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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: [email protected] (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
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riet
al.
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urn
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arth
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50
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53
55
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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
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fari
eta
l./
Jou
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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.
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