Avalonian and Cadomian terranes in North Dobrogea, Romania

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Precambrian Research 182 (2010) 217–229

Contents lists available at ScienceDirect

Precambrian Research

journa l homepage: www.e lsev ier .com/ locate /precamres

valonian and Cadomian terranes in North Dobrogea, Romania

on Balintonia,∗, Constantin Balicaa, Antoneta Seghedib, Mihai N. Duceac

Department of Geology, Faculty of Biology and Geology, “Babes-Bolyai” University, M. Kogalniceanu Str.1, RO-400084 Cluj-Napoca, RomaniaNational Institute of Marine Geology and Geoecology, 23-25 Dimitrie Onciul Str., Bucharest, RomaniaDepartment of Geosciences, University of Arizona, Gould-Simpson, Tucson, AZ 85721, USA

r t i c l e i n f o

rticle history:eceived 27 January 2010eceived in revised form 23 July 2010

a b s t r a c t

The North Dobrogea orogen is a collage of dismembered terrane fragments between the Moesian plat-form and East European craton (Baltica). It records Alpine and Variscan deformation, magmatism andmetamorphism. Its basement comprises three metamorphic complexes (Boclugea, Megina and Orliga)

ccepted 13 August 2010

eywords:orth Dobrogeaetrital zircon ages

that are separated by tectonic boundaries. Detrital zircon U/Pb ages suggest the Boclugea and Orliga com-plexes represent two peri-Gondwanan terranes of Avalonian and Cadomian affinities, respectively. Thenew data clarify the original relationships between the North Dobrogea terranes, and Baltica and Moesiaplatform.

© 2010 Elsevier B.V. All rights reserved.

errane provenanceoclugea and Orliga complexes

. Introduction

The paleo-tectonic reconstruction of pre-Alpine Europe west ofrans-European Suture Zone (TESZ) (Fig. 1, inset) hinges on thedentification of pre-Alpine terranes in the basement of Alpine oro-ens. In North Dobrogea (Fig. 1, inset), an isolated Alpine orogen isxposed (e.g. Sandulescu, 1984), made up of terranes of unknownffinity. This orogen has no apparent links toward the Carpathiansnd ends beneath Black Sea. Owing their proximity to the TESZ (e.g.haraoh, 1999), identification of these pre-Alpine components andheir provenance is essential to our understanding of geologicalistory of the southeastern Europe, including the Balkan Peninsuland western Turkey.

In order to clarify this issue, quartzite layers from severalock assemblages from the North Dobrogea orogen have beenampled for detrital zircon, the age distributions of which ineri-Gondwanan terranes have been shown to distinguish amongvalonian and Cadomian provenance (e.g. Nance and Murphy,994, 1996; Linnemann et al., 2004, 2007; Samson et al., 2005).nfortunately, no Sm/Nd data on North Dobrogea metamorphic

ocks are reported so far.

.1. Geological setting

The North Dobrogea Alpine orogen (Fig. 1) is located betweenhe Peceneaga-Camena transform fault to the south and Sfântu

∗ Corresponding author.E-mail address: [email protected] (I. Balintoni).

301-9268/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.precamres.2010.08.010

Gheorghe Fault to the north. To the west and east, the orogen isbounded by the Danube River and the Black Sea, respectively. Onthe southern side of the Peceneaga-Camena fault, Neoproterozoicrocks of Central Dobrogea are exposed (Fig. 1, inset), representingthe basement of the northeastern part of the Moesian platform (e.g.Seghedi et al., 2005a). The Alpine orogen of North Dobrogea con-sists of several Cimmerian nappe structures (Sandulescu, 1984) oralternatively high-angle thrusts, that involve relics of a Variscanorogen (Seghedi, 2001; Seghedi et al., 1999, 2004). These Cimme-rian tectonic units comprise a large variety of rock assemblages,including metamorphic, sedimentary and igneous complexes. Themetamorphic complexes are separated into three units: Orliga,Megina and Boclugea groups (Mirauta and Mirauta, 1962; Mirauta,1966; Patrulius et al., 1973; Seghedi, 1998). The Orliga and Meginagroups are medium-grade assemblages with sedimentary andigneous (mafic and acid) protoliths metamorphosed to kyanitegrade (Seghedi, 1975, 1980). The Boclugea group is a low-grademetamorphic rock assemblage comprising pure quartzites, blackquartzites, dark phyllites and mica-rich quartzites (Seghedi, 1986).The sedimentary successions include late Ordovician to Devonianfossiliferous formations, Carboniferous-Early Permian clastics andvolcaniclastic deposits, and Triassic, Jurassic and late Cretaceoussequences associated to the Alpine orogenic processes. Igneoussuites related to the Variscan and Alpine orogenies also occur.

The relationship between the three metamorphic complexes is

tectonic. Because of this and because each group originated in a dif-ferent tectonic setting and shows a different metamorphic history(e.g. Seghedi, 1999), the complexes can be described as parts of dis-tinct terranes. Based on indirect evidence, a Precambrian age hasbeen presumed for Orliga and Megina groups (Kräutner and Savu,

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Fig. 1. Geological map of North Dobrogea. Top inset: location of Dobrogea area (square) on a map showing the basement structure and Neoproterozoic, Caledonian, Variscanand Alpine deformation belts in Europe. TESZ – Trans-European Suture Zone; SC – South Carpathians; EC – East Carpathians; AP – Apuseni Mountains; M – Malopolska; US– Upper Silesia; SP – Scythian Platform; Armorican Terrane Assemblage: A – Armorica; MC – Massif Central; I – Iberia; BM – Bohemian Massif. Modified after Seghedi et al.(2005a). Upper right inset: main structural elements of Dobrogea. SfGF – Sfântu Gheorghe Fault; PCF – Pecineaga-Camena Fault; COF – Capidava-Ovidiu Fault; PLF – PalazuFault. Simplified after Seghedi et al. (2005a).

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I. Balintoni et al. / Precambrian Re

Table 1GPS coordinates of samples analyzed in this study. Map datum WGS84.

Sample no. GPS coordinates

336 N45 15.845 E28 09.474338 N45 15.762 E28 09.511

1bCS

dogT

1

rzctT

frgdom

CuDaiefiocg

wUw2

a(cua

y2

aammdf

339 N45 16.489 E28 07.318340 N45 23.274 E28 06.834345 N45 06.282 E28 16.601347 N44 21.467 E28 34.380

978; Seghedi et al., 1980, 1988; Kräutner et al., 1988). Similarly,ut supported by some palynological data, a late Proterozoic-earlyambrian age has been inferred for the Boclugea group (Vaida, ineghedi, 1999).

To better constrain the age of these complexes and thereby aeeper understanding of North Dobrogea geology, five outcropsf Boclugea quartzites and an additional quartzite from the Orligaroup have been sampled for U/Pb detrital zircon geochronology.he results form the subject of this paper.

.2. Samples mineralogy and analytical methods

Samples 336, 338, 340 and 345 from the Boclugea group rep-esent almost pure quartzites and contain accessory Fe-oxides andircon. Sample 347 (Boclugea group) additionally contains mus-ovite, whereas sample 339 from the Orliga group has minor rutile,ourmaline and zircon. Sampling location coordinates are given inable 1.

For zircon extraction, up to 10 kg of fresh material was sampledrom each outcrop. In order to extract the zircon grains, the mate-ial was subjected to the classical techniques of crushing, milling,ravitational separation and heavy liquids treatment. At least 100etrital crystals were randomly selected (regardless their size, formr color) from each sample using a stereomicroscope and thenounted in 25 mm epoxy and polished.The LA-ICP-MS measurements were performed at the Laser-

hron facility, Department of Geosciences, University of Arizonasing an ISOPROBE MC-ICP-MS equipped with a New WaveUV193 nm Excimer. A laser spot diameter of 35 �m was used forll analyses. Each grain analysis consisted of a single 20-secondntegration without laser firing to obtain on-peak background lev-ls, 20 one-second integrations with the laser firing, followednally by a 30-second purge with no laser firing in order to deliverut the remaining sample (e.g. Dickinson and Gehrels, 2003). Hgontributions to 204Pb were removed by taking on-peak back-rounds.

The ablated material was carried via argon gas into the IsoProbe,hich is equipped with a sufficiently wide flight tube to allow forand Pb isotopes to be measured simultaneously. Measurementsere made in static mode, using Faraday detectors for 238U, 232Th,

08–206Pb, and an ion-counting channel for 204Pb.Common Pb corrections were made using the measured 204Pb

nd assuming initial Pb compositions from Stacey and Kramers1975). Analyses of zircon standards of known isotopic and U–Pbomposition were conducted in most cases after each set of fivenknown measurements to correct for elemental isotopic fraction-tion.

The samples were analyzed in hard extraction mode, whichielded higher and more variable Pb/U fractionation. The06Pb*/238U values for the standards were corrected for an aver-ge of 15.3% (±2.6%) and 27.2% (±3.0%) fractionation (uncertainties

t 2� standard deviation of ∼20 analyses), respectively. The U/Pbeasurements, ratios, ages and errors are shown in Supplementaryaterial. Using the ISOPLOT program of Ludwig (2001), Concor-

ia diagrams (with data point error symbols at 1�) were plottedor each sample. The best ages, which are considered to be the

search 182 (2010) 217–229 219

206Pb/238U ages if younger than 800 Ma and the 207Pb/206Pb agesif older than 800 Ma (e.g. Gehrels et al., 2008 and referencestherein), have been additionally plotted on age vs. frequency his-tograms. Analyses with >10% uncertainty, and those more than10% discordant or 5% reverse discordant, are excluded from furtherconsideration.

2. Results

2.1. Boclugea quartzites

Sample 336. The zircon grains are well rounded and transparent,without inclusions. Some crystals are little elongated, and manyappear as prism fragments. Their appearance suggests significanttransport before deposition. The ages obtained on 72 zircon grainsrange between 500 and 3102 Ma (late Cambrian to Mesoarchaean)(Figs. 2 and 9). Significant peaks occur at 0.55–0.6 Ga, 1.15–1.2 Gaand 1.45–1.6 Ga with a spread of ages between 1.7 and 2.15 Ga. Onlyfour ages are older than 2.15 Ga. The maximum depositional age forthis sample (500 Ma) is Cambrian (Paibian Stage).

Sample 338. This sample shows a large grain size distributionof well-rounded grains with a wide variety of shapes. Ball-like orbarrel-like grains are transparent, colorless, or reddish and free ofinclusions. Ninety-seven dated grains yielded ages between 514and 2822 Ma (Figs. 3 and 9). The most prominent peak is between0.55 and 0.6 Ga, similar to the previous sample. A continuous agespread between 0.95 and 1.45 Ga is followed by significant ageclusters at 1.5–1.6 Ga, 1.7–1.9 Ga and 2.5–2.85 Ga. An importantage concentration occurs at 1.95–2.1 Ga, and only one age occursbetween 2.15 and 2.55 Ga. The maximum depositional age for thissample (514 Ma) is Cambrian.

Sample 340. The zircon grains in this sample are colorless orpinkish, transparent and free of inclusions. Eighty-eight datedgrains record ages between 502 and 2866 Ma (Figs. 4 and 9).The highly discordant age of 472.4 Ma was discarded. Age con-centrations occur at 0.5–0.65 Ga, 1.15–1.65 Ga, 1.75–2.2 Ga and2.55–2.8 Ga. There is also an isolated peak between 1.00 and1.05 Ga. The maximum depositional age for this sample (502 Ma) isCambrian, Epoch 3, Guzhangian Stage.

Sample 345 contains relatively large ball or barrel-like grainsthat are transparent colorless or reddish and free of inclusions.Sixty-seven dated grains from this sample show an age distributionbetween 536 and 2916 Ma (Figs. 5 and 9). A prominent peak occursat 0.55–0.6 Ga. The remaining ages are Mesoproterozoic with clus-ters at 1.9–2.15 Ga and 2.5–2.95 Ga, and a large gap between 2.15and 2.5 Ga. The maximum depositional age for this sample (536 Ma)is Cambrian, Terrneuvian Epoch, Fortunian Stage.

Sample 347. Slightly abraded, red longish zircon grains dominatethis sample, in contrast to those of other samples which appearintensely abraded. Ninety-eight dated grains show an age distri-bution between 896 and 2927 Ma (Figs. 6 and 9). The ages spreadcontinuously between 0.9 and 2.15 Ga. Following a gap between2.15 and 2.65 Ga, the remaining ages lie in the 2.65–2.95 Ga inter-val. The maximum depositional age for this sample (895 Ma) isNeoproterozoic, Tonian Period. However, we consider this age asaccidentally that old, probably due to some limiting conditions thatrestrained the sources distribution.

2.2. Orliga rock assemblage

Sample 339. This sample contains numerous, large well-roundedgrains. The majority are colorless, transparent and free of inclu-sions. However, several grains contain opaque inclusions and somecrystals are gray shaded and less transparent. No reddish or pink-ish grains were observed. Ninety grains from this sample record

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ple 33

aanti2t

Fig. 2. Binned plot of U–Pb best ages from sam

n age range between 513 and 3088 Ma (Figs. 7 and 9), with twodditional ages reset at 373 and 383 Ma. The first and most promi-ent age concentration occurs between 0.5 and 0.75 Ga, and only

wo ages occur in the 0.75–1.7 Ga interval. Within the 1.7–3.1 Ganterval, several peaks occur at 1.8–1.85 Ga, 2.0–2.1 Ga, 2.4–2.5 Ga,.55–2.6 Ga and 2.65–2.8 Ga. The maximum depositional age forhis sample (513 Ma) is Cambrian.

Fig. 3. Binned plot of U–Pb best ages from sample 33

6. Inset: Concordia plot of U–Pb isotopic ratios.

3. Discussion

3.1. Age of the North Dobrogea terranes

The Orliga terrane has been assumed to be of Precambrian age,whereas the age of the Boclugea terrane is inferred to be lateProterozoic-early Cambrian based on palynological data (see geo-

8. Inset: Concordia plot of U–Pb isotopic ratios.

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ple 34

latblae

Fig. 4. Binned plot of U–Pb best ages from sam

ogical background). However, our youngest U/Pb detrital zirconges indicate a maximum mid-late Cambrian deposition age forhe sedimentary protoliths of both the Orliga and Boclugea assem-

lages. Intrusive igneous protoliths in the Orliga group are therefore

ikely to be post-Cambrian in age. Due to the limited outcroppingrea of Orliga rocks that made impossible a detailed sampling strat-gy, only one metasedimentary sample was collected.

Fig. 5. Binned plot of U–Pb best ages from sample 34

0. Inset: Concordia plot of U–Pb isotopic ratios.

3.2. Terrane provenance

The origin of North Dobrogea is ambiguous. North Dobrogea was

assumed to be part of the southern margin of the Rheic Ocean andconsequently is of Saxothuringian affinity, that is, a Cadomian one(Pharaoh, 1999). Oczlon et al. (2007) view North Dobrogea as acomponent of the Hun superterrane, which also implies a Cadomian

5. Inset: Concordia plot of U–Pb isotopic ratios.

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ple 34

oNf

3

tb

Fig. 6. Binned plot of U–Pb best ages from sam

rigin. Our data, however, suggest a more complex architecture fororth Dobrogea involving a collage of several terranes (or terranes

ragments) with different provenances.

.3. Boclugea terrane

Because the five individual age distribution diagrams plotted forhe Boclugea quartzites are generally similar, they have been com-ined into a single one (Fig. 8). The main features of this diagram can

Fig. 7. Binned plot of U–Pb best ages from sample 33

7. Inset: Concordia plot of U–Pb isotopic ratios.

be summarized as follows: (i) the most prominent age group occursin the late Neoproterozoic-early Cambrian; (ii) the entire Mesopro-terozoic time interval is well represented by detrital ages; (iii) animportant age concentration occurs in Paleoproterozoic between

1.7 and 2.2 Ga, and (iv) there are a significant number of Neoar-chaean age clusters between 2.55 and 2.85 Ga. Age minima or gapsin the intervals 0.75–0.85 Ga, 1.65–1.7 Ga and 2.2–2.5 Ga.

According to Samson et al. (2005), Linnemann et al. (2007),Oczlon et al. (2007) and Rino et al. (2008), the main suppliers of

9. Inset: Concordia plot of U–Pb isotopic ratios.

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best a

Mozbebisetaz(rpc0zbDtcq(aBBoi

rpweapthes

Fig. 8. Binned plot of all U–Pb

esoproterozoic detrital zircons for the Paleozoic terranes locatedutboard of Baltican margin could be Baltica, Laurentia and Ama-onia. Because a period of magmatic quiescence occurs in Laurentiaetween 1.61 and 1.49 Ga (Samson et al., 2005) and Cadomianvents are absent (Linnemann et al., 2007), this continent cane excluded as the provenance of the Boclugea zircons. Discrim-

nation between a Baltican and an Amazonian provenance basedtrictly on detrital zircons is more difficult. A great resemblancexist between the present day detrital zircon age distribution pat-ern shown by Volga river sediments of Baltican origin (Rino etl., 2008) and that shown by the Boclugea quartzites. However,ircons with ages between 0.6 and 0.75 Ga are missing in BalticaKuznetsov et al. (2010). Their data are consistent with the dataeported by Zelazniewicz et al. (2009) who found a single Neo-roterozoic detrital zircon of 841.6 Ma in the Ediacaran sedimentsovering the western Baltican margin. Because the ages between.6 and 0.75 Ga are relatively well represented in the Boclugeaircon samples, a non-Baltican (Avalonian) provenance is plausi-le. Moreover, we favour this provenance because: (i) the Northobrogea orogen was affected by Variscan events, the Boclugea

errane being intruded by Variscan granites unknown in the Balti-an area (Seghedi, 1999); (ii) thick late Cambrian-early Ordovicianuartzites are not known in the cover of the Moldavian platformthe SW margin of the East European Craton in Romania) (Mutihacnd Ionesi, 1974); (iii) a Cadomian terrane lies adjacent to theoclugea terrane (see below) again an uncommon situation for thealtican margin; and (iv) the type and arrangement of the Pale-zoic fossiliferous sedimentary sequences in North Dobrogea arencompatible with a Baltican origin (Oczlon et al., 2007).

If one accepts an Avalonian provenance for the Boclugea ter-ane, then its quartzite formations might be part of the largeost-Pan African sedimentary cover of northern Gondwana thatas deposited during the late Cambrian-early Ordovician and is

xposed today from the Arabian Peninsula to Morocco (Avigad etl., 2005). We can assume that these sediments also covered, at least

artially, the future Avalonian and Cadomian terranes. Evidence ofhis is given by the Ordovician Armorican quartzites of Iberia, whichave also yielded Avalonian detrital zircons (e.g. Fernández-Suárezt al., 2002a). The hypothesis that the Amazonian detrital zirconources for the Armorican Quartzites moved toward North Africa

ges from Boclugea quartzites.

before their deposition (Fernández-Suárez et al., 2002b) is howeverproblematic, as it requires that fragments of Amazonia containingall the Mesoproterozoic detrital zircon sources migrated eastward.As an Avalonian terrane, Boclugea was probably part of Far EastAvalonia (e.g. Oczlon et al., 2007). This easternmost part of Avalo-nia was repeatedly fragmented along the southwestern margin ofBaltica during the Silurian and Devonian (Oczlon et al., 2007). Inaddition, North Dobrogea was the locus of new displacements dur-ing the Variscan and Alpine orogenies. Due to these reasons, thepresent location of Boclugea terrane probably differs significantlyfrom its original docking place.

3.4. Orliga terrane

The detrital zircon age distribution pattern in the Orliga ter-rane is quite different from that shown by the Boclugea quartzites.The histogram in Fig. 7 shows that only two ages fall in the0.75–1.7 Ga interval. This gap covers the entire Mesoproterozoicin sharp contrast with the Boclugea detrital zircon age distri-bution. Important age clusters occur at 0.5–0.75 Ga, 1.75–2.1 Ga,2.3–2.5 Ga and 2.55–2.85 Ga. This distribution of detrital zirconages shows striking similarities with those of SW Iberia and Cado-mia (Fernández-Suárez et al., 2002b), as well as with those ofSaxothuringia (Linnemann et al., 2004, 2007). Such patterns arecharacteristic of the Cadomian terranes (e.g. Samson et al., 2005),which originated close to the West African craton (e.g. Nance andMurphy, 1994, 1996; Linnemann et al., 2008). Hence, the Orligaterrane is considered to be a typical Cadomian terrane, unlike theAvalonian Boclugea terrane.

3.5. Orogenic sources of the detrital zircons

For both terranes, the Cadomian orogen in the sense ofLinnemann et al. (2008) is the most important detrital zirconsource. The ages ranging between 750 and 950 Ma contained by

Boclugea quartzites could be sourced in the Goias magmatic arcwhich flanks the Amazon craton in Tocantis Province, Brasil (e.g.Pimental et al., 2000). Such ages were found in Southern Mexico byNance et al. (2009) and interpreted as being sourced in that orogen.Regarding the Mesoproterozoic sources that supplied the Boclugea

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Table 2Terranes in the vicinity of TESZ, in Southern Poland. (1) Pharaoh (1999); (2) Winchester et al. (2002); (4) von Raumer et al. (2003); (9) Winchester et al. (2006); (13) Oczlon et al. (2007); (17) Zelazniewicz et al. (2009); (19)Kalvoda and Bábek (2010).

Provenance Peri-Amazonian pre-Avalonian Avalonian migratedpre-Avalonian

pre-Avalonian Avalonian Far EastAvalonia

EasternAvalonian

Baltican

Terranes

Moravo-Silezia (1) Moravo-Silezia (4)Bruno-Silezia (2) Bruno-Silezia (2)

Brunovistulia consisting of Thaya(Brno block)

Brunovistulicum (4) Bitesh (part of Moravicum)(19) Moravicum (9)

Slavkov (upper Silezia)Rzeszotary (upper Silezia, 17) Rzeszotary (13) upper Silezia (13)Malopolska (2) Malopolska (1, 9, 13, 17, 19)Lysogory (2) Lysogory-Malopolska (4) Lysogory (1, 9, 13, 19)

Table 3Terranes in the vicinity of TESZ, in SE-Europe and NW Turkey. (1) Pharaoh (1999); (2) Winchester et al. (2002); (3) Stampfli et al. (2002); (4) von Raumer et al. (2003); (6) Seghedi et al. (2005a); (7) Seghedi et al. (2005b); (8)Yanev et al. (2005); (9) Winchester et al. (2006); (10) Yanev et al. (2006); (11) Vaida and Verniers (2006); (13) Oczlon et al. (2007); (17) Zelazniewicz et al. (2009); (19) Kalvoda and Bábek (2010).

Provenance Peri-Amazonian pre-Avalonianor Gondwana derivedpre-Avalonian

Extension of Avalonia,Avalonian satellites orAvalonian

Far East Avalonia Cadomian, Cadomianpart of Hun, ATA

Associated toBrunovistulia orBaltican

Baltican Unclear affinity

Terranes

North Dobrogea (1, 13)Moesian Platform (2) Moesia (3, 4) Moesia (9) Moesian Platform (1, 8)Central Dobrogea (2) Central Dobrogea (7) Central Dobrogea (13) Central Dobrogea (9) Central Dobrogea (17)South Dobrogea (2) South Dobrogea (13) South Dobrogea (7, 9) South Dobrogea (17)

Zonguldak (2, 3, 10) Zonguldak (4)Istanbul (3, 4, 7) Istanbul (8, 10)East Moesia (6, 10, 19) East Moesia (11) East Moesia (17)

West Moesia (11) West Moesia (6, 13, 19) West Moesia (7)Istanbul + Zonguldak (17) Istanbul block (+Zonguldak, 9,

19)Istanbul-Zonguldak (13)

West Moesia (17)

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225

Table 4Pre-Alpine terranes in the basement of Carpathians, Serbo-Macedonean Massif, Menderes, Hellenides and central and Southern Turkey. (2) Winchester et al. (2002); (3) Stampfli et al. (2002); (4) von Raumer et al. (2003); (5)Munteanu and Tatu (2003); (7) Seghedi et al. (2005a); (8) Yanev et al. (2005); (9) Winchester et al. (2006); (10) Yanev et al. (2006); (12) Carrigan et al. (2006); (13) Oczlon et al. (2007); (14) Zulauf et al. (2007); (17) Zelazniewiczet al. (2009); (18) Meinhold et al. (2009); (19) Kalvoda and Bábek (2010).

Provenance Peri-Amazonianpre-Avalonian orBaltican

Avalonian Eastern Avalonia Avalonian or ATA(Cadomian)

Cadomian, Hun,Eastern Hun, EuropeanHunic, ATA

Minoan, EastMediterranean,NE-Gondwanan

Future Cimmerian Baltican Unclear affinity

Terranes

Pannonia (2)Taurus (2) Taurus (4)

Serbo-Macedonean(13)

Serbo-Macedonean (3,4)

Dinarides-Hellenides (4)Kirshehir (4)Menderes (4)

Rebra-Tulghes(E-Carpathians, 5)

Bretila(E-Carpathians, 5)

Danubian (17) Danubian (7)Balkan (8, 9, 10, 13, 19)

Thracian (Rhodope +S-Macedonia, 8)

Tatra (9)Rhodope (Thracian, 9)

Strandja (12) Strandja (9)Sakaria (, 19)Eastern Pontides (9)

Sredna Gora (12)Gemerides (13)South Carpathians(13)East Carpathians(13)

Pontides (13)Cyclades (14)Crete (14)Menderes-Taurus(14)

West Carpathians(14)

West Carpathians (14)

Zemplin (17)Apuseni Mountains(17)

Pirgadikia(S-Macedonia, 18)

Vertiskos (18)Outer Carpathians (19)Getic (19)Anatolide-Tauride (19)

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babili

qAaSbiVhagaST

Fig. 9. Normalized pro

uartzites, we refer to the data of Cordani and Teixeira (2007).ccording to these authors, numerous intrusions of 1.6–1.3 Gage are associated with the Rio Negro-Juruena and Rondonian-an Ignacio accretionary orogens of Amazonia. The important peaketween 1.5 and 1.55 Ga may be linked to the anorogenic gran-

tes that intrude the basement of the older Maroni-Itacaiunas andentuari-Tapajos orogens. Similarly, the peak around 1.0 Ga couldave been sourced in the Grenvillian-age Sunsas-Aguapei orogen,

ctive between 1.25 and 0.92 Ga. The source of the important ageroup between 1.25 and 1.15 Ga, mentioned by Samson et al. (2005)s characteristic of the Avalonian terranes, is less obvious. Theunsas-Aguapei granites are no older than 1120 Ma (Cordani andeixeira (2007). However, some detrital zircon ages of ca. 1215 Ma

search 182 (2010) 217–229

ty plots of all samples.

have been found in sediments from Nova Brasilandia belt. We sug-gest that the source of 1.25–1.15 Ga zircons has been eroded away.

The interval 2.2–1.7 Ga in the Boclugea quartzite detrital zirconage patterns could be sourced in the Maroni-Itacaiunas, Ventuari-Tapajos and Rio Negro-Juruena orogens of Amazonia (Cordani andTeixeira, 2007). Finally, the 2.55–2.95 Ga zircons were probablysourced in the Central Amazonian Province including its Carajaspart.

Regarding West Africa as a source of the detrital zirconsin the Orliga quartzite, we cite the compilation of Goodwin(2000), which identify ages of 2.2–1.9 Ga in the Eburnean domain,ages of 2.1–1.9 Ga and 1.8–1.6 Ga in the Reguibat shield, andages of 2.3–1.7 Ga in the Anti-Atlas domain. These ages span

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F SaxoS ir; 7 –M

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ig. 10. Paleogeography of peri-Gondwanan terranes at ca. 570 Ma. 1 – Armorica; 2 –erbo-Macedonean, Sredna Gora; 6 – Sakarya, Eastern Pontides, Menderes, Kirshehodified from Linnemann et al. (2004), Linnemann et al. (2008).

he 2.25–1.7 Ga age range present in the Orliga quartzite. The.3–2.85 Ga interval could be sourced in the equivalent of the Cara-

as domain in the West Africa, the Kenema-Man block (Cordani andeixeira, 2007).

.6. Boclugea and Orliga terranes provenance within the regionaleological frame

There are numerous references addressing the pre-Alpine ter-anes provenance within the central and SE-Europe and Anatoliaegion. Different controversial opinions presented in Tables 2–4ould be explained by the scarcity of reliable and consistenteochronological data supporting other geological evidences, withhe exception of Carrigan et al. (2006) for Sredna Gora and Strandja,ulauf et al. (2007) for Hellenides, Kohut et al. (2008) and Putist al. (2008) for West Carpathians, Zelazniewicz et al. (2009) for

runovistulia, Malopolska and Central Dobrogea and Meinhold etl. (2009) for Serbo-Macedonean Massif.

Due to the minor contribution of Grenvillian sources and the sig-ificant input from those of Mesoproterozoic and Paleoproterozoicge, a source in the eastern part of East Avalonia seems likely for

thuringia; 3 – Tepla-Barrandia; 4 – Proto-Alps; 5 – Carpathians (without Danubian),Orliga; 8 – Boclugea, Danubian and its correlatives in Balkans; 9 – Moesia.

Boclugea terrane, (Fig. 9). The Orliga terrane differs from the EastMeditarranean Cadomian terranes in lacking a Grenvillian input.This feature places it among the “true” Cadomian terranes originat-ing close to West Africa. These terranes are referred to as Cadomiaby Linnemann et al. (2007). The Boclugea terrane with Avalonianaffinity and the Orliga terrane with West African affinity repre-sent exotic blocks in the “Turkish plate, Aegean and Dobrogea”microplate of Linnemann et al. (2007) and their inferred initial loca-tions is shown in Fig. 10. The strong Variscan metamorphic imprinton the Orliga rocks (e.g. Seghedi, 1975, 1999) together with theVariscan granites intruded within the Boclugea terrane, suggestthat a portion of the Rheic suture is preserved in the North Dobrogeabetween the two terranes, with Boclugea terrane as the upper plate.It is currently difficult to determine if the Boclugea terrane of Aval-onian affinity accreted to Scythian platform (the thinned margin ofBaltica) or to Moesia. A solution hinges on the provenance of Moe-sia and its relationship with the South Carpathians and Balkans,

currently an unsolved problem. Presumably, Moesia was a peri-Amazonian pre-Avalonian terrane (Fig. 10). According to Balintoniet al. (2009, 2010) the pre-Alpine Carpathian terranes (except theDanubian terranes) show northeastern Gondwanan provenance,

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mplying they are eastern Mediterranean Cadomian terranes (theo called “Minoan terranes” of Zulauf et al., 2007). Similar to Northobrogea, the trace of Rheic suture is visible in South Carpathi-ns, between the Cadomian Sebes-Lotru terrane and the Danubianerranes of Avalonian provenance.

The basement tectonic architecture of North Dobrogea andouthern Carpathians may be similar. If true, then during theariscan orogeny the South Carpathians were connected to Northobrogea to the NW and North Dobrogea extended to NW beneath

he present East Carpathians toward the Moravo-Silesian zonehere the Rheic suture re-appears (Nance et al., 2010). The Northobrogea-South Carpathians continuity was broken during Earlyretaceous westward migration of Moesia, when the western Blackea basin opened (Balintoni and Baier, 1997). In this hypothesis, theanubian and Boclugea terranes, all of Avalonian affinity, accreted

o Moesia during the Early Paleozoic. Different North Gondwananrovenances of Orliga and Carpathian terranes support a frag-entary arrangement of ATA (Armorican Terrane Assemblage)

omponents (e.g. Tait et al., 2000) or European Hunic superterranee.g. Kroner et al., 2008). Cadomian terranes independently driftedoward Laurussia or were transported by strike-slip mechanismslong the continental margins.

. Conclusions

U–Pb detrital ages from the North Dobrogea orogen indicate aomplex pre-Alpine structure consisting of peri-Gondwanan ter-anes with both Avalonian (Boclugea terrane) and Cadomian (Orligaerrane) affinities. The youngest detrital zircons in the Boclugeand Orliga metamorphic units suggest a maximum Middle to Lateambrian deposition age.

The North Dobrogea orogen preserves a portion of the Rheicuture, tracing between Boclugea and Orliga terranes. This sutureould be connected with the Rheic suture, already known in theouth Carpathians. We further suggest that the Boclugea terranerom North Dobrogea together with the Danubian terranes fromouth Carpathians and their correlatives from Balkans accreted tooesia during Early Paleozoic.

cknowledgements

This research was financially supported by grant ID-480 CNCSIS.he authors wish to express their gratitude to Scott Samson andspecially to Damian Nance, for their careful revisions and insight-ul suggestions and observations which improved the quality ofhis paper. Dr. V. Valencia is gratefully acknowledged for his helpith analytical procedures and for his careful supervision of data

cquisition.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at doi:10.1016/j.precamres.2010.08.010.

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