GeolCarp_Vol60_No6_495

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA, DECEMBER 2009, 60, 6, 495—504 doi: 10.2478/v10096-009-0036-x

Introduction

The  present  architecture  of  the  Romanian  Carpathians  has
been  achieved  during  the  Alpine  tectonism  (e.g.  Săndulescu
1984; Balintoni 1997; Iancu et al. 2005). An overview of the
pre-Alpine basement components and of reliable isotopic ages
in the Romanian Carpathians was recently published by Balin-
toni et al. (2009). According to these authors, the main part of
the Carpathian basement consists of Gondwanan terranes con-
taining  Ordovician  orthogneisses  intensely  reworked  during
the Variscan orogeny. For example, Variscan nappes were de-
scribed in the Eastern Carpathians (e.g. Balintoni et al. 1983),
the Variscan thermotectonic events reached the eclogite facies
in  the  Southern  Carpathians  (e.g.  Medaris  et  al.  2003)  and
Variscan granitoid bodies intruded successively the basement
of the Apuseni Mountains (e.g. Pană 1998; Pană et al. 2002b;
Balintoni et al. 2007). The succession of the Variscan thermo-
tectonic events, their significance and their correlation among
the  three  Carpathians  segments  (i.e.  Eastern  Carpathians,
Southern  Carpathians  and  Apuseni  Mountains,  Fig. 1  inset)
are  not  well  established.  Moreover,  because  a  great  part  of
Central  and  Western  Europe  was  amalgamated  during  the
Variscan orogeny (e.g. von Raumer & Stampfli 2008), a good
knowledge  of  the  Variscan  orogen  in  its  entirety  is  vital  for
understanding the Pangea assemblage and its subsequent his-
tory.  Due  to  successive  granitoid  intrusions,  the  basement  of
the  Apuseni  Mountains  offers  a  good  opportunity  to  distin-
guish between different Variscan thermotectonic events.

Some of the existing Paleozoic ages in the Apuseni Moun-

tains were well constrained, whereas others had a preliminary

The emplacement age of the Muntele Mare Variscan granite

(Apuseni Mountains, Romania)

IOAN BALINTONI

, CONSTANTIN BALICA

, MONICA CLIVE I

, LI-QIU LI

HORST PETER HANN

, FUKUN CHEN

and VOLKER SCHULLER

Department of Geology, Faculty of Biology and Geology, “Babe -Bolyai” University, M. Kogălniceanu Str. 1, RO-400084 Cluj-Napoca,

Romania; ibalinto@bioge.ubbcluj.ro

Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing, 100029 China

Institut für Geowissenschaften, Universität Tübingen, 72076 Tübingen, Germany

(Manuscript received January 20, 2009; accepted in revised form August 26, 2009)

Abstract: Like the Alps and Western Carpathians, the Apuseni Mountains represent a fragment of the Variscan orogen
involved in the Alpine crustal shortenings. Thus the more extensive Alpine tectonic unit in the Apuseni Mountains, the
Bihor Autochthonous Unit is overlain by several nappe systems. During the Variscan orogeny, the Bihor Unit was a part
of the Some terrane involved as the upper plate in subduction, continental collision and finally in the orogen collapse
and exhumation. The Variscan thermotectonic events were marked in the future Bihor Unit by the large Muntele Mare
granitoid intrusion, an S-type anatectic body. Zircon U-Pb laser ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS) dating yielded a weighted mean age of 290.9 ± 3.0 Ma and a concordia age of 291.1 ± 1.1 Ma. U-Pb
isotope dilution zircon analyses yielded a lower intercept crystallization age of 296.6 + 5.7/—6.2 Ma. These two ages
coincide in the error limits. Thus, the Muntele Mare granitoid pluton is a sign of the last stage in the Variscan history of
the Apuseni Mountains. Many zircon grains show inheritance and/or Pb loss, typical for anatectic granitoid, overprinted
by later thermotectonic events.

Key words: U/Pb geochronology, Variscan orogeny, Apuseni Mountains, Muntele Mare granitoid pluton.

character, deduced from a limited number of analyses and in
the absence of in situ dating. Regarding the Muntele Mare plu-
ton, we mention the isotope dilution U-Pb age of 295 ± 1 Ma
reported  by  Pană  (1998)  and  of  278.4 ± 2.1 Ma  reported  by
Pană et al. (2002b). In an attempt to better constrain the age of
the Muntele Mare granitoid, we performed in situ zircon U-Pb
laser ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS)  dating,  avoiding  in  this  way  the  mixed  results
that  might  happen  in  the  case  of  complex  zoned  grains  with
inherited  cores,  new  magmatic  overgrowth  and/or  recrystal-
lized margins. We also used these data as a reference frame for
new U-Pb isotope dilution age data. A brief discussion of the
tectonic  significance  of  the  emplacement  age  of  the  Muntele
Mare pluton was also included. The pluton was re-sampled in
two locations, 22 km apart (Fig. 2).

Geological setting and samples

The Apuseni Mountains represent an isolated mountain

range in the interior of the Carpathian orocline (Fig. 1 inset).
They  consist  of  Alpine  tectonic  units,  which  include  in  geo-
metric succession from bottom to top: a) the Bihor Unit in an
autochthonous  position,  b)  the  Codru  Nappe  System,  c)  the
Biharia Nappe System and d) the Mure  Zone units at top (e.g.
Ianovici  et  al.  1976;  Bleahu  et  al.  1981).  The  Bihor  Unit  is
made predominantly of crystalline rocks overlain by Permian-
Mesozoic sedimentary and volcanic cover. The Codru Nappe
System comprises a single tectonic unit consisting of a meta-
morphic  basement  and  a  sedimentary  cover,  with  the  rest  of

496

BALINTONI, BALICA, CLIVE I, LI, HANN, CHEN and SCHULLER

the units including exclusively Permian and Mesozoic se-
quences. The Biharia Nappe System is formed entirely by
metaigneous and metasedimentary rocks, ranging in age from
lattermost Cambrian to Triassic (e.g. Dimitrescu in Ianovici et
al. 1976; Pană 1998; Pană & Balintoni 2000). These sequenc-
es are variously overprinted by early Cretaceous shearing and
low grade metamorphism (Pană 1998; Dallmeyer et al. 1999).

The tectonic units of the Mure  Zone are made up of Jurassic-
Cretaceous  mafic  and  felsic  igneous  rocks  (e.g.  Pană  et  al.
2002a) and associated sediments deposited in a rift-like setting
(e.g.  Bleahu  1974),  as  well  as  a  tectonic  slice  of  metamor-
phosed rocks (Balintoni & Iancu 1986).

The Apuseni Mountains basement (Fig. 2) is built up from

three pre-Alpine Gondwanan terranes, named Some , Biharia

Fig. 1. A sketch of the main Alpine tectonic units in the Apuseni Mountains (compiled according to Bleahu et al. 1981; Săndulescu 1984;
Kräutner 1997; Balintoni & Pu te 2002). The inset shows the position of the Apuseni Mountains within the Central-East European Alpine
orogenic frame: 1 – Flysch units; 2 – Neogene volcanics; 3 – Basement units in the Eastern Carpathians; 4 – Magura and Trans-Car-
pathian flysch units and sedimentary units in the Tauern window; 5 – Basement units in the Southern Carpathians; 6 – Dinarides, Var-
darides and similar units in Hungary and Slovakia; 7 – Basement units in Tauern window; 8 – Apuseni Mts, Mecsek, Western
Carpathians and Austroalpine basement units; 9 – Neogene and Paleogene volcanics; 10 – Mure Zone units.

497

THE EMPLACEMENT AGE OF THE MUNTELE MARE VARISCAN GRANITE (ROMANIA)

and  Baia  de  Arie   (e.g.  Balintoni  et  al.  2009).  They  were
probably  parts  of  some  larger  terranes  that  constituted  the
basement  of  all  the  Carpathian  branches  (e.g.  Pană  et  al.
2002b). According to the Romanian literature (e.g. Ianovici
et al. 1976; Balintoni 1997), the Some  terrane is composed
of  the  Some   metamorphic  sequence,  the  Biharia  terrane  of
the Biharia metamorphic sequence and the Baia de Arie  ter-
rane of the Baia de Arie  metamorphic sequence. The above
structural and metamorphic entities are shown in Fig. 2 and
in  Table 1  where  a  synopsis  of  the  Alpine  and  pre-Alpine
tectonic and metamorphic units of the Apuseni Mountains is
presented.

The Muntele Mare granitoid is a northerly trending elongat-

ed pluton (Fig. 2), that covers approximately 300 km

in the

lower Bihor Unit. The thermal contact aureole is expressed by
andalusite hornfels and in the roof pendants is characterized

by the sillimanite+cordierite mineral assemblage (e.g. Dimi-
trescu 1966; Mârza 1969).

The main rock type of the pluton is a biotite granodiorite

consisting of plagioclase, quartz, K-feldspar, biotite and mus-
covite  as  rock-forming  minerals  and  tourmaline,  apatite,  zir-
con,  monazite  and  allanite  as  accessory  minerals  (e.g.  Anton
2000). It intrudes and includes roof pendants of the Some  se-
quence (e.g. Dimitrescu 1966; Anton 2000). It has a porphyrit-
ic  texture  due  to  K-feldspar  megacrysts  and  can  locally  be
pegmatoid  or  microgranular.  The  Muntele  Mare  granodiorite
is a strongly peraluminous S-type granitoid, it plots in the late-
post-collisional field of the Hf-Rb-Ta diagram and zircon and
monazite  thermometers  indicate  a  crystallization  temperature
range  of  780—830 °C  consistent  with  decompression  melting
in  the  granulite  stability  field  (Anton  2000).  Such  tempera-
tures suggest the upper limit of granulite facies typical for de-

Fig. 2. A sketch of the main metamorphic units and pre-Alpine terranes in the Apuseni Mts (compiled from Ianovici et al. 1976; Balintoni
1997; Pană 1998; Dallmeyer et al. 1999).

498

BALINTONI, BALICA, CLIVE I, LI, HANN, CHEN and SCHULLER

hydration melting. Consequently, Muntele Mare granitoid
crystallized from an anatectic melt. Yet the zircon thermome-
ter temperature can be a little overestimated due to its signifi-
cant inheritance in the anatectic melts.

The emplacement age of the Muntele Mare pluton was uncer-

tain. Ten biotite and muscovite K-Ar ages reported by Soroiu
et al. (1969) and Pavelescu et al. (1975) range between 85 and
237 Ma and have problematic geological significance: the old-
est two dates of 232 and 237 Ma could be interpreted as mini-
mum emplacement ages, whereas the cluster of four dates

Table 2: Zircon U-Pb isotope dilution data for the Muntele Mare granite.

Atomic ratios

Apparent Ages (Ma)

206

208

206

207

206

207

Sample

204

206

238

2σ %

235

2σ % rho

206

2σ %

238

235

206

Sample on

diagram

109-II

430

0.1221

0.05043

1.09

0.3727

1.45

0.78

0.0874

0.19

317.2

321.6

354.1

0.8840

0.05735

0.76

0.7177

2.22

0.57

0.3694

0.09

259.3

549.3

1442

0.7080

0.07346

0.88

0.9075

2.71

0.57

0.3043

0.13

457.0

655.7

1417

377

0.1870

0.03757

2.04

0.2850

3.05

0.72

0.0935

0.38

237.8

254.7

413.4

0.6204

0.05486

1.47

0.5946

1.47

0.70

0.2783

0.13

344.3

473.8

1162

109-I

191

3.4354

0.04040

2.15

0.3214

2.27

0.95

0.1335

0.11

255.3

283.02 518.7

104

2.1833

0.05628

0.95

0.5230

1.88

0.60

0.2053

0.14

353.0

427.16 850.1

0.8289

0.05767

0.87

0.5746

3.63

0.52

0.4961

0.08

361.4

460.99 993.4

129

2.8023

0.05332

0.70

0.4133

2.04

0.48

0.1691

0.18

334.9

351.24 461.0

161-I

0.3854

0.04655

2.14

0.3352

4.88

0.53

0.1985

0.22

293.3

293.5

2814

318 0.1276 0.03949 2.37 0.2793 3.12 0.79 0.0899 0.34 249.7 250.1 1424

131 0.2863 0.06527 2.10 0.5066 2.86 0.77 0.1554 0.13 407.7 416.1 2407

1531 0.2227 0.09397 2.33 0.7718 2.81 0.85 0.1328 0.14 579.1 580.8 2136

161-II

179 0.2331 0.04868 2.21 0.3665 2.69 0.84 0.1263 0.16 306.5 317.1 2047

0.4434

0.03499

2.17

0.2446

4.48

0.56

0.2191

0.14

221.7

222.1

2974

191 0.2069 0.05548 2.08 0.3849 2.47 0.86 0.1179 0.14 348.2 330.6 1924

0.3730

0.04457

2.13

0.3513

3.71

0.63

0.1961

0.18

281.1

305.6

2794

Table 1: North Apuseni Mountains Structure. P – Permian, Tr – Triassic, J – Jurassic, K – Cretaceous.

between 85 and 119 Ma suggest an “Austrian” phase tectonic
overprint. An

Ar/

Ar muscovite analysis (Dallmeyer et al.

1999) yielded an age of 191 Ma, which may record the uplift
and  cooling  of  the  Muntele  Mare  Batholith  above  the  ca.
350 °C isotherm during the Early Jurassic. This age could be
influenced by the secondary muscovite (sericite) developed on
plagioclase, possibly partially due to the Alpine hydrothermal
fluids (see the Alpine reset ages in the Table 2). Anton (2000)
reported  Rb-Sr  ages  ranging  between  88  and  267 Ma.  Pană
(1998)  proposed  an  emplacement  age  of  at  least  295 ± 1 Ma

Pre-Alpine terranes

and their basement

Alpine metamorphosed cover

of the pre-Alpine terranes

Alpine tectonic units

Highiş-Muncel Nappe
Păiuşeni sequence

Baia de Arieş terrane

Baia de Arieş metamorphic

sequence

No metamorphic cover

Baia de Arieş Nappe
Baia de Arieş sequence
Biharia Nappe
Păiuşeni sequence Vulturese-Belioara marbles

Biharia sequence

Poiana Nappe
Păiuşeni sequence

P–Tr

Păiuşeni sequence

Biharia terrane

Biharia metamorphic sequence

Păiuşeni Permian

sequence

Vulturese-

Belioara Triassic

marbles

Arieşeni Nappe

Biharia sequence

P–Tr

Gârda Nappe

Someş sequence

har
ia N
ap

pe S
ys

tem

Coleşti Nappe Tr–J
Vaşcău Nappe

Tr–J

Moma Nappe

P–Tr

Dieva Nappe P–K

P–K

Finiş Nappe

Someş sequence

Vălani Nappe Tr–K

Co
dr

u N

app

P–K

Someş terrane

Someş metamorphic sequence

No metamorphic cover

Bihor Unit

Someş sequence

Bihor

Autochtho-

nous

Unit

499

THE EMPLACEMENT AGE OF THE MUNTELE MARE VARISCAN GRANITE (ROMANIA)

based  on  the  concordia  upper  intercept  with  a  regression  line
forced through origin and two multigrain U-Pb zircon analyses
with small discordance (2.7 % and 3.5 %, respectively). A later
attempt to date the Muntele Mare pluton, based on more analy-
ses  yielded  a  concordia  lower  intercept  age  of  278.4 ± 2.1 Ma
(Pană  et  al.  2002b).  The  data  variation  was  likely  caused  by
Alpine  thermotectonic  events  overprinting  and  the  employed
dating methods. For complex zircons, i.e. inherited zircons or
affected by lead loss or recrystallization, only the in situ dat-
ing methods can offer accurate data. In order to get more reli-
able ages we performed some new U-Pb datings on zircon by
isotope dilution and LA-ICP-MS methods.

For this study, we have used zircon grains extracted from

two samples collected from the southern part (Sample 109:
E 23°11’12”/N 46°25’53”) and from the central part (Sam-
ple 161: E 23°10’48”/N 46°37’40”) of the Muntele Mare
granitoid pluton (Fig. 2).

In the two samples, the Muntele Mare granitoid contains

plagioclase  (15—20 % An),  K-feldspar,  quartz,  biotite  and
muscovite  as  rock-forming  minerals  and  sericite,  epidote,
zoisite,  apatite,  sometimes  tourmaline,  allanite  and  zircon  as
accessory minerals.

The plagioclase is clouded and filled with sericite. The

epidote and zoisite also formed at the expense of plagioclase.
We do not exclude the possibility that at least partially, seric-
ite and epidote might have formed during the Alpine evolu-
tion of the Muntele Mare granite, as suggested by the Alpine
reset of the U-Pb ages (Table 2). A sign in this sense is the
secondary  replacement  of  albite  by  microcline.  Megablasts
of microcline often appear (1—2 cm thick and 4—5 cm long).
This  megablastic  microcline  probably  crystallized  in  the  fi-
nal stage of granite cooling from strongly differentiated flu-
ids when the plagioclase was altered, too (Dimitrescu 1966).
Zircon, allanite and apatite can be included in biotite. Biotite
dominates over muscovite and is frequently chloritized, with
sagenitic  rutile  included,  again  a  possible  Alpine  alteration.
A clear distinction between the mineral alterations due to the
residual fluids accumulated during granite cooling and those
due to the subsequent Alpine hydrothermal events is difficult
to do. No mineralogical differences between the two samples
are  observable,  and  nothing  pleads  for  a  genetic  difference
between them.

In both samples the zircon grains show two populations.

One population consists of thick, relatively short square
prisms, with pyramidal tips; their colour is honey yellow with-
out transparency and with rare inclusions. The other popula-
tion is formed of elongated, thin, flattened prisms, completely
transparent and colourless (Fig. 3).

Zircon U-Pb analytical methods

In order to extract zircon grains, 10 to 15 kg of fresh materi-

al have been subjected to the classical crushing, milling, sift-
ing, gravitational separation, heavy liquids treatment and
magnetic separation procedures. The best crystals were select-
ed using a stereomicroscope. For conventional U-Pb isotopic
dilution analyses, isotopic ratios were measured in the Labora-
tory of Radiogenic Isotope Geochemistry, Institute of Geolo-

gy and Geophysics, Chinese Academy of Sciences, Beijing,
using an IsoProbe-T thermal ionization mass spectrometer
manufactured by the GV company and equipped with 9 F 97
Faraday cups, 1 Daly receiver and 7 ion counters. A single zir-
con grain was shortly washed in warm 7 N HNO

and warm

6 N HCl, respectively, prior to dissolution, to remove surface
contamination after air abrasion. A mixed

205

Pb/

235

U-tracer

solution was added to the grain. Dissolution was performed in
PTFE (polytetrafluorethylene) vessels in a Parr acid digestion
bomb (Parrish 1987) using the vapour digestion method. The
bomb was placed in an oven at 210 °C for one week in 22 N
HF and for one day in 6 N HCl to dissolve fluorides into chlo-
ride  salts  and  avoid  U-Pb  fractionation.  No  separation  of  U
and  Pb  was  carried  out  by  the  ion  exchange  chromography
method.  Pb  isotopic  ratios  were  measured  statically  using
combination of Daly receiver and Faraday cups. U isotopic ra-
tios  were  measured  in  UO

+ using the Daly receiver in dy-

namic mode. Total procedural blanks were < 10 pg for Pb and
U. A factor of 1 ‰ per atomic mass unit for instrumental mass
fractionation was applied to all Pb analyses, using NBS 981 as
reference material.

Common Pb contribution remaining after correction for

tracer and blank was corrected using the values of Stacey &
Kramers (1975). U-Pb analytical data were evaluated with 2

standard error using the Pbdat program (Ludwig 1988). Re-
gression of the U-P data in concordia diagrams was done us-
ing the Isoplot program (Ludwig 2001). More details on
analytical techniques are given in Chen et al. (2000).

For in situ dating the zircon grains were mounted in 25 mm

epoxy and polished. After C-L imaging (Fig. 3), LA-ICP-MS
measurements were conducted at LaserChron facility, Depart-
ment  of  Geosciences,  University  of  Arizona  using  an  ISO-
PROBE  MC-ICP-MS.  The  ISOPROBE  MC-ICP-MS  was
equipped with a New Wave DUV193 nm Excimer laser-probe
with a spot diameter of 35 and 50 micrometers, depending on
grain size. Each grain analysis consisted of a single 20-second
integration on isotope peaks without laser-firing to obtain on-
peak  background  levels,  20  one-second  integrations  with  the
laser firing, followed finally by a 30-second purge with no la-
ser  firing  in  order  to  deliver  out  the  remaining  sample  (e.g.

Fig. 3. CL Images of typical zircon grains from sample 161. Most
of the grains exhibit elongate habit with weak or no zonation ex-
pressed as flat CL signal. Some of the grains show typical magmat-
ic zonation. Circles on images emphasize the ablation pits. Ages in
boxes represent

206

Pb/

238

Pb apparent ages (see Table 3).

500

BALINTONI, BALICA, CLIVE I, LI, HANN, CHEN and SCHULLER

Dickinson & Gehrels 2003). Hg contributions to

204

Pb were

removed by taking on-peak backgrounds. Each excavation pit
is ~ 20 µm in depth. The ablated material was carried via argon
gas into the IsoProbe, equipped with a sufficiently wide flight
tube allowing U, Th and Pb isotopes to be measured simulta-
neously. Measurements were done in static mode, using Fara-
day detectors for

238

232

Th,

208

Pb,

207

Pb,

206

Pb, and an

ion-counting channel for

204

Pb. Common Pb corrections were

made using the measured

204

Pb and assuming initial Pb com-

positions from Stacey & Kramers (1975). Analyses of zircon
standards of known isotopic and U-Pb composition were con-
ducted in most cases after each set of five unknown measure-
ments to correct for elemental isotopic fractionation. The
samples were analysed in hard extraction mode, which yielded
higher and more variable Pb/U fractionation. The

206

Pb*/

238

values for the standards were corrected for an average of
15.3 % ( ± 2.6 %) and 27.2 % ( ± 3.0 %) fractionation (uncer-
tainties at 2

σ standard deviation of ~20 analyses), respective-

ly. The U/Pb measurements, ratios, ages and errors are shown
in the Table 3. Using the ISOPLOT program of Ludwig
(2001), the data were plotted in weight averaged

206

Pb/

238

age diagrams, with data point error symbols at 1

σ (Fig. 5).

Analyses that have greater than 10 % uncertainty or are more
than 30 % discordant or 5 % reverse discordant are excluded
from further consideration.

Results

Isotope dilution data

A number of 17 single zircon grains (Fig. 4) separated

from  the  two  rock  samples  (8  and  9  grains,  respectively)
where  analysed  by  the  dilution  method.  The  analytical  data
for  the  U-Pb  ages  are  presented  in  Table 2.  Both  samples
analysed by the isotope dilution method were divided in two
populations  based  on  grain  size  and  shape  (short  and  thick
prisms  and  thin  and  long  prisms,  respectively).  For  sample
#161, five zircons out of eight plot on the concordia curve at
approximately  580 Ma,  410 Ma,  295 Ma,  250 Ma  and
222 Ma. Of the remaining three analyses, one shows a small
reverse  discordance  and  the  other  two  are  located  near  the
concordia (Fig. 4a). Out of them, the numbers 10, 13, 14 and
15  represent  short  and  thick  prisms.  For  sample  #109,  five
zircon  analyses  out  of  nine  are  strongly  discordant,  three
have relatively small discordances and one falls very close to
the concordia line at approximately 318 Ma (Fig. 4b). From
these grains the numbers 1, 3, 7, 8 and 9 represent short and
thick  prisms.  All  the  data  were  plotted  together  in  Fig. 4c.
The  relatively  large  age  scattering  offers  the  possibility  to
trace several regression lines and it is not easy to choose the
most accurate one representing the crystallization age of the
Muntele Mare granite. The LA-ICP-MS results were used in
order to solve this problem (see further), as a suggestion for
tracing the most reliable regression line. As a starting point we
have  considered  the  concordant  ID-TIMS  (isotope  dilution-
thermal ionization mass spectrometry) analysis # 12, the clos-
est one to the LA-ICP-MS age (Table 2). Using this analysis

Table 3:

Zircon

U-Pb

LA-ICP-MS

Analytical

data

for

sample

161.

Iso

top

e r

atio

aren

t a

ges

(

207

206

207

nal

(pp

)

235

)

238

)

238

235

(Ma

)

(Ma

)

t age

(Ma

)

(Ma

)

515

895

2 0.

6 0.

3 1

123 7

130

18.

895

3850

0528

5.0

4 1

137 8

781

18.

565

4184

0563

5.8

295

970

9 0.

3 0.

070

350

5 0.

7 0.

7 1

239 4

627

18.

478

3442

0461

8.2

8 1

333 7

667

18.

788

3288

0448

6.7

345

833

1 0.

3 0.

1521

1054

19.

143

2 0

329

5 0

462

3.5

435

026

2 0.

3 0.

040

796

6 0.

2 0.

030

512

4 0.

8 0.

1610

8829

18.

719

1 0

385

2 0

460

3.4

460

689

0 0.

1 0.

835

597

5 0.

9 0.

290

852

4 0.

2 0.

2 10

1415

9646

19.

282

7 0

316

9 0

464

3.9

515

932

2 0.

4 0.

650

379

8 0.

2 0.

501

THE EMPLACEMENT AGE OF THE MUNTELE MARE VARISCAN GRANITE (ROMANIA)

Fig. 4. Concordia projections of U-Pb isotopic ratios for: a – sample 161, and b – sample 109. c – Concordia projections of all isotopic
ratios corresponding to the samples 161 and 109. d – Concordia/discordia solution through points #5, 6, 12 and 14. Numbers shown on
diagrams represents analyses identifiers (see Table 2).

and the ID-TIMS analyses no. 5, 6 and 14 we got a lower in-
tercept  age  of  296.6 + 5.7/—6.2 Ma  with  a  robust  MSWD  of
0.80.  This  age  is  within  the  error  limits  of  the  LA-ICP-MS
weighted  mean  age,  interpreted  as  the  crystallization  age.
Fig. 4c  indicates  a  complex  zircon  crystallization  history
with many inherited grains and partially or totally reset crys-
tals, characteristic of anatectic melts.

LA-ICP-MS data

The LA-ICP-MS analytical data presented in Table 3 repre-

sent nineteen point analyses obtained from nineteen different
zircon grains of sample 161. All analyses are plotted in Fig. 5a.
Thirteen

206

Pb /

238

U apparent ages between 282.5 ± 6.7 Ma and

301.8 ± 6.8 Ma yielded a weighted mean age of 290.9 ± 3.0 Ma
and a concordia age of 291.1 ± 1.1 Ma (Fig. 5b). These ages cor-
respond to early Permian and are interpreted as crystallization
ages of the Muntele Mare granitoid parental magma. Six other
analyses yielded ages ranging between 302.1 and 359.8 Ma.

The in situ data facilitated the interpretation of the ID-TIMS
data and confirmed the age of ca. 295 Ma proposed by Pană
(1998) for the emplacement of the Muntele Mare granitoid.

Discussion

Muntele Mare crystallization age. The new age data pre-

sented  in  this  study  indicate  that  the  magma  of  anatectic
source was generated, emplaced and cooled in the Some  ter-
rane  basement  during  the  297—291 Ma  interval.  We  interpret
the Muntele Mare pluton as a late Variscan intrusion in a post-
collisional  setting,  following  the  Variscan  subduction  and
magmatic  arc  development  on  the  upper  Some   plate  at  ca.
350 Ma (e.g. Balintoni et al. 2007). The age spectra between
302.1  and  359.8 Ma  suggests  early  Variscan  inherited  zircon
more or less reset in the Muntele Mare magma.

Similar granitoid intrusions in the European Variscides.

In the larger picture of the Carpathian-Balkan region, late

502

BALINTONI, BALICA, CLIVE I, LI, HANN, CHEN and SCHULLER

Variscan intrusions are also known in the Southern Carpathians
(i.e.  Sichevi a-Poniasca  pluton,  311 ± 2 Ma;  Duch  sne  et  al.
2007), in Serbia (e.g. Brnjica, Neresnica, Beljanica, southern
extensions of the Sichevi a-Poniasca pluton and Gornjani plu-
ton,  304 Ma;  Kräutner  &  Krstić  2003)  and  in  Bulgaria  (e.g.
San  Nikola – 311.9 ± 4.1 Ma;  Petrohan – 304.6 ± 4.0 Ma;
Smilovene – 304.1 ± 5.5 Ma;  Hisara – 303.5 ± 3.3 Ma;  Ko-
privshtitza – 312.0 ± 5.4 Ma  and  Strelcha – 289.5 ± 7.8 Ma,
plutons, respectively; Carrigan et al. 2005). Such late Variscan
granitoid  intrusions  are  also  mentioned  from  other  European
Variscan massifs like the Harz Massif (Baumann et al. 1991)
and  Iberian  Massif  (Dias  et  al.  1998;  Bea  et  al.  1999;
Fernándes-Suárez et al. 2000; Azevedo et al. 2003).

Fig. 5. Concordia plot of LA-ICP-MS zircon U-Pb data (a), and weighted average plot
of relevant

206

Pb/

238

U apparent ages for sample 161 (b) (see Table 3). Inset: Concordia

plot of respective U/Pb isotope ratios.

cally  unrelated  to  the  Muntele  Mare  intrusion.  In  the  Car-
pathian region, records of the Triassic extensions are known
in the Eastern Carpathians, where the Ditrău Alkaline Massif
was emplaced at 229.1 Ma (e.g. Pană et al. 2000), and where
at  least  some  of  the  mafic  rocks  interpreted  as  “ophiolites”
are  associated  with  Triassic  limestone  (e.g.  Hoeck  et  al.
2009).  A  Triassic  rift  has  also  been  identified  in  the  North
Dobrogea  orogen  (e.g.  Savu  1980).  The  age  resetting  was
favoured  by  the  relatively  high  U  content  of  the  Muntele
Mare granitoid zircons (i.e. 883 ppm average).

Inherited and discordant ages. The 580 Ma age is an in-

herited Neoproterozoic age, well represented in the detrital
zircons from the metasedimentary rocks of the Some se-

Within the Alpine realm, Schaltegger &

Corfu (1992), von Quadt et al. (1994), Eich-
horn et al. (2000) reported U-Pb zircon ages
around  300 Ma  from  igneous  rocks.  In  the
Ve ká Fatra Mountains many samples yield-
ed zircon ages  ~ 310 Ma (Poller et al. 2005).
Carrigan  et  al.  (2005)  considered  nearly  all
these intrusions as post-collisional and gen-
erated after the main compresional and high
grade  metamorphic  events  of  the  Variscan
orogeny. For the Sichevi a-Poneasca pluton
in  Southern  Carpathians,  Duch

sne et al.

(2007) proposed thermal relaxation and heat
transfer along a lithospheric discontinuity,
following a linear lithospheric delamination
connected with a shear zone.

In our opinion, the Muntele Mare anatec-

tic pluton represents a late Variscan intru-
sion

generated

due

lithospheric

delamination of the Some  upper plate and
mantle  rise  after  continental  collision  ces-
sation  and  concomitant  to  withdrawal  and
exhumation  of  the  lower  plate  (Baia  de
Arie  terrane).

Post Variscan overprinting. The tectonic

significance  of  our  data  in  the  250  to
220 Ma range is still unclear. Based on well-
constrained emplacement ages of diorite (ca.
267 Ma) and granite (ca. 264 Ma) plutons in
the  Păiu eni  metamorphic  sequence  (Ta-
ble 1), Pană (1998) suggested a Permian rift-
like setting as a precursor to the widespread
Triassic extension. Our Middle to Early Tri-
assic data could record zircon resetting trig-
gered  by  thermal  and  hydrothermal  events
related  to  continued  extensions  that  finally
created  the  Alpine  rift  systems.  This  inter-
pretation  is  consistent  with  the  previously
reported K-Ar and Rb/Sr data. Thus, Anton
(2000)  recorded  Rb/Sr  ages  of  233  and
243 Ma  from  muscovite  and  of  267 Ma
from K-feldspar samples collected from the
Muntele Mare pluton. The same author ob-
tained  a  Rb/Sr  whole-rock  isochron  of
244.2 ± 16 Ma from pegmatite samples host-
ed  by  the  Some   sequence,  but  geochemi-

503

THE EMPLACEMENT AGE OF THE MUNTELE MARE VARISCAN GRANITE (ROMANIA)

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quence  of  maximum  mid-Cambrian  age  (Balintoni  et  al.
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partially  lost  its  radiogenic  Pb  in  the  younger  magma.  The
group  of  discordant  ages  visible  in  Fig. 4  probably  repre-
sents mixed ages in zoned zircon.

Conclusions

The S-type Muntele Mare granitoid pluton is late Variscan

in age. It may be related to late Variscan delaminations as pro-
posed  elsewhere  by  Stampfli  &  Mosar  (1999).  The  anatectic
origin  of  the  Muntele  Mare  granite  resulted  in  a  complex
structure of its zircons, with much inheritance from the previ-
ous hosts. The emplacement of the Muntele Mare pluton in the
Apuseni  Mountains  was  contemporaneous  with  a  group  of
young late Variscan plutons identified throughout the Balkan
Peninsula.

Acknowledgments:  This  paper  was  possible  through  finan-
cial  support  from  Grants  1/226  2005  CNCSIS,  37-01/2004-
2006 MEC and ID-480 CNCSIS. We are indebted to Cristina
Mari ,  from  COMINEX  S.A.  Cluj,  and  Adrian  Minu   from
Ro ia Montană Gold Corporation for help with the milling fa-
cilities. Mihai Ducea and Victor Valencia from Arizona Laser-
Chron  facility,  University  of  Arizona  are  gratefully  thanked
for  their  help  in  processing  the  LA-ICP-MS  samples.  We
thank Dinu Pană and an anonymous reviewer for their insight-
ful and constructive criticism of our manuscript.

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