Mineralogy and Petrology (2007) 89: 77–111DOI 10.1007/s00710-006-0138-4Printed in The Netherlands

Petrogenetic evolution of the Koziakasophiolite complex (W. Thessaly, Greece)

P. Pomonis, B. Tsikouras, and K. Hatzipanagiotou

Department of Geology, University of Patras, Section of Earth Materials,Patras, Greece

Received April 5, 2005; revised version accepted April 7, 2006Published online July 13, 2006; # Springer-Verlag 2006Editorial handling: J. Foden

Summary

The Koziakas ophiolitic complex is situated in W. Thessaly and is interpreted as anincomplete ophiolite sequence, thrust over the Western Thessaly Unit (W.T.U.). Twotectonically distinct units represent it: (1) the lower unit with a metamorphic sole and atectonosedimentary m�eelange and (2) the upper unit including mantle peridotitesand basaltic lavas. The mantle peridotites are composed by harzburgite, lherzolite andplagioclase lherzolite intruded by a sparse network of gabbroic, plagiogranitic anddoleritic dykes. The volcanic sequence of the upper unit can be geochemicallysubdivided into four groups of basalts with: (1) tholeiitic N-type MORB affinities, (2)low-Ti boninitic affinities, (3) subalkalic E-MORB type affinities and (4) alkalicharacteristics displaying a different petrogenetic evolution with respect to the othergroups. The magmatic history of the Koziakas ophiolite is in agreement with extensivefractional crystallization and variable degrees of partial melting of a heterogeneousmantle source, yielding, magmas mainly of MORB composition. Modal and crypticmetasomatic phenomena of the mantle peridotites as well as Sr-Nd isotopic ratios implythat this melt contained also a hydrous component derived from melting of a subductedlithosphere. The above geochemical characteristics and the correlation with the ad-jacent ophiolite suites of Pindos, Othris and Vourinos indicate that Koziakas ophioliticcomplex formed in a small backarc basin situated at the eastern margin of the greaterPindos Ocean, between the Western Thessaly Unit (W.T.U.) and the Pelagonian continent.

Introduction

In the last decades, much interest focused on the study of ophiolitic exposures as theyprovide direct information about processes controlling the petrogenetic evolutionof the upper mantle and the oceanic crust. Ophiolitic rocks in central-northern

mainland Greece are exposed along a NW-SE trending belt (Fig. 1) and representtectonic sutures, formed during progressive closure of the Mesozoic NeotethyanOcean. The ophiolitic complex of Koziakas, comprises a series of oceanic andmantle fragments, lying along the eastern slopes of Koziakas mountain range. Itoccupies a significant position between the External and Internal Hellenides as alink between the well-studied ophiolites of Pindos to the NW and Othris to the SE(Fig. 1, inset) which are believed to be continuous with the Vourinos and Kastoriaophiolites beneath the Meso-Hellenic molasse trough (Smith, 1979).

Despite the geological significance of the Koziakas ophiolitic complex, fewdata on the geology, petrology and geochemistry of these rocks have been reported(Capedri et al., 1985; Hatzipanagiotou et al., 1995).

In this paper we present new geologic, petrographic, mineralogical, isotopicand whole-rock geochemic results from the Koziakas ophiolitic complex and wecompare them with those from the adjacent Othris, Pindos and Vourinos ophiolites.Using these data, we discuss the nature, genesis and geotectonic significance of theKoziakas ophiolitic rocks.

Geological setting

The Koziakas ophiolite belongs to the Western Thessaly Unit – W.T.U.(Papanikolaou and Sideris, 1979), a series of sedimentary and volcanic rocks ofUpper Triassic to Eocene age. Extensive fieldwork in the ophiolitic complex ofKoziakas focused on the distribution and mode of development of the ophioliticrocks and a detailed geological map was produced (Fig. 1).

The basal unit of the Koziakas ophiolite is represented by Alpine-type sedi-mentary rocks of the W.T.U., which occurs in the western part of the Koziakasmountain range. The Portaikos limestones of Upper Triassic age, comprises thelower member of the W.T.U. These rocks are overlain by the Mouzaki formation,which consists of medium-bedded sequences of cherts, siltstones and oolithic lime-stones of Lower to Middle Jurassic age. The Koziakas limestone formation iscomposed of oolithic limestones of Middle to Upper Jurassic age. It is tectonicallyoverlain by the Mouzaki formation and locally underlain by the Thymiama lime-stones of Upper Cretaceous age (indicated by the occurrence of microfossils).Finally, both the Koziakas and the Thymiama limestones were thrust over the upperpart of the W.T.U., consisting of Palaeocene to Eocene flysch, which is transitionalto the Pindos flysch (Papanikolaou and Sideris, 1979; Lekkas, 1991).

The Koziakas ophiolitic complex is an incomplete ophiolite with an ophioliticm�eelange at its base and occupies the eastern part of the mountain range (Fig. 1).The ophiolitic m�eelange is thrusted over the Mouzaki formation and the Koziakaslimestones of the W.T.U., while it underlies the Ophiolitic Unit. It comprises achaotic multicoloured volcano-sedimentary sequence, of various rock fragments.These fragments have variable size from several centimeters to tens of meters andusually form tectonic blocks, surrounded by a shaly-silty matrix, which is stronglysheared and tectonized. These blocks include serpentinites, serpentinized peri-dotites, gabbros, dolerites, pillow-lavas, amphibolites, radiolarites, limestones (ofUpper Triassic, Middle-Upper Jurassic and Upper Cretaceous age), argillitic schistsand sandstones. Most contacts within the ophiolitic m�eelange appear to be highly

78 P. Pomonis et al.

Fig. 1. Geological map of the Koziakas ophiolitic complex

Petrogenetic evolution of the Koziakas ophiolite complex 79

foliated and tectonic. In places, however, igneous contact relationships are pre-served within large blocks, commonly juxtaposed with highly strained rocks. Char-acteristic exposures of the ophiolitic m�eelange are found close to Xylopariko village(Fig. 1), where slices of foliated serpentinized peridotites, pillow-lavas, radiolaritesand limestones of Upper Triassic and Middle-Upper Jurassic age alternate withlarge blocks of massive gabbro.

The ophiolitic m�eelange is locally thrust along a sub-ophiolitic metamorphicsole, composed of interlayered amphibolites and metasedimentary rocks. K-Ardating on hornblende separates from the amphibolite suggest a Late Jurassic age(174� 3 Ma and 161� 1 Ma, Pomonis et al., 2002); these ages are similar to thoseinferred for other ophiolites of the northern-central mainland Greece.

The lower part of the Koziakas Ophiolite Unit comprises ultramafic mantletectonites, which are by the far the most voluminous rocks of the unit. They arethrust over the ophiolitic m�eelange and locally over the amphibolites of the meta-morphic sole. These are predominantly spinel-harzburgites and lherzolites withminor plagioclase-bearing lherzolites. They are strongly sheared with foliationsoriented NW–SE with a dip of about 30�–50� to the SW. Most of the peridotitesare serpentinized, especially in the basal parts of the slices and along shear zones.

A sparse network of gabbroic (locally rodingitized), plagiogranitic and doleriticdykes intrudes the mantle tectonites. The medium to coarse-grained dykes showwell preserved chilled margins and are individually up to 2m wide. They transectthe host ultramafic rocks along two main cross-cutting directions: the first strikesNE–SW and dips 50�–70� to the NW and the second strikes N–S to NNW–SSE witha dip of about 65�–80� to the W. In places, intense deformation of gabbroic dykesalong shear-zones has resulted in tectonic lineation with plagioclase-rich domainsand mylonitic textures.

Massive basalts are thrust over peridotites and pass upwards into basaltic pil-low-lava flows. The lavas are usually dark green, dark grey, or blue-grey whenfresh. The thrust contact between massive basalt and serpentinized peridotites,forms cataclastic zones up to 5 m wide, where irregular fragments of these twolithologies interdigitate in a yellowish or greenish silty matrix. In places the pillow-lavas are intercalated with cherts rich in Mn-oxides of hydrothermal origin(Scarpelis et al., 1992).

At the NE part, the Koziakas ophiolitic complex is unconformably overlain bymolasse sediments of Miocene age. These sediments consist of alternations ofmarls, silty marls, sandstones and conglomerates. Finally, basin and fluvial depos-its, consisting of materials of various size and lithological composition, mainly ofcalcareous and siliceous cobbles, sands and clays of Quaternary age cover theKoziakas ophiolite in the east.

Sampling and analytical techniques

Sampling was focused on the Koziakas ophiolitic complex. Care was taken inscreening the samples since plastic deformation and secondary alteration haveaffected most of them. Only the freshest samples in terms of major and traceelements have been considered below. However, it is possible that alteration pro-cesses have affected some mobile elements.

80 P. Pomonis et al.

Whole-rock major, trace and REE analyses as well as quantitative microprobeanalysis were performed at the University of Bristol, Department of EarthSciences. Whole-rock major analyses were carried out using a JY24 SequentialSpectrometer (ICP-AES), while Si was determined by X-ray fluorescence, using aSpectro Analytical X-Lab 2000 XRF spectrometer.

Trace and rare earth elements (REE) were determined on totally digestedsamples by inductively coupled plasma-mass spectrometry (ICP-MS) using a VGElemental Plasma Quad II, following techniques described in Bailey et al. (1993)and Lewis et al. (1997). Detection limits were generally sub ppb in solution,equivalent to sub ppm levels in rock samples, taking into account dilution factors.

Quantitative microprobe analysis was carried out using a JEOL JXA-8600automated microanalyser equipped with an Energy Dispersive Spectrometer(EDS) and a Wavelength Dispersive Spectrometer (WDS), controlled by a Linksystem. Operation conditions were 20 kV accelerating voltage, a beam current of15 nA and a spot size of 5 microns.

Sr-Nd isotope determinations were carried out at Activation Laboratories,Ancaster-Ontario, using the TIMS method.

Petrography

Mantle tectonites of the Ophiolitic Unit

Mantle tectonites are represented by spinel-harzburgite and lherzolite with subor-dinate plagioclase-bearing lherzolite. They mainly show porphyroclastic texture,which features a bimodal grain size distribution of millimeter-scale porphyroclastsbeing worn down into a fine-grained matrix of neoblasts. Olivine and orthopyrox-ene occur both as porphyroclasts and neoblasts. The orthopyroxene porphyroclasts(<10 mm) show well-developed sub-grain boundaries and usually display bentexsolution lamellae of clinopyroxene. Olivine, orthopyroxene and clinopyroxeneneoblasts occur as small, polygonal strainfree grains (�2 mm) around the largerporphyroclasts or as fine grained assemblages, forming the rock matrix. Evidenceof plastic deformation is shown in strained olivine and orthopyroxene porphyro-clasts, which display undulatory extinction, kink-bands, rotations and a foliation,defined by elongate olivine grains. Lobate or subhedral Cr-spinel is also present. Inthe plagioclase-bearing lherzolite samples, interstitial plagioclase makes up lessthan 5% of the mode. Plagioclase occurs as single crystals with relatively widestraight twin lamellae, associated with clinopyroxene or orthopyroxene and con-tains much less evidence for intracrystalline deformation than the olivines andorthopyroxenes of the host peridotite. Due to the serpentinization effect, theprimary minerals are transformed to various degrees: olivine into hydrated associa-tions of serpentine minerals, orthopyroxene mainly into bastite and talc, clinopyr-oxene into actinolite and chlorite, and spinel into magnetite.

Gabbros

Occurrences of gabbros, which are present as block fragments into the Koziakasophiolitic m�eelange are relatively small. They have subhedral to anhedral granular

Petrogenetic evolution of the Koziakas ophiolite complex 81

to subophitic texture, most commonly medium- to coarse-grained. Their modalcontent of olivine varies from 10–15%. The crystallization order is: olivine!plagioclase! clinopyroxene

Dykes

The primary textures of gabbroic dykes cross-cutting mantle tectonites, have beenobliterated by deformation. They display porphyroclastic to mylonitic textures withstrained clinopyroxene and plagioclase porphyroclasts lying in a more or lessrecrystallized fine-grained groundmass of plagioclase, clinopyroxene and possiblyolivine neoblasts. In places of intense deformation (i.e. along shear-zones), gab-broic dykes show a distinct banding that parallels alternate plagioclase-rich andclinopyroxene-rich layers of different grain size. Accessory phases are Fe-Ti oxi-des and apatite. Dykes are pervasively modified by hydrothermal alteration, andtheir secondary phases are currently composed of actinolite, epidote, clinozoisite,chlorite, serpentine and albite.

Plagiogranitic dykes display mainly homogeneous structures. Textures rangefrom fine to medium-grained with subhedral plagioclase and orthoclase, set in a‘‘mosaic’’ consisting of anhedral quartz and minor euhedral hornblende. Fe-Tioxides represent accessory phases. Epidote, calcite, clinozoisite, albite and leucox-ene are alteration products characteristic of ocean-floor metamorphism. Frequently,plagiogranitic dykes are fine-grained near the margins and become medium-grainedtowards the cores.

Doleritic dykes display commonly fine-grained porphyritic textures with sub-hedral plagioclase phenocrysts set in either intergranular or subophitic ground-mass, in which microlites of plagioclase and clinopyroxene can be recognized.Accessory phases comprise Fe-Ti oxides. Alteration products are albite, actinolite,chlorite, epidote and calcite. Undulatory extinction in some plagioclase crystalsshows evidence of plastic deformation. The doleritic dykes are often crosscut byveinlets filled by epidote, albite, chlorite, calcite, tremolite and quartz.

Volcanic rocks

The volcanic sequence of the Ophiolitic Unit is mainly represented by pillowedbasalt, brecciated pillowed basalt and massive basalt. The pillow lavas display arange of textures from aphyric and variolitic to plagioclase-porphyritic. Laths ofplagioclase and interstitial clinopyroxene make up the intersertal to subophiticgroundmass. Few samples display calcite-filled amygdules. Massive lavas displayporphyritic texture with plagioclase and clinopyroxene phenocrysts settled in anintergranular to intersertal groundmass with microlites of plagioclase, clinopyrox-ene and olivine. Fe-Ti oxides are present in both pillow and massive lavas. Thesequence of crystallization in the Koziakas ophiolite volcanic rocks is interpret-ed to be: olivine! olivineþ plagioclase! olivineþ plagioclaseþ clinopyroxene(with associated Cr-spinel through to Ti-Mg phases throughout). Both types ofbasalt are altered, showing very low-grade ocean metamorphism with the devel-opment of quartz, albite, epidote, chlorite, pumpellyite, calcite, hematite, titaniteand actinolite.

82 P. Pomonis et al.

Mineral chemistry

Olivines

Representative microprobe analyses of olivine grains from the harzburgite, lherzo-lite, plagioclase lherzolite and gabbro from the ophiolite m�eelange, are reported inTable 1. They are rather homogeneous in composition and do not show distinctivezoning from core to rim. Furthermore, no significant compositional differencebetween porphyroclasts and neoblasts has been observed. The forsterite content(Mg#) in the analyzed crystals is slightly higher in the harzburgite (90.8–90.7)than in the lherzolite (90.1–89.8) and the plagioclase lherzolite (88.7–89.8). Theforsterite content drops to 70–83 in olivine from the gabbros. The analyzed oli-vines of plagioclase lherzolite are also slightly richer in FeO than those from theharzburgite and the lherzolite.

Spinels

Representative spinel analyses from the harzburgite, lherzolite and plagioclaselherzolite of the Koziakas mantle peridotites are listed in Table 1. The harzbur-gites contain spinel with higher Cr# (¼100�Cr=(CrþAl)) ranging from 47.5 to50.7, relative to the lherzolite and plagioclase lherzolite with Cr# 26.03–27.25and 28.6–33.8 respectively. TiO2 contents of spinels are higher in the harzburgiterelative to the lherzolite and plagioclase lherzolite, but less than 1.0 wt.%, analo-gous to that of spinels in most ophiolitic peridotites (e.g., Dick, 1977; Herbert,1982; Auge, 1987). Al content is significantly higher in the lherzolitic and plagio-clase lherzolitic spinels relative to the harzburgitic ones, while Fe content displaysimilar values between the harzburgitic and plagioclase lherzolitic spinels. Thelow Cr# (<60) of the analyzed spinels in all rock-types are similar to those fromophiolites of oceanic (including back-arc basins) origin (Dick and Bullen, 1984).The chemistry of the analyzed spinels from the Koziakas lherzolite reveals af-finities analogous to Alpine-type peridotites in terms of Cr# and Mg#, whilespinels from the plagioclase lherzolite are similar to those in Othris, which wereinterpreted as products of melt impregnation (Dijkstra et al., 2001; Barth et al.,2003) (Fig. 2a). They are also similar to spinels from Lesvos and Eastern Chalk-idiki ophiolites (Hatzipanagiotou et al., 2001, Fig. 2b). The high-Cr# values inanalyzed spinels with the low whole-rock Al2O3 abundances in both rock-types ofthe Koziakas peridotites (see Table 1), are characteristic for several upper mantleperidotites (Talkington and Malpas, 1984; Bonnati and Michael, 1989; Suhr andRobinson, 1994).

Pyroxenes

Representative microprobe data of pyroxene crystals from the Koziakas harzbur-gite, lherzolite, plagioclase lherzolite, gabbro, doleritic dykes and basalts are listedin Table 2. The ferric iron content has been calculated according to the method ofPapike et al. (1974). According to the I.M.A. classification (Morimoto et al., 1988),clinopyroxenes of the lherzolite, plagioclase lherzolite and gabbro (from the ophio-

Petrogenetic evolution of the Koziakas ophiolite complex 83

Tab

le1

.Representative

microprobedata

ofolivines

andspinelsfrom

theKoziakasophiolite

Oli

vin

esS

pin

els

Har

zburg

ite

Lher

zoli

teP

lag-l

her

zoli

teG

abbro

Har

zburg

ite

Lher

zoli

teP

lag-l

her

zoli

te

Sam

ple

A4

4A

49

A4

2A

46

A8

6A

60

0A

60

A6

0S

amp

leA

44

A4

9A

42

A4

6A

86

A6

00

An

aly

sis

10

21

12

13

51

01

40

27

71

33

51

11

21

48

14

2

SiO

24

1.0

64

0.7

44

0.5

94

0.9

44

0.4

84

1.3

37

.44

38

.51

TiO

20

.44

0.5

00

.08

0.0

60

.07

0.0

9F

eO9

.01

9.0

29

.69

9.2

09

.71

10

.99

27

.26

19

.38

Al 2

O3

27

.85

25

.63

42

.78

44

.08

36

.50

38

.61

Mn

O0

.10

0.1

30

.23

0.1

20

.08

0.1

30

.44

0.3

2C

r 2O

33

7.5

73

9.2

52

3.8

92

3.1

42

7.8

72

6.3

5M

gO

49

.66

49

.93

49

.38

49

.62

48

.34

48

.42

35

.58

41

.44

FeO

21

.91

18

.87

16

.86

14

.77

19

.90

19

.87

NiO

––

0.4

0–

0.3

5–

0.0

20

.08

Mn

O0

.23

0.2

20

.20

0.1

70

.26

0.1

1

To

tal

99

.86

99

.93

10

0.4

19

9.8

89

8.9

91

00

.87

10

0.7

49

9.7

3M

gO

11

.66

15

.08

15

.88

16

.87

15

.17

13

.93

To

tal

99

.66

99

.55

99

.61

99

.03

99

.70

98

.96

Str

uct

ura

lfo

rmula

eon

the

bas

isof

4oxygen

sS

truct

ura

lfo

rmula

eon

the

bas

isof

32

oxygen

s

Si

1.0

03

0.9

96

0.9

93

1.0

01

1.0

01

1.0

07

0.9

91

0.9

91

Al

8.0

56

7.3

60

11

.36

01

1.6

16

10

.371

10

.59

2F

eþ2

0.1

84

0.1

84

0.1

98

0.1

88

0.2

01

0.2

24

0.6

03

0.4

17

Cr

7.2

96

7.5

60

4.2

56

4.0

88

5.6

28

5.4

07

Mn

0.0

02

0.0

03

0.0

05

0.0

02

0.0

20

0.0

03

0.0

10

.00

7F

eþ3

0.5

68

0.9

84

0.3

68

0.2

88

0.8

89

0.5

60

Mg

1.8

08

1.8

19

1.8

01

1.8

08

1.7

83

1.7

59

1.4

04

1.5

9T

i0

.08

00

.09

60

.01

60

.00

80

.01

60

.01

6N

i–

–0

.00

8–

0.0

07

–0

.00

10

.00

21

61

61

61

61

61

62

.99

73

.00

63

.00

52

.99

92

.99

52

.99

43

.00

93

.00

7

Fo

90

.76

90

.81

90

.10

90

.58

89

.87

88

.70

69

.96

79

.22

Feþ

23

.99

22

.86

42

.80

82

.47

23

.02

43

.31

2M

g4

.26

45

.48

05

.32

85

.62

45

.27

24

.84

0M

n0

.04

80

.04

80

.04

00

.03

20

.04

80

.02

4C

r#4

7.5

25

0.6

72

7.2

52

6.0

33

3.8

63

1.4

Mg#

51

.65

65

.68

65

.49

69

.47

63

.55

59

.37

–bel

ow

det

ecti

on

lim

it;Fo

10

0�

Mg=

(Mgþ

Fe)

;Mg#

10

0�

Mg=(M

gþ

Fe2

þ);Cr#

10

0�

Cr=

(Crþ

Al)

84 P. Pomonis et al.

litic m�eelange) are diopsides, while orthopyroxenes from the harzburgite and thelherzolite, are enstatites. The clinopyroxenes from both doleritic dykes and basaltsare augites. The Koziakas harzburgite contains diopside with lower Al and Fe andenstatite with higher Mg relative to those from the lherzolite. The clinopyroxenefrom the Koziakas plagioclase lherzolite has higher Ti, Al, Fe and Na contents thanthose from the lherzolite (Table 2). The analyzed pyroxenes do not exhibit asystematic zoning and are rather chemically homogeneous.

Geothermobarometric calculations

The incorporation of AlVI in igneous clinopyroxene is pressure-dependent as haveshown melting experiments in basalts (Thompson, 1974; Mahood and Baker,1986). The observed low AlVI values in the augites of basalts and doleritic dykes(with few exceptions, Fig. 3), are consistent with low pressures of crystallization.Their AlVI=AlIV ratio is less than 0.25 (with few exceptions, see Fig. 3), which isthe boundary for pyroxenes crystallized between low and medium pressure(�5 kbar). The AlVI=AlIV ratio of the analyzed diopside in the gabbro is more than

Fig. 2. a Spinel compositions from the harzburgites and lherzolites of Koziakas in termsof Cr# (¼100�Cr=(CrþAl)) versus 100�Mg=(Mgþ Feþ2). Fields for chromites oc-curring in Alpine-type peridotites, abyssal peridotites, Tertiary boninites from the WesternPacific and Cape Vogel, Papua and island-arc rocks from Troodos, Othrys and Aegina(Greece), are shown for comparison. Data from Dick and Bryan (1979), Dick and Bullen(1984), Cameron et al. (1979) and Dietrich et al. (1987). b Chromite compositions fromother places are shown for comparison. Abbreviations are: E.Th.: Eastern Thessaly, V:Vourinos, Ve: Vermion, W.Ch.: Western Chalkidiki, O: Othris, R: Rodiani, Sk: Skyros,Rh: Rhodos, P: Pindos, E: Evia, E.Ch.: Eastern Chalkidiki, Le: Lesvos (data afterEconomou et al., 1986, Migiros and Economou, 1988; Gartzos et al., 1990 and Migiroset al., 2000)

Petrogenetic evolution of the Koziakas ophiolite complex 85

Tab

le2

.Representative

microprobedata

ofpyroxenes,feldspars

andamphibolesfrom

theKoziakasophiolite

Pyro

xen

esF

eldsp

ars

Har

zburg

ites

Lher

zoli

tes

Plg

-Lher

zoli

tes

Oli

vin

e-gab

bro

sD

ole

riti

cdykes

Bas

alts

Plg

-Lher

zoli

tes

Oli

vin

e-gab

bro

s

Sam

ple

A44

A49

A42

A46

A86

A600

A66

A66

F17

F17

A264

A272

A272

Sam

ple

A88

A88

A60

A60

Anal

ysi

s20

111

133

137

12

15

17

184

50

61

316

114

124

Anal

ysi

s2

412(c

)15(r

)

SiO

256.3

356.0

657.0

853.4

052.2

151.4

851.5

352.7

149.2

953.1

951.2

551.3

650.5

5S

iO2

44.3

444.4

246.9

753.6

8

TiO

20.0

1–

0.0

50.2

70.4

90.5

10.5

30.2

71.2

10.4

40.7

30.6

31.2

7T

iO2

––

–0.0

4

Al 2

O3

2.8

13.5

21.4

01.8

92.9

82.9

02.6

71.7

13.8

71.5

13.0

43.0

23.2

2A

l 2O

335.6

835.7

433.5

930.0

1

Cr 2

O3

0.5

50.6

80.1

90.4

40.9

30.9

20.1

60.0

80.0

90.2

20.3

20.2

90.2

2F

e 2O

3t

––

0.1

20.4

4

FeO

t6.1

56.0

26.6

92.2

52.8

72.8

66.4

56.3

09.5

18.6

08.2

28.4

87.7

8M

gO

––

0.0

30.0

8

MgO

34.3

033.4

834.2

916.8

217.0

816.9

014.8

215.5

314.4

618.2

316.8

416.9

715.6

2M

nO

––

0.0

20.0

1

MnO

0.1

40.1

40.1

30.0

70.0

80.0

80.2

40.1

60.2

30.2

30.2

10.2

90.1

5C

aO18.1

218.2

116.7

712.4

5

CaO

0.2

80.7

40.4

224.3

123.1

823.2

322.8

722.2

920.3

317.6

818.7

718.3

720.1

9N

a 2O

2.2

21.0

52.0

84.0

1

Na 2

O–

0.0

10.0

10.2

70.4

90.4

50.2

80.2

80.2

30.2

10.2

30.2

20.3

3K

2O

––

–0.0

3

K2O

–0.0

1–

0.0

1–

––

––

––

––

Tota

l100.3

699.4

299.5

8100.7

5

Tota

l100.6

100.6

6100.4

099.7

4100.3

299.3

399.5

499.3

399.2

1100.3

199.6

199.6

399.3

4

Str

uct

ura

lfo

rmula

eon

the

bas

isof

6oxygen

sS

truct

ura

lfo

rmula

eon

the

bas

isof

8oxygen

s

Si

1.9

29

1.9

23

1.9

63

1.9

46

1.8

89

1.8

82

1.9

10

1.9

51

1.8

47

1.9

45

1.8

92

1.8

95

1.8

78

Si

2.0

46

2.0

59

2.1

65

2.4

09

AlIV

0.0

71

0.0

77

0.0

37

0.0

54

0.1

11

0.1

18

0.0

90

0.0

49

0.1

53

0.0

55

0.1

08

0.1

05

0.1

22

Al

1.9

49

1.9

51

1.8

33

1.5

90

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

2.0

00

3.9

95

4.0

10

3.9

98

3.9

99

AlV

I0.0

43

0.0

65

0.0

20

0.0

27

0.0

16

0.0

07

0.0

26

0.0

26

0.0

17

0.0

10

0.0

25

0.0

26

0.0

19

Ti

––

–0.0

01

Ti

––

0.0

01

0.0

07

0.0

13

0.0

14

0.0

15

0.0

08

0.0

34

0.0

12

0.0

20

0.0

17

0.0

35

Fe3

þ–

–0.0

05

0.0

16

Cr

0.0

15

0.0

18

0.0

05

0.0

13

0.0

27

0.0

27

0.0

05

0.0

02

0.0

03

0.0

06

0.0

09

0.0

09

0.0

07

Mg

––

0.0

02

0.0

05

Feþ

30.0

12

–0.0

10

0.0

19

0.0

76

0.0

00

0.0

50

0.0

26

0.0

82

0.0

30

0.0

49

0.0

51

0.0

49

Mn

––

0.0

01

–

Feþ

20.1

64

0.1

73

0.1

82

0.0

50.0

11

0.0

90.1

50

0.1

69

0.2

16

0.2

30.2

05

0.2

11

0.1

93

Ca

0.8

96

0.9

04

0.8

28

0.5

99

Mg

1.7

52

1.7

12

1.7

58

0.9

10.9

21

0.9

20.8

19

0.8

57

0.8

08

0.9

90.9

27

0.9

24

0.8

65

Na

0.1

99

0.0

94

0.1

86

0.3

49

Mn

0.0

04

0.0

04

0.0

04

0.0

02

0.0

02

0.0

03

0.0

07

0.0

05

0.0

07

0.0

07

0.0

07

0.0

09

0.0

05

K–

––

0.0

01

Ca

0.0

10

0.0

27

0.0

15

0.9

49

0.8

99

0.9

10

0.9

08

0.8

84

0.8

16

0.6

93

0.7

42

0.7

38

0.8

04

1.1

00

1.0

00

1.0

20

0.9

70

Na

–0.0

01

0.0

01

0.0

19

0.0

35

0.0

32

0.0

20

0.0

20

0.0

17

0.0

15

0.0

16

0.0

15

0.0

24

2.0

00

2.0

00

1.9

96

1.9

99

2.0

00

2.0

02

2.0

00

1.9

97

2.0

00

2.0

00

2.0

00

2.0

00

2.0

01

Wo

0.5

21.4

20.7

849.1

47.0

747.4

46.9

545.5

542.3

135.4

038.4

742.1

641.9

6A

b18.1

79.4

218.3

436.7

8

En

90.2

089.3

589.2

547.3

48.2

647.9

42.3

444.1

641.8

850.8

048.0

344.8

045.1

6A

n81.8

390.5

881.6

663.1

2

Fs

9.2

89.2

39.9

63.6

64.6

74.6

810.7

110.2

915.8

213.8

013.4

913.0

512.8

8O

r–

––

0.1

1

(continued)

86 P. Pomonis et al.

Tab

le2

(continued

)

Fel

dsp

ars

Am

phib

ole

s

Dole

riti

cdykes

Bas

alts

Am

phib

oli

tes

Am

phib

oli

tes

Sam

ple

F18

F18

A272

A264

A264

A262

A282

Sam

ple

A262

A282

Anal

ysi

s218

312

119

309

310

28

Anal

ysi

s8

32

SiO

252.5

851.5

552.2

754.4

453.1

358.1

958.6

2S

iO2

46.5

244.8

3

TiO

20.0

90.0

60.1

10.0

30.0

3–

–T

iO2

0.5

30.1

8

Al 2

O3

30.0

930.8

330.9

428.7

130.2

026.1

126.2

3A

l 2O

312.1

412.8

8

Fe 2

O3

t1.7

70.8

40.7

40.8

10.7

4–

–C

r 2O

30.0

30.1

5

MgO

0.5

30.2

50.1

60.2

00.1

9–

–F

eO14.4

814.7

5

MnO

0.0

4–

0.0

1–

0.0

4–

–M

gO

11.4

211.0

2

CaO

8.8

212.6

312.3

110.5

912.8

06.6

87.3

2M

nO

0.2

20.2

9

Na 2

O6.0

93.9

94.1

25.1

73.7

58.1

77.9

8C

aO10.8

011.8

6

K2O

0.1

90.0

80.0

60.1

60.0

50.2

80.0

9N

a 2O

1.4

61.5

5

Tota

l100.1

9100.2

2100.7

2100.1

1100.9

299.4

3100.2

4K

2O

0.2

10.1

8

To

tal

97.8

197.6

9

Str

uct

ura

lfo

rmula

eon

the

bas

isof

8oxygen

sS

truct

ura

lfo

rmula

eon

the

bas

isof

23

oxygen

s

Si

2.3

86

2.3

40

2.3

56

2.4

58

2.3

88

2.6

18

2.6

21

Si

6.7

55

6.5

62

Al

1.6

13

1.6

58

1.6

42

1.5

39

1.6

08

1.3

83

1.3

79

AlIV

1.2

45

1.4

38

3.9

99

3.9

98

3.9

98

3.9

97

3.9

96

4.0

01

4.0

00

8.0

00

8.0

00

Ti

0.0

03

0.0

02

0.0

04

0.0

01

0.0

01

––

AlV

I0.8

31

0.7

82

Fe3

þ0.0

67

0.0

32

0.0

28

0.0

30

0.0

28

––

Ti

0.0

58

0.0

20

Mg

0.0

36

0.0

17

0.0

11

0.0

14

0.0

13

––

Cr

0.0

03

0.0

17

Mn

0.0

01

––

–0.0

02

––

Feþ

30.3

53

0.2

75

Ca

0.4

29

0.6

14

0.5

94

0.5

12

0.6

16

0.3

22

0.3

50

Feþ

21.2

69

1.4

83

Na

0.5

36

0.3

51

0.3

60

0.4

53

0.3

27

0.7

13

0.6

91

Mg

2.4

72

2.4

05

K0.0

11

0.0

05

0.0

04

0.0

09

0.0

03

0.0

16

0.0

05

Mn

0.0

13

0.0

18

1.0

80

1.0

20

1.0

00

1.0

20

0.9

90

1.0

51

1.0

46

Ca-

B1.6

80

1.8

60

Ab

54.9

236.1

937.5

846.5

134.5

767.8

466.0

6N

a-B

0.1

69

0.0

75

An

43.9

663.3

062.0

052.5

765.1

230.6

433.4

6N

a-A

0.2

42

0.3

65

Or

1.1

30.5

20.4

20.9

20.3

21.5

20.4

8K

-A0.0

39

0.0

34

–bel

ow

det

ecti

on

lim

it;plg

pla

gio

clas

e;c

cry

stal

core

;r

cryst

alri

m

Petrogenetic evolution of the Koziakas ophiolite complex 87

0.25, suggesting crystallization at higher pressures (Aoki and Shiba, 1973). On thebasis of Lindsley’s (1983) geothermometer, crystallization-temperature yieldedminimum temperatures of 600–850 �C, for diopsides in the gabbros and 850–1100 �C for augites in basalts (Table 3).

Equilibration temperatures for the mantle peridotites from the Koziakas ophio-litic complex have been calculated with several geothermometers. The thermo-metric calculations have been restricted to the porphyroclasts in order to unravel

Fig. 3. AlVI vs. AlIV diagram (Aoki and Shiba, 1973), for pressure estimation of theKoziakas clinopyroxenes. HP¼High-pressure field, LP¼Low-pressure field

Table 3. Geothermometric calculations (in �C) for the Koziakas ophiolitic rocks

Sample Lindsley Wells Brey & K€oohler

Min. Max. Two px Ca-Opx

A86 600 1000 842 982 1105Lherzolite 650 1000 820 910 992

600 1000 836 942 996

A41 750 1100 985 970 1093Harzburgite 800 1170 1000 988 1167

700 1100 1105 964 1154

A66 600 800Olivine-gabbro 620 830

600 850

A272 850 1000Basalt 870 1050

850 1100

Min. minimum; Max. maximum; px pyroxene; Opx Orthopyroxene

88 P. Pomonis et al.

the event that affected these rocks prior to deformation. Assuming a pressure of6–7 kb which is usual for upper mantle peridotites, the temperature conditions ofthe Koziakas mantle peridotites have been estimated on the basis of the followinggeothermometers and are summarized in Table 3.

– Tetrahedral projection of the orthopyroxenes and clinopyroxenes in the Di-En-Hd-Fs diagram (Lindsley, 1983).

– Partitioning of Mg and Ca between orthopyroxene and clinopyroxene (Wells,1977).

– Two pyroxenes (Brey and K€oohler, 1990).– Ca content in orthopyroxene (Brey and K€oohler, 1990).

The estimated temperatures are closing temperatures, as there is a lack ofcompositional equilibrium among the phases in the peridotite assemblages.

Amphiboles

A selection of representative microprobe analyses of metamorphic amphibolesfrom the Koziakas amphibolites is given in Table 2. The ferric iron content hasbeen calculated according to the method of Papike et al. (1974), while the calcula-tions of chemical formulae were done on the basis of 23(O). The analyzed amphi-boles are calcic and they are classified as magnesiohornblendes (nomenclatureafter Leake et al., 1997). The magnesiohornblendes display a slight range ofcomposition, mainly according to Si and Al values. Moreover, their Ti content(0.020–0.061) correlates with the lower-grade amphibolite facies according tothe Ti values given by Raase (1974).

Feldspars

Representative feldspars analyses from plagioclase-bearing lherzolites, olivine-gabbros, doleritic dykes and basalts are shown in Table 2. Plagioclase from theplagioclase-bearing lherzolite is unzoned bytownite-anorthite (An72-An90). Gabbrofrom the ophiolitic m�eelange contains plagioclase of labradorite-bytownite compo-sition (An56-An82). Some of the analyzed plagioclase crystals show normal zona-tion with Ca-rich cores (An74-An82) and rims poor in Ca (An66-An67, Table 2).Basalts and doleritic dykes contain usually unzoned plagioclases of andesite-lab-radorite composition (An34-An66). The orthoclase content is very low in all plagi-oclases, being similar to compositions from lithologies of MORB origin (Bryanet al., 1981; Le Roex et al., 1983, 1989; Table 2).

Whole-rock chemistry

Major and trace elements: alteration and general features

Major-, trace- and rare-earth element analyses of representative samples from theKoziakas ophiolitic complex, are reported in Table 4. Loss on ignition (L.O.I.),which is generally considered as an index of alteration, is rather low in the analyzedsamples (with few exceptions with about 4.20–5.20 wt.%). The linear correlations

Petrogenetic evolution of the Koziakas ophiolite complex 89

Tab

le4

.Representative

geochem

icalanalysesofsamplesfrom

therock

types

oftheKoziakasophiolite

Maj

or

elem

ents

(%w

t.)

Har

zburg

ites

Lher

zoli

tes

Pl-

Lher

zoli

tes

Oli

vin

eG

abbro

sG

abbro

icdykes

Bas

alts

-Dole

riti

cdykes

Am

phib

oli

tes

A41

A49

A42

A46

A63

A600

A308

A60

A66

A130

A259

A271

A30

A274

A263

A193

(==

)F12

A261

A280

a.S

iO2

43.2

244.1

042.9

043.4

042.2

843.8

345.9

447.0

146.9

647.1

251.1

050.7

755.6

057.1

950.6

249.7

649.3

347.3

947.0

0

b.T

iO2

0.0

20.0

20.0

90.0

30.1

80.0

80.0

90.1

90.5

30.0

91.1

31.3

70.2

10.1

91.4

21.8

51.9

10.7

00.9

6

Al 2

O3

1.7

1.6

22.2

51.8

92.7

62.6

516.1

417.5

619.2

819.1

215.3

114.6

811.6

010.7

514.7

414.5

314.0

015.4

813.7

7

Fe 2

O3

t8.4

58.1

28.7

08.2

07.5

57.7

24.7

46.4

56.2

17.2

18.7

38.8

68.9

78.7

09.8

29.4

510.4

27.8

38.5

0

MnO

0.1

30.1

20.1

30.1

20.1

50.0

90.0

90.1

00.1

00.1

20.1

80.1

60.0

90.0

80.3

20.2

60.1

90.1

40.1

4

MgO

44.4

740.4

041.6

039.0

037.6

938.2

014.8

013.7

17.8

47.8

39.2

48.5

210.5

310.7

07.7

37.1

94.5

810.0

66.9

0

CaO

1.2

01.1

01.9

01.8

03.6

42.8

214.0

411.3

313.2

013.5

68.3

68.0

37.8

06.9

27.9

58.3

98.5

813.0

813.6

9

Na 2

O–

0.0

20.1

50.3

20.3

60.2

81.0

21.8

61.9

61.8

13.5

24.1

52.7

23.2

84.0

14.4

23.7

22.4

63.0

2

K2O

––

0.1

50.0

20.0

60.0

90.0

40.0

90.5

50.4

40.3

40.3

90.0

50.2

10.1

70.8

50.2

60.4

30.8

0

P2O

5–

––

–0.1

4–

–0.0

20.0

20.0

10.0

90.1

1–

0.0

20.1

90.0

90.2

70.0

40.0

6

LO

I0.5

4.0

02.2

05.2

04.2

03.8

02.6

42.0

33.3

23.2

02.1

02.1

32.9

42.9

42.1

03.9

26.6

22.1

43.8

3

Tota

l99.6

999.5

1100.0

799.9

899.0

299.5

699.5

4100.3

599.9

7100.5

1100.1

099.1

7100.5

1100.9

899.0

7100.7

199.8

899.7

598.6

7

Tra

ceel

emen

ts(p

pm

)

c.V

56

48

58

59

65

41

99

79

133

139

285

281

271

235

283

265

125

203

257

Cr

2236

2812

2720

2932

2221

2136

972

920

242

225

298

316

566

510

289

275

�321

304

Co

��

��

��

45

52

29

�41

42

17

13

38

27

23

39

42

Cu

��

��

��

81

89

62

�60

22

�218

32

37

48

53

77

Ni

1743

1611

1268

1312

1682

1573

189

170

80

95

169

175

178

188

165

132

108

81

88

Zn

��

��

��

29

48

32

�68

44

��

44

70

78

43

43

Rb

–4

32

77

2.2

1.3

2.9

2.5

45

�4

54

38

12

Sr

––

33

23

330

113

262

245

177

183

163

40

160

132

297

743

162

Y–

–3

14

33

45

13

13

33

34

13

14

25

29

26

23

25

Zr

33

34

45

0.9

7.8

21

25

93

98

25

22

80

102

84

39

49

Nb

–2

25

11

––

–4

32

––

28

32

29

32

Ba

��

��

��

37

9178

15

35

29

�9

27

215

289

113

143

Sc

12

14

11

10

65

22

21

22

20

39

35

42

38

39

32

30

39

37

Hf

��

��

��

–0.2

0.9

0.7

3.0

3–

–3

7.0

11

1.2

01.7

0

Ta

��

��

��

––

––

0.4

0.1

––

–3.0

30

.12

0.1

2

Th

��

��

��

��

��

0.3

0.2

0.2

0.1

0.3

4.4

70

.30

0.2

0

U�

��

��

��

��

�0.9

�–

––

0.6

20

.10

0.2

0

(continued)

90 P. Pomonis et al.

Tab

le4

(continued

)

Maj

or

elem

ents

(%w

t.)

Har

zburg

ites

Lher

zoli

tes

Pl-

Lher

zoli

tes

Oli

vin

eG

abbro

sG

abbro

icdykes

Bas

alts

-Dole

riti

cdykes

Am

phib

oli

tes

A41

A49

A42

A46

A63

A600

A308

A60

A66

A130

A259

A271

A30

A274

A263

A193

(==

)F12

A261

A280

RE

E(p

pm

)

La

––

0.0

10.0

20.0

50.0

20.3

60.3

00.7

50.6

05.1

04.0

00.7

01.2

022.2

026.0

028.0

03.6

02.8

0

Ce

––

0.1

00.0

70.2

00.1

00.7

21.0

01.6

01.2

015.0

012.0

01.6

02.1

038.0

049.0

050.0

09.5

07.6

0

Pr

––

0.0

10.0

1–

–0.2

20.2

00.3

60.4

22.2

51.9

70.1

80.2

34.5

06.9

06.8

51.4

11.2

0

Nd

––

0.1

00.2

00.3

20.2

21.2

01.3

62.6

02.8

012.0

011.0

00.9

01.2

025.0

030.0

033.0

07.2

06.9

0

Sm

––

0.0

60.0

80.0

90.0

80.3

60.5

01.1

01.2

93.8

03.6

00.3

00.4

06.2

07.7

07.8

02.5

02.4

0

Eu

––

0.0

30.0

40.0

80.0

50.3

40.3

40.5

50.4

81.4

01.2

40.1

30.1

22.2

72.3

72.6

51.0

80.9

0

Gd

––

0.2

00.3

00.3

10.2

50.8

50.7

01.6

01.2

04.5

04.7

00.5

00.6

09.0

57.8

09.7

03.4

03.1

0

Tb

––

––

––

0.1

00.1

00.4

00.3

01.0

00.9

00.1

00.1

01.6

01.9

01.7

00.6

00.6

0

Dy

––

0.2

00.1

00.4

40.3

00.7

00.9

02.2

02.2

45.5

55.5

00.9

01.0

010.9

06.5

010.0

03.7

04.1

0

Ho

––

––

0.0

60.0

40.2

00.2

00.5

00.5

51.2

01.1

00.2

00.2

01.9

02.3

02.1

00.8

00.8

0

Er

––

0.2

00.1

00.3

00.2

00.5

00.5

01.4

01.3

03.7

03.7

00.7

00.9

06.1

06.9

06.5

02.4

02.6

0

Tm

––

––

––

0.0

80.0

80.2

20.2

00.6

60.5

90.1

30.1

70.6

40.8

60.9

90.3

00.4

2

Yb

––

0.2

00.2

00.3

00.4

00.5

00.5

01.3

01.5

53.3

53.3

01.0

01.1

07.8

08.3

06.2

02.0

02.5

0

Lu

––

0.0

30.0

20.0

40.0

40.0

80.0

80.2

10.2

00.4

80.5

10.1

70.1

80.9

20.9

60.9

60.3

20.3

7

(a)

XR

Fan

alyse

s;(b

)IC

P-A

ES

anal

yse

s;(c

)IC

P-M

San

alyse

s;–

bel

ow

det

ecti

on

lim

it;�

no

td

etec

ted

;(==)

do

leri

tic

dy

ke

Petrogenetic evolution of the Koziakas ophiolite complex 91

Fig. 4. Selected variation diagrams for analysed rock types from the Koziakas ophiolite

of Zr assumed here as a fractionation index, with high-field-strength (HFS) ele-ments used as petrogenetic indicators, such as Ti, Cr, P, as well as the large-ion-lithophile (LIL) element Mg, suggest that all these elements were relativelyimmobile during alteration (see Fig. 4).

Mantle tectonites

In agreement with their modal composition and phase chemistry, the major andtrace element contents of the Koziakas peridotites (Table 4) display residual char-acteristics compared with primitive mantle. MgO, Cr and Ni contents increasesignificantly from the plagioclase-lherzolite through the lherzolite to the harzbur-gite, as expected for partial melting residues (Fig. 4). Moreover, the MgO=FeOt

ratio of the plagioclase-lherzolite and lherzolite (4.49–5.20) is slightly lower thanthe harzburgite (4.98–5.58). These values are close to the MgO=FeOt ratio of theoceanic peridotites (approximately 5–6, Menzies, 1991).

The Koziakas harzburgite is depleted in the magmatophile and incompatibleelements Al and Ca relative to the fertile lherzolite and plagioclase-lherzolite. TheAl-rich chemistry of the lherzolite and plagioclase-lherzolite is consistent with thefertile character of this lithology. Similar to other suites of mantle rocks (e.g. Omanperidotites) the Koziakas peridotites show a broad positive correlation betweenAl2O3 and CaO (not shown), in contrast to dominantly lherzolitic suites (e.g.,Western Alps peridotites) that show nearly constant Al2O3=CaO ratios close toprimitive mantle estimates. Al2O3=CaO tends to decrease with increasing fertility(i.e., cpx and plg contents) from the harzburgite (1.42–1.47) to low values in theplagioclase-lherzolite (0.76–0.94).

The analysed Koziakas mantle tectonites display generally low REE abun-dances. The Koziakas harzburgite displays REE values below detection limits.The REE patterns of the lherzolite and the plagioclase lherzolite remainmostly subparallel and they have a convex upward shape with depleted LREE(Ce=Yb)N¼ 0.06–0.25 (Fig. 5a). These patterns have been frequently observedin Alpine-type peridotites, which also display very low REE concentrations (Frey,1984; Parkinson et al., 1992).

Gabbro and gabbroicdykes

Gabbro and gabbroic-dykes display a broad compositional range. The MgO variesfrom 13.71 to 14.80 wt.% in the gabbro and from 7.01 to 7.84 in the gabbroic-dykes (Table 4). The analyzed gabbro from the Koziakas ophiolitic m�eelange, dis-play higher MgO, Cr and Ni contents relative to the gabbroic-dykes. On the otherhand, the gabbroic dykes are more differentiated with lower MgO, Cr, Ni andhigher Al, Ca, Sr and Zr contents (Fig. 4).

The REE patterns of the gabbros have a convex downward shape with LREEdepletion ((Ce=Yb)N ¼ 0.12–0.65). The gabbroic-dykes show a slight enrichmentin absolute REE abundances relative to the olivine-gabbro, whereas their pat-terns remain mostly subparallel, suggesting that they are products of the samecrystal fractionation process (Fig. 5b). The positive Eu anomaly in the gabbropatterns is probably due to plagioclase accumulation. The Koziakas gabbro and gab-

P. Pomonis et al.: Petrogenetic evolution of the Koziakas ophiolite complex 93

broicdykes REE patterns are also subparallel to those from the lherzolite and theplagioclase lherzolite, implying that the latter could be the source rocks of themafic lithotypes. The REE contents of the Koziakas gabbros are also similar to

Fig. 5. Chondrite-normalized REE patterns of the Koziakas peridotites (a), gabbros (b), theMORB-type basalt group (c), the basalt with boninitic affinities group (d), the sub-alkalicgroup (e), the alkali basalts (f) and the amphibolites (g). The Koziakas gabbro envelope(shaded area) in diagrams (c)–(g) is given for comparison. Normalizing values afterNakamura (1974)

94 P. Pomonis et al.

those of oceanic gabbros from other ophiolitic complexes of back-arc basin ori-gin (e.g. Kelemen et al., 1997; Tsikouras and Hatzipanagiotou, 1998; Monnieret al., 1999).

Volcanic rocks

Selected chemical analyses of the volcanic rocks from the Koziakas ophiolitic com-plex are listed in Table 4. According to the Zr=TiO2 vs. Nb=Y diagram (Winchester

Fig. 6. MORB-normalized spidergrams of average values and envelopes (shaded areas)of the MORB-type basalt group (a), basalt with boninitic affinities (b), sub-alkalic group(c), alkali basalts (d) and the amphibolites (e). Normalizing values after Pearce (1982)

Petrogenetic evolution of the Koziakas ophiolite complex 95

and Floyd, 1977, not shown), the analyzed volcanic rocks are classified as basalts-andesites, sub-alkalic and alkali basalts. They display a wide compositional rangewith MgO content from 4.06 to 11.12 wt.%.

The first group of basalts displays SiO2 contents from 46.10 to 52.07 wt.%,while the TiO2 and FeOt vary from 1.10 to 1.84 wt.% and from 8.25 to 9.98 wt.%respectively (Table 4). Their MORB-normalized patterns are in general similar toMORB (Fig. 6a) with normalized HFSE values close to unity and slight enrich-ments in LILE. Rare earth elements values normalized to chondrite are cohesivewith almost flat patterns, similar to those of N-type MORB and remain mostlysubparallel (Fig. 5c).

However, some samples from this group (e.g. A30, A274 Table 3) displayhigher SiO2 content (55.60–59.34 wt.%). They have also high MgO (9.30–10.70 wt.%), as well as high Cr (510–566 ppm), Ni (178–195 ppm) and low valuesof TiO2, Al2O3, CaO and Zr. These features indicate a boninitic affinity (Falloonand Crawford, 1991; Pearce and Peate, 1995; Boily and Dion, 2002). Moreover,their high Cr and Ni contents reflect their primitive unfractionated nature. TheMORB-normalized LILE and HFSE values are below unity, whereas a noticeableZr ‘‘spike’’ relative to P and Sm (Fig. 6b) is an additional distinctive feature ofmany boninites (Hickey and Frey, 1982; Pearce et al., 1992). REE values normal-ized to chondrite display typically boninitic, concave upwards, shaped patternswith (Ce=Yb)N ratio ranging between 0.37 and 0.51(Fig. 5d).

The sub-alkalic group displays higher values in P, Y, Ba and lower concentra-tions in MgO, Ni, Cr, relative to the basalt-andesite group. Their MORB-normal-ized LILE values are higher relative to HFSE values, which are almost similar tothose of tholeiitic basalts (Fig. 6c). This group also exhibits negative anomalies ofNb and Zr. Such depletions are common in the mantle wedge, formed in an envir-onment of a subducted slab (Pearce and Norry, 1979; Saunders et al., 1980; Pearce,1982). Their MREE and HREE values are cohesive with MORB-like patterns,which remain mostly subparallel to the MORB-type basalt group (Fig. 5e). LREEenrichment and (Ce=Yb)N ratio ranging from 1.50 to 2.55 (Fig. 5e), indicate thatthe sub-alkalic basalts can be considered as enriched-type MORB (E-MORB,Monnier et al., 1999; Saunders and Tarney, 1984).

The alkali basalts, which were found as fragments into the ophiolitic m�eelange,are characterized by higher CaO, Na2O, P2O5, Ba, Sr values and lower SiO2, MgO,Cr contents relative to the other analyzed volcanic rocks. When normalized toMORB (Fig. 6d), their patterns are in general analogous to typical WPB. LILEvalues are in a similar range with the sub-alkalic group, while HFSE abundancesdisplay a progressive decrease. The alkali character of this group is also reflected intheir strongly fracionated REE patterns (Fig. 5f) similar to typical Oceanic-islandbasalts (Wilson, 1989).

Amphibolites

Whole-rock chemical analyses of representative samples from the Koziakas amphi-bolites are listed in Table 4. High Cr and Ni concentrations and low Zr=Ti ratios areindicative for their igneous origin. The low Nb=Y and Nb=Zr ratios, demonstratesubalkaline characters for the amphibolite precursors. The MORB normalized pat-

96 P. Pomonis et al.

terns of the analyzed samples display in general flat HFS elements similar toMORB-like affinities (Fig. 6e). However, some samples demonstrate relativelylower Zr, Y values and Zr=Nb ratios and higher Ti=V and Th values (Pomoniset al., 2002), revealing influence from a subduction component.

The chondrite-normalized REE patterns are flat, similar to MORB, without anydistinct Eu anomaly (Fig. 5g). These patterns remain mostly subparallel indicatingthat the protoliths of the amphibolites are products of the same crystal fractionationprocess. The amphibolite REE patterns are also subparallel to the gabbros and theMORB-type basalts from the Koziakas ophiolite, implying that the latter could bewell represent the protoliths of the amphibolites.

Sr-Nd isotopic results

Sr and Nd isotopic ratios from two representative volcanic samples, one gabbro andone lherzolite from the Koziakas ophiolite, are reported in Table 5. The Nd isotopiccomposition of ocean floor crust is relatively unaffected by seawater interaction,due to the extremely low relative concentration of this element in seawater (e.g.O’Nions and Pankhurst, 1976; Chen and Pallister, 1981; Calvez and Lescuyer,1991). In contrast, the Sr isotopic composition of samples from the upper oceaniccrust can be markedly affected (e.g. Spooner et al., 1977; McCulloch et al., 1981).The Sr and Nd isotopic values from the analyzed samples are rather variable.143Nd=144Nd values expressed as "Nd vary from 2.3 to 7.3, and are similar to valuesreported from the Pindos boninites and IAT-type lavas (143Nd=144Nd: 1.04–7.04,Pe-Piper et al., 2004). Moreover, the Sr isotopic compositions reported here(0.70359–0.70455) are similar to magmatic values reported for other ophiolites(Rautenschlein et al., 1985) and active back-arc basins (e.g. Volpe et al., 1987;Encarnation et al., 1999 and references therein).

The above-analyzed samples on the 143Nd=144Nd versus 87Sr=86Sr diagram(Fig. 7a), plot within the mantle array (e.g. De Paolo and Wasserburg, 1977;Zindler et al., 1982; Wilson, 1989). Sample (A271) from the NMORB-type groupwith higher Nd and lower Sr isotopic ratios relative to the other analyzed samplesplots within the field for N-MORB type rocks (Fig. 7b). In addition, gabbro (A60),which has Sr-Nd isotopic ratios close to sample (A271), also plots close to theN-MORB field, indicating a common origin from a N-MORB mantle source.

Table 5. Sr-Nd isotopic analyses from the Koziakas ophiolitic complex

Sample Rock type Sr(ppm)

Rb(ppm)

Nd(ppm)

Sm(ppm)

87Sr=86Sr 143Nd=144Nd "Nd

A600 Plag-lherzolite 2.7 b.d.l. 0.2 0.08 0.704400� 25 0.512881� 15 4.74A60 Olivine-gabbro 113 1.3 1.3 0.5 0.703719� 13 0.513010� 19 6.83A271 NMORB-type basalt 183 4.9 11 3.6 0.703595� 13 0.513034� 8 7.30A274 Basalt with

boninitic affinities40 3.9 1.2 0.4 0.704553� 19 0.512781� 12 2.36

The analytical error, including other sources of error, such as instrumental reproducibility, is 2�; b.d.l. belowdetection limit

Petrogenetic evolution of the Koziakas ophiolite complex 97

However, sample A274 with boninitic affinities and the lherzolite (A46) yieldedhigher Sr and lower Nd isotopic ratios than the other two samples, plotted in anarea where OIB and IAB fields overlap (Fig. 7b), implying the presence of aheterogeneous mantle source. Sample A274 is also plotted in the field of boniniticrocks from Tonga and Mariana regions, close to the Pindos boninite sample.

Petrogenetic evolution

The mantle tectonites of the Koziakas ophiolite are composed of refractory peri-dotites with extremely low trace element contents. The positive correlation ofAl2O3 and CaO (not shown here), shows the expected, and from other studies wellknown negative correlation with MgO. These correlations demonstrate a partialmelting control on the compositions of the Koziakas mantle tectonites. Further-more, the low TiO2=Al2O3 ratios (average¼ 0.04) of both the harzburgite and thelherzolite, which reflect low TiO2=Al2O3 ratios in their mineral phases, are within,or close to the range of oceanic peridotites (Menzies, 1991). Moreover, the TiO2

content of chromian spinels from the Koziakas lherzolite is low and in the range ofocean floor spinel peridotites (Dick and Bullen, 1984).

The high Cr and Ni as well as the low Al whole-rock abundances coupled withthe depletion in REE and incompatible elements, suggest a rather significantextraction of basaltic melt that depleted the Koziakas peridotites. The prominentconvex-upward type ((Ce=Yb)N<1) of their REE patterns has been frequentlyobserved in Mesozoic lherzolite and harzburgite (e.g., Melcher et al., 2002). The

Fig. 7. a 87Sr=86Sr vs. 143Nd=144Nd plot of selected analysed rocks from the Koziakasophiolite. b Sr-Nd compositions from other places are shown for comparison. Abbrevia-tions are N-MORB: Normal type Mid-ocean ridge basalt, IAB:Island arc basalt, OIB:Ocean-island basalt (data after Wilson, 1989; Rautenschlein et al., 1985; Falloon et al.,1989; Hickey-Vargas, 1989; Valsami-Jones and Cann, 1994)

98 P. Pomonis et al.

more magnesian olivines (Fo: 89.8–90.8), the Cr-rich and less aluminous spinelsand orthopyroxenes, as well as the low TiO2 clinopyroxenes imply also that theKoziakas peridotites have undergone a considerable amount of partial melting.Chemical differences between the harzburgitic spinels and the lherzolitic onesmight be indicative for the degree to which Cr has been enriched and Al depletedinto the spinel crystal, during partial melting.

The presence of less deformed interstitial An-rich plagioclase associated withclinopyroxene and orthopyroxene in the Koziakas plagioclase-lherzolite, as well asthe analogous chemical characteristics of the low Cr# lherzolitic spinels with theabyssal-type spinels, indicate that some fractions of less depleted mantle sourcematerial still remains in them. The PUM-normalized diagrams show that theKoziakas harzburgite is poorer in bulk elements relative to the analyzed lherzoliteand plagioclase-lherzolite (Fig. 8). The preferential enrichments of Hf over Zr andTa over Nb in the plagioclase lherzolite could imply that metasomatic enrichmentcontrols the budget of these elements (Weyer et al., 2003; Kelemen et al., 1992).

The higher Ti, Al, Fe and Na contents of the clinopyroxenes in the plagioclaselherzolite, coupled with the Cr-number of plagioclase lherzolitic spinels within therange of the Koziakas plagioclase-free peridotites, indicate similar affinities of theKoziakas plagioclase lherzolite with those from Othris (Dijkstra et al., 2001; Barthet al., 2003). Furthermore, the positive low "Nd value of the Koziakas plagioclaselherzolite is consistent with a depleted oceanic asthenosphere, which requires anadditional source of Sm and Nd with low "Nd value. Probable candidates for suchcontributions are subducted terrigenous sediments or OIB-type mantle (Pe-Piperet al., 2004). The above characteristics could lead to the assumption that partialmelting of the Koziakas peridotites, resulting in the formation of Cr-rich spinel,followed by melt impregnation and crystallization of plagioclaseþ clinopyroxeneas was suggested for the plagioclase lherzolites from Othris (Dijkstra et al., 2001;Barth et al., 2003). This interpretation is supported by the higher TiO2 contents of

Fig. 8. Whole-rock multielement diagram normalized to primitive upper mantle (PUM) forultramafic samples from the Koziakas ophiolite. Normalizing values after McDonough et al.(1992)

Petrogenetic evolution of the Koziakas ophiolite complex 99

the Koziakas plagioclase lherzolite compared with the harzburgite (Table 4), whichreflects addition of TiO2 by small volumes of impregnating melt (e.g. Cannat et al.,1990).

REE data and variation diagrams reflect that the main factor controlling themagma differentiation in the samples studied, is fractional crystallization. Thelinear correlations between many incompatible trace elements (Fig. 4), as wellas the subparallel REE patterns (Fig. 5), suggest that Koziakas peridotites are likelythe source of the mafic rocks. Moreover, the cohesive subparallel REE patternsindicate evolution from gabbro to basalt in terms of increasing fractionationen-route to the surface. The negative correlations of Ca, Al, Sc and Cr with Zr(Fig. 4), suggest that plagioclase and clinopyroxene have been the dominant phasesduring fractional crystallization of the Koziakas ophiolite volcanics as it was alsoimplied from the petrographic investigation. A slight decrease of Ti, Y and P trendsat the higher Zr values, are indicative for the onset of crystallization of titanomag-netite and apatite at the final stages of differentiation (Fig. 4).

The REE patterns of MORB-type and sub-alkalic basalts (see Fig. 5) are sub-parallel to the REE patterns of gabbros, indicating that they are products of thesame crystal fractionation process. The absence of a well-pronounced negative Euanomaly at the REE patterns of the MORB-type basalts and the subalkalic basalts,suggests that the conditions were oxidizing at this stage of magmatic evolution,rather a lack of significant plagioclase fractionation (in the light of the observedplagioclase phenocrysts). Under such conditions most of the Eu is converted intothe trivalent state and does not enter plagioclase (Hess, 1989). The formation ofFe-Ti oxides in the basalts is consistent with increasing fO2, during melt evolution.Such conditions typically occur in the vicinity of a subduction zone (Saunderset al., 1980; Wilson, 1989).

The LREE enriched patterns of the sub-alkalic basalts and their increased(Ce=Yb)N ratio relative to MORB-type basalt group could be attributed to varia-tions in source composition, mostly due to its reaction with more LREE-enrichedfluids and=or melts, produced from melting of a subducted lithosphere (see below).This is consistent with the presence of the basalts with boninitic affinities (Fig. 5d).Rogers and Saunders (1989) and Pearce et al. (1992) considered that these sig-nificant REE profiles can be interpreted as principal result of mantle peridotitemetasomatization and incomplete equilibration, possibly during ion-exchangereactions, by migrating, small-volume LREE-enriched melts and=or fluids derivedfrom the subducted slab.

The Cr vs. Y diagram (Fig. 9a) also suggests the fractional crystallizationprocess, where all samples display Cr decreasing trends with increasing Y, whichare compatible with the fractional crystallization paths (Pearce, 1983). High Cr andY contents are consistent with a MORB-like affinity for the Koziakas basalts-andesites and sub-alkalic basalts. The genesis of the different lava groups in theKoziakas ophiolites is in agreement with a melting model in which MORB-typeand sub-alkalic basalts were generated by 10–15% partial melting of an undepletedlherzolitic mantle source. On the other hand, the basalts with boninitic affinities areplotted close to the partial melting curve, in a field usually characteristic of boni-nitic rocks (Pearce et al., 1984). The presence of clinopyroxene phenocrysts andthe high Sc contents (38–44 ppm) suggest that the basalts with boninitic affinities

100 P. Pomonis et al.

are mostly comparable with high-Ca boninites (Crawford et al., 1989). This isbecause the high Sc contents indicate that clinopyroxene was present in the sourceand may not have been completely eliminated during melting. The Koziakasbasalts with boninitic affinities are also similar to the high-Cr boninites from thePindos ophiolite (Pe-Piper et al., 2004).

The observed scattering of Zr contents in the Zr=Y vs. Zr diagram (Fig. 9b)could be attributed to mixing of primitive magmas with evolved magmas (O’Hara,1977; Pearce and Norry, 1979; Crawford et al., 1989; Pearce et al., 1999). More-over, the rather variable Nd isotopic compositions, the depleted HFSE values of theanalyzed volcanics, the LILE enrichment and the transitional affinity of the sub-alkalic basalts, as well as the presence of the basalts with boninitic affinities, are allconsistent with a heterogeneous mantle source. The isotopic and trace elementvariations discussed above, provide evidence for the involvement of ‘‘N-MORB-source’’ and ‘‘OIB-source’’ end-members in a heterogeneous mantle source.

The absence of good element correlations of alkali basalts in the differentia-tion diagrams (Fig. 4), as well as the similarities of their REE patterns with those ofthe Ocean-island basalts (OIB) – which are not subparallel to the previous lithol-ogies – suggest a different petrogenetic evolution for these rocks. Alkali basaltwith OIB-like trace element assemblages is known from the Avdella m�eelange,interpreted by Robertson et al. (1990) as seamounts in the Pindos Ocean. The

Fig. 9. a Cr vs. Y diagram for the Koziakas volcanic rocks (Pearce, 1983). The partialmelting trend has been calculated from a source with composition Ol0.6Opx0.2Cpx0.1Pl0.1

(after Wood, 1979), b Variation diagram of Zr=Y vs. Zr (Pearce and Norry, 1979) forbasalts from the Koziakas ophiolite. Field for BABB after Floyd et al. (1991); C.A.:Continental Arc, O.A.: Oceanic Arc. Fields of the Rocas Verdes ophiolite (after Saunderset al., 1979) and the Marianas back-arc basalts (after Hawkins et al., 1990 and Stern et al.,1990) are shown for comparison

Petrogenetic evolution of the Koziakas ophiolite complex 101

Koziakas alkali basalt group displays also similar geochemical characteristics to theTriassic Glykomilia trachyandesites and to the Evia within-plate basalts (Pomoniset al., 2004).

Correlation with neighbouring ophiolites

In the broad vicinity of the Koziakas ophiolite complex there are three well-studiedophiolite suites, those of Pindos, Vourinos and Othris. Geophysical evidence (i.e.gravity and magnetic surveys; Makris, 1977) in combination with field, petrologi-cal and geochemical data support a continuation of these ophiolitic suites in cen-tral-north mainland Greece (Jones and Robertson, 1991; Smith, 1979, 1993). Theyare also believed to represent fragments of essentially the same slab of oceaniccrust, which may also continue north to the Kastoria ophiolite (Mountrakis, 1986).

The Pindos and Vourinos ophiolite, which is situated to the N of the Koziakasophiolite comprises ultramafic rocks with gabbros and volcanic rocks. Many linesof geochemical and structural evidence suggest that Pindos and Vourinos ophiolitesare of similar origin. Geochemically, the ophiolitic sequence units are of ‘‘supra-subduction zone’’ type (Pearce et al., 1984). Lavas of the Pindos and Vourinosophiolites display geochemical trends ranging from MORB, through MORB=IAT,IAT to boninite series volcanics (Kostopoulos, 1988; Saccani and Photiades, 2004).In both cases the mantle sequence rocks are highly depleted, represented by resi-dual harzburgitic mantle tectonite (Zimmerman, 1972; Rassios, 1991). Vourinos,however, contains economic chromite deposits, while chromite is rare in Pindosophiolite. Both Pindos and Vourinos ophiolites posses basal metamorphic soleswith similar ages to that of the Koziakas ophiolite (Spray et al., 1984; Pomoniset al., 2002). The Pindos and Vourinos ophiolites contain also basal ophiolitem�eelanges, characterized by a volcano-sedimentary chaotic nature.

Further southwards, the Othris ophiolite exhibits an extensive nappe consistingof mantle tectonites, ultramafic cumulates, gabbroic cumulates, sheeted dykes andlavas. The Othris volcanic rocks show typical MORB chemistry and little evidencefor IAT and boninitic affinities (Rassios, 1990). The mantle tectonites consistmainly of plagioclase lherzolite and minor harzburgite (Dijkstra et al., 2001; Barthet al., 2003). Economic chromite deposits are found in western Othris, largelyconfined to the contact zone at the base of the lherzolite and the top of muchsmaller, structurally lower harzburgite nappe.

The present data show that there are significant geological and petrologicalsimilarities between the Koziakas and the above-mentioned ophiolites. Moreover,the Koziakas volcanic rocks seem to have geochemical signatures analogous to thosefrom the Othris and Pindos-Vourinos ophiolites preserving a transitional MORB toIAT character and significant features which are consistent with a marginal basinsetting. Apparently, the Koziakas ophiolite differs in lacking an ultramafic and awell-developed mafic cumulate suite, as well as economic chrome deposits.

Geotectonic setting

As evidenced by the overall geochemical features of the Koziakas ophiolite suite,there are similarities with typical ocean floor lithologies. Moreover, the presence of

102 P. Pomonis et al.

An-rich plagioclase in the lherzolite assemblage, the occurrence of basalt withboninitic affinities, as well as some isotopic and geochemical particularities, dis-cussed above, imply the involvement of a heterogeneous mantle source with thecontribution of a subduction component.

The negative Nb and Zr anomalies at the MORB-normalized patterns of theKoziakas basalts and the generally low Zr=Nb, Nb=Y ratios coupled with the LILEand Th enrichment of the sub-alkalic volcanics, are common in the mantle wedgeformed above a subduction zone (Pearce and Norry, 1979; Saunders et al., 1980).A field for BABB (back-arc basin basalt), which often overlaps the MORB and IATfields, has been added to some diagrams for comparison (e.g. Fig. 9a, b). SomeBAB basalts also appear to be similar to E-type MORB (Saunders et al., 1980) as isthe case of for the Koziakas sub-alkalic basalts. This is evident from their LILEenrichments and flat REE patterns with no Eu anomaly as have been reportedfrom BABB (Wilson, 1989). The absence of negative Eu anomalies is also char-acteristic in several other ophiolites generated at a backarc basin environment(e.g. see Tsikouras and Hatzipanagiotou, 1998; Hoeck et al., 2002; Magganas,2002; Pe-Piper and Piper, 2002). Moreover the Sr-Nd isotopic compositions ofthe Koziakas analyzed samples are in the range of BAB basalts (Hickey and Frey,1982). Amphibolites from the Koziakas metamorphic sole, suggest also a transi-tional between MORB and IAT composition (Pomonis et al., 2002). These featuresare consistent with a marginal basin setting.

Analogous MORB-type rocks with IAT affinities are also present in Pindos,Vourinos, (Jones et al., 1991; Pe-Piper et al., 2004) and Othris ophiolites (Rassios,1990; Barth et al., 2003), of supra-subduction zone origin (Smith, 1993) advocatingto the hypothesis that there is a close genetic relationship between them and theKoziakas ophiolite. The Koziakas ophiolite is part of the western belt of ophiolitesin the Hellenides, which is thought to have formed in the Pindos Ocean. Further-more, the occurrence of rocks with boninitic affinities in Koziakas, Pindos, Vour-inos and Argolis peninsula ophiolites (Beccaluva et al., 1984; Kostopoulos, 1988;Clift and Dixon, 1998), has led to the suggestion for the operation of an intra-oceanic subduction within the Pindos oceanic strand, shortly after the formation ofthe oceanic lithosphere. The presence of ultramafic exposures in combination witha well-developed sub-ophiolitic m�eelange and a metamorphic sole at the base of thestudied ophiolitic complex is consistent with obduction as a feasible mechanismfor the emplacement of the Koziakas ophiolite suite. The absence of massivegabbros in the Koziakas Ophiolitic Unit and their presence as fragments in thesub-ophiolitic m�eelange is attributed to erosion, detachment and thinning duringobduction and final emplacement of the ophiolitic complex as in other ophiolites(e.g., Lippard et al., 1986).

In terms of its structure and tectonics, the Koziakas ophiolite could be classifiedas a ‘‘Cordilleran complex’’ which is represented by dismembered sections ofmantle, plutonic and volcanic rocks, commonly associated with metamorphic solesand tectonically emplaced onto or juxtaposed against the continental margin withinpolygenetic terranes, according to Beccaluva et al. (2004). Although, the presenceof basaltic rocks with boninitic affinities, the minor plagiogranite intrusives and theabsence of an extensive calcalkaline magmatic activity with acidic differentiates,indicate characteristics of ‘‘Tethyan complexes’’ (Beccaluva et al., 2004).

Petrogenetic evolution of the Koziakas ophiolite complex 103

All these features are consistent with a supra-subduction geotectonic settingsimilar to Pindos and Vourinos ophiolitic complexes of the western ophiolite belt inthe Hellenides (Jones and Robertson 1991, Robertson 2002). According to thismodel, a plausible hypothesis that could be proposed for the origin and emplace-ment of the studied ophiolite complex is given below: the Koziakas ophioliterepresents a small ocean basin (bound westwards by a residual continental block,the West Thessaly Unit (W.T.U.)) at the east margin of the greater Pindos Ocean.Compression, which followed the rifting phase in the Late Jurassic, caused a westwardintra-oceanic subduction in the small Koziakas basin. During this stage, an accre-tion prism was formed, reflecting the chaotic ophiolite m�eelange formation. Con-tinuous compression resulted in the beginning of oceanic detachment and ophiolitetransportation to the east, over the Pelagonian margin. In Early Tertiary, the colli-sion of the African with the Eurasian plate resulted in a new compressional episodethat closed the Pindos Ocean and resulted in obduction of Koziakas ophiolite overthe W.T.U., which was in turn thrust over Pindos flysch. An analogous setting withsimilar ophiolite emplacement histories has been proposed for many ophiolitecomplexes worldwide, e.g. the modern Cyclops ophiolites (Monnier et al., 1999)the Pozanti-Karsanti ophiolite (Polat et al., 1996) and the Oman Ophiolite (Boudieret al., 1988).

Conclusions

The Koziakas ophiolitic complex in west Thessaly is interpreted as an incompleteophiolite suite, thrust to the west over the W.T.U. It comprises mantle peridotiteswith an ophiolitic m�eelange and an amphibolite sole at its base, while the upperparts include small outcrops of olivine gabbro and basaltic lavas. The magmaticevolution of Koziakas ophiolite was controlled by the extensive fractionation ofplagioclase and clinopyroxene followed by a minor contribution of olivine, andFe-Ti oxides, under low pressure and increasing fO2 conditions. Equilibrium mini-mum temperatures estimated from the mantle peridotite pyroxenes are about 800–1100 �C, while from the gabbro and volcanic clinopyroxenes are 600–850 �C and850–1100 �C, respectively.

The plagioclase-lherzolite, lherzolite and harzburgite, are depleted in incompa-tible elements due to partial melt extraction. However, the Koziakas plagioclaselherzolite and the lherzolite display a more fertile chemical behaviour relative tothe harzburgite, as it contains more aluminous spinel and it is enriched in somemajor elements. Partial melting of the Koziakas peridotites, resulting in the forma-tion of Cr-rich spinel, followed by melt impregnation and crystallization of plagi-oclaseþ clinopyroxene. Moreover, the presence of basalts with boninitic affinities,which are considered as products of a primitive undifferentiated magma, provideimportant evidence for the existence of a subducting oceanic lithosphere.

Gabbros display MORB-like geochemical characteristics, while the Koziakasvolcanics have elemental ratios and absolute REE and incompatible element con-tents in the range of N- to E-MORB.

The magmatic history of the Koziakas ophiolite is in agreement with variabledegrees of partial melting of a heterogeneous mantle source, yielding magmasmainly of MORB-type composition. Sr-Nd isotopic ratios and geochemical affinities

104 P. Pomonis et al.

imply that the melts contained another component derived from the melting of asubducted lithosphere.

The alkali basalt group displays a different petrogenetic evolution according toits geochemical features. Amphibolites from the sub-ophiolitic metamorphic sole,display also affinities similar to MORB with slight IAT contributions indicatinginfluence from a subduction component.

The Koziakas ophiolite suite probably formed in a small backarc basin situatedat the east margin of the greater Pindos Ocean, between the W.T.U. and Pelagoniancontinent. A compression episode during Late Jurassic-Early Cretaceous resultedin the beginning of oceanic detachment and ophiolite transportation to thewest, over the Pelagonian margin. In Early Tertiary, the collision of the Africanwith the Eurasian plate caused a new compressional episode that closed the PindosOcean and resulted in the obduction of Koziakas ophiolite over the W.T.U., whichwas in turn thrust over Pindos flysch.

The similar radiometric ages together with the comparable geological andgeochemical characteristics of the Koziakas ophiolitic complex with the adjacentophiolite suites of Pindos, Vourinos and Othris imply that they all were probablydeveloped in the same marginal basin volcanic arc regime in the Pindos ocean.

Acknowledgements

We would like to thank Prof. Dr. B. J. Wood and the researchers of the University of Bristol,Department of Earth Sciences, for their assistance in elaborating whole-rock analyses, underfinancial support of a TMR Programme. We gratefully acknowledge Dr. M. G. Barth for athorough review of the manuscript. This study was supported through the ‘‘CaratheodoryProgramme’’ of the University of Patras.

References

Aoki K, Shiba I (1973) Pyroxene from lherzolite inclusions of Itinomegata, Japan. Lithos 6:41–51

Aug�ee T (1987) Chromite deposits in the northern Oman ophiolite: mineralogical constraints.Mineral Deposita 22: 1–10

Bailey EH, Kemp AJ, Ragnarsdottir KV (1993) Determination of uranium and thorium inbasalts and uranium in aqueous solution by Inductively Coupled Plasma Mass Spectro-metry. J Anal Atomic Spectrom 8: 551–556

Barth MG, Mason PRD, Davies GR, Dijkstra AH, Drury MR (2003) Geochemistry of theOthris Ophiolite, Greece: Evidence for refertilisation? J Petrol 44: 1759–1785

Beccaluva L, Ohnenstetter D, Ohnenstetter M, Paupy A (1984) Two magmatic serieswith island arc affinities within the Vourinos ophiolites. Contrib Mineral Petrol 85:253–271

Beccaluva L, Coltorti M, Giunta G, Siena F (2004) Tethyan vs Cordilleran ophiolites: areappraisal of distinctive tectono-magmatic features of supra-subduction complexes inrelation to the subduction mode. Tectonophysics 393: 163–174

Boily M, Dion C (2002) Geochemistry of boninite-type volcanic rocks in the Frotet-Evansgreenstone belt, Opatica subprovince, Quebec: implications for the evolution of Archeangreenstone belts. Precamb Res 115: 349–371

Bonatti E, Michael PJ (1989) Mantle peridotites from continental rifts to ocean basins tosubduction zones. Earth Planet Sci Lett 91: 297–311

Petrogenetic evolution of the Koziakas ophiolite complex 105

Boudier F, Ceuleneer G, Nicolas A (1988) Shear zones, thrusts and related magmatism inthe Oman ophiolite: initiation of thrusting on an oceanic ridge. Tectonophysics 151:275–296

Brey GP, K€oohler T (1990) Geothermobarometry in four-phase lherzolites. II. Newthermobarometers and practical assessment of existing thermobarometers. J Petrol31: 1353–1378

Bryan WB, Thompson G, Ludden JN (1981) Compositional variation in normal MORB from22–250 N: Mid-Atlantic ridge and Kane fracture zone. J Geoph Res 86: 11815–11836

Calvez JY, Lescuyer JL (1991) Lead isotope geochemistry of various sulphide depositsfrom the Oman Mountains. In: Pete TJ, Nicolas A, Coleman RG (eds) Ophiolitegenesis and evolution of the oceanic lithosphere. Kluwer, Dordrecht, Netherlands,pp 385–397

Cameron WE, Nisbet EG, Dietrich VJ (1979) Boninites, komatiites and ophiolitic basalts.Nature 280: 550–553

Cannat M, Bideau D, H�eebert R (1990) Plastic deformation and magmatic impregnation inserpentinized ultramafic rocks from the Garret transform fault (East Pacific Rise). EarthPlanet Sci Lett 101: 216–232

Capedri S, Lekkas E, Papanikolaou D, Scarpelis N, Venturelli G, Gallo J (1985) Theophiolite of the Koziakas range, Western Thessaly (Greece). N Jb Mineral Abh 152:45–64

Chen JH, Pallister JS (1981) Lead isotopic studies of the Samail Ophiolite, Oman. J GeophysRes 86: 2699–2708

Clift PD, Dixon JE (1998) Jurassic ridge collapse, subduction initiation and ophioliteobduction in the southern Greek Tethys. Eclogae geol Helv 91: 128–138

Crawford AJ, Fallon TJ, Green DH (1989) Classification, petrogenesis and tectonic settingof boninites. In: Crawford AJ (ed) Boninites and related rocks. Unwin, Hyman, London,pp 1–49

DePaolo DJ, Wasserburg GJ (1976) Nd isotopic variations and petrogenetic models.Geophys Res Lett 3: 249–252

Dick HJB (1977) Partial melting in the Josephine peridotite. I Am J Sci 277: 801–832Dick HJB, Bryan WB (1979) Variation of basalt phenocryst mineralogy and rock composi-

tion in DSDP hole 396B. Initial Reports DSDP 46: 215–225Dick HJB, Bullen T (1984) Chromian spinel as a petrogenetic indicator in abyssal

and Alpine-type peridotites and spatially associated lavas. Contrib Mineral Petrol 86:54–76

Dietrich VJ, Oberhaensli R, Mercolli I (1987) A new occurrence of boninite from theophiolitic m�eelange in the Pindus – Sub-Pelagonian zone S.L. (Aegina island, Saronicgulf, Greece). Ofioliti 12: 83–90

Dijkstra AH, Drury MR, Vissers RLM, Newman J (2001) On the role of melt-rock reaction inmantle shear zone formation in the Othris Peridotite Massif (Greece). J Struct Geol 24:1431–1450

Economou M, Dimou E, Economou G, Migiros G, Vacondios I, Grivas E, Rassios A,Dabitzias S (1986) Chromite deposits of Greece (UNESCO’s IGCP 197 Project Metal-logeny of ophiolites). In: Karamata S (ed) Series, Theophrastus Publ., SA, Athens,Greece, pp 129–160

Encarnacion J, Mukasa SB, Evans CA (1999) Subduction components and the generation ofarc-like melts in the Zambales ophiolite, Philippines: Pb, Sr and Nd isotopic constraints.Chem Geol 156: 343–357

Falloon TJ, Crawford AJ (1991) The petrogenesis of high-calcium boninite lavas dredgedfrom the northern Tonga ridge. Earth Planet Sci Lett 102: 375–394

106 P. Pomonis et al.

Falloon TJ, Green DH, McCulloch MT (1989) Petrogenesis of high-Mg and associated lavasfrom the north Tonga trench. In: Crawford AJ (ed) Boninites and related rocks. UnwynHyman, London, pp 357–395

Floyd PA, Kelling G, Gokeen SL, Gokeen N (1991) Geochemistry and tectonic environ-ment of basaltic rocks from the Misis ophiolitic m�eelange, south Turkey. Chem Geol 89:263–280

Frey FA (1984) Rare earth abundances in upper mantle rocks. In: Henderson P (ed) Rareearth element geochemistry. Elsevier, Amsterdam, pp 153–203

Gartzos E, Migiros G, Parcharidis I (1990) Chromites from ultramafic rocks of northernEvia (Greece)and theirgeotectonic significance.SchweizMineralPetrogrMitt70: 301–307

Hatzipanagiotou K, Lekkas E, Migiros G (1995) Plagiogranites in the ultrabasic rocks ofthe Koziakas Mountain (Central Greece). Z dt geol Ges 146: 479–486

Hatzipanagiotou K, Pomonis P, Tsikouras B (2001) Origin and evolution of ultramafic rocksfrom the Koziakas ophiolite, continental Greece. Braunschweiger geowiss Arb 24: 235–247

Hawkins JW, Londsdale PF, Macdougall JD, Volpe AM (1990) Petrology of the axial ridge ofthe Mariana Trough backarc spreading center. Earth Planet Sci Lett 100: 226–250

Herbert R (1982) Petrology and mineralogy of oceanic peridotites and gabbros. Somecomparisons with ophiolite examples. Ofioliti 7: 299–324

Hess PC (1989) Origins of igneous rocks. Harvard University Press, Cambridge, Massa-chussets, London

Hickey RL, Frey FA (1982) Geochemical characteristics of boninite series volcanics: impli-cations for their source. Geochim Cosmochim Acta 46: 2099–2115

Hickey-Vargas R (1989) Boninites and tholeiites from DSDP site 458, Mariana forearc. In:Crawford AJ (ed) Boninites, Unwin Hyman, pp 339–356

Hoeck V, Koller F, Meisel T, Onuzi K, Kneringer E (2002) The Jurassic Albanian ophiolites:MOR- vs. SSZ-type ophiolites. Lithos 65: 143–164

Jones G, Robertson AHF (1991) Tectono-stratigraphy and evolution of the Mesozoic Pindosophiolite and related units, northwestern Greece. J Geol Soc London 148: 267–288

Jones G, Robertson AHF, Cann JR (1991) Genesis and Emplacement of the Supra-Subduction Zone Pindos Ophiolite, Northwestern Greece. In: Peters TJ et al. (eds)Ophiolite genesis and evolution of the oceanic lithosphere, pp 771–799

Kelemen PB, Dick HJB, Quick JE (1992) Formation of harzburgite by pervasive melt=rockreaction in the upper mantle. Nature 358: 635–641

Kelemen PB, Koga K, Shimizu N (1997) Geochemistry of gabbro sills in the crust-mantletransition zone of the Oman ophiolite: implications for the origin of the oceanic lowercrust. Earth Planet Sci Lett 146: 475–488

Kostopoulos DK (1988) Geochemistry, petrogenesis and tectonic setting of the Pindosophiolite, NW Greece. Ph D Thesis, Univ. Newcastle, p 468

Le Roex AP, Dick HJB, Erlank Aj, Reid Am, Frey FA, Hart SR (1983) Geochemistry,mineralogy and petrogenesis of lavas erupted along the Southwest Indian Ridge betweenthe Bouvet triple junction and 11 degrees east. J Petrol 24: 267–318

Le Roex AP, Dick HJB, Fisher RL (1989) Petrology and geochemistry of MORB from 25� Eto 46� E along the Southwest Indian Ridge: evidence for contrasting styles of mantleenrichment. J Petrol 30: 947–986

Leake BE, Wooley AR, Arps CES, Birch WD, Gilbert MC, Grice JD, Hawthorne FC, Kato A,Kisch HJ, Krivovichev VG, Linthout K, Laird J, Mandarino J, Maresch WV, Nickel EH,Rock NMS, Schumacher JC, Smith DC, Stephenson NCN, Ungaretti L, Whittaker EJW,Youzhi G (1997) Nomenclature of amphiboles; report of the Subcommittee on amphi-boles of the International Mineralogical Association Commission on New Minerals andMineral Names. Eur J Mineral 9: 623–651

Petrogenetic evolution of the Koziakas ophiolite complex 107

Lekkas EL (1991) The presence of Western Thessaly Unit at Dafnospilia-Ktimeni area(S. Thessaly, Greece). Bull Geol Soc Greece 25: 231–344

Lewis AJ, Palmer MR, Sturchio NC, Kemp AJ (1997) The rare earth element geochemistry ofacid-sulphate and acid-sulphate-chloride geothermal systems from Yellowstone NationalPark, Wyoming, USA. Geochim Cosmochim Acta 61: 695–706

Lindsley DH (1983) Pyroxene thermometry. Am Mineral 68: 477–483Lippard SJ, Shelton AW, Gass IG (1986) The ophiolite of Northern Oman. Mem 11 Geol Soc

Blackwell Scientific Publications, Oxford, pp 178Magganas A (2002) Constraints on the petrogenesis of Evros ophiolite extrusives, NE

Greece. Lithos 65: 165–182Mahood GA, Baker DR (1986) Experimental constraints on depths of fractionation of mildly

alkalic basalts and associated felsic rocks: Pantelleria, strait of Sicily. Contrib MineralPetrol 93: 251–264

Makris J (1977) Geophysical investigations of the Hellenides. Hamburger GeophysEinzelschriften 34: 1–124

McCulloch MT, Gregory R, Wasserburg GJ, Taylor HPJ (1981) Sm-Nd, Rb-Sr and 18O=16Oisotopic systematics in an oceanic crustal section: evidence from the Samail ophiolite.J Geophys Res 86: 2721–2735

McDonough WF, Sun S, Ringwood AE, Jagoutz E, Hofmann AW (1992) Potassium, rubidiumand cesium in the Earth and Moon and the evolution of the mantle of the Earth. GeochimCosmochim Acta 56: 1001–1012

Melcher F, Meisel T, Puhl J, Koller F (2002) Petrogenesis and geotectonic setting ofultramafic rocks in the Eastern Alps: constrains from geochemistry. Lithos 65: 69–112

Menzies M (1991) Oceanic peridotites. In: Floyd PA (ed) Oceanic basalts. Blackie, Glasgow,London, pp 363–385

Migiros G, Economou GS (1988) Chromites in the ultrabasic rocks, East Thessaly complex(central Greece). Ofioliti 13: 127–136

Migiros G, Hatzipanagiotou K, Gartzos E, Serelis K, Tsikouras B (2000) Petrogeneticevolution of ultramafic rocks from Lesvos island. Chem Erde 60: 27–46

Monnier C, Girardeau J, Pubellier M, Polv�ee M, Permana H, Bellon H (1999) Petrologyand geochemistry of the Cyclops ophiolites (Irian Jaya – East Indonesia): consequencesfor the Cenozoic evolution of the north Australian margin. Mineral Petrol 65:1–28

Morimoto N, Fabries J, Ferguson AK, Ginzburg IV, Ross M, Seifert FA, Zussman J, Aoki K,Gottardi G (1988) Nomenclature of pyroxenes. Am Mineral 73: 1123–1133

Mountrakis D (1986) The Pelagonian zone in Greece: a polyphased deformed fragmentof the Cimmerian continent and its role in the geological evolution of the easternMediterranean. J Geol 94: 335–347

Nakamura N (1974) Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous andordinary chondrites. Geochim Cosmochim Acta 38: 757–775

O’Hara M (1977) Geochemical evolution during fractional crystallization of a periodicallyrefilled magma chamber. Nature 226: 503–507

O’Nions RK, Pankhurst RJ (1976) Sr isotope and rare earth element geochemistry of DSDPLeg 37 basalts. Earth Planet Sci Lett 31: 255–261

Papanikolaou D, Sideris C (1979) Sur la signification des zones �ultrapindique� et�b�eeotienne� d’apr�ees la g�eeologie de la r�eegion de Karditsa: l’unit�ee de Thessalie Occi-dentale. Ecl geol Helv 72: 251–261

Papike JJ, Cameron KL, Baldwin K (1974) Amphiboles and pyroxenes: Characterization ofother than quadrilateral components and estimates of ferric iron from microprobe data.Geol Soc Am Abstr Progr 6: 1053–1054

108 P. Pomonis et al.

Parkinson IJ, Pearce JA, Thirlwall MF, Johnson K, Ingram G (1992) Trace element geo-chemistry of Leg 125 Peridotites. Proc ODP Scientific Results 125: 487–506

Pearce JA (1982) Trace element characteristics of lavas from destructive plate boundaries.In: Thorpe RS (ed) Andesites. Wiley, Chichester, pp 525–548

Pearce JA (1983) Role of the sub-continental lithosphere in magma genesis at activecontinental margins. In: Hawkesworth CJ, Norry MJ (eds) Continental basalts andmantle xenoliths. Shiva, Natwich, pp 230–249

Pearce JA, Harris NBW, Tindle AG (1984) Trace element discrimination diagrams for thetectonic interpretation of granitic rocks. J Petrol 25: 956–983

Pearce JA, Kempton PD, Nowell GM, Noble SR (1999) Hf-Nd element and isotope per-spective on the nature and provenance of mantle and subduction components in westernPacific arc-basin systems. J Petrol 40: 1579–1611

Pearce JA, Norry MJ (1979) Petrogenetic implications of Ti, Zr, Y and Nb variations involcanic rocks. Contrib Mineral Petrol 69: 33–47

Pearce JA, Peate DW (1995) Tectonic implications of the composition of volcanic arcmagmas. Ann Rev Earth Planet Sci 23: 251–285

Pearce JA, Van der Laan SR, Arculus RJ, Murton BJ, Ishii T, Peate DW, Parkinson IJ (1992)Boninite and harzburgite from Leg 125 (Bonin-Mariana forearc): A case study of magmagenesis during the initial stages of subduction. In: Fryer P, Pearce J et al. (eds) Proc ODPSci Results 125 (Ocean Drilling Program): 623–659

Pe-Piper G, Piper DJW (2002) The igneous rocks of Greece: The anatomy of an orogen.Borntraeger, Science Publishers, Stuttgart

Pe-Piper G, Tsikouras B, Hatzipanagiotou K (2004) Evolution of boninites and island-arctholeiites in the Pindos Ophiolite, Greece. Geol Mag 141: 455–469

Polat A, Casey JF, Kerrich R (1996) Geochemical characteristics of accreted materialbeneath the Pozanti-Karsanti ophiolite, Turkey: Intra-oceanic detachment, assemblyand obduction. Tectonophysics 263: 249–276

Pomonis P, Tsikouras B, Hatzipanagiotou K (2002) Origin, evolution and radiometric datingof sub-ophiolitic metamorphic rocks from the Koziakas ophiolite (W. Thessaly, Greece).N Jb Mineral Abh 177: 255–276

Pomonis P, Tsikouras B, Hatzipanagiotou K (2004) Comparative geochemical study of theTriassic trachyandesites of Glykomilia and alkali basalts from the Koziakas ophiolitem�eelange (W. Thessaly): Implications for their origin. 10th GSG Congress, 15–17 April2004, Thessaloniki, Greece, 560–561

Raase P (1974) Al and Ti contents of hornblende, indicators of pressure and temperature ofregional metamorphism. Contrib Mineral Petrol 45: 231–236

Rassios A (1990) Geology and copper mineralization of the Vrinera area, east Othrisophiolite, Greece. Ofioliti 15: 287–304

Rassios A (1991) Internal structure and pseudo-stratigraphy of the Dramala peridotitemassif, Pindos Mountains, Greece. Bull Geol Soc Greece 25: 293–305

Rautenschlein M, Jenner GA, Hertogen J, Hofmann AW, Kerrich R, Schmincke HU, White RS(1985) Isotopic and trace element composition of volcanic glasses from the AkakiCanyon, Cyprus: implications for the origin of the Troodos ophiolite. Earth PlanetSci Lett 75: 369–383

Robertson AHF (2002) Overview of the genesis and emplacement of Mesozoic ophiolites inthe Eastern Mediterranean Tethyan region. Lithos 65: 1–67

Robertson AHF, Clift PD, Degnan PJ, Jones G (1990) Tectonic and sedimentary evolution ofthe Mesozoic-Tertiary Pindos ocean: Greece. In: Savascin MY, Eronat AH (eds) IESCA-1990 Proceedings, Ismir, pp 253–263

Rogers NW, Saunders AD (1989) Magnesian andesites from Mexico, Chile and theAleutian Islands: Implications for magmatism associated with ridge-trench colli-

Petrogenetic evolution of the Koziakas ophiolite complex 109

sion. In: Crawford AJ (ed) Boninites and related rocks: London, Unwin-Hyman,pp 416–445

Saccani E, Photiades A (2004) Mid-ocean ridge and supra-subduction affinities in thePindos ophiolites (Greece): implications for magma genesis in a forearc setting. Lithos73: 229–253

Saunders AD, Tarney J (1984) Geochemical characteristics of basaltic volcanism withinback-arc basin. In: Kokelaar BP, Howell MF (eds) Marginal basin geology. Geol SocLondon, Spec Publ 16: 59–76

Saunders AD, Tarney J, Marsh NG, Wood DA (1980) Ophiolites as ocean crust ormarginal basin crust: A geochemical approach. Proc Inter Oph Symp Cyprus 1979:193–204

Saunders AD, Tarney J, Stern CR, Dalziel IWD (1979) Geochemistry of Mesozoic marginalbasin floor igneous rocks from southern Chile. Geol Soc Am Bull 90: 237–258

Scarpelis N, Hatzipanagiotou K, Kaiserloglou M (1992) Manganiferous cherts in siliceoussediments overlying the Koziakas ophiolite, western Thessaly, Greece. Can Mineral 30:415–421

Smith AG (1979) Othris, Pindos and Vourinos ophiolites and the Pelagonian zone. In: 6th

Colloquium on the geology of the Aegean region (Vol. 3). Institute of Geological andMining Research, Athens, Greece, pp 1369–1374

Smith AG (1993) Tectonic significance of the Hellenic-Dinaric ophiolites. In: Prichard HM,Alabaster T, Harris NBW, Neary CR (eds) Magmatic processes and plate tectonics. GeolSoc Spec Publ 76: 213–243

Spooner ETC, Chapman HJ, Smewing J (1977) Strontium isotopic contamination andoxidation during ocean floor hydrothermal metamorphism of the ophiolitic rocks ofthe Troodos massif, Cyprus. Geochim Cosmochim Acta 41: 873–890

Spray JB, B�eebien J, Rex DC, Roddick JG (1984) Age constraints on the igneous andmetamorphic evolution of the Hellenic-Dinaric ophiolites. In: Dixon JE, RobertsonAHF (eds) The geological evolution of the Eastern Mediterranean. Geol Soc London,Spec Publ 17 Oxford, pp 619–627

Stern RJ, Lin P-N, Morris JD, Jackson MC, Fryer P, Bloomer SH, Ito E (1990) Enrichedback-arc basin basalts from the northern Mariana Trough: Implications for the magmaticevolution of back-arc basins. Earth Planet Sci Lett 100: 210–225

Suhr G, Robinson PT (1994) Origin of mineral stratification in the mantle section of theTable Mountain massif (Bay of Islands Ophiolite, Newfoundland, Canada). Lithos 31:81–102

Talkington RW, Malpas JG (1984) The formation of spinel phases of the White Hillsperidotite, St. Anthony complex, Newfoundland. N Jb Mineral Abh 149: 65–90

Tsikouras B, Hatzipanagiotou K (1998) Two alternative solutions for the development of amarginal basin in NE Greece. Ofioliti 23: 83–92

Thompson RN (1974) Some high-pressure pyroxenes. Mineral Mag 39: 768–787Valsami-Jones E, Cann JR (1994) Controls on the Sr and Nd isotopic composistions of

hydrothermally altered rocks from the Pindos Ophiolite, Greece. Earth Planet Sci Lett125: 39–54

Volpe AM, Macdougall JD, Hawkins JW (1987) Mariana Trough basalts (MTB): traceelement and Sr-Nd isotopic evidence for mixing between MORB-like and arc-like melts.Earth Planet Sci Lett 82: 241–254

Wells PRA (1977) Pyroxene thermometry in simple and complex systems. Contrib MineralPetrol 62: 129–139

Weyer S, Munker C, Mezger K (2003) Nb=Ta, Zr=Hf and REE in the depleted mantle:implications for the differentiation history of the crust-mantle system. Earth Planet SciLett 205: 309–324

110 P. Pomonis et al.

Wilson M (1989) Igneous petrogenesis: A global tectonic approach. Chapman and Hall,London

Winchester JA, Floyd PA (1977) Geochemical discrimination of different magma series andtheir differentiation products using immobile elements. Chem Geol 20: 325–343

Wood DA (1979) A variably veined suboceanic upper mantle – Genetic significance for mid-ocean ridge basalts from geochemical evidence. Geology 7: 499–503

Zimmerman J (1972) Emplacement of the Vourinos ophiolitic complex, northern Greece,In: Shagam R et al. (eds) Studies in earth and space sciences. Geol Soc Am Mem 132:225–239

Zindler A, Jagoutz E, Goldstein S (1982) Nd, Sr and Pb isotopic systematics in a three-component mantle: a new perspective. Nature 298: 519–523

Authors’ addresses: P. Pomonis, (corresponding author; e-mail: Ppomonis@upatras.gr), B. Tsikouras (e-mail: V.Tsikouras@upatras.gr), K. Hatzipanagiotou (e-mail:K.Hatzipanagiotou@upatras.gr), Department of Geology, University of Patras, Section ofEarth Materials, GR-265 00, Patras, Greece

Petrogenetic evolution of the Koziakas ophiolite complex 111