a terra rossa like paleosol complex from the upper jurassic of portugal the basal upper jurassic unconformity in the lusitanian basin of portugal commonly exhibits an irregular palaeokarstic surface developed in underlying middle jurassic carbonates in the serra da arrabida area south of lisbon wire cut quarry faces expose a thick upper jurassic paleosol complex overlying fissured and brecciated limestone veneered with a calcrete crust and associated with colluvial deposits the paleosol complex is a red mudstone with calcrete stringers which superficially resembles present day red mediterranean terra rossa soils a detailed micromorphological study indicates the absence of any clay illuviation in the paleosol unit which suggests that it is not comparable to the true terra rossa alfisols but more closely resembles present day aridisols this difference from true terra rossa soils probably reflects formation under a drier climate which is confirmed by the occurrence elsewhere in portugal of evaporitic lake deposits of the same age the paper stresses the role of soil petrography micromorphology in interpreting pedogenesis in paleosols

hierarchal genetic stratigraphy a framework for paleoceanography a detailed genetic stratigraphic framework for paleoceanographic studies can be derived by describing correlating interpreting and predicting stratigraphic sequences relative to a hierarchy of their constituent time stratigraphic transgressive regressive units t r units t r unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data but correlations can be enhanced or checked tested to confirm or deny with objective biostratigraphic magnetostratigraphic or chemostratigraphic data such chronostratigraphies can then be bracketed by radiometric ages so that average periodicities for t r units can be calculated and a hierarchal geochronology derived t r units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening shallowing units because the latter are noncorrelative intrabasinally boundaries between t r units are conformable or unconformable genetic surfaces of two types transgressive surfaces and climate change surfaces the latter are useful for correlating minor transgressive phases through nonmarine intervals thereby deriving information linking paleoclimatic and paleoceanographic processes permo carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic t r units having periodicities of 225 300 m y first order 20 90 m y second order 7 13 m y third order 0 6 3 6 m y fourth order 300 500 10 years fifth order and 50 130 10 years or less sixth order paleogeographic maps for the time of maximum transgression transgressive apex of successive fifth order t r units 5 25 m thick in the glenshaw formation upper pennsylvanian northern appalachian basin delineate delta lobes embayments islands and linear seaways relative extent of marine inundation on the fifth order maps was used to delineate fourth order t r units and the fourth order t r units constitute the transgressive half of a third order t r unit this third fourth and fifth order hierarchy is correlated more than 1200 km 750 miles to the western interior basin and is confirmed with limited objective biostratigraphy

focal mechanisms and stress variations in the caucasus and northeast turkey from constraints of regional waveforms abstract the continental collision between arabia and eurasia created large strike slip faults in turkey as well as mountains in the caucasus and the volcanic plateau between them in this study we use regional waveforms of a new seismic array deployed between 2008 and 2012 to constrain the focal mechanisms and depths of small to moderate sized earthquakes occurring in the western part of the central caucasus and northeast turkey the distribution of aftershocks and the twelve focal mechanisms involved in the sequence of the 2009 earthquake in racha are clearly a reactivation of a deeper segment of the 1991 m7 racha rupture zone the deeper segment is not well connected to the shallower decollement separating the basement and sedimentary basin the earthquakes we determined in northeastern turkey and southern georgia are related to the strike slip fault system we further combined all of the reliably determined focal mechanisms over the last 30 years to investigate the current stress status of the crust in three areas racha in the western greater caucasus javakheti near the lesser caucasus and in northeast turkey our results show that the directions of maximum compressional stress consistently fall within 2 to 14 n throughout the entire study region this appears to be controlled by the continental collision nonetheless the minimum compression switches from vertical in the greater caucasus to the east west direction in northeastern turkey due to the westward extrusion of the anatolia block which is driven partly by the hellenic subduction the transition of the stress field is close to the javakheti volcanic plateau in the lesser caucasus where the relative magnitude between the principal stresses appears to be strongly variable

tomographic imaging of the seismic structure beneath the east anatolian plateau eastern turkey the high level of seismic activity in eastern turkey is thought to be mainly associated with the continuing collision of the arabian and eurasian tectonic plates the determination of a detailed three dimensional 3d structure is crucial for a better understanding of this on going collision or subduction process therefore a body wave tomographic inversion technique was performed on the region the tomographic inversion used high quality arrival times from earthquakes occurring in the region from 1999 to 2001 recorded by a temporary 29 station broadband iris passcal array operated by research groups from the universities of bogazici turkey and cornell usa the data was inverted and consisted of 3 114 p and 2 298 s wave arrival times from 252 local events with magnitudes md ranging from 2 5 to 4 8 the stability and resolution of the results were qualitatively assessed by two synthetic tests a spike test and checkerboard resolution test and it was found that the models were well resolved for most parts of the imaged domain the tomographic inversion results reveal significant lateral heterogeneities in the study area to a depth of 20 km the p and s wave velocity models are consistent with each other and provide evidence for marked heterogeneities in the upper crustal structure beneath eastern turkey one of the most important features in the acquired tomographic images is the high velocity anomalies which are generally parallel to the main tectonic units in the region existing at shallow depths this may relate to the existence of ophiolitic units at shallow depths the other feature is that low velocities are widely dispersed through the 3d structure beneath the region at deeper crustal depths this feature can be an indicator of the mantle upwelling or support the hypothesis that the anatolian plateau is underlain by a partially molten uppermost mantle

teleseismic evidence for a break off subducting slab under eastern turkey abstract we present seismic images of the upper mantle beneath eastern turkey determined by teleseismic tomography the data are measured precisely from seismograms recoded by the eastern turkey seismic experiment network consisting of 29 portable stations and 2 permanent stations our results show that obvious high velocity high v anomalies of up to 2 are interrupted beneath eastern turkey and subcrustal earthquakes occurred along these high v anomalies pronounced low velocity low v anomalies are visible from the arabian foreland basin in the southwest to the caucasus region in the northeast which extend down to about 400 km depth these low v anomalies are consistent with the existence of late cenozoic volcanism in the region these results provide new constraints on the geodynamic processes in the east anatolian plateau suggesting that the break off of the arabian slab may play an important role in the formation of the anatolian plateau and the volcanism in the region these processes might be related to the collision of the arabian plate with the eurasian plate

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

crust mantle mechanical coupling in eastern mediterranean and eastern turkey present day crust mantle coupling in the eastern mediterranean and eastern turkey is studied using the global positioning system gps and seismic anisotropy data the general trend of the shear wave fast splitting directions in ne turkey and lesser caucaus align well with the geodetic velocities in an absolute plate motion frame of reference pointing to an effective coupling in this part of the region of weak surface deformation farther south underneath the bitlis suture however there are significant pn delays with e w anisotropy axes indicating significant lateral escape meanwhile the gps reveals very little surface deformation this mismatch possibly suggests a decoupling along the suture in the aegean the shear wave anisotropy and the pn anisotropy directions agree with the extensional component of the right lateral shear strains except under the crete basin and other parts of the southern aegean sea this extensional direction matches perfectly also with the southward pulling force vectors across the hellenic trench however the maximum right lateral shear directions obtained from the gps data in the aegean do not match either of these anisotropies seismic anisotropy from rayleigh waves sampled at 15 s corresponding to the lower crust match the maximum right lateral maximum shear directions from the gps indicating decoupling between the crust and the mantle this decoupling most likely results from the lateral variations of the gravitational potential energies and the slab pull forces

eastern turkish high plateau as a small turkic type orogen implications for post collisional crust forming processes in turkic type orogens abstract post collisional magmatism may be generated by extensive crustal melting in tibet type collisional environments or by falling out of slabs from under giant subduction accretion complexes in turkic type collisional orogens giving rise to decompression melting of the asthenospheric mantle replacing the removed oceanic lithosphere in turkic type post collisional magmatism the magmatic products are dominantly alkalic to peralkalic and greatly resemble those of extensional regions giving rise to much confusion especially in interpreting old collisional orogenic belts such magmatic regions are also host to a variety of economically valuable ore deposits including gold one place in the world where today active turkic type post collisional magmatism is present is the eastern anatolian high plateau produced after the terminal arabia eurasia collision in the late miocene the plateau is mostly underlain by the late cretaceous to oligocene east anatolian accretionary complex which formed south of the rhodope pontide magmatic arc this subduction accretion complex has been further shortening since the collision but it has also since been domed and became almost entirely covered by at least 15 000 km3 of volcanic rocks the volcanic rocks are calc alkalic in the north transitional in the middle and alkalic in the south of the plateau where the crust is thinnest today less than 38 km the volcanics are derived almost entirely from an enriched mantle the ages of the volcanics also become younger from north to south from about 11 ma to possibly 17th century ad we interpret the origin of the magmatic rocks as the result of decompression melting of the asthenospheric mantle sucked towards the exposed base of the east anatolian accretionary complex as the oceanic lithosphere beneath it fell out the lower density of the hot asthospheric material was the cause of the doming we believe that similar processes dominated the post collisional tectonics of such vast turkic type orogens as the altaids of central asia the late devonian early carboniferous lachlan belt in southeastern australia and the pan african collage of northeast afro arabia it is likely that archaean collisions were dominated by turkic type post collisional events rather than tibetan ones that only became common in the proterozoic

calcrete palaeosols from the lower carboniferous llanelly formation south wales abstract three calcrete bearing palaeosol units are described from the lower carboniferous llanelly formation in south wales and are named the tyle r bont pedocomplex the cwm dyar pedoderm and the llanelly pedocomplex these units were formed on semi arid to arid floodplains and are associated with sheet flood stream flood and meandering channel deposits three major processes operated during pedogenesis calcification pedoturbation and solution pedoturbation resulted in the formation of brecciated horizons pseudo anticlinal and prismatic structures and a predominance of disorthic nodules the soils developed in smectite rich clays under a seasonally arid climate resulting in strong argillipedoturbation

the petrology and palaeoenvironment of the sortino group miocene of se sicily evidence for periodic emergence the sortino group of carbonates consists of three formations which developed on a shallow marine shelf during tortonian and lower messinian times the two lower formations contain three bioherms and are intercalated with thick volcaniclastic sequences the youngest formation is dominated by shoal water lagoonal and peri tidal carbonates early submarine lithification is well developed within the bioherms and consists of construction by both algae and invertebrates the development of peloidal micrites and isopachous fringe growth superimposed upon these are a series of both meteoric phreatic and vadose textures related to episodic emergence of the bioherms these features include bladed cements showing cathodoluminescence pendent cements brecciation alveolar texture and palaeosols the sicilian strata may be directly correlated with the maltese islands sequence and collectively exhibit the effects of fluctuating mediterranean sea levels at an early stage in the late miocene salinity crisis

high frequency attenuation in the lake van region eastern turkey we provide a complete description of the characteristics of excitation and attenuation of the ground motion in the lake van region eastern turkey using a data set that includes three component seismograms from the 23 october 2011 m w 7 1 van earthquake as well as its aftershocks regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance frequency and magnitude peak ground velocities are measured in selected narrow frequency bands from 0 25 to 12 5 hz observed peaks are regressed to define a piecewise linear regional attenuation function a set of excitation terms and a set of site response terms results are modeled through random vibration theory see cartwright and longuet higgins 1956 in the log log space the regional crustal attenuation is modeled with a bilinear geometrical spreading graphic 1 characterized by a crossover distance at 40 km graphic 2 fits our results at short distances r is better at larger distances 40 r 200 km a frequency dependent quality factor q f 100 f f ref 0 43 in which f ref 1 0 hz is coupled to the geometrical spreading because of the inherent trade off of the excitation attenuation parameters and their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes after choosing a brune stress drop brune 4 mpa at m w 3 5 we were able to define 1 an effective high frequency distance and magnitude independent roll off spectral parameter eff 0 03 s and 2 a size dependent stress drop parameter which increases with moment magnitude from brune 4 mpa at m w 3 5 to brune 20 mpa at m w 7 1 the set of parameters mentioned here may be used in order to predict the earthquake induced ground motions expected from future earthquakes in the region surrounding lake van 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

seismic velocity and poisson s ratio tomography of the crust beneath east anatolia abstract eastern anatolia is a region in the early stages of continent continent collision and so provides a unique opportunity to study the early development of continental plateau located within the alpine himalayan fold thrust fault belt the anatolian plateau is geologically very complex with over half of the surface area covered with late cenozoic volcanics of diverse composition the plateau is also seismically active and is dissected by numerous seismogenic faults predominantly of strike slip motion in this study we determine 3 d tomographic images of the crust beneath eastern anatolia by inverting a large number of arrival time data of p and s waves from the obtained p and s wave velocity models we estimated the poisson s ratio structures for a more reliable interpretation of the obtained velocity anomalies our tomographic results are generally consistent with the major tectonic features of the region high p and s wave velocity anomalies are recognized near the surface while at deeper crustal layers low seismic wave velocities are widely distributed poisson s ratio exhibits significant structural heterogeneities compared to the imaged velocity structure the seismic activity is intense along highly heterogeneous zones and is closely associated with pre existing faults in the central and western parts of the study area results of the checkerboard resolution test indicate that the imaged anomalies are reliable features down to a depth of about 40 km the low velocity high poisson s ratio zones in the middle to lower crust are consistent with many geophysical observations such as strong sn attenuation low pn and sn velocity and the absence of mantle lid implying the presence of partial melt in the uppermost mantle

seismic structure crustal architecture and tectonic evolution of the anatolian african plate boundary and the cenozoic orogenic belts in the eastern mediterranean region the modern anatolian african plate boundary is represented by a north dipping subduction zone that has been part of a broad domain of regional convergence between eurasia and afro arabia since the latest mesozoic a series of collisions between gondwana derived ribbon continents and trench roll back systems in the tethyan realm produced nearly east west trending subparallel mountain belts with high elevation and thick orogenic crust in this region ophiolite emplacement terrane stacking high p and barrovian metamorphism and crustal thickening occurred during the accretion of these microcontinents into the upper plates of tethyan subduction roll back systems during the late cretaceous early eocene continued convergence and oceanic lithospheric subduction within the tethyan realm were punctuated by slab breakoff events following the microcontinental accretion episodes slab breakoff resulted in asthenospheric upwelling and partial melting which facilitated post collisional magmatism along and across the suture zones resumed subduction and slab roll back induced upper plate extension triggered a tectonic collapse of the thermally weakened orogenic crust in anatolia in the late oligocene miocene this extensional phase resulted in exhumation of high p rocks and mediumto lower crustal material leading to the formation of metamorphic core complexes in the hinterland of the young collision zones the geochemical character of the attendant magmatism has progressed from initial shoshonitic and high k calc alkaline to calc alkaline and alkaline affinities through time as more asthenosphere derived melts found their way to the surface with insignificant degrees of crustal contamination the occurrence of discrete high velocity bodies in the mantle beneath anatolia as deduced from lithospheric seismic velocity data supports our tethyan slab breakoff interpretations pn velocity and sn attenuation tomography models indicate that the uppermost mantle is anomalously hot and thin consistent with the existence of a shallow asthenosphere beneath the collapsing anatolian orogenic belts and widespread volcanism in this region the sharp north pointing cusp isparta angle between the hellenic and cyprus trenches along the modern anatolian african plate boundary corresponds to a subductiontransform edge propagator step fault which is an artifact of a slab tear within the downgoing african lithosphere

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

cenozoic evolution of the eastern black sea a test of depth dependent stretching models abstract subsidence analysis of the eastern black sea basin suggests that the stratigraphy of this deep extensional basin can be explained by a predominantly pure shear stretching history a strain rate inversion method that assumes pure shear extension obtains good fits between observed and predicted stratigraphy a relatively pure shear strain distribution is also obtained when a strain rate inversion algorithm is applied that allows extension to vary with depth without assuming its existence or form the timing of opening of the eastern black sea which occupied a back arc position during the closure of the tethys ocean has also been a subject of intense debate competing theories called for basin opening during the jurassic cretaceous or paleocene eocene our work suggests that extension likely continued into the early cenozoic in agreement with stratigraphic relationships onshore and with estimates for the timing of arc magmatism further basin deepening also appears to have occurred in the last 20 myr this anomalous subsidence event is focused in the northern part of the basin and reaches its peak at 15 10 ma we suggest that this comparatively localized shortening is associated with the northward movement of the arabian plate we also explore the effects of paleowater depth and elastic thickness on the results these parameters are controversial particularly for deep water basins and margins but their estimation is a necessary step in any analysis of the tectonic subsidence record stored in stratigraphy

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

organization of lithic technology at ein qashish a late middle paleolithic open air site in israel abstract ein qashish eq is a late middle paleolithic 60 ka open air site located in the yizra el valley east of mt carmel at the geographic center between some of the major middle paleolithic cave sites in northern israel three seasons of excavation at the site revealed a small faunal collection and a diverse lithic assemblage in this paper we discuss the composition reduction technology and raw material curation strategies represented in the assemblage the assemblage is flake dominated with low frequencies of retouched artifacts and of cores several reduction sequences were identified products of levallois methods appear in low frequencies the modified artifacts include lightly retouched flakes and blades side scrapers truncations and burins the low frequencies of primary elements core trimming elements and cores suggest that only part of the reduction sequence took place on site side scrapers may have been imported into the locality in contrast short non levallois reduction sequences were applied on site the expedient nature of the retouch and of local reduction sequences suggests that the site represents an ephemeral occupation s on the banks of the qishon stream the nature of the lithic assemblage is not consistent with specific tasks such as butchery or hunting technological aspects of the assemblage and its composition bear similarities to those observed in habitation sites found in caves in the late middle paleolithic

a rendzina from the lower carboniferous of south wales a thin calcrete crust horizon from the lower carboniferous llanelly formation of south wales consists of two parts an upper laminated unit and a lower peloidal unit the former is interpreted as a subaerial stromatolite and the latter as an a horizon of a palaeosol comparisons are made with the a horizons of rendzinas and it is concluded that the calcrete crust represents a complete rendzina profile this fossil rendzina contains abundant evidence of a soil fauna in the form of fecal pellets and small burrows

slab detachment beneath eastern anatolia a possible cause for the formation of the north anatolian fault in this paper we discuss the possibility that the north anatolian fault naf results from the deep deformation of the slab beneath the bitlis hellenic subduction zone we described the tectonic evolution of the anatolia aegean area in three main steps before during and after the formation of the naf we remark that the tectonic conditions that are assumed to have triggered the formation of the naf i e collision to the east and extension to the west was already achieved before the onset of that strike slip fault system we also highlight that the formation of the naf was accompanied by the uplift of the turkish iranian plateau and by a surge of volcanism in the eastern anatolia collisional area and probably by the acceleration of the aegean trench retreat we show tomographic images from global p wave model of piromallo and morelli c piromallo a morelli p wave tomography of the mantle under the alpine mediterranean area j geophys res 108 2003 doi 10 1029 2002jb001757 showing that the slab beneath the bitlis collisional belt is not continuous and that its possible rupture pursues to the west at least up to cyprus and possibly up to the eastern end of the hellenic trench all these observations suggest that the plate tectonic re organization occurred in the late miocene early pliocene in the region results from slab break off in the bitlis area and from its lateral propagation to the west this idea is tested in analogue laboratory experiments which confirm that the break of the slab under the collisional belt may trigger 1 the acceleration of slab retreat to the west due to the increase in slab pull force 2 the indentation of the continent in the collisional area and 3 produce the conditions that permit the lateral escape of material towards the west and the formation of the naf

tomographic evidence of slab detachment beneath eastern turkey and the caucasus summary teleseismic phase readings from the eastern turkey seismic experiment etse have been inverted using teleseismic tomography in order to create a 3 d image of the underlying mantle beneath eastern turkey the aim was to investigate the existence of an upper mantle negative velocity anomaly that is used to explain the uplift of eastern anatolian plateau and the potential pieces of detached oceanic slabs related to neo tethyan subduction suggested by previous studies using teleseismic waveforms from the 29 stations of the eastern turkey seismic experiment 2926 direct p phases from 146 events were picked by using adaptive stacking techniques in order to increase the station coverage and resolve the surrounding area the phase readings from the international seismological center isc bulletin have also been added the data set consists of 9571 p and pkp phase readings of 79 stations from 503 teleseismic events this study develops the first highresolution 3 d upper mantle p wave tomographic model for this region the tomographic results show the existence of an upper mantle negative velocity anomaly to a depth of 200 km beneath the eastern anatolian accreationary complex eaac as commonly observed in the previous studies that suggest a shallow partially molten asthenosphere the slab like high velocity anomalies beneath the eaac pontides and caucasus are interpreted as the detached southern and northern neo tethys slabs

late pleistocene intraplate extension of the central anatolian plateau turkey inferences from cosmogenic exposure dating of alluvial fan landslide and moraine surfaces along the ecemis fault zone here we documented the vertical displacement slip rate extension rate and geochronology of normal faults within a narrow strip along the main strand of the ecemis fault zone the kartal cevizlik and lorut faults are normal faults that have evident surface expression within the strip terrestrial cosmogenic nuclide geochronology revealed that the kartal fault deformed the 104 2 16 5 ka aged alluvial fan surface and the cevizlik fault deformed the 21 9 1 8 ka old moraine and talus fan surfaces our topographic surveys indicated 120 10 m and 13 1 1 4 m surface breaking vertical displacements along the kartal and cevizlik faults respectively accordingly we suggest a 1 15 0 21 mm a 1 slip rate and 0 66 0 12 mm a 1 extension rate for the last 104 2 16 5 ka on the kartal fault and a 0 60 0 08 mm a 1 slip rate and 0 35 0 05 mm a 1 extension rate for the last 21 9 1 8 ka on the cevizlik fault we believe that these structures are an integral part of intraplate crustal deformation in the central anatolia they imply that intraplate structures such as the ecemis fault zone may change their mode through time presently the ecemis fault zone has been deformed predominantly by normal faults the presence of steep preserved fault scarps along the kartal cevizlik and lorut faults point to surface breaking normal faulting away from the main strand and particularly signify that these structures need to be taken into account for regional seismic hazard assessments

shear wave velocity structure of the upper mantle beneath the northern zagros collision zone revealed by nonlinear teleseismic tomography and bayesian monte carlo joint inversion of surface wave dispersion and teleseismic p wave coda abstract the continental collision between the arabian and eurasian plates plays an important role in the geodynamical evolution of the zagros and iranian plateau in order to investigate the upper mantle structure across the collision zone we calculated the absolute and relative shear wave velocity structure along a dense and long temporary seismic profile in nw iran the probabilistic 1 d absolute shear wave velocity vs depth profiles beneath 23 seismic stations were calculated using a trans dimensional joint inversion approach of p wave coda together with the rayleigh wave phase and group velocity dispersion data these 1 d models are then interpolated to obtain a 2 d vs model along the profile in addition we used a nonlinear teleseismic tomography method to determine shear wave velocity variations beneath 44 seismic stations both the absolute and relative velocity models obtained by different data sets and methods show a thick 150 km high velocity anomaly beneath the northern part of the zagros which could be the thickened zagros lithosphere associated with continental shortening a relatively thin lithosphere 80 km and lower s wave velocity beneath central iran may suggest a weakened iranian mantle lithosphere by upwelling of the hot asthenosphere following slab break off the presence of a thickened lithosphere beneath the zagros implies that the arabian eurasian convergence is accommodated mainly as shortening in the mantle lithosphere beneath the zagros rather than underthrusting beneath central iran a narrow low velocity corridor between the zagros lithosphere and overriding plate central iran south of the sanandaj sirjan zone ssz probably due to delamination of the subducting arabian lithosphere from the zagros lower crust likely prohibits transferring stress from the zagros lithosphere to central iran causing less deformation in the ssz which is the edge of the overriding plate

shear wave splitting in a young continent continent collision an example from eastern turkey an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017390 shtml http atlas geo cornell edu turkey publications sandvol et al 2003b htm

geodynamics seismicity and seismic hazards of the caucasus abstract being a part of ongoing continental collision between the arabian and eurasian plates the caucasus region is a remarkable site of moderate to strong seismicity where devastating earthquakes caused significant losses of lives and livelihood in this article we survey geology and geodynamics of the caucasus and its surroundings magmatism and heat flow active tectonics and tectonic stresses caused by the collision and shortening gravity and density models and overview recent geodetic studies related to regional movements the tectonic development of the caucasus region in the mesozoic cenozoic times as well as the underlying dynamics controlling its development are complicated processes it is clear that the collision is responsible for a topographic uplift inversion and for the formation of the fold and thrust belts of the greater and lesser caucasus tectonic deformations in the region is influenced by the wedge shaped rigid arabian block indenting into the relatively mobile region and producing near n s compressional stress and seismicity in the caucasus regional seismicity is analysed with an attention to sub crustal seismicity under the northern foothills of the greater caucasus which origin is unclear whether the seismicity associated with a descending oceanic crust or thinned continental crust recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the lesser and greater caucasus the knowledge of geodynamics seismicity and stress regime in the caucasus region assists in an assessment of seismic hazard and risk we look finally at existing gaps in the current knowledge and identify the problems which may improve our understanding of the regional evolution active tectonics geodynamics shallow and deeper seismicity and surface manifestations of the lithosphere dynamics among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution e g continental collision and associated shortening and exhumation lithosphere structure deformation and strain stress partitioning and to the lack of comprehensive datasets e g regional seismic catalogues seismic gravity and geodetic surveys

tomographic pn velocity and anisotropy structure beneath the anatolian plateau eastern turkey and the surrounding regions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017391 shtml http atlas geo cornell edu turkey publications al lazki et al 2003 htm

the 2011 mw 7 1 van eastern turkey earthquake 1 we use interferometric synthetic aperture radar insar body wave seismology satellite imagery and field observations to constrain the fault parameters of the mw 7 1 2011 van eastern turkey reverse slip earthquake in the turkish iranian plateau distributed slip models from elastic dislocation modeling of the insar surface displacements from envisat and cosmo skymed interferograms indicate up to 9 m of reverse and oblique slip on a pair of en echelon nw 40 54 dipping fault planes which have surface extensions projecting to just 10 km north of the city of van the slip remained buried and is relatively deep with a centroid depth of 14 km and the rupture reaching only within 8 9 km of the surface consistent with the lack of significant ground rupture the up dip extension of this modeled wsw striking fault plane coincides with field observations of weak ground deformation seen on the western of the two fault segments and has a dip consistent with that seen at the surface in fault gouge exposed in quaternary sediments no significant coseismic slip is found in the upper 8 km of the crust above the main slip patches except for a small region on the eastern segment potentially resulting from the mw 5 9 aftershock on the same day we perform extensive resolution tests on the data to confirm the robustness of the observed slip deficit in the shallow crust we resolve a steep gradient in displacement at the point where the planes of the two fault segments ends are inferred to abut at depth possibly exerting some structural control on rupture extent

the sedimentary facies of a late bathonian regressive episode the kilmaluag and skudiburgh formations of the great estuarine group inner hebrides scotland the kilmaluag and skudiburgh formations of the bathonian great estuarine group represent a unique palaeoenvironment within the british jurassic the kilmaluag formation is divided into two distinctive facies the clastic facies of n skye comprises calcareous mudstones and shales with subordinate sandstones and argillaceous limestones the depositional setting was one of shallow ephemeral lagoons closed from the sea sublittoral lagoon mudflat and channel environments are identified and fossil faunas indicate low salinity the argillaceous limestone facies of southern skye eigg and muck formed in a similar depositional setting although sandstones are not present alternations of carbonate rocks some dolomitic and calcareous shales probably reflect palaeoclimatic fluctuations between humid and arid periods the overlying skudiburgh formation is interpreted as being alluvial floodplain channel and overbank deposits are identified by the presence of mottled mudstones sands and lensoidal silts syndepositional carbonate nodules are interpreted as calcrete which occasionally coalesced to form extensive hardpan calcrete horizons the vertical facies sequence reflects a late bathonian regression the coastal plain terrestrial environments of the skudiburgh formation were transgressed during the callovian stage an event which ended paralic deposition in the hebridean jurassic

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

review of the neotectonics of the eastern turkish armenian plateau by geomorphic analysis of digital elevation model imagery digital elevation model dem images provide synoptic views of the earth s surface allowing the analysis of landforms of still active tectonic and volcanic structures at regional scale a dem at 250 m pixel size constitutes regional scale data particularly efficient to investigate the late miocene quaternary deformation of the eastern turkish armenian plateau in the arabian eurasian area of convergence geomorphic analysis of the dem image associated with review of fault plane solutions of earthquakes show that faults are mostly strike slip with small vertical component here we show that the orientations of the tectonic and volcanic structures fit with a tectonic regime characterized by n s shortening and e w lengthening consistent with westward escape of anatolia perpendicular to the direction of the arabia eurasia shortening the uniform uplift of the plateau the predominance of strike slip faulting the lack of major thrusts and the occurrence of normal faults do not support a model of going on crustal thickening due to intracontinental convergence on the contrary our observations can be better interpreted in terms of lithospheric thinning and mantle upwelling related to gravity escape of anatolia

mantle flow induced crustal thinning in the area between the easternmost part of the anatolian plate and the arabian foreland e turkey deduced from the geological and geophysical data abstract eastern anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the arabian and eurasian plates this collisional and contractional zone is being accompanied by the tectonic escape of most of the anatolian plate to the west by major strike slip faulting on the right lateral north anatolian transform fault zone natfz and left lateral east anatolian transform fault zone eatfz which meet at karliova forming an east pointing cusp the present day crust in the area between the easternmost part of the anatolian plate and the arabian foreland gets thinner from north ca 44 km to south ca 36 km relative to its eastern eahp and western sides central anatolian region this thinner crustal area is characterized by shallow cpd 12 16 km very low pn velocities

terrestrial stromatolites and laminar calcretes a review abstract laminated carbonates are prominent features of subaerial exposure profiles and many types of calcareous soils including calcretes previously much attention was given to differentiating these laminites from marine or lacustrine microbial stromatolites and oncoids however recent research has shown that many subaerial laminated carbonates are biogenically formed mainly but not wholly by microbial activity this paper reviews the criteria for distinguishing terrestrial carbonate laminites from non terrestrial stromatolites and oncoids and for differentiating biogenic from abiogenic terrestrial laminites

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

sn attenuation in the anatolian and iranian plateau and surrounding regions an edited version of this paper was published in geophysical research letters by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018020 shtml http atlas geo cornell edu turkey publications gok et al 2003 htm

pn tomographic imaging of mantle lid velocity and anisotropy at the junction of the arabian eurasian and african plates an edited version of this paper was published by blackwell publishing in geophysical journal international copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02355 x http atlas geo cornell edu middleeastnorthafrica publications al lazki2004 htm

east anatolian high plateau as a mantle supported north south shortened domal structure an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017858 shtml http atlas geo cornell edu turkey publications sengor et al 2003 htm

crustal and uppermost mantle structure in the middle east assessing constraints provided by jointly modelling ps and sp receiver functions and rayleigh wave group velocity dispersion curves

constraining crustal and uppermost mantle structure beneath station tbz trabzon turkey by receiver function and dispersion analyses summary we jointly invert teleseismic radial component receiver functions and regional rayleigh and love surface wave group velocities for 1 d shear wave velocity structure beneath station tbz located on the northern side of the eastern pontides an influence factor is employed to control the relative influence of receiver function and surface wave dispersion on the resultant velocity depth profile radial and transverse component receiver functions at station tbz exhibit an azimuthal amplitude and polarity pattern consistent with 2 d receiver structure that has a general dip direction towards approximately south the radial component receiver functions are least affected by the dipping structures along the strike direction and thereby we prefer teleseismic events sampling along strike structures to alleviate the deflecting effect of dipping interfaces on the 1 d solution the 1 d inversion effectively reveals the two layer nature of the crust which is perturbed by high and low velocity layers and serves as a provisional model for the 2 d forward modelling minor to moderate changes to the 1 d model such as changing depth to and velocity contrast across an interface are needed to achieve the results with the 2 d modelling dipping interfaces and seismic anisotropy are included in the 2 d modelling to fit both radial and transverse component receiver functions the upper crust is characterized by a shear velocity of 3 5 km s 1 and cut through by a 4 km thick high velocity i e 3 8 km s 1 layer overlying the upper crust the sedimentary cover i e the top 5 km has velocities within the range 2 0 3 5 km s 1 a mid crustal velocity discontinuity between the upper granitic crust and the lower basaltic crust is identified at 16 km depth this boundary is analogous to the mid crustal discontinuity found under the black sea basin across which the shear velocity jumps from 3 5 to 4 1 km s 1 a relatively thick i e 12 km low velocity layer in the lower crust with a velocity reversal from 4 1 to 3 7 km s 1 is needed to better explain reverberations off this depth range we infer a 2 d moho discontinuity placed at 35 km depth beneath the station the proposed dip angle for the moho is rather steep i e 25 although coincident with regional gravity studies the associated sn velocity i e 4 4 km s 1 is rather low indicating disturbed upper mantle structure beneath the region initial amplitudes of transverse component receiver functions are rather energetic for which we propose substantial p and s velocity anisotropy 12 per cent for the topmost depths 5 km

love wave group velocity maps of turkey and surrounding regions summary we present the analysis of a love wave dispersion study performed across turkey and the surroundings group velocity dispersion curves were obtained from the local and regional earthquakes recorded at both permanent and temporary stations operated in the region lovewave group velocity maps in the period range of 10 50 s were computed using a tomographic inversion method the study shows the existence of significantly different crustal types in the area the group velocity anomalies are associated with the major geological structures in the region low group velocities at shorter periods 10 20 s are observed in the local sedimentary basins the eastern mediterranean and the black sea the eastern anatolia region is also characterized by low group velocities while pontides and bitlis p ot urge massif display higher group velocities the central anatolia exhibits uniform velocity distribution indicating more homogenous crust the isparta angle is marked by a wedge shaped low group velocity anomaly the low velocities observed in the isparta angle are related to crustal thickening and subduction related complex high velocities observed on the maps are associated with metamorphics magmatic arcs along the orogenic belts of pontides p

a new approach to obtaining a 3d shear wave velocity model of the crust and upper mantle an application to eastern turkey article i nfo we present a new approach to the joint inversion of surface wave dispersion data and receiver functions by utilizing common conversion point ccp stacking to reconcile the different sampling domains of the two datasets utilizing ccp stacking allows us to suppress noise in the data by waveform stacking and correct for backazimuthal variations and complex crustal structure by mapping receiver functions back to their theoretical location when applied to eastern turkey this approach leads to a higher resolution image of the subsurface and clearly delineates different tectonic features in eastern turkey that were not apparent using other approaches we observe that theslow seismic velocities near the karliova triple junction correlate to moderate strain rates and high heat flow which leads to a rheologically weak crust that has allowed for the upward propagation of miocene and younger volcanics near the triple junction we find seismically fast presumably rigid blocks located in the southeastern anatolian plate and arabian plate are separated by a band of low shear wave velocities that correspond to the east anatolian fault zone which is consistent with the presence of fluids in the fault zone we observe that the arabian plate has underthrust the eurasian plate as far as the northern boundary of the bitlis massif which can explain the high exhumation rates in the bitlis massif as a result of slab break off of the arabian oceanic lithosphere we also find a shallow 33 km anomaly beneath eastern turkey that we interpret as a localized wedge of mantle that was underthrust by a crustal fragment during the collision of arabia and eurasia these observations are possible because of the high resolution images obtained by combining common conversion point receiver function stacks with ambient noise dispersion data to create a data driven three dimensional shear wave velocity model

locally thin crust and high crustal vp vs ratio beneath the armenian volcanic highland of the lesser caucasus a case for recent delamination

petrogenesis of mafic silicic lavas at mt erciyes central anatolia turkey abstract new compositional data are presented for a suite of basaltic andesite to rhyolite flows from the flanks of the pliocene quaternary mt erciyes stratovolcano in central anatolia turkey the samples are all part of the most recent 2 contents between 56 wt and 72 wt that are attributed to mixing processes consistent with textural observations and mineral data particularly in the intermediate dacite flows two distinct plagioclase phenocryst populations clear an 33 53 cores vs sieve textured cores of an 59 80 wide compositional range for orthopyroxene phenocrysts mg from 63 to 90 we infer that basaltic melts of a heterogeneous shallow mantle source ponded in the mid to lower crust and underwent variable differentiation accompanied by crustal assimilation to form more evolved melt compositions with sio 2 55 wt these melts ascended to shallower crustal levels 4 10 km based on amphibole geobarometry where mixing of diverse melts and entrained crystals gives rise to the linear mixing trends shown by the erupted andesite dacite rhyolite lavas

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

isostasy of the eastern anatolia turkey and discontinuities of its crust this paper presents a probable isostatic model of the east anatolian region which lies in a belt of significant plate movements probable locations of the horizontal and vertical discontinuities in the crust structure were determined using the normalized full gradient nfg method for the purpose of explaining the mechanism that supports topography corresponding to the crust thickness in the region calculations of effective elastic thickness t e were carried out initially by utilizing admittance and misfit functions according to these results the effective elastic thickness value obtained was less than the crust thickness even though the isostatic model does not conform with the airy model consequently it was assumed that there could be problems beneath the crust hence the nfg method was applied on the bouguer gravity data of the region in order to investigate probable discontinuities in the crust structure according to the nfg results vertical structural transitions were observed at a depth ranging between 10 and 30 km which begin immediately north of the bitlis zagros suture zone bzsz and continue in a northerly direction the relationship between the effective elastic thickness t e 13 km in average as determined in the last stage and the seismogenic zone in the region was investigated if the t e value happens to be less then the crustal thickness then one can say that there are problems in the crustal structure of the region similar to eastern anatolia indeed when nfg results of the study area are examined numerous vertical and horizontal discontinuities in the crust can be observed these discontinuities which correspond to low bouguer gravity anomalies and shallow focal depth earthquakes are probably the source of the factors which rule the tectonic mechanism of the region

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

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

podogenic columnar calcite from the oolite group lower carboniferous south wales abstract calcrete palaeosols in the oolite group have microspar hardpan layers overlying clay rich nodular layers which in turn overlie the degraded host oolite within and immediately below hardpan layers there are extensive sheet like and fan developments of columnar calcite with individual crystals up to 30 cm long crystals range from those with straight extinction and normal growth zonation through feathery crystals to those showing sweeping extinction the calcretes accumulated within a seasonal climate with hardpan accumulation probably occurring through evaporation during the dry season the columnar calcite precipitated from more dilute solutions with maximum growth probably occurring during the wet season precipitation may have been partly or wholly bacterially mediated or induced by the reduction in p co 2 of fluids as they migrated out of the extremely restricted microporosity of the hardpan columnar fabrics reflect low supersaturations relative to those at which the hardpan accreted inhibition of crystal nucleation and of growth on x axis parallel faces and an excess of co 2 2 availability over ca 2 growth and nucleation may have been inhibited by the presence of particular organic compounds or clays the range in crystal form is related to the degree of poisoning of crystal growth faces by organic compounds

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

high frequency seismic wave propagation beneath the indian shield himalayan arc tibetan plateau and surrounding regions high uppermost mantle velocities and efficient sn propagation beneath tibet summary this paper reports the regional propagation characteristics of high frequhcy p p s and l waves 0 5 to 2hz and p pg and s velocities for several regions in central asia tibet and india an important result is that s waves propagate efficiently in the uppermost mantle beneath most of the tibetan plateau also s transmission in tibet is not affected by crossing many physiographic and tectonic boundaries such as the indus tsangpo suture these observations are similar to observations of s propagation in stable continental and shield regions efficient s propagation is also observed across the stable tarim basin along the tien shan and himalayan mountains and across the indian shield s is strongly attenuated across the northern tibetan plateau chang thang terrane such strong attenuation suggests the existence of a low q zone in the uppermost mantle beneath that region this interpretation is supported by recent geological observations of widespread quaternary to recent basaltic volcanism in the chang thang terrane l propagates efficiently across the tarim basin the indian shield and along the strike of the himalayan mountains l is also observed although less pronounced for paths crossing large portions of the complicated structures of tien shan karakoram and pamir l is not observed for paths crossing the tibetan plateau the southern boundary of the region of inefficient l propagation in tibet lies in the vicinity of the indus tsangpo suture zone the lack of l can be attributed to attenuation within the tibetan crust however other possibilities including scattering by structural discontinuities at the margins of tibet are equally plausible pg and s are the most prominent features on most short period wwssn seismograms at epicentral distances less than about 4 apparent pg velocity determined for the area of the himalayan mountains is 6 0 0 2 km s l apparent velocities of p and s waves that have at least 50 per cent of their paths in the uppermost mantle beneath the tibetan plateau are 8 42 it 0 10 and 4 73 f 0 06 km s respectively these velocities are quite similar to those determined for the himalayan mountains p 8 45 f 0 08 km s i s 4 74 0 05 km s and the indian shield p 8 40 0 08 km s s 4 69 k 0 04 km s p