Structural Evolution of the Vardar Root Zone, Northern Greece: Discussion and Reply

Structural evolution of the Vardar root zone, northern Greece: Discussion and reply

Discussion

C. M. BARTON"' Department of Geology, Sedgwick Museum, Downing Street, Cambridge CB2 3EQ, England

Zimmerman and Ross (1976) presented an interpretation of suggested in their abstract. Such well-documented stratigraphic Greek geology in which Vardar ocean crust was eliminated in two ages provide compelling evidence that ophiolite emplacement oc- successive directions (their Fig. 6). Their contribution is welcome, curred significantly before Late Cretaceous time, probably soon although it included a number of points that require clarification. after the first deformation of the Othris margin. A metamorphism First, it is generally agreed that northeast Greece has an ex- of about the same age (Early Cretaceous) is widespread in adjacent tremely complex post-Triassic (Alpine) history. However, in their Pelagonian rocks (Mercier, 1973b). "regional tectonic model" Zimmerman and Ross did not once Because both the direction and age of thrusting associated with specify the approximate dates of tectonism. Second, the Vardar the Othris zone ophiolites are fundamental to any tectonic model of zone is only one of two parallel belts in Greece which contain mafic the Hellenides, their position in Figure 6 of Zimmerman and Ross and ultramafic rocks interpreted as ophiolites. Fragments of similar needs clarifying. Certainly, no fragments of the Othris ocean (the oceanic affinity occur farther west in the Othris (= sub-Pelagonian) Vourinos, Pindos, or Othris ophiolites) could have been derived zone. If the authors' assertion is correct and the Othris zone from an area east of Olympos before Tertiary time, because the ophiolites are rooted farther east, then existing data from this zone Olympos platform records continuous Mesozoic shallow-water (which includes Zimmerman's own [1972] account of the Vourinos sedimentation. complex) must be taken into consideration. Not only are the Mount Olympos also provides evidence that Tertiary displace- ophiolites of the Othris zone better exposed and better dated (both ments in the Hellenides were not exclusively toward the southwest. by fossils and radiometric methods) than those in the Vardar, but Above the isolated carbonate stack of Olympos, a Tertiary thrust they are also far less deformed. fault carried a thin sheet of metamorphic basement in a direction Studies of Othris zone geology have shown that ophiolite that remains controversial. The carbonates below the fault have emplacement in Early Cretaceous time was almost certainly toward been interpreted in two ways: either as a tectonic inlier of the ex- the northeast. The position of the ocean before ophiolite emplace- tensive Mesozoic platform known in central and western Greece ment has been demonstrated by the detailed reconstruction of a (Godfriaux, 1962, 1968), in which case thrusting was toward the Mesozoic continental margin in the Othris area of eastern central southwest, or as the autochthon below a thrust fault of more local Greece (Hynes and others, 1972; Smith and others, 1975, Fig. 4; significance with thrusting toward the northeast (Barton, 1975). Price, 1976). When the effects of deformation have been removed, One of these interpretations is clearly incorrect, because the re- sedimentary facies relationships show that through most of Jurassic quired fault motions are in totally opposite directions. time, the Pelagonian "microcontinent" in eastern Othris bordered Zimmerman and Ross followed Godfriaux, who saw the similar an area of deeper water which lay farther west. The Othris margin uninterrupted stratigraphy of Olympos (Triassic—Pmiddle Eocene) was telescoped during Late Jurassic—Early Cretaceous time when in the platforms of western Greece. The Olympos platform has oceanic crust was emplaced from the west or southwest across the been correlated with either the Parnassos or Gavrovo-Tripolitza Pelagonian zone. zones; either correlation suggests a continuous Mesozoic carbonate The entire tectonic stack at Othris was in place by middle Creta- bank. An identical microfauna in the uppermost levels of both the ceous time (Smith and others, 1975). Both the Othris ophiolites and Olympos and Gavrovo platforms (Fleury and Godfriaux, 1974) the Vourinos complex along strike to the north are overlain by un- substantiates this view. If correct, paleogeography requires that deformed Upper Cretaceous (Cenomanian-Maestrichtian) lime- rocks between the Olympos and Gavrovo platforms (the Pelago- stones and a lower Tertiary "flysch." The age of this unconforma- nian, Othris, and Pindos zones) are allochthonous, and were ble sequence is difficult to reconcile with the destruction of an emplaced from an area east of Olympos. The resulting cumulative ocean basin in "Late Cretaceous" that Zimmerman and Ross displacement concealed by the Olympos thrust must, in this case, be several hundred kilometres. Other interpretations are more likely. The movement direction of * Present address: Institute of Geological Sciences, Overseas Division, the Olympos thrust can be demonstrated by field relations that in- 154 Clerkenwell Road, London EC1R 5DU, England. clude thrust geometry, the shape of imbrications in the (pa- ra)autochthon, and the attitude of minor structures associated with The article discussed was published in the Bulletin, v. 87, p. 1547—1550. emplacement. Tertiary thrusting was toward the area now oc-

Geological Society of America Bulletin, Parti, v. 90, p. 125-128, January 1979, Doc. no. 90118.

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cupied by the Vardar zone, rather than away from it. Such a sense the rapid variations in sedimentary facies that occur across the re- of movement requires that the Othris and Pindos zones have never gional strike (Mercier, 1966b, 1973b; Kauffmann and others, been transported across Olympos. It also implies that different 1976). Mercier divided the Vardar into three subzones on the basis "microcontinents" can exhibit identical carbonate stratigraphy of facies variations in Jurassic sediments. Two of the subzones while physically separated by small ocean basins. Also, because (Almopias and Peonias) contain both pelagic carbonates and ul- Vardar zone rocks were thrust toward the southwest in Tertiary tramafic rocks, while the: central (Pa'ikon) subzone contains neritic time, Olympos has been the locus of deformation by two thrust sediments. Zimmerman and Ross did not recognize facies changes faults. The relative timing of the two faults is still uncertain, in the Vardar, so it is uncertain how they have resolved their ideas although it is clear that movement on the Olympos thrust preceded with this work. A repetition of facies belts in steeply inclined zones the very last displacements of the Vardar. suggests either sedimentation in a complex tectonic setting such as Other recent accounts of Vardar zone geology have emphasized found close to an island arc, or extensive strike-slip faulting.

JAY ZIMMERMAN Department of Geology, Southern Illinois University at Carbondale, Carbondale, Illinois 62901 JOHN V. ROSS Department of Geological Sciences, University of British Columbia, Vancouver V6T 1 WS, British Columbia

Our contention that the majority of ophiolites in Greece, includ- North Bosnia massifs (Aubouin, 1965; Bernoulli and Laubscher, ing those of the Othris (sub-Pelagonian), Pelagonian, and Vardar 1972, Fig. 1). By virtue of its present exposed length, the Vardar zones were emplaced by southwestward thrust transport from an zone is by far the most dominant of the four Tertiary structural de- ocean basin now marked by the Vardar root zone is based on the pressions in or adjacent to which most Balkan ophiolites are found. following regional and more restricted considerations: (1) the gen- It is not inconceivable, however, that the zone originally extended eral distribution of ophiolites in Greece, Yugoslavia, and Albania; at least 200 km farther to the southeast in the area now covered by (2) the relative length of the Vardar zone and the total volume of its the Aegean Sea. At the present location of the Sporadhes islands, an ophiolites; (3) the fact that ophiolites are preserved in or adjacent extension of the Euboean-Boetian depression along its current to four rather than two Tertiary structural depressions; (4) the trend would effect an intersection with a continuation of the Var- eugeosynclinal lithologic character of much of the Vardar zone; (5) dar zone nearly identical to the termination of the Kozani depres- direct evidence of suture-related structural elements in the Vardar sion against the Vardar zone farther to the north (see Aubuoin, zone; and (6) the absence of direct structural evidence for a suture 1965, Fig. 39). Although it has not been established that the in any other ophiolite belt in the region. Other considerations are Sporadhes represent emerged parts of an original Vardar zone, it is also presented in this reply. interesting to note that Jacobshagen and others (1976b) have The majority of Greek ultramafites crop out in a broad belt that mapped mesoscopic polyphase folds with orientations similar to trends north-northwestward and is bounded by two Tertiary struc- the phase 1 and phase 2 structures in this zone northwest of tural depressions: the Vardar and Othris zones. The former zone Salonika (Zimmerman and Ross, 1976). defines the eastern boundary and the latter zone the western boun- In addition to its dimensional significance and the relative abun- dary of this belt (for the purpose of this discussion the Pindos mas- dance of its ophiolites, :he Vardar zone has rock types characteris- sif is considered part of the Othris zone). The Vardar and Othris tic of some sutures. These include metamorphosed (greenschist zones are separated by the Pelagonian massif, a positive area con- facies) eugeosynclinal, volcaniclastic, and shelf carbonate rocks sisting of Hercynian metamorphic rocks and erosional remnants of (Kockel and others, 1971, 1972; Mercier, 1973a, 1973b) jux- younger (principally Mesozoic) sediments. Two northeast-trending taposed along rotated thrust contacts. The interpretation of as- transverse structural lows of Tertiary age, the Konzani depression sociated mesoscopic and macroscopic structural elements (Zim- and the Euboean-Boetian depression, superimposed on the merman and Ross, 1976) will not be reviewed here. Barton states Pelagonian massif, contain volumetrically significant amounts of that the repetition of facies between the Almopias and Peonias mafic and ultramafic rock. These depressions provide reasonable subdivisions (Mercier, 1973a) is indicative of strike-slip faulting. It continuity of distribution between the ophiolites of the Vardar and is much more logically explained by partial erosion of folded Othris zones (see Aubouin, 1965, p. 158, Fig. 39; Renz and others, thrusts rooted in the Peonias subzone (see Zimmerman and Ross, 1954). Fig. 6). This interpretation is consistent with the results of Mercier The Vardar zone can be traced from the Aegean coast at Salonika (1973a, 1973b) from the Almopias subzone. In addition, the en (Greece) northward into central Yugoslavia for approximately 750 echelon patterns of folds and synthetic and antithetic faults charac- km. The Yugoslavian part of the zone forms a major internal unit teristic of much strike-slip—faulted terrane (Wilcox and others, of the Dinaride orogenic belt and contains several large ophiolite 1973) do not occur in the Vardar zone in Greece. complexes, including the South Serbia, West Serbia, Zlatibor, and Following Hynes and others (1972) and Smith and Woodcock

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(1976), Barton states that the ophiolites of the western belt were Vergely, 1974). This movement probably accompanied rotation of obducted in a northeasterly direction from an ocean basin located the complex during a phase of activity along high-angle normal west of the Pelagonian massif. Ultramafites of the Othris zone are faults bounding the Mesohellenic trough immediately to the west distributed in a shallow arc, concave to the northeast and about and may have concurrently produced additional small mesoscopic 400 km in length. At its southern limit the ophiolite trend termi- folds in rocks near the base of the complex (see Bernoulli and nates adjacent to the Pelagonian ultramafites in the Euboean- Laubscher, 1972, Fig. 3e). Boetian depression. At its northern extremity, the ultramafites of Timing of the events that resulted in emplacement of the ophio- the Othris zone swing abruptly northeastward toward the trend of lites is uncertain, although many investigators have suggested that the Dinaric internides and are terminated along the Pec-Scutari line, obduction began in latest Jurassic (post-Kimmeridigian) or Early a tectonic lineament in Albania and Yugoslavia which may repre- Cretaceous (pre-Cenomanian) time (for example, see Baumgartner sent the curving edge of a nappe (Bernoulli and Laubscher, 1972, and Bernoulli, 1976). By late Albian time, the ophiolites had been Figs. 1, 6) or a tear fault. Not only is the Othris zone significantly thrust over neritic rocks of the Pelagonian shelf. Regional green- shorter than the Vardar, but its shape and the trends of its northern schist grade metamorphism apparently accompanied and southern terminations suggest a spatial and perhaps a genetic emplacement-related deformation and has been noted in the Var- relationship with the Vardar suture. dar zone (Mercier, 1966a, 1973b; Kockel and others, 1971), the The hypothesis of a western origin for ultramafites in the Othris Pelagonian zone (Mercier, 1966a), and the Othris (sub-Pelagonian) zone developed from the palinspastic reconstruction of juxtaposed zone (Zimmerman, 1972). Earlier phases of this event correspond marine facies near the Othris massif (Hynes and others, 1972). to the Eohellenic Phase of Jacobshagen and others (1976a). In our Rocks representing successively deeper marine environments lie in model (Zimmerman and Ross, 1976, Fig. 6) initial ophiolite tectonically reversed sequence in thrust contact with the western emplacement onto neritic rocks accompanied partial subduction of Pelagonian shelf. The resulting suggestion of a deepening marine an attenuated Atlantic-type Pelagonian margin on the eastern side basin or trough to the west is not new and was included in Au- of the massif. During this period, subduction was eastward, and bouin's (1965) model of the evolution of isopic zones in west- opposed obduction occurred along east-dipping synthetic thrust central Greece. Deeper water, however, does not necessarily require faults. This phase initiated the processes that would lead to the the presence of oceanic lithosphere directly beneath it, and the gradual destruction of the ancestral Vardar ocean and which, in trough may well have been floored by thinned continental base- our view, continued throughout Late Cretaceous time, as stated in ment. The case for an Othris zone ocean would be significantly the abstract of our paper. These processes are not of a short-term strengthened by the presence of an Othris zone suture, yet few of variety. If our model is correct, sufficient additional time must be the features that characterize the Vardar root zone, for example, allowed for subduction-zone flip, subsequent subduction of the have been found west of the Pelagonian massif. In addition, there is eastern part of the Vardar ocean, partial subduction of the Rhodo- no direct structural evidence (Smith and Woodcock, 1976) that ul- pian margin probably attended by local northeast-directed synthe- tramafites of the Othris massif were obducted from the adjacent tic thrust faulting along the edge of the Rhodopian zone, and final trough and thrust to the northeast. Smith and Woodcock's (1976) locking of the Rhodopian continental plate against the Vardar su- model for such obduction indicates that it occurred along faults ture. Precise timing of the later events has not been established, but antithetic to an east-dipping subduction zone. It is much more there is evidence (Mercier, 1966b, 1973a, 1973b) that they oc- difficult to explain the mechanics of antithetic ophiolite obduction curred from latest Cretaceous through late Eocene time. In the than the more standard synthetic process (Roeder, 1973). If such Almopias subzone, neritic carbonates and carbonate-clastic se- obduction did occur, it should be characterized by numerous high- quences of certain and probable Late Cretaceous age are folded and angle (thick-skinned) thrusts cutting the continental margin edge or thrust faulted and lie in juxtaposition to allochthonous eugeosyn- trench inner wall landward from the usual stack of synthetic thrust clinal rocks of the Vardar root zone (see Mercier, 1973a, Figs. 71b, plates (Roeder, 1975, Fig. 4). No clearly established fault patterns 72, 73, 74, 76, and others). Carbonates of equivalent age overlying of either type have been reported from the vicinity of ophiolites in parts of the Vourinos complex and its environs are undeformed and the Othris zone. unmetamorphosed, suggesting that they had been transported a Investigation of rocks beneath the Vourinos ophiolitic complex, sufficient distance from the developing Vardar root zone flexure to also located in the Othris zone, has produced no unequivocal evi' escape deformation during its formation. If Mercier (1973a, p. dence for its sense of thrust emplacement (Zimmerman, 1972). 374—378) is correct in his dating of microflora in deformed vol- Small mesoscopic folds in and near the subjacent mélange verge caniclastic rocks of the Peonias subzone, terminal deformative and both to the northeast and southwest. Naylor and Harle's (1976) metamorphic (Mercier, 1966b) events in the evolution of the Var- study of such folds (see their Fig. 4c) should be judged on its own dar suture may have involved rocks as young as Priabonian. merits, but we consider the results of their "Hansen" analysis in- As Barton suggests, we were, perhaps, remiss in citing the general conclusive. The results of an analysis of the shear sense in mylonites period of ocean basin destruction (Late Cretaceous) rather than from the tectonite zone of the Vourinos complex (Zimmerman and specifically stating the probable lower and upper time limits of pro- others, 1977) must also be considered inconclusive at this time. cesses involved. These features, possibly formed at a depth of about 30 km during Our model suggests southwestward obduction of ophiolites in a an incipient stage of obduction, indicate thrust transport north- single nappe or a series of stacked thrust sheets commencing in ward — a direction incompatible with either obduction hypothesis, Early Cretaceous time. Most of this nappe has been removed by but perhaps more consistent with that of Barton. Similar fabric erosion in Yugoslavia, but remnants remain in Greece, having been analyses on the other ophiolites in the Othris zone should be com- preserved in or adjacent to the Tertiary depressions mentioned pleted in order to support these data. above. The present distribution of ophiolites in Greece suggests ap- Limited thrust transport of the Vourinos complex to the north- proximately 135 km of thrust transport rather than the "several east occurred after Pliocene time (Zimmerman, 1972; Faugères and hundred kilometres" cited by Barton. It might be noted, however,

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that Temple (1968) suggested at least 128 km of westward mid- tral Greece): Zeitschrift Deutschen Geologischen Gesellschaft, v. 123, Tertiary thrust transport across the Peloponnesos, and Bailey and p. 455-468. McCallien (1953) indicated 300 km of thrust transport of ultra- Jacobshagen, V., Risch, H., and Roeder, D., 1976a, Die eohellenische Phase, definition und interpretation: Zeitschrift der Deutschen mafic and related rocks in Turkey. Geologischen Gesellschaft, v. 127, p. 133-145. The problems of the Olympos window are admittedly difficult to Jacobshagen, V., Skala, W., and Wallbrecher, E., 1976b, Observations sur explain. Presence of an identical microfauna in the uppermost le développement tectonique des Sporades du Nord: Société levels of both the Olympos and Gavrovo platforms, however, im- Géologique de France Bulletin, XVIII, p. 281-286. Kauffmann, G., Kockel, F.. and Mollat, H., 1976, Notes on the stratig- plies similarity of water depth and paleolatitude of both locations raphie and palaeogeographic position of the Svoula Formation in the and not necessarily a "continuous Mesozoic carbonate bank" as innermost zone of the Hellenides (Northern Greece): Société stated by Barton. There is no entirely satisfactory explanation of Géologique de France Bulletin, ser. 7, v. 18, p. 225-230. the "uninterrupted" sedimentary sequence in the Olympos window Kockel, F., Mollat, H., and Walther, H. W., 1971, Geologie des Serbo- in our model. Bernoulli and Laubscher (1972, p. 113) have ad- Mazedonischen Massivs und seines mesozoischen Rahmens (Nordgriechenland): Geologisches Jahrbuch, v. 89, p. 529-551. dressed this problem, and the reader is referred to their discussion. ——1972, New facts and ideas on the innermost zones of the Hellenides: Owing to the allochthonous nature of so many lithologie units and Deutschen Geologischen Gesellschaft Zeitschrift, v. 123, p. 349-352. sequences in northern Greece, it is tempting to suggest that rocks Mercier, J., 1966a, Mouvements orogéniques et magmatisme d'âge juras- exposed in the window were simply not in their present location sique supérieur-eocrétace dans les zones internes des Hellénides during passage of ophiolite-bearing thrust sheets. Certainly, struc- (Macédoine, Grèce): Revue de Géographie Physique et de Géologie Dynamique, v. 3, p. 265-278. tural elements in units of the Pelagonian massif, its Mesozoic car- 1966b, Paleogéographie, orogénese, métamorphisme et magmatisme bonate cover, and adjacent rocks of the Vardar zone immediately des zones internes des Hellénides en Macédoine (Grèce): Vue northwest of the window show an overwhelming dominance of d'ensemble: Société Géologique de France Bulletin, ser. 7, v. 8, vergence to the south and southwest (Godfriaux, 1964, Figs. 2, 3) p. 1020-1049. indicative of thrust transport in that direction. Barton's (1975) 1973 a, Etude géologique des zones internes des Hellénides en Macédoine centrale (Grèce), Vol. I: Annales Géologiques des Pays analysis of Tertiary folding in and adjacent to the Olympos win- Helleniques, 1st ser., v. 20, p. 1-596. dow shows an opposite sense of vergence. These structures, how- 1973b, Contribution a l'étude du métmorphisme et de l'évolution ever, are relatively few in number and may be related to local magmatique des zones internes des Hellénides, Vol. II: Annales synthetic thrusting to the northeast which accompanied partial Géologiques des Pays Flelleniques, 1st ser., v. 20, p. 597-792. subduction of the Rhodopian margin during its collision with the Naylor, M. A., and Harle, T. J., 1976, Palaeogeographic significance of rocks and structures beneath the Vourinos ophiolite, northern Greece: Vardar suture (Zimmerman and Ross, 1976, Fig. 6C) or to rotated Geological Society of London Journal, v. 132, p. 667-675. antithetic thrusts (Roeder, 1973, 1975) produced during the same Price, I., 1976, Carbonate sedimentology in a pre-Upper Cretaceous conti- events. nental margin sequence, Othris, Greece: Société Géologique de France Bulletin, ser. 7, v. 18, p. 273 -279. 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