geochemistry and geochronology of hp mélanges from tinos and andros, cycladic blueschist belt,...

Lithos 117 (2010) 61–81

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Geochemistry and geochronology of HP mélanges from Tinos and Andros, cycladicblueschist belt, Greece

Florian Bulle ⁎, Michael Bröcker, Claudia Gärtner, Alan KeaslingInstitut für Mineralogie, Universität Münster, Corrensstraβe 24, 48149 Münster, Germany

⁎ Corresponding author. Department of Earth ScieNewfoundland, St. John's, Canada NL A1B 3X5.

E-mail address: [email protected] (F. Bulle).

0024-4937/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.lithos.2010.02.004

a b s t r a c t
a r t i c l e i n f o
Article history:Received 31 August 2009Accepted 11 February 2010Available online 19 February 2010

Keywords:HellenidesCycladesOphiolitesMélangeU–Pb zircon geochronology

U–Pb zircon geochronology, Sr–Nd isotope and bulk-rock geochemistry have been applied to meta-igneousand meta-sedimentary rocks from high-pressure metamorphic mélanges exposed on the Cycladic islands ofTinos, Syros and Andros. Ion microprobe (SHRIMP) U–Pb zircon dating of 7 samples representing meta-igneous blocks (Tinos), a blackwall zone (Tinos) and chlorite–talc schists from block-matrix contacts (Syrosand Tinos) yielded Cretaceous ages of c. 80 Ma. Many of the criteria commonly used to distinguish betweenmagmatic or metamorphic zircon genesis (internal structure, Th/U ratio, REE characteristics, Ti-in zirconthermometry, enclosed mineral phases) do not provide unambiguous constraints for the mode of formation.However, a magmatic origin for Cretaceous zircon of meta-gabbros and eclogites is considered likely.Supporting evidence for a previously suggested metamorphic origin for c. 80 Ma zircon in eclogite has notbeen found. Zircon of the same age occurring in chlorite–talc schists is presumably related to non-magmaticprocesses. Well-defined Cretaceous age groups clustering at c. 79 Ma also occur in the detrital zirconpopulations of 2 quartz mica schists representing the mélange matrix on Tinos, and suggest a much latertime for sediment accumulation than previously assumed. The importance of c. 57 Ma zircon ages remainsunclear, but may record either HP metamorphic processes or a post-57 Ma depositional age. The youngestage group in a third quartz mica schist from Tinos, collected outside the main mélange occurrences, clustersat c. 226–238 Ma. In all clastic metasediments from Tinos, most data points plot along the concordia betweenc. 300 and 900 Ma; single data points indicate concordant ages of c. 2.5 Ga, 2.3 Ga and 1 Ga, respectively. Theyoungest 206Pb/238U age group that has been recognized in a felsic paragneiss from Andros indicates an ageof 163.1±3.9 Ma, and mostly represents overgrowths around zircon with ages in the range from ∼272 to∼289 Ma. Single data points of other inherited cores provided 206Pb/238U ages of c. 630 and c. 930 Ma. Meta-gabbros from Tinos show a large compositional variability and were found at 4 locations, each with distinctcompositional characteristics, suggesting different crystallization histories, different sources and/orsignificant post-magmatic disturbance. The geochemistry of mélange blocks and the identical U–Pb zirconages suggest that the block-matrix associations on Tinos and Syros can be grouped together. On a broaderregional scale, there seem to be similarities between some meta-igneous rocks from Tinos and Evvia. Fieldrelationships indicate that the mélanges occurring in southern Andros and northern Tinos can be correlated,but supporting geochemical and/or geochronological evidence for this interpretation could not beestablished. Previously published Jurassic ages for mafic and felsic mélange blocks from Andros suggest agenetic relationship to the ophiolite occurrences exposed in the larger Balkan region. A similar regionalcorrelation is also considered likely for the Cretaceous meta-gabbros from Tinos and Syros, but cannot bedocumented with certainty.

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1. Introduction

The Attic-Cycladic Crystalline Belt (ACCB; Fig. 1) represents amajor tectonostratigraphic unit of the Hellenides and records acomplex structural and metamorphic evolution that illustratesmany aspects of subduction zonemetamorphism and the exhumation

of high-pressure/low-temperature (HP/LT) rocks. Meta-ophioliticmélanges form a widespread but volumetrically subordinate part ofthe lower main unit of the ACCB. The mélanges consist of blocks andtectonic slabs ranging between b1 m to several hundred meters,which are enclosed in an ultramafic or metasedimentary matrix (e.g.Dixon and Ridley, 1987; Bröcker and Enders, 1999; Katzir et al., 2000;Bröcker and Enders, 2001). The mélange exposed on Syros hasattracted much attention, due to excellent preservation of HPassemblages, lithological variability, high block abundance anddistinct metasomatic reaction zones at contacts between blocks and

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Fig. 1. Simplified map of the Eastern Mediterranean region (after Barr et al., 1999) with major ophiolitic occurrences (after Robertson, 2002). Black rectangle outlines area shown asclose-up in Fig. 2A. Major tectonostratigraphic units: PAZ = Pre-Apulian Zone; IZ = Ionian Zone; GTZ = Gavrovo-Tripolitza Zone; PZ = Pindos Zone; PA = Parnassos; SPGZ =Subpelagonian Zone; PGZ = Pelagonian Zone; SZ = Sakarya Zone; AIZ = Ankara-Izimir Zone; MM = Menderes Massif; LN = Lycian Nappes.

62 F. Bulle et al. / Lithos 117 (2010) 61–81

an ultramafic matrix (e.g. Dixon and Ridley, 1987; Bröcker and Enders,1999, 2001; Bröcker and Keasling, 2006; Miller et al., 2009). Lessprominent block-matrix associations were recognized on Tinos,Andros, Evvia and Samos (Fig. 2A). The nature and origin of thesemélanges is controversial and has alternatively been related tosedimentary or tectonic processes (e.g. Bröcker and Enders, 1999,2001 and references therein). Blocks and matrix have experiencedconcurrent Tertiary HP/LT metamorphism (e.g. Bröcker and Enders,2001; Putlitz et al., 2005; Lagos et al., 2007) but the pre-Tertiarygeological and metamorphic histories of individual fragments arelargely unknown. The number of dated blocks is still relativelyrestricted and protolith ages were reported only for some blocks fromSyros and Andros (Keay, 1998; Tomaschek et al., 2003; Bröcker andKeasling, 2006; Bröcker and Pidgeon, 2007).

The HP/LT mélanges of the ACCB display many similarities in field,petrological, geochemical and geochronological characteristics thatsuggest a common temporal, spatial and genetic relationship.Important questions which remain still open are: regional correla-tions between different Cycladic occurrences, the possible agediversity and provenance of isolated blocks, the metamorphic historyof individual fragments, the protolith ages of metasedimentary matrixrocks and the mode of mélange formation (sedimentary vs. tectonicorigin). Of special interest is the correlation of ophiolites occurring inthe Cyclades to those located in the Hellenide–Dinaride region(mainland Greece, Albania, former Yugoslavia) and in the Taurides(Turkey). A more substantiated understanding of the block-matrixassociations is expected to provide crucial information for large-scalegeodynamic reconstructions and interpretation of the regionaltectonometamorphic history.

The present study concentrates on the meta-ophiolitic mélangeexposed on Tinos and its potential correlation to block-matrixassociations on the neighboring islands of Syros and Andros. Newbulk-rock geochemical and Sr–Nd isotope data as well as ionmicroprobe U–Pb zircon ages for both blocks (Tinos, Andros) andmatrix rocks (Syros, Tinos) are used to address regional implications.

2. Geological background

2.1. Regional setting

The ACCB consists of two major structural groups that areseparated by low-angle normal faults (e.g. Dürr et al., 1978; Okruschand Bröcker, 1990; Avigad et al., 1997). The upper group is poorlypreserved (Fig. 2A) and comprises a heterogeneous sequence ofunmetamorphosed Permian to Mesozoic sediments, ophiolites,greenschist-facies rocks with Cretaceous to Tertiary metamorphicages, as well as Late Cretaceous granitoids and medium-pressure/high-temperature metamorphic rocks (e.g. Patzak et al., 1994 andreferences therein). Available geochronological data suggest that atleast parts of the upper unit experienced two distinct episodes ofCretaceous metamorphism (c. 100–90 Ma and c. 80–70 Ma) and aMiocene (c. 24–21 Ma) tectonometamorphic event (e.g. Bröcker andFranz, 2006).

The lower group (hereafter referred to as Cycladic blueschistunit = CBU) comprises a pre-Alpidic crystalline basement and ametamorphosed volcano-sedimentary succession (e.g. Dürr et al.,1978; Okrusch and Bröcker, 1990), which includes the mélanges(Fig. 2A). Protolith ages of the volcano-sedimentary succession arebroadly constrained by sporadic fossil occurrences (e.g. Dürr et al.,1978; Melidonis, 1980) and U–Pb ages of detrital zircons (Keay,1998), which indicate Triassic to Cretaceous sedimentation. Ionmicroprobe U–Pb zircon dating of felsic meta-volcanic intercalationswithin metasediments yielded Triassic protolith ages (c. 235–245 Ma;Bröcker and Pidgeon, 2007). Both basement and cover rock succes-sions experienced at least two stages of Tertiary metamorphism.During the first stage, eclogite- to epidote-blueschist-facies conditionswere reached (T=∼450–550 °C, P=∼12–20 kbar; e.g. Bröcker et al.,1993; Trotet et al., 2001). In the northern and central Cyclades,subsequent overprinting occurred at greenschist-facies conditions(T=∼450–550 °C, P=∼4–9 kbar; e.g. Bröcker et al., 1993; Parra et al.,2002), whereas the southern Cyclades (e.g. Naxos) experienced

Fig. 2. Simplified geological maps of the Cycladic archipelago and the studied islands including sample locations. (A) Regional overview, modified after Matthews and Schliestedt(1984); (B) Andros, modified after Papanikolaou (1978) and Mukhin (1996); (C) Syros, modified after Keiter et al. (2004); (D) Tinos, modified after Melidonis (1980).

63F. Bulle et al. / Lithos 117 (2010) 61–81

amphibolite-facies metamorphism and partial melting (e.g. Buick andHolland, 1989). Regional metamorphismwas followed by widespreadintrusion of granitoids (e.g. Altherr et al., 1982).

HP/LT rocks mostly yield Eocene (55–40 Ma) metamorphic ages,while ages for greenschist- to amphibolite-facies rocks cluster in thelate Oligocene and Miocene (c. 25–16 Ma) (e.g. Altherr et al., 1979,1982; Wijbrans and McDougall, 1988; Wijbrans et al., 1990; Bröckeret al., 1993; Bröcker and Franz, 1998; Bröcker et al., 2004; Bröcker andFranz, 2006). HP metamorphism is mostly considered to be restrictedto the Eocene (e.g. Tomaschek et al., 2003), but may have started asearly as the Cretaceous (c. 80 Ma; Bröcker and Enders, 1999, 2001;Bröcker and Keasling, 2006).

2.2. Local geology and field characteristics of HP mélanges

On Tinos a representative segment of the ACCB is exposed in atleast three tectonic subunits (Fig. 2D). The two tectonic subunits

occupying the highest structural levels (Akrotiri Unit and Upper Unit)belong to the upper main unit of the ACCB and record amphibolite-and/or greenschist-facies P–T conditions (e.g. Patzak et al., 1994;Katzir et al., 1996; Bröcker and Franz, 1998). Most of the island is apart of the CBU, which is represented by the marble-schist sequenceof the Lower Unit (about 1250 m to 1800 m in thickness). Remnantsof HP rocks are locally preserved, but pervasively overprinted rockswith greenschist-facies mineral assemblages are more common (e.g.Melidonis, 1980; Bröcker, 1990; Bröcker et al., 1993). The wholesuccession can be subdivided from top to bottom by means of threemappablemarble horizons (m3,m2,m1;Melidonis, 1980). The lower-most part of the metamorphic rock pile consists of dolomite marblesand minor phyllites, which have been interpreted as either a para-authochthonous Basal Unit (Avigad and Garfunkel, 1989), or as anintegral part of the Lower Unit (Melidonis, 1980; Bröcker and Franz,2005). In eastern Tinos (Fig. 2D) a composite Miocene granitoidintrusion (c. 17–14 Ma; e.g. Altherr et al., 1982; Bröcker and Franz,


1998) caused contact metamorphism that affected both the UpperUnit and the Lower Unit (e.g. Avigad and Garfunkel, 1989, 1991;Bröcker and Franz, 1994; Bröcker and Franz, 2000).

Variably rounded blocks and rock fragments of different sizes(mostly b1 to 10 m, but up to 300 m) occur widely scatteredthroughout the marble-schist sequence of the Lower Unit. Block-forming rock types mainly comprise meta-gabbros, glaucophanites,eclogites, and jadeitites. Ultramafic blocks are rare and have only beenreported from a single occurrence (Buzaglo-Yoresh, 1995). Protolithages of individual blocks are unknown. Multigrain U–Pb zircon datesof c. 61–63 Ma for a jadeitite were previously interpreted tocharacterize a discrete HP stage (Bröcker and Enders, 1999). Basedon the results of the present work, these multigrain U–Pb zircon agesaremost likely geologicallymeaningless due tomixing of different agecomponents. The mélange matrix is primarily composed of clasticmetasediments, whereas some rock fragments are surrounded by arelatively thin serpentinite or chlorite schist envelope. Most blocks areclosely associated with the m3 and m2 marble sequences (Buzaglo-Yoresh, 1995; Bröcker and Enders, 1999, 2001), even though amélange has also been recognized a few meters above the lowermostm1 calcite marble near Panormos. In this area, relatively small blocks(up to c. 2 m in length) are dispersed in a matrix consisting ofgreenschists and clastic metasediments. Here, most blocks are felsicgneisses, but jadeitite and strongly weathered metabasic rocks alsooccur. Layers of meta-conglomerates are abundant (Fig. 2D).

On Andros (Fig. 2B), the metamorphic succession can be sub-divided into two tectonic units, theMakrotantalon Unit and the LowerUnit. Structural position and geochronological constraints suggestthat theMakrotantalon Unit belongs to the upper group of units of theACCB (e.g., Avigad et al., 1997; Bröcker and Franz, 2006). The LowerUnit (up to 1200 m in thickness) can be correlated with the Cycladicblueschist sequences, and mainly consists of a volcano-sedimentarysuccession that comprises marbles, carbonate-rich schists, clasticmetasediments and metavolcanic rocks (Papanikolaou, 1978). Min-eral assemblages document severe greenschist-facies metamorphism,but relict HP rocks are sporadically preserved. Disrupted bodies ofultramafic, gabbroic and meta-acidic rocks (up to several hundredmeters in length) were recognized at various lithostratigraphic levels(Papanikolaou, 1978; Buzaglo-Yoresh et al., 1995; Mukhin, 1996).Some of these occurrences are probably related to boudinage (Bröckerand Pidgeon, 2007). The most striking block-matrix association isdefined by numerous mappable serpentinite lenses within clasticmetasediments that occur at the highest lithostratigraphic level of theLower Unit, close to the overlying Makrotantalon Unit (Papanikolaou,1978). Previous studies suggested a meta-olistostromatic origin forthis occurrence (Papanikolaou, 1978; Mukhin, 1996). For the presentstudy, a HP mélange exposed at Cape Steno is of special importance(Fig. 2B; Buzaglo-Yoresh, 1995; Mukhin, 1996). This mélangepredominantly consists of non-deformed to variably sheared meta-gabbros, meta-acidic gneisses and ultramafic rocks (c. 50 m) that aresqueezed in between a basal marble and a higher schist sequence(Mukhin, 1996). Previous ion microprobe U–Pb zircon dating of ameta-gabbro and a gneiss provided 206Pb/238U ages of c. 154–160 Ma,which were interpreted to constrain the time of magmatic crystalli-zation (Bröcker and Pidgeon, 2007). In addition, the zircon populationof the gneiss records Middle Proterozoic (c. 1126 Ma and c. 1421 Ma)and Permian (c. 273 Ma and c. 281 Ma) inheritance. The Cape Stenooccurrence is considered to represent a litho- or tectonostratigraphicequivalent to the succession exposed in NW Tinos, where mafic andultramafic blocks are found within clastic metasediments (Buzaglo-Yoresh, 1995).

On Syros (Fig. 2C), two allochthonous units are found on top of themetamorphic succession: the amphibolite-facies Vari gneisses and agreenschist-facies mylonite sequence. These units show no indica-tions of HP metamorphism and most likely represent down-faultedtectonic slices of the upper group of units (Ridley, 1984). The largest

part of the island belongs to the CBU, which occurs in twolithostratigraphic or tectonic subunits: an interlayered marble-schistsequence (up to c. 2000 m in thickness) and a meta-ophiolitic HPmélange (up to c. 200 m; e.g. Hecht, 1984; Dixon and Ridley, 1987). Inthe SW part of the island the structurally lowest part of the meta-morphic succession is exposed, which includes rock slices consideredto represent pre-Alpidic basement (Tomaschek et al., 2008).

The Syros mélange mostly occurs in a well-defined and mappablehorizon that is fault-bounded on top and at its base (Dixon and Ridley,1987; Keiter et al., 2004), whereas the metasediments overlying themapped mélange unit also contain some blocks (Keiter, pers. comm.,2006). The mélange comprises a wide variety of well-preserved HProck types (e.g. meta-gabbros, eclogites, glaucophanites, ultramaficrocks, jadeitites) of variable size (b1 m to several hundred meters;rounded blocks and tabular slabs) that are often surrounded bymetasomatic reaction rinds (e.g. Dixon and Ridley, 1987; Bröcker andEnders, 2001; Miller et al., 2009). These reaction rinds (‘blackwallzones’) developed due to fluid-assisted block-matrix interaction atcontacts with serpentinitic rocks (e.g. Dixon and Ridley, 1987; Bröckerand Enders, 2001; Marschall et al., 2006; Ague, 2007). Strong shearingand syn- or post-deformational alteration has often transformed theserpentiniticmatrix into chlorite-, talc- and actinolite-rich schists. P–Tconditions reported for blackwall formation range from 11.7–12.3 kbar and 500–550 °C (Breeding et al., 2004) to 6.2–7.2 kbar and400–430 °C (Marschall et al., 2006). Pressures for omphacite andglaucophane-bearing reaction zones are more likely at the upper endof this range, and consequently Miller et al. (2009) considered 12 kbarand 430 °C as a realistic P–T estimate. Although blocks with blackwallalteration are common, the matrix predominantly consists of clasticmetasediments, and numerous blocks are surrounded only by a ratherthin serpentinite or chlorite schist envelope (b50 cm). The blockpopulation includes rock fragments with Cretaceous (c. 80 Ma) andTriassic (c. 240 Ma) magmatic protolith ages (Keay, 1998; Tomascheket al., 2003; Bröcker and Keasling, 2006), whereas protolith ages ofmatrix rocks are unknown. Cretaceous ages of a special kind ofmélange blocks (jadeitites) were interpreted to indicatemetamorphicprocesses (Bröcker and Enders, 1999, 2001; Bröcker and Keasling,2006). Nevertheless, the importance of Eocene HP/LT metamorphismis well documented for both blocks and matrix (e.g. Bröcker andEnders, 2001; Putlitz et al., 2005; Lagos et al., 2007).

3. Analytical methods

For preparation of whole rock powders, fresh sample material wascrushed in a jaw-crusher and an aliquot was ground in either an agateor a tungsten carbide ringmill. Whole rock trace element analysis wasperformed by Activation Laboratories, Ancaster, Ontario, using the4Lithoresearch analytical protocol that incorporates lithium metabo-rate–lithium tetraborate fusion followed by acid digestion and LA-ICP-MS analysis (Supplementary Table 1).

For U–Pb geochronology, zircon was separated from 6–12 kgsamples by standard routines (jawbreaker, disc mill, Wilfley table,Frantz magnetic separator, heavy liquids). After polishing to exposethe grain interior, cathodoluminescence imaging (CL) was applied toreveal the internal structure and to guide spot positioning. Hand-picked zircon grains were mounted in 25 mm epoxy discs togetherwith pieces of the Temora-1 (Black et al., 2003) and 91,500 zirconstandards (Wiedenbeck et al., 1995; U=81.2 ppm). SIMS U–Pb datingwas carried out with the SHRIMP II ion microprobe at the Centre ofIsotopic Research (VSEGEI), St. Petersburg.

Including both spike-calibration and U decay constant uncertain-ties the total uncertainty of the Temora-1 standard is 416.8±1.3 Ma(Black et al., 2003), and a value of 417 Ma has been used for agecalculation in this study. Analytical procedures were similar to thosereported by Williams (1998) and Larionov et al. (2004). Cleanedzircon mounts were gold-coated and analyzed for U–Th–Pb isotopes


using a primary beam diameter of ∼20 µm. Before analysis, theprimary beam was rastered over the target area for ∼30 s. Thedata were collected in sets of five magnetic switched scans through196Zr216O+, 204Pb+, background (c.204.5), 206Pb+, 207Pb+, 208Pb+, 238U+,232Th16O+ and 238U16O+. The Temora-1 standard was analyzed afterevery fifth unknown. Data were reduced using the SQUID v. 1.12 ExcelMacro of Ludwig (2005a). Uncertainties given for individual SHRIMPdata points (ratios and ages) are reported with 1σ uncertainty; errorellipses on diagrams are shown with 2σ uncertainty. Weighted aver-ages are quoted as 206Pb/238U ages with 95% confidence limit (c.l.).CommonPb correctionswere performedusing the relevant Pb compo-sition after Stacey and Kramers (1975) and measured 207Pb/206Pb(Compston et al., 1984). Most analyses contain very little common Pband thus are insensitive to the choice of initial isotopic composition.Decay constants used for age calculation are those recommended bythe Subcommission on Geochronology of IUGS (Steiger and Jäger,1977). The data for all samples are presented in Tera-Wasserburg andWetherill concordia diagrams. All plots, regressions and weightedmean age calculations were carried out using Isoplot/Ex 3.22 (Ludwig,2005b).

Zircon trace element compositions were determined with a sectorfield ICP-MS (Element2, Thermo Finnigan) coupled to a 193 nm ArFExcimer laser system (UP193HE, New Wave Research) at the Institutfür Mineralogie, Universität Münster. The same SHRIMPmounts wereused, and spot selection was guided by the U–Pb pits induced by ionmicroprobe analysis. The instrument parameters for both the laserand the ICP-MS are similar to those reported by Bröcker et al. (2010)The system has been tuned (torch position, lenses, gas flows) onstandard glass NIST 612 by measuring 139La+, 232Th+ and 232Th16O+

to achieve stable signals and high sensitivity on 139La+ and 232Th+

peaks, as well as low oxide rates (232Th16O+/232Th+ ∼0.1%) duringablation. The NIST 612 glass was used as standard (using the preferredvalues of the GeoReM reference material database, version 11/2006).Groups of 5 unknowns were bracketed with 2 calibration standards onboth sides to track instrumental drift. The 91,500 zircon standard(Wiedenbeck et al., 1995) was measured in all sessions along with theunknowns to monitor accuracy (Supplementary Table 2). Concentra-tions of measured elements were calculated using the Glitter software(e.g.Griffinet al., 2008). Precision is usually better than10%butdependson the absolute concentration. Elemental abundances were normalizedto total Hf concentrations, which were determined with a JEOL 8900 MSuperprobe adjacent to the ablation pits, using natural and syntheticcalibration standards. Analytical conditions were 15 kV acceleratingpotential, 15 nA beam current, a spot size of∼1 μm, and a counting timeof 10 s on peaks and 5 s on background. SHRIMP and LA-ICP-MS resultsare reported in Table 1, Table 2 and in Supplementary Table 2.

Rb–Sr and Sm–Nd thermal ionization mass spectrometric analyses(TIMS) were carried out at the Institut für Mineralogie, UniversitätMünster. Analytical procedures for samples 3100–3143 were similarto those reported by Bröcker and Enders (2001), and includedissolution of whole rock powders in a HF-HNO3 mixture in Teflonscrew-top vials within steel autoclaves, and subsequent addition ofHClO4 to break down fluorides during evaporation on a hot-plate. Allother samples were dissolved using a tabletop HF-HNO3 digestiontechnique without addition of HClO4. In a previous study of zircon-rich samples from Tinos and Syros, both techniques ensured completedissolution (Bröcker and Enders, 2001).

Samples 3100–3143 were analyzed in 2002 using a VG Sector 54multicollector TIMS (dynamic mode for Sr and Nd, static mode forSm), and a single collector NBS-type Teledyne TIMS for Rb. At thattime, the long-term laboratory averages of the NBS 987 and the LaJollastandards were 87Sr/86Sr=0.710290±0.000044 (2σ, n=34) and143Nd/144Nd ratio=0.511860±0.000028 (2σ, n=39), respectively.All other samples were measured in 2008 in static mode using aThermo Finnigan Triton TIMS (Sr, Sm, Nd) and a VG Sector 54 TIMS(Rb). In the course of the second session, the external reproducibility

of NBS standard 987 gave an average 87Sr/86Sr ratio of 0.710199±0.000030 (2σ, n=23). Repeated runs of the LaJolla standard gave anaverage 143Nd/144Nd ratio of 0.511870±0.000020 (2σ, n=19).During both sessions, correction for mass fractionation was basedon 86Sr/88Sr=0.1194 and 146Nd/144Nd=0.7219. Rb ratios werecorrected for mass fractionation using a factor deduced frommultiplemeasurements of Rb standard NBS 607. Total procedural blanks wereb0.1 ng for Rb, b0.2 ng for Sr, b0.05 ng for Sm and b0.2 ng for Nd.

4. Results

4.1. Bulk rock compositions

Forty six samples were selected for geochemical studies. Samplelocations are indicated in Fig. 2B–D. GPS coordinates and mineralassemblages are summarized in Supplementary Table 3, whereas bulkrock compositions are shown in Supplementary Table 1.

4.1.1. Tinos–meta-gabbrosFour groups can be geochemically distinguished. Group 1 meta-

gabbros were collected from a single lens (up to 150 m thick and300 m wide) exposed at Mandrisia Bay (Fig. 3A). From thisoccurrence, we collected 6 samples along a vertical traverse fromthe top to the base of this block (3009–3015; Supplementary Table 1).With the exception of the highly shearedmargins, this meta-gabbro ischaracterized by an isotropic magmatic texture and the localpreservation of relict magmatic clinopyroxene. The mineral assem-blage mainly consists of plagioclase, phengite, actinolite and chlorite.Sodium amphibole was only recognized in two samples. Chondrite-normalized REE patterns indicate a LREE enrichment that descendsinto a relatively flat HREE pattern without a significant Eu-anomaly(Fig. 4A). At the Mavra Gremna location, smaller sized blocks of meta-gabbro (up to 7 m), eclogite, glaucophanite and jadeitite have beenliberated from their country rocks by erosion. The meta-gabbros(group 2; 3036, 3038, 3041–3043; Supplementary Table 1) have aflaser texture and HP phases (glaucophane, omphacite±garnet) areabundant. REE distribution patterns are distinct with a markeddepletion in LREE, a strong positive Eu anomaly and a flat HREEpattern (Fig. 4A). Meta-gabbros collected at the northern tip of theisland (Gavalas — group 3; 19.2, 19.2.2, 19.2.3; SupplementaryTable 1) are characterized by abundant plagioclase, quartz, actinoliteand epidote, whereas no HP mineral phases where recognized. Theserocks show a marked depletion in HFSE (Zr, Hf, Ce, Nb) and LILE(K, Rb). The shape of the REE patterns is comparable to those of group2 meta-gabbros, with generally lower amounts of REE, a depletion ofLREE, a less pronounced positive Eu anomaly and a slight decreasetowards the heavy HREE (Fig. 4B). A single meta-gabbro block thatcrops out at Korakou Folia (group 4; 20.1.3, 20.1.8, 20.1.11;Supplementary Table 1; Fig. 3B) is mainly composed of plagioclase,actinolite, quartz, chlorite and epidote, with Na amphibole present inminor amounts. Samples from this occurrence show the highestFe2O3

total concentrationswith 13–17.2 wt.% and the REE patterns exhibita trend similar to the patterns of group 1 meta-gabbros, only with a flatdistribution and a less pronounced decrease towards the HREE (Fig. 4B).

4.1.2. Tinos–glaucophanitesThis rock type is considered to represent a mineralogical variant of

gabbroic precursors, because the petrographic transition from meta-gabbro to glaucophanite was recognized on outcrop scale at thelocation Korakou Folia. The studied sample, collected from the blockmargin, displays major element concentrations comparable to theassociated meta-gabbro. Samples representing a glaucophanite blockat Kavos Manganistis (Fig. 3C) are dominated by Na amphibole,plagioclase, quartz, epidote and phengite in various proportions. TheREE patterns of the glaucophanitic rocks are generally flat withvariable slight enrichments, LaN/YbN ratios from 0.5–1.8 and Eu

http://dx.doi.org/10.1017/S0016756809990665

Table 1SHRIMP U–Pb–Th analytical data for zircons from mélange blocks (Tinos, Andros) and matrix (Syros, Tinos).

Spot ƒ 206Pb % U ppm Th ppm 232Th/238U Rad. 206Pb 238U/206Pb % err 1σ 207Pb/206Pb % err 1σ 206Pb/238U 1σ err

ppm uncorrected uncorrected age, Ma

Mélange blocks from TinosEclogite (Kionia)18-2.1.1 1.92 72 56 0.81 0.8 75.74 2.7 0.0629 8.2 82.9 2.318-2.2.1 1.42 103 82 0.82 1.1 80.94 2.2 0.0588 8.0 78.0 1.818-2.3.1 1.51 89 52 0.61 1.0 80.09 2.3 0.0596 7.4 78.8 1.918-2.4.1 1.46 47 18 0.40 0.5 79.23 2.9 0.0592 10.4 79.7 2.418-2.5.1 9.60 9 2 0.18 0.1 76.52 6.0 0.1236 15.8 75.7 5.018-2.6.1 0.47 109 83 0.78 1.2 81.45 2.5 0.0513 7.1 78.3 2.018-2.7.1 1.91 57 28 0.51 0.6 85.67 3.6 0.0627 9.8 73.4 2.718-2.7.1RE 2.05 93 60 0.67 1.0 82.14 2.2 0.0638 6.4 76.4 1.718-2.8.1 2.21 36 9 0.24 0.3 110.64 6.9 0.0647 12.8 56.7 3.918-2.9.1 2.74 83 44 0.55 0.9 81.13 2.5 0.0692 6.7 76.8 2.018-2.10.1 2.83 65 1 0.01 0.5 116.51 2.8 0.0695 8.7 53.5 1.6Meta-gabbro (Korakou Folia)20-1-7.1.1 1.36 28 19 0.72 0.3 81.51 3.5 0.0584 13.8 77.5 2.920-1-7.2.1 1.15 31 16 0.54 0.3 78.90 3.6 0.0568 14.0 80.3 3.020-1-7.3.1 0.21 1020 756 0.77 10.4 84.01 1.6 0.0492 2.1 76.1 1.220-1-7.4.1 4.05 60 30 0.52 0.6 79.67 2.7 0.0797 7.5 77.2 2.220-1-7.5.1 15.42 18 8 0.46 0.2 75.79 3.7 0.1697 9.3 71.5 3.220-1-7.7.1 4.45 33 13 0.42 0.4 78.04 3.1 0.0829 10.6 78.4 2.620-1-7.6.1 2.63 28 11 0.39 0.3 79.43 3.3 0.0685 13.5 78.5 2.720-1-7.8.1 2.72 18 8 0.44 0.2 79.61 4.0 0.0692 17.0 78.3 3.320-1-7.9.1 0.04 86 40 0.48 0.9 80.98 2.3 0.0479 9.2 79.1 1.920-1-7.10.1 2.10 26 13 0.53 0.3 81.02 3.6 0.0642 15.8 77.4 3.0Glaucophanite (Kavos Manganistis)19.9.3a_1.1 11.00 30 13 0.44 0.4 66.94 4.7 0.1349 18.1 84.5 4.919.9.3a_2.1 13.17 23 10 0.47 0.3 69.23 4.4 0.1521 12.1 79.8 4.119.9.3a_3.1 11.30 21 8 0.41 0.3 69.98 4.5 0.1373 15.2 80.6 4.419.9.3a_4.1 16.46 18 8 0.45 0.2 67.51 5.0 0.1782 11.0 78.7 4.519.9.3a_5.1 11.21 26 14 0.54 0.3 73.29 4.3 0.1365 10.5 77.1 3.719.9.3a_6.1 10.37 20 9 0.46 0.3 66.07 4.7 0.1300 15.1 86.2 4.719.9.3a_7.1 10.67 23 10 0.47 0.3 70.17 4.5 0.1322 12.2 81.0 4.119.9.3a_8.1 17.05 18 8 0.47 0.2 66.09 4.9 0.1829 14.1 79.8 5.019.9.3a_9.1 7.19 30 14 0.50 0.3 76.13 4.2 0.1046 11.8 77.5 3.519.9.3a_10.1 10.43 25 12 0.48 0.3 63.82 4.8 0.1306 15.0 89.2 4.9Matrix rocks from TinosBlackwall (Kavos Manganistis)19-13.1.1 17.73 31 14 0.48 0.4 67.18 3.5 0.1882 7.4 78.5 3.219-13.2.1 21.49 33 15 0.46 0.4 67.96 3.1 0.2179 12.8 74.0 4.019-13.3.1 15.87 21 9 0.44 0.2 75.85 3.5 0.1732 15.2 71.1 3.819-13.3.2 14.77 22 10 0.47 0.3 67.96 3.4 0.1648 7.4 80.3 3.119-13.4.1 6.91 27 12 0.48 0.3 73.97 3.2 0.1024 9.8 80.6 2.819-13.5.1 11.67 28 13 0.47 0.4 66.35 4.8 0.1403 9.8 85.3 4.419-13.6.1 0.34 1804 530 0.30 17.6 87.87 1.9 0.0502 2.2 72.7 1.419-13.7.1 15.38 31 15 0.48 0.4 66.17 3.1 0.1697 6.5 81.9 2.919-13.8.1 17.18 24 10 0.42 0.3 69.64 3.4 0.1838 12.0 76.2 3.619-13.9.1 20.57 16 7 0.43 0.2 63.77 4.4 0.2108 10.3 79.8 4.519-13.10.1 15.47 21 9 0.44 0.3 64.22 3.5 0.1705 7.5 84.3 3.4Chlorite schist (Kavos Manganistis)5224.1.1 14.35 16 8 0.53 0.2 77.83 4.1 0.1612 13.5 70.6 3.75224.2.1 8.49 42 20 0.49 0.5 76.25 2.6 0.1149 11.3 76.9 2.45224.3.1 16.46 14 6 0.42 0.2 65.04 4.7 0.1783 13.1 82.3 4.85224.4.1 10.28 21 10 0.50 0.2 72.28 3.4 0.1292 12.5 79.5 3.25224.5.1 7.66 46 20 0.44 0.5 76.06 2.8 0.1083 10.2 77.8 2.55224.6.1 21.38 14 7 0.50 0.2 70.69 4.1 0.2169 12.0 71.3 4.25224.7.1 11.27 20 11 0.56 0.2 72.92 3.4 0.1370 12.5 78.0 3.3Samples from SyrosChlorite schist (Cape Kalogheros)S29-1-2.1.1 8.64 43 26 0.62 0.5 74.82 3.6 0.1161 8.8 78.2 3.0S29-1-2.2.1 12.80 42 24 0.58 0.5 71.01 2.8 0.1491 13.1 78.7 3.1S29-1-2.3.1 4.96 63 71 1.18 0.7 76.53 2.6 0.0870 7.1 79.6 2.1S29-1-2.4.1 4.97 87 52 0.62 1.0 73.69 2.2 0.0871 8.3 82.6 2.0S29-1-2.5.1 1.96 256 216 0.87 2.8 79.30 1.8 0.0631 4.1 79.2 1.5S29-1-2.6.1 1.00 487 512 1.09 5.3 79.45 1.8 0.0555 3.3 79.8 1.4S29-1-2.7.1 0.96 800 660 0.85 8.4 81.96 1.9 0.0552 2.6 77.4 1.4S29-1-2.8.1 9.00 51 30 0.60 0.6 72.83 2.5 0.1190 11.2 80.1 2.5S29-1-2.9.1 6.64 56 36 0.66 0.7 72.09 2.5 0.1004 10.0 82.9 2.3S29-1-2.9.2 8.39 47 17 0.38 0.5 73.94 2.7 0.1142 7.5 79.4 2.4Chlorite schist (Palos)S27-2-1.1.1 1.42 23 12 0.54 0.3 78.52 3.6 0.0589 16.7 80.4 3.1S27-2-1.10.1 1.48 32 17 0.54 0.3 80.69 3.2 0.0593 25.6 78.2 2.9S27-2-1.2.1 0.99 181 128 0.73 2.0 79.42 1.9 0.0554 5.5 79.9 1.6S27-2-1.4.1 -0.01 361 357 1.02 4.0 77.41 1.8 0.0476 4.1 82.8 1.5S27-2-1.3.1 4.68 13 6 0.44 0.2 74.11 4.8 0.0848 19.3 82.4 4.3


Table 1 (continued)

Spot ƒ 206Pb % U ppm Th ppm 232Th/238U Rad. 206Pb 238U/206Pb % err 1σ 207Pb/206Pb % err 1σ 206Pb/238U 1σ err

ppm uncorrected uncorrected age, Ma

Chlorite schist (Palos)S27-2-1.5.1 2.44 30 16 0.55 0.3 76.59 5.6 0.0670 12.4 81.6 4.6S27-2-1.6.1 2.27 26 17 0.66 0.3 82.66 3.4 0.0655 14.1 75.8 2.7S27-2-1.7.1 1.23 95 50 0.55 1.0 81.77 2.2 0.0573 7.2 77.4 1.8S27-2-1.8.1 3.51 47 24 0.54 0.5 76.62 3.2 0.0755 9.6 80.7 2.6S27-2-1.9.1 4.35 34 14 0.42 0.4 77.90 4.2 0.0821 17.6 78.7 3.6Matrix rocks from TinosQuartz mica schist (Kavos Manganistis)T29_21.1 0.43 542 346 0.66 5.8 80.30 0.8 0.0510 3.0 79.4 0.6T29_34.1 1.99 311 225 0.75 3.5 77.31 2.0 0.0634 6.9 81.2 1.7T29_35.1 0.68 692 860 1.29 7.1 83.41 1.4 0.0530 4.9 76.3 1.1T29_36.1 1.51 381 264 0.72 4.1 79.67 1.8 0.0596 6.1 79.2 1.5T29_37.1 0.67 322 232 0.74 3.5 78.56 2.0 0.0530 7.0 81.0 1.6T29_38.1 2.17 430 265 0.64 4.6 80.98 1.7 0.0648 5.7 77.4 1.4T29_39.1 0.80 1285 563 0.45 13.7 80.42 1.2 0.0540 3.5 79.0 0.9Quartz mica schist (Kavos Manganistis)5220.5.1 0.18 693 438 0.65 7.4 80.59 1.7 0.0490 2.7 79.4 1.35220.12.1 0.77 388 242 0.64 4.1 81.00 1.8 0.0537 3.4 78.5 1.55220.13.1 0.30 438 375 0.89 4.7 80.04 2.0 0.0500 3.0 79.8 1.65220.21.1 0.44 489 367 0.77 5.1 82.84 1.7 0.0510 3.0 77.0 1.35220.22.1 0.90 305 195 0.66 3.3 80.04 1.8 0.0547 3.6 79.3 1.45220.24.1 0.06 2464 2373 1.00 26.7 79.16 1.7 0.0481 1.3 80.9 1.35220.27.1 0.70 234 118 0.52 2.4 82.26 1.9 0.0531 6.2 77.3 1.55220.30.1 0.17 717 413 0.59 7.4 83.57 1.8 0.0489 2.5 76.6 1.45220.31.1 0.40 318 292 0.95 3.3 82.24 1.8 0.0507 3.7 77.6 1.45220.8.1 0.12 651 364 0.58 5.0 112.43 1.7 0.0481 3.0 57.0 1.05220.8.2 0.60 681 417 0.63 5.3 109.63 2.4 0.0519 4.1 58.2 1.45220_38.1 1.56 595 315 0.55 4.5 113.01 1.7 0.0595 5.8 55.9 1.0Quartz mica schist (Isternia)5202.8.1 0.39 740 346 0.48 18.7 34.00 0.4 0.0529 1.5 186.2 0.85202.13.1 0.08 1037 542 0.54 31.8 28.03 0.3 0.0513 1.2 225.8 0.85202.24.1 0.05 508 496 1.01 15.7 27.80 1.3 0.0511 1.7 227.7 2.95202.18.1 0.28 1432 534 0.39 44.5 27.67 1.5 0.0529 1.5 228.2 3.35202.26.1 0.27 342 276 0.83 10.9 27.02 1.8 0.0530 2.0 233.7 4.25202.28.1 0.08 1255 520 0.43 40.4 26.72 2.2 0.0515 1.4 236.7 5.25202.16.1 0.27 321 289 0.93 10.4 26.49 0.6 0.0531 2.1 238.2 1.45202.17.1 0.13 887 233 0.27 38.9 19.57 1.0 0.0539 1.5 320.8 3.2

ƒ 206Pb % indicates the percentage of 206Pb that is common Pb; Rad. 206Pb = radiogenic 206Pb. Uncertainties are reported at the 1σ level.Ages are based on 207Pb corrected data assuming 206Pb/238U–207Pb/235U age-concordance.Errors in standard calibration were 0.55% (sample 18-2), 0.52% (samples 20.1.7, 19.13, S29.1.2, and S27.2.1), 0.72% (sample 19.9.3a), 0.43% (sample 5224), 0.65% (sample 5100),0.61% (sample T29), 0.62% (sample 5220), and 0.33% (sample 5202).


anomalies with EuN/EuN ratios between 0.83–1.37 (Fig. 4C). Twosamples from Kavos Manganistis are more enriched in REE and have asimilar trend than the meta-gabbros from Korakou Folia, probablyreflecting a more transitional type of glaucophanite.

4.1.3. Tinos–meta-dioritesThree meta-igneous mélange samples from Panormos (5572–5574),

most likely representing gabbroic to dioritic precursors, are typified bySiO2 contents between 51.9–57.6 wt.%, with high Al2O3 concentrationsfrom19.7–21.6 wt.% and lowFe2O3

total from5.7–6.3 wt.%. TheREEpatternsdisplay a strong LREE enrichment (LaN/YbN=9.0–11.5) with no distinctEu anomalies (EuN/EuN=0.90–0.92) and aflatHREEdistribution (Fig. 4C).

4.1.4. Andros–meta-gabbrosSamples from the Cape Steno mélange display a mineral

assemblage dominated by plagioclase, quartz, epidote and chlorite.HP phases are absent. Compared to all meta-gabbro groups from TinosK, Rb and Th values are higher. REE patterns display a moderate LREEenrichment and a negative Eu anomaly (0.71–0.85) (Fig. 4D).

4.1.5. Andros–meta-acidic rocksThe gneisses (SiO2=57.3–66.7 wt.%) have a broadly dacitic to

andesitic bulk rock composition, with distinct enrichments in K, Rband Th. REE patterns also indicate a strong enrichment in LREE (LaN/YbN=31–44), and a weakly pronounced Eu (1.08–1.40) anomaly(Fig. 4E). Sample 5100 represents a felsic orthogneiss of unknownorigin (SiO2=58.7 wt.%, Na2O=10.0 wt.%, Al2O3=18.9 wt.%). The

sample also displays a strong LREE enrichment (LaN/YbN=29.4)without a pronounced Eu-anomaly (0.87).

4.1.6. Syros and Tinos–chlorite schists and serpentinitesChondrite normalized REE patterns of chlorite schists show a flat

distribution with slight enrichments in LREE, a moderate negative Euanomaly (0.51–0.68) and a slight decrease in HREE (Fig. 4F). One samplefrom Tinos with a very low SiO2 concentration has a similar REE pattern,but displays a slightly positiveEu anomaly. Compared to thevalues of theserpentinites, total REE abundances of chlorite schists are 100 to 200×times enriched. The serpentinites show a relatively flat REE distributionwith a slight enrichment in HREE andminor scatter of the LREE (Fig. 4F).

4.2. Sr–Nd isotope characteristics

Sr and Nd isotope characteristics were determined for 34 samples.The results are summarized in Supplementary Table 4 and depicted inFig. 5A–B. Meta-gabbros from Tinos show a range of initial 87Sr/86Srratios of 0.70363 to 0.70747 and εNd values of 4.66 to 8.25, calculatedfor a presumed protolith age of 80 Ma. Sr isotopic compositions ofsamples from Gavalas (northern tip of Tinos) plot outside the Tinosdata cluster and outside the mantle array. Sr and Nd isotopecompositions of meta-gabbros from Andros (calculated for 160 Ma)can be clearly distinguished from the Tinos samples by generallyhigher 87Sr/86Sr=0.70613 to 0.70694 ratios and lower εNd=−3.77to −1.54 values.

Table 2SHRIMP U–Pb–Th analytical data for zircons from clastic metasediments from Tinos and a felsic gneiss from Andros.

Spot Mount ƒ 206Pb % U ppm Th ppm 232Th/238U Rad. 206Pb 207Pb/235U % Err 1σ 206Pb/238U % err 1σ Err corr 206Pb/238U 1σ err

ppm age, Ma

Matrix rocks from TinosQuartz mica schist (Kavos Manganistis)T29.1.1 A 0.12 339 83 0.25 22.3 0.58 2.3 0.0763 0.6 0.244 473.9 2.6T29.2.1 A 0.97 86 30 0.36 1.9 0.07 66.5 0.0245 2.2 0.033 156.3 3.4T29.3.1 A 0.18 87 62 0.74 8.4 1.04 3.4 0.1129 0.8 0.242 689.5 5.4T29.4.1 A 0.05 1087 32 0.03 52.2 0.41 1.1 0.0559 0.3 0.291 350.9 1.1T29.5.1 A 0.05 813 454 0.58 53.7 0.60 1.1 0.0769 0.3 0.320 477.7 1.6T29.6.1 A 0.36 373 1 0.00 16.1 0.37 3.5 0.0500 0.6 0.162 314.4 1.7T29.7.1 A 0.37 871 162 0.19 30.4 0.28 2.9 0.0404 0.4 0.147 255.0 1.1T29.8.1 A 0.01 749 261 0.36 32.2 0.35 2.0 0.0499 0.4 0.206 314.2 1.3T29.9.1 A – 775 315 0.42 33.6 0.36 2.3 0.0504 0.4 0.179 317.0 1.3T29.10.1 A 0.51 247 13 0.05 15.2 0.50 5.8 0.0706 0.7 0.122 440.1 3.0T29.11.1 A 0.12 425 106 0.26 22.3 0.42 4.0 0.0607 0.5 0.135 380.0 2.0T29.12.1 A 0.17 227 26 0.12 21.5 0.89 3.0 0.1094 0.6 0.213 669.4 4.1T29.13.1 A 0.38 334 149 0.46 14.4 0.37 2.5 0.0501 0.6 0.231 315.0 1.8T29.14.1 A 0.04 334 63 0.19 22.0 0.60 2.0 0.0767 1.3 0.631 476.1 5.8T29.15.1 A 5.29 16 1 0.06 0.4 0.49 15.3 0.0309 3.6 0.237 195.9 7.0T29.16.1 A 0.33 700 33 0.05 46.4 0.60 2.1 0.0769 0.9 0.438 477.4 4.2T29.17.1 A 0.75 296 1 0.01 13.4 0.38 5.4 0.0525 0.7 0.121 329.7 2.1T29.18.1 A 1.15 187 93 0.51 4.3 0.20 5.5 0.0267 1.0 0.175 170.2 1.6T29.19.1 A 0.08 707 9 0.01 33.7 0.40 2.3 0.0553 0.9 0.374 347.1 3.0T29.20.1 A 0.36 231 169 0.76 20.1 0.89 1.8 0.1015 0.9 0.526 623.2 5.6T29.21.1 A 0.43 542 346 0.66 5.8 0.09 3.7 0.0125 0.8 0.210 79.9 0.6T29.22.1 A 0.56 109 22 0.21 8.2 0.70 6.9 0.0865 1.0 0.150 534.9 5.3T29.23.1 A 0.07 185 43 0.24 11.7 0.56 2.9 0.0733 1.1 0.370 456.0 4.7T29.24.1 A – 4470 15 0.00 211.8 0.40 0.8 0.0551 0.6 0.732 346.0 2.0T29.25.1 A 0.14 446 53 0.12 28.0 0.57 1.6 0.0732 0.4 0.274 455.2 2.0T29.26.1 A 3.26 320 112 0.36 124.3 11.11 1.0 0.4522 0.9 0.917 2405.2 18.9T29.27.1 A 6.07 22 0 0.01 0.5 0.25 28.7 0.0247 3.7 0.128 157.1 5.7T29.28.1 A 0.16 664 18 0.03 41.9 0.57 1.8 0.0734 0.9 0.487 456.5 3.8T29.29.1 A 0.09 1452 244 0.17 115.2 0.76 2.3 0.0924 1.3 0.551 569.4 6.9T29.30.1 A 0.40 176 48 0.28 7.6 0.34 6.6 0.0499 0.9 0.132 313.6 2.7T29.31.1 A 0.18 517 227 0.45 21.2 0.33 4.1 0.0475 1.2 0.292 299.0 3.5T29.32.1 A 0.54 714 317 0.46 27.7 0.30 6.2 0.0448 3.5 0.571 282.4 9.7T29.33.1 A 0.31 305 54 0.18 19.7 0.59 2.3 0.0752 0.6 0.245 467.6 2.6T29_34.1 D 1.99 311 225 0.75 3.5 0.08 21.1 0.0127 2.3 0.110 81.3 1.9T29_35.1 D 0.68 692 860 1.29 7.1 0.08 10.3 0.0119 1.5 0.141 76.2 1.1T29_36.1 D 1.51 381 264 0.72 4.1 0.07 26.0 0.0123 2.2 0.086 78.8 1.7T29_37.1 D 0.67 322 232 0.74 3.5 0.07 23.4 0.0125 2.2 0.094 80.2 1.7T29_38.1 D 2.17 430 265 0.64 4.6 0.07 28.6 0.0120 2.2 0.079 77.0 1.7T29_39.1 D 0.80 1285 563 0.45 13.7 0.08 7.9 0.0124 1.2 0.157 79.2 1.0T29_40.1 D 0.28 704 607 0.89 26.8 0.31 5.0 0.0441 0.8 0.166 278.3 2.3Quartz mica schist (Kavos Manganistis)5220.1.1 B – 204 113 0.57 4.1 0.12 24.5 0.0230 2.2 0.091 146.7 3.25220.2.1 B 0.34 260 33 0.13 15.3 0.46 7.9 0.0679 1.8 0.227 423.6 7.45220.3.1 B 0.22 823 19 0.02 36.7 0.39 2.3 0.0519 1.6 0.694 326.4 5.25220.4.1 B 0.11 440 37 0.09 27.4 0.55 2.8 0.0723 1.6 0.577 449.9 7.05220.5.1 B 0.18 693 438 0.65 7.4 0.08 3.1 0.0124 1.7 0.534 79.5 1.35220.6.1 B 0.25 193 37 0.20 11.6 0.52 4.1 0.0696 1.7 0.419 433.7 7.25220.7.1 B 0.11 300 281 0.97 6.4 0.15 5.9 0.0246 1.7 0.291 156.8 2.75220.8.1 B 0.12 651 364 0.58 5.0 0.05 13.8 0.0088 1.8 0.130 56.4 1.05220.9.1 B 0.04 378 722 1.98 7.9 0.15 4.9 0.0243 1.7 0.338 155.0 2.55220.10.1 B 0.93 190 89 0.49 77.8 11.30 1.8 0.4772 1.7 0.964 2515.2 35.25220.12.1 B 0.77 388 242 0.64 4.1 0.05 23.2 0.0120 2.0 0.088 77.1 1.65220.11.1 B – 303 36 0.12 38.3 1.33 3.7 0.1465 3.2 0.881 881.4 26.65220.13.1 B 0.30 438 375 0.89 4.7 0.08 4.5 0.0125 2.0 0.453 79.9 1.65220.14.1 B 0.29 832 29 0.04 39.7 0.41 2.5 0.0554 1.6 0.630 347.3 5.35220.15.1 B 0.27 297 241 0.84 12.5 0.36 3.8 0.0489 1.6 0.435 307.8 4.95220.16.1 B 0.61 47 84 1.84 1.9 0.31 10.2 0.0465 2.1 0.204 293.3 6.05220.17.1 B 0.01 463 6 0.01 21.3 0.36 3.7 0.0533 1.6 0.435 334.5 5.25220.18.1 B 0.13 412 2 0.01 25.8 0.56 2.3 0.0726 1.6 0.706 452.0 7.05220.19.1 B 0.19 648 121 0.19 33.6 0.42 4.3 0.0600 1.8 0.422 375.4 6.65220.20.1 B 0.29 238 155 0.67 10.3 0.34 4.7 0.0499 1.7 0.352 314.1 5.15220.21.1 B 0.44 489 367 0.77 5.1 0.08 5.4 0.0120 1.7 0.320 77.2 1.35220.22.1 B 0.90 305 195 0.66 3.3 0.08 8.9 0.0124 1.9 0.209 79.3 1.55220.23.1 B 0.32 161 47 0.30 10.2 0.57 5.1 0.0737 1.7 0.332 458.2 7.45220.24.1 B 0.06 2464 2373 1.00 26.7 0.08 2.8 0.0126 1.7 0.595 80.8 1.35220.25.1 B 0.09 376 12 0.03 23.6 0.54 3.3 0.0727 1.6 0.483 452.7 7.15220.26.1 B – 169 15 0.09 12.9 0.69 4.2 0.0887 1.8 0.435 547.9 9.75220.27.1 B 0.70 234 118 0.52 2.4 0.07 19.7 0.0120 2.1 0.106 76.9 1.65220.28.1 B 0.06 854 295 0.36 37.7 0.37 2.0 0.0513 1.6 0.801 322.7 4.95220.29.1 B 0.57 194 89 0.48 11.5 0.51 6.9 0.0683 1.7 0.246 425.7 7.05220.30.1 B 0.17 717 413 0.59 7.4 0.08 3.1 0.0120 1.8 0.580 76.7 1.45220.31.1 B 0.40 318 292 0.95 3.3 0.07 11.3 0.0121 1.9 0.166 77.3 1.4


Table 2 (continued)

Spot Mount ƒ 206Pb % U ppm Th ppm 232Th/238U Rad. 206Pb 207Pb/235U % Err 1σ 206Pb/238U % err 1σ Err corr 206Pb/238U 1σ err

ppm age, Ma

5220.32.1 B 0.23 166 30 0.19 10.4 0.57 3.6 0.0733 1.7 0.478 455.8 7.55220.8.2 B 0.60 681 417 0.63 5.3 0.03 41.1 0.0089 2.7 0.066 56.8 1.55220_33.1 D 0.38 643 689 1.11 21.4 0.27 4.9 0.0385 0.9 0.180 243.6 2.15220_34.1 D 1.35 263 4 0.01 9.0 0.27 15.0 0.0391 1.9 0.125 247.5 4.55220_35.1 D 0.94 542 6 0.01 16.4 0.24 8.6 0.0349 1.3 0.152 221.2 2.85220_36.1 D 0.81 571 25 0.05 13.6 0.19 9.5 0.0275 1.6 0.168 174.8 2.75220_37.1 D 0.07 751 543 0.75 31.8 0.37 2.7 0.0493 0.7 0.275 310.2 2.35220_38.1 D 1.56 595 315 0.55 4.5 0.05 22.4 0.0087 2.1 0.092 55.8 1.1Quartz mica schist (Isternia)5202.1.1 C 0.37 84 16 0.20 9.4 1.19 3.2 0.1300 0.8 0.233 787.7 5.65202.2.1 C 0.46 67 73 1.12 5.5 0.77 6.1 0.0951 1.6 0.264 585.8 9.05202.3.1 C 0.20 360 220 0.63 28.0 0.74 1.7 0.0905 0.4 0.242 558.5 2.25202.4.1 C – 107 23 0.22 8.1 0.67 5.1 0.0878 3.9 0.772 542.5 20.45202.5.1 C 0.12 63 41 0.67 8.9 1.60 3.4 0.1642 1.0 0.278 980.3 8.75202.6.1 C 0.23 205 82 0.41 23.6 1.23 1.7 0.1338 0.7 0.436 809.7 5.55202.7.1 C 0.45 496 104 0.22 46.9 0.95 1.8 0.1096 0.4 0.219 670.6 2.55202.8.1 C 0.39 740 346 0.48 18.7 0.21 1.7 0.0294 0.4 0.244 186.8 0.85202.9.1 C 0.39 347 231 0.69 29.4 0.83 1.8 0.0983 0.5 0.261 604.6 2.65202.10.1 C 0.27 570 178 0.32 43.3 0.71 1.5 0.0883 0.4 0.266 545.5 2.05202.11.1 C 0.01 100 66 0.68 11.5 1.16 3.7 0.1326 1.9 0.512 803.0 14.15202.12.1 C 0.17 113 41 0.38 14.0 1.34 2.2 0.1443 0.6 0.295 869.2 5.25202.13.1 C 0.08 1037 542 0.54 31.8 0.25 1.5 0.0356 0.3 0.236 225.8 0.85202.14.1 C 0.03 557 82 0.15 46.1 0.79 1.4 0.0962 0.4 0.281 592.0 2.25202.15.1 C 0.25 266 76 0.30 36.3 1.57 1.9 0.1589 1.2 0.640 950.8 10.65202.16.1 C 0.27 321 289 0.93 10.4 0.27 2.4 0.0377 0.6 0.246 238.7 1.45202.17.1 C 0.13 887 233 0.27 38.9 0.37 2.0 0.0510 1.0 0.498 320.8 3.25202.18.1 C 0.28 1432 534 0.39 44.5 0.25 2.5 0.0361 1.5 0.597 228.4 3.35202.19.1 C 0.43 167 76 0.47 24.7 1.80 2.7 0.1724 2.4 0.868 1025.3 22.35202.20.1 C – 424 35 0.08 27.4 0.58 1.5 0.0753 0.9 0.585 468.1 3.95202.21.1 C – 126 71 0.58 9.4 0.68 4.1 0.0863 3.3 0.810 533.7 16.95202.22.1 C 0.14 1178 49 0.04 84.8 0.67 3.9 0.0837 3.8 0.962 518.3 18.95202.23.1 C 0.20 57 67 1.21 5.4 0.94 3.3 0.1095 1.0 0.317 670.1 6.75202.24.1 C 0.05 508 496 1.01 15.7 0.26 2.6 0.0360 1.3 0.504 228.1 2.95202.25.1 C 0.06 123 90 0.76 11.9 0.98 2.5 0.1126 0.7 0.285 687.8 4.75202.26.1 C 0.27 342 276 0.83 10.9 0.26 3.2 0.0369 1.8 0.577 233.8 4.25202.27.1 C 0.05 131 74 0.59 18.6 1.59 2.2 0.1645 1.0 0.461 981.5 9.45202.28.1 C 0.08 1255 520 0.43 40.4 0.26 2.7 0.0374 2.2 0.817 236.6 5.2Mélange block from AndrosFelsic gneiss (Cape Steno)5100_1.1 E 0.38 150 120 0.83 3.5 0.20 9.4 0.0271 2.6 0.276 172.1 4.45100_1.2 E 0.44 779 605 0.80 30.3 0.31 9.5 0.0450 1.1 0.115 283.8 3.05100_2.1 E 0.22 258 122 0.49 10.7 0.34 8.0 0.0479 1.4 0.177 301.3 4.15100_2.2 E 0.64 588 316 0.55 22.9 0.33 7.2 0.0451 1.0 0.141 284.5 2.85100_3.1 E 0.13 839 379 0.47 20.0 0.18 8.1 0.0276 1.0 0.125 175.5 1.85100_4.1 E 0.29 253 118 0.48 9.6 0.30 10.8 0.0439 1.7 0.155 277.0 4.55100_4.2 E 0.26 204 224 1.13 7.6 0.30 9.0 0.0432 1.6 0.177 272.4 4.35100_5.1 E 0.27 82 93 1.17 7.3 0.89 5.2 0.1027 1.8 0.346 629.9 10.75100_5.2 E 0.02 275 126 0.47 10.8 0.33 4.7 0.0458 1.3 0.280 288.5 3.75100_6.1 E 4.28 155 182 1.21 20.8 2.20 3.8 0.1551 2.7 0.702 929.6 23.25100_6.2 E 0.37 324 184 0.59 13.4 0.35 7.4 0.0480 1.3 0.174 302.0 3.85100_7.1 E 1.39 210 125 0.61 4.7 0.13 34.5 0.0252 2.4 0.071 160.6 3.95100_8.1 E 0.90 259 202 0.80 6.1 0.16 35.7 0.0267 2.4 0.069 170.1 4.15100_9.1 E 2.16 199 168 0.87 4.9 0.19 22.8 0.0281 2.5 0.111 178.6 4.55100_9.2 E 0.05 591 405 0.71 23.3 0.32 5.9 0.0458 0.9 0.150 288.8 2.55100_10.1 E 0.81 222 158 0.73 5.0 0.16 18.5 0.0259 1.9 0.100 164.7 3.05100_11.1 E 0.19 402 347 0.89 9.4 0.20 6.6 0.0273 1.2 0.190 173.4 2.15100_12.1 E 0.43 305 179 0.61 7.2 0.17 12.9 0.0272 1.4 0.112 172.8 2.55100_13.1 E 1.14 173 148 0.88 3.9 0.15 26.5 0.0256 2.3 0.085 163.0 3.65100_14.1 E 0.64 275 193 0.72 6.6 0.18 13.0 0.0277 1.6 0.127 175.9 2.95100_14.2 E 0.49 793 679 0.88 31.4 0.31 9.9 0.0458 1.1 0.110 288.4 3.1

ƒ 206Pb % indicates the percentage of 206Pb that is common Pb; Rad. 206Pb = radiogenic 206Pb. Uncertainties are reported at the 1σ level.Ages are based on 204Pb corrected data. Errors in standard calibration were 0.32% (mount A), 0.62% (mount B), 0.33% (mount C), 0.61% (mount D) and 0.65% (mount E).

Quartz mica schist (Kavos Manganistis)


4.3. Zircon CL characteristics and SHRIMP U–Pb results

4.3.1. TinosEclogite sample 18.2 was collected near Kionia. Almost all zircons

from this sample are euhedral and contain abundant mineral in-clusions. CL-images reveal complex cauliflower-like internal struc-tures and dark-CL oscillatory zoned domains mainly at the outercrystal parts (Fig. 6A–B). The highly irregular internal patchy textures

indicate variable degrees of recrystallization. Only small domainsof each grain escaped this process, and such areas were targetedfor ion microprobe dating. Nine SHRIMP spot analyses yielded aweighted mean 206Pb/238U age of 78.0±1.8 Ma (MSWD=1.2;Fig. 7A; Table 1). Two spots (not shown in Fig. 6) representingdomains with convoluted CL characteristics provided apparent agesof 56.7±3.9 Ma and 53.5±1.6 Ma (Table 1). U and Th concentrationswere 9–109 ppm and 1–83 ppm, respectively. The Th/U ratios ranged

Fig. 3. Field pictures from the HPmélange on Tinos (A–E) and Syros (F). (A–D) show various meta-igneous blocks in metasedimentary host rocks: (A) meta-gabbro at Mandrisia Bay,(B) and (C) meta-gabbro and glaucophanite lenses from Korakou Folia and Kavos Manganistis, respectively, selected for U–Pb dating (samples 20.1.7 and 19.9.3a) and (D) metabasicblock exposed near Panormos (NW Tinos). (E) Monomict meta-conglomerate near Panormos (NW Tinos). (F) Glaucophanite boulders in dated zircon-bearing chlorite schist(sample 29.1.2) near Cape Kalogheros (Syros).


from 0.01 in the convoluted CL domain to 0.82 in the dark-CLdomains.

A meta-gabbro sample (20.1.7) from the locality Korakou Folia(NW-Tinos) represents a c. 100 m long tectonic slab (Fig. 3B). Thezircon population consists of sub- to euhedral, blocky or short prismaticgrains which are often fractured. CL imaging revealed broad homoge-nous domains, sector- and/or oscillatory zoning (Fig. 6C–D). SHRIMPspot analysis of ten grains yielded a weighted mean 206Pb/238U age of77.3±1.4 Ma (MSWD=0.73; Fig. 7B; Table 1). U and Th concentrationsare mostly 18–86 ppm and 8–40 ppm, respectively, and Th/U ratiosrange from 0.39 to 0.72. A single data point is characterized byU=1020 ppm, Th=756 ppm and Th/U=0.77.

A glaucophanite (19.9.3a) representing an isolated c. 5–7 m longblock (Fig. 3C) in NW-Tinos (Kavos Manganistis) apparently occurs atthe same lithostratigraphic level as the previously described meta-gabbro slab from Korakou Folia (20.1.7). Both occurrences are found

only a few meters below marble horizon m3. Zircons show mainlysector-zoning and some weakly oscillatory zoned areas (Fig. 6E–F).Ten sub- to euhedral grains define an age of 80.8±2.7 Ma(MSWD=0.78; Fig. 7C; Table 1). U and Th concentrations are low(18–30 ppm and 8–14 ppm, respectively), and the Th/U ratios varybetween 0.41 and 0.54.

A chloritic blackwall zone (19.13) around a small glaucophanite blockwas collected near Kavos Manganistis (NW Tinos). At the same location,thin layers of strongly sheared chlorite–talc schist (sample 5224) occurwithin clastic metasediments. Zircon populations of both blackwall zoneand chlorite–talc schist consist of short- to normal prismatic, euhedralgrains. CL imaging showed sector-zoned grains with faint oscillatoryzoning towards the grain margins (Fig. 6I–J). SHRIMP analyses indicatefor the blackwall a weighted mean age of 79.5±2.9 Ma (MSWD 1.4;Fig. 7D; Table 1). U and Th concentrations are mostly very low (16–33 ppm and 7–15 ppm, respectively). Th/U ratios range from 0.30 to

Fig. 4. Chondrite-normalized REE patterns (normalization values are from Sun and McDonough, 1989) for mélange blocks (Tinos, Andros; A–E), chlorite schists and serpentinites(Tinos, Syros; F). Lines marked with stars are N-MORB (open) and E-MORB (filled) patterns (values are from Sun andMcDonough, 1989). Grey fields indicate compositional range ofmeta-gabbros from Evvia (A, D) and Syros (B), respectively. Data for Syros and Evvia are from Kötz (1989), Seck et al. (1996), Katzir et al. (2000) and Katzir et al. (2007).


0.48, whereas a single data point is characterized by U=1804 ppm,Th=530 ppm and Th/U=0.30.Seven zircon grains (Fig. 6O–P) fromsample 5224 yielded a weighted mean age of 76.8±2.4 Ma (MSWD=1.15; Fig. 7E, Table 1). U and Th concentrations are low (14–46 ppm and7–20 ppm, respectively), with Th/U ratios varying between 0.42 and0.56.

The quartz mica schists 5220 and T29 from NW Tinos represent themélange matrix of a block-bearing succession that is closely associatedwith the uppermost marble horizon m3. Sample 5220 was collectedc. 50 m above the glaucophanite block (19.9.3a) at Kavos Manganistis.Sample T29 represents a c. 10 m higher lithostratigraphic position.Quartzmica schist 5202 fromtheKalloni region comes fromablock-freepart of the metamorphic succession. Zircon grains of all three samplesshow euhedral to roundedmorphologies. CL images reveal both sector-and/or oscillatory zonation, as well as patchy domains. In order toconstrain the time of sedimentation, we specifically targeted rims ornear rim parts of individual grains using CL images for spot selection(119 spot analyses in 3 samples; Fig. 6Q–T). In samples 5220 and T29 a

coherent agegroupoccurs at c.79 Ma(Fig. 8A–F). Three spot analyses ontwo oscillatory zoned grains with inherited cores of sample 5220indicate an age of c. 57 Ma. In sample 5202 the youngest age groupoccurs at c. 226–238 Ma. A single data point yielded an age of c. 186 Ma.In all samples most data points plot along the concordia between c. 300and 900 Ma; single data points in samples T29, 5220 and 5202 indicateconcordant ages of c. 2.3 Ga, 2.5 Ga and 1 Ga, respectively, as oldestdetrital components. U and Th concentrations of the Cretaceous andPaleocene zircons mostly are 234–717 ppm and 118–438 ppm, respec-tively, but both can reach up to c. 2400 ppm. Th/U ratios mostly fall intothe range from 0.52 to 1.00 (Table 2).

4.3.2. AndrosA felsic paragneiss (5100) was sampled at Cape Steno. CL imaging

of zircon documents complex internal structures with homogeneous,sector- and/or weakly oscillatory zoned rims enclosing inherited coreswith oscillatory zoning (Fig. 6G–H). SHRIMP analyses of 21 spots on14 grains yielded a range in apparent 206Pb/238U ages from c. 163 Ma

Fig. 5. Sr–Nd isotope compositions of HP-mélange blocks from Tinos and Andros.(A) 87Sr/86Sr vs. 143Nd/144Nd plot for t=0Ma; schematic fields of comparison indicatedby abbreviations: N-MORB=Normal type Mid-Ocean ridge basalt; OIB=Ocean-Islandbasalt; IAB = Island arc basalt. (B) 87Sr/86Sr vs. 143Nd/144Nd plot with ratios calculatedfor t=80 Ma (Tinos) and t=160 Ma (Andros). Fields of comparison valid for t=0Ma(after Pomonis et al., 2007).


to c. 930 Ma. Zircon overgrowths yield concordia ages of 163.1±3.9 Ma (MSWD=0.34; n=3; Fig. 7H, Table 2) and 174.3±2.0 Ma(MSWD=0.58; n=7, Fig. 7H, Table 1), respectively. A third group ofzircon ages ranges from c. 272 to c. 289 Ma (Fig. 7H) and representsmainly the central grain parts of zircon, which are overgrown byJurassic rims. However, homogenous grains with such ages also occur.Other spot analyses of inherited cores provided 206Pb/238 U ages ofc. 630 and c. 930 Ma (Table 2). These cores are rimmed by c. 289 Maand c. 302 Ma old overgrowths, respectively.

4.3.3. SyrosTwo samples from the northern mélange belt were studied. These

rocks represent strongly sheared chlorite-rich schists that occur indirectcontact with blocks and boulders. One of the studied outcrops,represented by sample S29.1.2, has previously been described as peliticmeta-olistostrome (stop 4 of Dixon and Ridley, 1987). The small,rounded boulders of this occurrence (Fig. 3F) are massive glaucopha-nites (b30–40 cm) without blackwall zones. The second chlorite schistsample (S27.2.1) was in contact with a rock fragment that developed ametasomatic alteration rind. Zircons from both samples typically have ablocky to short-prismatic, mostly euhedral shape. CL patterns includebroad homogeneous domains of variable CL intensity, sector zoning andoscillatory growth zoning (Fig. 6K–N). Ten grains from chlorite schist

S29.1.2 define a weighted mean 206Pb/238U age of 79.6±1.2 Ma(MSWD=0.79; Fig. 7F). U and Th contents vary between 42–800 ppmand 17–660 ppm, respectively, and Th/U ratios range from 0.38 to 1.18(Table 1). Zircon of sample S27.2.1 yielded a weightedmean 206Pb/238Uage of 79.9±1.4 Ma (MSWD=1.01; n=10; Fig. 7G; Table 1). U and Thconcentrations are variable (13–361 ppm and 6–357 ppm, respective-ly), leading to Th/U ratios between 0.42 and 1.02 (Table 1).

4.4. Ti-in zircon thermometry and mineral phases enclosed by zircon

Zircons from all samples show very similar chondrite normalizedREE distribution patterns, with positive Ce and negative Eu anomalies(EuN/EuN=0.12–0.66) and steep HREE slopes (LuN/GdN=4.06–40.9),demonstrating HREE enrichment (Fig. 9, Supplementary Table 2).The total REE abundances (∑REE) range from 146 to 8971 ppm. Ticoncentrations vary between ∼3 ppm and 51 ppm. Ti-in-zircon tem-peratures (Watsonet al., 2006), uncorrected for SiO2- andTiO2-activitiesand pressure, vary between 618 °C in an internal patchy domain ofzircon from an eclogite (18.2) and 901 °C in a chlorite schist (S27.2.1)(see spot in Fig. 6 L; Supplementary Table 2). Corrected Ti-in-zircontemperatures that would comply with published temperatureestimates for the HP stage (c. 450–550 °C) would require a very lowaSiO2 (b0.04–0.1) assignment at aTiO2=1 (Ferry and Watson, 2007).

Mineral phases enclosed by zircon were studied in eclogites,chlorite schists and a meta-gabbro. CL, SE and BSE images were usedto identify pseudo-inclusions with obvious links to microfracturesand/or healed fissures. Selected inclusions were then analyzed withthe electron microprobe (EMP).

4.4.1. Tinos–eclogites (18.2, 1047A, 1047B, 1049)Between 10 to 14 inclusions were analyzed in the zircon

population of each sample. By means of EMP analysis, omphacite(15, see Supplementary Table 5), epidote (12), rutile (8), albite (7),quartz (2), apatite (2), actinolite (1) and phengite (1) were identified(Fig. 10A,B,C,D). All inclusions have a xenomorphic shape and occurdominantly in the highly recrystallized patchy domains. Someinclusions are surrounded by diffusion halos (“ghost zonation”;Gebauer et al., 1997; Corfu et al., 2003). BSE-images revealedthe presence of composite inclusions, which comprise mineralassociations of epidote and albite or omphacite, rutile and albite(Fig. 10B,C).

4.4.2. Tinos–meta-gabbro (20.1.7)10 spots were analyzed and revealed the presence of apatite (4),

quartz (3), albite (2) and biotite (1) (Fig. 10E). Most of the apparentinclusions are linked to small fissures and most likely representpseudo-inclusions (Fig. 10E).

4.4.3. Syros and Tinos–chlorite schists (S27.2.1, S29.1.2, (19.13)The well-preserved, large and mainly euhedral zircons of this rock

type contain abundant mineral inclusions. 49 spot analysis documen-ted the presence of chlorite (29), apatite (7), albite (6), quartz (2),augite (2), ilmenite (1), talc (1), and actinolite (1) (Fig. 10F,G,H). Onlyfew, however, are surrounded by bright CL halos, which mainly occuraround albite (Fig. 10H), whereas the majority of the inclusions islocated in either the dark or the bright areas of the sector- and/oroscillatory zoned domains.

5. Interpretation of SHRIMP results–linking zircon ages togeological processes

5.1. U–Pb zircon geochronology of mélange blocks

All newly dated blocks yielded Cretaceous ages that cluster atc. 80 Ma. Although it is generally difficult to link the time of zirconformation to a specific geological or metamorphic process, there is a

Fig. 6. CL-images of representative zircons of samples selected for U–Pb geochronology. (A–H) = mélange blocks from Tinos (A, B = eclogite; C, D = meta-gabbro; E, F =glaucophanite) and Andros (G, H =, felsic gneiss); (I–J) = blackwall from Tinos; (K–N) = chlorite schists from Syros and Tinos; (O–P) = chlorite schist from Tinos; (Q–T) = clasticmetasediments from Tinos. Numbers close to the circles denote spot identification numbers, 206Pb/238U age with 1σ uncertainty and Th/U ratio (see Table 1 and Table 2).


series of morphological and geochemical criteria of zircon, such as theexternal and internal structure, the Th/U ratio, distinct REE char-acteristics, the Ti-in zircon thermometry, or enclosed mineral phases,which eventually assist in unraveling the petrogenetic informationincluded in this phase. Nevertheless, the geological significance of

U–Pb zircon ages is often puzzling and misinterpretation of themode of formation may lead to wrong conclusions with far-reachingconsequences for the understanding of a geological history. In theCyclades, Cretaceous zircon ages may be related to either magmatic ormetamorphic processes (Bröcker and Enders, 1999; Tomaschek et al.,

Fig. 7. Tera-Wasserburg (A–G) and Wetherill (H, I) concordia diagrams showing U–Pb analytical data of zircons from mélange blocks and chlorite schists. Data point error ellipsesindicate 2σ uncertainties. Weighted mean 238U/206Pb ages (95% c.l.) without error in standard. If the error in standard calibration is taken into account the uncertainty on individualweighted averages increases by 0.1 to 0.4 Ma. Dashed line indicates mixing trend with a common Pb composition after Stacey and Kramers (1975) that represents t=80 Ma.A common Pb composition representing t=0 would not change the intercept age.


Fig. 8.Wetherill (A, C, E) and Tera-Wasserburg (B, D, F) concordia diagrams showing U–Pb analytical data of zircons from clastic metasediments. Data point error ellipses indicate 2σuncertainties. Mean 238U/206Pb ages (95% c.l.) without error in standard. If the error in standard calibration is taken into account the uncertainty on individual weighted averagesincreases by 0.1 to 0.4 Ma. Dashed line indicates mixing trend with common Pb after Stacey and Kramers (1975) representing t=80 Ma (B, D) and t=230 Ma (F). A common Pbcomposition representing t=0 would not change the intercept age.


2003; Bröcker and Keasling, 2006). There seems to be a general con-sensus that previously reported 206Pb/238U zircon ages of c. 75–80 Ma inmeta-gabbros and associated plagiogranitic rocks most likely constrainthe time of protolith formation. However, the interpretation of similarzircon ages in eclogites, omphacitites and jadeitites has proven to bemore difficult. Bröcker and Enders (1999, 2001) suggested that highmodal abundance of zircon in eclogite is related to focused infiltration ofZr-enriched fluids during pre-Eocene HP metamorphism. Similarly,zircon in jadeitite that yielded Cretaceous ages was considered to haveformed by direct precipitation from aqueous fluids in fracture systemsduring early subduction zone processes (Bröcker and Keasling, 2006).The importance of pre-Eocene HP metamorphism is still a contentiousissue, stemming from the lack of firm evidence for a specific zirconformation process.

In addition to the general geological context, the identification ofdistinct zircon-forming mineral reactions or a specific petrogenesis,the following criteria can help distinguish between different modes ofzircon formation: internal zircon structure, Th/U ratios, REE char-

acteristics, crystallization temperatures (e.g. based on Ti-in-zirconthermometry) and mineral inclusions.

Oscillatory zoning is commonly regarded to reflect precipitationfrom a melt, however, these internal structures can also be expectedin case of precipitation from aqueous fluids. Oscillatory zoning ofmetamorphic phases, e.g. garnet and clinopyroxene, has alsorepeatedly been documented and attributed to a variety of processesincluding e.g. fluid infiltration, progress of mineral reactions andvariations in P–T conditions (e.g. Yardley et al., 1991; Schumacheret al., 1999; García-Casco et al., 2002; Clechenko and Valley, 2003).Therefore, this feature alone allows no unambiguous interpretation.

The Th/U ratio of zircon has been proposed as useful parameter todistinguish between amagmatic or metamorphic origin (e.g.Williamset al., 1996). This concept assumes that moderate to high ratios aretypical for igneous zircon, whereas low to extremely low Th/U ratios(b0.1) indicate a metamorphic origin. We are not aware of any studydocumenting Th/U ratios higher than 0.1 for eclogitic zircon, but stillthis parameter alone is only of limited value, because Th/U in zircon

Fig. 9. Chondrite-normalized REE patterns of zircon from samples used for geochronological studies (normalization values are from Boynton, 1984); (A) mélange blocks from Tinos,(B) chlorite schists, (C) clastic metasediments, and (D) zircon from a chlorite zone around a rodingite shell, Sudetic ophiolite, SW Poland (Dubinska et al., 2004).


may record protolith characteristics and/or the local chemicalenvironment during formation (e.g. Harley et al., 2007 and referencestherein).

The Ti-in-zircon thermometer is based (a) on experimentsperformed in the temperature range between 1025–1450 °C and(b) on temperature estimates for natural samples, considered torepresent T=580–1070 °C (Watson et al., 2006). This thermometer issensitive to SiO2- and TiO2-activities and pressure (e.g. Ferry andWatson, 2007). Many aspects of this method are yet not fullyunderstood, and demand rigorous testing. Application of Ti-in-zirconthermometry to various rocks from HT metamorphic domains(N600 °C) often returns plausible temperature values (Fu et al.,2008b and references therein). In the present case, Ti-in-zircontemperatures uncorrected for aSiO2, aTiO2 and pressure, are between618–901 °C, which is higher than the metamorphic temperaturesestimated for the HP metamorphic stage (c. 450–550 °C). Thisobservation would support an interpretation suggesting magmaticzircon formation. However, even under ideal circumstances (well-known pressure, aSiO2 and aTiO2), it is unclear whether or not thismethod would provide correct temperatures for zircon that formedat the relatively low temperatures of the Cycladic HP metamor-phism, which are outside the calibrated temperature range of thisthermometer.

REE patterns of zircon are strongly influenced by contemporane-ous crystallization of other phases. Thus, zircon growth may be linkedto a specific metamorphic stage, especially if garnet and plagioclaseare involved (e.g. Rubatto, 2002; Rubatto and Hermann, 2003;Whitehouse and Platt, 2003). Zircons from all studied samples showREE patterns typical for crystallization from a melt or a fluid withunlimited REE reservoir, enriched in HREE. It is obvious that the zircondid not form together with garnet in a plagioclase-free environment.However, previous studies argued for infiltration of Zr-rich fluids inpre-existing eclogite (Bröcker and Enders, 1999, 2001). For such zircontypical features suggesting contemporaneous crystallization with

garnet cannot be expected at all. The question to resolve is whetheror not hydrothermal zircon formation (“hydrothermal” refers here todirect precipitation from aqueous fluids) can be distinguished frommagmatic crystallization (e.g. Hoskin, 2005; Fu et al., 2008a andreferences therein). To further evaluate the REE characteristics of suchzircons, we have analyzed zircons from a metasomatic rodingite shellof a Sudetic ophiolite, SWPoland,which are considered to have formedat c. 270–300 °C, 1 kbar, based on primary fluid inclusions, during ametasomatic process directly connected to fluid infiltration thatcaused serpentinization (Dubinska et al., 2004).

The REE patterns of this sample demonstrate obvious similaritiesto our samples, but have a less pronounced negative Eu anomaly andare several orders of magnitude less enriched in REE, particularly inHREE (Fig. 9D). Ti-in-zircon temperatures for the rodingite zircons,uncorrected for SiO2- and TiO2-activities, yielded temperatures ofc. 679 °C (after Watson et al., 2006). Considering SiO2- and TiO2-activities, the lowest apparent temperature indicated by the Ferry andWatson (2007) calibration is still much higher than those indicated byfluid inclusion data (c. 410 °C, assuming aSiO2=0.01 and aTiO2=1).These observations indicate that either the interpretation of Dubinskaet al. (2004) is wrong, or that under certain circumstances zircon,which directly crystallizes from aqueous fluids, develops traceelement characteristics nearly indistinguishable from those ofmagmatic zircon. With regard to zircon from the mélange rocks, thisimplies that the REE patterns might indicate either a magmatic or ahydrothermal origin.

Important details on the mode of formation of zircons can also beobtained from mineral phases that have been incorporated duringcrystal growth. Unfortunately, it can be challenging to distinguishbetween true inclusions and pseudo-inclusions, which grew duringmetamorphic overprinting due to in situ transformation of igneousphases, or due to fracturing and retrograde crystallization of newphases. In case of the eclogite samples, textural features (recrystalliza-tion, diffusion halos; Fig. 10A–D, H) suggest that the phases included in

Fig. 10. CL-images of inclusion-bearing zircon grains. representing various HP mélange blocks (A–E) including eclogites (A–C), a jadeitite (D) and a meta-gabbro (E) from Tinosand chlorite schists (F–H) from Tinos (F) and Syros (G–H), respectively; (Cpx = omphacite; Ept = epidote; Alb = albite; Rtl = rutile; Qtz = quartz; Bt = biotite; Apt = apatite;Chl = chlorite; numbers = grain identification code).


zircon (omphacite, rutile, epidote and albite) are of secondary origin.SHRIMP dating of the recrystallized part of such zircons indicated anapparent age of c. 53–56 Ma, suggesting that recrystallization andincorporation of matrix phases occurred during the Eocene HP stage.This does not automatically imply that the pristine Cretaceous domainsof the eclogite zircons are of magmatic origin. However, unequivocalevidence supporting a metamorphic origin for zircon of the Tinoseclogites (Bröcker and Enders, 1999, 2001) was not found. In themeta-gabbro, all enclosed phases are apparently connected tomicrofractures,rendering them useless for interpretation of the zircon formationprocess. Similarly, diffusion halos around albite (Fig. 10H) in zircon of

chlorite–talc schists are indicative for pseudo-inclusions, whereaschlorite, apatite and ilmenite show sharp contacts to the surroundingzircon. CL images did not reveal the presence of microfractures, butpolished grain sections only provide a two-dimensional picture andfractures perpendicular to the surface cannot completely be ruled out.Nevertheless, available observations suggest that chlorite, apatite andilmenite represent true inclusions.

In summary: in the present case, many of the criteria commonlyused to distinguish betweenmagmatic or metamorphic zircon genesisdo not provide unambiguous constraints for the mode of formation.True mineral inclusions of metamorphic phases in zircon can provide


this information, but identification of the accurate relationship to thehost zircon is very difficult. In themeta-gabbro and the eclogites, mostmineral phases enclosed in zircon are of secondary origin. Amagmaticorigin for Cretaceous zircon of meta-gabbros and eclogites isconsidered likely. In case of the chlorite–talc schists, texturalobservations support the interpretation that chlorite was enclosedduring non-magmatic zircon growth.

5.2. U–Pb zircon geochronology of matrix rocks

Geochronological data for the block-enclosing clasticmetasedimentsand/or the chlorite schists have not been reported in the literature. OnSyros, the clastic metasediments forming the mélange matrix do notcontain zircon or contain only relatively small grains, and thus are oflimited suitability for U–Pb studies. Samples with datable zircons werefoundon Tinos. In the three samples selected for ionmicroprobe studies,we specifically targeted the outermost zircondomainswithin individualgrains to obtain constraints on the time of sediment accumulation. Adetailed provenance study will be presented elsewhere. The U–Pb dataobtained documents heterogeneous zircon populations of mixedprovenance that include detritus from Precambrian, Paleozoic andMesozoic sources. An important result of this study is the evidence of adetrital Cretaceous age group (c. 80 Ma). It is noteworthy thatCretaceous zircons were also reported by Keay (1998) for a meta-quartzite from Syros, collected from an outcrop below the mélange beltthat is apparently unrelated to any block-bearing horizon.

Zircon from three chlorite schists from Syros and Tinos also yielded206Pb/238U ages of c. 80 Ma. Formation of the chlorite schists isconsidered to result from strong deformation and fluid-rock interac-tion affecting serpentinitic precursors, and may also include mixingwith block- and/or country rock components (e.g. Esteban et al., 2007;Spandler et al., 2008). The presumed ultramafic precursors aregenerally zircon-free, but on both islands some chlorite schistscontain considerable modal zircon. Morphology, internal structureand trace element patterns of Cretaceous zircons from chlorite schistsand clastic metasediments correlate well with zircon of the same agefrom meta-igneous blocks. There are at least three possible explana-tions for this conformity: (1) Block-derived zircon has beenincorporated during ductile deformation, due to mechanical disinte-gration of zircon-bearing blocks. (2) Cretaceous zircon is related tofluid infiltration and represents a newly grown phase that documentsprecipitation from HP metamorphic fluids. (3) Both meta-igneousblocks and Cretaceous zircons in the siliciclastic metasedimentsrepresent detritus derived from the same source area.

In case of the clastic metasediments the first explanation wouldrequire complete mechanical disintegration of blocks and subsequentredistribution of relict zircon. Complete in situ disintegration of blocksand redistribution in the clastic schist matrix over greater distances isvery unlikely. In the case of the chlorite–talc schists, it canbe argued thatthese rocks represent the remnants of a zircon-bearing blackwall zonethat has been reworked. If this assumption is correct, we would expectthat zircon would be frequently broken into smaller fragments.However, the zircon population of the chlorite–talc schists mostlycomprises euhedral grains, often of considerable size (500 μm) and, atleast in the caseof the two samples fromSyros, neither theblackwall northe boulders in direct contact with the studied samples contain zircon.

For the chlorite–talc schists, in situ formation of zircon due to fluidinfiltration (model 2) is a possible option. In that case, genesis of theserocks would be associated with channelized fluid flow at blockcontacts, and presumed primary inclusions of chlorite in zircon wouldagree with this interpretation. This model would require that blocksand enclosing matrix had already been juxtaposed at 80 Ma. In case offluid infiltration-related in situ growth of zircon in the clasticmetasediments, we would expect to find not only single grains butalso overgrowths on pre-existing zircon. In samples from the northernCyclades such overgrowths were not found in this or previous studies,

but it is worth mentioning that Keay (1998) described such rimsaround detrital zircons from southern Aegean islands.

In our view themost plausible interpretation is the third alternative,which suggests that blocks and Cretaceous zircons in the matrixrepresent detritus of 80 Ma old source rocks. The corresponding zirconages of meta-gabbros and a group of detrital zircons might indicateintra-oceanic brecciation and erosion (Rubatto et al., 1998). Anotherpossibility is that frontally accreted, obducted or exhumed slices ofCretaceous oceanfloor endedup in a part of the accretionarywedge thatwas affected by gravity-driven processes transporting blocks andcompletely disintegrated material back into the trench region., Theinferred detrital origin suggests a depositional age younger than 80 Ma,which is inmarked contrast to the previously assumed Triassic–Jurassictime of sedimentation for the clastic metasediments.

We have yet no satisfying explanation for two oscillatory zonedgrains with an age of c. 57 Ma. After identifying a single grain with thisapparent age and its distinct internal structure, we prepared a secondzircon mount for this sample and systematically searched for moregrains with similar CL characteristics. One additional grain was foundwhich yielded the same age in a subsequent SHRIMP session severalmonths later. These ages are not due to analytical problems and wehave no evidence for Pb-loss effects. This apparent age is identicalwithin error to the date obtained from the recrystallized interior ofeclogite zircons and thus may record HP metamorphic processes.Alternatively, it may indicate a post-57 Ma depositional age for theclastic metasediments. Well-documented geochronological evidencefor an active subduction system in the Eocene indicates that at leastremnants of an ocean basin remained open until this time.

6. Regional correlations

Ophiolites in collision belts represent remnants of vanishedoceanic domains and thus are important tools for reconstructingtheir original geodynamic setting and paleogeographic context. Muchattention has been given to the Mesozoic ophiolites exposed onmainland Greece, in the Balkan region, in Turkey and in other parts ofthe Eastern Mediterranean (e.g. Rhodes, Crete), which document theopening and closure of various basins of the Tethys Ocean (e.g. Pamićet al., 2002; Robertson 2002; Robertson et al., 2009; Papanikolaou,2009). Compared to the wealth of information available for theseoccurrences, knowledge is fragmentary for ophiolites exposed in theACCB. In contrast to the extensive intact ophiolite massifs of mainlandGreece and the Balkan region (tens to several hundred km2), thedisrupted ophiolitic occurrences exposed in the HP mélanges of theCyclades are exceedingly small. Previous work revealed mid-oceanridge to island arc affinities for meta-ophiolitic rocks (e.g. meta-gabbros and glaucophanites) from Syros, Tinos and adjacent islands,and this observation has been interpreted to indicate a back-arcsetting (e.g. Bröcker, 1990; Seck et al., 1996; Moçek, 2001). The newgeochemical results for mélange blocks from Tinos and Androscomplement existing datasets and further corroborate this conclu-sion. A detailed evaluation of the plate tectonic setting is beyond thescope of this paper. Here we examine whether or not geochemicalcharacteristics of meta-gabbros support correlations between litho-logically similar occurrences on different islands. This rock type wasselected because it occurs in all mélanges within the larger study area.The meta-gabbros commonly display preserved igneous textures, andoccasionally even igneous clinopyroxene, despite HP and greenschist-facies overprinting, and were probably less affected by compositionalchanges during metamorphism than other lithologies of the blockpopulation. Meta-gabbros from Tinos show a large compositionalvariability and were found at 4 locations, each with distinctcompositional characteristics, suggesting different crystallizationhistories or different sources. REE distribution patterns for samplesfrom NW Tinos show considerable inconsistencies interpreted asindication for post-magmatic disturbance. REE patterns of meta-


gabbros from other parts of the island are apparently undisturbed anddefine homogeneous, but compositionally different groups. Geo-chemical characteristics of blocks from Tinos and Syros show manysimilarities. For example, the REE patterns of samples from MavraGremna (Tinos) and Grizzas (Syros) suggest a co-magmatic relation-ship. On both islands, the block population includes mafic meta-igneous rocks, which are characterized by strong enrichment in highfield strength and rare earth elements (Seck et al., 1996; Bröcker andEnders, 1999, 2001). Seck et al. (1996) interpreted rutile-richeclogites and glaucophanites from Syros (up to 9 wt.% TiO2) asderivatives of Ti-rich gabbroic cumulates. However, it is not clearwhether very high TiO2 concentrations indicate magmatic character-istics or metasomatic alteration. Metamorphic redistribution isevidently indicated by veinlets filled with rutile and/or titanite.Neither local redistribution nor infiltration from nearby sources canbe yet ruled out. In any case, the geochemistry of mélange blocks andthe identical U–Pb zircon ages suggest that the block-matrixassociations on Tinos and Syros can be grouped together. On abroader regional scale, there seem to be similarities between somemeta-igneous rocks from Tinos and Evvia, but the geochemicalvariability of meta-gabbros and the unknown protolith ages of blocksfrom Evvia make regional correlations extremely difficult. The sameapplies to the inferred genetic relationship of the mélanges on Syrosand Samos (e.g. Candan et al., 1997; Ring et al., 1999).

Field relationships, petrographic and geochemical similarities,and U–Pb zircon ages reported for mélanges from Syros and Androsstimulated the working hypothesis that the block association onTinos may comprise a mixture of at least 3 of the age groups(240 Ma, 160 Ma, 80 Ma) recognized on the neighboring islands.Documentation of this age spectrum also on Tinos would haveprovided supporting evidence for correlating the mélanges of all 3islands. However, all studied rock fragments from Tinos yieldedCretaceous ages (c. 80 Ma), and the new chronometric data failed todemonstrate the complete equivalence with other northernCycladic block-matrix associations. On Tinos, the potential to getadditional blocks for dating is severely limited, due to the restrictedlevel of exposure and the widespread absence of zircon orbaddeleyite, as well as pervasive metamorphic overprinting thatobscured the record of pre-Eocene processes. Therefore, applicationof other chronometric methods is not promising either. We havetested the potential of Sm–Nd dating for obtaining protolith ages ofthe meta-gabbros. However, Sm–Nd isotope analyses applied to thelargest meta-gabbro lens exposed at Mandrisia Bay (Fig. 3A) (6whole rock samples, 1 mineral separate of igneous clinopyroxene)yielded no meaningful isochron age. The distinct Sr–Nd isotopecharacteristics of the Jurassic meta-gabbros from Andros and theCretaceous meta-gabbros from Tinos suggest that this feature canbe used as a proxy for the protolith age of samples that areunsuitable for chronometric studies. To further test this hypothesis,the construction of a Sr–Nd database for meta-gabbros occurring onEvvia, Syros and Samos is currently in progress.

Despite their close spatial relationship and similar lithostratigraphicposition it remains unclear whether or not mélanges occurring insouthern Andros and northern Tinos are genetically correlated. It is yetuncertain whether these occurrences represent equivalents of a singleblock-bearing horizon, or distinct block-matrix associations thatdeveloped at different times and/or at different pseudo-stratigraphiclevels. Bulk rock geochemistry of meta-gabbros, Sr–Nd isotopecharacteristics and Jurassic U–Pb zircon ages suggest that the CapeSteno mélange of S Andros represents a distinct group. This does notpreclude the possibility that a more diverse block population, havingfeatures in common with other mélanges, originally existed on Andros.The apparent singularitymight simply reflect restricted outcrop size andlimited exposure. The Jurassic protolith ages of mélange blocks fromAndros (Bröcker and Pidgeon, 2007; this study) clearly indicate arelationship to the ophiolite occurrences in the Hellenide and Balkan

region (e.g. Parlak and Delaloye, 1999; Koepke et al., 2002; Liati et al.,2004; Robertson et al., 2009).

More complicated to unravel is the relationship of the Cretaceousmeta-gabbros from Tinos and Syros to the ophiolite belts of theHellenide–Dinaride region and/or the Eastern Mediterranean. Creta-ceous meta-ophiolites are well known from the Taurides (e.g. Çeliket al., 2006), but are less common in the Hellenides/Dinarides, eventhough small back-arc basinsmost likely continued to exist there untilLate Cretaceous to Tertiary time (e.g., Pamić et al., 2002; Robertson2002; Brown and Robertson, 2004; Robertson et al., 2009 andreferences therein). Robertson et al. (2009) recently emphasizedthat the common assumption of an entirely Jurassic age of the Balkanophiolites is an oversimplification. Nevertheless, a correlation of thestudied Cretaceous meta-ophiolites to specific ophiolite belts occur-ring in the larger area is currently uncertain.

7. Conclusions

1. Petrological, geochemical and geochronological characteristicssuggest that the mélanges on Tinos and Syros are geneticallycorrelated. Field relationships indicate that this is also the case forthemélanges occurring in southern Andros and northern Tinos, butsupporting geochemical and/or geochronological evidence for thisinterpretation could not be established with certainty.

2. Zircons from all meta-igneous blocks from Tinos (meta-gabbro,eclogites, glaucophanite) yielded a single U–Pb age group of c.80 Ma. Chlorite–talc schists representing block-matrix reactionzones on Syros and Tinos also yielded c. 80 Ma zircon ages.

3. Cretaceous zircon in the mafic meta-igneous blocks recordsigneous crystallization. Supporting evidence for a metamorphicorigin of c. 80 Ma zircon in eclogite has not been found. Zircon ofthe same age occurring in chlorite–talc schists is presumablyrelated to non-magmatic processes.

4. Cretaceous zircons in clastic metasediments are interpreted to beof detrital origin, suggesting a much later time for sedimentaccumulation than previously assumed. The importance of c. 57 Mazircon ages remains unclear, but may record HP metamorphicprocesses, or a post-57 Ma depositional age.

5. Available data are in accord with a model relating Cretaceouszircons to the formation and closure of a back-arc basin andsubsequent reworking of parts of the accretionary wedge,suggesting that the block-matrix associations originated asolistostromes. Final mixing and mélange formation is a tectonicprocess during subduction and exhumation.

6. Jurassic U–Pb zircon ages of mélange blocks fromAndros documenta genetic relationship to the ophiolite occurrences in the largerBalkan region. A similar regional correlation is possible for theCretaceous meta-gabbros from Tinos and Syros but cannot bedocumented with certainty.

Acknowledgements

Thanks are due to H. Baier for laboratory assistance and for hersupport on the mass spectrometer. We gratefully acknowledge thehelp of J. Berndt on the EMP and the LA-ICP-MS. N. Rodionov and I.S.Presnyakov are thanked for their help at the VSEGEI in St. Petersburgthroughout the SHRIMP measurements. Constructive comments byGraham Layne are greatly appreciated. Thorough reviews of AnthiLiati and an anonymous reviewer helped to clarify the picture andconsiderably improved the manuscript.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.lithos.2010.02.004.


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geochemistry and geochronology of hp mélanges from tinos and andros, cycladic blueschist belt,...

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