first evidence of high pressure metamorphism in the cover series of the southern menderes massif tectonic and metamorphic implications for the evolution of sw turkey abstract the menderes massif occupies a large part of western turkey it is tectonically overlain by nappes of the izmir ankara suture zone including the bornova flysch zone on its northern flank the afyon zone on its eastern border and the lycian nappes on its southern flank the discovery of magnesiocarpholite kyanite assemblages in the mesozoic cover sequence of the southern menderes massif leads to the very first consideration that a major high pressure hp metamorphic event affected the massif during its alpine evolution estimations of minimum pressure temperature conditions about 10 12 kbar and 440 c suggest a minimum burial of 30 km for the metasedimentary rocks of the menderes massif similar to that for the eocene dilek blueschists which belong to the cycladic complex this finding of high pressure rocks within the menderes cover series as well as the recent description of low grade high pressure parageneses in the basal thrust sheets of the overlying lycian nappe complex has strong implications for the tectono metamorphic evolution of these units the characteristics of this high pressure metamorphism and the deformation features observed in the southern menderes massif allow consideration of a fast burial during alpine subduction and nappe stacking three high pressure units were piled up during the eocene collision of the sakarya continent and the tauride menderes block the lowermost unit consists of the imbricated core and cover of the menderes massif the intermediate unit is the cycladic blueschist complex dilek and samos regions and the uppermost unit is made of the lycian nappes the retrogression of high pressure parageneses from the menderes massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented n s to ne sw during the high pressure event and its exhumation we propose a tectono metamorphic model in three main stages 1 the southward translation of the high pressure lycian nappes and the burial of the menderes and cycladic metasediments to a depth of at least 30 km to allow their eocene high pressure metamorphism 2 a northward continuum of deformation responsible for top to the north fabrics associated with the main menderes metamorphism peak paleocene eocene and its progressive cooling late eocene north verging folding thrusting imbrication of core and cover series and n s to ne sw intense stretching associated with the menderes high pressure metamorphism and its exhumation these top to the north to top to the northeast movements are probably related to the northward backthrusting of the lycian nappes reactivating the contact between the menderes massif and the lycian nappes as a top to the ne shear zone that allowed exhumation of the lycian high pressure rocks 3 oligo miocene n s extension during which the final exhumation of the metamorphic rocks along kilometre scale low angle detachments occurred

instability of a lithospheric step beneath western north island new zealand lithospheres of different thicknesses are often juxtaposed by movement on a continental transform boundary such a boundary with a step change in densities may trigger a gravitational instability as lateral pressure gradients are created where normal mantle lithosphere terminates against less dense asthenospheric mantle here we show for plausible values of the lithospheric viscosity a mechanism by which the thicker mantle lithosphere will drip off into the lower density asthenosphere as the mantle deforms it also progressively thickens and then thins the overlying crust creating a topographic wave that migrates in concert with the removal of mantle lithosphere within western north island new zealand geophysical data define a sharp lithospheric step across the taranaki ruapehu line and geological observations provide a history of uplift and subsidence that has propagated southward in the past 12 m y the rate of observed north to south migration of the wave 30 mm yr its wavelength 250 km and amplitude 1 km are compatible with it being caused by progressive removal of mantle lithosphere if the viscosity of the uppermost lithospheric mantle is 5 10 20 pa s providing one of the clearest examples yet of this fundamental geological process

exhumation with a twist paleomagnetic constraints on the evolution of the menderes metamorphic core complex western turkey 1 much remains to be understood about the links between regional vertical axis rotations continental extension and shortening in western turkey miocene vertical axis rotations have been reported that occur simultaneously with the extensional exhumation of the menderes metamorphic core complex which has been related to back arc extension in the eastern part of the aegean back arc in this paper we explore the spatial and temporal relationships between vertical axis rotations in southwestern turkey and extensional unroofing of the menderes massif to this end we provide a large set of new paleomagnetic data from western turkey and integrate these with the regional structural evolution to test the causes and consequences of oroclinal bending in the aegean region the lycian nappes and bey daglari are shown to rotate 20 between 16 and 5 ma defining the eastern limb of the aegean orocline this occurred contemporaneously with the exhumation of the central menderes massif along extensional detachments and after the latest oligocene to early miocene exhumation of the northern and southern menderes massifs exhumation of the latter two was not associated with vertical axis rotations the lower miocene volcanics in the region from lesbos to usak to the north of the central menderes massif underwent a small clockwise rotation insignificant with respect to eurasia this shows that exhumation of the central menderes massif was associated with a vertical axis rotation difference between the northern and southern menderes massifs of 25 30 this result is in excellent agreement with the angle defined by the trends of buyuk menderes and alasehir detachments as well as the angle defined by the regionally curving stretching lineation pattern across the central menderes massif these structures define a pivot point rotation pole for the west anatolian rotations the rotation of the southern domain including the southern menderes massif the lycian nappes and bey daglari must have led to n s contraction east of this pole the eastern limit of the rotating domain is formed by the transpressional couple of the aksu thrust and kirkkavak fault in the center of the isparta angle previously reported clockwise rotations in the volcanic fields near afyon may be the result of distributed n s shortening east of the pivot point the precise accommodation of this shortening history remains open for investigation late oligocene to early miocene extension in the eastern part of the aegean back arc was ne sw oriented and likely bounded by a discrete transform this transform may be associated with an early evolution of the eastern aegean subduction transform edge propagator fault oroclinal bending in the west anatolian region is likely related to a reconnection of the eastern part of the aegean orocline with the african northward moving plate in tandem with roll back in the aegean back arc comparable to a recently postulated scenario for western greece

on the thermal regime of some tectonic units in a continental collision environment in romania an analysis of the evolution of the main tectonic units in romania shows that the thermal regime of the lithosphere should be derived according on the one hand to the particular tectonic interactions the various tectonic units have been involved in and on the other hand to the investigated depth interval a steady state conduction model of the crustal temperature field based on the heat flow distribution and information on the structure is presented for the romanian territory it shows large lateral thermal variations between tectonic units as a result of different geological and thermal histories within the frame of a complex modelling of the thermal evolution of the lithosphere in the east carpathians as proposed in this study the zero order thermal effects of the pre miocene oceanic subduction of the eurasian plate are evaluated the deep thermal structure of the subducted slab is derived and shown to be compatible with the velocity structure of the lithosphere and the intermediate depth seismicity of the vrancea area

isotopic evidence for a transition from subduction to slab tear related volcanism in western anatolia turkey abstract volcanic rocks in western turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the aegean subduction zone during the miocene slab segmentation during this period of trench roll back is thought to have imposed source region heterogeneity trending northwest to southeast in this study we present new sr nd pb and o isotopic analyses from the miocene volcanic rocks of the usak gure basin and compare these to previously published data the data demonstrate a change from subduction related sources around the menderes core complex to more asthenospheric sources in the afyon region isotopic compositions sr nd pb of volcanic rocks from the demirci and selendi basins to the west and the afyon volcanic area to the east indicate minimal upper crustal contamination the most primitive lavas also reveal increasing k contents from west the ne sw trending basins to east afyon region it is suggested that the composition of the western anatolian volcanic rocks change from orogenic with lithospheric mantle sources associated to denudation of the menderes massif core complex mmcc to anorogenic with asthenospheric mantle sources in the vicinity of the kirka afyon isparta kai volcanic province with time from early miocene to quaternary there is no asthenospheric contribution during the late miocene onwards in the eastern margin of the mmcc while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex we interpret the usak gure basin to reflect a structural boundary showing a transition from a subduction influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab tearing between the hellenic and cyprus slab segments the usak mugla transfer zone umtz most likely corresponds to slab tear related westernmost faults that were induced by initiation of slab segmentation processes following the late miocene circa 11 ma and possibly since the early miocene

uniformly processed strong motion database for himalaya and northeast region of india this paper presents the first uniformly processed comprehensive database on strong motion acceleration records for the extensive regions of western himalaya northeast india and the alluvial plains juxtaposing the himalaya this includes 146 three components of old analog records corrected for the instrument response and baseline distortions and 471 three components of recent digital records corrected for baseline errors the paper first provides a background of the evolution of strong motion data in india and the seismotectonics of the areas of recording then describes the details of the recording stations and the contributing earthquakes which is finally followed by the methodology used to obtain baseline corrected data in a uniform and consistent manner two different schemes in common use for baseline correction are based on the application of the ormsby filter without zero pads trifunac 1971 and that on the butterworth filter with zero pads at the start as well as at the end converse and brady 1992 to integrate the advantages of both the schemes ormsby filter with zero pads at the start only is used in the present study a large number of typical example results are presented to illustrate that the methodology adopted is able to provide realistic velocity and displacement records with much smaller number of zero pads the present strong motion database of corrected acceleration records will be useful for analyzing the ground motion characteristics of engineering importance developing prediction equations for various strong motion parameters and calibrating the seismological source model approach for ground motion simulation for seismically active and risk prone areas of india

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

geology of the bozdag area central menderes massif sw turkey pan african basement and alpine deformation the menderes massif consists of a precambrian core series that preserves evidence for a polymetamorphic history and a paleozoic mesozoic cover series that experienced only the alpine tectonometamorphic evolution structural petrographic and geochronologic investigations in the central menderes massif demonstrate that a part of the metamorphic and structural evolution of the precambrian basement is older than the undeformed 551 1 4 ma old birgi metagranite and b inferred alpine fabrics overprinting the cover series largely have the same attitudes as the old structures in the much older core series the inferred alpine fabrics include both contractional and extensional structures contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the core and cover series and generated an inverted metamorphic sequence by north directed thrusting during alpine extension most of the south dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions

geology structure and lithostratigraphic framework of the rakhine coastal ranges in western myanmar implications for the collision of the india plate and west myanmar block abstract termination of the eastward subduction of the indian plate is inferred to be latest eocene in age in the north easternmost assam and myanmar regions followed by the collision of the indian continent with the asia plate this event is typically represented by the underthrusting of the middle and upper eocene sylhet formation which was deposited on the western margin of india plate beneath the eocene disang formation while the northern margin of india collided against eurasia and tibet along a zone which lies south of the triassic jurassic deep marine sediments and yarlung ophiolite in the latest eocene later movement of the naga and disang thrusts to the east suggests convergence between the burma and indian plates as both moved northwards and india rotated anti clockwise after the collision the stratigraphic records indicate that an early oligocene emplacement of the deep marine sedimentary sequence on the india plate probably within 10 ma interval age during the india asia collision and moved northwards oblique convergence could also have resulted from possible clockwise rotation of se asia relative to the indian plate accompanying the eastward translation of south china along strike slip faults the deformation of western and southern myanmar is still active today with under thrusting related to subduction the basement of the indian plate below the indo myanmar ranges is moving towards the north with respect to the rest of asia this study provides the syn and post deformation history of neogene siliciclastic sequences of the rakhine coastal ranges in western myanmar allowing structural and kinematic interpretation of the oblique subduction and collision history the growth of these folds and faults and associated uplift were resulted from the tectonic processes and evolution in which the burma plate was wedged in the subduction zone and dragged towards the north with the indian plate between internal n s trending right lateral shearing and external e w shortening

discovered and undiscovered gold endowment of turkey a quantitative mineral resource assessment using gis and rank statistical analysis an assessment of the discovered and undiscovered gold endowment of turkey a prolific sector in the tethyan metallogenic belt is developed from a comprehensive geographic information system database containing 402 gold deposits and prospects the majority of the gold deposits and prospects are epithermal porphyry volcanic associated massive sulfides orogenic gold and skarn systems these five major deposit types form more than 90 of the known gold deposits and prospects just 87 corresponding to 21 6 of the deposits and prospects in the data set have current calculated gold reserve and or resources containing a total of 54 885 moz au current gold reserves of the country are 21 447 moz constituting 39 1 of the total gold resources of which 17 1 moz gold are contained in four deposits out of these 87 deposits and prospects only 27 contain significant gold reserve and or resources defined as equal to or more than 0 32 moz or 10 tons au and contain 91 8 of the total gold endowment of the country the cumulative frequency distribution model of the gold endowment of turkey abides by log normal distribution observed and estimated 10th 50th median and 90th percentiles of the data are 0 0046 moz 0 0045 moz estimated 0 1030 moz 0 0875 moz and 1 4969 moz 1 6938 moz respectively the 99th percentile of the data is 7 6444 moz 18 9636 moz the arithmetic mean of the known gold endowment is 0 657 moz and the swanson mean size is 0 492 moz the arithmetic mean of the 27 significant gold deposit or prospects is 1 94 moz zipf s law estimates of the undiscovered residual gold resources of turkey are based on the current size of the largest rank 1 gold deposit of turkey which is the kisladag porphyry deposit that has 17 481 moz gold endowment including past production zipf s law estimates a total of 88 261 moz natural or total gold endowment 57 133 moz or 65 of which has already been found this predicts at least 31 128 moz residual or undiscovered gold resources to be found in turkey though the lack of full delineation of the rank 1 deposit kisladag means that this figure is very conservative

menderes massif western turkey structural metamorphic and magmatic evolution a synthesis the menderes massif covers large areas in western turkey the better understanding of its tectono metamorphic history would provide insight for the alpine evolution of western turkey and the entire eastern mediterranean region this paper summarizes the available literature on the metamorphic rocks of western turkey and that of the menderes massif with special reference and emphasis to the papers presented in the special issue

oblique subduction of a newtonian fluid slab a newtonian fluid model is proposed to describe the oblique subduction of a planar 2 d slab the slab is assumed to subduct in response to the ridge push force exerted along the trench the slab pull force at the downdip of the slab the gravitational body force within the slab and the frictional resistance force at the upper surface of the slab because the slab motion along strike is being resisted by the frictional resistance at the interplate coupling area while the slab motion along the trench normal is being maintained by the gravitational pulling the slab turns gradually toward the trench normal direction as it subducts this model offers an alternative explanation for earthquake slip partitioning the observation that the earthquake slip vectors deflect away from the relative plate motion direction toward the trench normal direction along most of the oblique subduction zones worldwide numerical models suggest that slip partitioning caused by slab deformation could be as much as 30 at 100 km downdip of the slab the slab viscosity the plate coupling width the interplate resistance coefficient the slab pull force and the gravitational body force are all important in determining the geometry of the slab subduction

subduction in the indo burma region is it still active the indo burma region which includes longitude 92 96 e latitude 20 26 n is a subduction zone where the indian plate underthrusts the south eastern asian plate but the nature of subduction is complex i examine here the distribution of the p t and b axes of 37 earthquakes the time period 1977 1995 depths 0 153 km and magnitudes mb 4 8 6 8 with respect to the geometry of the wadati benioif zone the analysis shows that the t axes are clustered close to the down dip direction of the subducting slab implying a predominant down dip tensional stress regime within the slab which is typical of intermediate depth seismicity of active subduction zones these results suggest that the subduction in the indo burma region is possibly active

structure of the european upper mantle revealed by adjoint tomography the structure of the european crust and upper mantle is precisely known only in limited regions a new tomographic model for the entire european upper mantle identifies northeastward subduction of the adria plate beneath the dinarides mountains volcanism related to the upwelling eifel hotspot and mantle delamination beneath scandinavia

low sulfidation type au ag mineralization at bergama izmir turkey abstract bergama the center of bergama county is located in western turkey and includes the villages of ovacik narlica and saganci the ovacik epithermal gold silver deposit is located in the western anatolian volcanic and extensional province adjacent to the ene trending bergama graben some 100 km north of the city of izmir gold of economic grades at the ovacik deposit reserves 4 19 mt at 7 6 g t occurs in epithermal quartz veins which display low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias alteration minerals at both ovacik and narlica are dominated by smectite mixed layer illite smectite chalcedonic quartz and adularia whereas major kaolinite and minor mixed layer smectite illite 13 4 a occur at saganci the total sulfide content at ovacik is low geochemical variations in altered wall rocks at ovacik and narlica are generally characterized by two fold enrichments in k rb cs and 25 to 93 depletions in sr ca mg na and even higher depletions 96 to 99 decrease in the quartz adularia vein zone lanthanum ce pr hf zr sm eu gd tb and ho also exhibit up to 50 depletions in the wall rock and even more so up to 90 depletion for la and nd in the vein structure wall rock enrichment in au ag as hg and sc is by factors of 60 150 88 8 and 3 respectively the ranges of ree in both the altered volcanic rocks and quartz adularia veins are wide and may reflect either significant mobilization of ree during alteration and mineralization or their dilution by the metasomatic processes from fresh volcanic rocks through montmorillonite illite adularia altered wallrock to quartz adularia veins high rb sr ratios in adularia illite altered areas are closely related to the presence of k rich alteration minerals low rb sr ratios and corresponding low k values at saganci are due to acid leaching of volcanic rocks positive correlation coefficients between au and ag pb zn cd cu and sb in epithermal quartz veins all of which are 0 51 are significant silver and sb are remarkably enriched at higher levels of the deposit no correlation occurs between au and as or ag and as the ovacik quartz in au ag bearing veins has 18o values ranging from 9 5 to 15 7 whereas d values of fluid inclusions in quartz range from 89 to 125 however the narlica quartz in au ag bearing veins returned 18o values ranging from 5 9 to 8 3 whereas the d values of fluid inclusion in quartz range from 82 to 99 18o results indicate that ore forming hydrothermal fluids at ovacik and narlica had 18oh2o values ranging from 2 9 to 3 5 average 0 24 and from 2 96 to 0 6 average 1 6 respectively they are thus 18o enriched in comparison with present day meteoric and hydrothermal meteoric waters 5 4 18o 18oh2o and d values suggest that mineralizing solutions were a mixture of meteoric and magmatic waters the 34s sulfide data at ovacik and narlica range from 2 1 to 5 3 average 1 7 and from 4 6 to 2 7 average 0 36 respectively these 34s sulfide values are consistent with a magmatic source for s

comment on paleomagnetic evidence for an inverse rotation history of western anatolia during the exhumation of menderes core complex by uzel et al earth planet sci lett 415 2015 108 125 abstract in a recent article published in epsl uzel et al 2015 reported a paleomagnetic evidence on various rock types from western anatolia it has been suggested that vertical axis rotations driven by the differential stretching along the izmir balikesir transfer zone ibtz were caused by slab detachment and slab tear processes at the northern edge of subducting african slab although the paper supplies high quality data regarding the geological evolution of western anatolia some points need to clarified in light of recently published data

analysis procedures at the international seismological centre abstract analysis at the international seismological centre isc falls into three main categories association location and quantification difficulties of association on a global scale are not always appreciated the isc currently analyses 40 50 events a day and as the first arrivals from any particular earthquake may span a time interval of up to 20 min readings from events occurring in different parts of the world may overlap considerably in time the present association algorithm depends on time only and results in many chance mis associations or even the synthesis of fictitious events at present these mis associations are rectified by seismologists intervention but full use of amplitude and period information could help to detect these errors automatically revision of locations follows standard least squares procedures based on jeffrey s method of uniform reduction and jeffreys bullen travel times locations are made from p phases only including crustal phases but other first arrivals and secondary phases are identified and residuals calculated if depth cannot be determined by geometric means a search is made for depth phases or failing this the depth is restrained to that given by another agency or to a conventional value no provision is made for local variations in travel time body wave magnitudes are allocated within the distance range 21 100 from reported readings of a and t or their ratio using gutenberg richter calibration curves surface wave magnitudes are calculated from the prague formula using reports of long period a and t in the distance range 5 160 but only values from stations at distances of 20 or more are used to determine an average ms for a particular event there is no provision for the determination of local magnitude other than to reproduce values assigned by local agencies improvements in these procedures could be made through the automatic association of station readings the introduction of local travel times and better determination of earthquake size particularly for local events

crustal phases in earthquake location for crustal earthquakes of moderate or large size the first reported phases at distant stations are usually the first predicted by the crustal model used for smaller events however or for stations at larger distances the first phase detected is often a later crustal phase of larger amplitude this may be eitherpg which travels entirely in the upper crustal layer with a velocity of about 5 6 km s orp with a path mainly in the lower crustal layer at a velocity of about 6 7 km s many earthquake location programs do not take account of these phases and treat their arrivals as if they were the earlier phasepn at the international seismological centre we re identify up to 200 crustal phases each month this often results in significant improvement in position the direct determination of depth or even the obtaining of a formal solution where none was possible before we find that these re identifications are needed in most continental areas of the world and that the original crustal model of jeffreys and bullen still remains a useful standard

small scale heterogeneities below the grafenberg array germany from seismic wavefield fluctuations of hindu kush events summary small scale elastic heterogeneities 5 km are found in the upper lithosphere under neath the grafenberg array southeast germany the results are based on the analysis of broadband recordings of 17 intermediate depth 201 272 km events from the hindu kush region the wavefront of the first p arrival and the following 40 s coda are separated into coherent and incoherent scattered parts in the frequency range from 0 05 to 5 hz the frequency dependent intensities of the mean and fluctuation wavefields are used to describe the scattering characteristics of the lithosphere underneath the receivers it is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below approximately 1 5 2 5 hz and a strong fluctuation regime starting at 2 0 2 5 hz and continuing to higher frequencies in order to explain the observed wavefield fluctuations an approach with seismic scattering at random media type structures is proposed the preferred model contains heterogeneities with 3 7 per cent perturbations in seismic velocity and correlation lengths of 0 6 4 8 km in the crust this is compatible with models from active seismic experiments scattering in the lithospheric mantle is not required but cannot be excluded at weak velocity contrasts 3 per cent

assessment of earthquake location accuracy and confidence region estimates using known nuclear tests i have used the known epicenters and depths of 307 nuclear tests at the nevada test site nts and 75 tests at the east kazakhstan test site to compare the distances between actual and calculated hypocenters mislocations with calculated location confidence limits errors each test was located using its isc compiled p first arrivals a starting depth of 33 km and the iasp91 velocity model i also applied azimuth and incident angle dependent station corrections to the arrival times the most accurately located tests are those at the kazakhstan test site where all of the mislocations in latitude and longitude are less than 10 km and 90 of the depth mislocations are less than 20 km bayesian confidence limits calculated from the least squares covariance matrix satisfactorily account for these mislocations at the nevada test site 90 of the mislocations are less than 9 km in longitude 15 km in latitude and 33 km in depth the overestimates in depth are compensated for by origin times that are 2 to 5 sec late the larger mislocations at nts occur in spite of the fact that the closest recording sites are less than 200 km away compared to 1800 km away at the kazakhstan test site a significant fraction of the depth mislocations at nts are much larger than their calculated errors i interpret this failure of the calculated errors to adequately account for the nts mislocations as being due to systematically late arrivals at northwestern american stations relative to the predicted iasp91 values by using a locally determined three layer velocity model for the travel times of phases recorded at distances of less than 1500 km i was able to reduce 90 of the depth mislocations to less than 11 km as well as significantly reducing the latitude longitude and origin time mislocations i conclude that differences between the iasp91 model and velocities in the vicinity of the explosions may introduce a significant bias into the determined depths of nuclear tests a similar bias would therefore be expected in the similarly determined depths of shallow earthquakes

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

deformation of western turkey from a combination of permanent and campaign gps data limits to block like behavior 1 we present a new geodetic velocity field covering western turkey south of the north anatolian fault our velocity field is derived from a combination of continuously recording gps stations operating since 2003 survey type gps measurements carried out in the period 1997 2005 and velocities from reilinger et al 2006 the velocity field indicates that western turkey currently undergoes extension whose rate increases from the anatolia plateau to the aegean coast the overall extension in westernmost turkey is about 20 mm yr making it one of the fastest areas of continental extension in the world we test whether the observed deformation is better represented by the rotation of crustal blocks or by more distributed deformation while no deformation is detected in the central anatolian plateau we observe a deformation field west of the plateau that cannot be explained by block models unless the blocks are so small as to be essentially indistinguishable from a continuum although concentration of strain rates up to 140 nstrain yr are found across the major grabens strain rates above 50 nstrain yr are found throughout western turkey the distributions of topography and crustal thickness in western turkey agree with the distributions expected if the crust there had a constant thickness at 5 ma equal to that of the present central anatolian plateau and had subsequently been thinned at the present day distribution of strain rates our results therefore suggest that extensional strain affects the whole continental lithosphere of western turkey rather than being restricted to a small number of block boundaries

tracing deep thermal water circulation systems in the e w trending buyuk menderes graben western turkey abstract we present information on the spatial variation of helium isotope ratios and several conservative geochemical constituents that serve as natural tracers to identify thermal water flow systems along the e w trending buyuk menderes graben the air normalized r r a ratios where r sample 3 he 4 he and r a air 3 he 4 he of geothermal fluids in the graben range from 3 69 to 0 2 r r a ratios of the high temperature fluids display regular variation along the graben from high mantle values in the east to low crustal values in the west the highest r r a ratios showing significant mantle he signatures occur at the eastern segment of the graben in the central section r r a ratios are lower and vary between 1 82 and 1 14 the lowest ratio of 0 20 r a indicating a value of high crustal helium up to 98 was observed in the germencik field where one of the highest temperatures recorded was 232 c at the western segment of the graben a regional variation is also apparent in the co 2 he systematics mantle derived carbon proportions were found to be generally less than 2 but similar to the r r a ratios the higher mantle carbon proportions occur at the eastern segment of the graben the spatial distribution of all the data points over the entire extent of the graben shows a regularly decreasing trend of mantle derived he and co 2 contributions toward the west these results were interpreted as a progressive dilution process of mantle volatiles resulting from the systematic addition of 3 he depleted crustal co 2 components finally because the r r a ratios of geothermal fluids in the graben decrease continuously in e to w direction we propose a continuous dilution process involving the addition of crustal radiogenic 4 he associated with deep circulating fluid flow this conclusion is compatible with the b and cl concentrations of the thermal waters that show a westward increasing trend this trend appears to be controlled by water rock interaction and may be linked to a possible thermal water circulation system trending from e to w toward the aegean sea

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

the relationship between wadati benioff zone geometry and p t and b axes of intermediate and deep focus earthquakes for 865 earthquakes with focal depths exceeding 90 km this paper presents a concise global summary of the distributions of p t and b axes of their focal mechanisms with respect to the downdip along strike and normal axes of wadati benioff zones the focal mechanisms are best double couple solutions for the centroid moment tensors reported by the harvard group with the p t and b axes corresponding to the principal axes of the individual moment tensors we find as did previous investigators that events below 300 km have predominantly downdip p axes with 50 of all p axes of deep focus events lying within 28 of downdip for events between 90 and 300 km depth there are regional differences but most regions possess events with nearly downdip p axes or events with nearly downdip t axes in almost all regions having downdip p or t axes bingham statistics show that the greatest concentration of p or t axes lies somewhat below the plane of the wadati benioff zone for events of all focal depths in nearly all regions b axes cluster along the strike direction with 50 occurring within 38 of the strike from these regional results we define a typical focal mechanism as one having the b axis within 30 of the along strike and having either the t or p axis within 30 of the downdip such a focal mechanism might occur in response to a stress tensor having its greatest or least principal stresses channeled approximately along the downdip direction of the subducting slab with the intermediate principal stress lying horizontally within the slab controlled possibly by slab bending however by this criterion only 29 of the focal mechanisms for deep and intermediate events are typical thus the majority of the individual events cannot be explained simply as occurring in response to a downdip and slab normal greatest and least principal stress system with a horizontal along strike intermediate principal stress a few regions such as java and the marianas are clearly anomalous in that they possess significantly fewer typical focal mechanisms than do most other regions

collision of the ganges brahmaputra delta with the burma arc implications for earthquake hazard abstract we take a fresh look at the topography structure and seismicity of the ganges brahmaputra delta gbd burma arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential the gbd the world s largest delta has been built from sediments eroded from the himalayan collision these sediments prograded the continental margin of the indian subcontinent by 400 km forming a huge sediment pile that is now entering the burma arc subduction zone subduction of oceanic lithosphere with 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land the prism starts at an apex south of the gbd shelf edge at 18 n and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit the front of the prism is blind buried by the gbd sediments thus the deformation front extends 100 km west of the surface fold belt beneath the comilla tract which is uplifted by 3 4 m relative to the delta this accretionary prism has the lowest surface slope of any active subduction zone the gradient of the prism is only 0 1 rising to 0 5 in the forearc region to the east this low slope is consistent with the high level of overpressure found in the subsurface and indicates a very weak detachment since its onset the collision of the gbd and burma arc has expanded westward at 2 cm yr and propagated southwards at 5 cm yr seismic hazard in the gbd is largely unknown intermediate size earthquakes are associated with surface ruptures and fold growth in the external part of the prism however the possibility of large subduction ruptures has not been accounted for and may be higher than generally believed although sediment clogged systems are thought to not be able to sustain the stresses and strain weakening behavior required for great earthquakes some of the largest known earthquakes have occurred in heavily sedimented subduction zones a large earthquake in 1762 ruptured 250 km of the southern part of the gbd suggesting large earthquakes are possible there a large but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism and is the only known candidate for a rupture of the plate boundary along the subaerial part of the gbd burma arc collision zone

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

helium isotope variations in turkey relationship to tectonics volcanism and recent seismic activities the distribution of helium isotope ratios in the various tectonic provinces of turkey is examined through a synthesis of previously published data and the results of a recent survey along the north anatolian fault zone nafz following the catastrophic 1999 earthquakes the r ra values where r sample 3he 4he and ra air 3he 4he cover a wide range from 0 05 to 7 87 and the mantle derived helium is clearly identified in most locations the mantle derived component is high 50 of total he in a regions of central and eastern anatolia both of which are associated with historically active volcanoes and b the seismically active west to central segment of nafz while the mantle contribution reaches a maximum at nemrut volcano in eastern anatolia a region of dominantly compressional tectonics and with moderate enthalpy geothermal fields it is relatively low 50 in the western anatolian extensional province even though this region has the highest geothermal potential the average 3he enthalpy ratios estimated for the different provinces suggest lithospheric stretching and rise of the geotherm as the major mechanism of high heat flow yet limited intrusive activity in western anatolia is suggested as the reason for the comparatively low he additions and consequently low 1 7 106 atoms j 3he enthalpy ratios a more extensive magmatic activity appears to be responsible for the greater input of both heat and helium in eastern and central anatolia with intra province 3he enthalpy variations from 3 1 106 atoms j in eastern to 0 25 106 atoms j in central anatolia reflecting the ageing of hydro magmatic systems the relatively high 3he concentrations in low enthalpy waters of northern anatolia 2 8 106 atoms j are particularly significant since there is no evidence of volcanic activity associated with the strike slip motion along the seismically active segment of nafz continuous monitoring of he isotope compositions along nafz should lead to a better understanding of this apparent anomaly as well as the relationship if any between he isotope variations and seismic activities in this region

curie point depths based on spectrum analysis of aeromagnetic data west anatolian extensional province turkey the curie point depth map of western anatolia was constituted from spectral analysis of the aeromagnetic data the curie point depth values from 53 overlapping blocks 90 90 km in size have been estimated from the band pass filtered data the slope of the longest wavelength part of the radially averaged log power spectrum divided by the radial frequency produced the depth to the centroid z0 for the deepest crustal block the depth to the top zt was obtained by the slope of the second longest wavelength part of the spectrum from these depths the curie point depth was then calculated by using zb 2z0 zt the curie point depth estimates for western anatolia range between 8 2 and 19 9 km

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

regional heat flow in western anatolia using silica temperature estimates from thermal springs regional trends of variation of heat flow in western anatolia have been outlined using the silica temperature estimator on thermal springs silica heat flow values from 187 springs have been calculated the data are corrected for local long term mean annual surface temperature a mean value of heat flow for the western part of anatolia of 107 45 mw m 2 has been obtained which is about 60 above the world average the silica heat flow data are compared with available conventional heat flow values for this region a general agreement is observed and new patterns are recognized a close association exists between areas of high silica heat flow values above 100 mw m 2 and areas of tertiary and younger volcanism high heat flow is also observed in palaeozoic units of the menderes massif which is under tensional stress the highest heat flow estimate of 247 mw m 2 is obtained near gediz 38 57 n 29 13 2 e this area is part of a seismically active region and is located near a middle eocene subduction zone which is an area of later collision tectonics the new heat flow data from western anatolia improve our knowledge of the thermal conditions within the crust this information is important for the analysis of various geophysical and geological phenomena including seismicity

the geoelectrical structure of northwestern anatolia turkey the magnetotelluric method has been employed to generate a geoelectrical model that will reveal the rich geological pattern and dynamic character of western and northwestern anatolia turkey magnetotelluric data were collected from 53 sites along a profile of 290 km from the dardanelles to the alasehir graben magnetotelluric data were in the range of 0 00055 hz to 320 hz the models were obtained through 2 d joint inversion of transverse electric and transverse magnetic modes lateral changes in geoelectrical models are verified by using gravity and magnetic data in addition some of the seismological data presented here agree with proposed models that suggest a brittle ductile structure boundary at a depth of 20 km generally speaking a regional extensional regime caused reduction in the thickness of the crust and consequent uplift towards the south the constructed model delineates the western part of the north anatolian fault zone along the biga peninsula the current patterns of volcanic activity on the biga peninsula and at kula are related to conductive spots presented in the models the border of the gordes basin located between the izmir ankara suture zone and the menderes massif is also well delineated the north anatolian fault zone presents a pattern in which density and susceptibility anomalies attain relatively high values fillings covering most of the surface have lower density and susceptibility values than those of underlying structures

tectonic significance of synextensional ductile shear zones within the early miocene alacamdag granites northwestern turkey synextensional granitoids may have significant structural features leading to the understanding of the evolution of extended orogenic belts one of the highly extended regions the aegean region includes a number of metamorphic core complexes and synextensional granitoids that developed following the alpine collisional events the alacamdag area in northwestern turkey is one of the key areas where miocene granites crop out along the boundary of various tectonic units structural data from the early miocene alacamdag granites demonstrated two different deformation patterns that may provide insights into the development of granitic intrusions and metamorphic core complexes 1 steeply dipping ductile shear zones caused emplacement of syn tectonic granite stocks they include kinematic indicators of a sinistral top to the sw displacement this zone has also juxtaposed the izmir ankara zone and the menderes massif in the west and east respectively 2 gently dipping ductile shear zones have developed within the granitic stocks that intruded the schists of the menderes massif on the structurally lower parts kinematic data from the foliated granites indicate a top to the ne displacement which can be correlated with the direction of the hanging wall movement documented from the simav and kazdag metamorphic core complexes the gently dipping shear zones indicate the presence of a detachment fault between the menderes massif and the structurally overlying izmir ankara zone mesoscopic to map scale folds in the shallow dipping shear zones of the alacamdag area were interpreted to have been caused by coupling between ne sw stretching and the accompanying nw se shortening of ductilely deformed crust during early miocene times one of the ne trending shear zones fed by granitic magmas was interpreted to form the northeastern part of a sinistral wrench corridor which caused differential stretching between the cycladic and the menderes massifs this crustal scale wrench corridor the izmir balikesir transfer zone may have controlled the asymmetrical and symmetrical extensions in the orogenic domains the combination of the retreat of the aegean subduction zone and the lateral slab segmentation leading to the sinistral oblique slip tearing within the eurasian upper plate appears to be a plausible mechanism for the development of such extensive ne trending shear zones in the aegean region

source parameters of earthquakes and intraplate deformation beneath the shillong plateau and the northern indoburman ranges we determined the fault plane solutions and focal depths of 17 earthquakes beneath the shillong plateau and the northern indoburman ranges by combining results from the inversion of long period p and sh waveforms and amplitudes from polarities of first motions and from the identification of pp and sp phases on short period seismograms fault plane solutions of 15 earthquakes show mixtures of thrust and strike slip faulting but the p axes for these events are nearly horizontal and consistently oriented north northeast south southwest all of these earthquakes occurred at depths greater than 29 km beneath the shillong plateau one event occurred at a depth of 52 km the relatively large depths for earthquakes in an intraplate setting suggest that the indian lithosphere in this area is especially cold earthquakes beneath the northern indoburman ranges define a gently east southeast dipping zone from 30 to 45 km beneath the bengal basin to 40 to 90 km beneath the ranges this zone seems to steepen and connect with the zone of intermediate depth seismicity that dips eastward beneath burma these earthquakes cannot have occurred along the interface between a subducting indian plate and the overriding indoburman lithosphere because the p axes not the nodal planes are parallel to the north south trending seismic zone although a couple of the earthquakes might have occurred within the indoburman lithosphere most of this seismicity seems to have occurred within the indian plate recently and currently being subducted eastward beneath the indoburman ranges the consistent north northeast trend of the p axes implies that the orientation of maximum compressional strain in the indian plate throughout its northeastern pan is nearly perpendicular to that responsible for roughly north south trending folds of the indoburman ranges thus either recently in geologic time since 1 ma the orientation of maximum compression changed dramatically or more likely the deformation in the indoburman ranges is decoupled from that in the underlying indian plate meanwhile the seemingly identical northward displacement of india and the indoburman ranges with respect to south china must be accommodated farther east along the sagaing and other faults

ductile brittle transition along the alasehir detachment fault and its structural relationship with the simav detachment fault menderes massif western turkey abstract western turkey has experienced extensional deformation since the tertiary an early phase of extensional deformation resulted in the formation of detachment faults in the northern part of the menderes massif the alasehir and simav detachment faults the footwalls of these two detachment faults are mid crustal level rocks the alasehir detachment fault developed in metamorphic rocks and in a syn extensional intrusion the salihli granodiorite the salihli granodiorite shows a gradual change from undeformed isotropic granodiorite to protomylonite mylonite and ultramylonite towards its upper structural levels the deformed granodiorite in turn grades into a cataclastic zone whose uppermost part is the alasehir detachment surface this gradual upward change from the undeformed granodiorite to a brittlely deformed detachment surface suggests that tertiary extension resulted in a ductile deformation at depth and the ductilely deformed granitoids were brought to shallower depths where they were brittlely deformed the metamorphic wall rocks of the intrusion are also mylonitized structurally upward a similar transition has also been found in the footwall of the simav detachment fault the upper part of which is also a cataclastic zone leading to the simav detachment fault separating the low grade metamorphic rocks and or non metamorphic rocks in its hanging wall from mainly high grade metamorphic rocks and syn tectonic granitoids in its footwall during ductile extension greenschist facies grade mylonitic deformation developed in the metamorphic rocks and the granitoids shear sense indicators along the two shear zones show top to n ne sense shear consistent with the regional cenozoic extension direction in western turkey available radiometric age data from the granitoids in the footwall of the two detachment faults suggest that the cenozoic extension in western turkey was initiated in oligocene to early miocene and the simav detachment fault is older than the alasehir detachment fault extensional features of these detachment faults suggest that the simav detachment fault characterise the earlier stage of the tertiary extensional tectonics of the menderes massif and later stage of this deformation resulted in the development of the alasehir detachment fault