECTITE. Smectite was identified by the strong 001
reflection at about 15 A on air-dried preparates, shifting to about 17 A after glycolation, and the 002 reflection at about 8.45 ,~. After heating at 500~ for 1
h. these smectite reflections disappeared and the intensity of the first illite basal reflection increased. The
position of the (060) reflection at 1.499 ,~ is indicative
for dioctahedral smectite. Pure smectite was only
found in 3 sandstones and 4 pelitic samples of the
Subalpine Molasse near Appenzell (Figure 4), indicating temperatures <100~ (Velde 1985, p. 115).
KAOLINITE/SMECTITE
MIXED-LAYER
PHASE.
(K/S) was
identified by its characteristic peaks and shoulders at
spacings of 7.43-7.70 ,~ and 3.48-3.53 ,~ after glycolation and by the shift of these peaks after heat treatment at 375~ (Figure 5). In addition, a slightly elevated background was observed between 13-15 ~ 2 0
on glycolated and heat-treated XRD traces. From comparison with calculated diffractograms for the K/S
compositional series (Moore and Reynolds 1989, Ta-
ble 7.5), our K/S are randomly interstratified and contain about 7 5 %- 9 0 % kaolinite layers. K/S was detected in four pelitic samples from the Upper Cretaceous
(Amden shales) and the Lower Tertiary (Globigerina
shales) belonging to the S~intis nappe and Southhelvetic units near the Alpine border (Figure 4).
KAOHNITE. (Kln) was distinguished from chlorite by
resolved reflections at about 25 ~ 2 0 CuKc~. For kaolinite-poor samples containing large amounts of chlorite, an acid treatment with HC1 was used. A few kaolinite occurrences from the study area were already
reported by Briegel (1972) and Burger (1982), and
Frey (1987b) documented two localities containing kaolinite + pyrophyllite in the same sample. In the
course of this study, 29 new kaolinite occurrences
were found (Figure 6) mainly in pelites, marls and
sandstones of the Subalpine Molasse, Penninic and
South Helvetic units and the S~intis nappe. With one
exception, all kaolinite localities belong to the diagenetic zone (compare with Figure 2), while the K l n +
Prl locality at the eastern end of Lake Walen is from
the transition to the anchizone.
102
Wang, Frey, and Stern
Clays and Clay Minerals
730
740
750
I
]
I
250
O smectite
~
Ak Kaolinite/Smectite j l
4~ Paragoni~te/
N
O
240
760
250
5
10km
Appenzell
[]
O
240
230
230
~e w.m_en_:~..V.
220
220
210
210
4t
200
200
190
I
1
730
Figure 4.
740
I
I
750
760
190
Distribution map for smectite, mixed-layer kaolinite/smectite and paragonite.
PYROPHYLLITE. (Prl) was easily identified by its first
three basal reflections. Most of the pyrophyllite occurrences shown in Figure 6 were already documented by Frey (1987b). Three new occurrences of
pyrophyllite were added in this study, two from
Upper Liassic black shales and one from a Middle
Jurassic (Mols fm.) pelitic sandstone, all located
closely together in the lower Axen nappe between
Sargans and Lake Walen. These new findings allow
for a more precise location of the isograd Kin + Qtz
= Prl + H20 in the study area, running from the
eastern end o f Lake Walen in an almost west-east
direction and crossing the S~intis thrust. In terms of
IC data, this isograd is located approximately at
Vol. 44, No. 1, 1 9 9 6
Diagenesis and metamorphism of clay minerals in eastern Switzerland
I
I
I
I
I
I
196-Am69
r
8
o
7.868
\
1
12;259 II
14.118
I
5
9
9
9
3.53~:/ .
3.498
I
3.531 i
4.997
/~
9.904 ^~
9
103
I
I0
9
9
5.196/I 4.742
9
9
I
9
9
9
15
9
I
~/
.
.
.
.
20
Diffraction Angle (~
I
9
9
9
9
25
I
30
9
9
9
9
35
CuK( )
Figure 5. X-ray diffractograms for sample 196-Am69 containing mixed-layer kaolinite/smectite for CuKa radiation.
the transition from the diagenetic zone to the anchizone.
PARAGONITE.(Pg) was identified by its first four basal
reflections. However, the first paragonite basal reflection is only barely visible as a weak shoulder on the
high-angle side of the first illite basal reflection. The
presence of paragonite/muscovite mixed-layer (Pg/Ms)
was identified by two reflections at 4.9 and 3.26 A. 30
occurrences of paragonite, including those of Pg/Ms,
from various stratigraphic and tectonic units are depicted in Figure 4, and comparison with Figure 2
shows that paragonite begins to appear from the beginning of the anchizone.
CHLORITOIO. (Cld) was reported from a single locality
in the study area by Frey and Wieland (1975). This
chloritoid was found in middle Jurassic slates belonging to the parautochthonous cover of the Aar massif
south of the V~ittis window (Figure 6). The growth of
chloritoid postdates the main phase of folding and
thrusting (Calanda phase) in the Infrahelvetic complex
(Pfiffner 1982).
GLAUCONITE.(Glt) was identified under the optical microscope. On XRD traces, glauconite yields a strong
first and a very weak second basal reflection and a
(060) reflection at t.51 i 30 occurrences of glauconite are indicated in Figure 7, mainly from Cretaceous
limestones and sandstones of the Garschella formation
("Gault") of the S~intis nappe. All these occurrences
are restricted to the diagenetic zone.
Frey et al. (1973) described the progressive recta-
104
Wang, Frey, and Stern
Clays and Clay Minerals
Figure 6. Distribution map for kaolinite, pyrophyllite and chloritoid. The isograd Kin + Qtz = Prl + H20 crosses tectonic
nappe boundaries (cf. Figure 1).
m o r p h i s m o f g l a u c o n i t e - b e a r i n g f o r m a t i o n s a n d disting u i s h e d three m e t a m o r p h i c zones in the Glarus Alps.
T h e n e w o c c u r r e n c e s o f glauconite reported in this
study (Figure 7) a l l o w o n e to m a p the z o n e I/II b o u n d ary in s o m e detail, c o r r e s p o n d i n g to the isograd Glt +
Qtz • C h l = Stp + Kfs + H 2 0 + 02. T h e p r e s e n c e
o f n e o f o r m e d K - f e l d s p a r as a p r o d u c t was d o c u m e n t e d
b y Frey et al. (1973).
STILPNOMELANE. (Stp) o c c u r r e n c e s in F i g u r e 7 were alr e a d y d e p i c t e d b y F r e y (1987a, F i g u r e 2.12) but without g i v i n g further details. T h e three o c c u r r e n c e s in the
Vol. 44, No. 1, 1996
Diagenesis and metamorphism of clay minerals in eastern Switzerland
105
Figure 7. Distribution map for glauconite, stilpnomelane and biotite. The isograd for Glt + Qtz + Chl = Stp + Kfs + fluid
is shown as a dashed line parallel to the IC lines of Figure 2.
s o u t h e r n part o f the Santis n a p p e are f r o m C r e t a c e o u s
glauconite b e d s ( A l t m a n n s c h i c h t e n a n d " G a u l t " ) . T h e
n o r t h e r n m o s t o f t h e s e three localities w i t h coexisting
Glt + Stp was first d e s c r i b e d b y O u w e h a n d (1987, p.
162) f r o m a q u a r r y located S W o f R~fis in the R h i n e
valley. Note that these o c c u r r e n c e s o f s t i l p n o m e l a n e
are located in the diagenetic zone, a b o u t 2 - 3 k m
d o w n g r a d e f r o m the b e g i n n i n g o f the a n c h i z o n e , in
a c c o r d a n c e w i t h o b s e r v a t i o n s b y B r e i t s c h m i d (1982)
f r o m the R e u s s Valley, s o m e 7 0 k m further westsouthwest. T h e s t i l p n o m e l a n e o c c u r r e n c e in the A x e n
n a p p e directly n o r t h o f Sargans is f r o m m i d d l e Juras-
106
Wang, Frey, and Stern
I
I
I
I
I
i
g g
103-Mo6
I
10.01
Clays and Clay Minerals
sic iron ore (Niggli and Niggli 1965). The stilpnomelane locality west of the Vattis window is from the
Cretaceous (Lidernenscbichten) of the parautochthonous cover of the Aar massif. The occurrence with Stp
+ Bt at the southern end of the study area was mentioned by Frey et al. (1973, Abb. 3) and is also from
the Cretaceous of the parautochthonous cover of the
Aar massif. Biirgisser and Felder (1974) have shown
that the growth of such epizonal stilpnomelane postdates the main phase of folding and thrusting (Calanda
phase) in the Infrahelvetic complex.
Ordering of Illite/Smectite
GENERAL. Ordering of mixed-layer illite/smectite (US),
interpreted from XRD profiles, correlate with changes
in temperature due to burial depth (Pollastro 1993).
The alternation and position in d-spacing of I/S basal
reflections after glycolation can be used to determine
the different ordering types and percentage of illite in
US (Moore and Reynolds 1989). A reflection at 5 ~
indicates random interstratification (Reichweite -- R =
0), one near 6.5 ~
indicates R1 ordering, and a noticeable peak at angles greater than about 7 ~
suggests long-range ordering, that is R > 1 (Moore and
Reynolds 1989, p. 252).
7.14
10.06
293-Zs15
14.15 /
f74A'60__7_/ 5
I
2
i
6
I
I
10
I
I
14~
Figure 8. X-ray diffractograrns for five representative samples arranged from north (103-Mo6) to south (74-Am60).
Thick lines refer to air-dried patterns, thin lines to glycolated
patterns. The ordering state R of mixed-layer illite/smectite
is indicated. (CuKa radiation).
RESULTS. The Reichweite (ordering type) and the percentage of illite in I/S were determined using the method of Moore and Reynolds (1989) and the computer
program N E W M O D (Reynolds 1985). Representative
diffraction patterns arranged according to diagenetic/
metamorphic grade are shown in Figure 8, and the
calibration curve used to estimate the illite percentage
in I/S is depicted in Figure 9.
In our study area US is abundant in the diagenetic
zone, less abundant in the lower anchizone and not
detectable in the higher anchizone and the epizone.
The ordering type and the illite content in I/S were
determined in 279 samples, and the following four
zones are distinguished (Figure 10):
Zone 1 is defined by the presence of randomly interstratified 1/S (R = 0) with 20-50% illite in US. The
ordering types R = 1 with 50-85% illite in I/S and R
> 1 with > 8 5 % illite in US are also found in this zone.
Zone 1 is present in the NE part of the study area.
Zone 2 is defined by the presence of the US ordering
type R = 1 with 50-85% illite in US and the absence
of the R = 0 type. The ordering type R > 1 with
>85% illite in US is also found in this zone. Zone 2
covers large parts of the Santis nappe, including South
Helvetic units and Penninic klippes.
Zone 3 is defined by the presence of the US ordering
type R > 1 with 85-90% illite in US and the absence
of the R = 1 type. The ordering type R > 1 with
>90% illite in US is also found in this zone. Zone 3
comprises the SE part of the S~intis nappe, a major
Vol. 44, No. 1, 1 9 9 6
Diagenesis and metamorphism of clay minerals in eastern Switzerland
100
~
80
~I
60
107
Ledbetter 1993). In the present study, the Warren-Averbach technique is used to measure illite domain size.
40
10
11
12
13
14
d(001)1o/(001)17 (/~) spacing of I/S
after glycolation
Figure 9. Calibration curve used to estimate the illite percentage in mixed-layer illite/smectite. The curve is valid for
"dimica (1 Fe, 0.7 K) mixed with trismectite (1 Fe, 2 gly)"
using the terminology of NEWMOD (Reynolds 1985).
part of the Axen nappe northeast of the Seez valley,
and the Miirtschen nappe N of Lake Walen.
Zone 4 is defined by the presence of the US ordering
type R > 1 with >90% illite in US and the absence
of the other ordering types mentioned above. Zone 4
is mainly found in the Axen nappe N and N W of Sargans, the Fl~ischerberg, the MiJrtschen nappe SE of
lake Walen, and in the Infrahelvetic complex S and SE
of Sargans.
DISCUSSION. Zones 1-3 mentioned above are covering
the diagenetic zone as defined by IC data. In other
words, ordering L of US is a more sensitive indicator
of diagenetic grade than IC.
As recently reviewed by Pollastro (1993), the
changes in ordering of US may be used as a reliable
semiquantitative geothermometer. However, in zones
1-3 described above different ordering types were
found, presumably due to lithologic control and the
presence of detrital clay minerals. Therefore, this geothermometer cannot be applied in our study area.
Domain Size of Illite in the C-direction
GENERAL. XRD line broadening is caused by the coherent crystalline domain size or crystallite size, lattice
strain and instrumental factors (Klug and Alexander
1974, p. 618). The domain size of clay minerals may
be used as an indicator of incipient metamorphism
(Eberl et al. 1990). At least six methods exist separating the domain size from the general XRD line broadening (Scherrer 1918; Stokes 1948; Warren and Averbach 1950; Ergun 1968; Langford 1978; Balzer and
RESULTS. Line profiles of the first illite basal reflection
obtained after deconvolution were analyzed on airdried specimens by the Warren-Averbach method for
35 samples. In general, the position of the maximum
frequency position increases and domain size distributions spread out as diagenetic/metamorphic grade
increases. In the study area, the mean domain size of
illite increases from 11 nm in the north to 145 nm in
the south, with a major change occurring between km
210 and km 190 of the Swiss coordinate system. With
respect to illite "crystallinity," the illite average column length does not change much within the diagenetic zone, but shows a large increase within the anchi- and epizone (Figure 11).
The domain size of illite/smectite was also measured with the Warren-Averbach method, and it was
always found to be thinner than that of accompanying
illite. I/S domain size increases from 7 nm in the North
to 34 nm in the South, therefore showing the same
general tendency as illite.
DISCUSSION. Assuming the presence of strain-free illite,
the Scherrer equation was also used to calculate the
mean domain size of illite. A range from 7 to 97 nm
was obtained, compared with 11-145 nm by the Warren-Averbach method. This difference may be explained by the fact that the Scherrer equation does not
take account of the strain effects. Furthermore, the
Warren-Averbach technique is model-dependent and
will not correspond to a real distribution of grain sizes
of natural clays that may preserve strain across semicoherent packets, as discussed by Lanson and Ktibler
(1994).
Eberl et al. (1990) analyzed the particle thickness
distributions for 20 anchizonal and epizonal illites
from shales from the Glarus Alps, located directly in
the West of our study area. The general shape of particle thickness distribution curves obtained was similar
to those derived in this study, and it was concluded
that these illites underwent recrystallization by Ostwald ripening. However, these authors reported smaller illite average column length values than obtained
for illites of comparable grade in this study; e.g., <35
nm (Eberl et al. 1990) vs 100--145 nm (this study) for
epizonal illites. More work is needed to explain this
discrepancy.
Most recently, Warr and Rice (1994) proposed illite
domain (crystallite) sizes of 23 for the lower and 52
nm for the upper limit of the anchizone determined by
the Warren-Averbach method. These values are much
smaller than the limiting values of about 50 and 100
nm determined in this study. It should be mentioned
that Warr and Rice (1994) were using glycolated specimens for the domain size analyses but made a correlation with illite "crystallinity" determined on air-
108
Wang, Frey, and Stern
730
I
250
Clays and Clay Minerals
740
750
l
I
* R=0
760
11
,
250
10km
5
[] R = I
O
R>I, 85-90% I in I / S
R>I, >90% I in I / S
AppenzeU
[]
|
240
240
N
O
230
-
220-
~
~
- 220
210
200 d
210
"~I
]
,,-.~_
~J
~
; \ ~ 200
J
190
I
730
I
740
I
750
-
"
I
190
760
Figure 10. Distribution map for different ordering types of mixed-layer illite/smectite and percentage of illite in US. These
data allow for a four-fold zonation as discussed in text.
dried specimens. In addition, the correlation proposed
by these authors is based on four specimens only. The
authors of this article feel that much more experience
is needed with domain size analyses and that the limiting values of Warr and Rice (1994) should be regarded with caution.
Chlorite Polytypes
GENERAL. During late diagenesis and incipient metamorphism a change in the polytype of trioctahedral
chlorite is observed. Hayes (1970) proposed that the
polytype transformation sequence Ibd --->Ib 03 = 97 ~
Vol. 44, No. 1, 1 9 9 6
Diagenesis and metamorphism of clay minerals in eastern Switzerland
I
2.5
I
109
I
2.0
m
1.5
Qo
N
m
1.0
oo
r
0.5
9
N
u
<1
o
0.0
0
u
w
0
9
Anchizone
i
I
I
50
100
150
200
Illite Average Column Length (urn)
Figure 1I.
Variation of illite domain size or illite average column length vs illite "crystallinity" (Kiibler index).
-~ Ib (~ = 90 ~ --~ lib (13 = 97 ~ occurs in chlorites in
sedimentary rocks with increasing temperature, and
that the final transformation from type-I to type-II
chlorite requires a temperature of about 150-200~
However, as recently reviewed by Walker (1993), other factors including grain size of the host rock, may
be at least as important as temperature in controlling
the stability of type-I chlorite polytypes. In addition,
systematic studies suggest that type-II chlorite is stable
at temperatures well below 200~ and that it can form
as the initial chlorite phase without passing through
any intermediate polytypic stages (Walker 1993).
RESULTS. Chlorite polytypes were determined on 19
chlorite-rich samples following the methods proposed
by Bailey (1988) and Moore and Reynolds (1989). Interference with illite reflections were stripped by using
deconvolution technique. For 12 samples from the diagenetic zone (5 sandstones, 4 pelites and 3 limestones), exclusively the Ib (13 = 90 ~ polytype was
found, while in 7 pelites and marls from the anchizone
and epizone only the IIb chlorite polytype was present.
DISCUSSION.If compared to other indicators of incipient
metamorphism in the study area, the simple chlorite
polytype distribution pattern seems to follow the observations made by Hayes (1970), for example the Ib
([3 = 90 ~ chlorite polytype of the diagenetic zone is
followed by the IIb polytype in the anchizone and epizone. Therefore, the chlorite polytype conversion in
the study area appears to be controlled mainly by temperature.
bo of illite
GENERAL. The bo cell parameter of muscovite or illite
may be used as a semiquantitative geobarometer for
epizonal (Sassi and Scolari 1974) or upper anchizonal
(Padan et al. 1982) shales and slates. This geobarometer is based on two observations: 1) the celadonite
content of potassic white mica increases with increasing pressure (if temperature is held constant); and 2)
there exists a positive correlation between the bo parameter and celadonite content. Although this barometer uses unbuffered assemblages lacking K-feldspar,
it has been successfully applied in many field areas.
Therefore, the statement by Essene (1989) that "it
seems prudent to avoid the use of Sassi's phengite barometer for thermobarometry" seems not justified.
RESULTS. The bo parameter is usually determined
through the measurement of the d(060) spacing. If randomly oriented preparates are used for that purpose,
as was attempted in this study, then the (060) peak is
overlapped and obscured by the (531) peak and additional weak reflections. In order to test the reliability
of our bo determinations through the measurement of
illite d(060, 331) values, the bo cell dimension was
also calculated from a unit cell refinement using at
least 20 reflections. Results of this comparison for 33
samples ranging in grade from the diagenetic zone to
the epizone show a rather good linear correlation (Figure 12). bo values calculated from d(060, 531) are
slightly smaller than bo values obtained from unit cell
refinement, with a maximum deviation of 0.015 _~.
110
Wang, Frey, and Stern
I I I /j
,-,
Y = 0.28521 + 0.96883x
*~
R^2 =0.897
'.,./
9.03
i ~ '
9.05
100
Clays and Clay Minerals
I
N--34
I/
I
8.98
I
9.00
I
.I
I
80 -
9.01
240
~
8.99
'
Vertical error
bar=2~
_
~ ' ~ T
~/~
0
N=33
8.96
8.97
8.97
I
i
i
8.99
9.01
9.03
Figure 12. bo values calculated from d(331, 060) vs bo values calculated after least-square refinement. The thick line
refers to correlated data, the thin line is the equal data line.
This result is to be expected because the (531) peak
has a smaller d-value than the (060) peak (e.g., Borg
and Smith 1969). In conclusion, for illite bo-geobarometry using randomly oriented preparates, the bo par a m e t e r m a y be calculated from the relation bo = 6 •
d(060, 331) with some confidence.
The d(060, 531) values for 32 illites (including illite/smectite mixed-layer) from the Santis nappe range
from 1.495-1.503 ~ (mean value 1.499 A), for 12
lower anchizonal illites range from 1.500-1.506
(mean value 1.502 A), and for 18 upper anchizonal
and 4 epizonal illites range from 1.499-1.506 ,~ (mean
value 1.501 A).
oISCUSSIO~, b o or d(060, 531) of illite increases in the
study area with grade during incipient metamorphism,
in accordance with results reported by Padan et al.
(1982) and Yang and Hesse (1991). The bo parameter
increases with an increasing replacement of A1 by Fe
+ Mg in the octahedral layer and K in the interlayer
position (Radoslovich and Norrish 1962; Hunziker et
al. 1986). The general decrease of expandable layers
in illite/smectite from north to south means a concomitant increase of K, but whether Fe + Mg are also
increasing is not known.
Because lower and upper anchizonal illites of the
study area yielded almost identical b o values, lower
anchizonal samples were included in bo geobarometry.
A cumulative frequency plot of bo values for anchiand epimetamorphic samples indicates conditions of
an intermediate-pressure facies series as for northern
New Hampshire (Figure 13). The mean bo value of
9.010 A obtained for the southern part of the study
I
9.04
9.06
9.08
White K-Mica bo (/~)
9.05
"bo", calculated from d(0~,~31) (•)
I
9.02
Figure 13. Cumulative frequency curve of illite bo values
for 34 anchizonal and epizonal samples (thick line). Reference curves (thin lines) are from Sassi and Scolari (1974).
area is very similar to the 9.013 A reported by Frey
(1988) for North Helvetic flysch from the adjacent
Glarus Alps.
Correlation Between Indicators of Incipient
Metamorphism
The mineral distribution with increasing grade is
summarized in Figure 14. The presence of smectite in
the Subalpine Molasse at vitrinite reflectance <0.6%
Rmax (Erdelbrock 1994) indicates diagenetic zone 2
of Kiibler et al. (1979). Kaolinite is a typical index
mineral of the diagenetic zone, and the isograd Kin +
zones
Diagenetie
zone
Anchizone
R=0,1 and >1
illitein I/S:0-90%
11 - 50 (nm)
R>I
Ulite in I/S:85-100%
8,993 (,~)
9.009 (~)
Epizone
Glauconite
Stilpnomelane
Biotite
Smectite
Kaolinite/Smectite
Kaolinite
Pyrophyllite
Paragonite
Chloritoid
Illite/Smectite
Illite Domain Size
Illite bo
32 - 99
(nm)
>99 (nm)
Figure 14. Summary of indicators of diagenesis and incipient metamorphism for the Helvetic Alps of eastern Switzerland. The distribution of index minerals and various properties of mixed-layer illite/smectite and illite are plotted against
grade as defined by illite "crystallinity" data.
Vol. 44, No. 1, 1996
Diagenesis and metamorphism of clay minerals in eastern Switzerland
Qtz = Prl + H 2 0 is located at the b e g i n n i n g o f the
a n c h i z o n e (Figures 2 a n d 6). P h y s i c a l c o n d i t i o n s for
two localities a l o n g this isograd (Figure 6, stations
with Kin + Prl) were e s t i m a t e d as 2 4 0 - 2 6 0 ~
kbar
b a s e d o n coal r a n k and fluid i n c l u s i o n data (Frey
1987b). P a r a g o n i t e is w i d e s p r e a d in the a n c h i z o n e and
epizone. Glauconite-bearing sandstones and limestones are w i d e s p r e a d in the d i a g e n e t i c zone, a n d the
isograd Glt + Q t z • C h l = Stp + Kfs + fluid is
located in the u p p e r m o s t d i a g e n e t i c zone.
Several properties of m i x e d - l a y e r illite/smectite a n d
illite are also useful indicators o f i n c i p i e n t m e t a m o r p h i s m . T h e o r d e r i n g type or R e i c h w e i t e o f US c h a n g e s
f r o m R = 0 to R > 1, a l t h o u g h different o r d e r i n g types
w e r e f o u n d w i t h i n a restricted area. N e v e r t h e l e s s this
a l l o w e d to d i s t i n g u i s h four z o n e s with different R values a n d illite c o n t e n t s in US, a n d three o f t h e s e z o n e s
a l l o w e d a s u b d i v i s i o n o f the diagenetic z o n e as defined
b y illite " c r y s t a l l i n i t y . " Illite d o m a i n size generally
i n c r e a s e s w i t h i n c r e a s i n g grade, a n d l i m i t i n g values o f
50 a n d 100 n m w e r e d e t e r m i n e d for the l o w e r and
u p p e r b o u n d a r i e s o f the a n c h i z o n e .
R e g i o n a l Significance
T h r e e m a i n tectonic features o f the study area are
the G l a r u s thrust, the S~ntis thrust a n d the b a s a l Penninic thrust. In this section, p o s s i b l e b r e a k s in diagenetic or m e t a m o r p h i c grade across these thrusts will
b e discussed.
T h e p r e s e n c e o f d i o c t a h e d r a l s m e c t i t e in the Subalpine M o l a s s e a n d its a b s e n c e in similar lithologies
o f the Santis n a p p e indicates a h i g h e r diagenetic grade
for the u p p e r tectonic unit (Figure 1). S u c h a b r e a k in
g r a d e was also o b s e r v e d b y E r d e l b r o c k (1994) b a s e d
o n vitrinite reflectance data: R m a x < 0.6% for the
Subalpine Molasse around Appenzell and Rmax >
1.3% for the a d j a c e n t S~rltis nappe. U s i n g the termin o l o g y o f Kiibler et al. (1979), the S u b a l p i n e M o l a s s e
b e l o n g s to the diagenetic z o n e 2 w h e r e a s the S~intis
n a p p e b e l o n g s to zones 3 a n d 4. Obviously, the h i g h e r
g r a d e SSaatis n a p p e dislocated a l o n g the G l a r u s thrust
o v e r the S u b a l p i n e M o l a s s e c a u s i n g a d i s c o n t i n u o u s
i n v e r s e d i a g e n e t i c zonation.
T h e Helvetic n a p p e s show a general i n c r e a s e in diag e n e t i c / m e t a m o r p h i c grade f r o m n o r t h to south, m a i n ly d o c u m e n t e d by the r e g i o n a l distribution o f various
i n d e x minerals, illite " c r y s t a l l i n i t y " data, the overall
d i m i n u t i o n o f e x p a n d a b l e layers and the o r d e r i n g o f
illite/smectite. W i t h i n the H e l v e t i c n a p p e pile, grade
increases f r o m tectonically h i g h e r to l o w e r units. T h i s
is b e s t d o c u m e n t e d in the A l v i e r - S a r g a n s - l a k e W a l e n
area by vitrinite reflectance data ( E r d e l b r o c k 1994),
b u t is also s u p p o r t e d b y IC data (Figure 2) a n d the
Kin ~ Prl c o n v e r s i o n (Figure 6). A s m e n t i o n e d earlier,
the d i a g e n e s i s / a n c h i z o n e b o u n d a r y as well as the iso g r a d s K i n + Qtz = Prl + H 2 0 a n d Glt + Q t z • C h l
= Stp + Kfs + fluid a l m o s t c o i n c i d e in the s t u d y area,
111
a n d are c r o s s i n g n a p p e b o u n d a r i e s , i n c l u d i n g the Shntis thrust, thus indicating that i n c i p i e n t m e t a m o r p h i s m
was a late syn- to p o s t - n a p p e - f o r m i n g event.
F u r t h e r to the south, in the Pizol area, IC data indicates a d i s c o n t i n u o u s i n v e r s e m e t a m o r p h i c z o n a t i o n
across the G l a r u s thrust, separating the V e r r u c a n o f r o m
the Infrahelvetic c o m p l e x , with s o m e 5 - 1 0 k m o f postm e t a m o r p h i c thrusting. T h i s feature is in a c c o r d a n c e
w i t h the d i s c o n t i n u o u s i n v e r s e d i a g e n e t i c z o n a t i o n
near the A l p i n e b o r d e r m e n t i o n e d above.
A v a i l a b l e data f r o m this study a n d E r d e l b r o c k
(1994) s h o w no d i f f e r e n c e in diagenetic grade b e t w e e n
the S~intis n a p p e a n d P e n n i n i c klippen, i n d i c a t i n g n o
b r e a k in diagenetic grade across the b a s a l P e n n i n i c
thrust, a n d thus a c o m m o n late diagenetic h i s t o r y for
these tectonic units.
ACKNOWLEDGMENTS
Most samples used in this study were collected by Kersten
Erdelbrock. The first author is grateful to Josef Mullis for his
help during field investigations and additional sample collections. Reynald Handschin guided with the preparation of randomly oriented sample. Michael Dalla Torre and Meinert
Rahn provided additional help, Dennis D. Eberl and Eric Essene kindly reviewed the manuscript and improved the English. The first author was supported by Basel University.
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(Received 15 November 1994; accepted 12 June 1995; Ms.
2594)