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Mediterraneantectonics

E Carminati and C Doglioni , Universita ` La Sapienza,Rome, Italy

2004, Elsevier Ltd. All Rights Reserved.

s0005 Introduction

p0005 It is commonly accepted that Mediterranean geologyhas been shaped by the interplay between two plates,the African and European plates, and possibly alsosmaller intervening microplates. The Mediterraneanwas mainly affected by rifting after the VariscanOrogeny ( Europe: The Variscides Orogeny (00441)):during the Mesozoic, oceanic Tethys areas and passivecontinental margins developed, where widespreadcarbonate platforms were formed. During the lateMesozoic, the Mediterranean area was dominatedby subduction zones (from east to west, the Cimmer-ian, Dinarides, and Alps–Betics), which inverted theextensional regime, consuming the previously formedTethyan oceanic lithosphere and the adjacent contin-ental margins. The composition (oceanic or continen-tal), density, and thickness of the lithosphere inheritedfrom the Mesozoic rift controlled the location, distri-bution, and evolution of the later subduction zones.The shorter wavelength of the Mediterranean orogensrelative to other belts (for example, the Cordillera andthe Himalayas) is due to the smaller wavelength of thelithospheric anisotropies inherited from the Tethyanrift.

p0010 The Mediterranean basin was, and still is, a col-lector of sediments derived from the erosion of thesurrounding continents and orogens: the bestexamples are the Nile and Rhone deltas. In the past,other deltas deposited sediments in the bottom of theMediterranean, and their rivers were later discon-nected or abandoned: an example is the UpperOligocene–Lower Miocene Numidian Sandstone,which was derived from Africa, deposited in the cen-tral Mediterranean basin, and partly uplifted by theApennines accretionary prism. It is well known that,during the Messinian eustatic lowstand, the Mediter-ranean dried up several times, generating a salinitycrisis during which thick sequences of evaporites were

deposited in the basin. This generated a pulsatingloading oscillation in the Mediterranean, becausethe repetitive removal of the water led to significantisostatic rebound across most of the basin, particu-larly where it was deeper, as in the Ionian, theProvencal, and the central Tyrrhenian seas.

p0015The direction of the relative motion between Africaand Europe since the Neogene is still under debate.Most reconstructions show directions of relativemotion between north-west and north-east. Recentspace geodesy data confirm this overall trend, inwhich Africa has a north–south component of con-vergence relative to Europe of about 5 mm year 1,but they also show that the absolute plate-motiondirections of both Europe and Africa are north-eastand not north or north-west as is usually assumed (seethe NASA database on present global plate motions,http://sideshow.jpl.nasa.gov:80/mbh/series.html).

p0020The main Cenozoic subduction zones in theMediterranean are the Alps–Betics, the Apennines–Maghrebides, and the Dinarides–Hellenides–Taurides. Closely related to the Mediterraneangeodynamics are the Carpathian subduction and thePyrenees (Figure 1 ). The Mediterranean orogens showtwo distinct signatures, which are similar to thoseoccurring on opposite sides of the Pacific Ocean.High morphological and structural elevations, doublevergence, thick crust, involvement of deep crustalrocks, and shallow foredeeps characterize eastwards-or north-eastwards-directed subduction zones(Alps–Betics and Dinarides–Hellenides–Taurides).Conversely, low morphological and structuralelevations, single vergence, thin crust, involvementof shallow rocks, deep foredeeps, and a widely de-veloped back-arc basin characterize the westwards-directed subduction zones of the Apennines andCarpathians. This asymmetry can be ascribed to the‘westward’ drift of the lithosphere relative to themantle, at rates of about 49 mm year 1 as computedfrom the hotspots reference frame. All Mediterraneanorogens show typical thrust-belt geometries withimbricate-fan and antiformal-stack associations ofthrusts. The main factor that varies between orogensand within single belts is the depth of the basaldecollement. The deeper it is, the higher is thestructural and morphological elevation of the relatedorogen.

p0025Extensional basins are superimposed on these oro-genic belts: on the western side are the Valencia,Provencal, Alboran, Algerian, and Tyrrhenian basins,

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PROOFf0005 Figure 1 Present geodynamic framework. There are four subduction zones with variable active rates in the Mediterranean realm: the westwards-directed Apennines–Maghrebides; the

westwards-directed Carpathians; the north-eastwards-directed Dinarides–Hellenides–Taurides; and the south-eastwards-directed Alps. The Apennines–Maghrebides subduction-related

back-arc basin of the western Mediterranean stretched and scattered into segmented basins most of the products of the Alps–Betics orogen.

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on the eastern side is the Aegean Basin, and to thenorth is the Pannonian Basin (Figures 2 and 3).

p0030 The Mediterranean can be divided into western,central, and eastern basins. The western Mediterra-nean is younger (mainly less than 30 Ma) than thecentral Mediterranean and eastern Mediterranean,which are mainly relics of the Mesozoic to possiblyCenozoic Tethys Ocean.

p0035 Positive gravity anomalies occur in the deep basins(the Provencal, Tyrrhenian, and Ionian seas), wherethe mantle has been uplifted by rifting processes. Incontrast, negative gravity anomalies occur along thesubduction zones.

s0010 Western Mediterranean

p0040 A characteristic feature of the western Mediterraneanis the large variation in lithospheric and crustal thick-ness (Figure 4). The lithosphere has been thinned toless than 60 km in the basins (50–60 km in theValencia trough, 40 km in the eastern Alboran Sea,and 20–25 km in the Tyrrhenian Sea), while it is65–80 km thick below the continental swells(Corsica–Sardinia and the Balearic promontory).The crust mimics these differences, with a thicknessof 8–15 km in the basins (Valencia trough, AlboranSea, Ligurian Sea, and Tyrrhenian Sea) and 20–30 kmunderneath the swells (Balearic promontory andCorsica–Sardinia), as inferred by seismic and gravitydata. These lateral variations in thickness andcomposition are related to the rifting process thataffected the western Mediterranean, which is acoherent system of interrelated irregular troughs,mainly V-shaped, that began to develop in the LateOligocene–Early Miocene in the westernmost parts(Alboran, Valencia, Provencal basins), becoming pro-gressively younger eastwards (eastern Balearic andAlgerian basins), culminating in the presently activeeast–west extension in the Tyrrhenian Sea (Figures 1,2, 3, and 5). Heat flow data and thermal modellingshow that the maximum heat flows are encounteredin the basins: 120 mW m�2 in the eastern AlboranSea, 90–100 mW m�2 in the Valencia trough, and morethan 200 mW m�2 in the Tyrrhenian Sea. All thesesub-basins appear to be genetically linked to the back-arc opening related to the coeval ‘eastwards’ rollbackof the westward-directed Apennines–Maghrebidessubduction zone. Extreme stretching generated ocea-nic crust in the Provencal (20–15 Ma), Algerian(17–10 Ma), Vavilov , and Marsili (7–0 Ma) basins.Between 25 Ma and 10 Ma, the Corsica–Sardiniablock rotated 60� counterclockwise (Figures 1, 2, 3,and 4).

p0045 In the southern Apennines, the choking of the sub-duction zone with the thicker continental lithosphere

of the Apulia Platform slowed the eastwards migra-tion of the subduction hinge (Figure 6), whereas in thecentral and northern Apennines and in Calabria sub-duction is still active owing to the presence in theforeland of the thin continental lithosphere of theAdriatic Sea and the Mesozoic oceanic lithosphereof the Ionian Sea, allowing rollback of the subductionhinge.

p0050The western Mediterranean basins tend to closeboth morphologically and structurally towards thesouth-west (Alboran Sea) and north-east (LigurianSea; Figures 1 and 6). The eastwards migration ofthe arc associated with the westwards-directed sub-duction generated right-lateral transpression alongthe entire east–west-trending northern African belt(Maghrebides) and its Sicilian continuation, whereasleft-lateral transtension occurs along the same trendin the back-arc setting just to the north of the Africanmargin. The opposite tectonic setting is found in thenorthern margin of the arc.

p0055Subduction retreat generated calc-alkaline andshoshonitic magmatic episodes – particularly in thewestern margins of the lithospheric boudins – whichwere followed by alkaline-tholeiitic magmatism inthe back-arc to the west.

p0060Extension partly originated in areas previously oc-cupied by the Alps–Betics orogen, which formed inthe Cretaceous due to the ‘eastwards’-directed sub-duction of Europe and Iberia underneath the AdriaticPlate and a hypothetical Mesomediterranean plate(Figure 5). If Sardinia is restored to its position priorto rotation, it can be seen that during the early Ceno-zoic the Alps were probably joined with the Betics ina double-vergent single belt. The western Alps, whichare the forebelt of the Alps, were connected to theAlpine Corsica; the Alps continued south-westwardsinto the Balearic promontory and the Betics. The ret-robelt of the Alps, the southern Alps, also continuedfrom northern Italy towards the south-west. In adouble-vergent orogen, the forebelt is the frontalpart, which is synthetic to the subduction and vergestowards the subducting plate; the retrobelt is the in-ternal part, which is antithetic to the subduction andverges towards the interior of the overriding plate.

p0065The westwards-directed Apennines–Maghrebidessubduction started along the Alps–Betics retrobelt(Figures 3 and 4), where oceanic and thinned contin-ental lithosphere occurred in the foreland to the east.Subduction underneath the Apennines–Maghrebidesconsumed inherited Tethyan domains (Figures 4 and6). The subduction zone and the related arc migrated‘eastwards’ at a speed of 25–30 mm year�1.

p0070The western Late Oligocene–Early Miocene basinsof the Mediterranean nucleated both within the Beticsorogen (e.g. the Alboran Sea) and in its foreland (e.g.

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PROOFf0010 Figure 2 Palaeogeodynamics at about 15Ma. Note the ‘eastward’ vergence of both the Apennines–Maghrebides trench and the back-arc extensional wave. The Liguro-Provencal basin, the

Valencia trough, and the North Algerian basin were almost completely opened at 10Ma. The Dinarides subduction slowed down, owing to the presence of the thick Adriatic continental

lithosphere to the west, whereas to the south the Hellenic subduction was very lively owing to the presence in the footwall plate of the Ionian oceanic lithosphere. The Carpathians migrated

eastwards, generating the Pannonian back-arc basin, with kinematics similar to those of the Apennines.

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PROOFf0015 Figure 3 Palaeogeodynamics at about 30Ma. The locations of the subduction zones were controlled by the Mesozoic palaeogeography. The Alps–Betics formed along the south-

eastwards-dipping subduction of Europe and Iberia underneath the Adriatic and Mesomediterranean plates. The Apennines developed along the Alps–Betics retrobelt to the east, in which

oceanic or thinned pre-existing continental lithosphere was present. Similarly, the Carpathians started to develop along the Dinarides retrobelt (i.e. the Balkans). The fronts of the Alps–

Betics orogen were cross-cut by the Apennines-related subduction back-arc extension.

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the Valencia and Provencal troughs; Figure 3). At thattime the direction of the grabens (40�–70�) was ob-lique to the trend of the coexisting Betics orogen(60�–80�), indicating its structural independencefrom the Betics Orogeny. Thus, as the extensioncross-cut the orogen and also developed well outsidethe thrust-belt front, the westernmost basins of theMediterranean developed independently of the Alps–Betics orogen, being related instead to the innermost

early phases of back-arc extension in the hangingwall of the Apennines–Maghrebides subduction zone.In contrast to the ‘eastwards’-migrating extensionalbasins and following the ‘eastwards’ retreat of theApennines subduction zone, the Betics–Balearicthrust front was migrating ‘westwards’, producinginterference or inversion structures (Figure 4).

p0075The part of the Alps–Betics orogen that was locatedin the area of the Apennines–Maghrebides back-arc

f0020 Figure 4 During the last 45Ma, the evolution of the Mediterranean along the trace shown on the map (inset) is the result of three

main subduction zones: the early eastwards-directed Alpine subduction; the Apennines subduction switch along the Alps retrobelt;

and the Dinarides–Hellenides subduction. The last two slabs retreated at the expense of the inherited Tethyan Mesozoic oceanic or

thinned continental lithosphere. In their hanging walls, a few rifts formed as back-arc basins, which are progressively younger towards

the subduction hinges. The slab is steeper underneath the Apennines, possibly owing to the westwards drift of the lithosphere relative

to the mantle.

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f0025 Figure 5 Palaeogeodynamics at about 45Ma. The Alps were continuous with the Betics to Gibraltar, consuming an ocean located to the west.

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PROOFf0030 Figure 6 Main tectonic features of the Mediterranean realm, which has been shaped during the last 45Ma by a number of subduction zones and related belts: the double-vergent

Alps–Betics; the single eastwards-vergent Apennines–Maghrebides and the related western Mediterranean back-arc basin; the double-vergent Dinarides–Hellenides–Taurides and related

Aegean extension; the single eastwards-vergent Carpathians and the related Pannonian back-arc basin; and the double-vergent Pyrenees.

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basin (Figure 1) has been disarticulated and spreadout into the western Mediterranean (forming themetamorphic slices of Kabylie in northern Algeriaand Calabria in southern Italy). Alpine type basementrocks have been dragged up in the Tyrrhenian Sea.

p0080 Similarly, boudinage of the pre-existing Alps andDinarides orogens occurred in the Pannonian Basin,which is the Oligocene to Recent back-arc basin re-lated to the eastwards-retreating westwards-directedCarpathian subduction zone (Figures 1, 3, and 6). Inthe Pannonian basin, the extension isolated boudinsof continental lithosphere that had been thickened bythe earlier Dinarides orogen, such as the ApuseniMountains, which separate the Pannonian basinfrom the Transylvanian basin to the east. The westernMediterranean back-arc setting is comparable withAtlantic and western Pacific back-arc basins thatshow similar large-scale lithospheric boudinage, inwhich parts of earlier orogens have been scattered inthe back-arc area, like the Central America Cordillerarelicts that are dispersed in the Caribbean domain.

p0085 The Apennines accretionary prism formed in se-quence at the front of the pre-existing Alpine retrobelt,and, therefore, the central western Apennines alsocontain the inherited Alpine orogen of Cretaceous toMiocene age. There was probably a temporary coexist-ence of opposite subductions during the Late Oligoceneto Early Miocene (Figure 4). Structural and geophysicaldata support the presence of an eastwards-migratingasthenospheric wedge at the subduction hinge of theretreating Adriatic Plate. The subduction flip, from theAlpine eastwards-directed subduction to the Apennineswestwards-directed subduction, could be reflected inthe drastic increase in subsidence rates in the Apenninesforedeep during the Late Oligocene to Early Miocene.Westwards-directed subduction zones, such as theApennines, show foredeep subsidence rates that areup to 10 times higher (more than 1 mm year�1) thanthose of the Alpine foredeeps. The subduction flip(Figure 4) could also be reflected in the larger involve-ment of the crust during the earlier Alpine stages thanin the Apennines decollements, which mainly deformedthe sedimentary cover and the phyllitic basement. Ithas been demonstrated that the load of the Apennineand Carpathian orogens is not sufficient to gene-rate the 4–8 km deep Pliocene–Pleistocene foredeepbasins, and a mantle origin has been proposed forthe mechanism (slab pull and/or eastwards mantleflow).

p0090 Paradoxically, the extension that determined mostof the western Mediterranean developed in the con-text of relative convergence between Africa andEurope. However, it appears that the north–southrelative motion between Africa and Europe at thelongitude of Tunisia has been about 135 km in the

last 23 Ma, more than five times slower than themigration of the Apennines arc, which has movedmore than 700 km eastwards during the last 23 Ma(Figures 1 and 6). Therefore, the eastwards migrationof the Apennines–Maghrebides arc is not a conse-quence of the north–south relative convergencebetween Africa and Europe but is instead a conse-quence of the Apennines–Maghrebides subductionrollback, which was generated either by slab pull orby the ‘eastwards’ flow of the mantle relative to thelithosphere deduced from the hotspot referenceframe.

p0095The western Mediterranean developed mainly afterthe terminal convergence in the Pyrenees at about20 Ma, which resulted from the Late Cretaceous toEarly Tertiary counterclockwise rotation of Iberia,which was contemporaneous with the opening ofthe Biscay Basin.

p0100In northern Africa, south of the Maghrebides (andthe related Algerian Tell and Moroccan Riff), theAtlas Mountains represent an intraplate inversionstructure, in which extensional (north-north-east-trending) and left-lateral (about east–west-trending)transtensional Mesozoic intercontinental rifts werelater buckled and squeezed by Cenozoic compressionand right-lateral transpression in the foreland of theApennines–Maghrebides subduction zone. This isalso indicated by the Mesozoic sequences in theAtlas ranges, which are thicker than the adjacentundeformed mesetas.

s0015Central Mediterranean

p0105The Malta escarpment (Figures 1 and 5), along theeastern coast of Sicily, is a physiographic feature thathas been tectonically controlled since Triassic times.Rocks dredged from the Malta escarpment rangefrom Mesozoic to Tertiary in age. The escarpmentrepresents a Mesozoic continental margin that hasbeen reactivated as a transtensional feature since thePliocene. In spite of the Apennines and HellenidesNeogene subduction zones, two conjugate passivecontinental margins are preserved at the margins ofthe Ionian Sea, along the Malta escarpment to thesouth-west and the Apulian escarpment to the north-east. Based on the low heat flows (18–40 mW m�2)and the 4–8 km of sedimentary cover, the Ionian Sea isprobably a remnant of the Mesozoic Tethys Ocean,confined by the two conjugate passive continentalmargins. The transition from continental crust tooceanic crust appears to be sharper to the north-eastthan to the south-west. The basin between south-eastSicily and south-west Puglia was about 330 km wide.The inferred oceanic ridge could have been flattenedby thermal cooling and buried by later sediments.

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p0110 Stratigraphic and structural constraints to thenorth in the Apennines belt suggest that the IonianOcean continued to the north-west (Figure 5). Thispalaeogeography is supported by the seismicity of theApennines slab underneath the southern TyrrhenianSea, which implies subducted oceanic lithosphere.The adjacent absence or paucity of deep seismicitydoes not imply the absence of subduction but canbe interpreted as a reflection of the more ductilebehaviour of the subducted continental lithosphere.

p0115 The Sicily Channel and the Pelagian shelf off thecoast of eastern Tunisia have been undergoing exten-sion since at least Pliocene times; in other wordsAfrica is moving south-westwards in relation to Sicily(Figure 1). This process is responsible for the twograbens of Pantelleria and Malta deepening the sea-floor and for the generation of active alkaline mag-matism (e.g. the ephemeral Ferdinandea Island). Thelithospheric extension was active whilst the Apen-nines–Maghrebides accretionary prism advanced,generating an interplay of two tectonic settingsworking together, with thrusts advancing over anorthogonal extending area, generating both thrustscutting normal faults and normal faults offsettingthrusts. The rifting of the Sicily Channel seems to bephysically connected north-westwards to the rift insouth-western Sardinia (Campidano graben) andsouth-eastwards to the Sirte Basin, off the coast ofLibya. One possibility is that this rift is linkedthrough transfer zones in Egypt to the Red Sea andthe East African Rift.

s0020 Eastern Mediterranean

p0120 The Dinarides, Hellenides, and Taurides are a poly-phase orogen, representing the coalescence of at leasttwo or three subduction zones since Mesozoic times(Figures 1, 4, 5, and 6). The orogen has a part syn-thetic to the north-eastwards-directed subduction, i.e.the forebelt verging south-westwards. The conjugatepart of the orogen is the retrobelt, which vergesnorth-eastwards and northwards (Balkans and Pon-tides). The existence of three subduction zones issupported by the occurrence of two distinct oceanicsutures, preserved as the ophiolitic suites of Vardarand the Sub-Pelagonian units, which represent twoseparated branches of the Mesozoic Tethyan oceanand the present oceanic subduction of the Ionian Sea.It is commonly believed that the more internal(Vardar) suture zone is the older one.

p0125 The polyphase orogen exhibits a similar architec-ture to the Alps, but duplicated. The Rhodope–Serbo-Macedonian and Sakarya (northern Turkey) massifsmimic the internal massifs of the Alps, which repre-sent the continental margin of the hanging-wall plate.

On the other side, to the south-west of the Vardaroceanic suture, the Pelagonian (Macedonia–Greece)and Menderes (northern Turkey) massifs correspondto the external massifs of the Alps, representing thecontinental lithosphere of the footwall plate. ThePelagonian basement is at the same time the hang-ing-wall plate for the more external north-eastwards-directed subduction of the Sub-Pelagonian andPindos Ocean, which was eventually closed bycollision with the eastern margin of the Adriatic Plate.

p0130However, unlike the Alps, widespread extensiondeveloped in the Dinarides–Hellenides–Taurides oro-gen (Figures 1 and 6). This extension resulted in thelow topography of the orogen in comparison withbelts such as the Alps and the Zagros or the Hima-layas. In the Balkans, the Rhodope, and the Serbo-Macedonian massifs, structural and stratigraphicdata indicate an interplay of compressional and ex-tensional tectonics. A Cretaceous to Eocene compres-sive deformation was followed by the generation ofEocene grabens. A later (possibly Miocene) compres-sion inverted and uplifted these grabens, but it wasfollowed by extensional tectonics that have affectedthe Balkan peninsula since Pliocene times, determin-ing the north-west-trending normal faults and therelated east–west right-lateral and north–south left-lateral transtensive transfer faults. North-eastwards-directed subduction is continuing along the easternside of the Adriatic, in the Ionian Sea underneath theMediterranean Ridge (the accretionary prism), andon the northern side of the Levantine Sea, i.e. in theeastern Mediterranean beneath Cyprus (Figure 1).The convergence rates are faster underneath theMediterranean ridge (up to 40–50 mm year�1), de-crease eastwards along the Cyprus segment, andhave minimum values along the Adriatic coast. Theconvergence rate appears to be controlled by thecomposition of the foreland lithosphere: where it isoceanic and dense, such as in the Ionian Sea, thesubduction is faster than in the Adriatic and Cyprussegments, where the downgoing lithosphere is contin-ental and transitional oceanic–continental, respect-ively. In the orogen, calc-alkaline and shoshoniticmagmatism has accompanied most of the subductionsince Cretaceous times. The later extensional processin the anomalously called ‘back-arc’ is possibly re-sponsible for the transition to the alkaline magmaticsignature.

p0135One of the best-known ophiolitic sequences in theworld crops out in Cyprus: a complete oceanic sectionis exposed (from harzburgites and peridotites ofthe upper mantle to gabbros, sheeted dykes, lavas,and pelagic sediments of the crust). The island isan anticline involving the whole crust, and its cul-mination coincides with the Erathostene seamount



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in the subducting foreland. The Erathosteneseamount is a structural high inherited from theMesozoic–Cenozoic rift.

p0140 Since at least Miocene times, there has been anindependent and presently active subduction alongthe northern margin of the Black Sea, generating theCaucasus.

p0145 Geodynamic reconstructions of the eastern Medi-terranean explain the extensional tectonics either bywestwards Anatolian extrusion or by gravitationalcollapse of thickened lithosphere. However, thesemechanisms can be ruled out because plate-velocityvectors increase from eastern Anatolia to the Aegeanand Greece. This contradicts the basic rule that thevelocity field decreases away from the source of theenergy, i.e. the supposed squeezing of Anatolia bythe Arabia indenter, or the collapse of the Anatolianorogen. Moreover, the topographic gradient betweenAnatolia and the Ionian deep basin is too small (lessthan 1�) to provide sufficient energy to explain thepresent deformation. Instead, the simplistic view ofthe westward Anatolian escape would close theAegean Sea.

p0150 The plates involved in the geodynamic reconstruc-tions of the eastern Mediterranean are Africa, Greece,Anatolia, Eurasia, and Arabia. Deformation is veryactive in all these areas. The most prominent geody-namic factor shaping the eastern Mediterranean is thenorth-east-directed subduction of Africa underneathGreece and the Anatolian Plate (Eurasia). Seismiclines across the Cyprus Arc at the southern marginof the Anatolian Plate show clear active compressionand deformation of the seafloor.

p0155 The Aegean Sea is generally considered to be aback-arc basin resulting from the aforementionedsubduction. However, the Aegean Sea is characterizedby a relatively thick crust (20–25 km) in spite of long-standing subduction, which has probably been activesince at least the Cretaceous. The subduction zonemigrated south-westwards to the present position ofthe Cyprus-Hellenic subduction zone, and the associ-ated orogen was later replaced by extension. In theAegean Sea, Alpine-type crustal thickening with highpressures and low temperatures was followed by non-coaxial crustal-scale extension. This is consistent withthe initial emplacement of thrust-sheets of basementslices, which were later cross-cut by extensional ortranstensional faults. In addition, extension and asso-ciated magmatism were and are migrating south-south-westwards, and have developed particularlysince the Oligocene, while subduction began muchearlier. ‘Normal’ back-arc basins (e.g. the TyrrhenianSea) associated with westwards-directed subductionzones opened very fast (10–20 Ma) and are alwayscontemporaneous with the subduction. Moreover,

they are characterized by oceanization and eastwardsmigration of extension and related magmatism, fea-tures directly surrounded by a frontal accretionarywedge. In contrast, the accretionary wedge of theHellenic subduction zone is the south-eastern pro-longation of the Dinarides thrust belt, where noback-arc rift comparable to the Tyrrhenian Seaoccurs.

p0160The extension in western Turkey, the Aegean Sea,Greece, and Bulgaria appears to be the result of dif-ferential convergence rates in the north-eastwards-directed subduction of Africa relative to the hangingwall of disrupted Eurasian lithosphere. Relative toAfrica, the faster south-eastwards motion of Greecethan of Cyprus–Anatolia results in the Aegeanextension. The differences in velocity can be ascribedto differential decoupling with the asthenosphere.In the back-arc basins of the western Pacific theasthenosphere replaces a subducted and retreatedslab; however, the Aegean rift represents a differenttype of extension associated with a subductionzone, in which the hanging-wall plate overridesthe slab at different velocities, implying internaldeformation.

p0165According to this geodynamic scenario, during thecompressive events associated with north-eastwards-directed subduction, basement rocks (both continen-tal and ophiolitic slices) in western Anatolia and theAegean Sea were uplifted and eroded. Later extensioncaused subsidence in the area, and the basementslices were partly covered by continental and marinesediments.

p0170During its development, the Aegean extensionmigrated south-westwards (Figures 4 and 6). TheAegean rift affects the Aegean Sea and all of contin-ental Greece, and it can be followed to the east, whereit is widely expressed in Turkey, and to the north-westin Bulgaria, Albania, Macedonia, Serbia, and Bosnia.At the same time, from the Oligocene to the present,to the north, the Pannonian basin developed as theback-arc of the Carpathians subduction, but migrat-ing eastwards, and affecting mainly eastern Austria,Slovenia, Croatia, Hungary, and Romania. There-fore, in the central part of the former Yugoslavia,the Pannonian and Aegean rifts meet with oppositedirections of migration.

See Also

Tectonics: Plate tectonics: Overview (00127); Conver-

gent Plate Boundaries: Accretionary Wedges (00456);

Mountain Building and Orogeny (00129). Europe: The

Variscides Orogeny (00441); The Alps (00442); Neogene

mantle dynamics, magmatism and tectonics (00469);

Holocene (00470).

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Further Reading

Berckhemer H and Hsu KJ (eds.) (1982) Alpine Mediterra-nean Geodynamics. Geodynamics Series 7. Washington:American Geophysical Union.

Calcagnile G and Panza GF (1980) The main characteristicsof the lithosphere–asthenosphere system in Italy andsurrounding regions. Pure and Applied Geophysics 119:865–879.

Carminati E, Wortel MJR, Spakman W, and Sabadini R(1998) The role of slab detachment processes in theopening of the western–central Mediterranean basins:some geological and geophysical evidence. Earth andPlanetary Science Letters 160: 651–665.

Catalano R, Doglioni C, and Merlini S (2001) On theMesozoic Ionian basin. Geophysical Journal Inter-national 144: 49–64.

Cella F, Fedi M, Florio G, and Rapolla A (1998) Gravitymodeling of the litho-asthenosphere system in the CentralMediterranean. Tectonophysics 287: 117–138.

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