I

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2 79

THE BAiR-BASSIT (NORTHWESTERN SYRIA) OPHIOLITIC AREA

PARROT Jean-Françoi s

Laboratoire de Géologie, S.S.C.-O.R.S.T.O.M., 70-74, Route d'auinay, 93140, Bondy, France

she Bah-Basha opkio.!.Ú% nmbid comespovd 20 a pohtion 06 t he Tihyan

oceanic ~t 2h.tuh.t onto ,ththe Ambhn p l a t d o m &om nohth t o houth dwLing Mae-

hRhicktian , t h e . l t & composed by p & d o L W c t e d o n i t e s and c w n u a , t a y a -

ed gabbmb, sheeted diabasic comptex and ALoa d.i&@evtt Leveed 06 p.LUow-kua6,

t h e uppeh one phedenting, as i n Tkoodoh, a hypen-tholeiitic compobXon; " u m b ~ "

atre Linked ;to tk ib uppeh lev&. Moheoveh, t he &zh-&?hhi.t m a h i d c o m p ~ a &o

an .ín~tla-ppnido&Xíc metarro/rpkic hote belonging t o t h e deep gheen hcki6.tb and

ampkiboLLte d d e d , and a volcanic and bedim!xnaWcy henieA. she b;tudy O Q tki6 he-

~ Ú e d p m n L t 6 ;to doaRow the evoLlLtion 0 6 fie h o u t h m b o d a 04 t h e Tethyan ocean

duning .Li% donmation which began Ln the U p p a Thiadbic p d o d and otopped j u t

bedohe ;the t e c h n i c empkcemd 06 t h e opkioLLtíc nappa on t h e cantine^ mím- gin.

The .thhLL6fing oh obdudon would hucceed ;hua oh mohe hubbequd ocean-di-

h a t e d inixa-oceanic bubductionh and would have been induced by t h e L a s t one.

DwLing tki6 p/Loct?4h, a p a n t 0 6 ,ththe v0Lcan.k and oedhe-y b e A h would have been

engaged i n t h e b u b d M o n zone and metamohphohed i n deep gheen h C k i 6 . t b and ampk i -

boLLte daCia. She ~n&a-oceanic b u b d d o n .Lh emphized by fie phesence 06 bcatt-

a e d and b u b v d d diabasic diked c d n g t h e gabbhoh and phgiogtlavÚted going

up though t h e pehdo;ti;tes. On t h e o t h a hand, ,the uppeh lev& 06 ~ o w - k v a b

would have been domed d h g ;the a t b&ge 06 ,ththe donmation ob ,ththe oceanic ~ n u h t ,

and CO& be a Wi-tVIeAb 0 6 ,the voLcanic mc linked 20 t h e mohe hecent and mohe

how5m.n intm-oceank hubdudon.

" .

2 8 0

4 Km F , O-

n”

LATTAQUIE

4

2 8 1

INTRODUCTION

(i d

.

The northwestern Syrian ophiolites and related rocks, previously described by

Dubertret (1953) and Kazmin and Kulakov (1968) , have been recently re-examined

(Parrot, 1974a, 197413, 1977b; Delaune-Mayere and Parrot, 1976; Delaune-Mayere e t

al ., 1977; Whitechurch and Parrot, 1974; Whitechurch, 1977; Parrot and Whitechurch,

1978).

The Baër-Bassi t ophioli tes (NW Syria) belong t o the southernmost o r "external I'

be l t of Tethyan ophioli te nappes thrust onto the northern border of ihe Arabian

platform. They a re si tuated i n front of Cyprus, and represent an eastward prolongat-

ion of i t s formations and structures, t h u s forming the western end of the "peri-A-

rabic ophioli t ic crescent" (Ricou, 1971). In fac t , the close s imi la r i t i es existing

between the Baër-Bassit Massifs and those of Cyprus, Hatay, and Oman, indicate,that

they belong to the same geotectonic structure . \

The northwestern ophioli t ic assemblage and the related rocks are geographic-

a l l y and structurally comprised between a Jurassic and Cretaceous calcareous mas-

s i f - the Agraa mountain - situated northwards, and different transgressive ser ies

(the f i r s t one beginning i n the Upper Maestrichtian), surrounding the ophioli t ic

area ~-0ÚCto 6emu eastwards and southwards. The seashore limits ophiolite on i t s

western border. In f ac t , the Agraa mountain corresponds to an Arabian platform

window which divides presently the Baër-Bassit and the Hatay massifs located north-

wards, and which has been uplifted a f t e r the ophioli te emplacement, probably during

Miocene. The ophiolite nappes emplacement took place during Maestrichtian, as i n -

dicated by the Lower Maestrichtian age of the upper levels of the Agraa Mountain

on which ophiolites r e s t , and the Upper Maestrichtian age of the oldest terms of

post-emplacement transgression . On the other hand, the uninterrupted sedimentat-

ion from Upper Cretaceous to Lower Lutetian i n the Kurd Dagh (Dubertret, 1953;

Wolfart, 1963), northern ,barder of the Alaouite calcareous range situated south o f

I

F i g . 1 - Geological sketch map of north western Syria, 1: basement of the ophiol- 7

I * 4 1

i t i c sheets , Arabian-African platform limestones of Jurassic t o Upper Cre- taceous age; 2: metamorphic sole; 3: ophio l i t i c su i t e ; 4: volcano-sedi- mentary formation; 5: Upper Maestrichtian transgressive formations; A: thrusting contact of the ophioli t ic assemblage on the-Lower and Middle Maestrichtian limestones; B: sheet contact between ophioli t ic su i t e and volcano-sedimentary formation; C : post-nappe fau l t s .

I

2 8 2

the Baër-Bassit area, shows obviously t h a t t h i s p o r t i o n o f the Arabian p l a t f o r m

has never been covered by o p h i o l i t i c nappes, and t h a t those nappes went from nor th

t o south. Thus, t he Baër-Bassit area would correspond t o the f r o n t o f an impor tant

o p h i o l i t i c nappe, the roots o f which are found t o the nor th , i n Turkey (Ricou e t

a l . , 1975); and t h i s would exp la in the p e c u l i a r development o f an oceanic vo lcanic

'T and sedimentary ser ies pushed by the o p h i o l i t i c sheet

dur ing i t s emplacement. h

I m , m

so

o

THE OPHIOLITIC COMPLEX

As a l l t he o p h i o l i t i c massifs described by Mesor-

i a n (1973) i n eastern Mediterranean, the Baër-Bassit

o p h i o l i t i c complex consis ts o f h a r z b u r g i t i c t ec ton i tes ,

p e r i d o t i t i c cumulates which are sometimes f u l l y recry-

s t a l l i z e d as w e l l as gabbros which succeed them d i r e c t -

ly, layered gabbros w i t h some c ross -cu t t i ng dikes,

sheeted d iabasic d i ke swarms, and two layers o f p i l l o w -

lavas, the lower one t h o l e i i t i c and d i r e c t l y r e l a t e d t o

the d i ke complex, t h e upper one h y p e r t h o l e i i t i c and pre-

sent ing an unconformity w i t h the two e a r l i e r formations;

a f i n e magnesian c l a y formation f i r s t described i n Cy-

prus as "umber", i s associated w i t h the upper vo lcanic

l e v e l .

P e r i d o t i t e s

The northwestern Syr ian u l t ramaf i c u n i t 3 km

t h i c k , i s composed by h a r z b u r g i t i c t ec ton i tes and cu-

mulates, both s t rong ly serpentinized.

F ig . 2 - Synthet ic l o g o f Baër-Bassit o p h i o l i t i c formations. A: volcanic and sedi - mentary ser ies; 6: metamorphic so le; C : t ec ton i tes ; D: p e r i d o t i t i c cumul- ates; E: l h e r z o l i t i c and gabbroic ser ies; F: f e l d s p a t i c p e r i d o t i t e s ; G: layered gabbro sequence; H: p lag iog ran i te i n t r u s i o n s ; I: gabbroic ensemble w i t h sca t te red d iabasic dikes; J: sheeted complex; K: lower p i l low- lavas; L: upper p i l l ow- lavas ; M: umbers.

' y '

5

283

The tectonites characterized by metamorphic fabrics are essentially composed

by 60 t o 70% olivine (Fo go) , 38 t o 28% orthopyroxene (En 92) and Y 2% spin-

e l . The recrystall ization of the olivine phase i s the main feature of this

type, whereas the fol ia t ion i s always weak. Except Al O which, is very high fo r

such a harzburgitic type, the other elements are comprised i n the extremely re-

s t r i c t ed range i n composition which characterizes everywhere the tectoni tes

(Coleman, 1977).

The per idot i t ic cumulates are harzburgitic, partly lherzol i t ic , and some felds-

2 3

pathic peridotites w i t h a heteradcumulate structure have beea encountered a t

the base of the gabbroic sequence. These rocks present a l ight layering emphas-

ized by the development of ens t a t i t i c "laminae", and a dominant adcumulus

structure. The harzburgites contain 65 t o 70% olivine (Fo 85), 34 t o 29% ortho-

pyroxene (En 86-90) and 1% o r s o of spinel. The lherzolites contain 65 t o 76%

olivine (Fo 85), 18 t o 20% orthopyroxene ( E n 88), 14 t o 8% clinopyroxene, 2 t o

4% spinel and opaque minerals. The feldspathic peridotites contain 50 to 55%

olivine (Fo 80), O to 2% orthopyroxene, 22 t o 35% clinopyroxene and less than

0.5% spinel. The composition of olivine progressively increases in iron s t ra -

tigraphycally upwards and orthopyroxenes present more o r less the same trend.

The increase i n A1203 is naturally h i g h fo r feldspathic peridotites.

The Baër-Bassit massif contains a l o t of deformed cumulates w i t h numerous

traces of recrystall ization and cumulate structure re l ics . Since the supposed

tectonites of the Baër-Bassit area are mainly characterized by the recrystal 1-

ization of the olivine phase, the problem of the real or ig in of those rocks

remains, and the presence of res t i tes i n the Baër-Bassit massif i s s t i l l hy-

potheti c.

Gabbros

The gabbroic ensemble i s essentially represented by a layered ser ies 1 km

thick, the basic composition of which i s almost constant i f one does not take into

account the variation of calcic plagioclase percentages. The base of the gabbroic

ser ies i s formed by an alternation of gabbroic and per idot i t ic layers of about 1

m thick; this formation succeeds upwards the lherzol i t ic and/or feldspathic peri-

doti tes. The upper levels of the layered se r i e s are characterized by a l ight cumul-

2 8 4

a t e tex tu re w i t h a massive tex tu re tendency, and the presence o f d o l e r i t i c cross-

c u t t i n g dikes. The d i f f e r e n t cumulate textures o f the various gabbroic types ( a l l -

i v a l i t e s and t r o c t o l i t e s a t the base, and upwards gabbros and n o r i t i c gabbros w i t h

o r w i thou t o l i v i n e ) show t h a t these rocks have been formed by s e t t l i n g i n a magmat-

i c chamber (Wager, 1953; Hess, 1960; Jackson, 1971; Goode, 1976). As i t has been ob-

served i n various massifs o f Eastern Mediterranean, . i .e . Antalya nappes (Juteau,

1974) and Hatay (Parrot , 1973), the absence o f c r y p t i c evo lu t i on and the presence

o f u l t r a m a f i c minerals i n almost a l l the d i f f e r e n t c y c l i c u n i t s suggest t h a t the

magmatic chamber has been fed continuously dur ing coo l i ng and c r y s t a l l i z a t i o n (Par-

r o t and Ricou, 1976).

Diabasic dikes

Scattered and subver t i ca l diabasic dikes go across the upper gabbro ser ies,

the l a y e r i n g o f which i s perpendicular t o the general d i ke trend. I t appears t h a t

a t l e a s t t h i s gabbroic upper l e v e l had s o l i d i f i e d before the emplacement o f the

dikes . Dikes are a l so comprised i n d iabasic d i ke swarms, q u i t e s i m i l a r t o the sheet-

ed complexes o f Hatay (Parrot, 1973) and Troodos (Moores and Vine, 1971; Kidd and

Cann, 1974). As i n these two neighbouring massifs, one can f i n d an asymmetric c h i l l l -

i n g considered t o be the r e s u l t o f magmatic i n j e c t i o n s along a s i n g l e f rac tu re ,

each successive d i ke being emplaced w i t h i n the middle o f the prev ious ly s o l i d i f i e d

d i ke (Moores and Vine, 1971). I n f a c t , i n the Baër-Bassit area, the re la t i onsh ips

between the d i f f e r e n t dikes are n o t so p la in , and numerous dikes c u t across each

other, showing obv ious ly t h a t the sheeted complex i s formed by m u l t i p l e a r r i v a l s and

d i s t i n c t magmatic sources. Same observations have been recen t l y po inted ou t i n

Troodos by Desmet e t a l . (1977, 1978).

The sca t te red dikes conta in 50 t o 55% p lag ioc lases (An 70), 43% o r so augite,

2 t o 3% opaque minerals, and the dikes o f the sheeted complex 43 t o 47% plag io-

clases (An 60 - An 6 5 ) , 45 t o 51% augite, 6 t o 10% opaque minerals (magnetite and

t i tano-magnet i te) ; some c u t t i n g dikes o f t h i s complex present a small amount o f

qua r t z (see f i g . 3). A Na O t KzO versus S i O 2 diagram shows t h a t the p l o t t e d samples

are s i t u a t e d on a l l sides o f the Mac Donald and Katsatura (1964) d i v i d i n g l i n e , The

d i s t r i b u t i o n o f some samples i n the a l k a l i c zone i s considered as the r e s u l t o f a

2

2 8 5

150 m-

100-

50-

0-

. scattered dikes 1

"n Quam 0 Plagioclase 5 Orthopyroxene

Clinopyroxene (Augite) Clinopyroxens (Pigeonite) Glass Olivine Opaque minerals

Fig. 3 - Synthetic mineralogical composition and evolution of the dike complex and associated lavas.

p o s t igneous metasomatism rather than the mark of an important variation i n the

primary magma giving these dikes (Coleman, 1977). As a matter of fac t , numerous

dikes present complete o r partial transformations (urali t i za t ion and a lb i t iza t -

ion), and assuming tha t they have been enriched i n a lka l ic elements, their orig-

inal Na20 and K O contents can be supposed t o have been qui te close to tha t of

abyssal tho le i i tes . A t l e a s t , a part of them ac ts as feeding dikes for the over-

lying pillow-lavas.

2

286

P i llow-lavas

As on Troodos (Gass and Smewing, 1973; Searle, 1975), two distinct pillow u- nits have been defined i n the Baër-Bassit area (Parrot, 1974b, 1977b, 1977~) .

(a ) The lower u n i t , 200 m thick, is s t ruc tura l ly and chemically linked to the dikes

of the sheeted complex and i ts lavas a re more or less analogous to the MORB.

The unaltered pillows are formed (see f ig . 3) by 36 to 42% plagioclase (An 50),

40 t o 6% augite, 1 t o 3% magnetite and 4 t06% idiomorph olivine pseudomorphosis.

They are frequently transformed, leading to spil i t ic types and one can observe

the development of various zeolites similar to those found a t this level i n

Troodos and Oman (Smewing e t al . , 1976). Asl for the dike complex, i t seem

tha t the presence of these spilites is the resu l t o f a post-igneous metasoma-

tism, a l l the more as the Ti02 content i s always weak (0.6%) and remains unchang-

ed i n the transformed samples (Parrot, 1977b, p. 113); the same phenomena can be

observed i n the upper pillow-lavas (0.3% of Ti02 i n both fresh and altered la-

vas).

The upper level 100 m thick d i f fe rs from the lower one by the pillow shape, the

mineralogy and the chemistry, and i t presents an unconformity w i t h the two earl-

i e r formations, sheeted complex and lower pillow u n i t . The unaltered samples

present a quench structure and are formed by ‘52 to 63% feathershape or/and Pte- ridomorphows pigeonitic c r i s t a l l i t e s , 7 to 1% ens ta t i te , 8 t o 6% idiomorphic o- l iv ine (Fo 95) and 33 to 30% of b r u n i s h glass containing some traces of anal-

cime and rare corroded bytowni t i c phenocrysts. Mostly, the upper pi1 low-lavas

a re altered and transformed; they contain then feldspathic c r i s t a l l i t e s ( a lb i t e

and K-feldspar , probably ddularia), urali t ized pyroxenes, olivine phenocrysts

replaced by a mixture of ca lc i te and montmorillonite, and partly devitrif ied

glass w i t h improtant analcimic concentrations. I f the strongly altered samples

present important K20 and Na O contents (respectively 4 and 5%), the unaltered

lavas a re characterized by a “hypertholeii t ic“ composition which implies a

h i g h partial melting degree. These rocks are enriched i n MgO, Cr203 and N i O ,

and poor i n A l O

sen t a spinifex structure and are , fo r a l l these reasons, comparable t o komat-

2

( N, lo%) , Na20 (1%), K20 (0.1%) and Ti02 (0.3%); they pre- 2 3

i i t e s , the main features of which are:

(a ) high MgO, Cr203 and Ni0 percentages;

(b) an ultramafic composition;

( c ) a weak Fe/Mg r a t i o ;

(d) a s p i n i f e x s t ruc tu re ;

(e) a weak T i 0 content i n comparison w i t h the S i0 percentage. For Bebien 2 2

(1972), Pearce and Cann (1973), a weak T i 0

would be d i s t i n c t i v e f o r i s l a n d a rc t h o l e i i t e s . As for the lower p i l l ows , t he

upper p i l l o w T i 0 percentage does n o t vary w i t h the a l t e r a t i o n , meaning t h a t

the halmyro lys is o r deuter ic a l t e r a t i o n i s a post igneous phenomendn. The o r i -

g i n o f t he upper l e v e l could correspond t o the terminal phase o f the expansion

o r t o the beginning of an i n s u l a r a rc formation (Parrot, 1977a; 1977b; 1 9 7 7 ~ ) .

content i n o p h i o l i t i c e f fus i ves 2

2 7 d

3

Fe0 + .9 F e 2 0 3 A upper pillow-lavas

lower pillow-lavas

6 sheeted complex

4 scattered dikes 0 peridotitic cumulates

$ top of the gabbroic sequence

W layered gabbros

0 gabbros from the lherzolitic

and grbbroic series

0 feldspathic peridotites

Mg0 Na,O + K 2 0

Fig. 4 - AFM diagram f o r rock averages (see tab le 1 ) .

Umbers

The umber outcrops o f Baër-Bassit area are l i n k e d t o the upper p i l l ow- lavas ;

they form e i t h e r a cement between the p i l l ows , o r t h i n beds on top o f them. The

> Syr ian umbers present chemical and minera log ica l features, s i m i l a r t o those o f

4 ‘ - 1

the Troodos umbers s tud ies by E l d e r f i e l d e t a l . (1972), Despra i r ies and Lap ie r re

(1973), Robertson and Hddson (1973) and Robertson (1975). They are e s s e n t i a l l y

formed by goe th i te (40 t o 50%), d ioc taed r i c montomor i l lon i te A l (30 t o 35%) and

manganese hydroxides (20% o r so). They present h igh Fe and Mn contents and a

2 8 8

Table 1 - Chemical composition of the various petrographic types of the Baër-Bassit ophi o1 i t i c assemblage.

Si02

2'3

Fe203 Fe0

MnO

MgO Ca0

Na20

K2°

48.02 47.67

1.96 1.28 - -

8.11 9.24

0.12 0.13

39.56 40.62

2.09 0.83

0.06 0.08 - 0.05

44.65

4.95 -

10.16

0.13

34.48

5.37

0.13

0.01

49.48

18.71 -

5.63

O .O7

10.66

14.69

0.57

0.05

48.28

16.25 -

5.43

0.06

14.19

14.63

0.86

O .O7

50.81

15.97 -

6.39

0.12

10.36

9.88

2.06

0.18

53.36

15.92

1.50

6.79

0.18

8.73

7.49

3.61

0.56

53.78

16.40

1.50

7.51

0.16

7.22

9 .O6

3.37

0.59

54.53

14.91

1.50

7.09

0.15

8.11

11.35

3.57

0.32

54.55

13.29

1.50

6.86

0.18

10.45

1.23

0.24

Ti02 0.06 0.05 0.11 0.09 0.14 0.38 0.67 0.70 0.69 0.30

P205 0.01 '0.04 n.d. 0.05 0.09 0.04 0.05 0.05 0.07 0.05

Anhydrous averages with conversion of all Fe O to Feo: ( 1 ) : 5 tectonites, Parrot (1977) p. 34; (2) :*I$ peridotitic cumulates, p. 35; (3): 3 feldspatic peridotites, p. 34; (4): 3 gabbros of the gabbroic and lherzolitic se- quence, p. 54; (5): 17 gabbros of the layered series, p- 54 and 55; (6): 10 gabbros from the top of the gabbroic sequence, p. 55.

Anhydrous averages for FeZ03 equal to 1.50%: (7): 6 scattered dikes, p. 74; (8): 9 dikes of the seheted complex, p. 74; (9): 7 fresh lower pillow-lavas, p. 1Ql; (IQ): 5 fresh and typical upper pillow-lavas, p. 110, samples n. 70039, 72099, 73002, 73187 and 73616.

strong concentration of different trace elements such as V , Co, Ni, C u , As, W and

Pb (Parrot and Delaune-Mayere, 1974). As for the s imilar Troodos types (Robertson

and Fleet, 1976), the Baër-Bassit umbers (Courtois e t a l . , unpublished data) are

characterized by a high RE bulK w i t h an important depletion of Ce which could be ex-

plained by the role of sea-watqr during their formation. Parrot and Delaune-Mayere

(1974) and Parrot (1977~) have emphasized the l i n k existing i n Troodos, Baër-Bassit

and Oman between umbers and upper pillow-lava u n i t which presents, except Cry the

same trace element concentration as umbers, and they have shown tha t the upper

pillow-lava composition was a factor so important as the sea water.

289

P1 agi ograni tes

The Baër-Bassi t plagiograni tes , previously studied by Dubertret (1953), Kazmin

and Kulakov (1964-1968), Piro (1967) form cross-cutting dykes i n cumulate peridot-

i t e s and i n the lower level of the layered gabbro ser ies where, from place to place,

they coalesce i n small massifs. Thus, they d i f f e r completely, because of t he i r

structural p o s i t i o n , from the leucocratic associates described i n several ophiolit-

i c massifs (Coleman and Peterman, 1975). In return, they are mineralogically and

chemically similar t o the plagiogranites considered as the end product of different-

tation w i t h i n the ophioli t ic magmatic chamber. For Parrot (1977b, 1 9 7 7 ~ ) ~ a t l e a s t

i n Syria, such plagiogranitic rocks would come from magmas formed a t the expense of

oceanic volcanic and sedimentary ser ies involved i n a subduction zone with f r i c t ion

phenomena between oceanic lithospheric plates. Similar outcrops have been found by

the author in different ophiiioli t e massifs , including troodos (Parrot, 1980).

Infra-ophiol i ti c metamorphic sol es

The largest Baër-Bassit s l i c e of peridotites and gabbros presents a t i t s base

a thick sole (from 50 m to 300 m ) o f metamorphic rocks which consists of ampbibol-

i t i c sch is t s , calcschists, amphibolite-pyroxenites w i t h plagioclases, metahasalts,

marbles and quartzites (Chenevoy, 1959; Whitechurch and Parrot, 1974). The structur-

al study (Whitechurch, 1977) has pointed o u t the relationships existing between the

main phases of deformation, the synmetamorphic one being anterior t o the sheet em-

placement and related deformations which a f fec t e i the r peridotites or the volcanic

and sedimentary ser ies . Whitechurch (1977) has shown that fo r each metamorphic le-

vel there i s a corresponding non-metamorphic level of the volcanic and sedimentary

ser ies th rus t w i t h the ophioli t ic nappe. As a l l metamorphic soles occurring beneath

the ophioli t ic su i t e of numerous eastern Mediterranean massifs (Parrot and White-

church, 1978), the northwestern Syrian ophioli te-related metamorphic rocks belong

t o the deep green schists amphibolite facies.

Those metamorphic rocks would resu l t from the transformation of oceanic supra-

crustal se r ies s e t t l ed during expansion, and the metamorphism would occur i n in t ra -

oceanic subduction zones prior t o the tectonic emplacement on to the Arabian plat-

form (Parrot, 1977b; Whitechurch, 1977; Parrot and Whitechurch, 1978). Such a pheno-

menon i s emphasized by the relationships observed i n the neighbouring Pozanti-Kar-

290

santi massif (Cakir e t a l . , 1978; Cakir, 1978) where su.bvertica1 diabasic dikes went

across the matamorphic sole and the subsequent per idot i t i c tectonites.

Volcanic and sedimentary ser ies

The vollcanic and sedimentary formation is represented by a)continuous ser ies

from Upper Triassic t o Turonian. I t s formation has to be related w i t h the spreading

process g i v i n g r i se t o the Te,thyan oceanic crust . Thus, th i s se r ies would correspond

to the supra-oceanic Tethyan crust . On the other hand, s i l t s tones and de t r i ta l lime-

stones associated w i t h a l l the deep-sea members of the volcanic and sedimentary se-

r ies ( rad io la r i tes and cher t s ) , and the diminution from south to north of de t r i ta l

material, show the proximity of the continental platform over which this ser ies was

l a t e r thrust from north to south (Delaune-Mayere and Parrot, 1976).

The Upper Triassic volcanism would resu l t from the f irst stages of distension

which are responsible fo r the fracturing of the northern edge of the Arabian plat-

form. Delaune-Mayere e t a l . (1977) have emphasized the similari ty of the structural

arrangement between Halobia limestones and related volcanics and Lapierre and Par-

ro t (1972) have shown tha t the Baër-Bassit and the Mamonia area (Cyprus) present

same formations and same strutcural relationships, although the Baër-Bassit is d i s -

tinguished by the weak alkaline tendency of i t s Triassic volcanism i n comparison

w i t h the clean alkaline composition of the coeval effusive formations i n Mamonia

and other Mediterranean regions (Rocci e t a l . , 1979). On the other hand, the Cre-

taceous volcanic and sedimentary ser ies lacking i n Cyprus (Ealey and Knox, 1975)

i s well represented i n northwestern Syria (cherts and calcarenites) and contains

a t i t s base a second volcanic level which consists, from the base upwards, of bas-

anites, tephrites and lamprophyres, a l l i n pillow form, and considerable phonolite

flows w i t h some trachytes (Parrot, 1974~) .

As formerly proposed, these volcanic and sedimentary ser ies would be the ori-

ginal material for the infra-ophioli t ic metamorphic rocks, and eventually partly

the source o f plagiograni tes .

CONCLUSIONS

The Ba&-Bassit ophioli t ic area seems to correspond to the front of an ensem-

ble of nappes thrust over the edge of the Arabian plate during Maestrichtian. The

I

+1 f

1

2 9 1

roo ts o f these nappes are presumably seated t o the north, i n Turkey. These nappes

would represent a p o r t i o n o f t he Tethyan oceanic c r u s t which began t o form i n t h i s

reg ion dur ing the Upper T r i a s s i c o r the Lower Jurass ic per iod.

The t h r u s t i n g o r obduction o f t h i s c r u s t p o r t i o n onto the Arabian p l a t f o r m

would succeed an in t ra-oceanic subduction or , as advanced by Par ro t and Whitechurch

(1978), a succession o f ocean-directed mini-subductions, the witness o f which would

be the d i f f e r e n t east-west Turk ish o p h i o l i t i c b e l t s . Such a mechanism would be em-

phasized by the presence o f diabasic c ross -cu t t i ng dikes i n more and more s t r u c t u r -

a l l e v e l s northwards (gabbros i n Cyprus and 'Baër-Bassi t, p e r i d o t i t e s i n Antalya and

Pozanti-Karsanti), and would be responsib le f o r t he a c t i v a t i o n o f a f r o n t a l volcan-

i c a r c g i v i n g r i s e t o the formation o f h y p e r t h o l e i i t i c lavas a l l around the Arabian

platform, i n the most 'meridional '& o p h i o l i t i c b e l t .

The vo lcanic and the sedimentary se r ies formed i n the southern d i s t r i c t o f the

Tethyan oceanic c r u s t would have been p a r t i a l l y subducted and metamorphosed; the re -

s u l t i n g metamorphic rocks would have been p a r t l y ex t rac ted from the subduction zone

du r ing the f i n a l stages o f t h r u s t i n g on the Arabian p la t form. The unmetamorphosed

vo lcanic and sedimentary se r ies which correspond, i n the Baër-Bassit area, t o the

formations s e t t l e d i n v i c i n i t y o f the con t inen ta l margin and the re fo re n o t i nvo l ved

i n subduction, would have been fo lded and pushed i n f r o n t o f the oceanic c r u s t up-

t h r u s t dur ing the same stages.

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p 8 ,^ .... J