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K-Ar ages from the Kizil Dagh ophiolitic complex (Hatay, Turkey) and their interpretation
DELALOYE, Michel, VUAGNAT, Marc, WAGNER, Jean-Jacques
Abstract
Dans leur tentative de dater par la méthode géochronométrique K-Ar les ophiolites du Hatay, les auteurs ont reconnu la possibilité de réponses multiples. D'une part : l'âge vrai ou génétique, l'âge de la mise en place des ophiolites sur le plancher océanique, compte tenu du métamorphisme faible propre à cette situation; d'autre part l'âge tectonique ou âge de mise en place, en compagnie des formations sédimentaires, dans la position géologique actuelle. Nos résultats montrent que les âges mesurés sur les pillow lavas correspondent très probablement a l'âge tectonique tandis que les âges obtenus sur les diabases du complexe filonien sont très voisins de l'âge vrai. Les recherches en cours portent plus particulièrement sur les gabbros - roches totales et minéraux - pour tenter d'apporter un début de solution aux problèmes soulevés.
DELALOYE, Michel, VUAGNAT, Marc, WAGNER, Jean-Jacques. K-Ar ages from the Kizil Dagh ophiolitic complex (Hatay, Turkey) and their interpretation. In: Biju-Duval, Bernard & Montadert, L. Structural history of the Mediterranean basins = Histoire structurale des bassins méditerranéens . Paris : Editions Technip, 1977. p. 73-77
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K-AR AGES
BDITIONS TECHNIP, PARIS 1977, pp. 73·78
FROM THE KIZIL DAGH OPHIOLITIC COMPLEX (HATAY, TURKEY)
AND THEIR INTERPRETATION
M.l o: LALOYE, M. VUAGNAT and .J.-.J. WAGNER 111
RESUME
Dans leur tentative de dater par la me- thode geochronometrique K-Ar les ophiolites du Hatay, les auteurs ont reconnu la possi- bilite de reponses multiples. D'une part : l'age vrai ou genetique, l'age de la mise en place des ophiolites sur le plancher ocea- nique, compte tenu du metamorphisme faible propre
a
cette situation; d'autre part l'age tectonique OU age de mise en place, en com- pag:nie des formations sedimentaires, dans la position geologique actuelle. Nos resultats montrent que les ages mesures sur les pillowlavas correspondent tres probablement
a
l'age tectonique tandis que les ages obtenus sur les diabases du complexe f ilonien sont tres voisins de l'age vrai. Les recherches en cours portent plus particulierement sur les gabbros - roches totales et mineraux - pour tenter d'apporter un debut de solution aux problemes souleves.1. Scope of this paper
Isotopic age dating of ophiolites, parti- cularly by the potassium - argon method leads to several problems of interpretation. One is the problem to ascertain the cooling age of these rocks in the accreting ocean ridge, the other is to evaluate the effect of metamor-
phic overprints often related to processes of obduction and subduction along destruc- tive plate margins.
The aim of this paper is to present geochronological data on rocks of the Kizil Dagh ophiolite in a attempt to unravel the geological history of the Eastern Mediter- ranean region (Vuagnat et al. 1967). The significance of the radiometric ages is also critically discussed.
2. Introduction
In the Eastern Mediterranean, several ophiolitic complexes have been studied du- ring the last decade and interpreted in terms of plate tectonics. From west to east a long chain of massifs, for example Vourinos (Greece), Troodos (Cyprus), Kizil Dagh
(Hatay) are regarded as fragments of the oceanic lithosphere but the original lo- cation and age of this sequence is still a matter of controversy. For example the Troodos was considered by Gass (1968) as a slice of oceanic crust and mantle formed in an old Tethyan ridge whilst Miyashiro (1973) interpreted the same massif as part of an island arc. Dewey (1973) compares the Troodos with other western Pacific features and reaches the conclusion that this massif was formed in a marginal or back arc basin.
(I) Department of Mineralogy, The University, CH-1211 Geneva 4, Switzerland
K-AR AGES FROM THE KIZIL DAGH OPHIOLITES Similar arguments could be applied to the Kizil Dagh.
It should also be mentioned that Lapierre and Parrot (1972) compared the Paphos ophio- lite (near Troodos) and the Baer-Bassit ophiolite (located in Syria to the south of Kizil Dagh complex) and found strong simi- larities between them.
It is evident that geochronology alone cannot decide between these various hypo- theses. Several types of evidence should be considered in particular the geochemistry
(Pearce, 1975). This will be the subject of a forthcoming article. Here we will only show how our geochronological data fit within the stratigraphic evidence and complement it.
3. Stratigraphic evidence
Dubertret (1953) has described limestones of Vindobonian age (15 m.y.) which cover the Sheeted Complex of Kizil Dagh at Djebel Moussa. The se.dimentary sequence begins with
a basal conglomerate containing a large amount of ophiolitic pebbles. On the north side of the massif near Ulu~inar (formerly named Arsus), he has also described
Vindobonian limestones and conglomerates bearing ophiolitic material. In the middle part of the Kizil Dagh range near U~oluk, Maestrichtian limestone transgress over pil-
low lavas. In the vicinity of Ulu~inar Dubertret has also described Maestrichtian limestone dipping under the basic-ultrabasic sequence. From these observations Dubertret interpreted the Kizil Dagh basic-ultrabasic body as a huge flow in the Maestrichtian.
Unfortunately we were not able to find the lower contact near Ulu~inar. From other ob- servations we think that there is a strong probability that the lower contact (Maes- trichtian limestone under igeous rocks) is tectonic. Thus from field evidence and geo- chronology, Dubertret's model appears to be no longer valid.
4. K-Ar age determination
As the stratigraphical evidence is in- conclusive and does not give the true age of the ophiolitic complex, an attempt has been
made using the potassium-argon dating method.
For the technical details of our method see Delaloye et al. (1974). Table 1 gives the analytical data.
5. Discussion of the results
It is evident that the different rocks of the ophiolitic complex have undergone physi- cal and chemical changes during and after their emplacement. Because of the very low potassium content of most of the ultrabasic rocks of the sequence, age determinations were not possible for the dunites and harz- burgites. On the other hand, gabbros, dole- rites and pillow lavas contain enough potas- sium for potassium-argon dating.
A preliminary determination on a gabbro indicates a Maestrichtian age. It is evident from microscopic studies that the gabbros are in the range of low grade metamorphism. In consequence this rock was rejuvenated and its age is probably too young but it is not pos- sible to give a figure for the argon loss.
The sheeted complex is 5 km wide in the Kizil Dagh with almost 100% dolerite dykes.
The dated section represents some 500 meters of the section. The chilled margins of the dykes are so numerous that a low rate of accretion (in the range of 1 cm per year) is suggested. The results on dolerites lead to an age of 94 m.y. (Turonian-Cenomanian limit) on an isochron plot 40Ar/36Ar versus
40K;36Ar (fig. 1). To draw this isochron we have assumed that all dykes were cogenetic and contemporaneous. The initial ratio 40K;36Ar is close to 334 and does not seem to be significantly different from the atmospheric ratio 295.5 so that argon over- pressure cannot be held responsible for the spread of the ages. Traces of low grade type metamorphism (prehnite, laumontite, thompso- nite) have been observed under the microscope so that, here also, the calculated age is probably to young. According to our petro- physical study (Wagner et al., 1976), the sheeted complex has a predominantly normal magnetic polarity. If we accept the isotopic age results, the dolerites could have crystal- lised during the stable Cretaceous normal Interval (Irving et al., 1973 ; Larson et al., 1975).
Pillow lavas give potassium ages from 44 to 74 m.y .. These ages are significantly different from those of the sheeted complex.
Deep alteration of the pillow lavas either in situ on the sea floor or later on, during and after their tectonic emplacement, and atmos- pheric weathering can cause a rejuvenation.
We made measurements across several pillows.
Both of the ratios 40Ar/36Ar and 40K;36Ar do not decrease proportionally from the center to the rim which indicates some argon loss by alteration. On the other hand, the potas- sium content increases so that there is as well some indication of addition of potassium due to hydrothermal alteration on the ocean floor or through meteoric waters in the con- tiDental environment.
6. Comparison with other ophiolitic massifs from the same area
The neighbouring ophiolitic complexes such as the Troodos in Cyprus and the Vourinos in Greece have been extensively studied petrographically and structurally however only a few age determinations are available. Hynes et al. (1972) in their study of the Othris ophiolites from the subpela- gonian zone in Greece, have obtained ages of 125 and 127 m.y. interpreted as minimum pri- mary crystallisation ages. This is evidence for an earlier spreading in the Eastern Medi- terranean area. Rex and Dodson (1973) re- ported ages of 56 to 88 m.y. from the Troodos which have probably to be interpreted as al- teration ages. A systematic study of this massif is now being carried out by A. Desmet
in Nancy and will certainly be of great help in this matter. Gabbros from Kizil Dagh and the Troodos give similar ages but on the other hand the pillow lavas from Kizil Dagh seem to be somewhat younger. However it is not yet possible to conclude on the basis of these more or less similar alteration ages that the emplacement of both complexes was contemporaneous.
In the Taurus range, to the north of the Troodos-Hatay "axis", many ophiolitic out- crops occur. For example in the province of Burdur, Sarp (1976) has reported ages of 93 to 98 m.y. for basic dykes and has inter- preted these results as representative of the age of the metamorphism accompanying the em- placement of the Lycian Units. It is inter- resting to note that the ages for the tee-
tonic event in the Taurus and for the em- placement of the ophiolites in the Troodos as well as in the Kiz1l Dagh are almost the same. A relationship must exist between the opening of the marginal Troodos-K1z1l Dagh basin in the south and the displacement of the Taurus. This movement was apparently di- rected southward but it may also have re- sulted from the northerly underthrusting of the ocean floor.
7. Conclusion
Potassium-argon age determinations on ophiolitic rocks can be interpreted in several ways : as the age of cooling on the ocean floor or as the age of a metamorphic event more or less contemporaneous with their tectonic emplacement on to the conti- nental margin.
For the age of crystallisation only an upper limit is given by the Maestrichtian transgression on the pillow lavas. Neglecting a possible but minor rejuvenation of the doleritic dykes in the sheeted complex, the age of about 100 m.y. (Albian-Cenomanian limit) can be assumed to be a cooling age.
The younger ages on a gabbro and on pillow basalts are probably related to sea floor or tectonic metamorphic overprints.
We suggest that very interesting ages will be found for the gabbros in using both whole rocks and separated minerals. In the delicate task of dating ophiolites, agree- ment between geochronological, paleomagnetic and stratigraphic data is a prerequisite. As long as we are uncertain of the age of for- mation of these rocks, no valid reconstruc-
tion of the geological history of the region can be proposed.
ACKNOWLEDGMENTS
We thank Prof. R. Laurent and Dr. I.
Hedley for their constructive reviews of this text. This work was supported by the grant No. 2.322-075 from the Swiss National Science Foundation. Technical assistance was supplied by M.T.A. Ankara for which we are thankful.
K-AR AGES FROM THE KIZIL DAGH OPHIOLITES BIBLIOGRAPHY
DELALOYE, M. and J.-J. WAGNER. 1974 : Potas- sium-Argon Dating : an automatic equip- ment with digital output for computer processing. C.R. Soc. Phys. Hist. nat.
Geneve, 2_, 66-74.
DEWEY, J.F., PITMAN, W.C., RYAN, W.B.F. and T. BONIN. 1973 : Plate tectonics and the evolution of the Alpine System. Geol.
Soc. Am. Bull. 84, 3137-3180.
DUBERTRET, L. 1953 : Geologie des roches vertes du N.W. de la Syrie et du Hatay
(Turquie). Notes et Mem. sur le Moyen- Orient, Tome VI. 227 pages.
GASS, I.G. 1968 : Is the Troodos Massif of Cyprus a fragment of Mesozoic ocean floor ? Nature, 220, 39-42.
HYNES, A.J., NISBET, E.G., GILBERT SMITH, A., WELLAND, M.J.P. and D.C. REX. 1972 : Spreading and emplacement ages of some ophiolites in the Othris region (eastern central Greece),
z.
Deutsch. Geol. Ges., 123, 455-468.IRVING, E. and R.W. COUILLARD. 1973 : Creta- ceous Normal Polarity Interval. Nature, Physical Science, 244/131, 10-11.
LAPIERRE, H. et J.F. PARROT. 1972 : Identite geologique des regions de Paphos (Chypre) et du Baer-Bassit (Syrie). C.R. Acad.
76
Sc., Paris, 274, 1999-2002.
LARSON, R.L. and T.W.C. HILDE. 1975 : A Re- vised Time Scale of Magnetic Reversals for the Early Cretaceous and Late Juras- sic. J. Geoph. Res. 80/17, 2586-2594.
MIYASHIRO, A. 1973 : The Troodos ophiolite complex was probably formed in an island arc. E.P.S.L. !2_, 218-224.
PEARCE, J.A. 1975 : Basalt geochemistry used to investigate past tectonic environment on Cyprus. Tectonophysics 25, 41-67.
REX, D.C. and M.H. DODSON. 1973, in VINE, F.J., POSTER, C.K. and I.G. GASS : Aeromagnetic survey of the Troodos
igneous massif (Cyprus), Nature, physical Science, 224, 34-38.
SARP, H. 1976 : Etude geologique et petro- graphique du cortege ophiolitique de la region situee au N-W de Yesilova Burdur- Turquie. These, Universite de Geneve, no. 1731, 408 pages.
VUAGNAT, M. et E. COGULU. 1967 : Quelques reflexions sur le massif basique ultra- basique du Kizil Dagh, Hatay, Turquie.
C.R. Soc. Phys. Hist. Nat. Geneve, 2,
210-216. -
WAGNER, J.-J., DELALOYE, M., HEDLEY, I., VUAGNAT, M. and E. COGULU. 1976 : Magnetic properties of a fragment of Tethyan lithosphere. EGS abstract in EOS Am. Geophys. Union Trans., 57, 655.
•
TABLE
No
I
% KI
. 10 40Ar rad -10 moles/g % 40Ar rPillow lavas
KA-914 0.34 0.597 65.0
915 0.46 0.374 78.2
916 1.46 1.510 88.7
917 0.53 0.481 52.7
918 0.63 0.854 69.1
919 0.57 0.458 75.4
920 0.49 0.405 40 . 3
921 0.29 0.252 51.7
922 0.79 0.503 38.0
923 0.49 0.444 63.7
I 924 0.49 0.436 30.9
925 0.33 0 . 365 45.7
926 0.54 0.481 54.5
927 0.65 0.704 30.5
Dolerites from the sheeted complex
KA-930 0.23 0.579 28.4
933 0.23 0.465 20.4
934 0.32 o. 720 32.6
935 0.32 o. 727 32.5
936 0.27 0.710 31.0
938 0.41 0.790 41.3
939 0 . 36 0.900 36.2
940 0.46 0.925 35.5
942 0.43 0.856 41.1
943 0 . 39 0.920 38.7
Gab bro
KA-713
I
0.54I
0.675I
47.4I
40Ar/36Ar
Sheeted complex K1zll Dogh - Hotoy I Turkey
500
400
300
I
40 Ar/36Ar
I
0.929 103 0.135 104 0.263 104 0.623 103 0.957 103 0.121 104 0.494 103 0.612 103 0.475 103 0.811 103 0.427 io3
0.541 103 0.645 103 0.425 103
0.411 103 0.371 103 0.434 io3
0.440 103 0.431 103 0.502 103 0.462 103 0.457 103 0.500 103 0.481 103
-- I
-I~
40K/36Ar I
0.103 106 0.387 io6
0.674 106 0.108 io6
0.146 106 0.340 106 0 . 718 105 0.109 io6
0.846 105 0.170 106 0.443 105 0.669 105 0.118 106 0.355 105
0.136 105 0.112 105 0.181 105 0.188 105 0.150 105 0.318 105 0.202 105 0.243 105 0.309 105 0.235 105
-·-- I
90.\t'.'
mean error 95% confidence
Age
100.7 ± 6.0 45.5 ± 6.3 57.2 ± 1.8 50.2 ± 2.6 74.5 ± 3.1 44.4 ± 2.9 45.9 ± 2.5 47.9 ± 5.0 35. 5 ± 1.8 50.2 ± 1.9 49.3 ± 2.4 60.8 ± 2. 9 49.4 ± 2.7 60.1 ± 4.4
135.3 ± 9.6 109.4 ± 9.2 124.2 ± 9.9 122.4 ± 9.0 144.4 ± 8.8 106.0 ± 6.9 133.7 ± 6.9 108.6 ± 5.8 108.1 ± 6.0 128.1 ± 5.9
69.0 ± 2.7
200+-~~~~~~~~~~~~~~~...-~~~~~~~-.-~~~~~~~--.~~~~~~~~
40 • 103 40K/36Ar
0 10 20 30
Figure 1 Isochron plot 40Ar/ 36Ar versus
40K;3 6Ar from the Kizil Dagh dolerites.
