Geological section through the Hatay ophiolite along the Mediterranean Coast, Southern Turkey

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Reference

Geological section through the Hatay ophiolite along the Mediterranean Coast, Southern Turkey

DELALOYE, Michel, et al.

Abstract

Une coupe géologique de l'ophiolite du Kizil Dağ est décrite entre Çevlik et Uluçinar (Arsus) sur la côte méditerranéenne. Des informations succintes sont également données sur la pétrographie et la géochimie des roches rencontrées. Le complexe filonien présente de magnifiques intrusions qui illustrent l'expansion d'un fond océanique.

DELALOYE, Michel, et al . Geological section through the Hatay ophiolite along the Mediterranean Coast, Southern Turkey. Ofioliti , 1980, vol. 5, no. 2/3, p. 205-215

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Ofioliti, 1980, 5(2/3), 205-216

GEOLOGICAL SECTION THROUGH THE HATAY OPHIOLITE ALONG THE MEDITERRANEAN COAST, SOUTH- t ERN TURKEY

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^H.0,000, Vuagnat M.⁰ and Wagner J.-J.⁰

~ersity

of Geneva, Mineralogy Department,

Genev~,

Switzerland :

00Ege University, MUh. Bil. Fak., Yerbilimleri BolUmU, Bornova - Izmir, Turkey.

0000n leave from MTA EnstitUsU, Ankara, Turkey

K€y words: ophiolite, sheeted complex, petrology, geochemistry. Hatay, Turkey.

Summary

An entire geological section through the K1z1l Dag ophiolite along the Mediter- ranean seashore between ^~evlik and ^Ulu~inar (Arsus) is described. Short petrograph- ical and geochemical descriptions of the main rock types are given. The sheeted dyke complex offers very good examples of intrusions which illustrate a sea-floor spreading site.

Resume

Une coupe geologique de l 'ophiolite du K1z1l Dag est decrite entre ^~evlik et

Ulu~inar (Arsus) sur la cote mediterraneenne. Des informations succintes sont ega- lement donnees sur la petragraphie et la geochimie des roches rencontrees. Le com- plexe filonien presente de magnifiques intrusions qui illustrent 1 'expansion d'un

fond oceanique. ·

Introduction

The Hatay ophiolite, also known as the K1z1l Dag ophiolite, is situated in the southern part of the Amanos range near the border between Turkey and Syria. The major ophiol itic body occurs in Turkey,between the cities of Iskenderun ·(Alexan- drette) and Antakya (Antioch).

It is oriented SW-NE and represents a link between the Troodos of Cyprus and the various ophiolitic massifs outcropping in SE Turkey, Iran and as far as Oman, in the "Croissant ophiolitique peri-arabe" of Ricou (1971).

The Hatay ophiolite s.s. has a length of 45 km and a maximum width of 25 km.

The quality of the outcrops is generally good though much is forest-covered. Many small rivers cut very deeply into the massif, some even down to the supposed base of the thrust sheet (Aslaner, 1973). Good outcrops appear in these canyons, but are of difficult access.

Dubertret (1955) provided the first complete geological description of the area.

He was followed by Vuagnat et al. (1967), Cogulu (1973, 1974), Aslaner (1973) and Parrot (1973). Further studies on the massif using various tools such as palaeo- magnetism, geochemistry and geochronolpgy were carried out by ^C~gulu et al (1976), Delaloye et al. (1977, 1979a, b) and Wagner et al. (1976). One of the most impress- ive features of the Hatay ophiolite is probably the extraordinarily well-exposed outcrop along 25 km of sea-shore between ~evlik in the south and Arsus (Ulu~inar)

in the north. It is very probable that a major fault oriented approximately N-S is responsible of the straight shore line where a continuous well exposed outcrop is remarkably unweathered owing to constant erosion by the sea.

Vuagnat and Cogulu (1967) were the first to recognize a sheeted dyke complex in- truded into a gabbroic layer in the southern part of this section. Later on, Parrot (1973) described a profile along the same southern section. The aim of the present paper is to describe the entire section from cevlik to Arsus and to give the major characteristics of the encountered rocks. Particular points of interest will be emphasized especially in the sheeted dyke complex.

General description of the section

Field work in the Hatay area was carried out between 1975 and 1979, during which the complete coastal section was examined. Except for the pillow lavas found in the NE part of the massif, all other members of the ophiolitic suite are present in the coastal section (Fig. 1) .

They are from top to the bottom:

- sheeted dyke complex

- cumulate zone: gabbros and ultramafics - tectonites

From south to north the section consists of:

a) a sheeted dyke complex with gabbroic screens (5 km) b) gabbros (3 km)

c) ultramafics forming the heart of the massif (15 km)

d) gabbros associated with a small sheeted dyke complex at the northern end of the section.

The contacts between the different members of the ophiolite are of tectonic cha- racter (Parrot, 1973 and 'Tinkler et al . , 1980).

At ^~evlik, the ophiolite is covered unconformably by Miocene limestone dipping south (Dubertret, 1955). The first ophiolitic outcrop is 2 km long and consists of a diabasic (doleritic) sheeted dyke complex with gabbro screens. The screens are sometimes rather thick - 100 meters and more - and cumulitic textures can be observ- ed. Outcrops are not continuous here because of small landslides. Minor faults are present and responsible for the relative tilting of the various blocks.

The sheeted dyke complex continues for a further 3 km. A fine scale study shows that different types of dykes are present and some examples are described below.

Between Kale Dere and ^~anakl1 Dere there is an important outcrop of gabbros with many dykes. The gabbro banding is subvertical and oriented N 80° £. This part is probably a transition zone between the gabbro and the dyke complex. From ^~anaka11 Dere up to Ayval1 Cay, a distance of 2 km, the cumulate gabbros outcrop continuous- ly. Between Ayval1 ^~ay and Peri Dere, a zone of peridotites and dunites with frequent pegmatitic gabbro dykes is observed. This part of the section is interpreted as a transition zone between mafics and ultramafics. It is made up mainly of intensely

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From Peri Dere to a point just south of Ak yay, the peridotitic zone is more ho- mogeneous although doleritic and rodingitic dykes are present. From the river Ak yay and to the north of the lighthouse of Domuzburnu, there is a 11 km long coastal outcrop with very few interruptions. An important NS fault runs parallel to the coast 100 to 300 m inland. This normal fault with a downthrow to the west displaces the country rocks vertically and the coast is made of meter size blocks of serpen- tinized peridotite forming a large terrace 10 meters above sea-level.

North of the lighthouse of Domuzburnu, a tectonic contact is visible between ser- pentinized peridotites and gabbros. Toward the north, these gabbros are increasingly injected by diabase dykes until a small sheeted complex is developed. The dykes are oriented N 45° E_with a dip of 30°SE. This part of the section represents a good example of the relationships between gabbros and dykes as may occur at the top of magma chanbers at mid-ocean ridges.

·As in the south, Miocene limestones unconformably covered the dyke complex. The

limeston~s and the ophiolitic rocks were subsequently tilted 30° N.

Further ^nort~, outside the section in Fig. l, in direction of Arsus, important ultramafic bodies are again encountered. This is another indication of the tectonic character of the contacts between the main members of the ophiolite (dyke complex, cumulates, tectonites). On the other hand contacts between dolerites and gabbro screens are primary.

The tectonic history of the Hatay massif seems complex but the following sequen- ce of events has been recognized by Tinkler et al. (1980):

a) Post-Campanian to Pre-Maestrichtian emplacement;

b) Maestrichtian to Pre-Miocene folding and probable faulting;

c) Post-Maestrichtian to Pre-Lutetian phases of faulting;

d) Post-Miocene gentle folding;

e) Normal Post-Pliocene faulting;

f) Recent beach raising.

Examples in the sheeted dyke complex

Outcrops of the sheeted dyke complex of the Hatay are almost completely unweathered because of its situation along the sea . This allows a detailed structural study of the dykes, particularly the relationships among the dykes and between the dykes and the host-rock (normally a gabbro).

A statistical study of the position and frequency of the chilled margins did not show clearly any asymmetry of the type found by Kidd et al. (1974) in the Troodos ophiolite. Figure 3 shows clearly the intrusive relationships among the dykes.

The first example illustrates dyke injection with the sheeted complex where dykes no 2, 3 and 4 are encased while dyke no 5 with dark and strongly transformed miner- als represents a final stage of intrusion . The zone no l corresponds to the host- rock; it has the typical texture of a microgabbro. The second example is very cormnon in_the Hatay sheeted complex. The gabbro (l) has been intruded while still hot by the coarse _ diabase dykes (2) which explains the ab sence of chilled ma1·gins. The dia- bases, after cooling, have been _ injected by finer grained diabasic dykes (4) which exhibit well developed chilled edges.

The thirg example is more complex. It shows the various shapes-often contorted-do- leritic dykes can take as they intrude a host-rock . This host-rock can be either a dolerite or a gabbro. Here again the lack of chilled margin between two dykes (2-2) indicate that the older one was still hot when the younger one was intruded.

Fig. 2 - a) The sea-shore showing on the foreground the sediments covering the o- phiol ite and gabbros and sheeted dyke complex in the background.

b) Close view of the sheeted dyke complex showing chilled margins.

c) The transition zone between mafic and ultramafic members.

d) Zoned ultramafic outcrop showing a rodingitic dyke.

210

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212

General remarks can be made about this sheeted dyke complex:

a) The size of the dykes is metric except for very late and small picritic veins related to the end of the expansion process. ·

It seems that the K1z1l Dag dykes are somewhat thinner than those of the Troodos sheeted complex where dykes thicker than 2 meters are frequently found.

b) The complex history of the sheeted dyke complex can be summarized by saying that at least two important phases are visible: the first one is the intrusion of coarse diabases into a still hot gabbroic crust and the second one is an injec- tion of the same magma in a cooler environment (chilled margins) consolidating as a finer grained diabase.

c) Very frequently dark coloured basaltic veinlets and dykes represents the latest stage of intrusion.

Petrological outline of the rocks

Th~ sheeted dyke complex is composed of diabases which range from fine to medium- grained texture. The plagioclase is more or less albitized; other minerals include clinopyroxene, green hornblende, chlorite and accessory minerals. These rocks are metamorphosed in the zeolite to greenschist facies.

The gabbros often show cumulate structures. In the upper level they consist of basic plagiocalse (bytownite to anorthite), augite, actinolite or hornblende, chlor- ite and accessory minerals. Olivine is present in the lower levels. The base of the cumulate is characterized by the presence of feldspathic peridotites and olivine- rich gabbros.

The ultramafic unit of the ophiolite is composed in the cumulate zone by wehrl- ites, lherzolites, pyroxenites and feldspathic peridotites and in the tectonite zone by harzburgites and dunites. All these rocks show the typical mineral associat- ions. Chromite septa are common in this zone. The serpentinization is moderatly developed,

Compared with other basic-ultrabasic massifs, plagiogranites are less well deve- loped in the Hatay. They occur mainly as veinlets in the lower part of the sheeted complex but are also found in the gabbros. The main minerals are quartz, plagio- clase, biotite and hornblende.

Rock chemistry

From a detailed chemical study of all the various rocks of the Hatay ophiolite (major and trace elements including REE) we have summarized in table 1 the variat- ion (in weight percent) in major element content of the three most important groups of rocks. Typical compositions are plotted on various diagrams (Fig. 4) taken from Coleman (1977). It is evident that the values plotted for the Hatay agree fairly well with data from similar ophiolitic massifs.

The REE concentrations in pillow lavas, diabasic dykes (unpublished data) and from gabbros of different structures (Delaloye et al., 1979) show the same general pattern ^~ith a depletion in the Light REE; the pillow lavas being the richest in REE content. This REE distribution indicates that these rocks were derived from a uniform LREE depleted asthenosphere source (Shilling, 1975) at a spreading ridge.

The REE pattern cannot be used to indicate the particular tectonic setting of the ridge. The data do not permit";to specify the environment in which the Hatay ophiol- ite was formed. Beccaluva et al. (1979) in comparing island arc tholeiite and ocean floor tholeiite claim that the Ti/Cr vs. Ni diagram distinguishes between the two.

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214

This method has also been applied to various ophiolites and the results are used for comparison ^{( ~ ee} fig, 5). It would not favour an island arc setting for the Hatay.

Diabase Gabbro Ultra ma fites Si02 47.0 - 57.0 42.0 - 49 .0 36.0 - 40.0 Al 0 2 3 14.0 - 18.0 9.0 - 16.0 0.5 - l. 7 Ti02 0.5 - 0.9 O. l - l .0 0.0 - 0.2

FeO 4.2 - 5.3 4.0 - 6.0 2.4 - 4.7

Fe203 2.8 - 5.4 0.3 - 5.2 5.0 - 7.4 Cao 5.2 - 9.5 10.0 - 18.0 0.8 - l. 2 MgO 7.4 -10.0 5.0 - 18.0 38.0 - 43.0 Na20 1.3 - 6,5 0.3 - 5.4 0.2 - 0.7

K20 0.2 - 0.7 0.0 - 0.3 tr

MnO 0. l - 0.2 O. l - 0. 2 0. l - 0.2

P205 0. l - 0.2 O. l - 0.7 tr

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2.5 - 5.4 1.2 - 6.2 4.0 - 13.0 CONCLUSIONS

The geological section described along the sea-shore represents the most impress- ive features of the Hatay ophiolite. Except for pillow lavas and radiolarites, all members of a typical ophiolite are present. Good outcrops of pi llow lavas occur in the NE part of the Hatay (for example in Deliler Mahalesi, and KomUr ^{~ukuru) .}

The very fresh outcrops, specially in the sheeted complex show various and de- monstrative examples of expansion. Comparisons can be made between the K1z1l Dag and other ophiolites like Troodos or Oman. Hatay is probably more tectonized, more dismembered but easier to understand owing to its smaller size. Formation and em- placement ages are also certainly different. The Hatay ophiolite belongs definitely to ·the "Croissant P@ri-arabe".

ACKNOWLEDGEMENTS

_Financial support have been granted by the Swiss National Science Foundation to conduct researches in the Hatay Ophiolite. The Geological Survey of Turkey (M.T.A.) gave various field assistances. We are indebted to Dr. Ch. Tinkler for his help in structural geology . We are thankful to Dr. E. yogulu (Technical University, Istan- bul) and H. Sarp (Museum of Natural History, Geneva) for useful discussion on the field. Dr. H. de Souza is kindly acknowl~dged for reviewing the manuscript.

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Beccaluva, L., Ohnenstetter, D. and Ohnenstetter, M., 1979. Geochemical discrimin- ation between ocean-floor and island-arc tholeiites: application to some ophiol- ites. Can. J. Earth Sci. 16: 1874-1882.

Cogulu, E., 1973. New data on the petrology of Kizil Dagh massif (Hatay-Turkey).

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Delaloye,M., Piskin,

0.,

Voldet, P., Vuagnat, M. and Wagner, J.J., 1979. Rare Earth Element Concentrations in Mafics from the K1z1l Dag ophiolite (Hatay, Turkey) . . Bull. suisse Min. Petrogr., 59: 67-73.

Delaloye, M., de Souza, H., Wagner, J.J. and Hedley, I., 1980. Isotopic ages of o- phiolites from the Eastern Mediterranean. Int. Symp. on Ophiolites, Nicosia, Cyprus, April 1979. In press.

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Kidd, R.G.W. and Cann, J.R., 1974. Chilling statistics indicate an ocean floor spreading origin for the Troodos Complex, Cyprus. Earth Planet. Sci. Letters, 24:

151-155.

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Schilling, J.-C., 1975. Rare-Earth variations across "normal segment" of the Rey- kjanes Ridge 60°-35°N, Mid-Atlantic Ridge, 29° S, and East-Pacific Rise, 2°-19° S, and evidence on the composition of the underlying low velocity layer. J. Geophys.

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