GeolCarp_Vol62_No4_299

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, AUGUST 2011, 62, 4, 299—307 doi: 10.2478/v10096-011-0023-x

Introduction

Moesia is a major structural unit of the Carpathian and Balkan
foreland. It lies at the SE margin of the East European craton
(Fig. 1,  inset),  in  the  SE  part  of  the  Trans-European  Suture
Zone (TESZ), a fundamental terrane boundary separating the
Precambrian  craton  from  the  cluster  of  terranes  originating
from  Gondwana  (e.g.  Pharaoh  1999;  Yanev  et  al.  2005;
Oczlon et al. 2007). Inspite of the great progress in knowledge
of the litho- and biostratigraphy of the Moesian platform cov-
er,  the  pre-Mesozoic  paleocontinental  affinity  of  Moesia  is
still poorly known, due to the scarcity of reliable geochrono-
logical and provenance data. Classically, Moesia was regarded
as  a  southern  margin  of  Baltica  (Ziegler  1986).  Correlations
with  the  Avalonian  terranes  were  proposed  by  Matte  et  al.
(1990) and von Raumer et al. (2002, 2003). Other reconstruc-
tions relate the Moesia terrane to Gondwana-derived terranes
of the Armorican Terrane Assemblage (ATA) (Pharaoh 1999;
Golonka 2002). On the basis of various available types of data
Oczlon  et  al.  (2007)  conclude  that  Moesia  contains  four  dis-
tinct terranes, two of Avalonian (Central and South Dobrogea)
and two of Baltican (West Moesia and Palazu) origin, juxta-
posed during a long history of Paleozoic and Mesozoic strike-
slip displacements.

According to Żelaźniewicz et al. (2009) Brunovistulia,

Małopolska and Moesia formed at the end of the Neoprotero-
zoic the Teisseyre-Tornquist Terrane Assemblage (TTA), a
mixture of crustal elements derived from both Gondwana and
Baltica. Central and South Dobrogea are cited as fragments of

Peri-Amazonian provenance of the Central Dobrogea terrane

(Romania) attested by U/Pb detrital zircon age patterns

ION BALINTONI

, CONSTANTIN BALICA

1,3

, ANTONETA SEGHEDI

and MIHAI DUCEA

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

Romania;

ioan.balintoni@ubbcluj.ro

National Institute of Marine Geology and Geoecology, Dimitrie Onciul Str., 23—25 Bucharest, Romania

Department of Geosciences, University of Arizona, Gould-Simpson, Tucson AZ, 85721, USA

(Manuscript received May 6, 2010; accepted in revised form March 17, 2011)

Abstract: The Central Dobrogea Shield is a part of the Moesia, a Paleozoic composite terrane located southward of the
North Dobrogea Alpine orogen. The two geological units are separated from each other by a trans-lithospheric discon-
tinuity, the Peceneaga-Camena transform fault. Along this fault, remnants of a Variscan orogen (i.e. North Dobrogea),
recycled  during  the  Alpine  orogeny  come  in  contact  with  two  lithological  entities  of  the  Central  Dobrogea  Shield,
unaffected by the Phanerozoic orogenic events: the Histria Formation, a flysch-like sequence of Ediacaran age very
low-grade metamorphosed and its basement, the medium-grade metamorphosed Altîn Tepe sequence. Southward, along
the  reverse  hidden  Palazu  fault,  the  Histria  Formation  meets  South  Dobrogea,  formed  of  quite  different  geological
formations. Detrital zircon from the Histria Formation yielded U/Pb LA ICP MS ages that show provenance patterns
typical of peri-Amazonian terranes. Such terranes were sourced by orogens ranging from Paleoarchean to Neoproterozoic.
The ages between 750 and 600 Ma differentiate the Amazonian sources from the Baltican and Laurentian sources, since
they are lacking from the last ones. The youngest ages of 587 and 584 Ma suggest for the Histria Formation a maximum
late  Ediacaran  deposition  age.  At  the  same  time,  the  continuity  of  the  Ordovician  sediments  over  the  Palazu  fault
revealed by drill-cores favours a Cambrian junction between Central and South Dobrogea.

Key words: peri-Amazonian provenance, Central Dobrogea, terrane analysis, detrital zircon ages.

Baltican  origin.  Such  different  opinions  make  it  difficult  to
understand  the  real  geological  history  of  southeast  Europe.
For solving the terrane provenance issue, either paleomagnet-
ic, paleontological, sedimentological approaches or other can
be used. Yet, especially in the case of the metamorphosed pre-
Alpine basement, or in that of Precambrian sequences, the de-
trital  zircon  age  patterns  become  of  crucial  importance  (e.g.
Nance & Murphy 1996; Fernández-Suárez et al. 2002; Linne-
mann  et  al.  2004,  2007;  Samson  et  al.  2005;  Zulauf  et  al.
2007; Kuznetsov et al. 2010). In order to establish the prove-
nance of Central Dobrogea, we sampled for detrital zircon the
very  low-grade  metasediments  of  the  Histria  Formation,
which covers this area on large surfaces. The zircons were dat-
ed  by  U/Pb  LA-ICP-MS  method  at  University  of  Arizona,
Tucson, and the resulting data are the subject of this article.

Geological setting

Moesia

Moesia, called the Euxinic craton by Balintoni (1997),

represents a continental block of ca. 600 km long (east-west)
and 250—300 km broad (north-south), located on the present
territories of Romania and Bulgaria (Fig. 1, upper-left inset).
According to Balintoni (1997) it consists of the Central
Dobrogea Shield where the basement crops out on large sur-
faces and the Moesian platform where the basement is cov-
ered by thick Phanerozoic sedimentary deposits.

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GEOLOGICA CARPATHICA, 2011, 62, 4, 299—307

Fig. 1. Geological map of Central Dobrogea (drawn after Kräutner et al. 1988). Star mark indicates the sampling location (see text for GPS co-
ordinates). Topmost inset: Location of Dobrogea area (square mark) on a map showing the basement structure and the Neoproterozoic, Cale-
donian, Variscan and Alpine deformation belts in Europe. TESZ – Trans European Suture Zone; SC – South Carpathians; EC – East
Carpathians; AM – Apuseni Mountains; M – Małopolska; US – Upper Silesia; SP – Scythian Platform. Armorican Terrane Assem-
blage: A – Armorica; MC – Massif Central; I – Iberia; BM – Bohemian Massif. Drawn after Seghedi et al. (2005), modified. Upper
center inset: general simplified structure of Moesia. CD – Central Dobrogea; SD – South Dobrogea; PCF – Peceneaga-Camena Fault;
OSF – Ostrov-Sinoe Fault; COF – Capidava-Ovidiu Fault; IMF – Intra-Moesian Fault. Drawn after Seghedi et al. (2005), simplified. Up-
per right inset: general simplified structure of Dobrogea. SfGF – Sfântu Gheorghe Fault; PCF – Peceneaga-Camena Fault; COF – Capida-
va-Ovidiu Fault; PLF – Palazu Fault. Drawn after Seghedi et al. (2005), simplified.

The South Carpathian-Balkan Alpine chain surrounds

Moesia to the north, west and south. The eastern Moesian
margin is covered by the Black Sea and to the northeast the
Early Cretaceous Peceneaga-Camena dextral transform fault
(Balintoni & Baier 1997) forms the boundary with the North

Dobrogea  Cimmerian  orogen.  Moesia  played  a  prominent
role  in  forming  the  Carpathian-Balkan  oroclines  (e.g.
Ratschbacher at al. 1993) and it is overthrusted by the Car-
pathian  and  Balkan  tectonic  units  (e.g.  Săndulescu  1984).
According to Seghedi et al. (2005), West Moesia is separated

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from  East  Moesia  through  the  Intra-Moesian  Fault  (Fig. 1,
upper  center  inset).  Capidava-Ovidiu  Fault  delimits  at  the
surface Central Dobrogea from South Dobrogea, as compo-
nents  of  East  Moesia  (Fig. 1).  Oczlon  et  al.  (2007)  view
West Moesia, Central Dobrogea and South Dobrogea as sep-
arate  pre-Alpine  terrane  fragments.  The  authors  also  delin-
eate  the  small  Palazu  terrane  between  Central  and  South
Dobrogea.  Regarding  the  basement  (Fig. 2),  the  boundary
between Central Dobrogea and South Dobrogea is the Palazu
Thrust (Seghedi et al. 2005: fig. 7B). A thick cover of Paleo-
zoic,  Mesozoic,  Paleocene—Eocene,  Miocene,  Pliocene  and
Quaternary sedimentary deposits overlies the greatest part of
the  Moesia  basement.  In  many  areas  the  Moesian  platform
sedimentary cover starts with siliciclastic sediments ascribed
to  the  Ordovician  and  to  some  parts  of  the  Cambrian.  Four
main sedimentary cycles separated by intervals of uplift and
erosion have been described in the Moesian platform cover,
with some differences between East and West Moesia for the
Mesozoic and Cenozoic (Paraschiv 1979; Ionesi 1994). The
Cambrian—Westphalian  and  Permian—Triassic  cycles  are
common  for  the  whole  platform  cover.  The  following  two
cycles are late Liassic—Campanian and Late Badenian—Pleis-
tocene  for  West  Moesia,  and  Late  Bathonian—Early  Maas-
trichtian and Late Badenian—Romanian for East Moesia. The
basement of Moesia differs between the four components. In
South Dobrogea gneisses of possible Archean age underlie a
Paleoproterozoic  Banded  Iron  Formation  (BIF)  and  a
Neoproterozoic  volcano-sedimentary  suite  (Coco u  Group)
(Giu că  et  al.  1967;  Kräutner  et  al.  1988).  In  West  Moesia,
several boreholes bottomed in granites and metabasites. For
most  metamorphic  suites  the  Precambrian  evolution  is  still
poorly documented, and no protolith ages are available. The
Central Dobrogea basement is discussed further.

Central Dobrogea

In Central Dobrogea the basement is largely exposed

(Fig. 1) and consists of Neoproterozoic medium-grade meta-
morphic rocks (Altîn-Tepe Metamorphic Unit) and a thick

late  Neoproterozoic—early  Cambrian  turbidite  succession
(Histria  Formation,  Seghedi  &  Oaie  1995).  The  Altîn-Tepe
Metamorphic Unit crops out south of the Peceneaga-Camena
fault in the core of an antiformal NW trending and SE plung-
ing  fold  beneath  the  Histria  Formation.  It  consists  of  poly-
metamorphic  rocks,  with  staurolite  characterizing  the  first
thermotectonic event. Biotite from micaschists yielded K/Ar
ages  ranging  from  696  to  643 Ma  (Giu că  et  al.  1967)  and
hornblende  from  amphibolites  yielded  526 Ma  (Codarcea-
Dessila et al. 1966) (all ages recalculated by Kräutner et al.
1988). These data are interpreted either as the age of the am-
phibolite  facies  metamorphism  (Giu că  et  al.  1967),  or  due
to the partial Ar loss during the Cadomian metamorphism of
the Histria Formation (Kräutner et al. 1988). The Altîn-Tepe
Metamorphic  Unit  was  traditionally  regarded  as  the  base-
ment of the overlying Histria Formation (Ianovici & Giu că
1961; Giu că et al. 1967). The top of the metamorphic unit
shows a low-grade mylonitic zone along the contact with the
Histria  Formation  (Mure an  1971,  1972;  Kräutner  et  al.
1988; Seghedi & Oaie 1994). This contact was interpreted as
a tectonic window below the nappe of the Histria Formation
by Mure an (1971) or as a shallow extensional detachment,
as expressed by typical metamorphic core complexes (Seghe-
di et al. 1999). The Histria Formation is exposed over the en-
tire  area  of  the  Central  Dobrogea  Shield,  overlain  by  some
remnants of an eroded Late Jurassic carbonate platform suc-
cession.  West  of  the  Danube,  as  proved  by  boreholes,  Or-
dovician quartzitic sandstones and green shales overstep the
Histria  Formation.  The  Ordovician  age  is  established  based
on graptolite records (Murgeanu & Spassov 1968). The His-
tria  Formation  consists  of  a  turbiditic  succession  about
5000 m thick, representing submarine fan deposits, prograd-
ed  northward  in  a  deep  basin  floored  by  continental  crust
(Seghedi & Oaie 1995; Oaie 1999). Based on sedimentologi-
cal data, a foreland basin setting is supposed for the Histria
Formation  by  the  cited  authors.  It  includes  a  lower  and  an
upper member dominated by sandstones and a median mem-
ber  consisting  of  distal,  fine-grained  turbidites.  The  age  of
the Histria Formation was ascribed to the late Neoproterozo-
ic—Early  Cambrian  based  on  palynological  assemblages

Fig. 2. Cross-section through the southernmost part of Central Dobrogea and northern part of South Dobrogea (A—B line on Fig. 1), show-
ing the relationship between their basement rocks. Modified after Seghedi et al. (2005).

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(Iliescu  &  Mutihac  1965)  and  on  the  medusoid  record  (i.e.
Nemiana simplex Palij), identified in fine-grained turbidites
(Oaie  1992,  1999).  The  deformation  of  the  turbidites  ex-
pressed  as  open  folds  in  very  low-grade  metamorphic  condi-
tions took place at the end of Neoproterozoic according to K/Ar
data (Giu că et al. 1967; Kräutner et al. 1988). Mineralogical
studies indicate that the source of the turbidites was an active
continental  margin  and  its  volcanic  arc  (Seghedi  &  Oaie
1995;  Oaie  1999;  Oaie  et  al.  2005).  Several  detrital  zircons
(Żelaźniewicz  et  al.  2001)  yielded  U/Pb  SHRIMP  ages  of
1497 ± 8 Ma,  1050 ± 1 Ma,  603 ± 5 Ma  and  579 ± 7 Ma,  inter-
preted  as  Avalonia-type  sources  by  Seghedi  et  al.  (2005)  or
Far East Avalonia by Oczlon et al. (2007). The detrital zircon
ages  published  by  Żelaźniewicz  et  al.  (2009)  do  not  support
their inference that Central Dobrogea could be of Baltican af-
finity. This is quite clear in their figure 11, where the Baltican
margin has a single age projected for the entire Neoproterozoic.

Samples and method

Samples 346A and 346B (of coordinates N 44°21

’28.0”/

E 0.28°34

’22.8”) were picked up 3 meters stratigraphically

apart,  from  a  quarry  next  to  the  Black  Sea  shore,  on  the
southern  shore  of  Lake  Ta aul  (Fig. 1).  The  samples  are  a
very hard coarse-grained arkosian sandstone and a conglom-
erate, both grey to greenish in colour, with quartz, feldspar,
chlorite, epidote, muscovite, a little calcite and opaque min-
erals  in  matrix.  Polymictic  elements  consist  of  lithic  frag-
ments formed of the same minerals and quartz pebbles. The
chlorite  is  a  newly  formed  mineral  and  the  lithic  fragments
are derived from acid volcanics and orthogneiss sources. In
the  quarry,  a  depositional  bedding  is  visible,  but  no  schis-
tosity. Two samples with different granullometries from dis-
tinct  stratigraphic  levels  were  collected  for  checking  the
possible differences between the age distribution patterns.

For zircon extraction up to 10 kg of fresh material was

sampled  from  each  outcrop.  In  order  to  extract  the  zircon
grains, the material has been subjected to the classical crush-
ing, milling, gravitational separation and heavy liquids treat-
ment.  At  least  100  detrital  crystals  were  randomly  selected
out  of  each  sample  using  a  stereomicroscope  and  then
mounted in 25 mm epoxy and polished.

The LA-ICP-MS measurements were performed at the La-

serChron  facility,  Department  of  Geosciences,  University  of
Arizona using an ISOPROBE MC-ICP-MS equipped with a
New  Wave  DUV193  nm  Excimer  laser-probe  with  a  spot
diameter of 35 µm. 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 laser firing in order to deliver out the remaining sample (e.g.
Dickinson & Gehrels 2003). Hg contributions to

204

Pb were re-

moved by taking on-peak backgrounds.

The ablated material was carried via argon gas into the Iso-

Probe, equipped with a sufficiently wide flight tube allowing
for U and Pb isotopes to be measured simultaneously. Measure-
ments were done in static mode, using Faraday detectors for

238

232

Th,

208—206

Pb, and an ion-counting channel for

204

Pb.

Common Pb corrections were made using the measured

204

Pb and assuming initial Pb compositions from Stacey &

Kramers (1975). Analyses of zircon standards of known iso-
topic and U-Pb composition were conducted in most cases
after each set of five unknown measurements 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

U values for the standards were corrected for

an  average  of  15.3 %  ( ± 2.6 %)  and  27.2 %  ( ± 3.0 %)  frac-
tionation (uncertainties at 2  standard deviation of  ~ 20 ana-
lyses),  respectively.  The  U/Pb  measurements,  ratios,  ages  and
errors are shown in the Supplementary data Table (available in
the electronic edition at www.geologicacarpathica.sk).  Using
the  ISOPLOT  program  of  Ludwig  (2001),  Concordia  dia-
grams (with data point error symbols at 1 ) for each sample
were  plotted.  The

206

Pb/

238

U ages are considered best if

younger than 800 Ma and

207

Pb/

206

Pb ages if older than

800 Ma (e.g. Gehrels et al. 2008 and references therein), and
further plotted on binary age vs. number of ages distribution
diagrams. Analyses that have greater than 10 % uncertainty,
are more than 30 % discordant or 5 % reverse discordant, are
excluded from further consideration.

Results

Sample 346A

Some of the zircon grains are well rounded ball-like or bar-

rel-like in form, colourless or sometimes red in nuance, com-
pletely  transparent.  These  grains  suffered  a  long  transport.
Other grains represent prisms or prism fragments of different
sizes, broken during the processing of samples, not very well
abraded, transparent, colourless or slighty yellowish in colour,
sometimes  reddish.  Their  forms  suggest  a  relatively  short
transport.  The  ages  of  84  dated  zircon  grains  range  between
594 Ma and 3307 Ma, that is between the late Neoproterozoic
(Ediacaran) and late Paleoarchean (Supplementary data Table at
www.geologicacarpathica.sk).  We  point  out  the  important
Archean  source.  Significant  peaks  indicating  the  orogenic
sources  are  visible  between  0.55—0.75 Ga  (Neoproterozoic),
1.25—1.4 Ga  and  1.45—1.7 Ga  (Mesoproterozoic  to  the  latest
Paleoproterozoic),  1.95—2.2 Ga  (Paleoproterozoic)  and  be-
tween  2.7—3.0 Ga  (Neoarchean  to  Mesoarchean).  There  are
also several Paleoarchean ages. Age gaps or low density inter-
vals  appear  between  0.75—1.25 Ga,  around  1.8 Ga  and  be-
tween 2.2—2.7 Ga. Similar to the age peaks, the age gaps have
their significance from the point of view of sources.

Sample 346B

Zircon grains from this sample are similar to those from

sample 346A, but are a little bigger. The ages of 96 dated zir-
con grains range between 583 Ma and 3135 Ma (Supplemen-
tary data Table available at www.geologicacarpathica.sk). The
age distribution has similar patterns in the two samples
(Fig. 3a,b,d). It is only the number of ages in the correspond-
ing clusters that produce low or high peaks. In this sample the

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concentration  of  Archean  ages  is  higher,  with  ages  in  the
1.0—1.25 Ga interval (Grenvillian orogeny). As the two dia-
grams  show  similar  distribution  patterns,  it  seems  reason-
able  to  combine  them  in  a  single  diagram  (Fig. 3c).  The
orogenic sources of the detrital zircon are discussed later. We
signalize here the low U/Th ratio in the dated zircons (Sup-
plementary data Table at www.geologicacarpathica.sk) char-
acteristic  to  magmatic  zircon.  The  arrangement  of  ages
around  Concordia  (Fig. 4)  indicates  high  concordance  be-
tween

238

206

Pb and

235

207

Pb ages. This is a general fea-

ture of detrital zircon, due to natural selection during
weathering, transport and sedimentary processes.

Discussion

The age of the Histria Formation

The two samples yielded ten Ediacaran ages (5.5 %

from all the ages) ranging between 633 and 583 Ma. From
Histria Formation rocks Żelaźniewicz et al. (2009) also re-
ported five Ediacaran U/Pb ages based on detrital zircon,
ranging  between  622  and  579 Ma.  These  data  suggest  a
maximum  late  Ediacaran  depositional  age  for  the  Histria
Formation. Correlating the U/Pb detrital zircon ages with
the age indicated by the medusoid Nemiana simplex Palij
identified in fine-grained turbidites by Oaie (1992, 1999)
the  late  Ediacaran—possibly  earliest  Cambrian  age  of  the
Histria Formation is firmly established.

Terrane provenance

The significance of terms

It is necessary to constrain the meaning of some terms be-

cause the notions evolved through time. A recent classifica-
tion of peri-Gondwanan terranes (Nance et al. 2008)
discerns between the (1) Avalonian, (2) Cadomian, (3) Gan-
derian and (4) Cratonic type.

The Avalonian terranes originated as oceanic volcanic

arcs  within  the  Panthalassa  Ocean  surrounding  Rodinia.
These  terranes  accreted  to  the  Gondwana  margin  by  ca.
650 Ma. The Panthalassic island arcs were also called Pro-
to-Avalonian  terranes  by  Nance  et  al.  (2002).  Regarding
their  detrital  zircon,  the  Avalonian  terranes  were  derived
dominantly  from  the  Amazonian  craton.  The  Ganderian
and  Cratonic  terranes  also  represent  peri-Amazonian  ter-
ranes by their detrital zircon sources, formed either of re-
cycled crust (Ganderian terranes) or of material unaffected
by  the  Avalonian-Cadomian  continental  margin  magma-
tism (Cratonic terranes). The Cadomian terranes were pro-
videded  with  detrital  zircon  from  the  African  craton.
According  to  Nance  et  al.  (2008)  the  Avalonian  terranes

Fig. 3. U-Pb ages distribution of sample 346A (a) and 346B (b) and
overall distribution of both samples (c) without considering 1 ab-
solute errors. Stacked normalized probability plot of both samples
(d) is figured for a better comparison of age distribution spectra.

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rifted off from the Gondwana margin beginning in the Early
Ordovician.  However,  Winchester  et  al.  (2002)  and
Żelaźniewicz et al. (2009) advocate a peri-Amazonian prov-
enance  but  a  pre-Ordovician  (Cambrian)  drifting  for  some
terranes adjacent to TESZ. In summary, the peri-Amazonian
terranes  can  be  of  Avalonian,  Ganderian  or  Cratonic  type,
some of them leaving Gondwana margin during the Cambrian
Period and others during the Ordovician Period. In order to
distinguish between them we should say Cambrian-Avalon-
ian,  Cambrian-Ganderian,  or  Cambrian-Cratonic  type  terranes
and Ordovician-Avalonian, Ordovician-Ganderian or Ordovic-
ian-Cratonic type terranes.

Previous provenance hypotheses

In the following, the terms are those used by the cited au-

thors with or without distinction between the Moesia compos-
ite terrane and Moesian platform. Up to now the origin of the
Central Dobrogea has been discussed only in a very general
manner. According to Pharaoh (1999), “The affinity of the

terrane(s)  underlying  the  Moesian  Platform  is  poorly  con-
strained  at  present”.  According  to  Winchester  et  al.  (2002),
Central Dobrogea, Southern Dobrogea and the Moesian plat-
form have a common origin with the Bruno-Silesia, Łysogóry
and Małopolska terranes. Six hundred and fifty Ma ago they
were in contiguity with Amazonia and Baltica as components
of  the  supercontinent  Pannotia  and  left  Amazonia  between
550—520 Ma. Von Raumer et al. (2002) attached the Istanbul,
Moesia  and  Zonguldak  terranes  to  Baltica  before  490 Ma.
Stampfli et al. (2002) consider these terranes as Avalonia. Von
Raumer et al. (2003) view the Istanbul and Moesia terranes as
Avalonian satellites and attach the Zonguldak terrane to Balti-
ca.  Winchester  et  al.  (2006)  attribute  to  Central  Dobrogea  a
peri-Baltican  affinity,  together  with  Bruno-Silesia,  Łysogóry
and  Małopolska.  As  we  already  mentioned,  Seghedi  et  al.
(2005) and Oczlon et al. (2007) supposed an Avalonian prove-
nance  for  Central  Dobrogea  based  on  some  Rondonian  and
Grenvillian detrital zircon ages obtained by Żelaźniewicz et al.
(2001).  Żelaźniewicz  et  al.  (2009)  view  the  Central  (and
South) Dobrogea as having Baltican provenance inspite of the
presence of Neoproterozoic detrital zircon suppliers in Central
Dobrogea and the absence of these sources in Baltica, accord-
ing  to  their  own  data.  Kalvoda  &  Bábek  (2010)  incorporate
the Brunovistulia, Małopolska and West Moesia terranes into
the  late  Neoproterozoic—Cambrian  Baltican  margin.  Regard-
ing the Istanbul-Zonguldak, Bittesh and East Moesia terranes,
these authors say that they “may have been part of the Avalo-
nian  terrane  assemblage,  although  an  Arabian-Nubian  Shield
or Baltican provenance cannot be excluded”. Such contradic-
tory hypotheses reflect the insufficency of the data and an il-
lustration of them can be found in Balintoni et al. (2010a).

Provenance of Central Dobrogea

The main features of our diagrams can be summarized as

follows: i) an important age group is situated in the late
Neoproterozoic; ii) there is an age spreading along the Meso-
proterozoic with a peak around 1.5 Ga; iii) the Paleoprotero-
zoic contains age concentrations around 1.7 Ga and between
1.95—2.2 Ga; iv) the greatest age grouping is Archean, be-
tween 2.65—3.0 Ga; v) a very low frequency of data appears
around 1.8 Ga and between 2.2—2.6 Ga.

Comparing our data with the data from the Arabian-Nubian

Shield (Johnson & Woldehaimanot 2003) and from Iran
(Horton et al. 2008) we notice the absence of the Mesoprotero-
zoic zircons in these regions, except the Grenvillian sources.

Considering the data presented by Samson et al. (2005),

Linnemann et al. (2007), Rino et al. (2008) and Bogdanova et
al. (2008), suppliers for the Mesoproterozoic detrital zircon in
the terranes amalgamated between Gondwana and Laurussia
or docked to Laurussia during the Paleozoic could be Baltica,
Laurentia and Amazonia. Due to a magmatic quiescence peri-
od in Laurentia between 1.61 and 1.49 Ga (e.g. Samson et al.
2005) and the absence of the late Neoproterozoic Cadomian
events (e.g. Linnemann et al. 2007), this continent can be ex-
cluded as the original place of the Central Dobrogea terrane.

Discrimination between Baltica and Amazonia as the

motherland of the Central Dobrogea terrane can be done
based on the Neoproterozoic suppliers, because according to

Fig. 4. Concordia projection of detrital ages for samples 346A and
346B.

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Kuznetsov et al. (2010), the zircons with ages between 0.75
and 0.6 Ga are missing in Baltica. The data of Żelaźniewicz
et  al.  (2009)  are  in  accordance  with  this  point  of  view,  be-
cause they recorded a single detrital zircon age of 841 Ma in
the  Ediacaran  cover  of  the  East  European  Craton  margin.
This age span being well represented in the Central Dobro-
gea terrane, we conclude that it was a part of the Gondwanan
Amazonian  margin,  that  is,  it  has  a  peri-Amazonian  origin.
Whether the Central Dobrogea is of Cambrian-Avalonian or
-Ganderian type terrane depends on the Altîn Tepe sequence
U/Pb and Sm/Nd ages, unsolved until now.

Orogenic sources of the detrital zircons

For the Central Dobrogea terrane the Brasiliano orgen (e.g.

Nance et al. 2009) is the most important Neoproterozoic detri-
tal zircon source. Regarding the Mesoproterozoic, Paleoprot-
erozoic and Archean sources, they are quite similar to the
present-day sources of detrital zircon described by Rino et al.
(2008) at the Amazon and Niger rivers mouths (i.e. group 2 of
zircon population), which confirm the peri-Amazonian prove-

(2009). Central Dobrogea shows a similar pattern of the de-
trital  zircon  ages  with  those  from  Brunovistulia  and  West
Małopolska.  Brunovistulia  is  viewed  by  Żelaźniewicz  et  al.
(2009)  as  a  peri-Amazonian  composite  terrane,  which  mi-
grated  toward  Baltica  during  the  Cambrian.  Małopolska  is
considered a peri-Baltican terrane, but strictly the detrital zir-
con ages contradict this inference. As discussed, the Central
Dobrogea  attached  to  NE  Moesia  before  the  Ordovician,
knowing that sediments of this age cover the Palazu fault. As
a  conclusion,  Central  Dobrogea  correlates  with  Brunovistu-
lia  and  probably  Małopolska  from  the  provenance  and  mi-
gration time perspectives.

Conclusions

The Central Dobrogea terrane is constituted of the Altîn

Tepe basement of unknown age and its cover, the flysch-like
Histria Formation. A metasandstone and a metaconglomer-
ate sample from the Histria Formation furnished detrital zir-
con. A group of ten early Ediacaran ages yielded by the

Fig. 5. Paleogeographic configuration at 460 Ma of the peri-Amazonian terranes in
accordance with the data and hypotheses discussed in the text. Paleocontinents con-
figuration  drawn  according  to  Nance  et  al.  (2010).  The  peri-Amazonian  terranes
context is simplified and modified according to Balintoni et al. (2010: fig. 9d). The
stages  in  the  history  of  the  peri-Amazonian  terranes  are  presented  in  that  figure.
Peri-Amazonian terranes: A – Ordovician-Avalonia; D – Drăg an; LP – Lainici-
Păiu ; Mo – Moesia; CD – Central Dobrogea; G – Ordovician-Ganderia. Moesia
drifted to Baltica before 500 Ma. Post 500 Ma the Ordovician-Ganderia migrated to-
ward Baltica in front of the Ordovician-Avalonia, and a fragment of the first terrane
attached to Moesia (Lainici-Păiu  terrane). Behind Avalonia drifted the Drăg an ter-
rane, that attached to Lainici-Păiu  terrane.

nance of the Central Dobrogea. It is character-
istic to the Amazon River detrital zircons that
they  occur  along  the  entire  1.0—2.0 Ga  inter-
val but at a low frequency and the very impor-
tant peaks between 2.0—2.2 Ga and older than
2.5 Ga.  A  good  coverage  around  3.0 Ga,  as
visible in our diagrams is found in the Parana
River detrital zircons, classified in Group 3 of
zircon populations by Rino et al. (2008). If we
consider  the  granitoid  events  in  space  and
time  (Condie  et  al.  2009),  then  again  the  age
pattern of the South America detrital zircon is
the  closest  to  the  Central  Dobrogea  pattern.
Consequently,  the  Mesoproterozoic  and
Paleoproterozoic accretionary orogens as well
as  the  Archean  nuclei  (e.g.  Carajas)  of  the
Amazonian  craton  (e.g.  Cordani  &  Texeira
2007)  provided  the  detrital  zircon  within  the
Cadomian forearc basin of the Central Dobro-
gea.  The  relatively  slight  contribution  of  the
Grenvillian  sources  and  the  remarkable  input
from  Paleoproterozoic  and  Archean  sources,
suggest an initial location of the Central Dob-
rogea  not  far  from  the  West  African  Craton.
The  Amazonian  sources  illustrated  by  Nance
et  al.  (2009)  including  the  relative  gaps
around 1.8 Ga and between 2.2—2.6 Ga almost
perfectly correlate with the Central Dobrogea
sources.  Consequently,  the  Central  Dobrogea
terrane  represents  a  peri-Amazonian  crustal
fragment  that  joined  other  Moesia  basement
components during the Cambrian Period.

Correlations

Argumented correlations can be only based

on the data reported by Żelaźniewicz et al.

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GEOLOGICA CARPATHICA, 2011, 62, 4, 299—307

detrital zircon establish as late Ediacaran the maximum pos-
sible deposition age of the Histria Formation. The age distri-
bution  pattern  coincides  with  those  of  the  peri-Amazonian
terranes that received material from the Amazon craton oro-
gens,  that  is  the  Central  Dobrogea  has  a  peri-Amazonian
provenance.  Drill-holes  in  the  Moesian  platform  cover  met
Ordovician sediments overlying the Palazu reverse fault, the
boundary  between  Central  Dobrogea  and  South  Dobrogea.
This situation suggests a Cambrian junction between Central
Dobrogea and the other components of Moesia forming the
Moesia composite terrane that migrated toward Baltica dur-
ing the Cambrian Period, too (Fig. 5). Central Dobrogea can
be correlated with the Brunovistulia and probably Małopolska
terranes from Central Europe from the provenance and drift-
ing time perspective. Implicitly we suppose a Gondwanan ori-
gin of the whole of Moesia, because a peri-Amazonian terrane
became attached to its NE margin during the Cambrian and to-
ward  the  west  and  south  Ordovician-Avalonian  terranes
docked to it (Balintoni et al. 2010).

Acknowledgments:  This  research  was  financially  supported
by Grant ID-480 CNCSIS. The authors wish to express their
gratitude to Jiří Kalvoda and especially to Niko Froitzheim, for
their  careful  revisions  and  insightful  suggestions  and  observa-
tions,  which  improved  the  quality  of  this  paper.  V.  Valencia
is gratefully acknowledged for his help with analytical proce-
dures and for his careful supervision of data acquisition.

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All

uncertainties

are

reported

the

1-sigma

level,

and

includ

only

measurement

errors.

Systematic

errors

would

increase

age

uncertainties

1—2 %.

concentration

and

U/T

calibrated

relative

our

Sri

Lanka

standard

zircon,

and

are

accurate

~20 %.

ommon

correction

from

204

Pb,

with

composition

interpreted

from

Stacey

Kramers

(1975)

and

uncertainties

1.0

for

206

Pb/

204

Pb, 0.3 for

207

Pb/

204

Pb,

and

2.0

for

208

Pb/

204

Pb.

U/Pb

and

206

Pb/

207

fractionation

calibrated

relative

fragments

large

Sri

Lanka

zircon

564±4

(2-si

a).

decay

constants

and

composition

follows:

238

9.8485

-10

235

1.55125

-10

238

235

137.88