Eoalpine to Neoalpine magmatic and metamorphic processes in the northwestern Vardar Zone, the easternmost Periadriatic Zone and the southwestern Pannonian Basin

503

Tectonophysics, 226 (1993) 503-518 Elsevier Science Publishers B.V., Amsterdam

Eoalpine to Neoalpine magmatic and metamorphic processes in the northwestern Vardar Zone, the easternmost Periadriatic Zone and the southwestern Pannonian Basin Jakob Pam2 Institut za geoloika istraiivanja, Sachsova 2, 41000 Zagreb, Croatia (Received August 13, 1992; revised version accepted February 4,1993)

ABSTRACT The occurrence of Eoalpine-Neoalpine, genetically different, granitoids and penecontemporaneous volcanics are characteristic for the Vardar Zone. These rocks are mostly associated with Late Cretaceous-Paleogene basinal sedimentary rocks underlain by ophiohtes. The Late Cretaceous-Paleogene rocks were progressively metamorphosed under mediumpressure conditions and intruded by synkinematic Mesoalpine granitoids. The high-pressure blueschist metamorphism was related to a pre-Maastrichtian Eoalpine metamorphic event. Eoalpine and Mesoalpine magmatism and the related metamorphism of the Vardar Zone may have taken place along a magmatic arc, i.e., the subduction zone. The easternmost parts of the Periadriatic Zone are characterized only by Oligocene granitoids accompanied by penecontemporaneous volcanic rocks. Here, younger Alpine metamorphic phases only overprint and mylonitize older pre-Alpine formations. Most of the Mesoalpine granite plutonism both of the Vardar Zone and the easternmost area of the Periadriatic Zone was related to subsequent extension. The southwestern and southern parts of the Pannonian Basin contain the products of four pulses of Mesoalpine and Neoalpine synsedimentary volcanic activity (Egerian-Eggenburgian, Ottnangian-Carpathian, Badenian and post-Badenian) represented by predominant basalt-andesites, trachyandesites and trachydacites. This post-subduction volcanism was closely connected with the cyclic marine ingressions in the Pannonian Basin.

Introduction In numerous large-scale geological interpretations and correlations, many common and very important geological features of the AlpineHimalayan belt vanish in the area surrounding Zagreb, as, for example, the suture boundary between the African and Eurasian plates (see fig. 2 in Ricou et al., 1986). Whereas the existence of Alpine granite plutonism and at least two phases of Alpine metamorphism in the Alps (Frey et al., 1974; Callegari, 1983; and others) as well as in the southern Hellenides (Andriessen et al., 1979; Seidel et al., 1981; Altherr et al., 1982; and others) is now well established, there are no adequate data concerning the Alpine magmatism and metamorphism of the Dinarides (Fig. 1) and Vardar Zone s.s., this in contrast to Alpine domain. In this paper a correlation is presented between Eoalpine to Neoalpine granitoid and meta0040-1951/93/$06.00

morphic rocks along the easternmost parts of the Periadriatic Zone (PZ> and in that part of the Vardar Zone (VZ> s.1. located south and southwest of the Pannonian Basin (PB). The magmatism and metamorphism of the VZ is interpreted to have taken place along a presumed subduction zone active during the Late Jurassic, Cretaceous and Tertiary (Pamic, 1977). Tertiary volcanism within the PB was genetically related to subsequent extension. All recent geotectonic interpretations of the evolution of the PB are related to the Carpathians (Stegena et al., 1975; Royden et al., 1983; and others). However, the evolution of the southern marginal parts of the PB should be also considered in respect to the Dinarides. The Dinarides is a complex fold, thrust and imbricate belt characterized by a regular pattern in the spatial distribution of the characteristic lithologies. From the southwest to the northeast,

0 1993 - Elsevier Science Publishers B.V. Ah rights reserved

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i.e., the Apulia (or Adriatic microplate) to the northeast, the following lithological associations can be distinguished: (1) a carbonate platform of the Alpine passive continental margin (the external Dinarides); (2) carbonate-elastic sedimentary rocks of the Alpine passive continental margin; (3) ophiolites (open-ocean area); and (4) sedimentary, igneous and metamorphic rocks of the Alpine active continental margin represented by the VZ s.1. (Fig. 1). The last three lithological units are included within the internal Dinarides. Such a regular spatial pattern of characteristic hthologies cannot be found in the northern frame of the PB, i.e., the Carpathians whose internal Mesozoic facies units seem to be rather erratic (Csontos et al., 1992).

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The no~~weste~ Vardar Zone: J&alpine to Neoalpine magmatic and metamorphic processes The northwesternmost part of the VZ which includes the Prosara-Motajica-Cer-Bukulja (PMCB) unit (Fig. 11, is characterized by several rocks groups genetically related to an ancient magmatic arc, i.e., the subduction zone. The Late ~retace~~~-P~~e~~ene L!olca~ic-sedime~tary complex Late Cretaceous-Paleogene sedimentary rocks, represented mainly by shales, sandstones and limestones, define a flysch and flyschoid complex (Jelaska, 19’781, the lower parts of which are

200km

Fig. 1. Simplified geological sketch map of the Dinarides showing the distribution of characteristic EthoIogies. Mesozoic carbonate platform (I) and ctastic and carbonate sedimentary rocks (2) of the passive continental margin Ophiolite Zone (3) and its southern exte~ion-Mirdita Zone (3121,Vardar Zone s.1. (4) and Vardar Zone S.S. (da). Geographically, the original Kossmat’s (1924) definition of the Vardar Zone (s.s.) was restricted only to Macedonia. Recently, this term (the Vardar Zone s.l.) was extended to identical or similar rock units (mostly ophiolites, Late Cretaceous-Paleogene sediments and volcanics, and Alpine granitoids with andesites) of the Dinarides originated in the Vardar Ocean (Dercourt, 1972; and others). 5 = Pannonian Basin; 6 = SerboMacedonian Massif; 7 = Carpathians and Balkan; 8 = Peiagonides and Korab. Large transversal faults: SP = Skadar-PeE; SA = Sarajevo; ZK = Zagreb-E&s. PZ = Periadriatic Zone. The mountains built up of Alpine granitoids rt metamorphic rocks: B = Bukulja; Bo = Boranja; C = Cer; FG = Frugka Gora; J = Jastrebac; K = Karavanke; M = Motajica; Ph = Pohorje; P = Prosara.

ZONE.

PERIADRIATIC

ZONE

AND

PANNONIAN

BASIN

-

,

Fig. 2. Geological sketch map of the area adjoining the southern and southwestern parts of the Pannonian Basin and the northernmost and northwesternmost Dinarides. 1 = Neogene and Quaternary sedimentary rocks of the Pannonian Basin; 2 = Tertiary volcanic rocks; 3 = Alpine granitoids; 4 = AIpine metamorphic rocks; 5 = Oligocene tuffq 6 = Late CretaceousPaleogene sedimentary rocks f volcanics; 7 = carbonate platform; 8 = dastic and carbonate sedimental rocks of the passive continental margin; 9 = ophiolites; 10= Mesozoic basinal sedimentary rocks of the internal Dinarides; II = JuIian-Sa~nja nappe; 12 = Sava nappe; 13 = Triassic rocks of the area of Karavanke; 14 = Mesozoic horsts within the Pannonian Basin; 15 = Paleozoic regionally metamorphosed rocks f granitoids; I6 fault, normai; 17 = thrust fault; 18 = oil wells with Alpine granitoid and metamorphic rocks. Large-scale faults: U. = Cabot line; PZ = Periadriatic Zone; SDF = South Drava fault System; SF8 = Sava fault system; ZK = Zagreb-Kulcs. Mountains: B = Bohor; D = Dilj; I = IvanEica; L4 = Juhjske Alpe; K = Kalnik; KR = Karavanke; KD = Krndija; M = Motajica; MD = Medvednica; MG = MoslavaEka Gora; P = Papuk; PG = Poiegka Gora; PH = Pohorje; PR = Prosara; Ps= Psunj; R = Ravna Gora; S = StrahinXca; SA = Savinjske Alpe; SG = Samoborska Gora; V= VuEjak.

interlayered in some places with basalts, rhyolites and tuffs (Fig. 21. In numerous places, the volcanic-sedimentary complex is underlain by an ophiolitic melange of Late Cretaceous age (Pami& 1982). Late Cretaceous flysch sediments occur also within the southeastern extension of the VZ. Alpine medium-pressure metamorphic rock In the northern parts of the PMCB unit, Late Cretaceous-Paleogene sedimentary rocks were metamorphosed under medium-pressure conditions. In Mount Motajica (Fig. 31, complete sequences are best preserved showing progressive

zonation of chlorite to biotite to garnet to staurolite and, in some places, to andalusite (Pamii: and ProhiC, 19891. This progression from unmetamo~hosed Late Cretaceous sedimentary and igneous rocks up to amphibolite-grade rocks takes place over a distance of a few kilometres. Based on textural arguments, mineral zonations, changes in the oxygen isotopic composition and geobarometric data from white mica b,, the prograde metamorphic sequence of Mount Motajica can best be explained by two phases of metamorphism. In the first phase, regional syntectonic medium-pressure and low-temperature metamo~hism affected a

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broad zone, up to 3-4 km wide. This is overprinted by contact metamorphism under increasing temperature and decreasing pressure during diapiric uplift of granite intrusion. Locally, this developed into a narrow andalusite zone of medium-grade metamorphism including local partial melting and the formation of migmatites (PamiC et al., 1992). In the surrounding Mount Prosara (Fig. 21, Late Cretaceous sedimentary rocks were metamorphosed under P-T conditions of the greenschist facies; the prograde sequence is also only a few kilometres wide (PamiC and Lanphere, 1991). In the slates and phyllites from the mounts Motajica and Prosara, a Late Cretaceous-Paleogene microflora was determined (PantiC and Jovanovic, 1970). This age is found for the entire Motajica and Prosara prograde sequences proven by the presence of fossiliferous phyllites. Radiometric determinations, carried out on mediumgrade rocks, gave K-Ar ages of 48-38 Ma (PamiE, 1987). Alpine metamorphic rocks were also found in the westernmost extension of the PMCB unit as well as in some oil wells around the mentioned orographic units. Narrow zones of Alpine metamorphic rocks associated with Late Cretaceous sedimentary

.+r+

rocks occur also in the easternmost parts of the PMCB unit in the Mount Bukulja area and further to the south in the area of Mount Jastrebac in the southeastern parts of the VZ s.1. (AleksiC and PantiC, 1972). Unfortunately, until now these Alpine metamorphic rocks have not been studied in detail. For a long time all these Alpine metamorphic rocks from the VZ s.1. have been considered to be of Precambrian, early or late Paleozoic age without any paleontologic or radiometric age evidence. Alpine high-pressure metamorphic rocks

While some review papers and large-scale global geological maps give data on glaucophane schists from the VZ s.1. (Zwart, 1967; Coleman, 1972; Dobretsov, 1978; and others), detailed studies with reliable analytical results on high-pressure mineral paragenesis are sparse. In the Late Cretaceous sedimentary rocks of Mount Motajica affected by incipient very lowgrade metamorphism, a diabase-looking olistolith occurs which is composed of crossite, albite, epidote, and phengite with Si values between 3.36 and 3.47. This indicates P-T conditions of 2 7

*+ + + + +

A

+J

+

l

I

+

+ c

+

+ A..

A$..;.‘J .

..

_

Fig. 3. Geological map of the area of Mount Motajica modified from VariCak (1965). I = Quaternary and Neogene sedimentary rocks of the Pannonian Basin; 2 = Late Cretaceous sedimentary rocks; 3 = very low- and low-grade metamorphic rocks: 4 = medium- grade metamorphic rocks; 5 = granite plutons; 6(G) = glaucophane schists.

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to 9 kbar and .350-400°C (Majer and LugoviC, 1992). The mineral assemblage ferro-glaucophane + albite + quartz + phengite + chlorite was determined in paraschists from Mount FruSka Gora which occur as pebbles in Late Cretaceous conglomerates (KiSpatiC, 1887; AleksiC and CiEulic, 1972). The Late Cretaceous sedimentary rocks of Mount FruSka Gora, located north of the River Sava (Fig. 0, are allochthonous and they probably were tectonically transported from the PMCB zone. Accordingly, evidence gained from mounts Motajica and Frugka Gora indicates that a highpressure metamorphism must have taken place before the Late Cretaceous. Alpine granitoid rocks

Alpine metamorphic rocks of the PMCB unit are intruded by small- to medium-sized granite plutons (PamiC, 1987). However, such plutons are more common in the subsurface of the PMCB unit as indicated by geophysical prospecting data (LabaS, 1975; Vukalfinovic, 1991). Alpine grani-

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toid plutons also occur very frequently in the southeastern part of the VZ s.1. Geochemical data including S’*O indicate that Alpine granitoids belong to different genetical families: to the A-type in the mounts PoieSka Gora and Prosara and to the S-type in Mount Motajica (PamiE and Lanphere, 1991). The granitoids from mounts Cer and Boranja originated from mixed upper mantle and crustal melts (Karamata et al.; 1990). Available data on the isotopic ages of Alpine granitoids from the VZ s.1. are presented in Table 1. Several groups of radiometric ages can be distinguished: (1) Early Alpine (168-97 and 145143 Ma); (2) Eoalpine (73-71 Ma); (3) Mesoalpine (mostly between 48 and 30 Ma) and (4) Neoalpine (27-10 Ma). Alpine granitoids are in some areas associated with penecontemporaneous volcanic rocks: (1) Eoalpine granitoids with bimodal rhyolites and subduction-related basalts as indicated by the initial 87Sr/86Sr = 0.7041 (PamiC et al., 1988); (2) Mesoalpine granitoids with andesites and dacites; and (3) Neoalpine granitoids with latites (shoshonites), quartz latites and andesites.

TABLE 1 Compiled data on isotopic ages (in Ma) of Alpine granitoids from the Vardar Zone s.1. Locality

Rocks

K-Ar whole rock

Mt. PoieHka Gora Mt. Prosara Mt. Motajica Sava Depressions (oil wells) Mt. Cer Mt. Boranja Mt. Kopaonik Mt. ?eljin Vardar Zone S.S. Macedonia

A-type granite A-type granite S-type granite Varieties of granite and granodiorite Quartz monzonite to granodiorite Granodiorite and quartz monzonite Quartz monzonite and granodiorite Granite and granodiorite “Furka” granite

K-Ar monom. concentrates

18.1 f 6

Rb-Sr model

72-17 (4)

Sr-isochron

71.5 (5) 48 f 1.5? 48 f 1.5

72.7 f 2.2 to 61.0 f (4) 34.7 f 7 to 27.0 f 2 (2) 23 f 2 16*2 33.67-29.58 (14)

10.7-10.8 (2)

29.2-24 (3)

25.32-29.79 (7) 24.3-17.54 (4) 168-97 (17) 145-143(3)

Based on literature data published by Soptrojanova (1967); Deleon (1%9); PamiC et al. (1988); Delaloye et al. (1989); Karamata et al. (1990); PamiC and Lanphere (1991); Lanphere and Pami (1992). Numbers within brackets mark the number of the measured samples.

*%Pb- *3sU (zircone)

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Eoalpine and Mesoalpine ages of the granitoid plutonism and related volcanism fit well with the ages of “banatites” from Mount Apuseni and the Southern Carpathians. The banatites, represented mostly by diorites and granodiorites and their associated volcanic rocks originated during the latest Senonian and Paleocene-Eocene (Russo-Sandulescu et al., 1984). The easternmost part of the Periadriatic Zone: Mewalpine magmatic and metamorphic processes In the area of the PZ, the zoned pattern in the general spatial distribution of characteristic

lithologies, particularly those of the internal Dinarides, is masked by large masses of Triassic and young Paleozoic rocks of the Sava and JulianSavinja nappes (Fig. 2; MioE, 1982, 1984). The Sava and Julian-Savinja nappes The Sava and Julian-Savinja nappes consist of Carboniferous and Permian slates, sandstones, and conglomerates which are overlain by Groeden beds, represented mostly by quartz sandstones with slates, and capped by Bellerophon limestones. The Paleozoic complex is overlain by Triassic formations: Scythian beds (marly shales, sandstones, marly limestones and dolomites),

. A

I

C’.

G*HL~-e-

-KLAGENFURT

0

20km

5

,1-_I *1--_1 J---J ‘m Fig. 4. Sketch map of the area of the easternmost Von

Gosen

sedimentary

(1989).

I = Miocene

to Quatemary

,I’+‘*‘i J=J

parts of the Periadriatic sedimentary

rocks

,[LT11 ,/

Zone. Based on data of Buser and Draksler W90)

of the Pannonian

Basin;

2 = Oligocene

rocks of the Pannonian Basin f andesites; 3 = Periadriatic Zone; 4 = Permian-Triassic granitnids; tonalites; 6 = Eastern Alps; 7 = Southern Alps and Dinarides; 8 = main faults.

and

to Quatemaw 5 = Paleogene

MAGMATIC AND METAMORPHIC PROCESSES - VARDAR ZONE, PERIADRIATIC

Anisian dolomites and Ladinian platy limestones, in many places with shales, cherts, tuffs and volcanic rocks. The Late Triassic is represented by limestones conformably overlain by dolomites and limestones (MioE, 1984). However, below the Sava and Julian-Sava nappes Mesozoic basinal sediments locally occur which can be ascribed to the internal Dinarides (Fig. 2). In th e t ec t onic windows and faulted zones, a complete Jurassic-Late Cretaceous basinal sedimentary succession can be reconstructed (Cousin, 1972; BabiC, 1973; PleniEar and Premru, 1977; MioE, 1978; Buser, 1985; AniEiC, 1990; and others). Fragmental parts of the Jurassic-Cretaceous sequence can be traced from the easternmost parts (Mount Bohor) to the westernmost parts of the Sava nappe, in the area of Tolmin where the complete sequence is developed. The Sava nappe stretches without a break into the austroalpine unit represented by the Drauzug. The Sava nappe is thrust mainly onto the Mesozoic carbonate platform of the Dinarides and partly, in the area of Tolmin, onto the Jurassic and Cretaceous internal units (Fig. 2). The Sava nappe extends towards the southeast and corresponds to the Durmitor nappe of the central and southeastern Dinarides (MioE, 1984). The Julian-Savinja nappe might be correlated with the Pannonian nappe (Miladinovic, 1974) which is thrust over the Durmitor nappe. Further to the east, in the area of Zagreb, Hrvatsko Zagorje and Prigorje, lithologies typical of the internal Dinarides and Dinaridic and Alpine structural features are masked by Neogene sedimentary rocks of the PB. This area includes several mountains: Ravna Gora, StrahinSEica, IvanSEica, and Kalnik (Fig. 2) which can be interpreted as relics of the Sava and/or Julian-Savinja nappe(s). In the mounts Medvednica and Kalnik, predominant Triassic sedimentary rocks are also associated with Late Jurassic and Aptian-Albian basinal limestones, shales, marly shales and cherts with ophiolites. In some areas, Late Cretaceous breccias, conglomerates, shales, marly shales, carbonate turbidites, pelagic limestones and cherts are found (Crnkovic, 1963; &kid et al., 1979; SimuniC, 1983, 1992; and others). The present ambiguous structural setting of these

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“hoist” mountains is probably controlled by the system of subparallel transcurrent faults (Oluic, 1975) which represent the southwesternmost extension of the large Zagreb-Kulcs fracture zone (Wein, 1968). The area of the Smrekovec and Labor (Lavanttal) lines The easternmost parts of the PZ, known in Slovenia as the Smrekovec Line, can be traced along strike for about 50 km. Further to the east it is covered by Tertiary sedimentary rocks of the PB. The Smrekovec Line is intersected by the Labot (Lavanttal) Line separating the Karavanke from the Pohorje Mountains (Fig. 4; MioE, 1982). Petrologically, the most striking feature of the PZ is the presence of numerous smaller or larger tonalite plutons whose radiometric ages are essentially Oligocene, although Late Eocene ages have been also reported (Exner, 1976; Del Moro et al., 1983; Kagami et al., 1991; and others). Two tonalite plutons occur in the area of the Smrekovec Line (Fig. 4). The northern Pohorje laccolith, covering an area of about 150 km*, intrudes into multiple deformed metamorphic rocks. The laccolith and adjacent metamorphic rocks are cut by larger or smaller tonalitic dykes (MioE, 1978; and others). In Mount Karavanke, two E-W-elongated plutonic bodies, separated by a narrow zone of Paleozoic metamorphic rocks, are present along the Smrekovec Line (Faninger, 1976). The northern pluton, made up of some varieties of granites, is older (244-216 Ma) than the southern one (29.628.4 Ma) which consists of tonalite (Cliff et al., 1974; Lippolt and Pigeon, 1974; Scharbert, 1975). The latter can be traced along strike for about 20 km, with an average width of about 1.5 km, and continuing on into Austria. The tonalite isotopic ages may be too low because tonalite pebbles are redeposited in the surrounding conglomerates of the Socka beds which are paleontologically dated as Early Oligocene (KuSEer, 1967). This means that the tonalites may be older than the Middle Oligocene which is about 35-30 Ma or, alternatively, the

510

tonalite pebbles might have been eroded from an older part of the tonalite body. The tonalite bodies indeed consist mostly of biotite-quartz diorite grading into granodiorite and subordinate augite-hornblenda gabbrodiorite. The rocks from both areas are commonly distinctly foliated as in the other tonalite massifs along the PZ (Faninger, 1970, 1976). On the basis of the presence of magnetite, the high Na,O: K,O ratio and the relationship between CaO and total Fe (Chappell and White, 19741, tonalites from the mounts Pohorje and Karavanke can be classified as I-type granites. The metamorphic country rocks of the Pohorje tonalite are part of the central zone of the Eastern Alps. They are represented by (1) the Pohorje metamorphic series consisting of kyanite-bearing gneisses and mica schists with subordinate amphibolites, eclogites, and quartzites, and (2) the Koban metamorphic series consisting of staurolite-almandine-bearing mica schists and gneisses, and greenschists. Retrograded and mylonitic phyllonites are also common. There are no radiometric data available on the metamorphic complex which is probably Precambrian and shows a poly-phase deformation; the last phase, accompanied by retrogradation, probably took place during the Variscan orogeny. Mica schists from the contact area with the tonalite pluton were metamorphosed into andalusite-bearing mica schists (GermovSek, 1954; Hinterlechner-Ravnik, 1971, 1973; MioE, 1978, 1982; and others). In Mount Karavanke, the geological relations are much more complex around the Permian granite and Tertiary tonalite plutons. These are separated by a narrow zone of phyllites and mica schists which can be compared with the highly phyllitized lower suite of the Ordovician Magdalensberg series from Austria (Faninger and Struncl, 1978). In the western extension of the PZ in the Eisenkappel area, Von Gosen (1989) found andalusite-cordierite hornfelses which are genetically related’ to well documented D, a young Alpine deformational event. Unfortunately, there are no reliable analytical data on the effects of the Alpine metamorphic processes in the area of the Smrekovec Line. On the basis of some data, Alpine metamorphism

I PAM]<’

may have given rise to retrogradation, probably accompanied by mylonitization. HinterlechnerRavnik (1982) thinks that the phyllonitization of the Paleozoic Pohorje complex might have been brought about, at least partly, by an Alpine deformational event. Kyanite-bearing eclogites of the complex were also affected by Alpine retrogradation as well as the overlying phyllonites of the Pohorje metamorphic complex. Recent geochronological data indicate that major parts of the Southern Middle Austro-Alpine crystalline complex, which represents the northern extension of the Pohorje metamorphic unit, have been overprinted within Cretaceous amphibolite facies. In addition, a Cretaceous age of eclogites, incorporated in this crystalline complex, has been supported by geochronology (Frank et al., 1987; Thoeni and Jagoutz, 1991; and others). Late Cretaceous sedimentary rocks, which are so characteristic of the VZ s.l., are much sparser in the area of the Smrekovec and Labot Lines. Several small outcrops of Late Cretaceous sedimentary rocks are found along the northwestern margin of the Karavanke tonalite pluton and in the intersection area of the Smrekovec and Labot Line (Fig. 4). The Late Cretaceous is represented by basinal marly shales, marly limestones, in some places with rudist limestones, but also by flyschlike sandy and marly shales and sandstones, in other places with globotruncana limestones (MioE, 1978). Germovsek (1954) described contact-metamorphic marbles from the northernmost margin of Mount Pohorje with relict fossiliferous Late Cretaceous sedimentary rocks. No data on the possible regional metamorphism of the Late Cretaceous sediments are available. However, some metamorphic rocks in the area of the Piedmont ophiolite units and the Tauern window have been interpreted as representing metamorphosed Cretaceous flysch (Frisch, 1984). The southern parts of the Pannonian Basin: Neoalpine magmatic processes The last marine sedimentation in the Dinaridic parts of the Tethys ceased during the Eocene. The main deformational event (the Pyrenean

MAGMATIC AND METAMORPHIC PROCESSES - VARDAR ZONE, PERIADRIATK

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SLOVENIJA AN0 HRVATSKO ZAGORJE

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ROMANIAN

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PONTIAN

PANNONIAN

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KARPATHIAN OTTNANGIAN 19

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20.

; 9

21-P

zl

EGGENBURG

IAN

2223

212.

24. 2s.

iz

EGERIAN

0” 0 0 3

0

W z E 0 W

Fig. 5. Geological columns for the southwestern and southern marginal parts of the Pannonian Basin. I = gravels and conglomerates; 2 = breccias; 3 = sands and sandstones; 4 = clays; 5 = marls; 6 = coals; 7 = tuffs and volcanic breccias; 8 = dacites, andesites and trachyandesites; 9 = basal&; 10 = alkali-feldspar rhyolites.

512

phase) and the definitive uplift of the Dinarides gave rise to the separation of the Tethys into the Mediterranean, in the south, and the Paratethys, i.e., the PB in the north. These southern parts of the Paratethys remained periodically connected with the Mediterranean Basin. This gave rise to several facies exchanges being graded from marine to brackish and to fresh-water facies (Roegl and Steininger, 1984; Simunic, 1992; and others). These older marine ingressions were accompanied in some areas by a synsedimentary volcanic activity. The facies variations with synsedimentary volcanic rocks, are presented in columnar sections (Fig. 5) for the southern part of the PB which borders the VZ of the northernmost Dinarides and for the southwestern margin which borders the area of the Smrekovec Line. The Early Oligocene Socka beds (mostly sands, gravels, marls with sandstones, and conglomerates) of the PB are best exposed in the area of the Smrekovec Line in eastern Slovenia. Further to the east in Hrvatsko Zagorje and in the Mura Depression (Fig. 2) the same sediments belong to the Egerian and they are accompanied by synsedimentary volcanic rocks (SimuniC, 1992). The volcanism produced mostly andesites with subordinate dacites, propylitized in some places, associated with large quantities of pyroclastic rocks like the Smrekovec tuffs and volcanic breccias (Faninger, 1966; Hinterlechner-Ravnik, 1967). Equivalent exposures of the Egerian sedimentary and volcanic rocks have not been found so far in the southern parts of the PB adjacent to the northernmost Dinarides. The second marine cycle started by the beginning of the Eggenburgian and the Macelj sandstones and conglomerates, containing large quantities of andesite and tuff fragments, were deposited in the southwestern part of the Paratethys close to the PZ. The elastic sedimentation was accompanied by weak synsedimentary volcanic activity. It ceased by the end of the Eggenburgian and was followed by a shortly lasting emersion (SimuniC, 1992). In the southern parts of the Paratethys, Early Miocene conglomerates, sandstones, marls, and limestones, are poorly preserved close to the

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northernmost Dinarides. On the basis of present knowledge, they are not accompanied by any volcanic and pyroclastic rocks. The next marine ingression of the Tethys into the Paratethys took place in OttnangianKarpathian and shallow-marine breccias and conglomerates with marls and sands were deposited. In the southern parts of the PB which border the northernmost Dinarides, volcanic activity took place during this second marine cycle producing comparatively larger masses of trachyandesites and trachydacites with pyroclastics. The trachyandesites may have a crustal origin as indicated by a high initial 87Sr/86Sr ratio averaging 0.70566 (PamiC et al., 1993). Ottnangian-Karpathian sedimentary rocks of the southwestern parts of the PB adjacent to the PZ include only small masses of pyroclastic rocks. The next and probably last marine transgression took place by the beginning of the Middle Miocene, mainly in the middle Badenian. This was the strongest ingression of the Tethys which covered the complete area of the present SavaDrava interfluve. At the beginning, breccias and conglomerates and later on reef limestones and marls were deposited. The last transgression was accompanied by the strongest volcanic activity. It was particularly strong in the southern parts of the PB adjacent to the northernmost Dinarides where it gave basaltandesites with pyroclastic rocks (Lugovic, 1983; Pam% and Pikija, 1987; LugoviC et al., 1990; and others). It was also strong in the Mura Depression where it produced mainly andesites with tuffs, but the largest masses of Badenian basaltandesites were drilled in numerous oil wells in the Drava Depression. The basalt-andesitic melts may be of crustal origin as indicated by a comparatively higher initial 87Sr/86Sr ratio averaging 0.7063 (PamiC et al., 1993). This volcanic activity was weak in the area around the PZ and gave only interlayered pyroelastic rocks. A continuous sedimentation, but in brackish and gradually in fresh-water environments, went on after the Badenian during the Sarmatian, Late Miocene and Pliocene. Sands, marls, clays and gravels, in some places with coal lenses and seams,

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were deposited (Fig. 5). Only in a few oil wells from the Drava Depression, alkali basalts and basalts of a post-Badenian age (the Sarmatian?) were penetrated. Discussion While the external Dinarides and the Southern Alps have a uniform crustal thickness of about 40-50 km, the VZ s.1. shows distinct variations. The crustal thickness of the VZ s.1. with its southern extension adjoining the Serbo-Macedonian Massif, i.e., the Moesian microplate, amounts to about 40-50 km, but going further to the northwest in the area adjoining the PB it decreases to 25-30 km (DragaSeviC, 1977). This attenuation of the crust is probably genetically related to the uplift of the upper mantle which initiated the generation of the PB (Stegena et al., 1975; Royden et al., 1983; and others). The MohoroviU depth is 30 km under the Periadriatic Line and increases slowly and gradually southwards (Pfiffner et al., 1988). in spite of these differences in crustal thick-

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ness, surficial manifestations of the VZ s.1. are much more uniform due to the main common geological features. These are shown by the presence of: (1) comparatively large masses of Late Cretaceous, mostly flysch sediments, frequently interlayered with volcanics and associated with ophiolites but also with Late Jurassic and Early Cretaceous basinal sediments; (2) Alpine mediumand high-pressure regionally metamorphosed rocks; and (3) Eoalpine to Neoalpine granitoids which are associated with penecontemporaneous Alpine volcanic rocks of the andesite formations. It has been previously assumed (Pam%, 1977, 1987) that the Alpine granitoids with associated Alpine metamorphic rocks and volcanic rocks of the andesite formations might have been generated in a geotectonic setting correlatable with modem magmatic arc. The Late Cretaceous flysch complex might have been related to the magmatic arc and been deposited in the adjacent fore-arc and trench; axial parts of the latter probably mark an ancient subduction zone along which the Mesozoic oceanic crust of the Dinaridic parts

boundary (Aubouin et al., 1986) with the proposed correction for the 6. Palinspastic sketch map for Jurassic-Cretaceous extension of subduction zone in front of the Moesian microplate. 1 = oceanic subduction; 2 = thrust; 3 = spreading ridge; 4 = horizontal fault. B = B~an~nn~s; E = Eastern Pontides; L = Lombard, I& = Lower Austro-Alpine; M = Moesia; A&a = Middle Austro-Alpine; RH = Rhodopes; TA = Tatras; UAa = Upper Austro-Alpine; VL Valais; Wp = Western Pontides.

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of the Tethys was consumed. Southwesterly and westerly vergences of the Dinaridic folds and thrusts suggest a NE- and E-dipping subduction. Along the subduction zone, the emplacement of ophiolites may have taken place; based on radiometric data (Lanphere et al., 1975), it commenced in the Late Jurassic and ended before the Late Cretaceous flysch sedimentation started (Pam%, 1982). It is very probable that high-pressure blueschist metamo~hism was related to the ophiolite emplacement. Based on variations in granitoid ages, the evolution of the inferred magmatic arc can be speculated. These variations are lateral; generally, the oldest ages (Late Jurassic) are characteristic for the southernmost part of the magmatic arc, i.e., the VZ S.S. and going towards the north and northwest they become younger, mostly Paleogene (50-30 Ma) and Late Cretaceous (70 Ma). This age variation of granitoids along a single geotectonic structure results from di~erentiated tectonics and various amounts of erosion. This idea fits quite well with the recently proposed subduction zone in front of the Moesian block, i.e., the VZ s.1. (Aubouin et al., 1986). This subduction zone may represent a continuous northwestern extension of the long subduction structure proposed by Dercourt et al., (1986) which stretches from the area of the present VZ s.1. to the Zagros Range (Fig. 6). Smith and Spray (1985) presented the idea that the part of this subduction structure, located in front of the MoeSian microplate, may have been disrnpted by a Late Jurassic sinistral transcurrent fault along the eastern margin of the present VZ s.1. The termination of subduction processes probably gave rise to a regional and definitive uplift of the Dinarides. The uplift might have been brought about by the presence of deep-seated lithospheric slabs no longer in dynamic equilibrium with subduction. These geodynamic changes were related to the last strong compression (the Pyrenean phase) and might have given rise to the heating and generation of energetic flux for the synkinematic medium-grade regional metamorphism of the Late Cretaceous-Paleogene sedimentary rocks. The metamorphism was accompanied by pulses of synkinematic granite plutonism which

produced numerous smaller granite plutons. Under such periplutonic conditions, the geothermal gradients must have varied and narrow zones of low-pressure medium-grade rocks overprinted previously originated the medium-pressure metamorphosed rocks (ParniL et al., 1992). Could such a scenario be used for the northwesternmost parts of the Dinarides close to the Smrekovec Line? Small but numerous exposures of Jurassic and Cretaeeous basinal sedimentary rocks correlatable with those from the internal Dinarides including the VZ s.l., which are masked by the Sava nappe, indicate that the same basinal sedimentation in fundamentally same environments might have taken place in the northwesternmost and narrowed (?) Dinaridic part of the Tethys. Such narrowings and wedgings of the sedimentation areas within the Alpine-Himalayan belt are commonly explained by the rotation and kinematics of separate microplates during the Mesozoic evolution. There are different opinions on the kinematics of the Apulia microplate (Dewey et al., 1973; Channel and HorvLth, 1976; and others) but Dercourt et al. (1986) emphasize that the 80-65 Ma (Late Cretaceous/Tertiary boundary) and 38 Ma (Late Eocene/ Oligocene boundary) periods show major plate boundary reorganization between Africa and Asia. Therefore, it is very probable that these final tectonic movements might have shifted Apulia towards the north and thus have narrowed originally wider sedimentation areas. Anyhow, is spite of the presence of basinal lithologies in the northwesternmost parts of the Dinarides, there are no products of any Alpine magmatic and metamorphic processes which would indicate any subduction in the area of the Smrekovec Line. Concerning the Alpine magmatic processes, a distinct correlation between the VZ s.1. and the easternmost parts of the PZ starts with granitic plutonism and andesite volcanism related to Oligocene extension. In spite of the presence of Late Jurassic and Cretaceous granitoids, the most commdn isotopically measured ages in the VZ s.1. fall in the interval between 40 and 30 Ma like the granitoids along the PZ. On the basis of radiometric data obtained on granitoids, the PZ is

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characterized by Mesoalpine granitic plutonism (Laubscher, 1983) whereas the granitoids from the VZ s.1. were mainly generated during the Boalpine and Mesoalpine phases. As to the changes in geotectonic setting (compression versus extension), the problem of timing of the granite plutonism is not as simple as it looks in our generally accepted schemes. The last impressional event (the Pyrenean phase) took place in Late Eocene which is about 40-35 Ma. This and older Laramian Sr-isochron ages of granitoids were measured in the northwestern part of the VZ s.1. whereas younger ages (40 and 30 Ma) were obtained from granitoids from the eastern extension of this zone. It is true that most of the isotopic ages measured on single granitoid plutons along the PZ gave the Oligocene age. However, based on more than 100 Rb-Sr and K-Ar measurements on systematically sampled granitoids from the largest Adamello batholith, Del Moro et al. (1983) showed that its emplacement lasted over a 12 Ma span, from 42 to 30 Ma. Besides that, the isotopic ages averaging 30 Ma are not always concordant with more reliable geological ages as indicated by tonalite pebbles redeposited in Early Oligocene conglomerates in the area of the Smrekovec Line. Accordingly, the oldest plutonic phases along the PZ might have been also partly related to subduction processes. Oligocene granitoids both of the PZ and VZ s.1. are characteristically associated with more or less coeval and post-subduction andesites, commonly with large masses of pyroclastic rocks. The Oligocene volcanic rocks in the southwestern marginal parts of the PB are genetically related to the initial extensional processes, i.e., the beginning of the generation of the PB. In the southern parts of the PB, these initial extensional processes were followed by volcanic activity which produced Oligocene andesites with dacites, Early Miocene trachyandesites and Badenian andesites and basalts. The Early-Middle Miocene andesites and dacites, in some places associated with penecontemporaneous granitoids, are also very common in the VZ s-1. As distinguished from Late Cretaceous subduction-related basalts of upper mantle origin, these Neoalpine volcanic rocks have a post-subduction character

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or were strongly contaminated by the continental crust as indicated by their initial Sr isotopic composition. If the evolution of the present PB was really due to extensional processes brought about during the attenuation of the crust and by the uplift of the upper mantle, then one may ask what existed in this area before the formation of the PB? Jelaska (1978) emphasized that Late Cretaceous-Paleogene flysch of the northern Dinarides can be correlated with the stratigraphically identical flysch of the Carpathians and Balla (1986) presented the idea that flysch basins of both mountain systems represented one single paleogeographic unit during the Late Cretaceous and Paleogene. If so, then the present Dinarides and internal Carpathians may have represented a single paleogeographic unit before the beginning of the evolution of the PB. Accordingly, two proposed relict subduction zones bounding the PB, i.e., the northern one in front of the Carpathians (Stegena et al., 1975; and others) and the southern one in front of the Dinarides (Pamic, 1977; and others) should be complementary to each other. It is probable that they might represent a complementary pair originating from a previous single magmatic arc of the Tethys. This presumption is supported by the following facts: (1) The paleotransport direction and heavy minerals in Late Cretaceous-Paleogene flysch sediments of the northern Dinarides indicate that the source area was located north of the present Dinarides. (2) The scarcity of Mesozoic ophiolites in the Carpathians. (3) The correlation between the Triassic sedimentary successions of the southern PB and Carpathians (Kovacs et al., 1989). (4) The correlation between Late Jurassic and Early Cretaceous basinal sediments of the VZ in front of the Moesian block and the Monti Metalliferi. “Banatites” of the southern part of the Carpathians fit quite well in chronology and petrology with Eoalpine and Mesoalpine granitoids from the VZ s.1. On the basis of paleomagnetic data, Russo-Sandulescu et al. (19841, concluded that the initial position of paleotectonic elements, with

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a basic rock basement, of the South Apuseni mounts must have been a N-S one that fits with the southern part of the VZ s.1. It can be assumed that the separation of the Dinarides and Carpathians was related to extension, i.e., the crustal attenuation and uplift of the upper mantle which gave rise to the generation of the Pannonian back-arc-type basin. Continental extension and separation is characteristic of orogens (Dewey, 1988) and in our particular case the extension may have started in the upper magmatic arc axis, i.e., the loci with the thinnest and weakest lithosphere and the thickest magmatic arc crust. Finally, the Carpathian loop can be a splendid example of curvature resulting from back-arc spreading. Acknowledgements The author is indebted to Drs. L. Csontos, J. Desmons, A. Hinterlechner-Ravnik, F. HorvBth, S. Kovacs, M. Sandulescu, S. Schmid and two anonymous reviewers for the critical reading of the draft of the manuscript. References AleksiC, V. and &uliC, M., 1972. Prethodno saopStenje o nalazu glaukofanskih Skriljaca in situ u FruHkoj Gori. Zapis. SGD, pp. 191-200. AleksiC, V. and PantiC, N., 1972. Mezozojski i paleogeni metamorfiti i dalja istraiivanja u juinoj grani alpske geosinklinalne oblasti. Zapis. SGD, pp. 221-233. Altherr, R., Kreuzer, H., Wendt, J., Lenz, H., Wagner, G.A., Keller, J., Harrer, W. and Hoendorf, A., 1982. A Late Oligocene/Early Miocene high temperature belt in the Attic-Cycladic crystalline complex (SE Palagonian, Greece). Geol. Jahrb., E, 23: 97-164. Andriessen, P., Boelrikj, N., Hebeda, E., Priem, H., Verdumen, E. and Verschure, R., 1979. Dating the events of metamorphism and granitic intrusion in the Alpine orogen of Naxos (Cyclades, Greece). Contrib. Mineral. Petrol., 69: 215-255. Ani&& B., 1990. GeoloHke razmere na Orlici. Geologija, 33: 233-287. Aubouin, J., Le Pichon, X. and Monin, A.S., 1986. Evolution of the Tethys. Part II. Maps. Tectonophysics, 123: 1-7. BabiC, Lj., 1973. Bazenski sedimenti gornjeg titona, berijasa i valendisa zapadno od Bregane. Geol. Vjes., 26: l-27.

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Balla, Z., 1986. Paleotectonic reconstruction of the central Alpine-Mediterranean belt for the Neogene. Tectonophysics, 127: 213-243. Buser, S., 1985. TumaE za Osnovnu geologku kartu 1: 100.000, list Tolmin. Sav. Geol. Zavod, Beograd, 78 pp. Buser, S. and Draksler, V., 1990. GeoloSka karta Slovenije 1: 500.000. Geol. Zavod Slovenije. Callegari, E., 1983. Geological and petrological aspects of the magmatic activity at Adamello (Northern Italy). Mem. Sot. Geol. Ital., 26: 83-103. Channel, J.E.T. and Horvith, F., 1976. The African/Adria promontory as a paleogeographycal premise for Alpine orogeny and plate movements in the Carpatho-Balkan region. Tectonophysics, 35: 71-101. Chappell, B.W. and White, A.J.R., 1974. Two contrasting granite types. Pac. Geol., 8: 173-174. Cliff, R., Holzer, H.F. and Rex, D.C., 1974. The age of Eisenkappel Granite and the history of the Periadriatic Lineament. Verh. Geol. Bundesanst., 2/3: 347-350. Coleman, R.G., 1972. Blueschist metamorphism and plate tectonics. 24th Int. Geol. Congr. Montreal, 2: 19-26. Cousin, M., 1972. Esquisse geologique des confins italoyougoslaves: leur place dans le Dinarides et Alpes meridionales. Bull. Sot. Geol. Fr., 7, 12(6): 1034-1047. Crnkovid, B., 1963. Petrografija i petrogeneza magmatita sjeverne strane Medvednice. Geol. Vjesn., 16: 63-160. Csontos, L., Nagymarosy, A., HorvLth, F. and Kovacs, M., 1992. Tertiary evolution of the intra-Carpathian area: a model. Tectonophysics, 208: 221-241. Delaloye, M., LovriC, A. and Karamata, S., 1989. Age of Tertiary granitic rocks of the Dinarides and Vardar zone. XIV. Congr. CBGA, Sofia, pp. 1186-1189. Deleon, G., 1969. Pregled rezultata odredjivanja apsolutne starosti granitoidnih stena u Jugoslaviji. Rad. Inst. Geol. Rud. Istraz. Ispit. Nukl. Sirovina, 6: 165-182. Del Moro, A., Ferrara, G., Tonarini, S. and Callegari, E., 1983. Rb-Sr systematics on rocks from the Adamello batholith (Southern Alps). Mem. Sot. Geol. Ital., 26: 261284. Dercourt, J., 1972. The Canadian Cordillera, the Hellenides and the sea-floor spreading theory. Can. J. Earth. Sci., 9: 709-743. Dercourt, J., Zonenshain, L.P., Ricou, E.L., Kazmin, V.G., Le Pichon, X., Knipper, A.L., Grandjacquet, G., Sbortchikov, I.M., Geyssant, J., Lepvrier, C., Pechersky, D.H., Boulin, J., Sibuet, J.C., Savostin, L.A., Sorokhtin, O., Westphal, M., Bazhenov, M.L., Lauer, J.P. and Biju-Duval, B., 1986. Geological evolution of the Tethys belt from the Atlantic to the Pamirs since the Lias. Tectonophysics, 123: 241-315. Dewey, J.F. 1988. Extensional collapse of orogens. Tectonics, 7: 1123-1139. Dewey, J.F., Pitman, W.C., Ryan, W.B.F. and Bonnin, J., 1973. Plate tectonics and the evolution of the Alpine system. Geol. Sot. Am. Bull., 84: 3137-3170. Dobretsov, N.L., 1978. Glauchophane metamorphism and ophiolites. Pac. Geol., 13: 87-100.

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