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

palinspastic reconstruction versus cross section balancing how complete is the central taurides fold thrust belt turkey in many fold thrust belts cross section derived shortening estimates are significantly lower than predicted based on plate convergence this has led to controversial hypotheses that shortening may be largely underestimated due to wholesale underthrusting convergence without shortening below far traveled continent or ocean derived nappes the late cretaceous eocene taurides fold thrust belt southern turkey may contain a highly incomplete shortening record of convergence likely caused by wholesale underthrusting to estimate this underthrusting we calculate convergence across the belt using a map view palinspastic reconstruction that takes into account major rotations of tectonic units during their accretion we use paleomagnetic and fault kinematic analysis timing of accretion and africa eurasia convergence to constrain our reconstruction our paleomagnetic results confirm an 40 clockwise vertical axis rotation of the geyikdagi nappe that forms the core of the belt which we interpret is accommodated by a lateral gradient in underthrusting on faults structurally above and below the geyikdagi nappe we reconstruct 400 450 km of convergence across the taurides during their accretion we compare this predicted convergence to shortening calculated from balanced cross sections in which we reconstruct a minimum of 154 km shortening 57 km within far traveled nappes 70 km thrusting of far traveled nappes over the geyikdagi nappe and 27 km shortening within the geyikdagi nappe shortening in the taurides created a significant nappe stack but the majority of convergence was accommodated by wholesale underthrusting with barely a trace at the surface including 160 km of convergence by rotation of the belt and 90 130 km related to missing africa eurasia convergence

kinematics of a former oceanic plate of the neotethys revealed by deformation in the ulukisla basin turkey kinematic reconstruction of modern ocean basins shows that since pangea breakup a vast area in the neotethyan realm was lost to subduction here we develop a first order methodology to reconstruct the kinematic history of the lost plates of the neotethys using records of subducted plates accreted to former overriding plates combined with the kinematic analysis of overriding plate extension and shortening in cretaceous paleogene times most of anatolia formed a separate tectonic plate here termed anadolu plate that floored part of the neotethyan oceanic realm separated from eurasia and africa by subduction zones we study the sedimentary and structural history of the ulukisla basin turkey overlying relics of this plate to reconstruct the tectonic history of the oceanic plate and its surrounding trenches relative to africa and eurasia our results show that upper cretaceous oligocene sediments were deposited on the newly dated suprasubduction zone ophiolites 92 ma which are underlain by melanges metamorphosed and nonmetamorphosed oceanic and continental rocks derived from the african plate the ulukisla basin underwent latest cretaceous paleocene n s and e w extension until 56 ma following a short period of tectonic quiescence eo oligocene n s contraction formed the folded structure of the bolkar mountains as well as subordinate contractional structures within the basin we conceptually explain the transition from extension to quiescence to shortening as slowdown of the anadolu plate relative to the northward advancing africa anadolu trench resulting from collision of continental rocks accreted to anadolu with eurasia until the gradual demise of the anadolu eurasia subduction zone

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

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

dating the exhumation of a metamorphic dome geological evidence for pre eocene unroofing of the nigde massif central anatolia turkey the timing of exhumation of metamorphic rocks and granitoids of the nigde metamorphic dome at the southern tip of the central anatolian crystalline complex is a matter of debate according to some authors the metamorphic rocks are overlain nonconformably by a sedimentary sequence of late maastrichtian to late palaeocene age in contrast other authors recently argued that the nigde dome represents an extensional core complex of oligocene early miocene age finally unroofed during late miocene times on the one hand the results of our study contradict the latter interpretation a sedimentary sequence of earliest eocene to early middle eocene age nonconformably overlies the high grade rocks of the nigde dome on its southeastern flank pebbles from the metamorphic rocks are ubiquitous in the conglomerates of this sequence as a result the nigde metamorphic rocks must have reached the surface before eocene times or at the very beginning of the eocene at the latest the uckapili granite whose crystallization age has been inferred to be early miocene has intruded the metamorphic complex during exhumation the granite is also found as pebbles within the conglomerates of the eocene sedimentary sequence and thus is actually older than the eocene apatite fission track dates of 12 11 ma across the nigde dome do not indicate that the metamorphic rocks were still on their way to the surface at that time instead they must reflect a later event which is most probably heating during late neogene magmatism lastly there is no ductile then brittle extensional detachment in the two areas where it has been invoked that is on the western and southern flanks of the dome an extensional detachment nevertheless exists at the top of the nigde dome best documented in its northern part where the detachment fault superposes a superficial unit made up of massive ophiolitic rocks onto the high grade metamorphic sequence field evidence indicates that this detachment developed before eocene times on the other hand our observations do not confirm the nonconformity of the sedimentary sequence dated as late maastrichtian late palaeocene onto the nigde high grade rocks field relations show either a tectonic contact between the two or the direct nonconformity of the eocene sediments onto the metamorphic rocks the lack of coarse clasts originating from the nigde high grade rocks within the maastrichtian palaeocene sequence further suggests that the metamorphic dome did not reach the surface before late palaeocene times these results compare well with available data from the northwestern part of the central anatolian crystalline complex suggesting that exhumation has been broadly synchronous on the scale of the massif as a result of an episode of high magnitude extension that affected the region in campanian to palaeocene times

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

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

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

first u pb shrimp zircon and 40ar 39ar ages of metarhyolites from the afyon bolkardag zone sw turkey implications for the rifting and closure of the neo tethys abstract the afyon bolkardag zone abz is one of the most important metamorphic zones in turkey this zone consists of metasedimentary and metavolcanic rocks which have undergone regional greenschist facies metamorphism the metavolcanic rocks are dominated by rhyolite dacite and trachyandesite in the ilgin konya area the low grade metavolcanics were originally rhyolitic lavas and tuffs we present new precise sensitive high resolution ion microprobe shrimp 206 pb 238 u age analyses of zircons and 40 ar 39 ar age data of phengite from metarhyolites that enable a more precise reconstruction of the abz shrimp analyses of euhedral or sub euhedral magmatic zircons from two metarhyolite samples yield weighted means 230 2 ma and 229 2 ma these ages are interpreted as formation age of rhyolitic volcanics implying they were formed in the late triassic time carnian we suggest that these upper triassic magmatic rocks were formed in an extensional tectonic setting on the northern active margin of gondwana which led to the development of the northern branch of the neo tethys 40 ar 39 ar dating of two phengite samples from metarhyolites gave plateau ages of between 63 7 0 1 ma and 62 6 0 1 ma these dates are interpreted as the metamorphic age of these volcanic rocks and as the age of metamorphism that affected the abz consequently these earliest tertiary ages also constrain the timing of the closure of the neo tethys

reassessing the age of karpathos ophiolite dodecanese greece consequences for aegean correlations and neotethys evolution while the neogene history of the eastern mediterranean region is now fairly well understood our knowledge of older regional palaeogeographies is less accurate especially the positions of blocks and nappes constituting the aegean islands prior to the cenozoic our study focuses on the ophiolite exposed on the island of karpathos dodecanese which is located in the aegean fore arc at a pivotal position between the western and eastern ophiolites of the mediterranean region and where conflicting late jurassic and late cretaceous ages have led to diverging tectonic and palaeogeographic interpretations to test these ages we targeted the radiolarian cherts that depositionally overlie the ophiolite and extracted diagnostic radiolarian assemblages of aptian 125 113 ma early middle albian 113 105 ma and turonian 93 9 89 8 ma ages these results suggest that previous late cretaceous k ar isotopic ages from 95 3 4 2 ma to 81 2 1 6 ma may have been reset by late cretaceous metamorphism or affected by argon loss overall the new early cretaceous ages show that the karpathos ophiolite should not be correlated with the pindos nappes of greece or the ophiolites of cyprus or syria but rather with the lycian nappes of turkey and their root located in the izmir ankara erzincan suture zone therefore the karpathos ophiolite represents a remnant of the northern neotethys not the pindos ocean or the proto eastern mediterranean basin

late cretaceous extensional denudation along a marble detachment fault zone in the kirsehir massif near kaman central turkey abstract in the central anatolian crystalline complex cacc 100 km scale metamorphic domains were exhumed in a context of north south plate convergence during late cretaceous to cenozoic times the timing kinematics and mechanisms of exhumation have been the focus of previous studies in the southern nigde massif in this study we investigate the unexplored northern area regarding the tectonic features preserved on the edges of the kirsehir massif based on detailed field mapping in the kaman area where high grade metasediments non metamorphic ophiolites and monzonitic plutons are locally exposed together close to the contact with the ophiolites west dipping foliated marble rich rocks display mylonites and discrete protomylonites with normal shear senses indicating a general top to the w nw direction both of these structures have been brittlely overprinted into cataclastic corridors parallel to the main foliation the mylonite series and superimposed brittle structures together define the kaman fault zone the study of the evolution of calcite deformation fabrics along an ew section supported by electron back scattered diffraction measurements ebsd on representative fabrics indicates that the kaman fault zone represents an extensional detachment in omerhacili in the vicinity of the baranadag quartz monzonite the metamorphic sequence shows static annealing of the calcite mylonitic fabrics this evidence suggests that intrusion took place at shallow depth 10 km into an already exhuming metamorphic sequence as a consequence for the kaman area buried metasediments have been rapidly exhumed between 84 and 74 ma 1 km ma where exhumation along a detachment zone displaying a top to the w nw shear motion took place in the mid to upper crust prior to magmatic intrusion in the late campanian as the intrusion cut through the detachment fault the main shearing deformation ceased brittle tectonics coupled with erosion likely took over during the final unroofing stages at a slower rate

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

the role of the early tertiary ulukisla basin southern turkey in suturing of the mesozoic tethys ocean the maastrichtian late eocene ulukisla basin is representative of the tectonic and sedimentary evolution of prominent early tertiary basins in central anatolia including the tuzgolu and arkisla basins the ulukisla basin overlies an ophiolitic melange of late cretaceous age between the bolkar carbonate platform to the south and the nigde kirsehir metamorphic massif to the north the basin stratigraphy records successive phases of transgression subsidence volcanism evaporite deposition deformation and uplift subsidence curves are consistent with an extensional or transtensional basin origin terminated by uplift the ulukisla basin includes a thick succession c 2 km of upper paleocene lower eocene basaltic to andesitic submarine pillow lavas lava flows volcaniclastic rocks and intercalated limestones whole rock xrf chemical analysis indicates a within plate origin with a marked subduction influence believed to be inherited rather than contemporaneous the ulukisla basin formed after late cretaceous ophiolite and melange emplacement and ended with late eocene emergence deformation and onset of oligo miocene non marine deposition we propose that late cretaceous ophiolite and melange emplacement reflect initial ocean basin closure this was followed by a long period c 30 ma of microcontinental adjustment including possible strike slip palaeorotation and suture tightening during which the early tertiary ulukisla basin developed possible driving forces were regional slab pull of a relict subduction zone or oblique diachronous convergence suture tightening was complete by late eocene time marked by collisional deformation and regional uplift

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

the last koy yukon interglaciation in the yukon comparisons with holocene and interstadial pollen records paleoclimatic reconstructions for the last interglacial lig isotope substage 5e have achieved new importance for testing climate model simulations and predicting the outcome of global warming lig deposits at ch ijee s bluff northern yukon display high fossil spruce pollen frequencies extralimital species and a lack of interglacial permafrost all evidence of a warmer than present climate at the site comparisons between the ch ijee s bluff lig pollen record and late glacial holocene pollen stratigraphy demonstrates a high degree of similarity that implies similar patterns and rates of species migration and regugia compared to mid and early wisconsinan pollen stratigraphy the climate of the wisconsinan interstades was not as warm as that of the lig or today s lig warmth was insufficient for the spread of pine into northern yukon alder so important in the northern forests now appears to have had a less important role during the lig perhaps indicating less widespread permafrost and paludification fossiliferous deposits beneath hungry creek till hughes et al 1981 are reassigned to the lig

alpine high p low t metamorphism of the afyon zone and implications for the metamorphic evolution of western anatolia turkey abstract carpholite chloritoid pyrophyllite association occurs widely in the triassic metaclastic rocks of the afyon zone in west central turkey fe mg carpholite is associated with rare aragonite pseudomorphs and glaucophane in marbles and metabasites respectively the afyon zone consists stratigraphically of a pan african basement and an overlying mesozoic cover sequence the pan african basement which shows barrovian type amphibolite facies metamorphism comprises garnet mica schists intruded by sodic amphibole bearing metagabbros and leucocratic metagranites it is unconformably overlain by a continuous metasedimentary sequence extending from triassic to early palaeocene this cover sequence begins with metaconglomerates which pass upwards into phyllites fe mg carpholite occurs within this metaclastic sequence as rosette like crystals in metapelites and fibres in quartz segregations the metaclastic rocks are succeeded by metamorphosed platform carbonates grading into latest mesozoic metamorphosed pelagic limestones which in turn progress up to a late mesozoic early tertiary olistostrome this sequence is tectonically overlain by the blueschists of the tavsanli zone fe mg carpholite bearing assemblages imply temperatures of about 350 c and minimum pressures of 6 9 kbar corresponding to burial depths of about 30 km for the mesozoic passive continental margin sediments and the underlying pan african supracrustal metasediments and metaintrusives the metamorphic rocks of the afyon zone are unconformably overlain by upper palaeocene lower eocene sedimentary rocks indicating a paleocene age for the regional hp lt metamorphism this implies continuous younging of hp lt metamorphism in the anatolides related to northward subduction of the anatolide tauride platform beneath the sakarya zone from north to south this involved the tavsanli zone campanian 80 5 ma the afyon zone palaeocene the menderes massif middle eocene and the lycian nappes late cretaceous eocene all of which were probably derived from the frontal part of the anatolide tauride platform

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

39ar 40ar ages from the yozgat batholith preliminary data on the timing of late cretaceous extension in the central anatolian crystalline complex turkey abstract isotopic dating of sheared and unsheared rocks can be important in understanding deformational processes in orogenic belts this study examines 40ar 39ar dating of granitoids and mylonitic rocks to constrain intrusive and deformational events within the northern part of the central anatolian crystalline complex cacc the kerkenez granitoid within this complex comprising primarily quartz monzonite and hornblende granite contains discrete ductile shear zones these zones are characterized by protomylonite and mylonite formations with metamorphism conditions that reach lower amphibolite facies mylonitic foliations and lineations and asymmetric kinematic indicators e g asymmetric porphyroclasts composite shear bands with top to the northwest shear senses considering the high closure temperatures 500 c for hornblende and 350 c for k feldspar both hornblende quartz monzonite and hornblende granite in the kerkenez granitoid may have cooled rapidly suggesting that hornblende quartz monz

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

a plate tectonics oddity caterpillar walk exhumation of subducted continental crust since plate tectonics began on earth grandiose subduction factories have continually shaped the continents accreting continental blocks and new crust at the convergent plate boundaries an enigmatic product of subduction factories is the high pressure to ultrahigh pressure hp uhp metamorphic crustal rocks regurgitated to earth s surface sometimes from depths as great as 200 km the aegean backarc domain comprises two continental blocks that underwent hp metamorphism during the subduction of the african plate here we use thermomechanical numerical simulations to show that subduction of small continental lithosphere blocks separated by oceanic domains induces variations in the slab buoyancy giving rise to episodic rollback exhumation cycles the single self consistent numerical model successfully reproduces the major structural patterns and pressure temperature time paths of hp rocks across the aegean we suggest that the caterpillar walk of exhuming hp rock units revealed by our simulations is a fundamental mechanism behind hp exhumation globally

late jurassic magmatism and stratigraphy in the eastern sakarya zone turkey evidence for the slab breakoff of paleotethyan oceanic lithosphere abstractmiddle late jurassic cimmerian events in turkey have been actively discussed in the past three decades but proposed tectonic models associated with magmatism metamorphism and stratigraphic features remain controversial to address this issue upper jurassic mafic lavas are investigated at three locations alucra gumushane and olur in the eastern sakarya zone northeastern turkey these lavas are submarine and form planar flows parallel with the bedding plane in the upper jurassic carbonate sequence near the base or just below in the clastic sedimentary rocks the basaltic lavas show calc alkaline features and possess nb ta values and nb u nb la and ce pb ratios that are greater than those of island arc basalts multielement patterns are almost hump shaped similar to ocean island basalts which experience pb depletion and weak negative nb ta zr hf and ti anomalies the low initial 87sr 86sr ratios 0 70372 0 70554 positive initial end values 2 7 to 4 4 and initial pb isotope rat

subslab mantle of african provenance infiltrating the aegean mantle wedge the presence of a tear in the subducting african slab has a strong effect on neogene magmatism in western turkey but its influence on volcanism in the quaternary aegean arc to the west is unknown in order to investigate to what extent arc volcanism can be affected by slab parallel mantle flow from a slab window we present new trace element and nd pb isotope data for nisyros and santorini volcanoes trace element modeling allows quantification of the infiltration of trace element enriched mantle of subslab provenance through the slab tear into the depleted aegean mantle wedge primitive nisyros magmas record melting of a mixed source that contains as much as 10 of the enriched subslab mantle component and a contribution of this component can be traced as far west as santorini 250 km away from the slab tear we conclude that trace element and nd pb isotope variations between nisyros and santorini do not require along arc variations in subducting sediment composition but reflect the heterogeneous nature of the aegean mantle wedge related to infiltration of subslab mantle through the slab tear our geochemical evidence is in excellent agreement with predictions made on the basis of mantle tomography and anisotropy that indicate toroidal mantle flow around the edge of the aegean slab this implies that suction related to slab rollback can lead to the infiltration of subslab mantle material and slab parallel mantle flow thus potentially strongly influencing arc volcanism processes that perhaps need greater assessment in other arc systems

45 m y of aegean crust and mantle flow driven by trench retreat the available seismic anisotropy data in the aegean shallow mantle and their relationship with crustal deformation are used for deciphering the lithosphere scale flow pattern driven by rollback of the hellenic subduction slab in the north and central aegean the directions of mantle seismic anisotropy trend parallel to stretching lineations in core complexes of the overlying crust suggesting that crust and mantle have undergone the same direction of flow at the scale of the entire aegean crustal extension is controlled by dextral rotation around a pole located at scutary pec albania that is related to the hellenic trench retreat the intensity of mantle anisotropy increases as a function of distance from the pole and of amount of rotation surface geology reveals that this rotating flow pattern resulted in strains accumulated since 45 ma a slab tear model is suggested to integrate the observed variations of geological events in time and space to subduction dynamics

first balanced cross section across the taurides fold thrust belt geological constraints on the subduction history of the antalya slab in southern anatolia eastern mediterranean subduction accommodated africa eurasia convergence since mesozoic time and produced multiple subducted slab fragments in the mantle below anatolia these included the north dipping cyprus and ene dipping antalya slabs which are currently separated by an upper mantle slab gap segmentation of these slabs and associated mantle flow may have contributed to 400 km of post to middle eocene plate convergence was accommodated between the taurides and its beydaglari platform foreland and instead must have been accommodated south of beydaglari the associated southward plate boundary jump separated the antalya slab from the african plate and the cyprus slab the isolated antalya slab was left in an intraplate setting and is probably still attached to beydaglari today we suggest the continental composition of the antalya slab may have prevented its detachment finally the gap between the antalya and cyprus slabs existed since at least eocene time their decoupling likely did not contribute to late neogene central anatolian plateau uplift

new sedimentological and structural data from the ecemis fault zone southern turkey implications for its timing and offset and the cenozoic tectonic escape of anatolia fig 1 map of the cukurba abg demirkazik area adapted from cetin 2000 fig 6 tcu is the

a long lived late cretaceous early eocene extensional province in anatolia structural evidence from the ivriz detachment southern central turkey abstract central anatolia exposes previously buried and metamorphosed continent derived rocks the kirsehir and afyon zones now covering an area of 300 400 km so far the exhumation history of these rocks has been poorly constrained we show for the first time that the major 120 km long top ne ivriz detachment controlled the exhumation of the hp lt metamorphic afyon zone in southern central anatolia we date its activity at between the latest cretaceous and early eocene times combined with previously documented isolated extensional detachments found in the kirsehir block our results suggest that a major province governed by extensional exhumation was active throughout central anatolia between 80 and 48 ma although similar in dimension to the aegean extensional province to the east the central anatolian extensional province is considerably older and was controlled by a different extension direction from this we infer that the african slab s that subducted below anatolia must have rolled back relative to the aegean slab since at least the latest cretaceous suggesting that these regions were underlain by a segmented slab whether or not these early segments already corresponded to the modern aegean antalya and cyprus slab segments remains open for debate but slab segmentation must have occurred much earlier than previously thought

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

structure and petrology of tauride ophiolites and mafic dike intrusions turkey implications for the neotethyan ocean cretaceous neotethyan ophiolites occur in four east west trending subparallel zones within the tauride tectonic belt in southern turkey the ophiolites of the inner intermediate and outer zones tectonically overlie the mesozoic platform carbonates of the tauride belt and are commonly underlain by a cenomanian ophiolitic melange these ophiolites consist mainly of tectonized mantle rocks mafic ultramafic cumulates and gabbros and commonly lack sheeted dike complexes and extrusive rocks of a complete ophiolite sequence metamorphic soles that are several hundred meters thick occur as thrust faulted slices beneath these ophiolites and show well developed metamorphic field gradients ophiolitic units and the metamorphic soles are intruded by mafic dike swarms that are truncated at the contact with the underlying melange unit dike rocks are made of subalkalic basalt to andesite typical of evolved island arc tholeiites they display large compositional variations with sio 2 content between 50 and 60 wt and mgo between 8 and 4 wt and contain higher ti augite phenocrysts and significantly less calcic plagioclase than their host cumulates the majority of the analyzed dike rocks show a slight depletion in light rare earth elements ree with low la smn ratios and are depleted in both high field strength hfs and heavy rees while enriched in large ion lithophile elements lile relative to normal mid ocean ridge basalt morb these characteristics suggest a mantle source that underwent previous melt extractions and subsequent metasomatism by lile and light ree enriched fluids geochemical modeling of trace elements shows that melting occurred at relatively low pressures under hydrous conditions and that it may have required the existence of an asthenospheric window in which the dike magmas developed through tapping and mixing of melts generated within a rising melting column starting slightly within the garnet stability field or in a transitional zone between the garnet and spinel stability fields at about 60 km depth this asthenospheric window was probably created during subduction of a neotethyan ridge system magmas ascending from the melt column within this window generated dikes that crosscut the metamorphic soles and were injected into the overlying mantle wedge and oceanic lithosphere the new 40 ar 39 ar hornblende dates of 92 90 ma and 90 91 ma from the metamorphic soles and dike swarms respectively show that evolution of these two geologic units was closely related in time and space and that they formed at the same intraoceanic subduction zone within the inner tauride seaway these data suggest that the tauride ophiolites within the three zones to the north originated from the same root zone situated north of the tauride carbonate platform and that they constitute remnants of a single ophiolitic nappe sheet derived from the inner tauride seaway within the neotethyan ocean

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

diachronous demise of the neotethys ocean as a driver for non cylindrical orogenesis in anatolia continent continent collision drives crustal deformation topographic rise and geodynamic change africa eurasia convergence accommodated in the eastern mediterranean involved subduction of the neotethyan oceanic lithosphere in anatolia subduction was followed by collision of continental crust of greater adria with eurasia to form the izmir ankara erzincan suture zone discerning the effects of this collision from pre collisional ophiolite obduction related orogeny of greater adria is notoriously difficult estimates on the timing of collision in central anatolia are based on a forearc to foreland basin transition along the eurasian margin and suggest a 60 ma age of initial collision here we assess whether this age is also representative for collision in eastern anatolia and across the cenozoic sivas basin that straddles the greater adria europe suture to this end we retro deform regional block rotations in the pontides the kirsehir block and the taurides building a first order regional block circuit around the sivas basin we show that up to 700 km of convergence must have been accommodated across the sivas basin after central anatolian kirsehir pontide collision at 60 ma an order of magnitude more than estimated crustal shortening and that wholesale lithospheric subduction must have occurred throughout much of the cenozoic paleocene collision would require that this subduction consumed continental lithosphere which is unlikely we consequently infer that oceanic subduction continued much longer in eastern anatolia perhaps well into the miocene we postulate that prolonged oceanic subduction and slab pull drew the eastern taurides north relative to the central taurides leading to shortening and oroclinal bending in central anatolia the diachronous demise of the neotethys ocean in anatolia as a function of its paleogeography is thus a likely driver for the strong non cylindricity of the cenozoic anatolian collisional orogen

recrystallization of high pressure marble sivrihisar turkey abstract in the sivrihisar massif turkey the southern margin of a blueschist facies terrane was affected by heating and deformation associated with later regional barrovian metamorphism creating a recrystallization front that can be observed in calcite microstructures calcite marble records a progression from high pressure h p textures in a northern domain to completely recrystallized greenschist to amphibolite facies textures in a southern domain with intermediate stages of partial recrystallization of the h p textures h p marble is characterized by rod shaped calcite aragonite pseudomorphs arranged in series with the long axis of each grain oblique to compositional layering obliquity varies from 50 to nearly parallel but high angles are most common in a narrow 200 m thick transition zone that contains partially retrogressed blueschist and eclogite the h p texture is partially overprinted by chains of small equant recrystallized grains that preserve the crystallographic orientation of the pre existing rod shaped calcite as revealed by electron backscatter diffraction analysis rod shaped crystals occur locally in a 100 m thick zone south of the transition zone all calcite grains are equant but have a crystallographic preferred orientation further south in the barrovian sequence recrystallized marble contains equant calcite that is randomly oriented the similarity in fabric elements foliation lineation of the two domains further shows the effect of barrovian related processes on the h p domain including the rotation of the calcite rods during shearing along foliation planes white mica 40 ar 39 ar ages for phengite in h p marble are 88 ma and for muscovite in barrovian marble are 59 ma indicating 30 ma time interval between initial exhumation and cooling of the h p rocks and final cooling of the rocks that were deformed and heated during the later metamorphic event

coeval extensional shearing and lateral underflow during late cretaceous core complex development in the nigde massif central anatolia turkey 1 the nigde massif at the southern tip of the central anatolian crystalline complex consists of two structural units foliations in the lower unit define a dome cored by migmatites the contact between the two units bears all the elements of a ductile to brittle extensional detachment hence the nigde massif represents an extensional metamorphic core complex top to ne ene shearing at higher levels of the lower unit relates to displacement along the detachment deeper levels of the lower unit display high temperature top to ssw ductile shearing the two shearing deformations show a difference in the mean trend of stretching lineations of up to 58 new 40ar 39ar ages combined with previously published data enable us to infer that the two shears were contemporaneous in our favored interpretation oblique shearing in the core of the dome reflects lateral underflow i e horizontal flowing of the lower crust in a direction highly oblique to the direction of extension as a result of the interaction between lateral underflow and downdip shearing along the overlying detachment distinct structural domains are expected to exist within the migmatitic part of the core complex with observed counterparts in the nigde dome lateral underflow may reflect inward flow on the scale of the core complex regional scale channel flow is an alternative that would better account for the record of non coaxial deformation in the core of the dome more generally we suspect that the development of lateral underflow in a metamorphic core complex more likely reflects regional channel flow rather than local inward flow

reconstructing the geometry of central anatolia during the late cretaceous large scale cenozoic rotations and deformation between the pontides and taurides the central anatolian crystalline complex cacc exposes metamorphic ophiolitic and igneous rocks that were formed and deformed during closure of the neotethyan ocean the cacc is located in central turkey between the pontides in the north and the taurides in the south separated by major fault zones composite plutons intruded the meta sedimentary and ophiolitic units between 95 and 75 ma and form linear magmatic belts 100 km long along the western and northern margins of the cacc exhumation of the metamorphic and igneous complex was finalized by the paleocene time in this study we paleomagnetically study fifteen plutons spanning the entire non deformed upper cretaceous granitoid belt to test whether the initial configuration of the cacc was modified by vertical axis rotations after its exhumation our results show three internally coherent domains with significantly different vertical axis rotations 1 in the north east the akda block ayb records 151

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

tectonic evolution and paleogeography of the kirsehir block and the central anatolian ophiolites turkey in central and western anatolia two continent derived massifs simultaneously underthrusted an oceanic lithosphere in the cretaceous and ended up with very contrasting metamorphic grades high pressure low temperature in the tavsanli zone and the low pressure high temperature in the kirsehir block to assess why we reconstruct the cretaceous paleogeography and plate configuration of central anatolia using structural metamorphic and geochronological constraints and africa europe plate reconstructions we review and provide new 40ar 39ar and u pb ages from central anatolian metamorphic and magmatic rocks and ophiolites and show new paleomagnetic data on the paleo ridge orientation in a central anatolian ophiolite intraoceanic subduction that formed within the neotethys around 100 90 ma along connected n s and e w striking segments was followed by overriding oceanic plate extension already during suprasubduction zone ocean spreading continental subduction started we show that the complex geology of central and southern turkey can at first order be explained by a foreland propagating thrusting of upper crustal nappes derived from a downgoing dominantly continental lithosphere the kirsehir block and tavsanli zone accreted around 85 ma the afyon zone around 65 ma and taurides accretion continued until after the middle eocene we find no argument for late cretaceous subduction initiation within a conceptual inner tauride ocean between the kirsehir block and the afyon zone as widely inferred we propose that the major contrast in metamorphic grade between the kirsehir block and the tavsanli zone primarily results from a major contrast in subduction obliquity and the associated burial rates higher temperature being reached upon higher subduction obliquity