New geological, geochronological and geochemical investigations

on the Khoy ophiolites and related formations, NW Iran

Morteza Khalatbari-Jafaria,b, Thierry Juteaub,*, Herve Bellonb,Hubert Whitechurchc, Jo Cottenb, Hashem Emamia

aGeological Survey of Iran, Tehran, IranbIUEM and UMR6538, Domaines oceaniques, Universite de Bretagne Occidentale, 29280 Plouzane cedex, France

cEOST, Universite Louis Pasteur, 67000 Strasbourg, France

Received 12 November 2002; revised 7 July 2003; accepted 27 July 2003

Abstract

This paper gives a detailed geological description of the region of Khoy (NW Iran) and its ophiolites, and presents a new geological map.

The main conclusion is that there are not one, but two ophiolitic complexes in the Khoy area: (1) an old, poly-metamorphic ophiolite,

tectonically included within a metamorphic subduction complex, whose oldest metamorphic amphiboles yield a Lower Jurassic apparent40Kn–40Ar age, and whose primary magmatic age should logically be pre-Jurassic; (2) a younger non metamorphic ophiolite of Upper

Cretaceous age, overlain by a turbiditic, flysch-like volcanogenic series, of Upper Cretaceous-Lower Paleocene age. This latter ophiolite was

created at a slow-spreading oceanic center, according to the lherzolitic mantle sequence, the small volume of gabbroic rocks, the absence of a

diabasic sheeted-dike complex, and the abundant phyric basalts in the extrusive sequence. A scenario for the geodynamic evolution of the

Khoy oceanic basin is proposed in conclusion.

q 2003 Elsevier Ltd. All rights reserved.

Keywords: Ophiolites; Iran; Tethys; 40K–40Ar ages; Metamorphism; Trace element patterns

1. Introduction

Tethyan evolution in Iran and neighboring Turkey,

Oman, and Baluchistan is very complex and hard to work

out. General models, notably those of Sengor and his fellow

workers (Sengor and Yilmaz, 1981…), have not everywhere

proved to be easily reconcilable with the results of local

studies. With a view to helping to resolve the complexities,

we report here the results of intense field and laboratory

work in the Khoy region (Figs. 1–3).

The Khoy ophiolites are exposed in an area located to the

northwest of the city of Khoy, in the northwestern part of

the Iranian Azerbaidjan province, extending practically to

the Turkish border (Fig. 1).

The geology of the area is still poorly known. Kamineni

and Mortimer (1975) gave a general description of the

geology of the Khoy region, writing mainly of its

metamorphic rocks and the presence of high-pressure

glaucophane-bearing schists and amphibolites. More useful

information is given by GSI geological maps of the sheets of

Khoy at 1/250,000 (Ghorashi and Arshadi, 1978), of Khoy

at 1/100,000 (Radfar et al., 1993), and of Dizaj at 1/100,000

(Amini et al., 1993). The authors of these maps (including

one of us, MK) have recognized and defined the ophiolite

complex of Khoy and attributed it to the Upper Cretaceous,

on the basis of micropaleontological data (Globotruncana in

limestone beds associated to the ophiolitic pillow lavas).

More recently Hassanipak and Ghazi (2000) gave a first

report on the petrology and geochemistry of the Khoy

ophiolite. In this paper, the authors distinguished, in the

ophiolitic volcanic sequence, a lower pillow basalt unit

displaying REE patterns intermediary between E-MORB

and N-MORB profiles, and an upper massive basalt unit

with E-MORB-type REE patterns. The REE patterns for the

gabbros and diorites indicate that the crustal rock suite was

derived by fractional crystallization from a common basaltic

melt, generated by 20–25% partial melting of a simple

lherzolite source. In their conclusion, the authors suggest

1367-9120/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jseaes.2003.07.005

Journal of Asian Earth Sciences 23 (2004) 507–535

www.elsevier.com/locate/jseaes

* Corresponding author. Address: Domaine d’Orio, rue Orio, Hendaye

64700, France. Tel.: þ33-5-59-48-16-34.

E-mail address: juteau@wanadoo.fr (T. Juteau).

that the “Khoy ophiolite is equivalent to the inner group of

Iranian ophiolites (e.g. Nain, Shahr-Babak, Sabzevar,

Tchehel Kureh and Band-e-Zyarat), and was formed as a

result of closure of the northwestern branch of a narrow

Mesozoic seaway which once surrounded the Central

Iranian microcontinent”. Unfortunately, their description

of the geology of the Khoy area is extremely schematic and

often erroneous, and the analyzed samples are not located.

Ghazi et al. (2001) proposed the existence, beneath the

ophiolite, of a basal metamorphic zone, displaying an

inverse thermal gradient, ranging from the amphibolite

facies to the greenschist facies. These authors present two40Ar – 39Ar plateau ages of 158.6 ^ 1.4 Ma and

154.9 ^ 1.0 Ma for hornblende gabbros, and conclude that

the plutonic rocks of the Khoy ophiolite were formed during

Late Jurassic. They present also four 40Ar–39Ar plateau

ages of about 104–110 Ma for hornblendes from the

amphibolites of the basal metamorphic zone, marking a

tectonic emplacement of Mid-Albian age for the ophiolite

complex. As the pelagic limestones interbedded with the

ophiolitic pillow lavas give microfaunas of somewhat

younger ages (Upper Albian to Lower Cenomanian, around

100 Ma), the authors have some difficulty in explaining how

the plutonic gabbros and the volcanic pillow lavas in the

same ophiolite complex show a difference in age of more

than 50 Ma, and how the pillow lavas can be younger than

the metamorphic sole, supposed to mark the beginning of

the detatchment and obduction process.

We present here the results of new field and laboratory

studies, leading to the distinction of two ophiolitic

complexes in the Khoy area, which resolves many apparent

contradictions (see Figs. 2 and 16):

(1) An older meta-ophiolitic complex, forming huge

tectonic slices within what we called the ‘eastern

metamorphic complex’. We suggest that this

metamorphic complex consists of several slabs of

various Mesozoic ages, piled up and tectonically

stacked in a subduction complex, developed beneath

the Central Iran Block southwestern margin. In our

view, these meta-ophiolites represent the remains of a

Neo-Tethyan oceanic lithosphere, created in the Khoy

Fig. 1. Distribution of the ophiolite belts in Iran after Emami et al. (1993), and location of the Khoy area. Main iranian ophiolite complexes: BZ: Band-e-

Ziyarat (also called Kahnuj complex). KM: Kermanshah. NA: Nain. NY: Neyriz. SB: Sabzevar. SHB: Shar Babrak. THL: Torbat Hydariyah. TK:

Tchehel Kureh.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535508

Fig. 2. Simplified geological map of the region of Khoy, showing the main geological units described in this paper. The yellow lines show the location of the geological sections (Figs. 5–6 and 9–10–11)

presented in this paper.

M.

Kh

ala

tba

ri-Jafa

riet

al.

/Jo

urn

al

of

Asia

nE

arth

Scien

ces2

3(2

00

4)

50

7–

53

55

09

Fig. 3. Geological map of the region of Khoy, by Morteza Khalatbari-Jafari and Thierry Juteau. Yellow line AB: location of the general geological section.

M.

Kh

ala

tbari-Ja

fari

eta

l./

Jou

rna

lo

fA

sian

Ea

rthS

ciences

23

(20

04

)5

07

–5

35

51

0

oceanic basin during most of the Mesozoic times.

Subduction began after the collision of the Central Iran

Block with Eurasia during Middle Upper Triassic,

trapping and stacking the early Tethyan oceanic

lithosphere.

(2) A younger non-metamorphic ophiolite of Late

Cretaceous age, outcropping in the western part of

the studied area, and devoid of any trace of regional

metamorphism. The pillows still have their delicate

glassy crust, and the layered gabbros are amphibole-

free, displaying numerous and delicate cumulate

structures and textures.

We think that this ophiolite represents the last oceanic

ridge activity in the Khoy basin. This oceanic ridge was

active just in front of the subduction trench, filled with a

thick turbiditic and volcanic series. It was obducted

southwestward over what we called the ‘western

metamorphic complex’, representing the Arabian

continental plateform, or more probably a detached

fragment of it. This ophiolite has the same Late Cretaceous

age as other well-known ophiolites of western Iran, Turkey

and Oman, belonging to the peri-arabic ‘ophiolitic crescent’

(Ricou, 1971).

2. Geological description of the Khoy region

Fig. 2 shows schematically the main geological units of

the Khoy region. These units are grossly disposed along

NW–SE stripes. From NE to SW, we shall describe

successively: (1) the south-western margin of the Central

Iranian Block, (2) an eastern metamorphic complex

including disrupted slices of metamorphic ophiolites, (3) a

turbiditic and volcanic-sedimentary unit of Late Cretaceous

age, (4) an Upper Cretaceous, non metamorphic ophiolite

complex of Khoy s.s., (5) a western metamorphic complex.

Fig. 3 presents our new detailed geological map of

the Khoy region made at 1/50,000, presented here at scale

1/300,000.

2.1. The south-western margin of the Central Iranian Block

Formations of this block crop out to the NNE of the city

of Khoy, close to the villages of Hydarabad and Zagheh.

They belong to the Central Iran Zone units, as defined by

Stocklin (1968, 1974), and consist of an unmetamorphosed

Paleozoic sedimentary series (Cambrian and Permian),

overlain by Oligocene-Miocene sediments and Quaternary

deposits. Fig. 4 gives a schematic stratigraphic section of

these formations.

Cbt unit. This unit is made of an alternation of chert- and

shale-bearing dolomites and recrystallized limestones,

including pinkish siltstones. Chert beds and nodules are

abundant at the base and top of this unit, well visible near

the village of Zagheh (60–80 m thick). This unit is

comparable to the Barut Formation described by Stocklin

et al. (1965), in the northwest of the Soltanieh mountains

(NW of Zanjan), dated there by stromatolites, and attributed

by these authors to Infracambrian. We did not find any

faunas in this unit in the Khoy region.

Cz unit. This unit, well exposed in the Zagheh village and

valley, in the core of a half-anticline, overlains conformably

the previous one and consists of arkosic sandstones and

purple-brown shales. Sandstones (Eb) predominate in the

upper part of this unit, attributed by us to Lower Cambrian,

by analogy with the classical Zaigun Formation.

Cl Unit. This unit consists of red arkosic sandstones

including rare red slate and siltstone beds. The sandstones,

including conglomeratic lenses with red clayey matrix,

show typical graded and cross-bedding structures.

White quartzites and quartz-arenites develop at the top.

This unit is comparable to the well-known Lalun Formation,

Fig. 4. Schematic geological section across the Central Iran Zone units outcropping to the north of Khoy in the studied area.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 511

of Lower Cambrian age, described in the vicinity of Fasham

and Zaigun village, north of Teheran (Asseretto, 1963), and

known in many places in Central Iran (Stocklin, 1968).

Cm Unit. Exposed also near Zagheh, this unit consists of

thick chert- and shale-bearing dolomite beds, nicely

folded here. It corresponds likely to the classical Upper

Cambrian/Lower Ordovician Mila Formation described at

Mila Kuh, near Damghan (Stocklin et al., 1964), well dated

by Trilobites, Brachiopods and coral faunas. We did not find

any fauna in this unit.

Pd Unit. This unit erodes and rests unconformably over

the previous formation. It consists of red sandstones,

quartzites and siltstones, passing upward to thick

conglomerate beds and shales. This unit devoid of faunas

is comparable to the Lower Permian Dorud Formation

described at Dorud village, north of Teheran (Asseretto,

1963).

Pr Unit. This units extends widely north of Zagheh, and

consists of thick, massive dolomitic limestones and

limestones. It is thrust over the Pliocene-Quaternary

conglomerate unit, and is overthrust by the Lower

Cretaceous Orbitolina-bearing limestone unit. It is

comparable to the Upper Permian Ruteh Formation

described by Asseretto (1963) in the Jairud valley (Central

Elburz). We found in it the following faunas (geological

map of the Khoy Quadrangle at 1/100,000, Radfar et al.,

1993): Hemigordius sp., Agathamina sp., Glomospira sp.,

Staffella sp., Schubertella sp., Frondina sp., Vermiporella

sp., fusulinidae.

Js Unit. Exposed near Zagheh, this unit consists of

coal-bearing sandstones and shales. Devoid of faunas and

non metamorphic, this unit exhibits tectonic contacts with

all neighbour units. It was formerly attributed to

Precambrian on the GSI maps, and would be the equivalent

of the Kahar Formation. Alternately (and most likely,

because of the presence of coal), this unit could be

comparable to the Lower Jurassic sandstones and shales of

the Shemshak Formation, described by Asseretto (1966) in

Central Elburz.

Kl Unit. This is a thick massive limestone unit of Lower

Creataceous age, exposed in the north-east of the area. It is

thrust over the Pr Unit (Ruteh Formation), and is

comformably overlain by the Oml Unit. The following

microfaunas were found in this unit: Orbitolina lenticularis,

Orbitolina sp. Lithocodium, Aggregatum Elliotte,

Acicularia sp., giving an Aptian-Albian age (lower

Cretaceous). These Orbitolina limestone are known (under

various names) in many places of Central Iran. They were

probably deposited in a wide and shallow epicontinental

marine basin.

Oml Unit. This units crops out widely to the north of

Khoy, and is mainly made of limestones and marls. Its base

includes poorly sorted conglomerates (OmC Unit) of

variable thickness (several meters to 30 m). In Central

Iran, the first limestone beds in this unit (known as the Qom

Formation) have an Oligocene age, but here in the Khoy

area, they have a Miocene age, determined after the

following microfaunas: Miogypsinoides sp., Miogipsina

sp., Rotalia cf. vienneti. Corals and Cephalopods are also

found in these limestones, which form the highest

mountains in the northeast of the mapped area.

Pl-Q Unit. These conglomerates and sandstones of

Pliocene-Quaternary age cover large areas in the north of

the studied area. They are generally strongly folded and

rest unconformably over the Oml Unit.

In summary, the Paleozoic units of these formations

show the classical stratigraphic succession of the ‘Gondwa-

nian Iran’ before its separation from Arabia and Africa, with

its characteristic stable platform shelf deposits. The Lower

Paleozoic Barut, Zaigun, Lalun and Mila Formations,

well known in the Zagros, High-Zagros, Alborz and Central

Iran are easily recognizable here in the Khoy area. They are

followed, as in most of these regions, by a long sedimentary

gap, and unconformably covered by the Lower Permian

Dorud sandstones, followed by the Ruteh limestones.

The epicontinental Mesozoic and Cenozoic units are highly

discontinuous, since only Lower Jurassic, Lower

Cretaceous and Miocene marine deposits were identified,

probably separated by long periods of emersion and erosion.

2.2. The Eastern metamorphic complex

The next formation to the SW is a metamorphic complex,

just north of the city of Khoy, with a general NW–SE trend.

On its northeastern margin, this complex has tectonic

contacts with the Central Iran Block margin), which is thrust

southwestward over it. On its southwestern margin, the

metamorphic rocks are thrust over the Upper Cretaceous

turbidites and volcano-sedimentary series outcropping to

the southwest. This metamorphic zone includes huge

tectonic slices of metamorphosed ophiolites, mainly

serpentinized peridotites, with associated metagabbros.

Structurally, these rocks are characterized by isoclinal

folding, and by the development of shear zones at all scales,

generally oriented NW-SE. The main foliation (S1) is itself

folded, generating a second foliation (S2), and locally a

third (S3).

2.2.1. Metamorphic units

Besides the meta-ophiolites, we distinguished and

mapped four units in the metamorphic series, called m1 to

m4, grossly distributed from east to west in that order

(Figs. 3 and 5):

m1 unit. This unit consists of an alternation of gneiss,

micaschists and fine-grained amphibolites, passing upward

to metaquartzites, marbles and gneiss. Near the village of

Hydarabad, the east-west trending foliations are flat,

with north-south lineations.

m2 unit. This is the main metamorphic unit in the Khoy

area. It consists mainly of fine-grained amphibolites and

amphibole schists, with interbedded micaschists,

metaquartzites and calcschists. Many mafic dikes, sills and

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535512

small intrusive bodies, transformed to amphibolites, intrude

these rocks. They show tight isoclinal folds, often with

evidence of incipient anatexis (Plate 1, Fig. 4), and three

successive deformation stages marked by foliations S1, S2,

and locally S3 (Plate 1, Fig. 5). Shear zones oriented

NW–SE are abundant in this unit (Plate 1, Fig. 6).

m3 unit. This unit is mainly composed of metasediments,

including greenschists and calcschists, sometimes with

interlayered massive marble beds.

m4 unit.This unit consists mainly of metavolcanics

(metabasalts and meta-andesites). Meta-rhyolites with

gneissic fabrics were observed north of Dashpasak village.

In the Dizaj valley, the metavolcanics exhibit numerous

angular gabbroic inclusions (typically decimetric in size).

Many isolated diabase dikes, transformed to amphibolites

and tectonically deformed, intrude these rocks.

2.2.2. Meta-ophiolitic tectonic slices

Huge tectonic slices of metamorphosed ultramafic/mafic

rocks appear in the middle of the Eastern metamorphic

complex, showing systematic tectonic contacts with the

various metamorphic units (Fig. 6). Although

highly tectonized, these rocks constitute a dismembered

meta-ophiolitic assemblage, including meta-tectonites

(lherzolites, harzburgites), meta-cumulates (dunites, banded

meta-gabbros and hornblendites), and various types of

fine-grained amphibolites and meta-ankaramites (Fig. 7).

ut unit. These are the main tectonic slices of ultramafic

rocks, consisting of lherzolitic and harzburgitic tectonites

showing spectacular mantle deformations, outlined by

flattened and stretched orthopyroxene crystals on the

outcrops (Plate 1, Fig. 1). Under microscope, these rocks

have a typical porphyroclastic texture, with deformed and

stretched orthopyroxenes and clinopyroxenes, kinked oli-

vine porphyroclasts, set in a recrystallized and granulated

matrix of olivine with triple junctions at 1208. The accesory

chromite appears as deformed porphyroclasts, or as tiny

disseminated and granulated grains in the matrix. In some

places, we found small dunitic bodies, made of fine-grained

and non-deformed olivine, intruding the tectonites,

associated with small stratiform chromitite lenses. These

dunitic bodies and associated magmatic chromitites

probably represent the residues of former partial melting

channels developed in the peridotites during an oceanic

accretion episode. Coarse-grained, often pegmatitic

pyroxenite dikes are also found in these peridotites.

In various areas, the ultramafic tectonites are crosscut by

abundant and huge sills, dikes or small intrusions of

metagabbros (Plate 1, Fig. 2). They are labelled ma on the

geological map (Fig. 3). Most of these are banded

amphibolites corresponding to ancient sills of layered

gabbros (Plate 1, Fig. 3), including dunitic and anorthositic

layers. Others are massive amphibolites corresponding to

former isotropic gabbros. These rocks were often deformed

and sheared along ductile shear zones, marked by

pronounced porphyroclastic and mylonitic structures and

textures, with rotated pyroxene porphyroclasts, set in a

fine-grained, recrystallized matrix.

Fig. 5. Schematic geological section across the four metamorphic units of the Eastern metamorphic complex in the studied area. See location on Fig. 2.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 513

mc unit. This unit is visible to the north of the village of

Aqbash, and also near Hodar village. It consists of former

ultramafic cumulates (mainly dunites, wehrlites, lherzolites

and harzburgites), showing clear cumulate textures under

microscope, and only weak ductile deformations.

Delicate chromite layers could be observed by places,

outlining a former magmatic layering in these rocks, which

are strongly serpentinized and often severely crushed (fish-

like structures on the outcrops). Small amphibolite lenses

and veins represent ancient gabbro veins. Metamorphic

amphiboles have developed in these ultramafic cumulates.

In summary, these meta-ophiolitic slices include the

relicts of a residual mantle sequence with its characteristic

high-temperature plastic deormations, and of a plutonic

crustal sequence with recognizable cumulate textures.

Significant parts of the m2 fine-grained amphibolites

might represent the volcanic extrusive sequence (Fig. 7).

2.2.3. 40K/40Ar mineral datings of the Eastern metamorhic

complex: metamorphic unit and associated meta-ophiolitic

slices

Mineral separates of amphibole, muscovite, biotite, and

feldspar were dated by the 40K/40Ar method in our

laboratory in Brest. The locations of the dated samples are

shown in Fig. 13, where the samples are coded as in the first

column of Table 1. As shown in Table 1, the separated

Plate 1. The Eastern metamorphic complex and associated meta-ophiolites. 1. Well foliated meta-harzburgite outcrop, with main foliation (L1) outlined by

chromite grains (CR) and elongated orthopyroxene crystals (OPX). South of Ajidgah. 2. Meta-gabbroic intrusive body (MG) in serpentinized meta-lherzolite

(SL), along earth road to Aqbash. 3. Banded meta-gabbro, recrystallized with abundant metamorphic amphiboles, north of Aqbash. 4. Folded amphibolites

from m2 unit, showing evidences of incipient anatexis, north of Aqbash, north of Khoy. 5. Folded epimetamorphic schistose serpentinites, with well visible

S2/S3 foliations, north of Kordkandi. 6. Shear-zones in micaschists from m2 unit, north of Aqbash.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535514

amphiboles, biotites and muscovites in this unit display a

wide range of apparent ages, suggesting a long, polyphased

metamorphic history. These ages are interpreted as

reflecting the time when the different minerals crossed

their respective isotopic closure temperatures (Villa, 1998).

Besides, the following remarks can be done about these

isotopic ages:

(a) The ages of separated amphiboles from various

amphibolites of the metamorphic complex

(189–102 Ma), and from the meta-ophiolitic complex

(195–112 Ma in hornblendites and metagabbros)

cover the same period of time, confirming the

impression that both complexes evolved together

from Lower Jurassic to Upper Cretaceous.

The amphibole ages are reliable, because their K2O

content measured by atomic absorption spectrometry

(AAS) is very close to that measured by electron

microprobe (MP), as indicated in Table 1.

(b) The ages of separated micas (muscovite, biotite) in

various gneiss, micaschists and pegmatites from the

metamorphic complex cover also a wide period of

time, ranging from 181.8 to 69.4 Ma. The K2O content

of the separated mica crystals population measured by

AAS is somewhat lower than that measured by electron

microprobe (MP), indicating some possible inferences

on the isotopic ages linked to the presence of K2O-poor

phases (quartz mainly) in the separates. In this

particular case (quartz pollution), the error on

the calculated age is small and can be neglected.

(c) In two samples where both feldspar and amphibole

phases could be separated, the isotopic ages for

feldspar are discordant with the ages given by

amphiboles. In sample no. 11, a metagabbro from the

meta-ophiolitic unit, the amphibole gave 154.9 Ma,

and the plagioclase 108.4 Ma (for K2O ¼ 0.45%).

In sample no. 18, an amphibolite from m2 unit, the

amphibole gave 102.1 Ma and the plagioclase

115.6 Ma (for K2O ¼ 0.07%). And in sample no. 22,

a fine-grained amphibolite from m1 unit, the amphi-

bole gave 189.3 Ma (average), and the plagioclase

106.9 Ma. In this latter case, the K2O content of the

plagioclase is ten times higher in the separated phase

(1.06% by AAS) than in the corresponding microprobe

analysis (0.1% by MP). This means that the plagioclase

separates either are polluted by amphibole fractions

(richer in K2O), or more probably are altered by

sericite (not analyzed by microprobe).

We propose to distinguish four groups of chronological

events, based on the measurements done on separated

amphiboles and micas:

(1) The Lower Jurassic group (195–181 Ma). The oldest

apparent ages were found in two rock types: (a) in

amphibole-rich pegmatitic metagabbros from the meta-

ophiolite association (Fig. 13). In these metagabbros,

showing spectacular ductile deformations, there are

locally (site 12, Fig. 13) small blocks of weakly

deformed gabbros with Lower Jurassic apparent

Fig. 6. Geological sections across the meta-ophiolites and their surrounding metamorphic rocks of the Eastern metamorphic complex. See locations on Fig. 2.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 515

average ages (194.8 ^ 10.1 Ma). These ages suggest

that the primary cooling age of these gabbros was

somewhat older, perhaps Upper Triassic. (b) In fine-

grained amphibolites exposed in the base of the (m1)

metamorphic group, with a range between 196.3 ^ 10.7

and 182.3 ^ 4.3 Ma. The quartz-muscovite pegmatite

veins crosscutting these amphibolites have an apparent

age of 181.8 ^ 4.2 Ma.

(2) The Middle Jurassic group (160–155 Ma). The second

group of apparent ages is found in the following

metamorphic facies:

(a) in amphiboles of metagabbros and ortho-amphi-

bolites from the meta-ophiolitic complex, at

160.8 ^ 12.7 and 160.7 ^ 12.9 Ma (north of

Aghbash village), and at 155.6 ^ 11.9 Ma (east

of Ajidgah village). Under microscope, they show

recrystallized amphiboles containing some pyrox-

ene relicts, and recrystallized plagioclases with

abundant triple junctions, suggesting ductile

deformations in shear fault zones (Passchier and

Trouw, 1995).

(b) in the (m1) metamorphic group, the muscovites of

the gneisses of Hydarabad village

(160.5 ^ 3.7 Ma) and the amphiboles from the

amphibolites of Gheh Yashar village

(151.0 ^ 11.5 Ma). Also, well crystallized micas-

chists gave both muscovites and biotites with an

apparent age of 146.3 ^ 3.4 Ma.

(3) The Lower Cretaceous group. The third group of

isotopic ages was found in the metamorphic complex

(m1, m2) and in the meta-ophiolitic gabbros.

They include: (a) two datings of amphiboles at

121.2 ^ 6.2 Ma from the fine-grained and recrystal-

lized amphibolites (north Ghekh Yashar village), and

102.1 ^ 5.4 Ma from the amphibolites of Ajidgah

village; (b) two datings obtained from the amphiboles

of meta-ophiolitic gabbros, at 116.5 ^ 6.0 Ma

(north Ajidgah) and 112.9 ^ 8.6 Ma (west Ravand).

Fig. 7. Tentative reconstruction of the ‘ophiolitic log’ in the highly dismembered meta-ophiolitic slices in the Eastern metamorphic complex.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535516

Table 1

New 40K/40Ar datings in the region of Khoy

Iran–Khoy

Reference

to Fig. 13

Sample Location Rock type Dated

fraction

Average age

^ error (Ma)

Age ^ error

(Ma)

K2O

(wt%)

40ArR

(1027 cm3 g21)

40ArR (%) Analysis

number

Longitude Latitude

Upper Cretaceous non metamorphic Khoy ophiolite

1 00-3KH56 S.Todan Porphyric diabase dike in gabbro Plagioclase 64.9 ^ 3.8 0.13 2.77 35.0 5881 4482605000 3883400000

2 00-3KH190 S.Todan Isotropic gabbro Plagioclase 72.6 ^ 5.0 0.046 1.10 19.5 5891 4482503000 3883501000

3 01-2KH211 Qorshanlo Plagioclase vein in gabbro Plagioclase 100.7 ^ 6.0 0.25 8.34 31.6 5890 4482001500 3883504000

Meta-ophiolitic unit

4 99-KH92 North Aghbash Weakly deformed gabbro Amphibole 80.2 ^ 4.6 82.4 ^ 4.6 0.106 2.88 42.5 5894 4483802000 3885203000

77.9 ^ 4.6 0.106 2.72 31.1 6000

5 99-KH-242 West Ravand Metagabbro Amphibole 112.9 ^ 8.6 0.175 6.57 69.2 5632 4484403000 3884901000

6 99-KH-134 North Aghbash Metagabbro Amphibole 116.5 ^ 6.0 0.215 8.34 67.2 5664 4483602000 3885104000

7 00-3-KH14 South Aghbash Metagabbro Brown amphibole 134.7 ^ 7.1 0.245 11.05 53.0 5665 4483502500 3884903000

8 00-3-KH9 East Ajidgah Metagabbro Amphibole 155.6 ^ 11.9 0.165 8.64 69.8 5630 4484404500 3884605000

9 99-KH102 North Aghbash Metagabbro Amphibole 160.4 ^ 12.7 160.8 ^ 12.7 0.052 2.82 40.4 5631 4483703000 3885201000

160.0 ^ 12.4 0.052 2.81 47.4 5655

10 99-KH145 N.Aghbash Metagabbro Amphibole 160.7 ^ 12.9 0.057 3.09 35.9 5633 4483701000 3885103000

11 99-KH359a North Khoy Amphibole pegmatitic gabbro Feldspar 108.4 ^ 6.0 0.45 16.2 42.7 5322 4485502500 3883600000

99-KH359 Amphibole 154.9 ^ 11.8 0.17 8.86 66.9 5676

12 99-KH291b North Khoy Amphibole pegmatitic gabbro Amphibole 194.8 ^ 10.1 192.3 ^ 2.9 0.492 32.2 91.0 5646 4485405000 3883702000

197.3 ^ 10.1 0.492 33.1 90.8 5656

Eastern Metamorphic complex

13 00-4KH78 Qorol-Ajai Gneissic granite Muscovite and biotite 67.5 ^ 1.6 7.06 156.6 76.8 5990 44843004500 3885005500

14 00-4KH69 Qorol-Ajai Gneissic dike Muscovite 75.3 ^ 1.8 10.37 257.0 73.9 5874 4484603500 3885103000

15 99-KH357 Ajidgah Quartz, feldspar, muscovite vein Muscovite 93.5 ^ 1.5 8.9 275.3 78.4 5303 4484405000 3884802000

16 99-KH314 North Dizaj Micaschist Muscovite 69.4 ^ 1.6 6.56 149.6 82.6 5991 4484502000 3883901500

17 00-3KH7 Ajidgah Micaschist Muscovite 81.2 ^ 1.2 7.07 189.2 92.5 5644 4483601000 3885305000

18 99-KH-358 Ajidgah Amphibolite Amphibole 102.1 ^ 5.4 102.3 ^ 5.3 0.27 9.16 71.8 5645 4484601500 3885303000

103.9 ^ 5.4 0.27 9.31 67.5 5675

100.1 ^ 5.4 0.27 8.96 49.2 5323

Plagioclase 115.6 ^ 3.7 0.075 2.89 33.8 5678

19 99-KH353 Ghekh yashar Fine-grained amphibolite Amphibole 121.2 ^ 6.2 0.46 18.6 75.5 5648 4485204500 3883801000

20 99-KH191 Ghekh yashar Amphibolite Amphibole 151.0 ^ 11.5 0.195 9.90 63.5 5663 4485305000 3883705000

21 00-4KH71 Hydarabade Micaschist Muscovite and biotite 146.3 ^ 3.4 8.03 394.4 93.7 5892 4385405000 3884100500

22 01-4KH81 Hydarabade Fine-grained amphibolite Amphibole 189.3 ^ 10.7 182.3 ^ 4.3 0.48 29.7 74.8 5982 4385500000 3884204000

196.3 ^ 10.7 0.48 32.1 75.7 5998

Feldspar 106.9 ^ 2.5 1.06 37.6 81.5 5993

23 01-4KH76 Hydarabade Gneiss Muscovite 160.5 ^ 3.7 8.7 470.7 84.6 5981 4485500000 3884304000

24 01-4KH97 Hydarabade Quartz and muscovite vein Muscovite 181.8 ^ 4.2 9.78 603.2 93.3 5865 4483005000 3884200000

(continued on next page)

M.

Kh

ala

tba

ri-Jafa

riet

al.

/Jo

urn

al

of

Asia

nE

arth

Scien

ces2

3(2

00

4)

50

7–

53

55

17

This metamorphism of lower Cretaceous age is

associated with thick ductile shear zones oriented

NW–SE to NS, affecting both the metamorphic

complex and the meta-ophiolites, with evidences of

incipient partial melting.

(4) The Upper Cretaceous group. The muscovites of the

micaschists from Ajidgah, gave an age of

81.2 ^ 1.2 Ma. The muscovites separated from

micaschists north of Dizaj gave 69.4 ^ 1.6 Ma (Maes-

trichtian); this young age can be related to tectonic

element that caused the local S3 deformation.

In the vicinity of Qorol-Ajai village, a gneissic granitic

intrusion crosscuts the metamorphic rocks, extending to the

north of the studied area. Many quartz-feldspar-bearing

dikes and veins, probably related to this granite, crosscut the

metamorphic rocks. The separated pegmatitic muscovites

from granitic veins from Ajidgah give an age of

105.8 ^ Ma, coarse-grained muscovites of other granitic

dikes in the vicinity of Qorol-Ajai give an age of

75.3 ^ 1.8 Ma, and the separated muscovites and biotites

from the Qorol-Ajai granite-gneisses give an age of

67.5 ^ 1.6 Ma.

Finally, the separated fine-grained amphiboles from a

weakly deformed, unmetamorphosed gabbro intruding the

meta-ophiolites gave an Upper Cretaceous average age of

80.2 ^ 4.6 Ma.

2.3. The supra-ophiolitic turbiditic

and volcanic-sedimentary unit

This unmetamorphosed unit is exposed along a wide strip

developed to the SW of the Eastern metamorphic complex.

The contacts between both units are tectonic, with thrusting

of the meta-ophiolites or other metamorphic units over the

turbidites in the north. On its SW margin, this unit rests

unconformably over the pillow lavas of the Upper

Cretaceous ophiolite of Khoy s.s. We distinguished four

members in this unit (Fig. 8), which are from bottom to top:

(1) turbidites and associated syn-sedimentary breccias,

(2) epiclastic volcanic breccias and pillow lavas, (3) ankar-

amitic volcanic breccias, (4) upper volcanic-sedimentary

member.

The age of this unit is well constrained by biostrati-

graphic data. Numerous beds of chert-bearing, red-pinkish

limestones contain microfaunas of Upper Cretaceous-Lower

Paleocene age. The limestones of members (1) to (2) contain

microfaunas of Santonian to Campanian age, those of

member (3) contain microfaunas of Campanian to Maes-

trichtian age, and those of member (4) gave ages ranging

from Campanian-Maestrichtian to Early Paleocene.

2.3.1. Turbidites

This is the main turbiditic unit, well exposed for instance

in the Badalan-Hesar valley, in the vicinity of the Abshar

cascade (Plate 2, Fig. 2), near the village of Rezel Arol, orTab

le1

(co

nti

nu

ed)

Iran

–K

ho

y

Ref

eren

ce

toF

ig.

13

Sam

ple

Lo

cati

on

Rock

typ

eD

ated

frac

tio

n

Av

erag

eag

e

^er

ror

(Ma)

Ag

e^

erro

r

(Ma)

K2O

(wt%

)

40A

r R(1

02

7cm

3g2

1)

40A

r R(%

)A

nal

ysi

s

nu

mb

er

Lo

ng

itu

de

Lat

itu

de

Up

per

Mio

cene

mo

nzo

dio

riti

cin

tru

sio

ns

25

01

-5K

H1

16

Av

rine

Mo

nzo

dio

rite

Am

ph

ibo

le1

0.5

^0

.71

.37

4.6

42

6.8

59

83

4483

40 2

500

4485

80 1

500

Fel

dsp

ar1

2.2

^0

.34

.24

16

.85

1.7

59

92

26

01

-4K

H1

17

So

uth

Diz

ajM

onzo

dio

rite

Bio

tite

11

.5^

0.3

8.5

23

1.7

60

.15

93

84

482

30 0

000

3884

00 0

000

Ala

nde

Fel

dsp

ar1

3.8

^0

.42

.42

10

.77

54

.65

86

6

27

01

-4K

H8

5Y

akm

aleh

Mo

nzo

dio

rite

Fel

dsp

ar1

4.0

^0

.36

.68

30

.27

8.2

58

93

4481

50 4

500

3885

30 3

000

See

Fig

.1

3fo

rlo

cati

on

of

sam

ple

s.Is

oto

pic

anal

yse

sh

ave

bee

np

erfo

rmed

inth

eU

MR

65

38

lab

ora

tory

inB

rest

.

Po

tass

ium

con

ten

tsu

sed

for

age

calc

ula

tio

ns

wer

em

easu

red

by

ato

mic

abso

rpti

on

spec

trom

etry

on

min

eral

sep

arat

es(c

olu

mn

AA

S)

and

wer

eal

soch

eck

edb

yel

ectr

on

-mic

rop

rob

ean

aly

ses

(colu

mn

MP

).

See

tex

tfo

rd

iscu

ssio

n.

Arg

on

iso

topic

rati

os

and

con

cen

trat

ion

sar

em

easu

red

by

mas

ssp

ectr

om

etry

usi

ng

the

spik

em

eth

od

des

crib

edin

Bel

lon

etal

.(1

98

1).

Ag

esar

eca

lcu

late

du

sin

gth

eco

nst

ants

pro

po

sed

by

Ste

iger

and

Jag

er(1

97

7).

Err

ors

are

qu

ote

dat

on

esi

gm

ale

vel

foll

ow

ing

Mah

oo

dan

dD

rak

e(1

98

2).

40A

r R,

sub

scri

pt

Rm

eans

rad

iog

enic

argo

n;

(%)

40A

r Rre

fers

tora

dio

gen

icar

go

n4

0/t

ota

lar

go

n4

0(a

tmo

spher

ican

dra

dio

gen

ic).

Av

erag

eag

ein

Ma

isg

iven

for

du

pli

cate

anal

yse

s.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535518

near the village of Kordkandi (Plate 2, Fig. 1). Most of this

formation is made of rather well-bedded, fine-grained,

decimetric beds of volcanic and sedimentary sands and

clays, including interbedded black shales and thin,

grey limestones. Lenses of coarse-grained breccias, contain-

ing allochtonous limestone pebbles and fragments, are

commonly interbedded within the fine-grained turbidites

(Plate 2, Fig. 3). In the Hesar valley, spectacular slided

blocks of red, vertical limestone beds, several hundreds of

meters long, are associated with volcanic/sedimentary

breccias (Plate 2, Figs. 4–6). In several places, slump

structures are widespread.

These allochtonous limestones contain microfaunas of

Santonian-Campanian age (and even Campanian-Maes-

truchtian in one sample), with the following fossils:

Globotruncana arca, Globotruncana Lapparenti, Globo-

truncana bulloides, Globotruncana Lapparenti-Tricari-

nata, Globotruncana spp., Globotruncana gansseri,

Globotruncana lapparenti-lapparenti, Globotruncana

confusa, Globotruncana stratiformis, Hedbergella sp.,

Heterohelix sp., Radiolaria. The autochtonous and grey

limestone beds in the turbidites, however, contain faunas

of Santonian age, with the following fossils: Globotrun-

cana sp., Hedbergella sp., Heterohelix reossi.

The lenses of coarse-grained volcanic and sedimentary

breccias contain both perfectly rounded volcanic pebbles,

and very angular volcanic fragments of all sizes, ranging

from millimetric to plurimetric, and showing a wide range

of textures, from totally aphyric to highly phyric.

Cherts, radiolarites and fine limestone beds develop at the

top of this sequence.

2.3.2. Epiclastic volcanic breccias and pillow flows

Pillow basalts (150 m thick). This member is mainly

made of basaltic pillow flows, which are aphyric or slightly

phyric at the base, and phyric at the top, with a few sheet

Fig. 8. Schematic stratigraphic log of the supra-ophiolitic volcanic and sedimentary unit, resting unconformably over the Upper Cretaceous ophiolite of Khoy.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 519

flows. Some sedimentary beds, made of cherts, radiolarites

and pink limestones are interbedded within this volcanic

sequence. These sediments contain the following

microfaunas, supposed to be of Campanian-Maestrichtian

age: Globotruncana calcarata, Globotruncana aff.

Falsostuarzi, Globotruncana sp., Hedbergella sp.,

Lenticulina, Radiolaria.

2.3.3. Ankaramitic volcanic breccias

This member, bounded by strike-slip faults, is well

exposed near the village of Dashpasak. Its thickness is

about 170 m. The volcanic fragments in these breccias

are characterized by the presence of coarse and black

augitic phenocrysts, which can be very abundant, and by

a very high vesicularity. Decimetric inclusions of

fresh clinopyroxenites were found in these lavas.

Carbonates associated to fine-grained volcanic sands

constitute the matrix around the volcanic fragments,

and fill the abundant vesicles. Under microscope, the

pyroxene phenocrysts are unaltered, whereas less abun-

dant olivine phenocrysts are totally replaced by

carbonates and iron oxides. Pinkish, recrystallized and

barren limestones appear at the base and at the top of

this member.

Plate 2. The supra-ophiolitic formations. 1. Turbiditic sediments (T) of Upper Cretaceous age, resting over the ophiolitic extrusives, overlain with

unconformity by a thick massive layer of Upper Paleocene-Lower Eocene conglomerates (Co), west of Kordkandi. 2. Turbiditic sediments from the Abshar

cascade, containing coarser conglomeratic lenses. 3. Turbiditic sediments in the vicinity of the Abshar cascade. Detail of conglomerate lenses containing

limestone pebbles, and angular or rounded volcanic fragments. 4. A massive pink limestone bed (Li) slided within the turbiditic breccias (Br), north of Hesar. 5.

Upper Cretaceous limestone (Li) in stratigraphic contact with turbiditic sediments, north of Hesar. 6. Angular blocks of upper Cretaceous pink limestones (Li)

slided within the turbiditic breccias (Br), north of Hesar. 7. Outcrop showing the uppermost pillow lava series (Pi), overlain by pink Upper Cretaceous

limestones and cherts (Li), west of Dizadj.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535520

2.3.4. Upper volcanic-sedimentary member

This upper member extends widely to the North and NW

till the Turkish border. It consists mainly of volcanic

breccias, turbidites and tuffs, tuffites, cherts and radiolarites,

chert-bearing pinkish limestones, and altered pillow flows

(Plate 2, Fig. 7). In the south of Zavieh and west of

Sekmanabad, these formations were tectonized and crushed

with the upper Paleocene-early Oligocene limestones

resting over them. We have found microfaunas of Late

Cretaceous age in the autochtonous sediments of Member 4

(specially in the pinkish limestones), in particular:

Globotruncana cf. stuarti, Globotruncana catarata, Globo-

truncana stuartiformis, Globotruncana arca, Globigerina

sp., heterohelix sp., Cibides sp., lagena sp., Rotalia sp.,

Radiolaria, Milialidis.

2.4. The non metamorphic, Upper Cretaceous ophiolite

of Khoy s.s

This is the ophiolite complex of Khoy, sensu stricto. It is

composed, from bottom to top (SW to NE), of serpentinized

peridotites, layered gabbros, isolated diabase dikes and a

huge volcanic pile, mainly pillow lavas. We did not found

any trace of a diabasic sheeted dike complex, contrarily to

previous descriptions (Hassanipak and Ghazi, 2000).

The complex has not suffered the effects of regional

metamorphism, although it is tectonized. All major

lithological contacts are generally tectonized. In spite of

teconics, the primary structural organization of this

ophiolite compex is relatively easy to restore (Fig. 8):

a residual mantle sequence made of foliated lherzolites,

containing small intrusive bodies of layered gabbroic

cumulates, is directly overlain by a huge volcanic submarine

pile. We describe now the various lithological units of this

ophiolitic assemblage.

2.4.1. The plutonic sequence

2.4.1.1. Serpentinized peridotites. This huge unit crops out

south of the Hesar, Tudan and Dizaj Aland villages, and

can be followed westward till the Turkish border.

Smaller serpentinite bodies crop out also near Dizaj

Aland and Balasur villages. Its southern boundary is

tectonically overthrust by Eocene limestones, themselves

overthrust by the metamorphic series of the western

metamorphic complex (Fig. 9A). Its northern boundary is

also tectonized against the volcanics, which generally

overthrust them. One of these tectonic contacts can be

observed in the vicinity of Hesar village, where the

pillow lava unit is thrust over Eocene Nummulites-

bearing conglomerates and sandstones, themselves resting

over the serpentinized peridotites (Fig. 9B). These rocks

are deeply serpentinized and show no obvious mantellic

deformation structures. Under microscope, they generally

Fig. 9. Two geological sections across the plutonic sequence of the Upper Cretaceous ophiolite of Khoy. (A) Habash section. (B) Todan section. See locations

on Fig. 2.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 521

contain clinopyroxene, orthopyroxene, residual olivine

and chromite grains. Both lherzolites and harzburgites are

represented. They are crosscut by isolated diabase dikes,

often tectonized, boudinated and transformed to

rodingites, and by listvenite dikes, made of dolomite,

quartz, serpentines and iron oxides/hydroxides.

2.4.1.2. Layered gabbros. Layered gabbros occur typically

as small intrusive bodies inside the peridotites (Figs. 8

and 9, and Plate 3, Fig. 1). They do not constitute a

continuous layer over them, as in Oman or Cyprus

ophiolites. These gabbros exhibit splendid magmatic

layering structures and cover a wide range of facies,

ranging from olivine gabbros and troctolites to pyroxene

gabbros, ferrogabbros and anorthosites. On the outcrops,

typical magmatic features such as viscous folds, graded

mineral layers or compaction faults may be currently

observed (Plate 3, Figs. 2–6). In several places they are

intruded by wherlitic sills and dikes (Plate 3, Fig. 7). Sills,

veins and dikes of gabbro pegmatites and pyroxenites

crosscut these layered cumulates, as well as numerous

isolated diabase dikes. Under microscope, these rocks

show no evidence of metamorphic recrystallization.

Typical magmatic cumulate textures are widespread. A

network of millimetric black amphibole veins, probably of

hydrothermal origin, crosscuts also the layered sequence.

Plate 3. The upper Cretaceous ophiolite of Khoy (non metamorphic). (A) The plutonic sequence. 1. Landscape showing the serpentinized ultramafic series (S),

and associated intrusive layered gabbros (GL), road from Dizadj to Qoshanlu. 2. Vertical layering in layered gabbros (road from Dizadj to Qoshanlu). 3.

Magmatic layering and viscous deformations in layered gabbros (south of Todan). 4. Dynamic flow and viscous fault in layered gabbros (south of Todan). 5.

Regular banding in layered gabbros (south of Todan). 6. Layered gabbros (south of Todan). 7. Wehrlitic intrusions with lobate coontacts (dark rocks), intrusive

in layered gabbros (north of Hesar).

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535522

2.4.2. The submarine extrusive sequence

Huge piles of submarine basalts cover wide surfaces in

the NW of the studied area. They are distributed in two main

massifs separated by a saddle of Upper Cretaceous and

Tertiary sediments and volcanics (Figs. 2 and 3).

The internal structures in the lava piles (strikes and dips

of pillow lava tubes, and of massive lava flows) indicate a

general syncline structure: pillow lava tubes dip

southward in the northern volcanic massif, and northward

or north-eastward in the southern volcanic massif. It is then

very likely that both masifs are connected beneath the

saddle, and form a single and unique volcanic sequence.

2.4.2.1. The southern volcanic massif. This massif is

tectonically thrust all along its southern and western contact

over the serpentinites and serpentinized peridotites.

We never met any evidence of a sheeted dike complex

between the lavas and the coarse-grained rocks of the

ophiolitic association. On its eastern and northern margin,

this massif is overlain by the Upper Cretaceous turbidites

described previously, generally with a tectonized contact.

Along the road from Sekman Abad to Dizadj Aland at the

top of the volcanic pile, Upper Cretaceous pelagic

limestones are interbedded with the pillow lava flows

(Plate 4, Fig. 7).

The volcanic pile is deeply dissected by narrow canyons

providing spectacular surfaces of observation along vertical

cliffs, several hundreds of meters high (Plate 4, Fig. 1).

Stratigraphic correlations across such a huge volcanic pile

are difficult to establish. We obtained our most complete

reference section in one of these canyons, along a tributary

of the Jehennem Dere valley, in the south-eastern part of the

massif (Fig. 10A and 12A), and completed it by two more

sections, respectively called here the Qezel Aqol (Fig. 10B

and 12C) and the Barajok (Fig. 10C and 12B) sections.

All three sections have a SW-NE strike (see locations on

Fig. 2).

Jehennem Dere section (Figs. 10A and 12A).

This reference section provides a complete section across

the whole volcanic pile. Its base rests tectonically over the

Paleocene conglomerates and sandstones, themselves

resting over the ophiolitic serpentinites and gabbros. Its top

is overlain by the turbiditic unit decribed previously.

The volcanics consist essentially of tubular, interconnected

basaltic pillow lavas (Plate 4, Fig. 2), dipping north-

eastward, with interbedded sheet flows, fossil lava lakes and

hyaloclastic breccias. No significant sedimentary beds were

found between the lava flows, indicating a high extrusive

rate, without significant interruptions of the volcanic

activity. Lenses of pelagic sediments were however locally

observed in several outcrops.

The total thickness of this huge volcanic pile is estimated

to be close to 1000 m. Fig. 12A gives a synthetic log,

tentatively subdivided into eight main units. At the base,

about one hundred meters of massive plagioclase-bearing

sheet flows, interbedded with some aphyric and vesicular

pillow lava flows, rest over the Paleocene conglomerates

(Unit 1). Lenses of pink pelagic limestones interbedded with

the lavas contain Campanian microfaunas, with Globotrun-

cana renzi, Globotruncana concarata, hedbergella sp.,

heterohelix sp., Radiolaria.

Unit 2 consists of about 170 m of aphyric pillow

lavas, becoming poorly phyric upwards. Pelagic

limestones in the pillow matrix gave the same micro-

faunas as in Unit 1. Some diabase dikes and sills

crosscut these lavas, and also a number of hydrothermal

veins or dikes, generally oriented N–S. At the top, the

pillows are more phyric, with plagioclase, clinopyroxene

and olivine pseudomorphs. Unit 3 consists of phyric

pillow lava flows (Plate 1, Fig. 6), rich in plagioclase

phenocryst clusters, resting over hyaloclastic breccias.

These autoclastic breccias are made of angular glass

shards and basalt fragments, in a glassy matrix (Plate 5,

Figs. 1 and 2). Unit 4 is made of aphyric pillow lava

flows forming very long tubes (Plate1, Fig. 13).

These pillows are slightly vesicular, and have a

hyaloclastic matrix cemented by pelagic limestones

with Upper Cretaceous radiolarians (Plate 4, Fig. 5).

Small sheet flows are interbedded by places. Unit 5 is

made of phyric pillow lava flows with plagioclase

(and more rarely clinopyroxene) phenocrysts, overlain

by hyaloclastic breccias. Unit 6, about 200 m thick,

consists of aphyric to poorly phyric pillow flows, with

minor interbedded sheet flows. Small diabase dikes

crosscut this unit. At the top of this unit, there is a

thick hyaloclastic breccia, whose glassy fragments have

crenulated margins and small vesicles. Unit 7 consists of

phyric pillow lava flows, and Unit 8 (270 m thick) is a

thick pile of aphyric pillows, becoming progressively

more phyric upwards. These pillows have a carbonate

matrix with hyaloclastic breccias, and are slighly

vesicular, with chlorite, calcite and quartz filling the

vesicles.

On top of the volcanic pile, a huge epiclastic breccia

made of pillow breccias, avalanche flows and mass debris

flow deposits reworks all kinds of lavas (Plate 5,

Figs. 5–7).These spectacular breccias include, at the

junction between the tributary and the Jehennem Dere,

huge slided blocks (several tens of meters long) of pink

cherty pelagic limestones, containing the following Santo-

nian-Campanian microfaunas: Globotruncana lapparenti,

Globotruncana lapparenti tricarenata, Globotruncana can-

torata.

The Jehennem Dere section is remarkable by the variety

of volcanic breccias exposed all along the section: hot

autoclastic and hyaloclastic breccias, cold breccias (Plate 5,

Fig. 3), including talus rubble breccias (Plate 5, Fig. 4),

epiclastic slope breccias including debris flows, avalanche

breccias, etc.

The two other sections done in the southern volcanic

massif Qezel Aqol and Barajok sections) are less complete.

They confirm however the regular alternation of phyric and

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 523

aphyric basaltic pillow lava flows over hundreds of meters

(Figs. 10B and C, 12B and C).

2.4.2.2. The northern volcanic massif. This massif is

located to the west of the Kordkandi village, and

provides splendid geological sections in the Goldagh

Kuh (Goldagh mountain). The lavas are tectonically

overlain by Paleocene-Eocene turbidites and massive

limestones. Many excellent outcrops are visible along the

main earth road passing through this massif (Plate 4,

Figs. 3, 4 and 9). We have chosen to present here the

reference geological section, about 700 m thick, starting

from this road and going up to the top of the Goldagh

mountain (Figs. 11 and 12D).

Plate 4. The Upper Cretaceous ophiolite of Khoy (non metamorphic). (B) Pillow lava and sheet flows of the extrusive sequence. 1. Thick pillow lava sequence

exposed along a cliff, about 300 m high (southern volcanic massif, Jehennem Dere). 2. Spectacular pillow lava tubes, Jehennem Dere. 3. Aphyric pillow flow,

exposed along the road from Kordkandi to Sadre, northern volcanic massif. 4. Pillow lava flows exposed along the road from Kordkandi to Sadre, northern

volcanic massif, showing radial columnar jointing and Globotruncana-bearing pelagic limestone matrix. 5. Aphyric pillow flow, cemented by abundant Upper

Creataceous pelagic limestones (Jehennem Dere, southern volcanic massif). The central pillow is a hollow tube, filled with sediment. 6. Plagioclase-rich phyric

pillow lava (Jehennem Dere, southern volcanic massif). 7. Pillow lava flow, overlying Upper Cretaceous pelagic limestones (road from Sekman Abad to Dizadj

Aland, southern volcanic massif). 8. Thick massive lava flow, interbedded between pillow lava flows, with columnar jointing at the bottom, possibly a fossil

lava lake (Goldagh section, northern volcanic massif). 9. Massive sheet flow with columnar jointing, interbedded between pillow flows, road from Kordkandi to

Sadre, northern volcanic massif. 10. Pillow tubes (Goldagh section). 11. Pillow tubes (Goldagh section). 12. Pillow flow (Goldagh section). 13. Long pillow

tubes (Jehennem Dere).

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535524

Goldagh section. At the base, just over the earth road,

aphyric to poorly phyric pillow lava flows alternate with

some massive lava flows (sheet flows, 3–5 m thick). Pelagic

limestones in the pillow matrix have given a Turonian-Late

Campanian age, with the following microfaunas: Globo-

truncana arca, Globotruncana gansseri, Globotruncana

falsostuarti, Globotruncana lapparenti, Globotruncana

ventricosa, Globotruncana conica, Globotruncana helve-

tica, Globotruncana fornicata, Heterohelix sp., Gavelinella

sp., Calcispherula innominata.

Unit 2 is made of phyric pillow lava flows (abundant

plagioclase, scarce clinopyroxene and olivine pseudo-

morphs). Going upwards, thick massive basaltic flows are

interbedded with the pillow flows. One of these massive

flows, about 12 m thick, exhibits a regular columnar jointing

at its base, evoking a fossil lava lake (Plate 4, Fig. 8). Its core

is rich in felsitic minerals and micropegmatites, as a result of

in situ magmatic differentiation. Unit 3 is composed of

aphyric, vesicular pillow lavas. The pelagic limestones in

the pillow matrix contain Santonian-Campanian microfau-

nas: Hedbergella sp., Radiolaria. Unit 4 is a very thick

(about 460 m), monotonous unit made of phyric pillow lava

flows made of splendid and unusually long lava tubes (Plate

4, Figs. 10–12). Thick basaltic dikes (up to 5–8 m thick)

crosscut this unit. Unit 5 is made of less phyric pillow flows

with associated autoclastic pillow breccias. Pelagic lime-

stones found in the matrix of the breccias contain

Globotruncana sp. and Radiolarians of Upper Cretaceous

age. Unit 6 is made again of phyric pillow lavas, up to the

top of the Goldagh mountain.

In summary, the submarine extrusive sequence consists

of a huge pile of interbedded pillow lava flows (about 80%

in volume), massive sheet flows or lava ponds (10%) and

hyaloclastites (10%). We refute the idea of a ‘massive lava

unit’ lying over a ‘pillow lava unit’, as proposed by

Hassanipak and Ghazi (2000): in all the studied sections,

the massive basaltic flows are interbedded within the pillow

lava pile at all levels, as is usual on modern oceanic ridges

(Juteau and Maury, 1999).

2.4.3. 40K/40Ar datings of the non metamorphic ophiolite

of Khoy

The non metamorphic ophiolite of Khoy is difficult to

date by the 40K/40Ar method, because of the absence of

amphiboles and the very low contents in potassium of the

feldspar phases. As the extrusive volcanic sequence is

already well dated by micropaleontological faunas, we tried

to date the gabbros of the plutonic sequence.

Two apparent ages were obtained on separated

plagioclases from the layered gabbros (Table 1, Fig. 13).

Fig. 10. Three geological sections in the southern volcanic massif (Upper Cretaceous ophiolite of Khoy). (A) Jehnnem section (complete section). (B) Qezel

Aqol section (partial section). (C) Barajok section (partial section). See locations on Fig. 2.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 525

The first one is at 100.7 ^ 6.0 Ma, from the feldspars of

plagioclase-rich veins in the layered gabbros close to

Qorshanlo village. These veins are parallel to the magmatic

layering, or cut it at low angle. This value may indicate the

probable cooling age of the layered gabbros. The second

value obtained is 72.6 ^ 5.0 Ma from an isotropic gabbro

vein, south of Todan village, crosscutting the layered

gabbros. These isotopic ages are compatible with the

paleontological datings obtained on the ophiolitic pillows

basalts (Turonian to Campanian, that is, 92–72 Ma).

The third value concerns the plagioclase phenocrysts of

late porphyritic diabasic dikes crosscutting the layered

gabbro sequence. It is close to the Upper Cretaceous-Lower

Paleocene boundary, at 64.9 ^ 3.8 Ma.

2.5. The Western metamorphic complex

This unit extends in the southwest part of the

mapped area (Figs. 2 and 3) till the Turkish border. It

is mainly formed of metavolcanics, greenschists, very

fine-grained amphibole schists, sericite schists, and

locally massive marble beds (more than 200 m thick

south of Hesar). The metavolcanics range from basaltic

to andesitic and trachy-andesitic compositions. No

fossils were found in it, and 40Ar–39Ar datings are

presently missing. These metamorphic rocks are

overlain with disconformity by red conglomerates,

sandstones and shales of Upper Paleocene to Lower

Eocene age.

Plate 5. The upper Cretaceous ophiolite of Khoy (non metamorphic). (C) Volcanic breccias of the extrusive sequence. 1. Hyaloclastic breccias, Jehennem Dere.

2. Hyaloclastic breccias (detail), Jehennem Dere. 3. Cold pillow lava breccia, made of angular pillow fragments in abundant limestone matrix (Jehennem

Dere). 4. Talus rubble. Dense angular pillow fragments with minor carbonate matrix (Jehennem Dere). 5. Thick sequence of slope breccias, resting over the

extrusive sequence and below the supra-ophiolitic turbidites (Jehennem Dere). 6. Slope breccias (detail). 7. Slope breccias (detail).

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535526

This unit may represent an eastern extension of the

Puturge-Bitlis metamortphic belt of eastern Turkey, where

similar metamorphic lithologies were described (Goncuoglu

and Turhan, 1984). In particular, the Mutki Group described

by these authors includes quartzites, quartz-albite-sericite

schists, albite-sericite-chlorite schists, calcschists, marbles

and metavolcanics of various lithologies, ranging in age from

Middle-Devonian to Upper triassic. These formations,

lying unconformably over pre-Devonian, highly metamor-

phosed gneisses, are interpreted as metamorphosed platform

sediments and volcanics representing the margin of a

Tethyan micro-continent, separated from the Arabian-

African shield during Triassic, eventually the southern

margin of the Anatolian micro-continent.

If this comparison is valid, the Late Cretaceous Guleman

ophiolites, thrust over the Bitlis metamorphics, and their

Maden wildflysch cover, of Late Cretaceous-Early

Paleocene age, would be the analogs of the Khoy ophiolite

and its turbiditic cover.

2.6. Post-Cretaceous sediments, volcanics and subvolcanic

intrusions

2.6.1. Post-Cretaceous sediments

These sediments are found to the south and to the north of

the studied area, generally resting with disconformity over

the Upper-Cretaceous ophiolite, or over the supra-ophiolitic

turbidites and volcanic-sedimentary series (Fig. 3).

To the south, they consist of red conglomerates,

sandstones and shales containing limestone lenses, and

capped by massive limestones containing microfossils of

Upper Paleocene to Lower Eocene age, in particular:

Assilina sp., Discocyclina sp., Operculina sp., Flesculina

pasticilata, Alveolina sp., Alveolina (Floculina) sp.,

Opertor-Bitolites sp., Roralia sp., Miliolids, shell

fragments, and algae debris.

To the north, these sediments begin by black sandstones

and shales containing reworked limestone pebbles, and are

capped also by massive limestones containing microfaunas

of Late Paleocene (Thanetian) to Late Oligocene age, in

particular: Valvulina sp., cymopolia cf. herachi, Ethelia

Broechella sp., Rotalia viennetti, heterostegina sp.,

operculina sp., Asterigena sp., Rotalia sp., Amphistegina

sp., Victoriella sp., Peneroplis sp., Miliolids, Bryozans,

Subterranophyllum thomasi, Lithothamnium sp.

2.6.2. Post-Cretaceous volcanics and magmatic intrusions

2.6.2.1. Eocene–Oligocene volcanics. These rocks are

exposed to the west of the studied area. They can locally

cover the ophiolitic extrusives. They consist of porphyric

andesitic basalts, with subordinate pyroclastic breccias and

rhyo-dacitic lavas. They are crosscut by monzodioritic--

monzonitic dikes (of Lower Miocene age, see below),

generally extremely altered by their own hydrothermal

fluids.

Fig. 11. Geological section in the northern volcanic massif (Upper Cretaceous ophiolite of Khoy). Goldagh section. See location on Fig. 2.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 527

2.6.2.2. Monzonitic to monzodioritic intrusions of Miocene

age. In the western part of the studied area, several

subvolcanic monzodioritic to monzonitic bodies, oriented

NW–SE, intrude the ophiolitic extrusive sequence, and also

the post-Cretaceous volcanic and sedimentary rocks

(see Fig. 2 and 3). On the GSI maps, these intrusions were

attributed to the Pliocene with a question mark. North of

Dizadj Aland, they intrude and deform the layering of the

supra-ophiolitic turbidites, developing a slight contact

metamorphism. In the same area, these rocks form also

NW–SE trending dikes, parallel to the main fault zones of

the area. In the southernmost part of the studied area,

they form the beautiful Arvine peaks, the highest summits of

the region (3622 m for the Big Arvine peak), well known

from the local climbers and alpinists.

These rocks show typically a porphyric texture, with

centimetric feldspar phenocrysts (orthoclase, plagioclase),

in a fine-grained groundmass. They also contain numerous

centimetric to decimetric inclusions of hornblende-rich

aggegates of amphiboles and plagioclases.40K/40Ar datings of the young monzodioritic intru-

sions. Our data give an Upper Miocene age to these sub-

volcanic monzodioritic intrusions (Table 1), which had

not been dated before. They were presumed to have a

Pliocene age (with a question mark) on the geological

map of Khoy at 1/100,000 (Radfar et al., 1993).

The K-feldspar phenocrysts from Yakmaleh intrusion

gave an apparent age of 14.0 ^ 0.3 Ma, with an identical

content in K2O by AAS and by electron microprobe

(see Table 1). The separated mineral phases (feldspar

phenocrysts and biotite) from the monzodiorite south of

Dizaj Aland village gave slightly discordant ages, of

13.8 ^ 0.4 Ma, and 11.5 ^ 0.3 Ma, respectively.

The separated feldspar phenocrysts from the Avrine

Fig. 12. Schematic logs of the submarine extrusive sequence of the Upper Cretaceous ophiolite of Khoy, according to the four geological sections shown in

Figs. 10 and 11. Sections A, B and C are in the southern volcanic massif. Section A is the only complete section, with a volcanic pile about 1000 m thick.

Section D (more than 700 m thick) is in the northern volcanic massif.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535528

village intrusion gave 12.2 ^ 0.3 Ma, and the amphibole

from the same sample gave 10.5 ^ 0.7 Ma. Moderate

excess argon in the feldspar phenocrysts in these three

intrusions may be responsible for the slight discrepancies

between mineral ages, with somewhat older ages given

by the feldspars.

2.6.3.3. Quaternary volcanic rocks. These rocks are

exposed to the north of the studied area, forming small,

discrete fluidal andesitic flows (sometimes with nice

columnar jointings), and also scoriaceous pyroclastic

deposits resting over quaternary alluvial sediments.

They extend northward out of the studied area, covering

important surfaces near the city of Maku.

3. Selected geochemical data

The complete petrological and geochemical results of

our study will be published in a separate paper. We give

here, in Figs. 14 and 15, a selection of our geochemical data,

those necessary to support the geodynamic interpretations

presented at the end of this paper. All trace element analyses

were done at Brest University by ICP-AES (analyst:

J. Cotten).

3.1. Geochemistry of the Upper Cretaceous ophiolite,

and later intrusive rocks intruding this ophiolite

3.1.1. The submarine extrusive sequence

The diagrammes of Fig. 14A and B show the multi-

element spidergrams and REE profiles of various kinds

of basalts sampled along the Jehennem Dere section

(southern volcanic massif), and along the Goldagh

section (northern volcanic massif). In both massifs, the

profiles are remarkable by their parallelism and their

regularity, except for the large lithophile elements (Rb,

Ba, Th, K), which are clearly randomly redistributed by

low temperature alteration processes, mainly in the

Jehennem Dere section. The lavas of the northern

volcanic massif are quite fresher, as observed also

under the microscope.

Both sections show T-MORB affinities for the

submarine basalts of the Upper Cretaceous ophiolite of

Khoy, without any ‘supra-subduction’ signature (no Nb

negative anomaly for instance). The slope of the REE

profiles in the southern massif is somewhat smoother,

specially for the LREE, indicating a transition to

E-MORB affinities. Anyhow, these profiles are quite

distinct from N-MORB profiles, as indicated in Fig. 14,

and suggest the presence of a hot spot component in the

mantle source. Each volcanic series shows a range of

fractionation. Phyric and aphyric basalts present more or

Fig. 13. Location of the 27 samples dated by the 40K/40Ar method in the region of Khoy. Geological contours are from Fig. 3. Nos. 1–27 refer to sample labels

of Table 1. The letters refer to the mineral separates (A ¼ Amphibole, B ¼ Biotite, M ¼ Muscovite, F ¼ Feldspar). The last number is the calculated age in

millions years.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 529

less the same range of fractionation. We observe also

that the massive or sheet flows, interbedded between

pillow flows all along both sections, exhibit the same

profiles as the pillow lavas. Our data do not confirm a

geochemical distinction between pillow and massive lava

flows, as suggested by Hassanipak and Ghazi (2000).

Isolated diabase dikes crossing the gabbro cumulates

exhibit the same T-MORB patterns (not shown in this paper)

as those of the lava flows.

3.1.2. Late isolated diabase dikes cutting through

the lava pile

Three diabase dikes crosscutting the Goldagh pillow

lavas exhibit completely different patterns (Fig. 14C),

with a strong Nb negative anomaly, and less pronounced

Zr and Ti negative anomalies. The slope of the REE

profiles is steep, with a strong enrichment in LREE.

These calk-alkaline, supra-subduction basaltic compo-

sitions indicate an important modification of the geody-

namic environment of the Khoy ophiolite before the

intrusion of the late diabase dikes, suggesting a

supra-subduction environment. We have taken these

data into account in our geodynamic scenario (see

discussion and Fig. 16).

Diabase dikes cutting through the layered gabbros do not

show such calk-alkaline patterns. On the contrary, they

exhibit exactly the same T-MORB patterns as the lava

flows. This is a good argument for associating genetically

the peridotite-gabbro assemblage with the overlying lavas.

Up to now, we did not find these calk-alkaline diabase dikes

in the peridotite-gabbro assemblage, which should logically

feed those observed in the lavas.

Fig. 14. Multi-element spider-diagrammes (left) and REE profiles (right) showing T-MORB affinities for the submarine basalts of the Upper Cretaceous

ophiolite of Khoy, (A) in the southern volcanic massif (Jehnnem Dere section), (B) in the northern volcanic massif (Goldagh section). (C) Three diabase dikes

crosscutting the Goldagh pillow lavas exhibit completely different (supra-subduction) patterns. (D) The intrusive monzodiorites of Miocene age crosscutting

the Upper Cretaceous ophiolite exhibit typical calk-alkaline profiles. Normalizations according to Sun and Mc Donough (1989).

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535530

3.1.3. Intrusions of Miocene subvolcanic monzodiorites

The intrusive monzodiorites of Miocene age crosscutting

the Upper Cretaceous ophiolite exhibit typical calk-alkaline,

supra-subduction profiles, with typical Nb, Zr and Ti

negative anomalies (Fig. 14D).

3.2. Geochemistry of the supra-ophiolitic complex

The turbidites of the supra-ophiolitic complex rework

two kinds of basaltic fragments, whose spidergrams are

given in Fig. 15A and B. Many volcanic fragments exhibit

T-MORB profiles very similar to those of the Upper

Cretaceous extrusive sequence (Fig. 14A). Other fragments

show a flat REE profile and a clear negative Nb anomaly.

These data suggest that the turbiditic basin established over

the Upper Cretaceous ophiolite at the end of Upper

Cretaceous was fed in volcanic clastic fragments by the

erosion of two sources: the first one would be the Upper

Cretaceous ophiolite itself, after being uplifted, and the

second one would be a supra-subduction source, for instance

an immature volcanic arc.

3.3. Geochemistry of some basic rocks of the Eastern

metamorphic complex

Fig. 15C and D show the spidergrams and REE profiles

of selected basic metamorphic rocks (amphibolites from m1

and m2 units, meta-basalts from m4 unit). The m1

amphibolite has an enriched REE profile, with strong

enrichment in LREE, and a spider-diagramme showing

Fig. 15. Multi-element spider-diagrammes (left) and REE profiles (right) for (A) Low-Nb volcanic fragments reworked in turbidites (Supra-ophiolitic unit), (B)

Volcanic fragments reworked in turbidites (Supra-ophiolitic unit); (C) m1 and m2 amphibolites in the Eastern metamorphic complex, (D) Meta-volcanic rocks

of m4 unit (Eastern metamorphic complex). Normalizations according to Sun and Mc Donough (1989).

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 531

moderate negative anomalies in Nb, Zr and Ti. The three

m2 amphibolites show flat REE profiles suggesting

E-MORB-type profiles, with variable spider-diagramme

profiles. The three m4 meta-basalts show a calk-alkaline

REE profile and negative Nb, Zr and Ti anomalies typical of

supra-subduction lavas.

Our interpretation is that the protoliths of the

metamorphic rocks composing the Eastern metamorphic

complex include volcanic and volcaniclastic rocks fed here

also by two main sources: a MORB-type source and a

supra-subduction source.

4. Interpretations and discussion

4.1. Existence of two ophiolitic bodies in the region of Khoy

Previous surveys have interpreted the ophiolites of the

Khoy area either as a tectonic ‘coloured melange’

(Kamineni and Mortimer, 1975), or as a unique, tectonized

and partly metamorphosed ophiolitic assemblage of Upper

Cretaceous age (Ghorashi and Arshadi, 1978; Radfar et al.,

1993; Amini et al., 1993; Hassanipak and Ghazi, 2000).

Our data show that there are clearly two distinct ophiolitic

assemblages in the Khoy area Khalatbari et al., 2003:

(1) An older, metamorphic and pre-Cretaceous ophiolitic

assemblage, consisting of huge tectonic slices of mantle

tectonites, associated with lenses and dikes of metagabbros,

amphibolites and metadiabases. The mafic rocks are

metamorphosed in the amphibolite facies, and the 40K/40Ar

ages on the metamorphic minerals have yielded Lower

Jurassic to Upper Cretaceous ages. These dismembered

ophiolite fragments are narrowly associated with the

Eastern metamorphic zone.

What is then the significance of the eastern metamorphic

complex, mainly composed of meta-ophiolites, associated

with meta-sediments (micaschists, gneisses, etc.), and

crosscut by foliated granitic plugs and veins? We think

that this unit represents a subduction complex, developed

during most of the Mesozoic times, at least from Lower

Jurassic (Upper Triassic?) to Upper Cretaceous. Subduction

began after the collision of the Central Iran Block with

Eurasia during Middle-Upper Trias (Berberian and King,

1981; Ricou, 1994), trapping and stacking the early Tethyan

oceanic lithosphere in an accretionary subduction wedge,

beneath the southwestern margin of the Central Iran Block.

We refute the idea that this metamorphic complex may

represent an infra-ophiolitic metamorphic sole, as suggested

by Hassanipak and Ghazi (2000), because: (1) we did not

observe any ‘inverse metamorphic gradient’; (2) the meta-

ophiolites and the surrounding metamorphic units were

obviously metamorphosed together, and exhibit the same

poly-metamorphic history.

(2) A younger, non metamorphic and Upper Cretaceous

ophiolitic complex (the Khoy ophiolite sensu stricto).

This ophiolite represents the last oceanic ridge activity in

the Khoy basin, obducted over the Arabian continental

plateform, or a detached fragment of it. It has the same age

as other well-known ophiolites of western Iran, Turkey and

Oman, belonging to the peri-arabic ‘ophiolitic crescent’

Fig. 16. Proposed scenario for the geodynamic evolution of the region of Khoy.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535532

(Ricou, 1971). All these ophiolites, devoid of regional

metamorphism, were obducted during Late Cretaceous over

the southern continental margin of the Neo-Tethys ocean

(Arabian-African platform), or over ‘Gondwanian’

continental fragments, detached from the Gondwana block

during Permian-Triassic times.

The Upper Cretaceous ophiolite, in the Khoy area,

exhibits many characteristics typical of slow-spreading

oceanic ridges, for instance (Juteau and Maury, 1999):

The residual mantle rocks are mainly composed of

lherzolites and clinopyroxene-rich harzburgites, pointing

to a ‘LOT-type’ residual mantle (Nicolas, 1989).

The gabbros do not constitute a thick and continuous

layer over the mantle rocks, but appear as small intrusive

bodies inside the upper mantle.

The submarine extrusives rest directly over the ultrabasic

or gabbroic rocks, without any evidence of an

intermediary sheeted dike complex of diabases.

The volcanics are often extremely phyric.

These characteristics are those found on slow-spreading

oceanic ridges, such as the Mid-Atlantic Ridge (Cannat,

1993) or the Southwest Indian Ridge. They were described

also in various Tethyan ophiolites, considered to represent

remains of slow-spreading oceanic ridges, for instance in

the Jurassic ophiolites of western Alps and Apennines

(Elter, 1971; Decandia and Elter, 1972; Lemoine, 1980;

Lagabrielle et al., 1984; Lagabrielle and Cannat, 1990).

4.2. Geodynamic evolution

The geology of the region of Khoy is so poorly

known that nobody has tried to reconstruct its geological

evolution through time. In the conclusion of their recent

paper, Hassanipak and Ghazi (2000) consider ‘two

possible scenarios’. In the first one, the Khoy ophiolite

would belong to the Upper Cretaceous Bitlis-Zagros

ophiolitic suture, including the Troodos (Cyprus), Bare-

Bassit (Syria), Hatay, Kizil Dagand Cilo (Turkey), then

Kermanshah and Neyriz in Iran, and the Semail ophiolite

in Oman. They cite the Esfandagheh massifs in this list,

but the ultramafic-mafic complexes of Sikhoran and

Sorghan are polygenetic and quite older (Sabzehi, 1974;

Ghasemi et al., 2002).

In the second scenario, the Khoy ophiolite would belong

to the inner group of Iranian ophiolites, e.g. Nain, Shahr-

Babak, Sabzevar, Tchehel Kureh and Band-e-Zeyarat, also

known as the Kahnuj ophiolite (Kananian et al., 2001),

formed in a narrow seaway opened during Mesozoic times

between the Sanandaj-Sirjan metamorphic belt and the

Central Iran Block. The authors conclude that they prefer

this second hypothesis.

The problem is that none of these scenarios can be

claimed, for two reasons: (1) the position of the Khoy

ophiolite with respect to the Sanandaj-Sirjan zone is

unknown, because this zone disappears beneath Tertiary

volcanics and sediments at the approach of lake

Urumieh; (2) the significance of the Western meta-

morphic complex of the Khoy area, and other similar

metamorphic series running along the Turkish and

Irakian borders, is obscure: is it an extension to the

north of the Sanandaj-Sirjan metamorphic complex, or

the metamorphic Arabian margin, or else the eastern

margin of a continental block detached from Africa like

the Turkish Anatolian micro-continent, or the Puturge-

Bitlis metamorphic belt?

Many uncertainties remain on these problems. Compari-

sons with eastern Turkey, where ophiolite belts or massifs

were described at four different structural levels (Michard

etal.,1985), remaindifficult.Theauthors (SengorandYilmaz,

1981; Yazgan et al., 1983; Yazgan, 1984; Sengor, 1990),

disagree about the number of oceanic basins, the number and

the vergence of subduction zones, etc.

We propose here our own scenario for the geodynamic

evolution of the Khoy area, summarized in Fig. 16. It is

based on the various geological units we have mapped, on

the datings we have got and on our geochemical data:

After opening of the Neo-Tethys ocean during Upper

Permian, the Khoy oceanic basin developed by seafloor

spreading. Subduction began north-eastward beneath the

Central Iran Block, after the collision of this micro-

continent with Eurasia (Upper Triassic).

From Upper Triassic to Upper Cretaceous, the Khoy

oceanic basin was simultaneously opening by seafloor-

spreading, and subducting along its eastern margin

beneath the Central Iran Block. During this period,

slabs of oceanic lithosphere were stacked and metamor-

phosed along the Benioff zone, including also turbiditic

clastic sediments reworking the erosion products of the

active continental margin. A metamorphic subduction

complex was progressively thickening, including ortho-

and meta-amphibolites of mixed origins (MORB-type

oceanic crust and supra-subduction arc products), slices

of oceanic lithosphere and various kinds of detritic

sediments.

The last oceanic lithosphere was produced during

Upper Cretaceous in a closing oceanic basin.

This oceanic lithosphere was never subducted and

remained unmetamorphosed, giving the Upper Cretac-

eous ophiolite complex of Khoy. Volcanoclastic

turbidites accumulated in the subduction trench, and

unmetamorphosed igneous bodies (gabbros, granites)

intruded the subduction metamorphic complex. At that

time, the last oceanic ridge segments were close to the

subduction trench, and probably oriented perpendicular

to it, as observed in present-day triple-junctions of that

kind (Chile triple-junction for instance).

Somewhat later (Lower Paleocene), the western margin

of the basin began to be underthrusted beneath the

Upper Cretaceous oceanic lithsophere, with production

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 533

of late swarms of isolated calk-alkaline diabase dikes,

crosscutting the whole ophiolite of Khoy. Just before

collision, the ophiolite of Khoy was obducted over the

western metamorphic complex, probably representing a

fragment of the Arabian-African shield.

After collision, folding and retro-thrusting of the

western metamorphic series, calk-alkaline subvolcanic

intrusion of monzodiorites were intruded during Upper

Miocene in the Khoy ophiolite and its Paleocene-

Eocene cover, leading to the present-day structural

position. These late intrusions may have been con-

temporaneous of the final closure of the Tethys oceanic

realm (Woodruff and Savin, 1989).

Acknowledgements

This study is the result of a PhD work (Khalatbari,

december 2002), carried out in the frame of a French-Iranian

cooperative programme, supported by the French Ministry of

ForeignAffairs, the Cultural Service of the French Embassy at

Tehran, and the Geological Survey of Iran (GSI). The new

geological map presented here (Figs. 2 and 3), was done by

MK after eight field campaigns, during which he was

accompanied by several of us (TJ, HE and HW).

J. C. Philippet has greatly contributed to rock and mineral

K-Ar datings in our laboratory, and M. Bohn to the

microprobe analyses (Western microprobe in Brest

Camebax SX 50). We thank M. Partoazar, Dr F. Mohtat,

Q. Asgari, Mrs. Allahmadadi, and F. Vakili, members of the

Paleontological Group of the Geological Survey of Iran who

made the numerous paleontological determinations for more

than fifty sites. We thank also Dr M. Korehi, General

Director of GSI, Dr M. Ghorashi, Dr A. Saidi and

A.R. Babakhani for their precious help, M. Radfar, Amini,

J. Behruz and A. Ajdari for fruitful discussions on the field,

the GSI technicians A. Somadian, F. Hydari and S. Hydari,

and our drivers H. Kashipasha, H. Salehi, S. Ahmadi,

A. Kalantari and Kazemi.

References

Amini, B., Radfar, J., Khalatbari, M., Behrudi, A., 1993. Geological map of

the Dizaj Quadrangle, Scale 1/100,000, Geological Survey of Iran

Asseretto, P., 1963. The Paleozoic formations in Central Elburz (Iran)

(Prelim. note). Riv. Italiana Paleontologia e Stratigrafia 69 (4),

503–543.

Asseretto, P., 1966. The Jurassic Shemshak Formation in Central Elburz

(Iran). Riv. Italiana Paleontologia e Stratigrafia 72 (4), 1133–1182.

Bellon, H., Quoc Buu, N., Chaumont, J., Philippet, J.-C., 1981.

Implantation ionique d’argon dans une cible-support. Application au

tracage isotopique de l’argon contenu dans les mineraux et les roches.

C.R. Acad. Sci. Paris, sie II 292, 977–980.

Berberian, M., King, G.C.P., 1981. Towards a paleogeography and tectonic

evolution of Iran. Can. J. Earth Sci. 18, 210–265.

Cannat, M., 1993. Implacement of mantle rocks in the sea floor at mid-

ocean ridges. J. Geophys. Res. 98, 4163–4172.

Decandia, A., Elter, P., 1972. La zona ofiolitifera del Bracco nel settore fra

Levanto e la Val Graveglia ’Apennino ligure). Mem. Soc. Geol. Italia

11, 503–530.

Elter, G., 1971. Schistes lustres et ophiolites de la zone piemontaise entre

Orco et Doire Baltee. Hypothese sur l’origine des ophiolites. Geologie

Alpine, Grenoble (France) 47, 147–169.

Emami, M.H., Sadegi, M.M., Omrani, S.J., 1993. Magmatic map of Iran,

Scale 1/1,000,000, Geological Survey of Iran

Ghasemi, H., Juteau, T., Bellon, H., Sabzehi, M., Whitechurch, H., Ricou,

L.E., 2002. The mafic-ultramafic complex of Sikhoran (central Iran): a

polygenetic ophiolite complex. C.R. Geosciences, Academie des

Sciences, Paris 334, 431–438.

Ghazi, M., Pessagno, E., Hassanipak, A., Kariminia, M., Campbell, K.,

2001. Tectonogenesis of the Khoy ophiolite, NW Iran: results from

biostratigraphic/chronostratigraphic and 40Ar/39Ar studies. Inter. Conf.

Geology of Oman, Abstract Volume, Sultan Qaboos University, Oman

Sultanate, 34–35.

Ghorashi, M., Arshadi, S., 1978. Geological map of the Khoy Quadrangle,

Scale 1/250 000, Geological Survey of Iran

Goncuoglu, M.C., Turhan, N., 1984. Geology of the Bitlis Metamorphic

Belt. In: Tekeli, O., Goncuoglu, M.C. (Eds.), Geology of the Taurus

Belt, Proceedings of the Ankara Intern. Symposium, 26–29 sept. 1983,

MTA, Ankara (Turkey), pp. 237–244.

Hassanipak, A., Ghazi, M., 2000. Petrology, geochemistry and tectonic

setting of the Khoy ophiolite, northwest Iran: implications for Tethyan

tectonics. J. Asian Earth Sci. 18, 109–121.

Juteau, T., Maury, R., 1999. The oceanic crust, from accretion to mantle

recycling, Springer-Praxis, Chichester, UK, p. 390.

Kamineni, D.C., Mortimer, C., 1975. The structural environment of Khoy

region. NW Iran Geol. Rundschau, 831–835.

Kananian, A., Juteau, T., Bellon, H., Darvishzadeh, A., Sabzehi, M.,

Whitechurch, H., Ricou, L.E., 2001. The ophiolite of kahnuj (western

Makran, southern Iran): new geological and geochronological data.

C.R. Acad. Sci., Paris, Sciences de la Terre et des Planetes 332,

543–552.

Khalatbari, M., Juteau, T., Bellon, H., Emami, H., 2003. Discovery of two

ophiolite complexes of different ages in the Khoy area (NW Iran). C.R.

Acad. Sci., Paris in press.

Khalatbari, M., 2002. Etude geologique, petro-geochimique et geochrono-

logique des ophiolites de la region de Khoy (Iran). PhD Univ. Bretagne

Occidentale, Brest, France, 252 p

Lagabrielle, Y., Polino, R., Auzende, J.M., Blanchet, R., Caby, R., Fudral,

S., Lemoine, M., Mevel, C., Ohnenstetter, M., Robert, D., Tricart, P.,

1984. Les temoins d’une tectonique intraoceanique dans le domaine

tethysien: analyse ds rapports entre les ophiolites et leurs couvertures

metasedimentaires dans la zone piedmontaise des Alpes franco-

italiennes. Ofioliti 9 (1), 67–88.

Lagabrielle, Y., Cannat, M., 1990. Alpine Jurassic ophiolites resemble the

modern central Atlantic basement. Geology 18, 319–322.

Lemoine, M., 1980. Serpentinites, gabbros and ophicalcites in the piemont-

ligurian domain of the western Alps: possible indicators of oceanic

fracture zones and associated serpentinite protrusions in the jurassic-

Cretaceous Tethys. Arch. des Sci., Geneve 33, 103–116.

Mahood, G.A., Drake, R.E., 1982. K–Ar dating young rhyolitic rocks: a

case study of the Sierra la Primavera. Mexico. Geol. Soc. Am. Bull. 93,

1232–1241.

Michard, A., Whitechurch, H., Ricou, L.E., Montigny, R., Yazgan, E.,

1985. Tauric subduction (Malatya-Elazig provinces) and its bearing on

tectonics of the Tethyan realm in Turkey. Spec. Publ. Geol. Soc.

London 17, 361–373.

Nicolas, A., 1989. Structures of Ophiolites and Dynamics of Oceanic

Lithosphere, Kluwer, Dordrecht, p. 367.

Passchier, C.W., Trouw, R.A.J., 1995. Microtectonics, Springer, Berlin,

p. 283.

Radfar, J., Amini, B., Behrudi,A., Khalatbari, M., 1993. Geological map

of the Khoy Quadrangle, Scale 1/100, 000, Geological Survey of

Iran

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535534

Ricou, L.E., 1971. Le croissant ophiolitique peri-arabe. Une ceinture de

nappes mises en place au Cretace superieur. Revue de Geographie

physique et Geologie dynamique, XIII, Paris, 327–350.

Ricou, L.E., 1994. Tethys reconstructed: plates, continental fragments and

their boundaries since 260 Ma from central America to South-eastern

Asia. Geodynamica Acta, Paris, 169–218.

Sabzehi, M., 1974. Les melanges ophiolitiques de la region

d’Esfandagheh (Iran meridional. Etude petrologique et structurale,

interpretation dans le cadre iranien. These d’Etat, University of

Grenoble, France, 205 p

Sengor, A.M.C., 1990. A new model for the late Paleozoic-Mesozoic

tectonic evolution of Iran and implications for Oman. In: Robertson,

A.A.F., Seorle, M.P. Ries, A.C. (Eds.), The Geology and Tectonics of the

Oman Region, Geological Society Special Publication N8, 49, 797–831.

Sengor, A.M.C., Yilmaz, 1981. Y. Tethyan evolution of Turkey; a plate

tectonic approach, Tectonophysics, 75, 181–241

Steiger, R.H., Jager, E., 1977. Subcommission on geochronology:

convention on the use of decay constants in geo- and cosmochronology.

Earth Planet. Sci. Lett. 36, 359–362.

Stocklin, J., 1968. Structural history and tectonics of Iran: a review. Am.

Assoc. Petroleum Geol. Bull. 52 (7), 1229–1258.

Stocklin, J., 1974. Possible ancient continental margins in Iran. In: Burke,

C.A., Drake, C.L. (Eds.), The Geology of Continental Margins,

Springer, New York, pp. 873–887.

Stocklin, J., Ruttner, A., Nabavi, M., 1964. New data on the lower

Paleozoic and pre-Cambrian of North Iran. Iran Geol. Survey Rept

N81 29 p.

Stocklin, J., Nabavi, M., Samimi, M., 1965. Geology and mineral

resources of the Soltanieh Mountains (northwest Iran). Iran Geol.

Survey Rept 2, 44.

Sun, S.S., McDonough, J.D., 1989. Chemical and isotopic systematics of

oceanic basalts: implications for mantle composition and process. Geol.

Soc. Spec. Paper 42, 313–345.

Villa, I.M., 1998. Isotopic closure. Terra Nova 10, 42–47.

Woodruff F., Savin S.M., 1989. Miocene deep water oceanography.

Paleooceanography 4, 87–140.

Yazgan, E., 1984. Geodynamic evolution of the Eastern Taurus region. In:

Tekeli, O., Goncuoglu, M.C. (Eds.), Geology of the Taurus Belt, MTA,

Ankara, pp. 199–208.

Yazgan, E., Michard, A., Whitechurch, H., Montigny, R., 1983. Le taurus

de Malatya (Turquie orientale), element de la suture sud-tethysienne.

Bull. Soc. Geol. France 1, 59–69.

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 535