oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

upwelling asthenosphere beneath western arabia and its regional implications two distinct phases of continental magmatism are evident in western arabia the first from about 30 to 20 ma produced tholeiitic to transitional lavas emplaced along nw trends the second from about 12 ma to recent produced transitional to strongly alkalic lavas emplaced along n s trends the older phase is attributed to passive mantle upwelling during extension of the red sea basin whereas the younger phase is attributed to active mantle upwelling but was facilitated by minor continental extension perpendicular to plate collision the younger magmatic phase is largely contemporaneous with a major period of crustal uplift to produce the west arabian swell after about 14 ma a variety of evidence suggests that the west arabian swell is thermally supported by hot upwelling asthenosphere in contrast to the distinct asymmetry of uplift and magmatism on opposing sides of the red sea basin these processes were symmetric across a n s line marking the central axis of the west arabian swell this axis coincides with two fundamental features the ha il rutbah arch in the north and the makkah madinah nafud mmn volcanic line in the south the symmetry of magmatism is demonstrated by petrochemical evidence that the mmn harrats were derived by greater degrees of partial melting at shallower depths than those harrats lying to the west and east of the mmn line the potential temperature of the asthenosphere is estimated to be about 1436 c beneath the mmn line and about 1354 c beneath the flanking more undersaturated harrats the source of upwelling is either a mantle plume centrally located beneath the west arabian swell or an elongated and extended lobe of hot asthenosphere emanating from the ethiopian mantle plume convective flow may have been channelled along a preexisting regional flexure in the continental lithosphere which concentrated hot asthenosphere beneath the central axis of the afroarabian dome this crest of mantle upwelling underlies the mmn line in the north and the danakil depression and ethiopian rift system in the south it also passes through the red sea basin at the midpoint of an unusual doubly propagating rift system where axial seafloor spreading began 4 5 m y ago the nw trend of the red sea basin was well established by crustal attenuation during the older magmatic phase the pliocene invasion of this basin by a n s zone of mantle upwelling has resulted in seafloor spreading parallel to the preexisting structure along a rift system that has continued to propagate away from its eccentric mantle source in two opposing directions

late cenozoic tectonics and volcanism in the northwestern corner of the arabian plate a consequence of the strike slip dead sea fault zone and the lateral escape of anatolia abstract the study area is the northwestern corner of the arabian plate near the triple junction of anatolian arabia and africa late cenozoic tectonics and volcanism have developed essentially east of the dead sea fault zone dsfz the strike slip boundary of the arabian and african plates including vents situated in front of the bitlis collisional belt isotopic and rare elements data indicate deep mantle sources for volcanism our mapping based on radar imagery and digital elevation models suggests that elongate volcanoes volcanic ridges and linear clusters of adjacent volcanic vents are rooted on tension fractures which are a kilometer or several kilometers in length and infers similar development in depth we have also observed non volcanic tension fractures we have been able to map the northern segment of the dsfz as a continuous but broken fault line the ghab pull apart basin connects with appended faults including the choukhour fault that ends northward in a tail crack feature and the aafrine fault that ends in a tail thrust the amik pull apart basin is bounded in the west by a small but distinct scarp shown by radar imagery our image analysis and field data suggest that the left lateral amanos fault has a reverse throw component in consequence the amanos range has to be regarded as an anticline and the karasu valley as a syncline in the southern part of the study area the regional stress field is mainly strike slip with n020 striking tension fractures east of the amanos fault it becomes transpressive with n120 to n140 striking tension fractures in the north near the triple junction albeit compressional faults and belt environment predominate it is influenced by e w lowering horizontal stress component triggered by the lateral escape of anatolia and remains of the strike slip type associated with n020 striking tension fractures more east of the dsfz in front of the bitlis belt isolated volcanoes e g karacadag elongated n160 show in the rigid arabian crust local weak lines that can be influenced at a distance by the lowering horizontal stress component

chronology of neogene and quaternary uplift and magmatism in the caucasus constraints from k ar dating of volcanism in armenia abstract the greater caucasus is one of earth s highest actively uplifting mountain ranges the adjoining caspian sea basin contains a substantial proportion of its hydrocarbon reserves like other parts of the former soviet union the neogene and quaternary chronology of these important regions has not previously been well defined it has thus been impossible to obtain reliable estimates for rates of processes such as uplift of the caucasus and sedimentation in the caspian sea previous studies have established the relative timings of events in the region using correlation schemes between volcanism glaciations and the stratigraphy of the caspian basin however a range of absolute chronologies has previously been proposed for these sediments and igneous rocks based mainly on different interpretations of their magnetostratigraphic records by k ar dating we determine the ages of volcanism at three localities in armenia as 1 1 0 8 and 0 8 ma using these data and other evidence we propose a revision to the chronology of this region in which a distinctive brief interval of normal magnetic polarity in the local sedimentary and volcanic magnetostratigraphic records is matched to the cobb mountain event in the global record rather than the olduvai event or an earlier subchron as had previously been thought we thus interpret a 1 5 ma timing for the start of volcanism in the lesser caucasus and also suggest a 1 2 ma timing for the late akchagyl transgression of the caspian sea a key event in the regional stratigraphy when this water body reached its greatest extent we tentatively correlate this transgression with the melting event following glaciation during stage 36 of the oxygen isotope timescale which was thus the first time during the pleistocene when eastern europe was covered by a lowland ice sheet time averaged since 1 ma the flanks of the eastern greater caucasus mountains are shown to have uplifted at 0 6 mm a 1 and the lesser caucasus at 0 3 mm a 1 we show that the rate and spatial scale of this uplift are too great to be the result of plate convergence and suggest instead that this uplift is caused by crustal thickening due to inward lower crustal flow to beneath these mountain ranges at the start of magmatism in both the greater and lesser caucasus the estimated crustal thickness was 45 km we thus suggest that this magmatism has been caused by heating of the mantle lithosphere due to earlier crustal thickening the temperature rise required to initiate magmatism being the same in both cases

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

new data on the late cenozoic basaltic volcanism in syria applied to its origin abstract new data on geology and 21 k ar dates of the late oligocene quaternary basalts in syria combined with analysis of the new and previous data are used to reconstruct the volcanic history and relations between it and tectonic events volcanism began at the end of oligocene 26 24 ma and was concentrated in the late oligocene early miocene along a n trending band which stretches from the jebel arab harrat ash shaam up to kurd dagh and southern turkey activity waned in the middle miocene 17 12 ma but was resumed in the same band in the tortonian and increased in the messinian and early pliocene 6 3 4 ma when volcanism spread to the shin plateau and its coastal extension after a brief hiatus 4 3 5 ma volcanism became still more intensive and spread from the n trending band to the east into the northern margin of the mesopotamian foredeep and to the west into the dead sea transform zone additional eruptions continued into the holocene volcanism lasted 25 million years in the jebel arab highland and 15 million years in the aleppo plateau the long duration of volcanism in the same parts of the moving arabian plate and absence of records of one way migration of the activity mean that the magmatic sources moved together with the plate i e they were situated within the lithosphere mantle coincidence of the tectonic and volcanic stages of the arabian plate development proves that volcanic activity depended on the geodynamic situation caused by the plate motion situated within the lithosphere magmatic sources within this transverse band were possibly caused by thermal and deforming influences of the asthenospheric lateral flow moved laterally from the ethiopia afar deep superplume

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

deformation around stepovers in strike slip fault zones abstract this stuck addresses the kinematics of stepovers in strike slip fault zones where left lateral faults step rightward or right lateral faults step leftward a stepover is regarded as containing an internal strike slip fault whose ends link to transform faults surrounded by uniformly distributed deformation the kinematics are governed by k the ratio of slip rates on the internal fault and transform faults and gq the angle between these taults the convergence direction across the deformation at angle to the internal fault is an azimuth along which vectors do not rotate around vertical axes the lebanon stopover on the dead sea fault zone and the big bend stepover on the san andreas fault zone provide case studies in lebanon the time averaged deformation since 15 ma involves k 0 06 32 and 34 it accounts for 30 of anticlockwise rotation of cretaceous magnetization vectors in the lebanon mountains and 50 rotation of jurassic vectors the present phase of deformation around the big bend which began at 5 7 ma and imolves k 0 89 20 and 98 has instead only caused small rotations both clockwise and anticlockwise much of this region s structure including the dramatic up to 80 clockwise rotation of magnetization vectors in the transverse ranges is shown to relate instead to an earlier deformation phase with much lower k

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

lower crustal flow in an extensional setting constraints from the halloran hills region eastern mojave desert california postextensional uplift and tilting of quaternary lake sediments in the halloran hills eastern mojave desert california suggest that regional scale flow within the lower crust is occurring in response to tectonic loads created during upper crustal extension in late miocene time the concept that significant flow within the lower crust may occur for millions of years after the cessation of extension indicates that topographic gradients can be modified by regional scale flow within the lower crust and that direct constraints on lower crustal flow can be obtained by quantitative analysis of rates of postextensional surface tilting an analytic solution developed in this paper combines viscous flow in the lower crust flexural bending within the midcrust and isostasy into an invertible linear differential equation that describes the topographic response to upper crustal extension assuming that there was no topographic relief across the halloran hills region prior to extension inversion of modern topographic data indicates that crustal thinning above the halloran hills detachment increases westward with a listric geometry and that little crustal thinning has occurred east of the western flank of clark mountain in good agreement with the known geometry of the fault and the location of its breakaway zone incorporation of quaternary tilting data indicates that the modern viscosity beneath the halloran hills assuming a 10 km lower crustal channel is a maximum of 1019 pa s and that the viscosity of the lower crust has decreased by at least 1 to 2 orders of magnitude since 8 ma this corresponds to a temperature increase of at least 75 to 100 c at the moho in our opinion the most likely source of this temperature increase is a regional scale thermal event within the underlying mantle and diffusion of heat upward into the lower crust if correct these results have important implications for the way in which crustal extension is linked to mantle heating within the basin and range province

the multistage tectonic evolution of the gulf of suez and northern red sea continental rift from field observations field surveys in the gulf of suez northern red sea area revealed the structural pattern and evolution of this tertiary continental rift and provided constraints on the continental rifting process the structure has been controlled at every scale by four major trends of faults n0 20 e n100 120 e n140 e 160 e and n40 60 e observations of sealed faults and folds and superposed structures and the detailed analysis of the fault surfaces are coherent and indicate that as least two different stages of deformation characterize the evolution of the rift the initiation of the rift late oligocene aquitanian corresponds to the creation of large rhomboidal basins weakly subsident and partly bounded by oblique strike slip faults this framework which resulted from the reactivation of inherited weakness zone in the basement controlled the subsequent creation of large tilted blocks upper aquitanian lower burdigalian these structures were trangressed by the upper burdigalian deposits then the blocks were sliced by a secondary horst and graben pattern which was progressively sealed by middle miocene units since the upper miocene the deformation has been focused along some major faults located in the central part of the rift the determination of paleostresses from measurements of striae confirms that the initiation of the rift was controlled by a tectonic regime characterized by an horizontal compressive stress parallel to the rift and its subsequent evolution was controlled by triaxial and radial extensional regimes with horizontal minimum stress 3 predominantly trending n70 80 e the rifting process was not induced by regional doming but by a new distribution of intraplate stresses at approximately oligocene miocene time passive rift uplift of the rift shoulders began in the upper burdigalian cross sections of the rift emphasize its asymmetry large basement blocks are tilted toward the edge of the rift where a major recently active fault and a distinct morphological unit which we call a banquette are located several homogeneous tilt direction provinces can be defined they are separated by transverse hinge zones that correspond to inherited basement trends rifting deformation is expressed in the basement by steep faults arranged in a zig zag pattern and in neogene quaternary sediments by steep faults and listric faults associated with decollements therefore the style of shallow deformation cannot be extrapolated to deeper levels structures formed during the beginning of the rift show different charateristics according to their orientation but their initial shape was generally complicated by later deformation

present day kinematics of the middle east and eastern mediterranean the middle east and eastern mediterranean regions contain three major strike slip fault zones the dead sea fault zone dsfz and the north and east anatolian fault zones nafz and eafz these accommodate northward motion of the african and arabian plates relative to eurasia and westward motion of the small turkish plate this study deduces an internally consistent solution for the present day kinematics of these plates which is accurate to better than 20 and applicable throughout time since 5 ma by constraining the slip senses and rates on these strike slip fault zones the 7 0 5 mm yr 1 left lateral slip rate on the dsfz is associated with counterclockwise rotation of arabia relative to africa at 0 33 m y 1 around an eulcr pole near 33 n 23 e the nafz takes up counterclockwise rotation of the turkish plate relative to eurasia at 0 83 m y 1 13 around a pole at 31 n 35 5 e with right lateral slip rate 15 mm yr 1 the resulting prediction for the eafz involves 14 mm yr 1 left lateral motion and 2 mm yr 1 of shortening between arabia and turkey the triple junction of africa arabia and turkey is near the city of kahramanmaras this locality contains a narrow promontory bounded by ssw trending left lateral faults at the edges of the arabian and turkish plates which is loosely attached to the african plate moving westward relative to its interior at 4 mm yr 1

dependence of active normal fault dips on lower crustal flow regimes two key questions are raised by the presence in the basin and range province of subhorizontal normal faults which were active in and around the miocene first how did they develop when their existence seems to be precluded by elementary rock mechanics arguments second if they did slip in the recent geological past why do normal faults now active in the brittle upper crust have steeper dips both in the western usa and elsewhere one may now answer both questions by considering the stress field in regions where the isostatic response during extension involves horizontal flow in the plastic lower crust this stress tensor will have inclined principal axes making it possible for normal faults to form with either very steep or subhorizontal dips depending on the sense of flow this can be controlled by environmental conditions which influence rates of hanging wall sedimentation and footwall erosion and thus determine lateral variations in lithostatic pressure in the lower crust regional scale lateral variations in the geothermal gradient caused by subduction can also influence lower crustal flow regimes in adjacent zones of continental extension enabling extension to occur on low angle normal faults dipping away from the active continental margin

a late weichselian stable isotope stratigraphy compared with biostratigraphical data a case study from southern sweden late weichselian lake sediments from a site in southern sweden were analysed for stable carbon and oxygen isotopes as well as plant macrofossils and insect remains by comparison of independent d

subduction related shoshonitic and ultrapotassic magmatism a study of siluro ordovician syenites from the scottish caledonides syenites are important or predominant components of several plutonic complexes emplaced between 456 and 415 ma along the nw margin of the caledonian orogenic belt adjacent to the lewisian foreland in w and nw scotland although there are in detail chemical differences between the syenites from each centre they form a well defined compositional group overall ratios amongst their trace elements especially very high values of la nb are quite different from those trachytes and syenites formed by fractional crystallisation of ocean island basalts and their continental equivalents emplaced in regions of anorogenic crustal tension instead the scottish caledonian syenites closely resemble chemically the fractional crystallisation residua of potassic subduction related magmas such as the shoshonitic series a comendite minor intrusion from a swarm associated with the loch borralan and loch ailsh syenitic complexes is remarkably similar in composition to recent obsidian from the shoshonitic volcano of lipari in the aeolian arc published sr and pb isotopic ratios preclude a significant component of either upper proterozoic moine schists or lower crust granulite facies archaean lewisian or proterozoic grenvillian gneisses in all these syenites except in local syenitic facies of the glenelg ratagain complex fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas the phases involved in this process may have included plagioclase alkali feldspar pyroxene amphibole biotite garnet fe ti oxide sphene allanite apatite zircon and zirconolite and therefore all the ratios amongst even the so called incompatible elements may have changed during the evolution of the leucocratic magmas nevertheless a detailed study of the glen dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas these appear to be picritic shoshonite mgo 15 ni 400ppm la yb 20 la nb 5 for the glen dessarry loch borralan and loch ailsh syenites and picritic ultrapotassic magmas mgo 15 ni 400 ppm la yb 60 la nb 7 such as would crystallise to minettes for the loch loyal and glenelg ratagain syenites mafic shoshonites were erupted amongst the 410 ma lome lavas of this region and also occur as widespread approximately contemporaneous volcanic feeder plugs minettes of similar age are also common as dykes in nw scotland numerous large tonalite granite complexes with minor diorites and gabbros were emplaced in w and nw scotland between 435 and 400 ma these are generally acknowledged to be mixtures of magmas from crustal and mantle sources their more mafic members show compositional features such as very high ba and sr which group them with the rare syenites and the lorne lavas of the same region into a distinctive geochemical province within which shoshonitic and allied magmas were the mantle derived component two models are presented to account for the generation of strongly potassic subduction related magmas several hundred km behind a nw directed subduction zone or during the period immediately following continental collision

the structural relationship between the east anatolian and dead sea fault zones in southeastern turkey abstract the complex structural relationship between the east anatolian and dead sea fault zones is examined mostly based on field observations in southeastern turkey where the two fault zones are close together several faults previously poorly documented can be traced to connect either to the east anatolian fault zone or to the dead sea fault zone one of these faults connects the dead sea fault zone to the east to the amanos fault to the west the amanos fault a n trending normal fault is a part of the east anatolian fault zone since it is apparently a left step fault between the main and southern strands of the east anatolian fault zone the dead sea fault zone also is connected to the east anatolian fault zone northeast of the town of narli and or northeast of the hazar lake therefore we suggest that the two fault zones can be considered as one broad fault system in southeastern turkey although they are well recognized as two different fault zones this fault system is responsible for several complex neogene structural features of the western part of the southeastern turkey one of these is the hatay graben which can be divided into southern central and northern parts the graben contains down to the west normal faults in its southern part the central part of the graben is a divergent strike slip basin and the northern part is a half graben

new evidence and model on the evolution of the southeast anatolian orogen this paper describes the orogenic evolution of the southeast anatolian orogenic belt based mostly on new geologic data collected from its constituent tectonic units in the course of new mapping programs of the past decade the southeast anatolian orogenic segment of the alpides may be divided into three approximately east west trending zones from south to north they are the arabian platform followed by a zone of imbrication and then a zone of nappes the arabian platform includes a mostly marine sedimentary succession deposited from early cambrian to middle miocene time the zone of imbrication is a narrow belt sandwiched between the arabian platform and the zone of nappes it consists of imbricated thrust slices emplaced onto a late cretaceous to early miocene sequence the zone of nappes is the highest tectonic unit consisting of two stacks of nappes simply designated the lower and upper nappes the lower nappe is represented by the slices of a polyphase metamorpbic ophiolitic assemblage and the maden group the upper nappe rests on the lower nappe and is represented by the bitlis and poturge metamorphic massifs southeastern anatolia underwent two major episodes of alpide deformation the first occurred during the late cretaceous period when ophiolite was emplaced on the arabian platform this event was not the consequence of a continental collision the ophiolite obduction onto the arabian platform was followed by a regionwide extension and a new marine transgression over the platform immediately after the ophiolite obduction the second episode of deformation occurred during middle eocene miocene time in two distinct stages as a result of the progressive elimination and complete closure of the ocean s which led to the collision between the zone of nappes located to the north being a part of eurasia and the arabian plate the maden marginal basin formed north of the subduction zone that eliminated the ocean between eurasia and arabia along the southern margin of the taurus belt and abutted the arabian plate much later during the final collision the second episode of deformation formed the present orogenic segment leading to the amalgamation of different tectonic units these amalgamated nappes collided with the arabian plate and welded onto it at the latest stage of the orogenic evolution during the miocene epoch

observations on the complexity of the east anatolian fault turkey abstract that the east anatolian fault is made up of discrete segments of different strike and diverse structural style is well illustrated by oblique hand held photographs taken from the space shuttle linear and curvilinear faults plus major folds show the variable deformability of the collage of material that constitutes the anatolian plate now undergoing the early stages of collision tectonics

the golbaoi basin southeastern turkey a complex discontinuity in a major strike slip fault zone we show that the 33 km long golbaoi basin on the east anatolian fault zone marks the triple junction between the african arabian and turkish plates the main strand of the turkish arabian plate boundary the goksu fault enters this basin from the ene before splaying to form faults which develop farther southwest into the turkish african and african arabian boundaries the golba i turko u fault the turkish african boundary is shown to have slipped 16 km the prevously unrecognised kirkpmar fault the african arabian boundary has slipped 17 km we propose that this fault geometry developed at c 3 ma following earlier slip starting at c 5 ma on other strike slip faults nearby which marked the start of westward motion of the turkish plate

late palaeogene neogene evolution of the triple junction region near maras south central turkey the marao region of turkey includes the anatolian arabian african triple junction the african arabian margin is marked by left lateral transtension along the dead sea kara su rift motion on the anatolian arabian boundary is partitioned between the left lateral east anatolian fault and a fold thrust belt termed the engizek zone equivalent to the bitlis suture further east the african anatolian boundary lies along the cyprus misis andirin trend and is expressed near the triple junction as the aslantao iskenderun zone now undergoing slow left lateral transtension the neogene evolution of these boundaries is largely recorded in the stratigraphy and structure of the basins that lie along the anatolian arabian lice basin and anatolian african aslantao iskenderun basin boundaries these basins appear to have developed in the early miocene along major strike slip zones large half graben in the pre neogene 9basement9 of the western misis andirin block developed contemporaneously with motion on the anatolian african boundary these extensional features evolved subsequent to the intense shattering of the mesozoic carbonate sequence in the misis andirin block and its mixing with panels of deep water palaeogene strata to form an extensionally disrupted assemblage transpression and conversion of both anatolian african and anatolian arabian boundaries to fold thrust belts occurred in the late miocene transpression continues along the anatolian arabian boundary but transtension has recurred along the anatolian african boundary since the pliocene

a review of the tectonics of the northern middle east region the structure of the northern part of the arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region the palmyra and sinjar zones share a common history of development involving two stages of rifting one in the triassic jurassic and the other during late cretaceous to early tertiary times deformation of the palmyra zone during the mio pliocene is attributed to north south compression on the eastern block of the dead sea transcurrent system which occurred after continental collision in the north in southeast turkey the asymmetry of the palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow triassic evaporites an important nw se cross plate shear zone has been identified which can be traced for 600 km and which controls the course of the river euphrates over long distances in syria and iraq transcurrent motion along this zone resulted in the formation of narrow grabens during the late cretaceous which were compressed during the mio pliocene to a large extent present day structures in the region result from compressional reactivation of old lineaments within the arabian plate by the transcurrent motion of the dead sea fault zone and subsequent continental collision

oligocene deposits of the zara hafik region sivas central turkey evolution from storm influenced shelf to evaporitic basin new stratigraphical and micropalaeontological data supplemented by detailed sedimentological and petrographical observations have been obtained from an almost completely exposed oligocene miocene succession near celalli in the zara hafik basin which forms part of a long lived zone of subsidence associated with the north anatolian fault system four laterally extensive lithostratigraphical units have been distinguished and ostracod microfaunas indicate that the lower two units are of middle oligocene age while bivalve brachiopod faunas from the third unit are also oligocene the status of the uppermost unit of redbeds remains equivocal but microfaunas from the capping marls are of lowermost miocene age

ophiolitic and metamorphic assemblages of southeast anatolia and their significance in the geological evolution of the orogenic belt the southeast anatolian orogen may be divided into three roughly east west trending structural zones formed as a result of continental collision between the taurus platform and the arabian continent along the orogenic belt metamorphic and ophiolitic rocks occur widely the ophiolites represent remnants of the ocean or oceans which were totally consumed between these converging continental blocks during late cretaceous to miocene period metamorphic rocks formed from the oceanic as well as the continental rocks which were incorporated into a nappe stack during the consumption of the oceanic lithosphere and the progressive southward advance of the nappes toward the arabian continent the metamorphic units together with the ophiolite associations provide stratigraphic and petrologic evidence indicating time place and environment of formation of these units the metamorphic units also provide evidence of nappe transportation stages which are complementary to the data derived from the sedimentary successions in the evaluation of the orogenic evolution of southeast anatolian orogen

recent volcanism tectonics and plate kinematics near the junction of the african arabian and anatolian plates in the eastern mediterranean abstract in the eastern mediterranean plate convergence occurs between africa arabia and anatolia the africa arabia motion is a strike slip displacement along the dead sea fault the africa anatolia motion is taken up by subduction south of cyprus the convergence between arabia and anatolia is taken up along the east anatolian fault the analysis of the regional fault surfaces reveals the presence of two major tectonic phases that affected southeastern turkey near the junction of these three plates the older deformations are related to a n s compression the more recent movements are directed mainly westward and associated with strike slip and extension tectonics near the triple junction since 2 ma a fissure volcanism produced tholeiite followed by alkali basalt along the amanos fault the northern end segment of the dead sea fault in addition reconstruction of rigid plate kinematics between arabia africa and anatolia using recent plate motion parameters and space geodesy data suggest for the east anatolian fault a slip rate of 7 8 9 mm year the maximum finite displacement recognised for this structure being around 15 km we have obtained 1 9 ma as the maximum age for the fault formation the volcanic tectonic and kinematic data converge to propose a ca 2 ma age for the change of local tectonic regime in the junction area the structural mapping the geometry of the fractures used by the magma to reach the surface and the presence of alkali basalt of mantle source suggest that the deformation along the northern end of the dead sea transform i e the amanos fault was modified by the formation of the east anatolian fault zone in this region apparition of the east anatolian fault accommodating westward motion of the anatolian plate resulted in oblique slip tension along the amanos segment of the dead sea transform giving rise to a fissure fed mantle derived alkaline volcanism at ca 2 ma which lasted until recent times 0 4 ma

sedimentology of a late cenozoic collisional sequence the misis complex adana southern turkey abstract this study is concerned with miocene sequences formed within part of the cukurova basin of southern turkey a major downwarp created during the early stages of collision between the afro arabian plate and the tauride anatolian microplate assemblage we report here the results of a combined stratigraphical sedimentological structure and geochemical study of the misis complex a structurally elevated segment of cukurova basin fill this analysis has demonstrated the structurally imbricated nature of the misis sequences and the tectonic juxtaposition of originally well separated coeval facies the initial discernible phase of basin filling pre burdigalian was marked by deep marine conditions and marginal tectonic instability probably related to a late phase of tauride nappe advance the subsequent phase of crustal extension burdigalian early tortonian produced expansion of the cukurova basin limits and an upwards shoaling succession in which sediment transport towards the southwest gradually became dominant as a result of earlier suturing and uplift in northeasterly sectors of the collision zone the miocene arenites of the misis complex are petrographically diverse with common siliciclastic and carbonate detrital admixtures and mineralogically immature and their position in petrotectonic fields indicates a compound provenance from both recycled orogen and magmatic arc sources a noteworthy petrographic feature is the compositional similarity of arenites from both shallow and deep marine facies the general succession of neogene facies observed in the cukurova basin and misis complex is consistent with their evolution within a perisutural foreland basin but this interpretation is complicated by petrographic and geochemical features attributed to remnants of an older magmatic arc later stages of basin filling are also marked by the local occurrence of anomalous palaeoenvironmental associations including olistostromic units attributed to contemporaneous intra basinal tectonism

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

moho imbrication in the middle urals new processing of part of the europrobe s seismic reflection profiling in the urals esru reflection seismic data in the middle urals shows a southwest dipping moho imbrication and crustal underthrusting that was not previously imaged the area of thickening associated with it roughly coincides with a deepening of the moho imaged by the granit refraction data this feature does not fit with the currently known palaeozoic crustal architecture of the uralides or with its geodynamic history geological data suggest that it is not related to a relict southwest dipping subduction zone based on its lower crustal and moho reflection seismic character it is presently interpreted to be a post uralide feature possibly related to mesozoic intraplate shortening in the area its coincidence with a locus of mild earthquake activity further suggests that it might be active today

stratigraphic and structural development of the eastern pontides turkey this paper describes the stratigraphic and structural development of the eastern pontides north turkey based on section logging at eight localities construction of three structural profiles across the mountains and published literature the eastern pontides comprise a late carboniferous to miocene sequence resting on a basement of hercynian metamorphics late carboniferous to scythian sediments are continental clastics interpreted as having been deposited in an extensional half graben the middle triassic is limestone reflecting the development of a south facing passive margin in the late triassic the ocean palaeotethys began to close flysch was deposited in most places with minor shallow water limestones in the sinemurian above an inverted half graben all pre aalenian strata were deformed during the cimmerian orogeny after a phase of subduction related volcanism in the mid jurassic limestones were deposited during the late jurassic and early cretaceous mainly in shallow water the aptian and albian are absent due to doming in the western pontides prior to the opening of the western black sea but there is a thick sequence of upper cretaceous arc volcanic rocks and intervening turbidites the upper palaeocene is absent possibly due to rifting in the eastern black sea major compression affected the pontides from the eocene to the pliocene associated with the closure of the tethyan ocean oligocene and younger rocks are accordingly non marine

structure and deformation history of the bitlis suture near lake hazar southeastern turkey detailed mapping of the bitlis suture zone near lake hazar shows that it is composed of three tectonostratigraphic units which crop out as distinct north dipping thrust slices from south to north these are the puturge metamorphic complex the maden melange and the elazig igneous complex the puturge metamorphic complex consists of pre tertiary continental margin sediments metamorphosed to the greenschist facies during the campanian maastrichtian and deformed by four generations of structures these are in sequence 1 isoclinal folds and a transposition foliation 2 open folds crenulation cleavage and north dipping thrust faults 3 kink bands and 4 small displacement faults the maden melange represents middle eocene back arc basin sediments and volcanics metamorphosed to the greenschist facies and deformed by three generations of structures 1 a north dipping cleavage 2 kink bands and 3 small displacement faults the elazig igneous complex comprises an imbricated maastrichtian early eocene island arc and young marginal basin terrain thrust faults between units are north dipping listric and form a thin skinned system these features suggest the following deformational and tectonic history the puturge metamorphic complex was generated by isoclinal folding and metamorphism of sediments composing the arabian continental margin during campanian maastrichtian ophiolite obduction to the south the elazig arc developed on the deformed margin because of subsequent southward subduction of oceanic lithosphere the arc migrated to the north opening a back arc basin by the early eocene the back arc basin was filling with volcaniclastics of the maden melange and the elazig arc collided with a continent to the north during middle to late eocene convergence caused thrust stacking of the elazig maden and puturge complexes second generation deformation in the puturge complex and first generation deformation in the maden melange continued convergence with the arabian plate in the late miocene caused kink banding in the puturge and maden complexes since the late miocene this convergence has been accommodated by shortening and thickening along numerous internal faults

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

source parameters of large earthquakes in the east anatolian fault zone turkey summary the east anatolian fault zone accommodates most of the motion between the arabian plate and the apparently little deforming interior of central turkey the direction of overall slip across this zone is crucial to the determination of the slip rate on the north anatolian fault we use long period p and sn waveforms to determine the source parameters of the four largest earthquakes that occurred in or near the east anatolian fault zone in the last 35 years only one of these actually involved left lateral strike slip motion on a ne sw fault but the other three and the nearby 1975 lice earthquake all had steeply dipping nodal planes with a nnw strike if these were the auxiliary planes then all the earthquakes had a slip vector direction within about 10 of 063 if this direction represents the arabia turkey motion then the slip rate on the north anatolian fault must be in the range 31 to 48 mm yr with a probable value of 38 mm yr and the overall slip rate across the east anatolian fault zone must be about 29mmyr with a range of 25

upper cretaceous plate rupture and development of leaky transcurrent fault ophiolites in southeast turkey abstract field observations in the thrust fault belt in southeastern turkey reveal two contradictory relationships regarding the existence of the turkish microplate and the southern tethys jurassic and early cretaceous sediments on the platforms of the turkish and arabian plates can be correlated this weakens the hypothesis that the turkish plate was separated from africa in the triassic on the other hand stratigraphic relationships on slivers of continental crust between ophiolite strips do not allow the ophiolites north and south of such continental blocks to be linked this necessitates postulating the previous existence of distinct oceanic basins between the continental slivers the ophiolites in southeastern turkey are of upper cretaceous age the separation of the turkish microplate and the generation of southern tethys in southeastern turkey did not take place in triassic times but in the late cretaceous plate rupture was probably caused by a major change in plate motions 80 m y ago the turkish plate was completely sheared off the northern edge of africa by northeasterly trending transcurrent faults through southeastern turkey mantle leakage along such transcurrent faults must have generated the ophiolites of the thrust fault belt of south eastern turkey in narrow ocean basins between ribbons of continental crust