kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern mediterranean region since the late cretaceous the relationship between subduction dynamics and crustal deformation in the mediterranean region has been recently studied using three dimensional 3d numerical models such models require however a detailed information concerning the past geological evolution we use stratigraphic petrologic metamorphic structural paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern mediterranean region since the late cretaceous using the principle of non rigid domains the motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations the directions and amounts of displacement on crustal scale shear zones and the burial and exhumation histories of the main metamorphic units extracted from these reconstructions paleotectonic maps and lithospheric scale cross sections illustrate that the present day subduction zone has been continuously retreating southward since the late cretaceous and has accreted several small continental domains in the process we find evidence for two back arc related extensional events 1 slow extension along the balkans and the pontides in the late cretaceous while the trench was long and linear and 2 faster extension in the rhodope aegean west anatolian region since the eocene oligocene rapid rotation of the hellenides between 15 and 8 ma probably indicates a slab tearing event below western anatolia that could have further accelerated this extensional kinematics spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation

spatial and temporal isotopic domains of contrasting igneous suites in western and northern sulawesi indonesia abstract palaeocene to pliocene magmatism in nw sulawesi shows a progression from an older series with calc alkaline tholeiitic signatures 51 17 ma to a younger series of mafic intermediate high k magmas 14 5 ma and felsic k rich calc alkaline cak magmas 9 2 ma the isotopic and geochemical compositions of the older series samples indicate that the more westerly samples have been generated in a continental arc setting and the more easterly samples in an oceanic arc this distinction defines the boundary between the western and northern sulawesi tectonic terranes the younger series high k magmas have unusual isotopic compositions with variable but low 143nd 144nd high 87sr 86sr values and high 208pb 204pb for their 206pb 204pb ratios compared to subduction related magmas the diversity of the isotopic compositions points towards a source with a long and heterogeneous geochemical evolution most likely located within the australian subcontinental lithospheric mantle the younger series felsic cak magmatism has a more homogeneous isotopic and geochemical signature and reflects melting of continental crust of australian origin this geochemical progression in time is very similar to that seen in central sulawesi chem geol 156 1999a 67 and is best explained by normal subduction of an oceanic plate followed by melting of an underthrust sliver of australian continent the size of this microcontinent can be estimated from the areal extent of low nd isotope magmas in western sulawesi ranging from approximately 4 s to 1 n underthrusting must have happened prior to 14 ma indicating that this event cannot be equated to the collision between sulawesi and the sula platform which occurred at 5 ma while subduction beneath western sulawesi ceased prior to the onset of potassic magmatism in this region it continued beneath northern sulawesi producing predominantly calc alkaline suites

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

late cenozoic deformation of the hellenide foreland western greece the late cenozoic structural evolution of western greece involved the shortening of mesozoic passive continental margin and cenozoic foreland basin sequences in a foreland propagating fold and thrust system and superimposed neotectonic deformation related to the development of an active island arc although the pre apulian zone has been regarded as the undeformed western foreland to the thrust belt three dimensional exposures in the ionian islands of kephalonia and zakinthos afford evidence of significant late neogene and quaternary shortening including thrusting on reactivated normal faults time relations and fault kinematics show that these structures are compatible with the westward migration of the locus of hellenide thrusting beyond its previously recognized limit and outer arc compression related to active subduction the presence of the pre apulian zone in the west contrasts with other aegean foreland areas where no such intermediate block lay between the thrust pile and old mesozoic oceanic crust consequently the pre apulian block took up continued hellenide shortening in the late miocene while oceanic crust was being overridden subducted in southern parts of the arc to the east the pre apulian zone subsequently overrode the ocean floored ionian sea during the late neogene the confusion in determining driving mechanisms for late cenozoic deformation in western greece and the apparent conflict between evidence for the age of initial subduction in different parts of the arc are explained by this model which is consistent with regional considerations including structuration in adjacent areas and important paleomagnetic rotations in the arc

u pb zircon geochronology of the paleogene neogene volcanism in the nw anatolia its implications for the late mesozoic cenozoic geodynamic evolution of the aegean abstract the northern aegean region was shaped by subduction obduction collision and post collisional extension processes two areas in this region the rhodope thrace biga peninsula to the west and armutlu almacik nallihan the central sakarya to the east are characterized by extensive eocene to miocene post collisional magmatic associations we suggest that comparison of the cenozoic magmatic events of these two regions may provide insights into the late mesozoic to cenozoic tectonic evolution of the aegean with this aim we present an improved cenozoic stratigraphy of the biga peninsula derived from a new comprehensive set of u pb zircon age data obtained from the eocene to miocene volcanic units in the region the compiled radiometric age data show that calc alkaline volcanic activity occurred at 43 15 ma in the biga peninsula 43 17 ma in the rhodope and thrace regions and 53 38 ma in the armutlu almacik nallihan region which are slightly overlapping we discuss the possible cause for the distinct cenozoic geodynamic evolution of the eastern and western parts of the region and propose that the rhodope thrace and biga regions in the north aegean share the same late mesozoic to cenozoic geodynamic evolution which is consistent with continuous subduction crustal accretion southwestward trench migration and accompanying extension all preceded by the late cretaceous paleocene collision along the vardar suture zone in contrast the armutlu almacik nallihan region was shaped by slab break off and related processes following the late cretaceous paleocene collision along the izmir ankara suture zone the eastern and western parts of the region are presently separated by a northeast southwest trending transfer zone that was likely originally present as a transform fault in the subducted tethys oceanic crust and demonstrates that the regional geodynamic evolution can be strongly influenced by the geographical distribution of geologic features on the subducting plate

nappe stacking resulting from subduction of oceanic and continental lithosphere below greece we quantitatively investigate the relation between nappe stacking and subduction in the aegean region if nappe stacking is the result of the decoupling of upper crustal parts 5 10 km thick from subducting lithosphere then the amount of convergence estimated from balancing the nappe stack provides a lower limit to the amount of convergence accommodated by subduction the balanced nappe stack combined with the estimated amount of completely subducted lithosphere indicates 700 km of jurassic and 2400 km of post jurassic convergence from seismic tomographic images of the underlying mantle we estimate 2100 2500 km of post jurassic convergence we conclude that 1 the imaged slab represents the subducted lithosphere that originally underlay the nappes 2 since the early cretaceous subduction in the aegean has occurred in one single subduction zone and 3 the composition of the original basement of the nappes indicates that at least 900 km of sub upper crust continental lithosphere subducted in the aegean

petrogenesis and 40ar 39ar geochronology of the volcanic rocks of the usak gure basin western turkiye abstract in spite of much research over the past 30 years the dynamic evolution origin of the volcanism and geometrical stratigraphical relations of the ne sw trending basins in western anatolia are poorly understood the usak gure basin is one of the prominent ne sw trending basins developed on the northern part of the menderes massif core complex three distinct volcanic successions are found in the usak gure basin 1 the beydagi volcanic unit composed of shoshonite latites and rhyolitic lavas followed by dacitic and andesitic pyroclastic deposits 2 the payamtepe volcanic unit composed of potassic intermediate composition lavas latites and trachytes and 3 the karaagac dikes composed of andesite and latite the beydagi volcanic unit occurs in three different ne sw trending volcanic centers beydagi itecektepe and elmadag calderas from southwest to northeast respectively the oldest radiometric ages for the beydagi volcanic unit are from the elmadag volcanic center in the north and range from 17 to 16 ma the data indicate that volcanism was active during the latest early miocene the youngest radiometric age for the beydagi volcanic unit is obtained from the beydagi caldera located 12 ma in the south the data indicate that beydagi volcanism was active in the late middle miocene and migrated from north to south with time 40ar 39ar ages of the payamtepe volcanic unit are restricted to a short period between 16 0 and 15 9 ma volcanic rocks of the usak gure basin are characterized by strong enrichment in lile and lree and depletions of nb ta and ti on morb normalized multi element diagrams geochemical features of the volcanic rocks suggest that they experienced mixing processes between mafic and felsic end members and also fractional crystallization of dominantly plagioclase and pyroxenes from mixed magma compositions crustal contributions to the magma sources may also have occurred during magmatic evolution these processes have resulted in scattered major and trace element variations with respect to increasing silica contents geochemical features of the most mafic samples agree with the results of previous studies from other volcanic areas in western anatolia suggesting that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the african and eurasia plates the volcanic activity in the region which developed synchronously with the formation of the menderes massif core complex is best explained by delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction related processes

structural analysis of a complex nappe sequence and late orogenic basins from the aegean island of samos greece the island of samos in the aegean sea exposes high pressure metamorphic rocks of the cycladic blueschist unit which are sandwiched between the mildly blueschist facies kerketas nappe below and the overlying non metamorphic kallithea nappe structural and metamorphic analysis shows that deformation can generally be divided into four main stages 1 eocene and earliest oligocene 0ese wnw oriented nappe stacking d1 and d2 associated with blueschist and transitional blueschist greenschist facies metamorphism m1 and m2 d2 caused emplacement of the blueschist unit onto the kerketas nappe indicating that thrusting occurred during decompression 2 a subsequent history of oligocene and miocene horizontal crustal extension d3 before and after greenschist facies metamorphism m3 ductile flow during d3 was characterized by a high degree of coaxial deformation but in general caused displacement of upper units towards the ene nonetheless the late stage d3 emplacement of the kallithea nappe between 9 and 10 ma had a top to the nw nnw sense of shear 3 a short period of brittle e w crustal contraction d4 occurred between 8 6 and 09 ma 4 a phase of n s directed normal faulting d5 8 6 ma to recent ese wnw directed tectonic transport during d1 through d3 is in contrast to uniform nne sswdirected tectonic transport in the adjacent cyclades greece as well as in the neighbouring menderes massif of western turkey published paleomagnetic data reveal sinistral rotation between the cyclades and western turkey we interpret this rotation as a consequence of diaerential extension between the severely extended aegean and the moderately extended menderes massif during d3 the onset of d3 crustal extension is coeval with a marked change in the thermal structure we propose that the thermal reorganization was associated with the retreat of the subduction zone towards the external hellenides in the early oligocene and a subsequent increase in magmatic activity 1999 elsevier science ltd all rights reserved

mesozoic tertiary tectonic evolution of albania in its regional eastern mediterranean context abstract research carried out since the opening of albania to the western geological community in the 1990s allows the geology and tectonics of this small balkan country to be integrated into an overall interpretation of neotethys in the eastern mediterranean region specifically greece and the former yugoslavia region albanian geology is most famous for the occurrence of contrasting ophiolites of jurassic age the country is sub divided into three main geotectonic units those in the west i e sazani ionian kruja krasta cukali and the albanian alps relate to the western margin of apulia effectively part of north africa from early mesozoic time onwards in the east is the korabi zone interpreted as a microcontinent located further northeast within neotethys between the two is the mirdita zone dominated by two contrasting jurassic ophiolites the western type ophiolite and the eastern type ophiolite taking account of evidence from greece and former yugoslavia the following tectonic evolution is proposed from early mesozoic time onwards neotethys in albania existed as a northward continuation of the pindos oceanic basin in greece pindos mirdita ocean a korabi microcontinent was rifted off apulia in the early mid triassic followed by passive margin subsidence until late middle jurassic time a rifted slow spreading mor type ophiolite formed within the western pindos mirdita oceanic basin in late triassic early late jurassic time using present co ordinates the shkoder peje scutari pec lineament in the north of albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire mesozoic early tertiary rift drift emplacement history of the pindos mirdita ocean taking account of evidence from the greek and former yugoslavia ophiolites the easterly albanian ophiolites formed within the pindos mirdita ocean above a westward dipping intra oceanic subduction zone in the early late jurassic metamorphic soles were formed during initial intra oceanic displacement ca 162 174 m y and underlying melanges originated as subduction accretion complexes the mor western type ophiolite evolved into the iat boninitic eastern type ophiolite after subduction began during tithonian berriasian time trench margin collision emplaced the ophiolites eastwards over the korabi margin coupled with redeposition of ophiolitic and continental margin material as exotic blocks debris flow deposits and turbidites these were emplaced onto the upper surface of the ophiolitic thrust sheet during the latest stages of emplacement onto the korabi microcontinent following collision in the east oceanic crust remained within a small remnant pindos mirdita oceanic basin passive conditions were restored in the mid late cretaceous with shallow water carbonate deposition on microcontinental units and both pelagic and redeposited carbonates in basinal settings from the maastrichtian onwards africa eurasia convergence resulted in large scale westward thrusting deforming the apulian foreland in oligo miocene time the suture zone was re activated in oligo miocene time as the albanie thassalie piggy back type basin in central and southern albania albania as a whole was rotated 45 clockwise as part of the western aegean arc in post eocene time coastal and offshore albania experienced strong subsidence after early miocene time forming the periadriatic basin including the tirana depression interpreted as a foredeep related to continuing regional convergence southern albania experienced extensional tectonics in plio quaternary time related to southward roll back of the aegean active margin

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

underthrusting and exhumation a comparison between the external hellenides and the hot cycladic and cold south aegean core complexes greece 1 after their emplacement in the course of the late mesozoic and the cenozoic the hellenic nappes became fragmented during late orogenic extension since the late eocene here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension to this end we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the tripolitza and ionian nappes which were exhumed in the cycladic and south aegean windows with newly obtained data on the sedimentary stratigraphic and structural development of the part of these nappes in the foreland in front of the subduction thrust the results allow the identification of two major events event 1 took place around the eocene oligocene transition and marks the onset of underthrusting of the tripolitza nappe below the pindos nappe and the ionian nappe below the tripolitza nappe respectively this led to the uplift and erosion of the pindos unit and the onset of deposition of the tripolitza and ionian flysch in front of the pindos thrust together with the formation of mylonites at the base of the metamorphosed portions of the pindos unit related to the underthrusting of the tripolitza unit event 2 occurred in the latest oligocene to earliest miocene and marks the decoupling of the ionian unit from the underthrusting plate the accretion of the tripolitza and ionian units to the overriding plate and the onset of late orogenic extension and exhumation in the overriding plate this led to the formation of the south aegean and cycladic core complexes and the subsidence of the klematia paramythia half graben throughout the early miocene

mechanisms of blueschist creation and preservation in an a type subduction zone mount olympos region greece deformation and metamorphism in the mount olympos region greece are the result of subduction of continental crust a type subduction during the alpine orogeny new structural and petrologic data from this region provide insight into the creation of low geothermal gradients in a type subduction zones and the preservation of blueschist facies assemblages early convergent deformation was accompanied by greenschist amphibolite facies metamorphism blueschist facies mineral assemblages overprinted higher grade assemblages during large scale episodic shortening that occurred during and after continental collision prehnite pumpellyite facies assemblages are postkinematic with respect to contractional fabrics but predate a prolonged period of extension that was not accompanied by metamorphism under plating and extension permitted unroofing and preservation of the blueschists with no over printing by greenschist facies assemblages

bacteriohopanepolyols preserved in silica sinters from champagne pool new zealand indicate a declining temperature gradient over the lifetime of the vent siliceous sinters from champagne pool cp a geothermal vent in the taupo volcanic zone north island new zealand contained exceptionally well preserved bacteriohopanepolyol bhp distributions bhps were present in a range of sinters deposited over the lifetime of cp 900 yr before present the distributions correlated well with the presence of members of bhp producing bacterial orders known to inhabit cp for example acidothiobacillales burkholderiales and pseudomonadales are known sources of composite bhps with a more complex functional group at c 35 such as bacteriohopanetetrol cyclitol ether found in high relative abundance in each cp sinter analysed the bhp distributions preserved in cp sinters were different from those described previously for any other environmental setting with pentafunctionalised bhps accounting for up to 55 of the total assemblage furthermore composite bhps were the most abundant compound type in each sample and accounted for up to 80 of the total bhp distribution as the age of sinter increased a general increase in bhp abundance was observed similarly in older sinters the complexity of the bhp compounds increased the observations are consistent with a higher temperature of vent water in the past the excellent preservation of bhps in this setting over the lifetime of the vent highlights the usefulness of bhps as biomarkers for reconstructing modern and ancient geothermal vent bacterial communities 2014 published by elsevier ltd

dynamics of intraoceanic subduction initiation 1 oceanic detachment fault inversion and the formation of supra subduction zone ophiolites subduction initiation is a critical link in the plate tectonic cycle intraoceanic subduction zones can form along transform faults and fracture zones but how subduction nucleates parallel to mid ocean ridges as in e g the neotethys ocean during the jurassic remains a matter of debate in recent years extensional detachment faults have been widely documented adjacent to slow spreading and ultraslow spreading ridges where they cut across the oceanic lithosphere these structures are extremely weak due to widespread occurrence of serpentine and talc resulting from hydrothermal alteration and can therefore effectively localize deformation here we show geochemical tectonic and paleomagnetic evidence from the jurassic ophiolites of albania and greece for a subduction zone formed in the western neotethys parallel to a spreading ridge along an oceanic detachment fault with 2 d numerical modeling exploring the evolution of a detachment ridge system experiencing compression we show that serpentinized detachments are always weaker than spreading ridges we conclude that owing to their extreme weakness oceanic detachments can effectively localize deformation under perpendicular far field forcing providing ideal conditions to nucleate new subduction zones parallel and close to or at spreading ridges direct implication of this is that resumed magmatic activity in the forearc during subduction initiation can yield widespread accretion of suprasubduction zone ophiolites at or close to the paleoridge our new model casts the enigmatic origin of regionally extensive ophiolite belts in a novel geodynamic context and calls for future research on three dimensional modeling of subduction initiation and how upper plate extension is associated with that

kinematics of cretaceous subduction and exhumation in the western rhodope chalkidiki block in the chalkidiki peninsula of northern greece a thrust complex made of a basement vertiskos unit a cover circum rhodope belt and arc back arc units chortiatis magmatic suite and eastern vardar ophiolites is exposed in the chalkidiki peninsula of northern greece the complex forms the western part of the rhodope metamorphic province and lies on the hanging wall of the kerdylion detachment the structure responsible for the exhumation of the southern rhodope core complex and the most prominent and visible ductile structure related to the tertiary aegean extension the chalkidiki thrust complex arguably preserves a complete record of cretaceous deformation and related fabrics in this contribution we describe the geometry of foliation stretching lineation and shear sense s on a regional scale the regional foliation strikes nw se and displays different patterns in the three studied units i dominantly dipping at low angle in the vertiskos unit ii affected by upright folding in the circum rhodope belt and iii systematically steeply dipping to the ne in the chortiatis magmatic suite stretching lineation trend dominantly sw ne in the three mentioned units on the basis of new mapping neglecting local perturbations and deformation related to tertiary extension we infer the regional kinematics of cretaceous syn metamorphic thrusting and subsequent exhumation of the metamorphic units thrusting took place toward the sw in present day coordination and the related fabrics are recorded throughout the metamorphic pile on the contrary exhumation related fabrics are related to shear toward the ne and are preferentially recorded in the uppermost part of the metamorphic pile suggesting that extension was more localised and of less finite intensity compared to thrusting

the link between tectonics and sedimentation in back arc basins new genetic constraints from the analysis of the pannonian basin the architecture of sedimentary basins reflects the relationship between accommodation space and sediment supply their rates and localization being variable during basin evolution the mechanisms driving the interplay between tectonics and sedimentation in extensional back arc basins overlying rheological weak zones inherited from an earlier orogenic evolution are less understood a typical example is the pannonian back arc basin of central europe it is floored by continental lithosphere and was affected by large amounts of extension driven by the subduction rollback that took place in the carpathians and or dinarides a novel kinematic and seismic sequence stratigraphic interpretation calibrated by wells allows the quantification of the link between the formation of half grabens and coeval sedimentation in the great hungarian plain part of the basin while the lower order tectonic induced cycles characterize the main phases of extension in various subbasins the higher order cyclicity and associated unconformities define individual moments of fault re activation our novel interpretation of a temporal and spatial migration of extension during miocene times explains the contrasting present day strike of various subbasins as a result of their gradual clockwise rotation incorporating the observed asymmetry in particular the associated footwall exhumation infers that the amount of extension is much larger than previously thought the quantitative link between tectonics and sedimentation has allowed the definition of a novel model of sedimentation in asymmetric basins that can be ported to other natural scenarios of similarly hyperextended back arc basins observed elsewhere

continental plate collision unstable vs stable slab dynamics we study possible scenarios for the evolution of continental collision zones by using a dynamic thermomechanical model that includes brittle elastic ductile rheology surface erosion and explicit metamorphic changes this paper focuses primarily on the influence of four key parameters 1 geotherm or thermotectonic age which controls the rheological profile 2 lower crustal composition weak or strong rheology 3 convergence rate and 4 metamorphic changes in the downgoing crust the experiments suggest that de pending on these parameters plate convergence is accommodated by four distinct mech anisms stable subduction shortening by pure shear thickening or folding and rayleigh taylor instabilities it appears that stable oceanic type subduction can only occur in the case of cold lithospheres moho temperature tmoho 550 8c and basically needs high convergence rates 4 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction it appears that in the case of weak metamorphic rheologies phase changes only slightly improve chances for stable subduction lithospheric shortening becomes a dominant mechanism when tmoho 550 8c or convergence rates are 4 5 cm yr pure shear thickening becomes important in all cases of hot lithospheres tmoho 650 8c large scale folding is favored in the case of tmoho 5 500 650 8c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust grav itational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho 800 8c and may lead to development of subvertical cold spots

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

resolving cambrian carboniferous permian and alpine monazite generations in the polymetamorphic basement of eastern crete greece by means of the electron microprobe the electron microprobe based investigation of accessory monazites in polished thin sections is a helpful tool in resolving the geochronology of a polymetamorphic basement the method was applied to variably altered gneisses and micaschists from the retrogressed originally amphibolite facies basement in eastern crete greece the presented data indicate that most monazite formed or recrystallized in response to high fluid activity during alpine low temperature metamorphism this low temperature monazite is characterized by distinctly low yttrium uranium and thorium contents however older grains were able to survive in less retrogressed samples and have been traced with the electron microprobe using microstructural and compositional criteria in situ chemical th u pb dating of these pre alpine monazites provides evidence for an igneous event in the cambrian and two different metamorphic events in the carboniferous and permian

mid holocene tectonic geomorphology of northern crete deduced from a coastal sedimentary archive near rethymnon and a late bronze age santorini tsunamite candidate abstract the late bronze age lba tsunami and the a d 365 tsunami are supposed to have affected the northern coasts of crete however near coast sedimentary archives have been rarely investigated in this area and sedimentary archives including palaeotsunami fingerprints are still unknown the main objective of our research was to search for appropriate tsunami sediment traps in order to gain detailed insights into the holocene palaeotsunami history of northern crete we found an excellent fine sediment archive near pirgos located to the west of rethymnon based on a multi electrode geoelectrical survey and an 11 m deep sediment core we analysed the event geochronostratigraphical record by means of sedimentological geochemical geochronological geomorphological and microfossil investigations the pirgos record revealed a thick unit of homogeneous mud of a lagoonal environment starting 6000 years ago the lagoon was affected by five high energy events leaving layers of allochthonous sand microfossil analyses of these layers revealed a mixed foraminiferal assemblage including species from brackish habitats but also displaced and transported species from open marine and deep water environments considering sedimentary characteristics the local wave climate of the cretan sea and the overall geomorphological setting we interpret these layers as related to extreme wave events ewe based on a local radiocarbon age depth model we identified one ewe layer as a reliable candidate for the lba santorini tsunami another ewe layer is most probably associated with the a d 365 tsunami this ewe ended abruptly the lagoonal conditions at pirgos because of to the 1 64 m coseismic uplift at the site the pirgos lagoon existed between the first half of the 6th mill b c and at least the end of the 2nd mill b c we found that the area around pirgos has continuously subsided over 3000 or so years reflecting constant tectonogeomorphological conditions dominated by the nearby subduction zone between the aegean and african plates

tearing segmentation and backstepping of subduction in the aegean new insights from seismicity abstract this study revisits subduction processes at the hellenic subduction zone hsz including tearing segmentation and backstepping by refining the geometry of the nubian slab down to 150 180 km depth using well located hypocentres from global and local seismicity catalogues at the western termination of the hsz the kefalonia transform fault marks the transition between oceanic and continental lithosphere subducting to the south and to the north of it respectively a discontinuity is suggested to exist between the two slabs at shallow depths the kefalonia transform fault is interpreted as an active subduction transform edge propagator fault formed as consequence of faster trench retreat induced by the subduction of oceanic lithosphere to the south of it a model reconstructing the evolution of the subduction system in the area of peloponnese since 34 ma involving the backstepping of the subduction to the back side of adria provides seismological evidence that supports the single slab model for the hsz and suggests the correlation between the downdip limit of the seismicity to the amount of subducted oceanic lithosphere in the area of rhodes earthquake hypocentres indicate the presence of a nw dipping subducting slab that rules out the presence of a ne sw striking subduction transform edge propagator fault in the pliny strabo trenches region earthquake hypocentres also allow refining the slab tear beneath southwestern anatolia down to 150 180 km depth furthermore the distribution of microseismicity shows a first order slab segmentation in the region between crete and karpathos with a less steep and laterally wider slab segment to the west and a steeper and narrower slab segment to the east thermal models indicate the presence of a colder slab beneath the southeastern aegean that leads to deepening of the intermediate depth seismicity slab segmentation affects the upper plate deformation that is stronger above the eastern slab segment and the seismicity along the interplate seismogenic zone

reconciling the geological history of western turkey with plate circuits and mantle tomography abstract we place the geological history since cretaceous times in western turkey in a context of convergence subduction collision and slab break off to this end we compare the west anatolian geological history with amounts of africa europe convergence calculated from the atlantic plate circuit and the seismic tomography images of the west anatolian mantle structure western turkish geology reflects the convergence between the sakarya continent here treated as eurasia in the north and africa in the south with the anatolide tauride block atb between two strands of the neotethyan ocean convergence between the sakarya and the atb started at least 95 90 myr ago marked by ages of metamorphic soles of ophiolites that form the highest structural unit below sakarya these are underlain by high pressure low temperature metamorphic rocks of the tavsanli and afyon zones and the oren unit which in turn are underlain by the menderes massif derived from the atb underthrusting of the atb below sakarya was since 50 ma associated with high temperature metamorphism and widespread granitic magmatism thrusting in the menderes massif continued until 35 ma after which there is no record of accretion in western turkey plate circuits show that since 90 ma 1400 km of africa europe convergence occurred of which 700 km since 50 ma and 450 km since 35 ma seismic tomography shows that the african slab under western turkey is decoupled from the african plate this detached slab is a single coherent body representing the lithosphere consumed since 90 ma there was no subduction re initiation after slab break off atb collision with europe therefore did not immediately lead to slab break off but instead to delamination of subducting lithospheric mantle from accreting atb crust while staying attached to the african plate this led to asthenospheric inflow below the atb crust high temperature metamorphism and felsic magmatism slab break off in western turkey probably occurred 15 myr ago after which overriding plate compression and rotation accommodated ongoing africa europe convergence slab break off was accommodated along a vertical ne trending subduction transform edge propagator step fault zone accelerating southwestward slab retreat of the aegean slab the se aegean slab edge may have existed already since early miocene times or before but started to rapidly roll back along the southeastern aegean step in middle miocene times penetrating the aegean region in the pliocene

representing the global scale water masses in ocean general circulation models abstract a hierarchy of coarse resolution world ocean experiments were integrated with a view to determining the most appropriate representation of the global scale water masses in ocean general circulation models the largest scale response of the simulated ocean to the prescribed forcing in each model run is described the world ocean model eventually has a realistic approximation of continental outlines and bottom bathymetry the model forcing at the sea surface is derived from climatological fields of temperature salinity and wind stress the first experiment begins with a quite unrealistic and idealized world ocean subsequent experiments then employ more realistic surface boundary conditions model geometry and internal physical processes in all 16 changes to the model configuration are investigated a fundamental dynamical constraint in the drake passage gap appears to limit the outflow rate of bottom water in the antarctic region this constraint acts to decouple the extreme antarctic waters

time constraints for low angle shear zones in the central rhodopes bulgaria and their significance for the exhumation of high pressure rocks in the central rhodopes of southern bulgaria an eclogite bearing rock sheet belonging to the middle allochthon starcevo unit is over and underlain by eclogite free amphibolite facies rock units along low angle shear zones the borovica shear zone at the top and the starcevo ardino shear zone at the base the age of these shear zones is determined by u pb zircon dating of pre syn and posttectonic magmatic rocks mostly pegmatite veins using la sf icp ms zircons from pre to syntectonic pegmatites within the borovica shear zone yielded ages of ca 45 43 ma indicating that the shear zone was active at that time and zircons from a pretectonic pegmatite and a posttectonic granitoid body within the starcevo ardino shear zone yielded ages of ca 45 and ca 36 ma respectively giving a time frame for the activity of that shear zone which probably rather postdated the activity of the borovica shear zone by combining the ages with the kinematics of the shear zones and the metamorphic history of the rock units the following scenario is sketched soon after the starcevo unit reached peak pressure eclogite facies it was exhumed to a mid crustal level by top to the north west extensional unroofing along the borovica shear zone in a kinematic framework of orogen parallel extension beginning at ca 40 ma the partly exhumed starcevo unit was underthrust from the south west by continental crust of the foreland apulia forming the lower allochthon of the rhodopes along the starcevo ardino shear zone these results underline the significance of orogen parallel extension for the exhumation of high pressure rocks with respect to regional geology of the hellenides and the aegean it is found that the tectonic architecture of the rhodopes is essentially of tertiary age cretaceous syn metamorphic shear zones do exist but are largely restricted to higher levels of the nappe stack upper allochthon the rhodopes do not represent an older essentially mesozoic core of the hellenides but are formed by the internal higher metamorphic portions of the same major nappe systems as occur in the hellenides

cretaceous slab break off in the pyrenees iberian plate kinematics in paleomagnetic and mantle reference frames the pyrenees at the iberia europe collision zone contain sediments showing albian cenomanian high temperature metamorphism and coeval alkaline magmatic rocks stemming from different views on jurassic cretaceous iberian microplate kinematics two schools of thought exist on the trigger of this thermal pulse one invoking hyperextension of the iberian and eurasian margins the other suggesting slab break off competing scenarios for mesozoic iberian motion compatible with pyrenean geology comprise 1 transtensional eastward motion of iberia versus eurasia or 2 strike slip motion followed by orthogonal extension both favoring hyperextension related heating and 3 scissor style opening of the bay of biscay coupled with subduction in the pyrenean realm favoring the slab break off hypothesis we test these kinematic scenarios for iberia against a newly compiled paleomagnetic dataset and conclude that the scissor type scenario is the only one consistent with a well defined 35 counterclockwise rotation of iberia during the early aptian we proceed to show that when taking absolute plate motions into account aptian oceanic subduction in the pyrenees followed by late aptian early albian slab break off should leave a slab remnant in the present day mid mantle below nw africa mantle tomography shows the reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500 km depth below southern algeria mantle tomography is therefore consistent with the scissor type opening of the bay of biscay coupled with subduction in the pyrenean realm slab break off may thus explain high temperature metamorphism and alkaline magmatism during the albian cenomanian in the pyrenees whereas hyperextension that exhumed pyrenean mantle bodies occurred much earlier in the jurassic

cenozoic granitoids in the dinarides of southern serbia age of intrusion isotope geochemistry exhumation history and significance for the geodynamic evolution of the balkan peninsula two age groups were determined for the cenozoic granitoids in the dinarides of southern serbia by high precision single grain u pb dating of thermally annealed and chemically abraded zircons 1 oligocene ages kopaonik drenje eljin ranging from 31 7 to 30 6 ma 2 miocene ages golija and polumir at 20 58 20 17 and 18 06 17 74 ma respectively apatite fission track central ages modelling combined with zircon central ages and additionally local structural observations constrain the subsequent exhumation history of the magmatic rocks they indicate rapid cooling from above 300 c to ca 80 c between 16 and 10 ma for both age groups induced by extensional exhumation of the plutons located in the footwall of core complexes hence miocene magmatism and core complex formation not only affected the pannonian basin but also a part of the mountainous areas of the internal dinarides based on an extensive set of existing age data combined with our own analyses we propose a geodynamical model for the balkan peninsula the late eocene to oligocene magmatism which affects the adria derived lower plate units of the internal dinarides was caused by delamination of the adriatic mantle from the overlying crust associated with post collisional convergence that propagated outward into the external dinarides miocene magmatism on the other hand is associated with core complex formation along the southern margin of the pannonian basin probably associated with the w directed subduction of the european lithosphere beneath the carpathians and interfering with ongoing dinaridic hellenic back arc extension

rapid exhumation of high pressure metamorphic rocks in kythera peloponnese greece revealed by apatite u th he thermochronology abstractapatite u th he and apatite fission track cooling ages from high pressure hp metamorphic rocks in the south aegean forearc along the kythera strait kythera and southeastern peloponnese suggest rapid exhumation during middle to late miocene times hp rocks from the kythera strait exhibit two perpendicular extensional structures samples with arc normal or arc parallel extensional fabrics yielded apatite u th he cooling ages of 8 10 ma the more precise u th he ages are consistent with previously reported apatite and zircon fission track ages obtained from the same rock units the less precise but still accurate fission track data provided a reference for u th he dating on relatively young uranium poor apatites the combined data therefore precisely and accurately constrain the exhumation history of hp rocks and indicate that localized arc parallel extension in the kythera strait was active for an 5 m yr interval during the regional arc expansion

is the palea kavala bi te pb sb au district northeastern greece an intrusion related system abstract intrusion related gold systems are generally characterized by a au bi te sn w metal assemblage genetically linked to the emplacement of granitoids the palea kavala ore system greece consists of 150 minor fe mn pb zn ag fe mn au fe as au fe cu au and bi te au occurrences that occur primarily in quartz calcite sulfide veins hypogene mineralization or as supergene bodies in overlapping zones centered on the 21 22 ma granodioritic kavala pluton which intrudes metamorphic rocks of the paleozoic rhodope metamorphic core complex the pluton consists mostly of granodiorite with lesser amounts of diorite tonalite and monzodiorite which was emplaced along the regional e w trending kavala komotini fault the recently discovered 4 km long e w trending so called kavala vein is a sheeted quartz vein system of bi te pb sb au mineralization that crosscuts the kavala pluton and the schists and gneisses of the rhodope massif the kavala vein system is comprised of quartz with lesser amounts of k feldspar plagioclase and muscovite quartz sericite pyrite alteration is pervasive but minor kaolinite is also present pyrite 5 of vein volume contains inclusions of tetradymite some gold bearing bismuthinite and cosalite sulfur isotope values n 27 of pyrite from the kavala and chalkero veins as well as pyrite and galena from garizo hill fe mn pb vein range from 1 9 to 1 0 with one outlier of 4 6 and suggest a magmatic sulfur source homogenization temperatures th of type i two phase aqueous liquid vapor and type ii three phase h2o co2 rich fluid inclusions that homogenize into the liquid phase in quartz from the kavala and chalkero veins range from 216 0 to 420 0 c n 216 and 255 7 to 414 0 c n 112 respectively the th of type iii two phase aqueous liquid vapor which homogenize into the vapor phase ranges from 210 4 to 323 4 c n 28 the salinities of type i and type ii inclusions range from 15 9 to 22 6 wt nacl equiv and 5 5 to 11 2 wt nacl equiv respectively eutectic temperatures of 58 5 to 44 3 c for type i inclusions suggest the presence of appreciable cacl2 in addition to nacl clathrate melting temperatures for type ii inclusions of 56 7 c indicate that co2 is the major component of the gaseous phase however up to 6 ch4 is present in some inclusions the presence of a zoned metallogenetic district centered on bi te pb sb au mineralization within the kavala pluton the presence of both magnetite and ilmenite in the kavala pluton and the two high temperature high salinity immiscible carbonic and aqueous fluids associated with the kavala and chalkero veins are consistent with them being part of an intrusion related gold system that formed along the ilmenite magnetite buffer

numerical simulation of 3 d mantle flow evolution in subduction zone environments in relation to seismic anisotropy beneath the eastern mediterranean region abstract seismic anisotropy is a key parameter in understanding subduction zone dynamics in relation to the recent deformation history it is usually controlled by the mantle flow patterns resulting from the dynamic interactions between a relatively dense subducting oceanic plate and the surrounding mantle a proper modelling of mantle flow in subduction systems helps our understanding of the seismic anisotropy source strength and evolution in time this study further examines shear wave splitting parameters one of the most well established measuring methods of seismic anisotropy and their anisotropy source based on 3 d geodynamic modelling applied to the eastern mediterranean sea and anatolia our model setting is chosen to be a first order representation of the present day tectonic setting as it consists of a deforming anatolian micro plate that is indented by slow moving african and arabian plates and an oceanic plate in between the retreat of the slab in the aegean region the alleged tear in the subducting slab close to the cyprus trench and the break off in the slab in eastern anatolia are considered in our modelling study in order to further explore their influence on mantle flow and splitting parameters the synthetically calculated fast polarization directions fpds mostly showed a reasonable matching with those inferred from previous seismological observations that are mainly sks splitting measurements regions of fpd similarities between synthetic and observed shear waves mostly indicate n s to ne sw orientations of fast shear waves which are parallel to the extension in the back arc region and in general perpendicular to the trench the pattern of fpds seems to be more complex nearby the trench our modelling results suggest that the development of a tear in the african slab and the detachment occurring within the arabian plate break off appear to have a significant influence on the fpds due to stronger mantle flow through the slab windows the mantle flow through the tear close to cyprus and the break off in the east can be identified clearly despite their recent appearances a circular pattern around the edges of the slab can be observed as well as disruptions of the overall general fast polarization direction due to the flow through the tear

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

revision of the timing magnitude and distribution of neogene rotations in the western aegean region to evaluate the dimension and the timing of the clockwise rotating domain and the nature of the structures that accommodate the rotating domain in the western aegean region paleomagnetic analyses were carried out in northern western and southwestern greece the results show that the rotating domain covers an area including the external albanides western mainland greece including evia and probably at least partly the peloponnesos smaller clockwise rotations on the order of 30 408 were reported previously from the chalkidiki peninsula and the islands of skyros and limnos previously two phases of approximately 258 of rotation were suggested the last one during the plio pleistocene our analysis shows that the western aegean domain rotated approximately 408 clockwise between 15 13 and 8 ma followed by an additional 108 after 4 ma the rotating domain is accommodated in the north by deformation associated with the scutari pec fault zone and in the west by the ionian thrust and the hellenic subduction zone to the south no rocks older than 10 ma are available so no conclusive data are obtained to the east of the rotating domain extensional detachment systems of the cyclades and rhodope areas were active during the rotation phase and may explain at least part of the differences in finite amounts of rotation between nonrotation or counterclockwise rotations observed in northern and eastern greece and the large clockwise rotations in western greece d 2004 elsevier b v all rights reserved

the pindos fold and thrust belt greece inversion kinematics of a passive continental margin continuous exposure in the pindos mountain chain greece and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the pindos fold and thrust belt pftb and to approach quantitatively some parameters which controlled foreland evolution the 160 km wide passive continental margin of the apulian continent in greece was progressively shortened from east to west at rates of 6 mm year between the early oligocene and late eocene from the rear to the frontal part of the wedge fault bend folds duplexes and imbricates were formed while strain was partitioned into faulting 34 layer parallel shortening 23 and buckling 9 foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted apulian passive margin changes in the thickness of the pre orogenic sediments and reactivated transform faults induced salients during the lower miocene the orogenic wedge in the peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the palaeozoic rift zone of the phyllite quartzite series which was reactivated and returned to the earth s surface during the hellenic orogeny

neotethys closure history of anatolia insights from 40ar 39ar geochronology and p t estimation in high pressure metasedimentary rocks the multiple high pressure hp low temperature lt metamorphic units of western and central anatolia offer a great opportunity to investigate the subduction and continental accretion related evolution of the eastern limb of the long lived aegean subduction system recent reports of the hp lt index mineral fe mg carpholite in three metasedimentary units of the gondwana derived anatolide tauride continental block namely the afyon zone the oren unit and the southern menderes massif suggest a more complicated scenario than the single continental accretion model generally put forward in previous studies this study presents the first isotopic dates white mica 40ar 39ar geochronology and where possible are combined with p t estimates chlorite thermometry phengite barometry multi equilibrium thermobarometry on carpholite bearing rocks from these three hp lt metasedimentary units it is shown that in the afyon zone carpholite bearing assemblages were retrogressed through greenschist facies conditions at c 67 62 ma early retrograde stages in the oren unit are dated to 63 59 ma in the kurudere nebiler unit hp mesozoic cover of the southern menderes massif hp retrograde stages are dated to c 45 ma and post collisional cooling to c 26 ma these new results support that the oren unit represents the westernmost continuation of the afyon zone whereas the kurudere nebiler unit correlates with the cycladic blueschist unit of the aegean domain in western anatolia three successive hp lt metamorphic belts thus formed the northernmost tavsanli zone c 88 82 ma the oren afyon zone between 70 and 65 ma and the kurudere nebiler unit c 52 45 ma the southward younging trend of the hp lt metamorphism from the upper and internal to the deeper and more external structural units as in the aegean domain points to the persistence of subduction in western anatolia between 93 90 and c 35 ma after the accretion of the menderes tauride terrane in eocene times subduction stopped leading to continental collision and associated barrovian type metamorphism because by contrast the aegean subduction did remain active due to slab roll back and trench migration the eastern limb below southwestern anatolia of the hellenic slab was dramatically curved and consequently teared it therefore is suggested that the possibility for subduction to continue after the accretion of buoyant e g continental terranes probably depends much on palaeogeography

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

s velocity structure and radial anisotropy in the aegean region from surface wave dispersion summary the lithospheric structure of the aegean region is investigated by analysis of rayleigh wave fundamental mode dispersion measurements isotropic 1 d models for almost 100 two station ray paths across the region display distinct variations in the moho depth and crustal s wave velocities the descending slab of the subducting african plate can be resolved down to 120 km depth beneath the volcanic arc three different regions are distinguished in terms of moho depth 1 the forearc with large crustal thicknesses between 38 and 48 km and an average of 43 km 2 the northern aegean with an average moho depth of 28 km and 3 the southern aegean central volcanic arc i e cyclades and sea of crete with an even thinner crust of around 25 km lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc collocated with pronounced changes in trench and slab geometry as well as published deformation rates s velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the peleponnesus to crete an abrupt change occurs between western and central crete in terms of the visibility of the aegean moho and the seismic structure of the lithospheric mantle wedge an aegean mantle wedge with s velocities above 4 4 km s 1 is only observed to the east of central crete whereas to the west velocities of less than 4 0 km s 1 occur down to the plate contact these low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths a low velocity asthenospheric layer is observed beneath the sea of crete and the cyclades below 40 km depth between the thinned lithosphere above and the slab below the observed radial anisotropy in the northern part of the aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust possibly caused by lateral ductile flow associated with recent lithospheric extension

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

oligocene miocene basin evolution in se anatolia turkey constraints on the closure of the eastern tethys gateway the oligocene miocene was a time characterized by major climate changes as well as changing plate configurations the middle miocene climate transition 17 to 11 ma may even have been triggered by a plate tectonic event the closure of the eastern tethys gateway the marine connection between the mediterranean and indian ocean to address this idea we focus on the evolution of oligocene and miocene foreland basins in the southernmost part of turkey the most likely candidates to have formed this gateway in addition we take the geodynamic evol ution of the arabian eurasian collision into account the musand elazog u basins located to the north of the bitlis zagros suture zone were most likely connected during the oligocene the deepening of both basins is biostratigraphically dated by us to occur during the rupelian early oligocene deep marine conditions between 350 and 750 m prevailed until the chattian late oligocene when the basins shoaled rapidly to subtidal intertidal environment in tropical to subtropical conditions as indicated by the macro fossil assemblages we conclude that the emergence of this basin during the chattian severely restricted the marine connection between an eastern indian ocean and western mediterranean marine domain if a connection persisted it was likely located south of the bitlis zagros suture zone the kahramanmarasbasin located on the northern arabian promontory south of the bitlis zagros suture zone was a foreland basin during the middle and late miocene possibly linked to the hatay basin to the west and the lice basin to the east our data indicates that this fore land basin experienced shallow marine conditions during the langhian followed by a rapid dee pening during langhian serravallian and prevailing deep marine conditions between 350 and 750 m until the early tortonian we have dated the youngest sediments underneath a subduc tion related thrust at c 11 ma and suggest that this corresponds to the end of underthrusting in the kahramanmarasregion i e the end of subduction of arabia this age coincides in time with the onset of eastern anatolian volcanism uplift of the east anatolian accretionary complex and the onset of the north and east anatolian fault zones accommodating westward escape tec tonics of anatolia after c 11 ma the foreland basin south of the bitlis formed not or no longer a deep marine connection along the northern margin of arabia between the mediterranean sea and the indian ocean we finally conclude that a causal link between gateway closure and global climate change to a cooler mode recorded in the mi3b event d 18 o increase dated at 13 82 ma cannot be supported

thrust sequences in the central part of the external hellenides the model of a foreland propagating sequence already presented for the external hellenides is significantly modified in this paper new data are used including structural maps cross sections stratigraphic determinations and seismic profiles in general thrusts formed a foreland propagating sequence but they acted simultaneously for a long period of time thus during the middle eocene the pindos thrust resulted in the formation of the ionian gavrovo foreland and acted in tandem with the newly formed gavrovo thrust within the basin until the late oligocene the gavrovo thrust consists of segments showing that out of sequence thrusting was important thrust nucleation and propagation history is strongly influenced by normal faults formed in the forebulge region of the ionian gavrovo foreland basin shortening rates within the gavrovo ionian foreland are low about 1 mm year although thrust load played an important role in the formation of this basin the additional load of 3500 m thick clastics in the basin enhanced subsidence and underthrusting

north aegean core complexes the gravity spreading of a thrust wedge the north aegean core complexes developed in middle eocene soon after the end of continental block convergence and piling up of the hellenic thrust wedge they formed during back arc extension driven by the hellenic slab rollback at the back of the thrust wedge a series of scaled laboratory experiments was performed to test whether the gravity spreading of a thrust wedge is a suitable process for the development of the north aegean core complexes during back arc extension wedge shaped sand silicon models with variable boundary displacement velocities and different geometries of the upper sand layer were used to study the effects of variations in wedge rheology on the pattern of extension the models exemplify that extension either distributed wide rift mode or localized core complex mode is always located at the wedge rear core complex development was favored in models with thicker brittle layer higher frictional strength and low stretching rate lower ductile strength both core complex location at the wedge rear and detachment location and dip are interdependent and intrinsically related to the initial wedge shape of the extending system the experimental model displays striking similarities with the extensional pattern of the north aegean in terms of i location size and shape of core complexes as well as their sequence of development and ii detachment location and dip we conclude that it is the initial wedge geometry of the system and the weak nature of the crust at the onset of extension that controlled the extensional pattern of the north aegean domain

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

chemical versus mechanical denudation in meta clastic and carbonate bedrock catchments on crete greece and mechanisms for steep and high carbonate topography on crete as is common elsewhere in the mediterranean carbonate massifs form high mountain ranges whereas topography is lower in areas with meta clastic rocks this observation suggests that differences in denudational processes between carbonate rich rocks and quartzofeldspathic units impart a fundamental control on landscape evolution here we present new cosmogenic basin average denudation rate measurements from both 10be and 36cl in meta clastic and carbonate bedrock catchments respectively to assess relationships between denudation rates processes and topographic form we compare total denudation rates to dissolution rates calculated from 49 new and previously published water samples basin average denudation rates of meta clastic and carbonate catchments are similar with mean values of 0 10 mm a and 0 13 mm a respectively the contribution of dissolution to total denudation rate was 10 in the one measured meta clastic catchment and 40 for carbonate catchments 0 05 mm a suggesting the dominance of physical over chemical weathering at the catchment scale in both rock types water mass balance calculations for three carbonate catchments suggests 40 90 of surface runoff is lost to groundwater to explore the impact of dissolution and infiltration to groundwater on relief we develop a numerical model for carbonate denudation we find that dissolution modifies the river profile channel steepness and infiltration changes the fluvial response time to external forcing furthermore we show that infiltration of surface runoff to groundwater in karst regions is an efficient way to steepen topography and generate the dramatic relief in carbonates observed throughout crete and the mediterranean

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

the mediterranean ridge backstop and the hellenic nappes the core of the mediterranean ridge backstop consists of a pile of hellenic nappes that migrated outward from the aegean continent within the adjacent mediterranean basins during late middle miocene about 15 ma and the present mediterranean ridge has developed since that time by accretion of a new wedge the arguments we use are 1 a similarity in thickness seismic velocity and structure between the backstop and the hellenic nappes in southern peloponnesus 2 the geometry of the westward limit of the backstop that is the one expected from the amount of relative displacement of the nappes on land 3 an agreement between the estimated ages of the present accretionary wedge and the period of activity of two major faults connecting the backstop to the adjacent aegean continent the seaward limit of the backstop is situated about 170 km southwest of western crete where the displacement of the nappes is maximal and it is close to the margin near the ionian islands where their displacement is small we assume that the hellenic subduction zone migrated southwestward relative to eurasia during middle miocene and that the corresponding gravity collapse of the aegean continent was maximum at this time because the westward extrusion of anatolia had not yet started

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

what caused the denudation of the menderes massif review of crustal evolution lithosphere structure and dynamic topography in southwest turkey the deformation of earth s lithosphere in orogenic belts is largely forced externally by the sinking slab but can also be driven by internal delamination processes caused by mechanical instabiliti

fracture zones in the north atlantic from combined geosat and seasat data we present a new tectonic fabric map of the northern and central north atlantic ocean floor from 10 s to 66 n based on combined geosat and seasat altimetry data short wavelength vertical gravity along track was derived by hilbert transforming and high pass filtering geosat and seasat deflection of the vertical profiles the along track gravity data were used in conjunction with magnetic anomaly data to locate a large number of fracture zones as well as extinct spreading ridges and v shaped structures we traced many fracture zones more continuously and closer to adjacent continental margins than was previously possible we also mapped a number of unnamed fracture zones and fracture zone segments many of which were previously uncharted we have evaluated the agreement between the mapped fracture zones and synthetic flow lines as predicted from recent plate models for the opening of the north central north and south atlantic most fracture zones in this area correlate quite well with synthetic flow lines supporting the proposition that geosat seasat altimetry data serve as a useful tool to map fracture zones where insufficient bathymetric data are available many fracture zones including some small offset fracture zones in the central north atlantic have been stable and follow tectonic flow lines for tens of millions of years however many other fracture zones do not reflect a railroad track pattern of plate motions the geometry of many small and medium offset fracture zones indicates that the ridge axis discontinuities that produce them can migrate along the ridge causing off axis traces that deviate from tectonic flow lines velocity space diagrams constructed using a recent relative and absolute present day plate motion model indicate that some low angle v shaped troughs and ridges are likely formed by migration of the plate boundary relative to a mesospheric reference frame other low angle v shaped structures reflect slow migrations oscillations of small offset ridge axis discontinuities that are distinct from both tectonic flow lines and v shapes reflecting absolute plate motions high angle v shaped structures are the result of fast migrating ridge axis discontinuities propagating rifts