GeolCarp_Vol64_No5_375

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, OCTOBER 2013, 64, 5, 375—382 doi: 10.2478/geoca-2013-0025

Introduction

Provenance  studies  based  on  dating  of  detrital  minerals  en-
ables  the  establishment  of  the  source,  especially  when  the
hinterland is distinct in the age of crystalline basement rocks
(e.g. Dallmeyer & Takasu 1992; Capuzzo et al. 2003; Hodges
et  al.  2005;  Neubauer  et  al.  2007;  von  Eynatten  &  Dunkl
2012 for review). Such studies also allow monitoring of tec-
tonic processes in the source region as well as their tectono-
thermal  history  when  sufficient  data  are  known  in  the
respective source regions (Ruhl & Hodges 2005).

The results of recent field work and collaborative

Ar/

dating  of  detrital  white  mica  from  the  synorogenic  Upper
Cretaceous  Sinaia  Flysch  Formation  in  the  Southern  Car-
pathian orogen have enabled conclusions as to the origin of
sediments  deposited  in  that  synorogenic  trench.  These  new
data  demand  significant  revision  of  previous  interpretations
of  the  tectonothermal  evolution  of  the  Southern  Carpathian
orogen, and provide constraints for regional Late Cretaceous
geodynamics.

Geological setting

The Southern Carpathian orogen is comprised of a sequence

of metamorphic basement nappe complexes structurally sepa-
rated by variably metamorphosed intercalations of Upper Pa-
leozoic and Mesozoic “cover” sequences (e.g. Burchfiel 1976,
1980; Kräutner et al. 1981, 1988; Săndulescu 1984; Kräutner

Origin of sediments during Cretaceous continent—continent

collision in the Romanian Southern Carpathians:

preliminary constraints from

Ar/

Ar single-grain dating

of detrital white mica

FRANZ NEUBAUER and ANA-VOICA BOJAR

Department of Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria; franz.neubauer@sbg.ac.at

(Manuscript received January 7, 2013; accepted in revised form June 5, 2013)

Abstract: Single grains of detrital white mica from the lowermost Upper Cretaceous Sinaia Flysch have been dated
using the

Ar/

Ar technique. The Sinaia Flysch was deposited in a trench between the Danubian and Getic

microcontinental pieces after the closure of the Severin oceanic tract. The Danubian basement is largely composed of a
Panafrican/Cadomian basement in contrast to the Getic/Supragetic units with a Variscan-aged basement, allowing the
distinction between these two blocks. Dating of detrital mica from the Sinaia Flysch resulted in predominantly Variscan
ages (329 ± 3 and 288 ± 4 Ma), which prove the Getic/Supragetic source of the infill of the Sinaia Trench. Subordinate
Late Permian (263 ± 8 and 255 ±10 Ma), Early Jurassic (185 ± 4 and 183 ± 3 Ma) and Late Jurassic/Early Cretaceous
(149 ± 3 and 140 ± 3 Ma) ages as well as a single Cretaceous age (98 ± 4 Ma) are interpreted as representing the exposure
of likely retrogressive low-grade metamorphic ductile shear zones of various ages. Ductile shear zones with similar

Ar/

Ar white mica ages are known in the Getic/Supragetic units. The Cretaceous ages also show that Cretaceous

metamorphic units were already subject to erosion during the deposition of the Sinaia Flysch.

Key words: provenance study, nappe stacking, retrogressive shear zone, Ar-Ar dating, white mica.

1993;  Berza  &  Iancu  1994;  Iancu  et  al.  2005;  Schmid  et  al.
2008; Balintoni et al. 2010, 2011; Balintoni & Balica 2012).
Their  palinspastic  origins  were  between  the  European  plate
(Moesian promontory) and the Vardar-Mure  oceanic domain
(a  western  extension  of  the  Tethys)  exposed  to  the  west  and
north  of  the  present-day  Southern  Carpathians  (Fig. 1)  (e.g.
Channel & Kozur 1997).

The tectonostratigraphic succession exposed within the

Southern  Carpathian  orogen  comprises  four  major  nappe
complexes  (Iancu  et  al.  2005  and  references  therein).  From
structurally lower to higher parts, these include (Figs. 1, 2):
(1) The Danubian nappe complex (with Cadomian granitoids,
and  medium-grade  metamorphic  sequences  with  granulite-
like  gneisses,  orthogneisses  and  meta-granitoids  –  Liegois
et al. 1996; Balintoni et al. 2011; Balintoni & Balica 2012);
(2)  the  Jurassic/Cretaceous  Severin  ophiolite-bearing  unit;
(3) the Getic nappe complex (with mainly Variscan medium-
grade  metamorphic  sequences  with  orthogneiss,  paragneiss
and garnet-micaschist); and (4) the Supragetic nappe complex
(mainly  Variscan  medium-grade  metamorphic  sequences).
The Danubian nappe complex is locally structurally separated
from the Getic nappe complex by the Severin Nappe that in-
cludes  Jurassic  rift  and  Cretaceous  deep-water  sedimentary
sequences,  namely  the  so-called  Sinaia  Flysch  (Burchfiel
1976;  Săndulescu  1984;  Iancu  et  al.  2005).  Sedimentary  se-
quences have been interpreted as records of the Jurassic sepa-
ration of an originally combined Danubian/Getic  continental
basement  and  comprise  several  facies  realms  (Fig. 2).  The
chronology of the assembly of the present nappe architecture

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GEOLOGICA CARPATHICA, 2013, 64, 5, 375—382

generally resembles that of Austroalpine units in the Eastern
Alps and Western Carpathians, and resulted from mid-Late
Cretaceous nappe assembly (e.g. Burchfiel 1980; Săndulescu
1984; Dallmeyer et al. 1996, 1998; Bojar et al. 1998; Neubauer
2002).

In detail, the Danubian nappe complex comprises several

Alpine  nappes  (Berza  et  al.  1994;  Iancu  et  al.  2005).  Tec-
tonically lower nappes consist of Cadomian medium-grade
metamorphic  sequences  (Lainici-Păiu   Group)  intruded  by
discordant granitic plutons also of Cadomian age. Structur-
ally  higher  Alpine  Danubian  nappes  include  the  Drăg an
Amphibolite  Group,  which  is  also  intruded  by  granitoids
(Berza & Iancu 1994). The Drăg an Amphibolite is tectoni-
cally  juxtaposed  with  Ordovician  to  Mississippian,  low-
grade  metasedimentary  units  along  ductile  shear  zones.
Structural relationships within the contrasting upper Danu-
bian  nappes  have  been  interpreted  to  at  least  partially
record  a  Variscan  tectonic  evolution  because  Jurassic  se-
quences  locally  stratigraphically  overlie  all  crystalline
nappe  units  (e.g.  Iancu  et  al.  2005;  Ciulavu  et  al.  2008).
Three  cover  domains  are  distinguished  in  the  Danubian
realm.  These  are  from  west  to  east:  the  Svini a-Svinecea,

Fig. 1. Simplified tectonic map of the Southern Carpathian orogen (modified after Bojar et al. 1998 and mainly based on Berza et al. 1994).
b. – basin, k. – klippe.

Presacina  and  Cerna-Jiu  domains.  The  Presacina  domain
includes  rift  volcanics.  Previous  geochronological  results
of  mineral  dating  reported  from  the  Danubian  basement
sequences  include  Late  Proterozoic  U-Pb  zircon  ages  of
augengneiss  and  granitoids  ranging  from  811.3 ± 2.2  to
582 ± 7 Ma, and an 825 ± 156 Ma Sm-Nd whole rock age for
the  Drăg an  Amphibolite  (Grünenfelder  et  al.  1983;  Pave-
lescu  et  al.  1983;  Liegeois  et  al.  1996;  Balintoni  &  Balica
2012). K-Ar ages reported for whole-rock samples and con-
centrates  of  amphibole,  muscovite  and  biotite  display  a
range between ca. 550 and 70 Ma (Grünenfelder et al. 1983;
Kräutner et al. 1988; Ratschbacher et al. 1993; Dallmeyer et
al. 1996, 1998; Bojar et al. 1998). Considered together, the
available  radiometric  results  have  been  interpreted  as  a
record  of  the  effects  of  penetrative  Cadomian/Baikalian
(late  Precambrian)  tectonothermal  activity  (e.g.  Balintoni
&  Balica  2012),  which  has  been  variably  and  only  locally
overprinted by retrogressive Variscan (Late Paleozoic) and/
or Alpine tectonothermal events (e.g. Kräutner et al. 1988;
Bojar et al. 1998; Willingshofer et al. 2001). The exact age
of  the  Alpine  metamorphic  overprint  is  still  unresolved,
and  is  generally  within  very  low-grade  conditions  to  at

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GEOLOGICA CARPATHICA, 2013, 64, 5, 375—382

most upper greenschist facies metamorphic conditions
(Iancu et al. 2005; Ciulavu et al. 2008; Bojar et al. 2010).
Age data for Alpine metamorphism are scarce (Kräutner et
al. 1988; Ratschbacher et al. 1993). The

Ar/

Ar and K-Ar

ages argue for a succession of events starting at ca. 100 Ma
with ductile shear zone formation and continuing with exten-
sion  shear  zones,  which  formed  at  80 Ma  in  northernmost
areas  (Neubauer  et  al.  1997).  The  youngest  ages  are  at
around  70 Ma  (Grünenfelder  et  al.  1983;  Ratschbacher  et
al.  1993)  displaying  terminal  tectonic  events.  Combining
radiometric ages with the stratigraphic ages of sedimentary
cover  units,  a  two-stage  history  of  Alpine  nappe  assembly
was presented (Bojar et al. 1998; Schmid et al. 1998; Iancu
et al. 2005).

The Severin ophiolite comprises Jurassic rift and ophiolite

successions.  The  ophiolite  is  overlain  by  the  Sinaia  Flysch
displaying  the  overthrusting  by  the  Getic  Nappe.  The  Sinaia
Flysch  ranges  in  stratigraphy  from  Late  Jurassic  to  Aptian
(Pop  1996)  and  comprises  mainly  turbiditic  limestone  and
sandstone beds and marly/shaly interlayers. Bojar et al. (1998)
found zircon fission track ages ranging between 220 ± 27 and
188 ± 19 Ma in sandstones from the Sinaia Flysch.

The Getic Nappe largely comprises Variscan medium-grade

metamorphic sequences (locally eclogite-bearing paragneisses
and  micaschists  intruded  by  pegmatites)  and  minor  granites
(Kräutner et al. 1988; Iancu & Mariuntu 1994). Published ra-
diometric  results  include  an  upper  intercept,  1100—1000 Ma
U-Pb  zircon  age  for  gneiss,  and  a  lower  intercept  310 Ma
U-Pb zircon age for granite (Pavelescu et al. 1983). A discor-
dant granite yielded a U-Pb zircon age of ca. 350 Ma (Stan et
al. 1992). K-Ar ages range between 350 and 70 Ma (Grünen-
felder  et  al.  1983;  Kräutner  et  al.  1988;  Ratschbacher  et  al.
1993).  Conventional  multi-grain

Ar/

Ar dating of white

mica revealed a Variscan age of the penetrative amphibolite-
grade metamorphism with white mica ages of ca. 320—290 Ma
(Dallmeyer et al. 1996, 1998), which represent the age of
cooling through the Ar retention temperature of white mica at
ca. 425 °C according to Harrison et al. (2009).

The Supragetic Nappe includes medium-grade metamor-

phic sequences that have been partially retrogressed along dis-
tinct,  locally  penetrative  ductile  shear  zones.  Low-grade
sequences  include  fossiliferous  Cambrian  to  Silurian,  and
Upper Devonian to Mississippian successions in north-west-
ern  sectors  of  the  region  (Kräutner  et  al.  1988).  Vast  areas

Fig. 2. Simplified stratigraphic sections of individual units exposed within the Danubian and Getic nappe complexes within the Southern
Carpathian orogen (modified after Bojar et al. 1998).

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are characterized by monotonous micaschist, plagioclase-
rich paragneiss and augengneiss. Conventional multi-grain

Ar/

Ar dating of white mica revealed the Variscan age of

the  penetrative  amphibolite-grade  metamorphism  with  white
mica ages of ca. 320—290 Ma (Dallmeyer et al. 1996, 1998).
Retrogressed ductile shear zones were dated and interpreted
as  records  of  an  event  at  ca.  200 Ma  (ca.  Triassic/Jurassic
boundary  (Dallmeyer  et  al.  1998)).  Low-grade  metamorphic
Pennsylvanian  cover  successions  also  argue  for  an  Alpine
metamorphism dated to ca. 119 Ma (Early Cretaceous) (Dall-
meyer et al. 1996). Dragusanu & Tanaka (1999) found similar
K-Ar mineral ages of 188 ± 3 and 119 ± 2 Ma in the Supragetic
domain in the east.

Ar/

Ar analytical methods

Preparation of the mineral concentrates was performed at

the University of Graz. Preparation for irradiation,

Ar/

analyses,  and  age  calculations  were  carried  out  at  the
ARGONAUT  Laboratory  of  the  Geology  Division  at  the
University  of  Salzburg  using  methods  similar  to  those  de-
scribed in Ilic et al. (2005). Mineral concentrates were packed
in  aluminium-foil  and  loaded  in  quartz  vials.  For  calculation
of the J-values, flux-monitors were placed between each 4—5
unknown samples, which yielded a distance of ca. 5 mm be-
tween adjacent flux-monitors. The sealed quartz vials were ir-
radiated  in  the  MTA  KFKI  reactor  (Debrecen,  Hungary)  for
16 hours. Correction factors for interfering isotopes were cal-
culated from 10 analyses of two Ca-glass samples and 22 anal-
yses of two pure K-glass samples (Wijbrans et al. 1995), and
are:

Ar/

(Ca)

= 0.00026025,

Ar/

(Ca)

= 0.00065014,

and

Ar/

(K)

= 0.015466. Variations in the flux of neu-

trons were monitored with the DRA1 sanidine standard for
which a

Ar/

Ar plateau age of 25.03 ± 0.05 Ma has been

reported (Wijbrans et al. 1995). After irradiation the miner-
als were unpacked from the quartz vials and the aluminium-
foil packets, and handpicked into 1 mm diameter holes
within one-way Al-sample holders.

Ar/

Ar analyses were

carried out using a UHV Ar-extraction line equipped with a
combined MERCHANTEK

UV/IR laser ablation facility,

and a VG-ISOTECH

NG3600 Mass Spectrometer.

Total fusion analyses of single grains were performed using

a defocused ( ~ 1.5 mm diameter) 25 W CO

-IR laser operating

in Tem

mode at wavelengths between 10.57 and 10.63 µm.

The laser is controlled from a PC, and the position of the laser
on the sample is monitored through a double-vacuum window
on the sample chamber via a video camera in the optical axis
of  the  laser  beam  on  the  computer  screen.  Gas  clean-up  was
performed using one hot and one cold Zr-Al SAES getter. Gas
admittance  and  pumping  of  the  mass  spectrometer  and  the
Ar-extraction  line  are  computer  controlled  using  pneumatic
valves. The NG3600 is a 18 cm radius 60° extended geometry
instrument, equipped with a bright Nier-type source operated
at  4.5 kV.  Measurement  was  performed  on  an  axial  electron
multiplier  in  static  mode,  peak-jumping  and  stability  of  the
magnet are controlled by a Hall-probe. For each increment the
intensities of

Ar,

Ar, and

Ar were measured,

the baseline readings on mass 35.5 are automatically sub-

tracted.  Intensities  of  the  peaks  were  back-extrapolated  over
16 measured intensities to the time of gas admittance either by
a  straight  line  or  a  curved  fit.  Intensities  were  corrected  for
system  blanks,  background,  post-irradiation  decay  of

Ar,

and  interfering  isotopes.  Isotopic  ratios,  ages  and  errors  for
individual  steps  were  calculated  following  suggestions  by
McDougall  &  Harrison  (1999)  using  decay  factors  reported
by Steiger & Jäger (1977). Age calculations were carried out
using ISOPLOT/EX (Ludwig 2001).

Petrography of investigated samples

Two samples from different localities were investigated

(see  Figs. 1  and  2  for  sample  locations).  Both  samples  are
from the Sinaia Formation of the Severin Nappe exposed to
the east (sample AVB-194) and west (sample AVB-195) of
the  Getic  Bahna  klippe.  The  area  belongs  to  the  Cerna-Ciu
domain. According to geological maps, sample AVB-194 is
a Turonian to Senonian sandstone of the cover of the Danu-
bian  Unit  (location:  N 44°54

’08”, E 22°41’09”). Sample

AVB-195 is likely an Aptian sandstone close to the Severin
ophiolites (location: N 44°52

’38”, E 22°41’56”) representing

the cover of the Severin Nappe.

Sample AVB-194 is an immature arkose arenite with angu-

lar  clasts  with  a  grain  size  ranging  from  0.1  to  0.5 mm.  The
main constituents are quartz, K-feldspar, plagioclase and some
white mica, degraded chlorite and garnet. K-feldspar (in part
microcline)  and  plagioclase  (in  part  oligoclase  according  to
optical  properties),  are  both  only  slightly  sericitized  and  to-
gether constitute ca. 30 percent, with a slight dominance of
K-feldspar. White mica is sometimes intergrown with slightly
degraded  biotite.  Garnet  clasts  are  often  chloritized.  Lithic
components  are  rare  and  a  sericite—chlorite  occurs  in  several
signs.  The  subordinate  matrix  is  composed  of  fine-grained
quartz/feldspar, sericite and chlorite.

Sample AVB-195 is a carbonate sandstone with a low per-

centage of siliciclastic material and calcite cement. The clasts
are 0.1 to 0.4 mm in size. Among the limestone clasts, micritic
clasts  are  dominant,  while  microsparite  and  monocrystalline
calcite clasts are rather rare. The siliciclastic fraction ( < 10 per-
cent)  is  composed  of  unaltered  feldspars  (polysynthetically
twinned  plagioclase  and  K-feldspar),  quartz,  white  mica  and
rare  biotite  as  well  as  rutile  and  Cr-spinel.  Among  the  lithic
clasts, phyllite, greenschist and slate dominate.

In summary, although largely different with respect to car-

bonate clast content, both samples are dominated by non-ret-
rogressed  clasts  like  plagioclase  (in  part  oligoclase),  which
could  best  represent  an  amphibolite  facies  grade  metamor-
phic  succession  with  lithologies  like  gneiss  and  micaschist.
Low-grade clasts (e.g. phyllite) are subordinate.

Ar/

Ar dating results

The grain size fraction 125—160 µm was selected to also

find possible fine-grained micas from Early Cretaceous-aged
low-grade metamorphic rocks. The selected grain size is too
small to perform step-wise heating experiments. Dating re-

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GEOLOGICA CARPATHICA, 2013, 64, 5, 375—382

Table 1:

Ar/

Ar step-wise heating results of detrital white mica.

Sample 1 (field no. AVB-195)

J-Value: 8.588 ± 0.078

Grain no.

Ar/

Ar*

Age [Ma]

Error [Ma]

measured 1-sigma corrected 1-sigma measured 1-sigma

1-sigma

0.00265

0.00031

0.10449

0.00028

3.321

0.091

76.4

98.4

3.6

0.00205 0.00024 0.17616 0.00023 4.229 0.070 85.7 139.4

2.9

0.00590 0.00090 0.06666 0.00086 8.594 0.267 79.7 254.7

9.6

0.00368 0.00075 1.06172 0.00075 8.094 0.221 86.6 263.0

8.0

0.00359 0.00026 0.78637 0.00028 8.588 0.078 87.7 280.1

3.7

0.00180 0.00031 0.03937 0.00038 8.300 0.092 93.6 286.3

4.1

0.00028 0.00041 0.40478 0.00030 7.848 0.122 98.9 287.2

4.9

0.00287 0.00033 0.16035 0.00028 8.809 0.098 90.4 293.2

4.3

0.00004 0.00032 0.53313 0.00047 8.109 0.096 99.9 298.8

4.3

0.00121 0.00038 1.28402 0.00027 8.444 0.113 95.8 300.6

4.7

0.00189 0.00041 0.05693 0.00057 8.855 0.122 93.7 304.2

5.0

0.00201 0.00075 0.46551 0.00090 9.016 0.224 93.4 309.6

8.1

0.00017 0.00041 0.92277 0.00032 8.614 0.122 99.4 315.7

5.0

0.00008 0.00026 0.03596 0.00029 8.677 0.077 99.7 316.3

3.9

0.00015 0.00028 0.27945 0.00037 8.820 0.084 99.5 321.0

4.1

0.00057 0.00026 0.02164 0.00028 9.077 0.076 98.2 324.7

3.9

Sample 2 (field no. AVB-194)

J-Value: 8.5884 ± 0.077

0.00133 0.00032 0.02556 0.00045 8.934 0.096 95.6 312.5

4.1

0.00112 0.00022 0.00920 0.00029 8.845 0.064 96.3 311.6

3.4

0.00076 0.00021 0.00588 0.00026 8.323 0.063 97.3 297.5

3.3

0.00065 0.00031 0.07927 0.00042 8.696 0.093 97.8 311.5

4.1

0.00104 0.00016 0.02274 0.00017 8.588 0.049 96.4 303.8

3.0

0.00169 0.00021 0.24884 0.00023 8.859 0.063 94.4 307.1

3.3

0.00005 0.00016 0.12754 0.00020 8.491 0.047 99.8 310.6

3.0

0.00142 0.00026 0.04951 0.00033 4.322 0.078 90.3 149.3

3.2

0.00103 0.00018 0.17408 0.00021 5.128 0.053 94.1 183.3

2.5

0.00159 0.00020 0.06423 0.00028 9.484 0.060 95.0 328.5

3.4

0.00103 0.00018 0.16080 0.00023 8.661 0.054 96.5 306.6

3.1

0.00139 0.00032 0.28068 0.00032 5.259 0.093 92.2 184.6

3.7

0.00271 0.00064 0.88424 0.00062 9.863 0.191 91.9 332.4

6.9

0.00245

0.00067

0.47814

0.00081 10.866

0.200

93.3

366.9

7.2

0.00152

0.00102

4.13000

0.00090

8.690

0.302

94.8

313.9

10.5

0.00046 0.00046 0.70924 0.00054 8.500 0.137 98.4 308.5

5.3

0.00074 0.00033 0.22917 0.00027 9.058 0.099 97.6 323.2

4.3

0.00112 0.00023 0.43878 0.00023 8.770 0.067 96.2 310.2

3.4

0.00151 0.00035 0.74211 0.00034 8.925 0.103 95.0 312.4

4.3

0.00246 0.00042 1.49037 0.00042 9.407 0.125 92.3 321.2

5.0

0.00209 0.00044 0.55796 0.00040 9.366 0.130 93.4 321.0

5.1

0.00086 0.00031 1.07124 0.00032 7.974 0.093 96.8 287.6

4.0

a — measured, b — corrected for post irradiation decay of

Ar (half-live = 35.1 days).

Ar* — radiogenic

Ar.

Fig. 3. Histograms showing the new

Ar/

Ar single-grain ages of

detrital white mica.

sults are shown in Table 1 and, graphically, in Fig. 3. The
data are treated by statistical methods proposed by Sircombe
(2004), which include the age and the error of age.

Twelve from a set of sixteen grains of AVB-194 gave age

values of 325 ± 4 to 280 ± 4 Ma. A further grain yielded an age
of 98 ± 4 Ma with a relatively low proportion (76 %) of radio-
genic

Ar. Another grain gave an age of 140 ± 3 Ma, and

two further grains yielded ages of 263 ± 8 and 255 ± 10 Ma.

Eighteen grains of sample AVB-195 yielded age values

ranging between 329 ± 3 and 288 ± 4 Ma. A further grain gave
an older age of 367 ± 7 Ma. Three grains gave younger ages
with 185 ± 4, 183 ± 3 and 149 ± 3 Ma. Because of the high pro-
portion of radiogenic

Ar, these ages are considered to be

geologically significant.

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Discussion

The new single-grain

Ar/

Ar ages of detrital white mi-

cas from sandstones collected within the Sinaia Flysch of
two different units, namely the cover of the Danubian realm
and of the Severin Nappe, are very similar to previously re-
ported multigrain

Ar/

Ar and to most K-Ar ages from Getic

and  Supragetic  basement  units  reported  during  the  last  de-
cades  (Kräutner  et  al.  1988;  Dallmeyer  et  al.  1996,  1998;
Neubauer et al. 1997; Dragusanu & Tanaka 1999 and refer-
ences therein). Most are Variscan ages, but a low percentage
is younger (see below), making them similar to those recorded
by  zircon  fission  track  ages  (Bojar  et  al.  1998;  Fügenschuh
&  Schmid  2005)  and

Ar/

Ar white mica ages from the

Getic  basement  (Dallmeyer  et  al.  1998).  This  argues  for  a
source-sink relationship between the Getic/Supragetic base-
ment  units  and  the  Sinaia  Formation  (Fig. 4a,b).  Conse-
quently, the Sinaia Flysch is considered to represent the infill
of a basin on the lower plate, which was progressively over-
ridden  by  the  Getic/Supragetic  nappe  complex  representing
the terrestrial source.

The Sinaia Flysch (or Formation) was deposited in a

trench located between the Danubian and Getic microconti-
nental pieces after the closure of the Severin oceanic seaway
(e.g. Bojar et al. 1998 and references therein).

Ar/

Ar sin-

gle grain ages of detrital white mica from the early Late Cre-
taceous Sinaia Flysch clearly demonstrate the predominance
of Variscan ages (329 ± 3 and 288 ± 4 Ma). These ages can be
linked to a source from the Getic/Supragetic source with its
Variscan

Ar/

Ar white mica ages in metamorphic rocks

and exclude the Panafrican/Danubian block as a possible
source for the infill of the Sinaia Trench (Fig. 4b).

Subordinate ages with Late Permian (263 ± 8 and

255 ± 10 Ma), Early Jurassic (185 ± 4 and 183 ± 3 Ma) and Late
Jurassic/Early Cretaceous (149 ± 3 and 140 ± 3 Ma) as well as
a  single  late  Early  Cretaceous  age  (98 ± 4 Ma)  were  also
found. These ages are considered to represent either (1) Var-
iscan  mica  grains,  which  were  variably  reset  by  subsequent
thermally  induced  overprint  during  the  Triassic/Jurassic  or
(2) Early Cretaceous or new grains formed within local duc-
tile  shear  zones  within  greenschist  facies  conditions.  The
Permian,  Early  Jurassic  and  Early  Cretaceous  ages  closely

Fig. 4. Model for the Late Cretaceous tectonic evolution of units exposed within the Danubian window of the Southern Carpathian orogen.
a – Simplified Middle Jurassic paleogeographic section displaying the rift stage. b – Early Late Cretaceous paleogeography due to age
dating results.

381

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GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2013, 64, 5, 375—382

resemble ages reported from retrogressive, low-grade ductile
shear  zones  by  Dallmeyer  et  al.  (1998).  The  small  selected
grain size does not allow for step-heating to be carried out on
single grains in order to discriminate between these two pos-
sibilities.  The  ages  are  considered  to  be  geologically  sig-
nificant  because  similar  Permian  to  Cretaceous  ages  were
actually found along ductile shear zones within the Getic Unit
(Dallmeyer et al. 1996, 1998). The ages around 185—183 Ma
are  similar  to  zircon  fission  track  ages  reported  by  Bojar  et
al.  (1998)  and  are  interpreted  as  records  of  tectonothermal
events during rifting and opening of the Severin oceanic sea-
way (Fig. 4a). Willingshofer et al. (2001) reported a variety
of similar zircon fission track ages from the Getic basement,
which  are  similar  to  all  the  above-mentioned  age  groups
(Fig. 4).  The  Early  Cretaceous  mica  ages  (140 ± 3 Ma  and
98 ± 4 Ma) also demonstrate the exposure of Cretaceous-aged
metamorphic units during the Late Cretaceous. Similar K-Ar
muscovite  (99 ± 5 Ma  –  Ratschbacher  et  al.  1993),  zircon
fission track ages (145 ± 10.8 Ma and 88.3 ± 8.5 Ma – Fügen-
schuh  &  Schmid  2005)  from  upper  Danubian  and  Getic
Units and apatite fission track age populations (150 ± 22 Ma,
125 ± 17 Ma,  102 ± 9 Ma)  from  sandstones  of  the  Oligocene
Petro ani Basin (Fig. 1; Moser et al. 2005) were also report-
ed. We consider these detrital muscovites to have their origin
either in the Supragetic, Getic and/or in upper Danubian tec-
tonic units, which were overthrust during the late Early Cre-
taceous.  This  question  remains  open  and  requires  further
consideration and work.

Finally, Wiesinger (2006) records a similar Variscan age

group from Upper Cretaceous infill of Gosau-type basins in
the Ha eg Basin, which formed on top of the Getic Nappe
and in the Apuseni Mountains. This indicates the dominance
of Variscan sources in the Carpathians.

Conclusions

Ar/

Ar single grain dating of detrital white mica from

the  lowermost  Upper  Cretaceous  Sinaia  Formation  resulted
in predominant Variscan ages (329 ± 3 to 288 ± 4 Ma) repre-
senting  the  Getic/Supragetic  source  of  infill  of  the  Sinaia
Trench.  Subordinate  ages  with  Late  Permian  (263 ± 8  and
255 ± 10 Ma),  Early  Jurassic  (185 ± 4  and  183 ± 3 Ma)  and
Late  Jurassic  (149 ± 3  and  140 ± 3 Ma)  as  well  as  a  single
Cretaceous  age  (98 ± 4  Ma)  likely  represent  the  exposure  of
ductile  shear  zones  of  various  ages,  including  the  exposure
of  low-grade  metamorphic  units.  These  Late  Permian  and
Mesozoic ages are considered to be geologically significant
because of similar ages in corresponding basement units.

Acknowledgments:  The  paper  benefited  from  discussions
with Tudor Berza, Harry Fritz and Ernst Willingshofer. We
gratefully acknowledge detailed and constructive reviews by
Bernhard Fügenschuh and Liviu Matenco and by the respon-
sible  editor,  Dušan  Plašienka.  Isabella  Merschdorf  polished
the  English  of  the  final  version  of  the  manuscript.  Miron
Brezuleanu is thanked for support during the field work. The
work  has  been  supported  by  Grant  P-15,646-N06  from  the
Austrian Research Foundation to FN.

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