GeolCarp_Vol60_No4_319

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA, AUGUST 2009, 60, 4, 319—329 doi: 10.2478/v10096-009-0023-2

Introduction

The  orogenic  evolution  of  the  Eastern  Alps  was  driven  by
two  collisional  events  that  occurred  during  Cretaceous  and
Paleogene times (Froitzheim et al. 1996; Genser et al. 1996).
Both  events  were  followed  by  orogen-parallel  extension
which resulted in the exhumation of deeper crustal rocks to
higher crustal levels (e.g. Neubauer et al. 1995).

Subsequent to the early Late Cretaceous closing of the

Meliata Ocean (e.g. Schmid et al. 2004), the newly formed
Eoalpine  nappe  stack  collapsed  during  Late  Cretaceous  to
Paleogene  times  and  formerly  deeply  buried  metamorphic
rocks of the Austroalpine units were exhumed (Neubauer et
al.  1995;  Bojar  et  al.  2001;  Kurz  &  Fritz  2003;  Tencer  &
Stüwe 2003; Robl et al. 2004; Wiesinger et al. 2006; Krenn
et al. 2008). The reconstruction of the metamorphic pattern
in  this  tectonic  setting  is  hampered  by  the  fact  that  meta-
morphic  index  minerals  are  very  often  missing.  However,
the hanging wall units of Late Cretaceous to Paleogene de-
tachments are formed partly by metasediments containing a
significant  amount  of  organic  matter.  This  enables  the  ap-
plication of the “Raman spectroscopy of carbonaceous ma-
terial”  (RSCM)  thermometer  (Beyssac  et  al.  2002a,b)  to
separated organic materials (Rantitsch et al. 2004) as a sim-
ple  technique  to  determine  metamorphic  gradients.  Using
this  approach,  Rantitsch  et  al.  (2004,  2005)  proposed  that
low- to very low-grade metamorphic hanging wall units at
the  eastern  segment  of  the  Eastern  Alps  (Graz  Paleozoic
and  Eastern  Greywacke  Zone,  see  Fig. 1),  tectonically
overlying  decompressed  middle-  to  high-grade  metamor-
phic rocks, were overprinted by advective heat and convec-
tive fluids during Late Cretaceous to Paleogene times.

By the Eocene collision of the European Plate with the

Apulian Plate (e.g. Kurz et al. 1998, 2001; Kurz 2006), the

Alpine metamorphism in the central segment of the Western

Greywacke Zone (Eastern Alps)

GERD RANTITSCH

and KATALIN JUDIK

Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner Straße 5, A-8700 Leoben, Austria;

gerd.rantitsch@unileoben.ac.at

Institute for Geochemical Research, Hungarian Academy of Sciences, Budaörsi út. 45, H-1112 Budapest, Hungary; judik@geochem.hu

(Manuscript received July 17, 2008; accepted in revised form December 18, 2008)

Abstract: The metamorphic pattern of the central Western Greywacke Zone (Austroalpine, Eastern Alps) was investi-
gated by organic matter reflectance, Raman spectroscopy on organic matter and clay mineralogical methods. Raman
data map a 10 km wide thermal aureole along the contact zone of the Greywacke Zone to the Penninic Tauern Window.
The estimated maximum temperatures of 400 °C to 200 °C decrease from South to North, that is from the contact to the
uppermost parts of the Greywacke Zone. This pattern is explained by an Oligocene to Miocene thermal pulse, related to
the rapid exhumation of formerly deeply buried rocks of the Penninic unit. During this event, advective heat transport
and circulating fluids overprinted the Cretaceous higher anchi- to lower epizonal metamorphic pattern of the central
Western Greywacke Zone.

Key words: Eastern Alps, Greywacke Zone, Raman spectroscopy, organic matter, illite Kübler index.

Austroalpine  tectonic  units  were  thrusted  over  the  Penninic
nappes.  During  subsequent  exhumation  of  the  Penninic
rocks,  the  Tauern  Window  (Fig. 1)  was  formed  (e.g.  Frisch
et al. 2000).

This study focuses on the metamorphic imprint on a N-S-sec-

tion across the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP)
Fault  Zone,  representing  the  northern  margin  of  the  Tauern
Window (Fig. 1). The study area covers the central Western
Greywacke Zone, an Austroalpine tectonic unit directly adja-
cent to the tectonically lower Penninic unit (Fig. 1). Because
this  unit  is  composed  of  metasediments,  lacking  metamor-
phic index minerals, the RSCM thermometer is used to esti-
mate metamorphic peak temperatures. The reaction progress
of organic and inorganic temperature indicators are different
(e.g. Hillier et al. 1995; Sachsenhofer et al. 1998). Therefore,
clay  mineralogical  data  are  discussed  together  with  the
RSCM data. The obtained data constrain the thermal effects
during the exhumation stage of the Penninic units and dem-
onstrate  the  significance  of  advective  heat  transport  during
late-stage orogenic processes within the Eastern Alps.

Geological setting

The studied section cuts the contact between the Penninic

Tauern Window and the Austroalpine nappe pile, represent-
ed by the central Western Greywacke Zone and the Northern
Calcareous Alps (Fig. 1). The exposed crustal section result-
ed from the subduction of the Penninic Ocean (e.g. Schmid
et al. 2004) and the subsequent Eocene continent-continent-
collision of the European lower plate with the Apulian upper
plate  (e.g.  Kurz  et  al.  1998,  2001;  Kurz  2006).  The  present
contact  between  those  units  is  represented  by  the  SEMP
Fault  Zone  (Ratschbacher  et  al.  1991;  Linzer  et  al.  1997;

320

RANTITSCH and JUDIK

Fig. 1. Location of the study area and sample localities (white circles; for the coordinates see the Appendix) within the Eastern Alps (sim-
plified geological map and section after Pestal et al. 2005 and Heinisch et al. 1995, 2003).

321

ALPINE METAMORPHISM OF THE WESTERN GREYWACKE ZONE (EASTERN ALPS)

Wang  &  Neubauer  1998;  Neubauer  et  al.  1999;  Cole  et  al.
2007;  Rosenberg  &  Schneider  2008),  active  since  the  Late
Eocene/Oligocene (Urbanek et al. 2002) during exhumation
of the Penninic Tauern Window in a sinistral wrench corri-
dor (Ratschbacher et al. 1989; Peresson & Decker 1997; Rei-
necker & Lenhardt 1999; Frisch et al. 2000). This brittle to
ductile (Cole et al. 2007; Rosenberg & Schneider 2008) fault
zone  separates  the  low-grade  metamorphic  (Hoinkes  et  al.
1999) rocks of the central Western Greywacke Zone from for-
merly  deeply  buried  greenschist-  to  eclogite-grade  metamor-
phic rocks of the Penninic Tauern Window. In a N-S section,

Ar/

Ar age data from fine white mica fractions decrease

from 113—120 Ma (Frank & Schlager 2006) in the Mesozoic
cover of the Greywacke Zone (Northern Calcareous Alps) to
90—115 Ma  in  the  Greywacke  Zone  (Urbanek  et  al.  2002)
and 28—35 Ma at the northern margin of the Tauern Window
(Urbanek et al. 2002). This indicates a dominant Cretaceous
(Aptian to Cenomanian) tectono-metamorphic imprint of the
Greywacke Zone (Frank & Schlager 2006) succeeded locally
by  a  tectonothermal  event,  causing  partial  reset  of  the  Ar
geochronometer  in  latest  Eocene  to  Oligocene  times  along
the  contact  between  the  Greywacke  Zone  and  the  Penninic
units in the Tauern Window.

In the study area, the Penninic unit comprises from bottom

to top, the Venediger Nappe (a Subpenninic nappe according
to  Schmid  et  al.  2004),  the  Glockner  Nappe  (a  Lower  Pen-
ninic nappe according to Schmid et al. 2004) and the Klam-
mkalk Zone (part of the Upper Penninic nappes according to
Schmid  et  al.  2004).  The  Venediger  Nappe  is  composed  of
crystalline rocks intruded by Variscan granitoides (“Zentral-
gneis”)  and  partly  covered  by  post-Variscan  metasediments
of  Carboniferous  to  Cretaceous/Paleogene  age  (e.g.  Frisch
1980).  The  Glockner  Nappe  and  the  Klammkalk  Zone  are
composed mainly by calcareous schists (“Bündner Schiefer”)
of the former Penninic Ocean (e.g. Frisch 1980).

The polyphase metamorphic evolution of the central Pen-

ninic unit (e.g. Frank et al. 1987; Hoinkes et al. 1999; Kurz
et al. 2001) resulted in a north-to-south increase (Frank et al.
1987)  of  the  Eocene/Oligocene  greenschist  to  amphibolite
facies metamorphic overprint (“Tauern event”). In the Vene-
diger  Nappe  peak  temperatures  are  about  500—550 °C  (e.g.
Hoinkes  et  al.  1999;  Schuster  et  al.  2004)  at  ca.  30 Ma,
whereas cooling below 300 °C occurred at 25—30 Ma in the
central  part  of  the  Venediger  Nappe  (Handy  &  Oberhänsli
2004).  At  the  northern  margin  of  the  Tauern  Window,  the
metamorphic peak reached lower- to upper greenschist facies
(380  to  400 °C;  Frank  et  al.  1987;  Dingeldey  et  al.  1997;
Bousquet et al. 2008), 28—35 Ma (

Ar/

Ar fine white mica

fractions age data from Urbanek 2001; see also Ratschbacher
et  al.  2004)  ago.  Subsequent  cooling  during  Early  to  Late
Miocene  (23—13 Ma)  extensional  related  exhumation
(Ratschbacher et al. 1989; Frisch et al. 1998, 2000; Liu et al.
2001;  Glodny  et  al.  2008)  is  recorded  by  fission  track  data
(Grundmann & Morteani 1985; Staufenberg 1987; Dunkl et
al.  2003).  According  to  Kuhlemann  et  al.  (2001),  at  17 Ma
the exhumation rate was accelerated for a short time interval
(1  to  1.5 Myr)  from  1.5—2 mm/yr  to  5 mm/yr.  During  the
Middle  Miocene  (14—10 Ma)  the  Penninic  rocks  were  al-
ready exposed to the surface (Frisch et al. 2000).

The Western Greywacke Zone comprises Ordovician to

Mississippian  (Ebner  et  al.  2008)  metasediments  and  basic
volcanics  (Heinisch  et  al.  1987)  of  several  tectonic  units
(Wildseeloder  Unit,  Hochhörndler  Imbricate  Zone,  Glem-
mtal Unit, Uttendorfer Imbricate Zone; Heinisch et al. 1995,
2003; Fig. 1). This sequence is overlain by Permian to Lower
Triassic  clastics  and  Triassic  to  Lower  Cretaceous  carbon-
ates of the Tirolian Nappe System of the Northern Calcare-
ous Alps (Fig. 1). In the Greywacke Zone, illite Kübler index
data  (Schramm  1980,  1982;  Kralik  et  al.  1987;  Kralik  &
Schramm  1994)  indicate  a  Cretaceous  (Kralik  1983;  Kralik
&  Schramm  1994;  Urbanek  et  al.  2002;  Frank  &  Schlager
2006; Schmidlechner et al. 2006) epizonal metamorphic im-
print.  According  to

Ar/

Ar age data, synkinematically

grown muscovite flakes record the metamorphic peak at 98
to 102 Ma and also give evidence for a second metamorphic
event  at  ca.  70 Ma  (Schmidlechner  et  al.  2006).  The  later
event  may  be  explained  by  an  advective  heating  during  ex-
humation of the underlying Austroalpine metamorphic com-
plexes  (Schmidlechner  et  al.  2006).  In  the  vicinity  of  the
SEMP Fault Zone, a rejuvenation of the Cretaceous

Ar/

age  data  to  Early  Oligocene  (28—35 Ma)  ages  (Urbanek
2001;  Urbanek  et  al.  2002)  suggests  a  thermal  overprint  of
the  southern  segment  of  the  Greywacke  Zone  during  exhu-
mation of the underlying Penninic unit.

Samples and methods

The investigated section is covered in the Greywacke

Zone  by  22  samples  of  black  slates,  lydites  and  siltstones.
One  calcareous  slate  sample  was  taken  in  the  Penninic  unit
(Fig. 1,  Appendix).  Only  samples  without  microscopic  evi-
dence of oxidation were analysed.

On sections cut perpendicular to the foliation, the rank of

organic  maturation  was  determined  by  measurement  of  the
maximum  and  minimum  organic  matter  reflectance  (Rmax,
Rmin)  under  oil  immersion  in  polarized  light  at  a  wave-
length of 546 nm.

Samples were cleaned, crushed and disaggregated by slight

grinding in an agate mortar for one minute. Because the Ra-
man  spectra  of  carbonaceous  material  (CM)  are  strongly  af-
fected  by  disorder  due  to  friction,  samples  for  Raman
microspectrography  are  separated  using  a  hydrochloric  and
hydrofluoric acid-treatment. Raman spectra were acquired by
using  a  Dilor  confocal  Raman  spectrometer  equipped  with  a
frequency-doubled  Nd-YAG  laser  (100 mW,  532.2 nm)  and
diffraction  gratings  of  1200  and  1800  grooves/mm.  Detec-
tion  is  with  a  Peltier-cooled,  slow-scan,  CCD  matrix-detec-
tor.  Laser  focusing  and  sample  viewing  are  performed
through  an  Olympus  BX  40  microscope  fitted  with  a  50

long-working distance objective lens. To obtain a better sig-
nal to noise ratio five scans with an acquisition time of 30
sec in the 700—2000 cm

—1

(first-order) and 2200—3200 cm

—1

(second-order) region are summed to a composite spectra. On
each sample, five composite spectra were recorded on differ-
ent measurement spots. We focus on the first-order peaks at
~ 1350 cm

—1

(D1 band), ~ 1580 cm

—1

(G band), ~ 1610 cm

—1

(D2 band), and ~ 1500 cm

—1

(D3 band), and on the second-

322

RANTITSCH and JUDIK

order peaks at ~ 2700 cm

—1

(S1 band), ~ 2400 cm

—1

and

~2900 cm

—1

(S2 band). Peak position, band area and band

width  (full  width  at  half  maximum,  FWHM)  of  these  peaks
were  determined  using  the  computer  program  Labspec  2.08
(Dilor SA). Decomposition of the spectra was attained by fit-
ting  a  combination  of  Gaussian  and  Lorentzian  functions  to
the recorded data.

X-ray powder diffractometric (XRPD) patterns were ob-

tained using a Philips PW-1730 diffractometer (with com-
puterized APD system) with the following instrumental and
measuring conditions: CuK

α radiation, 45 kV/35 mA, pro-

portional counter, graphite monochromator, divergence and
detector slit of 1°, and collection of data with 0.01 and 0.02°
2

Θ steps, using time intervals of 1 and 5 s, respectively. Dif-

fraction  patterns  were  performed  from  non-orientated  and
highly orientated powder mounts of whole rock and  < 2 µm
spherical equivalent diameter (SED) size fraction samples in
order to determine bulk-rock mineral assemblages, b cell di-
mension,  and  illite  Kübler  indices  (KI,  see  Guggenheim  et
al.  2002).  The  < 2 µm  grain  size  fraction  samples  were  ob-
tained  using  the  following  procedure.  Rock  samples  were
disaggregated under standard conditions using a jaw crusher
followed by crushing in a mortar mill for 3 min. Further dis-
aggregating  was  achieved  by  repeated  shaking  in  deionized
water.  The  < 2 µm  grain  size  fraction  was  separated  from
aqueous  suspension  based  on  the  differential  settling  of
grains  of  different  diameters.  Following  the  technique  of
Kübler  (1975),  aqueous  suspensions  of  3 mg/cm

were

mounted  onto  glass  slides  and  dried  at  room  temperature.
Portions of air-dried  < 2 µm grain size fraction were saturat-
ed with ethylene glycol (60 °C overnight) in order to identify
the  possible  swelling  phases  of  the  samples.  The  measured
KI data are calibrated using the standards of the Kübler lab-
oratory (for details see Árkai et al. 1995). The boundaries of
the anchizone are defined by KI values of 0.25 and 0.42

∆°2θ,

respectively  (Kübler  1967,  1968,  1990).  The  determination
of  the  illite/K-white  mica  b  dimension  is  a  widely  used
method for the estimation of the pressure conditions of low-
and  very  low-grade  metamorphic  alteration  of  fine-grained
siliciclastic rocks (Sassi 1972; Sassi & Scolari 1974; Padan
et  al.  1982).  Diffraction  patterns  were  performed  as  de-
scribed above from non-orientated powder mounts of whole
rock  samples  with  a  mineralogical  composition  as  recom-
mended by Guidotti & Sassi (1976, 1986).

Results

XRPD indicates that the samples contain dominantly

quartz,  chlorite  and  illite/K-white  mica,  subordinately  pla-
gioclase, pyrite and rutile, as well as calcite and dolomite in
variable proportions. No swelling clay mineral phases can be
detected  in  the  sample  set.  In  two  samples,  paragonite  is
present (Table 1). The KI data of the examined samples (Ta-
ble 1) generally fall into the high-temperature part of the an-
chizone  (0.35 < IC  [

∆°2θ] > 0.25) and into the epizone

(KI < 0.25

∆°2θ). Higher ranked (epizonal) samples are ob-

served in the southern segment of the examined section
(Fig. 2). The obtained b values (Table 1) mainly fall in the

Sample KI

0.210 9.018

0.233 9.016

0.227 9.013

0.280 9.008

0.274 8.993

0.239 8.999

0.226 9.018

0.221 9.011

0.239 -

0.218 9.002

0.242 9.005

0.249 8.995

- 9.001

0.249 8.999

37a

0.246 9.006

0.240 9.019

0.250 9.002

0.221 9.043

0.239 -

0.250 -

- 9.006

0.265 -

0.236 -

0.287 -

Table 1: Kübler Index (KI) in

∆°2θ (underlined samples contain

paragonite) and K-white mica b dimension (

) of the investigated

samples.

Sample R

max

sd N R

min

7.55

0.63

2.69

0.31

7.96 0.39 18 2.39 0.33 18

Table 2: Vitrinite reflectance (R

max

, R

min

) in two samples of the cen-

tral Western Greywacke Zone (sd = standard deviation, N = number
of measurements).

medium-pressure zone or lie at the boundary between the
low- and medium pressure zones of Guidotti & Sassi (1986).

Only two samples (20, 50) contain organic particles suitable

for reflectance measurements. Organic matter reflectance of
these samples (Table 2) indicates the Meta-Anthracite stage of
the ASTM classification.

The Raman spectra (Table 3) reflect the continuous ordering

of CM by a progressive thermal overprint (Fig. 3; Beyssac et
al.  2002a,b).  The  calculated  R2  peak  area-ratio  (D1/
(G+D1+D2))  correlates  inversely  to  the  peak  metamorphic
temperature  (Beyssac  et  al.  2002a,b).  In  low  metamorphic
conditions  (R2 > 0.70),  no  variation  of  the  peak  positions
and  widths  can  be  observed.  With  rising  metamorphic  rank
(R2 <  0.70),  the  D1,  D2,  S1,  and  S2  peaks  shift  to  higher,
the G peak shifts to lower Raman values  and the first-order
FWHM  values  become  narrower  (Fig. 4).  The  regional  pat-
tern of the R2 ratios is presented in Fig. 5.

Discussion

The observed KI data do not trace a metamorphic gradient.

This is explained by a lower sensitivity of this parameter
compared to organic temperature indicators. However, if the

323

ALPINE METAMORPHISM OF THE WESTERN GREYWACKE ZONE (EASTERN ALPS)

idth

sdv

sd w

idth

sd w

03 38

03 41

.8 1.

37A

.0 1.

.1 2.

.8 2.

.6 2.

.3 1.

.4 2.

73 0.

75 0.

5 20

3 13

03 23

Table 3:

Mean

values

and

standard

deviation

(sd)

the

parameters

(pos

ition,

width

full

width

half

maximum)

obtained

from

the

composition

Raman

spectra

per

sample.

Peak

meta-

morphic

temperatures

(Temp)

were

calculated

after

Rahl

al.

(2005).

major  KI  zones  are  mapped  (Fig. 2),  a
south-to-north decrease of the metamor-
phic  overprint  can  be  detected  from  the
data. Most of the samples do not contain
CM large enough for reliable reflectance
measurements. Therefore, organic matter
reflectance  is  also  not  suitable  for  a  de-
tailed  mapping  of  the  metamorphic  pat-
tern.  However,  Figure 5  demonstrates
that RSCM is able to reconstruct a meta-
morphic field gradient in the study area.

Rantitsch et al. (2004) modified the

temperature calibration of Beyssac et al.
(2002b),  being  valid  in  the  temperature
range  between  330  and  650 °C.  On  the
basis  of  low-temperature  thermo-chro-
nological  data,  Rahl  et  al.  (2005)  ex-
tended the calibration range to tempera-
tures  down  to  100 °C.  To  relate  the
observed  high  R2  ratios  consistently  to
metamorphic  temperatures,  the  calibra-
tion of Rahl et al. (2005) is used in this
study  (Table 3).  This  results  in  the  re-
construction of a temperature gradient of
400 °C  to  200 °C,  decreasing  from  the
SEMP  Fault  Zone  towards  the  base  of
the Northern Calcareous Alps (Fig. 5). It
is  important  to  note  that  there  is  no
break in the peak metamorphic tempera-
ture  across  the  boundary  between  the
Penninic  unit  and  the  Greywacke  Zone.
The  internal  faults  of  the  Greywacke
Zone also do not disturb the temperature
pattern. There is no correlation between
the Raman parameter and the altitude of
the sample locality. Due to the regional
geological setting, we exclude therefore
a  trend  of  rising  metamorphic  tempera-
tures into deeper structural levels. Up to
a distance of ca. 10 km from the SEMP
Fault Zone, the trend is exposed contin-
uously.  Further  to  the  North  the  RSCM
thermometer  suggests  a  more  homoge-
neous pattern.

The estimated temperature of the sam-

ple  from  the  Penninic  unit  is  in  good  ac-
cordance  with  the  estimate  from  the
calcite-dolomite geothermometry of Frank
et al. (1987) and supports therefore the re-
liability  of  the  RSCM  thermometer
(Beyssac et al. 2002a,b; Rantitsch et al.
2004; Rahl et al. 2005) in rock sequenc-
es  lacking  pressure-temperature-critical
mineral  assemblages.  The  comparison
between the Raman and KI data demon-
strates a higher sensitivity of the organic
parameter  in  contrast  to  the  inorganic
parameter  in  very  low-  to  low-grade
metasediments.

324

RANTITSCH and JUDIK

Fig. 3. Representative examples for first- and corresponding second-order Raman
spectra (R2 is the R2 peak area ratio [D1/(G+D1+D2)]). The R2 values indicate a tem-
perature rise from top to bottom.

Fig. 2. Distribution of illite Kübler-indices (KI) in the study area (Legend see Fig. 1).

The described metamorphic pattern can be explained by

the thermal influence of the rising Penninic unit on the over-
lying Greywacke Zone. This hypothesis is supported by the
age data of Urbanek (2001). Further evidence is given by the
regional paleo-heat flow pattern within Miocene sedimentary
basins, formed as pull-apart basins during the Early- to Mid-

dle Miocene uplift of the Penninic unit (Sachsenhofer 1992,
2001). The data suggest that in the area above the rising Pen-
ninic unit, the heat flow extremely increased to > 200 mW/m

(Sachsenhofer 2001). Over greater distances, the heat flow
decreased circularly (Sachsenhofer 2001). The central part of
this heat flow anomaly covers the Wagrain Basin (Fig. 1),

subsiding  directly  above  the  central  Western
Greywacke  Zone.  Consequently,  we  see  in
the  study  area  evidence  for  a  high  heat  flow
during Early- to Middle Miocene times. Sub-
sequently,  during  the  Late  Miocene,  the  heat
flow  decreased  to  75 mW/m

(Fügenschuh

1995).

In the area of the Early- to Middle Miocene

heat  flow  maximum,  the  estimated  peak
metamorphic temperature in the hanging wall
unit  (southern  margin  of  the  central  Western
Greywacke Zone) corresponds to the Eocene/
Oligocene  metamorphic  temperature  maxi-
mum  in  the  footwall  unit  (northern  segment
of  the  Penninic  unit).  Therefore,  we  suppose
an isothermal decompression of the Penninic
unit  between  30  and  15 Ma  (see  also  Dachs
1990;  Neubauer  et  al.  1999),  giving  rise  to  a
thermal overprint of the overlying Greywacke
Zone. This is in accordance to geochronologi-
cal  data,  indicating  a  cooling  of  the  Penninic
rocks  below  400 °C  in  the  time  interval  be-
tween 24 and 15 Ma (24—17 in the East, 17—15
in the West; Dunkl et al. 2003).

325

ALPINE METAMORPHISM OF THE WESTERN GREYWACKE ZONE (EASTERN ALPS)

Fig. 4. Relationship between the Raman peak parameter and the R2 peak area ratio [D1/
(G+D1+D2)]; the centre of the ellipses plot the mean values, and the half-axes corre-
spond to 2 standard deviations of the repeated measurements. Decreasing R2 values indi-
cate rising metamorphic temperatures.

Some unpublished Cretaceous

Ar/

Ar white mica ages

without evidence for a later thermal overprint have been re-
ported from the southern segment of the Western Greywacke
Zone (W. Frank and F. Neubauer, pers. comm. 2008). This

indicates that 400 °C, the temperature de-
termined  for  the  Oligocene  to  Miocene
overprint,  may  have  been  too  low  to
cause Ar resetting in the interior parts of
the  Greywacke  Zone.  The  Ar-isotopic
system in white mica closes in a tempera-
ture interval between ca. 350° (e.g. Dall-
meyer  &  Takasu  1992;  Lips  et  al.  1998)
and ca. 500 °C (Hames & Cheney 1997),
and other factors like ductile deformation
or  fluid  flow  may  control  the  resetting
(e.g.  Villa  1998;  Balogh  &  Dunkl  2005;
Kurz et al. 2008). This fact explains a re-
set  of

Ar/

Ar white mica ages at the

SEMP Fault Zone and a missing over-
print of

Ar/

Ar age spectra within the

area of the observed thermal aureole.

If the intermediate pressure character

of  the  obtained  K-white  mica  b  dimen-
sions  is  taken  into  account,  it  may  be
supposed that the KI values record Creta-
ceous  thrusting  rather  than  the  Miocene
thermal overprint. If the clay mineralogi-
cal  reactions  were  triggered  by  the  later
event, b dimensions should resemble the
low pressure values (<9.000

) common-

ly found in extensional basins (Robinson
& Bevins 1986; Merriman & Peacor
1999). Thus, if this supposition is correct,
the data give evidence for a decoupling of
inorganic and organic metamorphic pro-
cesses.

The detected Early- to Middle Miocene

thermal  aureole  on  the  southern  margin
of  the  central  Western  Greywacke  Zone
resembles in its structural setting the Late
Cretaceous  aureole  within  the  eastern
segment  of  the  Greywacke  Zone  (Ran-
titsch  et  al.  2004).  Similarly  to  the  Late
Cretaceous  anomaly  (Rantitsch  et  al.
2004),  the  Early-  to  Middle  Miocene
anomaly may have been accompanied by
a convective heat loss due to fluid circu-
lation  (Neubauer  et  al.  1999),  which  re-
sulted  in  a  structurally  controlled  gold
mineralization in the Penninic unit (Neu-
bauer 2002; Putz et al. 2003).

Conclusions

Up to a distance of ca. 10 km from the

SEMP Fault Zone, the Cretaceous high-
temperature anchizonal to epizonal meta-
morphic pattern of the central Western

Greywacke  Zone  is  overprinted  by  a  thermal  aureole.  The
temperature  influence  diminishes  from  the  South  towards
the North, that is from the contact with the Penninic rocks to
the  internal  segments  of  the  Greywacke  Zone.  By  applying

326

RANTITSCH and JUDIK

Fig. 5. Raman R2-ratio (Beyssac et al. 2002b) in the study area (Legend see Fig. 1). Isolines contour the temperature zonation according to
the RSCM calibration of Rahl et al. (2005).

the  “Raman  spectroscopy  of  carbonaceous  material”  ther-
mometer, the organic metamorphic pattern can be explained
by a temperature gradient of 400 °C to 200 °C. This pattern
is explained by an Oligocene to Miocene thermal pulse, re-
lated  to  the  rapid  exhumation  of  formerly  deeply  buried
rocks of the Penninic unit. During this event, advective heat
transport  and  circulating  fluids  overprinted  the  Cretaceous
high-temperature anchi- to lower epizonal metamorphic pat-
tern of the central Western Greywacke Zone.

Acknowledgments: This study was financially supported by
the Austrian Academy of Science and the Austrian Agency for
International  Cooperation  in  Education  and  Research
(OEAD).  Th.  Windisch,  M.  Windisch,  D.  Reischenbacher,
P.M. Sándor, O. Komoróczy, K. Temesvári and A. Müller are
thanked for their technical assistance. Thanks are due to Prof.
P.  Árkai  for  numerous  discussions.  We  are  grateful  for  the
critical reviews and constructive comments by A. Biroň (Ban-
ská Bysrica), I. Dunkl (Göttingen) and R. Schuster (Vienna).

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329

ALPINE METAMORPHISM OF THE WESTERN GREYWACKE ZONE (EASTERN ALPS)

Appendix

Sample localities (coordinates in the WGS84 coordinate system, formation names according to Heinisch et al. 1995, 2003).

Sample N

Tectonic

Unit

Locality

Formation

Lithology

47.42531 12.56854

Hochhörndler Imbricate Zone Weissenstein Mine

Black slate

47.33041 12.72292

Schmittenhöhe

Black

slate

47.33015 12.71022

Schmittenhöhe

Black

slate

47.33195 12.70931

Schmittenhöhe

Slate

47.34452 12.70447

Schmittenhöhe

Lydite

47.33747 12.70358

Schmittenhöhe

Slate

47.32878 12.70028

Schmittenhöhe

Löhnersbach

Fm Slate

47.32151 12.74653

Breiteckalm

Siltstone

47.30883 12.76508

Areitalm

Slate

47.33168 12.62537

Klinglertörl

Klinger-Kar

Fm Black

slate

47.33200 12.62536

Klinglertörl

Klinger-Kar

Fm Black

slate

47.33199 12.62531

Klinglertörl

Klinger-Kar

Fm Lydite

47.33109 12.62507

Klinglertörl

Klinger-Kar

Fm Black

slate

47.33195 12.62500

Klinglertörl

Klinger-Kar

Fm Black

slate

47.33315 12.62389

Klinglertörl

Schattberg

Siltstone

37a

47.33315 12.62389

Klinglertörl

Schattberg

Siltstone

47.33559 12.62465

Klinglertörl

Klinger-Kar

Fm Black

slate

47.36656 12.68918

Roseggraben

Slate

47.37757 13.00242

Dienten

Black

slate

47.34420 13.01273

Glemmtal Unit

Sonnberg Dienten

Black slate

47.30124 12.68460

Walchen

Lydite

47.29535 12.58487

Greywacke Zone

(Austroalpine

Unit)

Uttendorfer Imbricate Zone

Uttendorf

Black

slate

47.27032 12.61434

Penninic Unit

Glockner Nappe

Abendsberg

Bündnerschiefer

Calcareous slate