New geological, geochronological and geochemical investigations on the Khoy ophiolites and related formations, NW Iran

Journal of Asian Earth Sciences 23 (2004) 507–535 www.elsevier.com/locate/jseaes

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 a

b

Geological Survey of Iran, Tehran, Iran IUEM and UMR6538, Domaines oce´aniques, Universite´ de Bretagne Occidentale, 29280 Plouzane´ cedex, France c EOST, 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 apparent 40 Kn– 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 (S˘engo¨r 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 * Corresponding author. Address: Domaine d’Orio, rue Orio, Hendaye 64700, France. Tel.: þ 33-5-59-48-16-34. E-mail address: [email protected] (T. Juteau). 1367-9120/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2003.07.005

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

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

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 two 40 Ar – 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

M. Khalatbari-Jafari et al. / Journal of Asian Earth Sciences 23 (2004) 507–535 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. 509

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

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.

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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 amphibolefree, 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.

511

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 Sto¨cklin (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 Sto¨cklin 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.

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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 (Sto¨cklin, 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 (Sto¨cklin 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 ‘Gondwanian 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

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

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 olivine 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.

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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.

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 (fishlike 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

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515

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

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 amphibole 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 metaophiolite 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

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

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 finegrained 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-amphibolites 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 pyroxene 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 micaschists 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 recrystallized 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).

Table 1 New 40K/40Ar datings in the region of Khoy Iran– Khoy Reference Sample to Fig. 13

Location

Rock type

Dated fraction

40

40

Average age Age ^ error ^ error (Ma) (Ma)

K2O (wt%)

64.9 ^ 3.8 72.6 ^ 5.0 100.7 ^ 6.0

0.13 0.046 0.25

2.77 1.10 8.34

35.0 19.5 31.6

5881 5891 5890

448260 5000 448250 3000 448200 1500

388340 0000 388350 1000 388350 4000

82.4 ^ 4.6 77.9 ^ 4.6 112.9 ^ 8.6 116.5 ^ 6.0 134.7 ^ 7.1 155.6 ^ 11.9 160.8 ^ 12.7 160.0 ^ 12.4 160.7 ^ 12.9 108.4 ^ 6.0

0.106 0.106 0.175 0.215 0.245 0.165 0.052 0.052 0.057 0.45

2.88 2.72 6.57 8.34 11.05 8.64 2.82 2.81 3.09 16.2

42.5 31.1 69.2 67.2 53.0 69.8 40.4 47.4 35.9 42.7

5894 6000 5632 5664 5665 5630 5631 5655 5633 5322

448380 2000

388520 3000

448440 3000 448360 2000 448350 2500 448440 4500 448370 3000

388490 1000 388510 4000 388490 3000 388460 5000 388520 1000

448370 1000 448550 2500

388510 3000 388360 0000

154.9 ^ 11.8 192.3 ^ 2.9 197.3 ^ 10.1

0.17 0.492 0.492

8.86 32.2 33.1

66.9 91.0 90.8

5676 5646 5656

448540 5000

388370 2000

67.5 ^ 1.6 7.06 75.3 ^ 1.8 10.37 93.5 ^ 1.5 8.9 69.4 ^ 1.6 6.56 81.2 ^ 1.2 7.07 102.3 ^ 5.3 0.27 103.9 ^ 5.4 0.27 100.1 ^ 5.4 0.27 115.6 ^ 3.7 0.075 121.2 ^ 6.2 0.46 151.0 ^ 11.5 0.195 146.3 ^ 3.4 8.03 182.3 ^ 4.3 0.48 196.3 ^ 10.7 0.48 106.9 ^ 2.5 1.06 160.5 ^ 3.7 8.7 181.8 ^ 4.2 9.78

156.6 257.0 275.3 149.6 189.2 9.16 9.31 8.96 2.89 18.6 9.90 394.4 29.7 32.1 37.6 470.7 603.2

76.8 73.9 78.4 82.6 92.5 71.8 67.5 49.2 33.8 75.5 63.5 93.7 74.8 75.7 81.5 84.6 93.3

5990 5874 5303 5991 5644 5645 5675 5323 5678 5648 5663 5892 5982 5998 5993 5981 5865

4484300 4500 448460 3500 448440 5000 448450 2000 448360 1000 448460 1500

388500 5500 388510 3000 388480 2000 388390 1500 388530 5000 388530 3000

448520 4500 448530 5000 438540 5000 438550 0000

388380 1000 388370 5000 388410 0500 388420 4000

North Aghbash Weakly deformed gabbro

Amphibole

5 6 7 8 9

99-KH-242 99-KH-134 00-3-KH14 00-3-KH9 99-KH102

West Ravand North Aghbash South Aghbash East Ajidgah North Aghbash

Metagabbro Metagabbro Metagabbro Metagabbro Metagabbro

Amphibole Amphibole Brown amphibole Amphibole Amphibole

10 11

99-KH145 N.Aghbash 99-KH359a North Khoy

Metagabbro Amphibole pegmatitic gabbro

Amphibole Feldspar

12

99-KH359 99-KH291b North Khoy

Amphibole pegmatitic gabbro

Amphibole Amphibole

Eastern Metamorphic complex 13 00-4KH78 Qorol-Ajai 14 00-4KH69 Qorol-Ajai 15 99-KH357 Ajidgah 16 99-KH314 North Dizaj 17 00-3KH7 Ajidgah 18 99-KH-358 Ajidgah

Gneissic granite Gneissic dike Quartz, feldspar, muscovite vein Micaschist Micaschist Amphibolite

Muscovite and biotite Muscovite Muscovite Muscovite Muscovite Amphibole 102.1 ^ 5.4

19 20 21 22

99-KH353 99-KH191 00-4KH71 01-4KH81

Ghekh yashar Ghekh yashar Hydarabade Hydarabade

Fine-grained amphibolite Amphibolite Micaschist Fine-grained amphibolite

Plagioclase Amphibole Amphibole Muscovite and biotite Amphibole 189.3 ^ 10.7

23 24

01-4KH76 01-4KH97

Hydarabade Hydarabade

Gneiss Quartz and muscovite vein

Feldspar Muscovite Muscovite

80.2 ^ 4.6

160.4 ^ 12.7

194.8 ^ 10.1

448550 0000 388430 4000 448300 5000 388420 0000 (continued on next page)

517

Meta-ophiolitic unit 4 99-KH92

ArR (%) Analysis Longitude Latitude number

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Upper Cretaceous non metamorphic Khoy ophiolite 1 00-3KH56 S.Todan Porphyric diabase dike in gabbro Plagioclase 2 00-3KH190 S.Todan Isotropic gabbro Plagioclase 3 01-2KH211 Qorshanlo Plagioclase vein in gabbro Plagioclase

ArR (1027 cm3 g21)

388400 0000

388530 3000

448230 0000

448150 4500 Monzodiorite

Monzodiorite

27

01-4KH117 South Dizaj Alande 01-4KH85 Yakmaleh 26

See Fig. 13 for location of samples. Isotopic analyses have been performed in the UMR 6538 laboratory in Brest. Potassium contents used for age calculations were measured by atomic absorption spectrometry on mineral separates (column AAS) and were also checked by electron-microprobe analyses (column MP). See text for discussion. Argon isotopic ratios and concentrations are measured by mass spectrometry using the spike method described in Bellon et al. (1981). Ages are calculated using the constants proposed by Steiger and Ja¨ger (1977). Errors are quoted at one sigma level following Mahood and Drake (1982). 40 ArR, subscript R means radiogenic argon; (%) 40ArR refers to radiogenic argon 40/total argon 40 (atmospheric and radiogenic). Average age in Ma is given for duplicate analyses.

448580 1500

5983 5992 5938 5866 5893 26.8 51.7 60.1 54.6 78.2 1.37 4.24 8.52 2.42 6.68 Upper Miocene monzodioritic intrusions 25 01-5KH116 Avrine

Monzodiorite

Amphibole Feldspar Biotite Feldspar Feldspar

10.5 ^ 0.7 12.2 ^ 0.3 11.5 ^ 0.3 13.8 ^ 0.4 14.0 ^ 0.3

4.64 16.8 31.7 10.77 30.2

40

ArR (1027 cm3 g21)

40

K2 O (wt%) Average age Age ^ error ^ error (Ma) (Ma) Dated fraction Rock type Location Reference Sample to Fig. 13

Iran –Khoy

Table 1 (continued)

448340 2500

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518

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 (Maestrichtian); 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) ankaramitic volcanic breccias, (4) upper volcanic-sedimentary member. The age of this unit is well constrained by biostratigraphic 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 Maestrichtian 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, or

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

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, containing 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-Maestruchtian in one sample), with the following fossils: Globotruncana arca, Globotruncana Lapparenti, Globotruncana bulloides, Globotruncana Lapparenti-Tricarinata, 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: Globotruncana 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

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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.

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 abundant 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.

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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, Globotruncana 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

521

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 Nummulitesbearing 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.

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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).

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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 northeastward, 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

523

pillow lava flows, rest over the Paleocene conglomerates (Unit 1). Lenses of pink pelagic limestones interbedded with the lavas contain Campanian microfaunas, with Globotruncana 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 microfaunas 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 Santonian-Campanian microfaunas: Globotruncana lapparenti, Globotruncana lapparenti tricarenata, Globotruncana cantorata. 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

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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).

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).

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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.

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: Globotruncana arca, Globotruncana gansseri, Globotruncana falsostuarti, Globotruncana lapparenti, Globotruncana ventricosa, Globotruncana conica, Globotruncana helvetica, Globotruncana fornicata, Heterohelix sp., Gavelinella sp., Calcispherula innominata. Unit 2 is made of phyric pillow lava flows (abundant plagioclase, scarce clinopyroxene and olivine pseudomorphs). 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 microfaunas: 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 limestones 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).

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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).

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.

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

This unit may represent an eastern extension of the Pu¨tu¨rge-Bitlis metamortphic belt of eastern Turkey, where similar metamorphic lithologies were described (Go¨ncuoglu 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 metamorphosed gneisses, are interpreted as metamorphosed platform sediments and volcanics representing the margin of a Tethyan micro-continent, separated from the ArabianAfrican 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.

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. Post-Cretaceous sediments, volcanics and subvolcanic 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.

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).

2.6.2. Post-Cretaceous volcanics and magmatic intrusions

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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.

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. 40 40 K/ Ar datings of the young monzodioritic intrusions. Our data give an Upper Miocene age to these subvolcanic 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

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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.

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 multielement 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

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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).

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 compositions indicate an important modification of the geodynamic 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.

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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).

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).

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.

3.2. 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

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

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

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 metaophiolites 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’

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(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), BareBassit (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, ShahrBabak, 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

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unknown, because this zone disappears beneath Tertiary volcanics and sediments at the approach of lake Urumieh; (2) the significance of the Western metamorphic 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 Pu¨tu¨rgeBitlis metamorphic belt? Many uncertainties remain on these problems. Comparisons with eastern Turkey, where ophiolite belts or massifs were described at four different structural levels (Michard et al., 1985),remain difficult. The authors (S˘engo¨rand Yilmaz, 1981; Yazgan et al., 1983; Yazgan, 1984; Sengo¨r, 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 microcontinent with Eurasia (Upper Triassic). From Upper Triassic to Upper Cretaceous, the Khoy oceanic basin was simultaneously opening by seafloorspreading, and subducting along its eastern margin beneath the Central Iran Block. During this period, slabs of oceanic lithosphere were stacked and metamorphosed 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 orthoand 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 Cretaceous 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

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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 PaleoceneEocene cover, leading to the present-day structural position. These late intrusions may have been contemporaneous 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 Foreign Affairs, 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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