Aegean and Surrounding Regions: Complex Multiplate and Continuum Tectonics in a Convergent Zone

Aegean and surrounding regions: Complex multiplate and continuum tectonics in a convergent zone

J. F. DEWEY I Department of Geological Sciences, State University of New York at Albany, Albany, New York 12203 A. M. CELAL §ENGOR j

ABSTRACT in intracontinental convergence be resolved strike-slip faults and fold-thrust systems into the relative motion of a number of whose close spacing prohibits their being The tectonics of the Aegean region in- small plates, or, conversely, does a con- considered as plate boundaries. The evolu- volves complex slip patterns across the tinuum or semicontinuum behavior domi- tion of arrays of close-spaced grabens, boundaries of several microplates that seg- nate, with short-term strains distributed strike-slip faults and fold-thrust systems is ment the end of the Anatolian plate, which more uniformly within the convergent zone, characteristic of orogenic belts and wide is moving in a westward direction from the or is there a combination of the two modes zones of intracontinental foreland defor- Bitlis zone, an intracontinental suture zone, of behavior? Another way of asking this mation associated with collisional suturing to consume oceanic lithosphere in the east- question is (1) are the large finite strains ob- (Dewey, 1977). These relations suggest that ern Mediterranean. The segmentation of served in intracontinental orogenic belts the although stresses may be transmitted for the western end of the Anatolian plate into result of relatively continuous small-scale large distances into orogenic forelands and scholles with adjacent zones of grabens, deformation over the whole convergent re- major high-strain zones and in such areas strike-slip, and thrust semicontinuum gion, (2) are they the sum of incremental may be considered as the boundaries of tectonics results from "locking" across the strains developed along plate boundaries scholles in relative motion, many of these two North Anatolian transform strands that constantly change their position, (3) do smaller scholles undergo continuum or where they change orientation at the west- they develop by exceedingly heterogeneous semicontinuum strain on a scale that pre- ern end of the Sea of Marmara. This fast strain distribution with high strain zones vents the useful employment of plate lateral motion of buoyant continental sliv- bounding scholles1 within which strains are tectonics sensu stricto within intracontinen- ers is a transient phase of the early stages of very small, or (4) do they result from a tal convergent zones. continental collision resulting from the ir- combination of the above? The Aegean region is an area of intense regularity of colliding margins. It is, how- Within the Alpine-Himalayan system, the seismic activity compared with surrounding ever, a tectonic phase that leaves a funda- distribution of seismicity is not homoge- regions and one in which seismic first mo- mental signature on the convergent zone by neous, indicating that, at least instantane- tions (Fig. 1, C) and Neogene-Quarternary imprinting a complex widespread series of ously, convergent strain is not homogene- geology indicate, spatially, a very complex structures that mask, and make difficult the ous but concentrated in high strain zones and rapidly varying tectonic picture. interpretation of, earlier structures. (for example, Das and Filson, 1975), many The broad tectonic framework of the of which are major strike-slip faults, such as Aegean, Turkey, and the eastern Mediter- INTRODUCTION the North Anatolian fault (Ketin, 1969; ranean region (Fig. 2, C) is dominated, as McKenzie, 1972) and Altyn Tagh fault shown by McKenzie (1972), by the rapid It is well known that intracontinental (Molnar and Tapponnier, 1975). It is westward motion of the Anatolian plate zones along which plate convergent dis- equally clear that although many of these relative to the Black Sea plate and west- placement is converted into convergent high strain zones are very long features with southwestward motion relative to the Afri- strain are usually wide diffuse regions large displacement rates that mandate their can plate. The Anatolian plate may be re- within which complex relationships exist penetration of the lithosphere as plate garded as a buoyant continental sliver plate between extensional, compressional, and boundaries, there are many more smaller being driven westward from the intraconti- strike-slip deformations (McKenzie, 1972; nental Bitlis suture zone, the southern edge Dewey and Burke, 1973; Molnar and Tap- 1 The term Scholle (German: lump, clod of of the Arabian-European convergent strain ponnier, 1975; $engor, 1976). This con- earth, or flake) has been used by German- zone. This kind of lateral escape of buoyant trasts with the narrower strain zones of speaking geologists since the early days of this continental fragments from intracontinen- oceanic and continental margin convergent century to describe the deformational pattern of tal convergent strain zones is common, and the Alpine foreland, caused by the interaction of boundaries and probably is related to the rigid and semirigid crustal blocks bounded by re- it involves motion on major transforms buoyancy and lower shear strength of con- verse, normal, and/or strike-slip belts (see Kober, whose strike is at a high angle to the continental rocks compared with the higher 1933). This term is appropriate to describe also vergent slip vector (Molnar and Tappon- density, stronger oceanic rocks (McKenzie, the crustal fragments and splinters that form, as a nier, 1975). The Anatolian plate is clearly result of complex strain patterns, during conti- 1969, 1972). A critical question, addressed nental collision, and by the virtue of their "escaping" westward into the western by McKenzie (1972) is, To what extent can tectonic nature and behavior cannot be termed Mediterranean oceanic tract, where its mo- instantaneous or short-term deformations "plates." tion, relative to Africa, is taken up by sub-

Geological Society of America Bulletin, Parti, v. 90, p. 84-92, 3 figs., January 1979, Doc. no. 90113.

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duction at the Hellenic Trench. However, sion, the Izmit-Sapanca graben, and the Cephalonia and Zante is suggested by the the widespread seismicity roughly encir- Gemlik-Iznik graben north of Bursa (Ketin, northward termination of the Hellenic cling the Aegean region and the numerous 1968). These grabens are the northernmost Trench and an offset in seismicity. The active faults of western Anatolia and the of the east-west—striking graben swarm of upper part of the Gulf of Corinth is a west- northern Aegean indicate that the Aegean is western Anatolia (Fig. 1, C). There has been northwestward—striking graben (M'uller not a rigid integral western part of the considerable debate over the westward and Logters, 1974), compatible with its in- Anatolian plate, which itself is currently in- continuations of the two strands. Alptekin terpretation as a second-order extensional ternally deforming along east-west— (1973) considered the northern strand in- feature in a zone of northeastward-striking oriented normal faults and thus forms a active and continued the southern strand right-lateral shear. North of the Gulf of more feeble easterly continuation of the westward as a single transform across the Corinth, normal fault first-motion solutions Aegean strain zone (Salomon-Calvi, 1936; northern Aegean to cut Greece between (Fig. 1, C) are consistent with second-order Alptekin, 1973), and that a multi—small- Euboea and the entrance of the Gulf of extensional faulting in a zone of right- plate and/or continuum tectonic behavior Corinth. Bingol (1976) completely disre- lateral shear. These features therefore dominates. garded the southern strand and connected suggest a mechanism whereby right-lateral McKenzie (1972, Fig. 2) suggested that the northern one with a hypothetical east- motion is taken up from a triple junction at two plate boundaries dominate Aegean southeastward-trending extensional zone. the northern termination of the Hellenic tectonics: an Anatolian-Aegean boundary Brinkmann (1976) continued both strands Trench to the southwestern end of the diffusely defined by the east-west graben into, and terminated them in, the northern Sporades Trough: a wide zone of second- complexes of western Anatolia, and an Aegean. We suggest that seismicity and order extensional grabens striking roughly Aegean-Greek boundary defined more pre- morphologic expression (Ketin, 1966a; west-northwestward (Fig. 1, A). cisely by a ridge-transform system running Allen, 1975, Fig. 12) indicate that both Between the Gulf of Saros and Rhodes from the Dardanelles to the Gulf of strands are active and continue into the (Fig. 1, C), western Anatolia and the north- Corinth. He proposed that these two boun- Aegean — the northern strand into the eastern Aegean are dominated by a swarm daries meet a quadruple junction at the Saros and Sporades Troughs and the south- of roughly east-west grabens (Philippson, western end of the Sea of Marmara. In this ern strand into the Skiros Trough. Both 1918; Ketin, 1968,1970; Arpat and Bingol, paper we show how relative motion be- strands, however, show a deflection to a 1969; Brinkmann, 1976) that close east- tween the western edge of the Anatolian more southwesterly strike at the western ward and terminate westward along a line plate and adjacent plates is accommodated, end of the Sea of Marmara; the northern from the east side of Euboea to Rhodes. and we suggest an alternative solution for strand is offset between the Saros and These grabens control the major west- Aegean tectonics that involves rather wide Sporades Troughs, and both strands termi- flowing consequent drainage system of diffuse "plate" boundaries, or arrays of nate — the northern just north of Euboea western Anatolia, including the famous scholles, which have evolved since late and the southern just north of Skiros. Meander (Buy'uk Menderes) River; the in- Miocene time and comprise a great variety Seven first-motion fault-plane solutions tervening horsts control lateral subsequent of grabens, en echelon grabens, transforms, give motion consistent with the Saros, streams (Erinf, 1955a, 1955b). The grabens transforms in oblique compression, and Sporades, and Skiros Troughs being as- are bounded by active normal faults (Zes- short ridge segments. sociated with right-lateral transforms. Also, chke, 1954; Arpat and Bingol, 1969; Arpat two normal fault plane solutions are consis- and $aroglu, ] 975), and first-motion fault TECTONICS OF THE AEGEAN tent with short, roughly northwestward- plane solutions (McKenzie, 1972; Alptekin, striking extensional segments joining the 1973) indicate fairly consistent east-west— The right-lateral North Anatolian trans- Saros and Sporades Troughs and the ends striking normal faulting with, occasionally, form, which began in middle to late of the Skiros and Sporades Troughs. The a small component of right-lateral slip. The Miocene time (Ketin, 1969; Seymen, 1975) bends in the two strands of the North grabens and intervening horsts are the sites to take up the relative motion between the Anatolian transform at the western end of of numerous hot springs (Pinar, 1949; Anatolian and Black Sea plates, consists, the Sea of Marmara suggest that west of Erentoz and Ternek, 1968), sometimes with south of Istanbul, of two strands, the north- these bends the transforms are in a locking associated travertine terranes (§engor, ern strand entering the Sea of Marmara and geometry and therefore should be in 1975), and the Gediz and Simav grabens the southern passing just north of Bursa oblique compression, provided that a major have associated recent basaltic volcanic (Fig. 1, C). Fault-plane solutions (McKen- triple junction does not occur at the bends. rocks. The Gediz volcanic rocks are alkalic zie, 1972), and surface deformation during This appears to be inconsistent with the as- basalts in the form of hornblende-leucite- earthquakes (Ketin, 1966a) are consistent sociation with deep grabens. Alptekin nepheline basalt (kulait) (Washington, with right-lateral motion on both strands. (1973) and Papazachos (1976), however, 1894; Philippson, 1913; Ketin, 1961; Local normal fault solutions with a north- have adduced first-motion evidence of Erinp, 1970). More widespread Neogene west-striking null vector and surficial dip- roughly east-west compression over much plateau basalts, perhaps fed from fissures slip normal faulting, adjacent to these of the northern Aegean west of the bends in associated with the Gediz graben, gave way strands (see, for example, Canitez and Tok- the transform strands, suggesting that the to more restricted plateau basalts in early soz, 1971, Erentoz and Kurtman, 1964) are strands here are in compression (Fig. 1, A). Quaternary time and in turn to localized, compatible with the development of Although a right-lateral transform may today beautifully preserved, mixed lava- second-order extensional faults. The region pass through the Trikeri Straits Between tephra cones in late Quaternary time (Erinf, associated with and between both strands is Othris and Euboea (Fig. 1, C), it does not 1970). characterized by active grabens, such as the continue across Greece as a single structure, The grabens contain thick Quaternary Sea of Marmara itself, its eastward exten- although a right-lateral transform between sedimentary sequences (Fig. 1, B) and

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although, at least in the case of the B'uyuk boundaries of an assemblage of scholles, transform strands, with two short exten- Menderes graben, faulting can be demon- which are zones of extensional and com- sional segments (5 and 6 in Fig. 2, B), strated to have begun in late Miocene time pressional strain that may be regarded as thrusting in the region enveloping these (Erentoz and Ternek, 1968), the grabens wide plate boundary zones or zones of in- transforms, and into north-south extension did not begin to sink rapidly to accumulate traplate strain. In particular, the two across the western Anatolian graben sys- thick sequences until Pleistocene time strands of the North Anatolian transform tem. Northwest-southeast-trending normal (Erinp, 1955b; Arpat and Bingol, 1969). deflect slightly southward at points 1 and 2 faulting (3) may be related to the latter gra- Thus, western Anatolia and the northeast- (Fig. 2, C) west of which Papazachos (1976) ben system or to second-order extension as- ern Aegean is a diffuse, yet cohesive, region has argued, from fault plane solution sociated with right-lateral motion on the of roughly north-south extension that studies, the existence of a wide zone of as- North Anatolian transform. began to form in late Miocene time. That sociated east-west compression resulting in Southwest of the terminations of the this extension, albeit on a smaller scale and thrust faulting (point 4) and right-lateral North Anatolian transform strands north with less distinct morphologic expression, strike-slip faulting. This is consistent with and east of Euboea, several fault plane so- continues into the Anatolian plate to near the Anatolian transform strands bending lutions suggest that the relative motion be- Nigde in central Anatolia is indicated by the into a "locking" orientation in the northern tween the Peloponnisian and Macedonian east-west-striking normal faulting first Aegean that obstructs the westward motion plates is taken up across a broad zone of en motions (Alptekin, 1973). of the Anatolian plate relative to Greece echelon second-order extension fractures in and the Balkans. This obstructive locking a right-lateral zone of shear that narrows TECTONIC SYNTHESIS OF geometry may be responsible for the ripping abruptly at the mouth of the Gulf of THE AEGEAN of the Macedonian plate from the Black Sea Corinth to a transform that terminates the plate; the Macedonian-Black Sea exten- Hellenic subduction zone west of Zante. Part B of Figure 2 is a generalized sum- sional boundary, which may be partially re- This en echelon zone appears, from fault mary of our suggested tectonic framework sponsible for the Neogene basin in Thrace, plane solutions (Fig. 1, C), to extend for the Aegean region. Part C is a further joins the North Anatolian transform system northward into Greece (Fig. 2, B), perhaps simplified version placed in the broader at a triple junction where the fault strands reflecting an attempt by the Peloponnisian context of eastern Mediterranean tectonics. bend to the south. The widespread western plate to rip Albania and part of Greece from Part A is a slip vector system for the relative Anatolian graben system (12 in Fig. 2, B) is Macedonia, much as perhaps the Anatolian motion of Africa, Europe, and the smaller situated on a very broad dome (Arpat and plate is ripping the Macedonian plate from intervening plates and fragments, to be dis- Bingol, 1969) and may owe its origin to the the Black Sea plate. At triple junction 10 cussed below, that is rigorously constrained locking geometry of the North Anatolian (Fig. 2, B), relative motion changes sharply only by the Africa-Europe relative motion transform strands, the east-west compres- from a rapid (~4 cm/yr) northeastward determined from finite difference solutions sion being relieved by north-south exten- convergence between the Peloponnisian and based upon Atlantic magnetic lineation sion. The continuation of the north-south African plates at the Hellenic Trench to fitting (Pitman and Talwani, 1972) and by extension on a smaller scale into Anatolia is north-south right-lateral convergence be- the Eurasia (Black Sea plate)-Anatolia mo- consistent with such an interpretation. tween the African and Macedonian plates tion determined from an Arabia-Europe- However, disregarding this small extension along a somewhat diffuse intracontinental Anatolia velocity triangle (McKenzie, in central Anatolia, the western Anatolian boundary that passes into Albania and 1972). The Aegean region is sufficiently graben system could be regarded as a wide Yugoslavia. diffuse plate boundary between the Anato- small that it may be treated without serious Deformation patterns in the southern lian plate and the Peloponnisian plate. error, for the purpose of this paper, as a flat Aegean are difficult to resolve, but we ten- Thus, we suggest that the western Anato- surface on which relative plate motion may tatively suggest the possible existence of a lian graben system, the region of east-west be illustrated as a nest of velocity triangles. small Cretan plate (Fig. 2, B) moving very compression associated with the deflected The Anatolian plate is defined clearly to slowly eastward relative to the Peloponni- Anatolian transform strands and the the north, east, and south (Fig. 2, C). To the sian and Anatolian plates. This would in- Macedonian—Black Sea extensional bound- west, although a well-defined subduction volve a zone of east-trending left-lateral ary, is the result of the resistance to the zone extends from Zante to Rhodes (point shear, suggested by three fault plane so- westward motion of the Anatolian plate 10 to point 13, Fig. 2, B), we suggest that lutions (Fig. 1, C) and by the Amorgos and relative to the Black Sea and Macedonian seismicity, fault plane solutions, and Scarpanto Troughs, which would bear a plates and that the east-west compression is neotectonics indicate a complex strain pat- second-order extensional relationship to resolved into northwest to east-northeast tern, west of a line from Rhodes to the Sea such a zone of left-lateral strike slip. strike slip, mainly on the North Anatolian of Marmara, that involves slip across the Thus, as argued by McKenzie (1972), the

<_ Figure 1. A. Simplified summary of Aegean tectonics showing regions of compression, extension, and strike slip inferred from first- motion studies (McKenzie, 1972; Alptekin, 1973; Papazachos, 1976). B. Sections across grabens of western Anatolia: B'uyuk Menderes simplified after Erentoz and Ternek (1968). Simav simplified after Zeschke (1954). Gediz simplified after Ketin and Canitez (1972). C. Simplified map of Aegean showing first-motion stereographic projections (McKenzie, 1972; Alptekin, 1973). White = dilational quadrants; black = compressional quadrants. Neogene-Quaternary grabens (stippled) modified after Ketin (1968, 1970) and unpublished tectonic map of Turkey (Ketin); open circles = hot springs; black in part B = Quaternary basalts; heavy lines (broken where poorly defined) = faults; heavy lines with open triangles on upper plate = subduction zone.

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westward motion of the Anatolian plate is that has been taken to indicate the time of Late Cretaceous terminal collision occurred the escape of a pear-shaped continental closure of the Bitlis-Zagros ocean (Biju- in the Bitlis-Zagros zone, that further plate from the Bitlis suture zone, a process Duval and others, 1978). However, these Arabia-Europe convergence was accommo- that partially avoids subduction and/or zones are characterized by major Neogene dated by the elimination of oceans at thickening of continental crust. Its west- convergent deformation, involving late Pontide-Caucasian subduction sites to the ward escape is facilitated or allowed by the Miocene nappe emplacement in the Bitlis north, and that renewed shortening in the subduction of the oceanic floor of the east- zone (Rigo de Righi and Cortesini, 1964; Bitlis-Zagros zone resulted from the total ern Mediterranean at the Hellenic Trench. Hall, 1976; Innocenti and others, 1976) elimination of Pontide-Caucasian oceans in Although the westward motion is accom- and Pliocene folding of the Zagros shelf se- late Miocene—Pliocene time. We believe this plished simply at the Hellenic Trench and quence (Ketin, 1966b). We consider that latter argument to be incorrect, for the fol- along the East and North Anatolian trans- these events are related to late Miocene- lowing reasons. First, the final closure of the form faults, the motion is retarded by in- Pliocene closure of a Bitlis-Zagros ocean Pontide ocean took place during late Bur- tracontinental locking between the Sea of and, thus, that the Late Cretaceous ophiol- digalian time or earlier and terminally su- Marmara and the northern end of the Hel- ite obduction was a pre—terminal collision tured the Pontide and Anatolide zones lenic Trench. This locking results in a com- event. Dewey (1976) and Smith and Wood- (Seymen, 1975). Second, Eocene-Oligocene plex pattern of grabens, en echelon grabens, cock (1976) have pointed out that there are silicic-intermediate plutonism in a zone and thrust and strike-slip deformation that numerous ophiolite obduction modes that parallel with and northeast of the Zagros segment the western end of the Anatolian do not involve continent-continent colli- crush zone in Iran suggests a Paleogene plate and the southwestern corner of the sion. Alternatively, it might be argued that northeast-dipping subduction zone that Black Sea plate into a number of small scholles with wide zones of boundary deformation.

ANTIQUITY AND EVOLUTION OF PRESENT TECTONIC REGIME

If the westward motion of the Anatolian plate is the lateral escape of a buoyant continental lithosphere sliver from the Arabia-Europe intracontinental convergence zone to consume oceanic lithosphere in the Hellenic subduction zone (for an alternative interpretation, see Alptekin, 1973), it probably dates from the time of total elimination of easily subductable oceanic lithosphere between Arabia and Europe. According to this hypothesis, the timing of development of the North and East Anatolian transforms and the fragmen- tation of the western end of the Anatolian plate resulting from locking against Macedonia should correlate with the time of the last major collisional events between Arabia and Europe. These collisional events may have been distributed among a number of possible subduction sites, including the Bitlis zone (Dewey and others, 1973), a zone along the southern edge of the Pon- tides (Seymen, 1975), and a zone connect- ing the Black and Caspian Seas through the Khoura depression between the Major and Minor Caucasus. The Bitlis zone, from which the North and East Anatolian transforms emanate west of a triple junction west of Lake Van (Fig. 2, C), continues into Figure 2. A. Schematic slip vector system for plates and scholles in and around Aegean the Zagros crush zone, the line of suturing region. A = Anatolian, AF = African, BS = Black Sea, C = Cretan, E= European, M= between Arabia and Iran. In the Bitlis zone Macedonian, P = Peloponnisian. B. Schematic tectonic interpretation of Aegean region. and southwest of the Zagros crush zone, Numbered localities referred to in text. C. Plate tectonic scheme for eastern Mediterranean ophiolite obduction occurred in Late Creta- region modified from McKenzie (1972) and Dewey and others (1973). Dots = oceanic ceous time (Rigo de Righi and Coretsini, crust; lengths of arrows give rough proportionality of relative velocities. Eastern Anatolian 1964; Glennie and others, 1973), an event convergent zone highly schematized.

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consumed oceanic crust in the Zagros crush beginning its westward motion from the sequent shut-off in volcanism at the north- zone. Innocenti and others (1976) have Bitlis suture zone during late Miocene time ern end of the associated volcanic arc. concluded that in southeastern Anatolia the (Brinkmann, 1976; Biju-Duval and others, Today (Fig. 3, D), all that remains of the arc Bitlis ocean closed during late Miocene 1978, Fig. 11; Boccaletti and others, 1974). is the South Tyrrhenian volcanic province time, on the basis of their study of the During middle Miocene time (Fig. 3, A), the above a conical northwest-dipping Benioff chemistry of the volcanic rocks in eastern motion of Africa relative to Europe was a zone. If the present Adriatic is a fingerlike Turkey. Third, the Gulf of Oman, clearly an counterclockwise rotation about a pole projection of the African plate, relative mo- oceanic tract, lies northeast of the obducted near Gibraltar (Dewey and others, 1973). tion at its western border is oblique exten- Semail Ophiolite Complex, between the Africa-Europe convergence was taken up in sion. The late Pliocene tectonic reconstruc- Oman and the Makhran mélange terrane of the Helvetic root zone of the Alps (Triimpy, tion suggests an origin for the Pantelleria southeastern Iran. 1975) and by right-lateral movement along Line, a complex rift or bathymetric scar be- Geologic data from the North Anatolian the Pustertal Line, which wedged out the tween Sicily and Tunisia, as a right-lateral transform, the East Anatolian transform, northern part of the Apulian plate and transform with a small component of ex- and the western Anatolian graben system caused radial thrusting in the outer zones of tension (Fig. 3, C). also indicate a late Miocene-early Pliocene the Carpathians (Burchfiel, 1978), in the The westward motion of the Anatolian date for their origination. Detailed struc- Apennines by thrusting of the allochthons plate, beginning in late Miocene time, tural studies by Seymen (1975) in the Kelkit onto the Umbrian platform, and along the caused a great change in the direction and Valley region, near Rejadiye, have shown southern side of the Aegean and Turkey rate of relative motion across the Hellenic that a convergent margin existed there from (Biju-Duval and others, 1978) and in the Trench, from roughly north-south to Early Cretaceous to Burdigalian time, when Bitlis-Zagros ocean by subduction of roughly east-northeast, producing, in the the Pontide and Anatolide zones terminally oceanic lithosphere. Other subduction Pliny-Stabo trench complex, a change from sutured. This suturing has resulted in zones in the Caucasus also may have been convergent to transform motion (Fig. 3, C large-scale overthrusting marking the su- taking up some of the convergence. In late and D), perhaps explaining the present very ture belt. The North Anatolian transform Miocene time, we suggest, a major series of straight double "trench" configuration. The cuts this suture at an acute angle and dis- changes in tectonic configuration occurred Mediterranean Ridge, interpreted by places it for 85 ± 5 km right laterally. Ab- (Fig. 3, B). First, the Africa-Europe relative Rabinowitz and Ryan (1970) as a com- dusselàmoglu (1959) has shown, in the motion changed to an increased con- pressive fore-trench bulge, closely follows Mudurnu Valley near Akyazi, that the fault vergence rate about a pole south of the the arcuate form of the Hellenic-Pliny- must have begun moving before Pliocene Azores (Dewey and others, 1973). Second, Strabo trench system. If the Mediterranean time. This therefore brackets the initiation the Bitlis ocean closed (Hall, 1976), with Ridge originated as a compressive feature, of the North Anatolian transform between the consequent generation of the North and its origin must have been prior to late early middle Miocene and early Pliocene East Anatolian transform faults, resulting in Miocene time, because its eastern half lies time. the westward motion of the Anatolian plate parallel to what is now a transform The East Anatolian transform offsets from the Bitlis suture (Brinkmann, 1976). Anatolia-Africa boundary. marine Miocene outcrops near Gòyniik for Third, Italy began to separate from about 22 km left laterally (Arpat and Corsica-Sardinia as the Tyrrhenian Sea CONCLUSIONS §aroglu, 1972). Brinkmann (1976) believed opened. The rotation of Italy is well documented (Lowrie and Alvarez, 1974, it to be roughly contemporaneous with the Continental collision, involving irregular 1975; Cocozza and Sch'afer, 1974; Kloot- North Anatolian transform. Therefore, margins with "embayments" (Levantine wijk and van der Berg, 1975), and although although detailed investigations of this re- Ocean) and "promontories" (Arabia), leads considerable convergence between Italy and cently discovered fault are not yet available, to the lateral escape of buoyant continental the Balkans is unavoidable, it is not clear its age can probably be placed as late slivers from "promontory" suture zones how this convergence was accomplished. Miocene or early Pliocene. (Bitlis suture) across which oceanic litho- The final folding phases in the Dinarides In the Aegean region, middle and late sphere has been eliminated, into embay- and the Hellenides (Burchfiel, 1978) may Miocene time are characterized by gentle ments where the sideways-moving slivers partly answer the problem. Furthermore, block faulting (Berckhemer, 1977). Erentòz subduct oceanic lithosphere (Hellenic the arcuate Roman-Southern Tyrrhenian and Ternek (1968) have shown that during Trench). This leads to the development of volcanic province (Alvarez, 1975) may have late Miocene time, weak taphrogenic activ- mosaics of small plates and scholles been related to a west-dipping subduction ity had already set in. However, the final (Anatolian, Macedonian, and so forth) be- zone between Calabria and Apulia (Italian collapse of the western Anatolian struc- tween converging larger plates. The bound- subduction zone), along what is now a tures, with large amounts of fault throw, aries of the smaller sideways-moving conti- sediment-filled trough, or within what is occurred during Pliocene and Pleistocene nental plates form a system in which rapid now the Adriatic Sea (Adriatic subduction time. The age relations of the Imolosschutt transform motion (North and East Anato- zone). In whichever of these sites subduc- in the Biiyiik Menderes and Gediz grabens lian transform faults) dominates, except tion occurred, the slip vector changed from strengthen this argument (Erinf, 1955b); along boundaries between these continental rapid roughly east-west convergence at its Chaput (1936) similarly observed Neogene plates and remnant oceanic tracts where southern end to slower northeast-southwest deposits preserved in fault troughs near either transforms (Pliny/Strabo boundary) convergence at its northern end. As Italy ro- Aydin, the western end of the Biiyiik Men- or subduction zones (Hellenic Trench) de- tated further (Fig. 3, C), the slip vector deres graben. velop. It is interesting that as the collisional, across the northern end of the subduction We suggest, therefore, that the geological sideways-moving, splinter phase begins, zone changed to strike slip, with the con- data are consistent with the Anatolian plate relative motion will change across earlier

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/1/84/3434326/i0016-7606-90-1-84.pdf by guest on 24 September 2021 Figure 3. Suggested tectonic evolution of central and eastern parts of Alpine System Africa relative to Europe. Heavy lines with open triangles = subduction zones (triangles on since middle Miocene time. In late Miocene, Africa-Anatolia relative-motion vector upper plate), those with short lines across them = sutures. Broken lines indicate poorly changes as Anatolian plate begins its westerly motion, from 1 to 2. By this time the Dead defined features. Dotted areas in northern Aegean and on Mediterranean Ridge are regions Sea transform was active (Freund, 1965), and Arabia was moving northward faster than of compression.

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subduction zones so that parts that experi- tive motion rates, is likely to dominate the the Libyan Arab Republic, p. 355-377. enced earlier head-on subduction begin to final orogenic result (for example, the Pan- Arpat, E., and Bingòl, E., 1969, Ege bòlgesi graben sisteminin gelijimi tizerine diijiinceler: nonian Basin and the Carpathians). undergo transform or more oblique sub- Maden Tetkik ve Arama Enstitusu Dergisi, duction and vice versa. Another particularly important aspect of no. 73, p. 1-9. A further important facet of the side- this phase is that it will segment and lat- Arpat, E., and Jaroglu, F., 1972, The East ways-moving splinter phase is that trans- erally transpose earlier fades belts, making Anatolian Fault System: Thoughts on its forms, across which fast slip occurs, may their proper paleogeographic interpretation development: Mineral Research and Explo- ration Institute of Turkey Bulletin no. 78, p. have locking compressional segments and difficult, if not impossible. Such difficulties 33-39. oblique extension segments that inhibit and have been encountered in the Pannonian 1975, Tùrkiye'deki bazi ònemli genç tek- facilitate motion, respectively. Locking Basin and the northwestern sector of the tonik olaylar: Tùrkiye Jeoloji Kurumu Bïil- segments lead to the generation of wide- Carpathians (see, for example, Tollmann, teni, v. 18, p. 91-101. Balogh, K., and Korossy, L., 1974, Hungarian spread regions of intraplate compression 1969). Furthermore, this tectonic phase, Mid-mountains and adjacent areas, in (Northern Aegean), resolved extension captured in the present Alpine system, is Mahel, M., ed., Tectonics of the Carpathian (West Anatolian graben system), thrust and likely to be followed and overprinted, when Balkan regions: Bratislava, Czechoslovakia, strike-slip displacements, and the ripping of all the oceanic lithosphere in the system is Geological Institute, Dionyz Stur, p. 391- corners from, to subdivide, adjacent plates eliminated and if the convergence con- 403. Berckhemer, H., 1977, Some aspects of the (Macedonian plate). tinues, by a phase of bulk intracontinental evolution of marginal seas deduced from Thus, the collisional sideways-moving shortening and thickening with silicic- observations in the Aegean regions, in splinter phase produces extremely complex potassic magmatism that invades adjacent Biju-Duval, B., and Montadert, L., eds., microplate tectonics and wide regions of as- forelands for thousands of kilometres (for Structural history of the Mediterranean basins: Paris, Editions Technip, p. 303-313. sociated semicontinuum tectonics in which example, Tibetan Plateau; Dewey and Biju-Duval, B., Letouzey, J., and Montadert, L., Burke, 1973) with continued major trans- plate boundary displacements and bulk 1978, Structure and evolution of the strains do not directly reflect convergent form motion to laterally displace huge areas Mediterranean basins, in Initial reports of slip vectors between the larger bounding of continental lithosphere from the widen- the Deep Sea Drilling Project, Volume 42A: plates. A very similar, but now largely inac- ing and lengthening convergence zone Washington, D.C., U.S. Government Print- ing Office (in press). tive, collisional sideways-moving splinter (Molnar and Tapponnier, 1975; §engor, Bingòl, E., 1976, Evolution géotectonique de and its related deformational effects have 1976). l'Anatolie de l'Ouest: Société Géologique de been described by Burchfiel (1978) in the France Bulletin, v. 18, p. 431-450. Eastern Alpine—Pannonian-Carpathian re- ACKNOWLEDGMENTS Boccaletti, N., Guazzone, G., and Manetti, P., gion, where the northernmost part of the 1974, Evoluzione paleogeografica e geodinamica del Mediterraneo: J. bacini Apulian plate was squeezed sideways We thank Professor Ihsan Ketin of Istan- marginali: Società Geologica Italiana toward the east along the Pustertal Line and bul Teknik Universitesi, Maden Fakiiltesi, Memoria, v. 13, p. 1-39. resulted in the radial thrusting in the Car- Istanbul, and Esen Arpat of Maden Tetkik Brinkmann, R., 1976, Geology of Turkey: pathians during Miocene time. Numerous ve Arama Enstitusu, Ankara, for discus- Stuttgart, Ferdinand Enke Verlag, 158 p. Burchfiel, B. C., 1978, The Alpine Mountain northeast-trending graben structures in the sions on the western Anatolian graben sys- Chain of Eastern Europe and the Carpa- Pannonian Basin formed also during this tem and for the unpublished data they thian orocline: An example of collision time (Balogh and Korossy, 1974) and are generously provided, and Dr. Ihsan Seymen tectonics: Tectonophysics (in press). probably related to the extension produced of Instanbul Teknik Universitesi, Maden Canitez, N., and Toksòz, M. N., 1971, Focal by the splintering of the eastern end of the Fakiiltesi for discussions on the age of the mechanism and source depth of earthquakes from body- and surface-wave data: Pustertal Line and to locking of the east- North Anatolian transform and the tectonic Seismological Society of America Bulletin, northeastward movement of the splinter evolution of the Pontides and for a copy of v. 61, p. 1369-1379. along this bend (Burchfiel, 1978; 1976, per- his book on the tectonics of the North Chaput, E., 1936, Voyages d'études géologiques sonal commun.). Thus, at least the northern Anatolian fault zone in the Kelkit Valley et géomorphogénique en Turquie: Institut part of the Pannonian Basin is a homolog of region. Professor Nezihi Canitez critically Français d'Archéologie d'Istamboul Mémoire, 312 p. the Aegean area (Burchfiel, 1976, personal read the manuscript and offered helpful Cocozza, T., and Sch'àfer, K., 1974, Cenozoic commun.). 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