tectono stratigraphy of the cankiri basin late cretaceous to early miocene evolution of the neotethyan suture zone in turkey the cankoro basin straddles the izmir ankara erzincan suture zone which demar cates the former position of the northern branch of the neotethys it includes more than 3 km of pre middle miocene in fill related to late cretaceous to pre middle miocene evolution of the region the basin has developed on the upper cretaceous subduction complex and arc related basins of the neotethys ocean the basin fill includes an upper cretaceous forearc sequence over lain by paleocene with a local unconformity the upper cretaceous configuration of the cankoro basin is interpreted as a part of a forearc basin the paleocene and younger history is interpreted as a foreland sequence dominated by progressively southwards migrated depocenters in front of southward migrating thrust faults upon which a series of piggy back basins were developed ter mination of the forearc setting and beginning of foreland basin conditions indicates complete sub duction of the neotethyan oceanic crust and onset of collision between the pontides laurasia and the taurides gondwana in the paleocene thrusting and related sedimentation continued until the aquitanian early miocene

structural evolution of the tuzgolu basin in central anatolia turkey abstract the central anatolian segment of the alpine himalayan orogen contains interior basins the largest of which is the tuzgolu salt lake basin 20 000 km2 it is bounded on the east by the tuzgolu salt lake fault zone and on the west by the yeniceoba and cihanbeyli fault zones structural stratigraphic and sedimentologic evidence suggests that the tuzgolu basin started as a fault controlled basin during late maastrichtian tectonism when the present day northwest trending faults that bound the basin were initiated these faults may have been formed as normal faults suggesting extension or strike slip faults with a normal component of movement indicating a large transtension at the time of their initiation the late maastrichtian faults were reactivated as strike slip faults in response to late eocene compression in the region that produced the central anatolian thrust belt to the north and the late eocene south dipping thrust faults of the ulukisla basin to the south this reactivation is su

late surge glacial conditions on bakaninbreen svalbard and implications for surge termination 1 bakaninbreen is a polythermal glacier in southern spitsbergen svalbard that last surged between 1985 and 1995 seismic reflection data were acquired during early quiescence in spring 1998 just upstream of the surge front the results were combined with complementary ground penetrating radar data to investigate the glacial structure and basal conditions we find no difference between the ice thickness values determined from the seismic and radar methods suggesting that any layer of basal ice cannot be greater than 5 m thick interpretation of the amplitude of the seismic reflections indicates the presence of permafrost close to the glacier base a thin layer of thawed deforming sediment separates the glacier from this underlying permafrost in an area just upstream of the surge front the permafrost becomes discontinuous and may even be absent the ice being underlain by 10 15 m of thawed sediments overlying deeper bedrock high pressure water is believed to have been required to maintain the propagation of the surge and this area of thawed sediment is interpreted as a route for that water to escape from the basal system when the surge front passed over this thawed bed the escaping water reduced the pressure in the subglacial hydraulic system initiating the termination of the surge surge termination was therefore primarily controlled by the presurge permafrost distribution beneath the glacier rather than any feature of the surge itself this termination mechanism is probably limited to surges in polythermal glaciers but the techniques used may have wider glaciological applications

radio echo sounding studies of englacial water movement in variegated glacier alaska une crue glaciaire du variegated a ete enregistree a l aide d un emetteur mono impulsion de 3mhz les discontinuites intraglaciaires ont ete observees dans le domaine des 12 a 30 mhz les changements dans la forme des echos sont interpretes en terme de redistribution de l eau dans les canaux glaciaires et les cavites reliees au lit a quelque distance a l aval

strike slip tectonics and granite petrogenesis transpression is a process that thickens the crust and therefore in obliquely convergent orogens as in normally convergent orogens there is the potential to generate granitic melts individual transcurrent shear zones may not only control the ascent paths siting and emplacement mechanisms of plutons but they may also cause the genesis of the granitoids themselves two contrasting situations are examined in the hercynian shear zones of iberia thickening together with hydrous fluxing along shear zones created intracrustal wet melting of fertile gondwanan sediments to produce syntectonic granites in the northern part of the british caledonides the association of compositionally expanded granitoids with a major mantle component and transcurrent shear zones may be explained by melting of continental crust at the lower limits of crustal transpressional faults detaching into the moho

single zircon evaporation ages and rb sr dating of four major variscan batholiths of the urals abstract using single zircon stepwise evaporation 207pb 206pb and whole rock rb sr methods we have dated the main facies of four variscan batholiths of the urals syrostan verkhisetsk murzinka and dzhabyk from different geodynamic environments syrostan and verkhisetsk are subduction related batholiths of the accreted terrains in the west closely related to the main uralian fault syrostan is composed of metaluminous epidote bearing synkinematic gabbros diorites and granodiorites 87sr 86srinit 0 7029 0 7035 dated at 333 3 ma and postkinematic granites 87sr 86srinit 0 7035 0 7038 dated at 327 2 ma whose zircons occasionally have cores with an age of 1800 ma the presence of these relict zircon cores probably indicates the contribution of russian platform materials to subduction related magmas verkhisetsk 250 km north of syrostan comprises deformed amphibole and epidote bearing granodiorites 87sr 86srinit 0 7042 0 7044 dated at 318 3 ma and undeformed granites 87sr 86srinit 0 7044 that record a long history of recurrent partial melting and crystallization from 310 ma to 275 ma murzinka and dzhabyk are continental type batholiths in the east uralian zone dzhabyk in the southern urals postdates the kartali seismic reflector and is composed of several coeval intrusions of metaluminous monzonites 87sr 86srinit 0 7049 and peraluminous granitoids 87sr 86srinit 0 7043 dated at 291 4 ma murzinka 600 km north of dzhabyk also comprises two coeval intrusions of peraluminous granites with different chemical and isotopic compositions 87sr 86srinit 0 7045 and 0 7093 dated at 254 5 ma these data indicate that the age of cessation of movements along the main uralian fault and the transition from subduction to continent continent collision migrated northwards the age of granite magmatism also migrated gradually northwards and eastwards suggesting an oblique convergence with a se movement of the converging continent so that the closure of the uralian palaeo ocean started in the south and then migrated progressively northwards

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

the permian emplacement of granite gneiss complexes in the east uralian zone and implications on the geodynamics of the uralides abstract in the southern uralides permian magmatism tectonism and metamorphism concentrate in the east uralian zone such that this zone provides the key for understanding of the late phase of the uralian orogeny carboniferous distal marine sediments and lenses of amphibolite serpentinite associations show that the lithospheric precursor of the east uralian zone was largely oceanic in the latest carboniferous the kazakhstanides collided with the uralides but relics of the oceanic basin between both units were conserved and accommodated a large part of permian deformation structural data provide evidence that a nw directed plate convergence was partitioned in w directed compression and n directed strike slip additionally they show that granitic melts which had formed in the thickened crust of the uralides migrated eastward into the strike slip belt of the east uralian zone also the exhumation of the plutonic rocks occurred eastward oblique to the direction of regional extension indicating that upper crust and lower crust deformed mainly decoupled from one another we suggest that the emplacement of the granite gneiss complexes contributed significantly to the consolidation of the orogenic crust in the eastern urals

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

a stationary impulse radar system for autonomous deployment in cold and temperate environments l mingo acknowledges the sr ed tax incentive program of the cra for offsetting some r d costs of the sipr g flowers and d bigelow are grateful to nserc cfi csa nstp pcsp and sfu for funding kluane first nation yukon government and parks canada for access to yukon field sites and s williams l goodwin a pulwicki j crompton f beaud and canadian astronaut d saint jacques for support and field assistance c schoof and c rada provided time lapse imagery and 2017 water pressure data a crawford and d mueller acknowledge funding from nserc transport canada pkc nstp and the garfield weston foundation as well as support from arctic net the ccgs amundsen crew and pilots o talbot a roy and g carpentier

the formation of gneisses in the southern east uralian zone a result of late palaeozoic granite ascent and emplacement abstract geochemical and radiogenic age data are incompatible with the idea that the gneiss complexes of the east uralian zone are microcontinental blocks that collided with the magnitogorsk island arc during the uralian orogeny field and microstructural data from the dzhabyk and suunduk complexes presented in this paper enable us to suggest an alternative model that interprets the gneisses as deformed margins of the batholiths of the uralian granite axis the gneisses have been formed from a granitic protolith by a continuous fabric transformation on a retrograde metamorphic path all structures in the gneisses can be assigned to the ascent and emplacement of batholiths in an active strike slip belt

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

the post collisional stabilization of thickened crust in the southern urals abstract the urals are characterized by a depression of the moho to a depth of 57 km this structure is interpreted as a relic orogenic root which has been conserved because no significant post collisional processes occurred however there is evidence that voluminous post collisional magmatism affected the lower crust in this paper we use thermal finite element models to quantify the influence of the post collisional magmatism on the stabilization of the root we show that at least 70 of the heat producing elements migrated in granitic melts from the lower crust to the upper crust as a result the crustal heat flow reduced and the lithosphere could stabilize at a thickness of 180 km furthermore we propose that a granulite metamorphic event during the thermal relaxation of the collision zone prevented the 57 km thick crust from delamination these results strongly indicate that post collisional processes were necessary for the stabilization of the uralian crust and lithosphere

crustal rheology and faulting at strike slip plate boundaries 2 effects of lower crustal flow we present a numerical model of deformation at a strike slip plate boundary within a linear viscoelastic crust which is driven by far field plate motions and basal mantle velocities the crust is assumed to have uniform elastic properties but continuously varying viscosity as a function of depth brittle faulting is represented by static elastic dislocations that are imposed when stresses exceed a critical threshold for fracture or frictional sliding the locations and depth extents of faults in this model are not prespecified but instead are governed by stress evolution within the crust we find that when a primarily elastic upper crust is underlain by a low viscosity lower crustal layer the deformation zone broadens in time to encompass many parallel strike slip faults in an interacting network in contrast when the entire crust behaves elastically the deformation zone remains narrow and focused on a single plate bounding fault reflecting imposed mantle motions surface strain rate patterns within the interacting fault network are complex and reflect significant faulting related strain rate perturbations that decay over timescales of postseismic relaxation in the lower crust 10 100 years the fault network has a characteristic spacing with complex fault interactions and with the depth extents of faults increasing with time to a maximum depth governed by crustal rheology the maximum depth of faults is limited by stress relaxation and large scale viscous flow in the lower crust which confines brittle failure to shallow and midcrustal levels

protolith and deformation age of the gneiss plate of kartali in the southern east uralian zone the southern east uralian zone consists of granite gneiss complexes that are embedded in geological units with typical oceanic characteristics these gneisses have been interpreted as parts of a microcontinent that collided during the uralian orogeny the gneiss plate of kartali forms the south eastern part of the gneiss mantle surrounding the dzhabyk pluton its post collisional protolith age of 327 4 ma is inconsistent with the microcontinent model the deformation of the gneisses took place in 290 4 ma at the time of the intrusion of the dzhabyk magmas granites and gneisses cooled and were exhumed together therefore we interpret the gneiss complexes of the east uralian zone as marginal parts of the granitic batholiths that were deformed during the ascent and emplacement of the pluton from nd and sr isotope constraints we conclude that the magma source of the gneiss protolith was an island arc since no evidence for old continental crust has been discovered in the east uralian zone the uralian orogeny can no longer be interpreted as a continent island arc microcontinent collision instead the geochemical data presented within this paper indicate that the stacking and thrusting of island arc complexes played an important role in the uralian orogeny

structural framework of the bashkirian anticlinorium sw urals the bashkirian anticlinorium of the southwestern urals shows a much more complex structural architecture and tectonic evolution than previously known pre uralian proterozoic extensional and compressional structures controlled significantly the uralian tectonic convergence a long lasting proterozoic rift process created extensional basement structures and a riphean basin topography which influenced the formation of the western fold and thrust belt with inversion structures during the uralian deformation a complete orogenic cycle during cadomian times including terrane accretion at the eastern margin of the east european platform resulted in a high level cadomian basement complex which controlled the onset of uralian deformation and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the main uralian fault the uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes tectonic convergence started in the late devonian with ophiolite obduction tectonic accretion of basin and slope units and early flysch deposits zilair flysch the accretionary complex prograded from the se to the nw continuous nw se directed convergence resulted finally in the formation of an early orogenic wedge thrusting the cadomian basement complex onto the east european platform the main tectonic shortening was connected with these two stages and although not well constrained appears to be of late devonian to carboniferous age in the permian a final stage of e w compression is observed throughout the sw urals in the west the fold and thrust belt prograded to the west with reactivation of former extensional structures and minor shortening in the east this phase was related to intense back thrusting the east european platform was subducted beneath the magnitogorsk magmatic arc during the late paleozoic collision the thick and cold east european platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening tectonic stacking and high strain at its eastern margin whereas the first orogenic wedge is of thick skinned type with the involvement of crystalline basement even the later west directed wedge is not typically thin skinned as the depth of the basal detachment appears below 15 km and the involvement of archean basement can be assumed

structural controls of lode gold mineralization by mafic dykes in late paleozoic granitoids of the kochkar district southern urals russia the kochkar gold district in the east uralian zone of the southern urals is located in late paleozoic granite gneisses of the plast massif gold mineralization is associated with tabular quartz lodes that are preferentially developed along the margins of easterly trending mafic dykes fabric development indicates that dykes had a profound influence on the development of shear zones in granitoids ene and se trending dykes have been reactivated as dextral and sinistral oblique strike slip shear zones respectively forming a set of approximately conjugate shear zones related to the permian regional scale e w directed shortening dyke shear zone relationships in the plast massif are the result of strain refraction due to the presence of biotite rich incompetent dykes in more competent granite gneisses deformation and the formation of associated gold quartz lodes occurred close to peak metamorphic upper greenschist to lower amphibolite facies conditions strain refraction has resulted in partitioning of the bulk strain into a component of non coaxial mainly ductile shear in mafic dykes and a component of layer normal pure shear in surrounding granitoids where deformation was brittle ductile brittle fracturing in granitoids has resulted in the formation of fracture permeabilities adjacent to sheared dykes that together with the layer normal dilational component promoted the access of mineralizing fluids both ore controlling dykes and gold quartz lodes were subsequently overprinted by lower greenschist facies mainly brittle fault zones and associated hydrothermal alteration that post date gold mineralization

the isostatic state of the southern urals crust the uralide orogen in central russia is the focus of intense geoscientific investigations during recent years the international research is motivated by some unusual lithospheric features compared with other collisional belts including the preservation of a a collisional architecture with an orogenic root and a crustal thickness of 55 58 km and b large volumes of very low grade and non metamorphic oceanic crust and island arc rocks in the upper crust of a low relief mountain belt the latter cause anomalous gravity highs along the thickened crust and the isostatic equilibrium inside the uralides lithosphere as well as the overthrust high metamorphic rocks the integrated urseis 95 seismic experiment provides fundamentally new data revealing the lithospheric architecture of an intact paleozoic collisional orogen that allows the construction of density models in the urals lithosphere different velocity structures resolved by wide angle seismic experiments along both the urseis 95 and the troitsk profile they can be used to constrain lithospheric density models a first model consists of a deep subducted continental lower crust which has been highly eclogitized at depths of 60 90 km to a density of 3550 kg m3 the second model shows a slightly eclogitized lower crust underlying the uralide orogen with a crustal thickness of 60 km the eclogitized lower crust causes a too small impedance contrast to the lithospheric mantle resulting in a lack of reflectors in the area of the largest crustal thickness both models fit the measured gravity field analyzing the isostatic state of the southern urals lithosphere both density models are in isostatic equilibrium

late cretaceous to paleocene oroclinal bending in the central pontides turkey 1 the turkish pontide fold and thrust belt formed since the paleozoic and is an important element in the africa eurasia convergence and the resulting closure of the neo tethys ocean it has a peculiar arc shaped geometry in its central part along the black sea coast which may have resulted from oroclinal bending we have determined the vertical axis rotation history of this area using paleomagnetism on cretaceous to eocene rocks from 47 sites and critically analyzed previously published data we applied the same reliability criteria to all data our results show that late cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central pontides in the eastern pontides they show only local rotations paleocene to eocene rocks in the central and eastern pontides show no rotation we conclude that the central pontide northward arc shaped geometry results from oroclinal bending in latest cretaceous to earliest paleocene times the timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from neo tethys closure between the pontides and the metamorphic promontory of the anatolide tauride block earlier studies on the southerly located cankiri basin reveal that clockwise and counterclockwise rotations occurred in eocene oligocene times this implies that the entire region underwent continuous deformation from late cretaceous to eocene caused by convergence of the pontides and the anatolide tauride block with a southward moving deformation front deformation was first localized in the northern part of the central pontides until the paleocene resulting in oroclinal bending and from at least eocene times it shifted toward the cankiri basin region

the geological setting of lode gold deposits in the central southern urals a review the late paleozoic uralides represent one of the largest lode gold metallogenic provinces in the world in the southern urals gold distribution is heterogeneous and is confined mainly to two tectonostratigraphic zones namely the main uralian fault and the east uralian zone the important lode gold districts within and in the immediate hangingwall of the first order crustal suture of the main uralian fault are characterized by a complex tectonic history of earlier compressional tectonics involving thrusting folding and reverse faulting and later transcurrent shearing gold mineralization is hosted by second and third order brittle to brittle ductile strike slip faults that developed late during the kinematic history of the main uralian fault strike slip reactivation of earlier compressional structures was related to the late stage docking of the passive margin of the east european platform with island arc complexes of the southern urals an event that is tentatively related to changes in plate motion during the final stages of terrane accretion during the upper permian and lower triassic gold mineralization was controlled by the permeability characteristics of the hydrothermal conduits as well as by competence contrasts and geochemistry of the mainly volcanic host rocks mineralization occurred at relatively shallow crustal levels 2 6 km and largely post dates peak metamorphism of the host rocks the large and very large up to 300 to au gold deposits of the east uralian zone are hosted by upper paleozoic granitoid massifs gold mineralization is temporally associated with the main phase of regional scale compressional tectonics and granite plutonism during the upper carboniferous and lower permian controlling structures have a dominantly east west strike and occur as hybrid shear tensional vein systems in competent granitoids subjected to east west directed regional shortening deformation textures and alteration mineral assemblages indicate lower amphibolite facies conditions of mineralization close to peak metamorphic conditions that are associated with the mid permian regional metamorphism and tectonism gold deposits in the southern urals are therefore polygenetic and are temporally and genetically distinct in each of the two major mineralized tectonostratigraphic zones of this well preserved collisional orogenic belt the different timing of ore fluid generation and fluid discharge is interpreted to be the result of the different tectonic metamorphic and magmatic evolution of terranes in the southern urals

late eocene evolution of the cicekdagi basin central turkey syn sedimentary compression during microcontinent continent collision in central anatolia abstract the central anatolian crystalline complex cacc exposes metasediment rocks overlain by cretaceous ophiolites and intruded by granitoids following late cretaceous exhumation of its high grade metamorphic rocks the cacc started to collide with the central pontides of southern eurasia in the latest cretaceous to paleocene here we present the sedimentary stratigraphic and tectonic evolution of the cicekdagi basin located in the northwest of the cacc magnetostratigraphic dating supported by 40 ar 39 ar geochronology shows a late eocene basin age the basin fill unconformably overlies metamorphic basement in the south and ophiolites of the cacc in the north it consists of red conglomerates sandstones and siltstones which overlie a sequence of nummulitic limestones in the south these limestones are 10 m thick are underlain by a few meters of conglomerate unit unconformably covering the cacc metamorphics in the north the limestones are underlain by a 200 m thick sequence of volcanics and fine grained clastics intercalating with shallow marine black shales the upper eocene sediments of the cicekdagi basin were deformed into a syn anticline pair progressive unconformities in the northern flank and a rapid and persistent 180 switch in paleocurrent directions from southward to northward in the southern flank of the anticline demonstrate syn sedimentary folding we interpret the folding to result from a southward progression of the cankiri foreland basin as a result of ongoing collision between the cacc and the pontides

interpretation of radio echo returns from internal water bodies in variegated glacier alaska u s a des sondages radios ont revele la presence de cavites remplies d eau dans le glacier variegated alaska discussion sur l origine et les consequences glaciologiques de ces cavites

the effect of lower crustal flow on continental extension and passive margin formation the great variety of styles of continental extension may reflect different crustal thickness and thermal states of continental lithosphere during the initiation of rifting to investigate how these and other factors affect rifting and the development of passive continental margins we develop a simplified model of lithospheric extension we consider the evolution of extensional deformation for a three layer model lithosphere bounded laterally by much stronger lithosphere the cold part of the crust and mantle are treated as thin brittle plastic layers the lower crust is approximated as a thin viscous channel each brittle plastic layer can extend in only one location determined by the strength of the layer shear of the lower crust and buoyancy forces related to both crustal thickness variations and thermally induced density differences the lower crust flows in response to crustal thickness variations and is sheared when the loci of extension for the two brittle plastic layers are horizontally offset a situation we term shear decoupling as in previous studies we see three distinct patterns or modes of extensional deformation that occur under different sets of model parameters the core complex mode the wide rift mode and the narrow rift mode shear decoupling occurs only in cases with a crustal rheology at the weak end of the spectrum of laboratory estimated values we are aware of no observations that require that the upper crust and upper mantle strain at laterally displaced positions we show that for large magnitudes of extension there can be transitions between modes as inferred for some highly extended continental areas predicted patterns of crustal thickness and heat flow for some models are similar to observations at several rifted continental margins including very wide and asymmetric margins

radio and electrical measurements on glacial streams we discuss the suggestion that small under water transmitters might be used to illuminate the interior of major englacial water channels with radio waves once launched the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss receivers placed within the channels or at the glacier surface could be used to detect the signals they would provide valuable information about the connectivity of the water system the electrical conductivity of the water is of crucial importance a surface stream on storglachlren in sweden was found using a low frequency technique to have a conductivity of approximately 4 x 10 4 s m i although this is several hundred times higher than the conductivity of the surrounding glacier ice the contrast is not sufficient to permit us simply to use electrical con ductivity measurements to establish the connectivity of englacial water channels however the water conductivity is sufficiently small that under favourable circumstances radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel in a preliminary field experiment we demonstrated se mi quantitatively that radio waves do indeed propagate as expected at least in surface streams we conclude that under water radio transmitters could be of real practical value in the study of the englacial water system provided that sufficiently robust devices can be constructed in a subglacial channel however we expect the radio range would be much smaller the environment much harsher and the technique of less practical value

preliminary fission track results from the southern urals sterlitamak to magnitogorsk abstract results are reported from a pilot fission track study of a west east traverse across the southern urals from sterlitamak through to the dzhabyk granite east of magnitogorsk which was undertaken in order to study the low temperature 300 c thermotectonic post uralian history of the mountain belt the transect crosses the major tectonic units including the main uralian fault the suture zone which separates the east european craton from palaeozoic oceanic island arc and continental terranes of asia zircon fission track ages range from 226 ma to 604 ma in the foreland thrust and fold belt with a single age of 262 ma in the magnitogorsk zone an age grouping of about 250 ma for zircons on either side of the main uralian fault suggests that there has been no differential movement identifiable through fission track analysis along this line since the triassic the similarity of apatite ages ranging from 180 to 210 ma further verifies little differential movement within the footwall to the suture since the jurassic in the central part of the magnitogorsk zone apatite ages are older they are slightly annealed crystallisation cooling ages but further confirm that there has been only little tectonic activity since the triassic except in the east uralian zone apatite fission track analysis reveals variable denudation rates the highest rates occurred during the permo triassic ending at about 210 ma just prior to the final development of the jurassic peneplain this was followed possibly by a period of burial before final cooling exhumation from approximately middle cretaceous onwards

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

role of melt in the formation of a deep crustal compressive shear zone the maclaren glacier metamorphic belt south central alaska the maclaren glacier metamorphic belt is an exhumed portion of a deep crustal shear zone where hot upper amphibolite facies rocks were emplaced over cooler lower grade rocks it is located in south central alaska within the collision zone between terranes previously accreted to north america and the wrangellia superterrane crosscutting relationships and orientations of thin granitoid sills within the hanging wall show that melt was repeatedly intruded into the shear zone during overall compression in addition a 1 km thick tonalite sill the valdez creek tonalite was emplaced into the shear zone while it was active this conclusion is based on the presence of a well developed foliation within the sill which is concordant to the fabric of the shear zone the alignment and tiling of plagioclase laths the presence of highly strained mafic enclaves within a matrix which shows no evidence of any subsolidus deformation and the preservation of a delicate magmatic texture which indicates that a magmatic fluid was still present after deformation in the sill had ceased a one dimensional thermal model for sill shaped plutons of varying thicknesses which are emplaced into country rocks at different initial temperatures indicates that melt can be present for long periods of time in the deep crust 1 m y an important factor controlling the length of time that a sill remains molten is the temperature of the surrounding rocks which in the lower crust can be as high as the solidus temperature of granitoid melts if the amount of time for melt to crystallize is sufficiently long potentially large amounts of strain will be accommodated by zones containing melt due to the low strength of melt compared to rock in the maclaren glacier metamorphic belt the amount of time needed for the valdez creek tonalite to fully crystallize is calculated to be about 90 000 years this is a minimum value since the original thickness of the sill is not known nevertheless using the 90 000 year value and assuming that the bulk of convergence between north america and wrangellia was concentrated within the valdez creek tonalite a displacement of at least 10 km could have been accommodated across the sill while melt was present

tectonomagmatic evolution of bimodal plutons in the central anatolian crystalline complex turkey abstract the nw trending agacoren intrusive suite ais on the east side of the salt lake tuz golu turkey is part of a curvilinear volcanoplutonic complex along the western edge of the central anatolian crystalline complex cacc granitoids constitute the predominant lithological group within the ais and range in composition from monzonite through granite to alkali feldspar granite gabbroic rocks occur as irregular intrusive bodies with sinusoidal irregular contacts with the granitoid plutons and vary from dioritic compositions at the contacts to cumulate amphibole gabbros in their center these gabbroid to granitoid rocks are all subalkaline and display tholeiitic to calcalkaline affinities respectively modeling of the major element and trace element chemistry of the granitoids to gabbroids together with their field relations suggest that these rocks formed synchronously from a melt source that involved both mantle and crustal components mafic magmas were likely derived from a metasomatized u

reply to genc and yurur s comments on late cretaceous extensional denudation along a marble detachment fault zone in the kirsehir massif near kaman central turkey we appreciate the interest of dr yurdal genc and dr tekin yurur in the work we carried out in central turkey in our paper we presented a detailed structural study focused on one single fault zone located in the kaman area in the northwestern metamorphic massif of central anatolia the aim of our work was to provide clear structural evidence to assess the nature and kinematics of this fault zone and to test whether it could be held responsible for part of the exhumation of the high grade metamorphic rocks in the region we demonstrated that the kaman fault is an extensional detachment that was active in the late cretaceous and concluded that it was contemporaneous with late cretaceous extension and exhumation of metamorphic rocks of the central anatolian crystalline complex cacc documented previously this extensional phase has been discussed in numerous works such as the structural and metamorphic analysis from the southern nigde crystalline massif gautier et al 2002 whitney et al 2003 whitney et al 2007 and gautier et al 2008 structural and geochronological data from discrete shear zones across large magmatic intrusions in the north yozgat and the west agacoren of the cacc isik et al 2008 and isik 2009 and the tectonic evolution of the large basins surrounding the cacc e g the tuzgolu and sivas basins cemen et al 1999 and dirik et al 1999 following extension the region underwent compression during the paleogene due to the convergence and consequent collision between the cacc and the central pontides gorur et al 1984 gorur et al 1998 kaymakci et al 2000 kaymakci et al 2009 and meijers et al 2010 in contradiction to the generally accepted tectonic evolution for central anatolia genc and yurur 2010 recently proposed an alternative model based on inferences from digital elevation data and local field observations they interpreted the cenozoic tectonic regime of central anatolia to be dominated by extension associated with coeval compressional zones resulting from gravitational movements taking that into consideration genc and yurur have in their discussion listed several points that they consider to be incoherencies in this reply we answer each point addressed in the comment discussing the validity of our statements and data and taking the opportunity to clarify the ideas that the authors of the comment may have misunderstood

tectonic controls on metamorphism partial melting and intrusion timing and duration of regional metamorphism and magmatism in the nigde massif turkey protracted heating and melting of orogenic middle crust followed by emplacement of a syn extensional pluton during decompression and cooling are demonstrated for a metamorphic core complex in central turkey new geochronologic data for the nigde massif of the central anatolian crystalline complex document an interval of melting crystallization and pb loss at elevated ambient temperature 85 92 ma determined by u pb shrimp within a single sample of peraluminous granite crustal melting was syn to post peak metamorphism 725 c dated at 91 0 2 0 ma by shrimp analysis of zircon rims in sillimanite schist that is part of the country rock to the pluton metamorphic monazite in sillimanite schist yields a younger age of 84 7 0 7 ma for matrix grains and inclusions in garnet hornblende 40ar 39ar ages from amphibolites interlayered with the sillimanite schists coincide with the timing of emplacement of magma into metamorphic country rock that had experienced cooling and decompression to 12 km and 550 c the similarity of 40ar 39ar ages for biotite in the pluton 79 ma and hornblende 79 81 ma biotite 74 76 ma and muscovite 78 83 ma in the metamorphic country rock document rapid cooling 100 c my following intrusion the coincidence of the youngest u pb magmatic zircon ages and the oldest 40ar 39ar ages combined with structural evidence for normal sense shearing and tectonic unroofing in the late cretaceous suggests that intrusion was driven by extension we propose that crustal melting occurred in the middle crust during prograde metamorphism and or initial decompression and that ascent and emplacement of magma as a pluton were only triggered once extension occurred and removed upper crustal rocks

acoustic televiewer logging in glacier boreholes the acoustic televiewer is a geophysical logging instrument that is deployed in a water filled borehole and operated while trolling it generates a digital magnetically oriented image of the borehole wall that is developed from the amplitudes and transit times of acoustic waves emitted from the tool and reflected at the water wall interface the transit time data are also converted to radial distances from which cross sectional views of the borehole shape can be constructed because the televiewer is equipped with both a three component magnetometer and a two component inclinometer the borehole s trajectory in space is continuously recorded as well this instrument is routinely used in mining and hydrogeologic applications but in this investigation it was deployed in two boreholes drilled into upper fremont glacier wyoming u s a the acoustic images recorded in this glacial setting are not as clear as those typically obtained in rocks due to a lower reflection coefficient for water and ice than for water and rock results indicate that the depth and orientation of features intersecting the boreholes can be determined but that interpreting their physical nature is problematic and requires corroborating information from inspection of cores nevertheless these data can provide some insight into englacial structural characteristics additional information derived from the cross sectional geometry of the borehole as well as from its trajectory may also be useful in studies concerned with stress patterns and deformation processes

crustal architecture of the southern uralides from true amplitude processing of the urals seismic experiment and integrated studies urseis vibroseis profile true amplitude processing of the urals seismic experiment and integrated studies urseis vibroseis deep reflection seismic data acquired by the urseis consortium shows the southern uralide crust to be composed of four major blocks with distinctive reflection characteristics these blocks are juxtaposed along crustal scale boundaries the foreland thrust and fold belt developed from the east european craton crust is imaged as subhorizontal to east dipping reflectivity that can be related to its paleozoic and older tectonic history the moho beneath the foreland thrust and fold belt is not imaged in the vibroseis data set the main uralian fault the major arc continent suture is unreflective but its subsurface location can be inferred by the truncation of the reflection pattern of the east european craton and its contrast with that of the magnitogorsk arc the magnitogorsk arc reflectivity is characterized by patchy noncoherent to coherent reflections in the upper 10 15 km that are interpreted to be related to the arc volcanic rocks below this reflectivity is diffuse or the arc crust is transparent and the moho is not imaged the east magnitogorsk fault zone which juxtaposes the arc against the east uralian zone is not imaged by the data the upper 5 to 6 km of the east uralian zone corresponding to the dzhabyk granite is transparent below the granite the crust is characterised by east dipping patches of moderately coherent high amplitude reflections that in the east become shallowly west dipping a 10 km thick west dipping band of coherent high amplitude reflections between 12 and 35 km depth corresponding to the kartaly reflection sequence extends beneath almost the entire east uralian zone the crust beneath the easternmost east uralian zone reaches 53 km in thickness the upper and middle crust of the trans uralian zone is characterized by a series of east and west dipping concave upward moderately coherent high amplitude reflections the lowermost middle and lower crust displays thin bands of west dipping coherent low amplitude reflectivity the moho is imaged as a sharp transition from reflective lower crust to transparent upper mantle at 49 km depth and the lower crustal reflections appear to merge with it the urseis vibroseis data are integrated with results from the explosion source reflection data the wide angle reflection data and the surface geology to place constraints on the crustal architecture of the orogen and on the timing of its assemblage

a radar transparent layer in a temperate valley glacier bench glacier alaska radar surveys of bench glacier alaska collected over five field seasons between 2002 and 2006 reveal a surface layer of radar transparent ice in this temperate valley glacier the transparent layer covers the up glacier half of the ablation zone and is defined by a distinct lack of the radar scattering events considered typical of temperate ice radar scattering ice underlies the transparent zone and extends to the surface elsewhere on the glacier we observed the layering in constant offset radar surveys conducted with characteristic frequencies ranging from 5 mhz to 100 mhz the radar transparent layer extends from the surface to 20 m depth on average but up to 50 m in some places bench glacier s transparent layer appears similar to the cold surface layer of polythermal glaciers however observations in over 50 boreholes on bench glacier suggest there is no cold ice corresponding to the radar transparent layer we conclude that spatially extensive radar transparent layers normally used to identify cold ice in polythermal glaciers are present in some temperate glaciers copyright 2009 john wiley sons ltd

when did the roof collapse late miocene north south extension in the high himalaya revealed by th pb monazite dating of the khula kangri granite th pb ion microprobe measurements made on 12 monazite grains from the khula kangri granite tibet bhutan frontier are interpreted to indicate that crystallization occurred at 12 5 0 4 ma the leucogranite is cut by the gonto la detachment part of the southern tibet detachment system that has allowed upper level north directed extension of the himalayan orogen significant orogen normal extension in southern tibet appears to have continued 8 10 m y later than previously recognized this is the first reported crystallization age for a leucogranite east of the yadong cross structure an apparent 70 km offset of the high himalaya and southern tibet detachment west of the yadong cross structure reliable ages for high himalaya events major main central thrust slip granite generation and emplacement attainment of critical topography and major detachment extension group between ca 24 and 19 ma we interpret the west to east change across the yadong cross structure to be due to either 1 an abrupt 10 m y younging of principal high himalayan events or 2 a deeper thus younger exposed part of the footwall of the southern tibet detachment near khula kangri the southern tibet detachment is cut by the highly oblique yadong gulu rift a manifestation of tibet plateau east west extension integrated estimates of magnitude and rate of detachment displacement suggest that the observed postcrystallization north directed extension lasted for 1 3 m y after which time the yadong gulu rift formed this interpretation is consistent with initiation of east west extension of tibet at ca 8 ma

peraluminous granites frequently with mantle like isotope compositions the continental type murzinka and dzhabyk batholiths of the eastern urals murzinka and dzhabyk are continental type batholiths of the middle and southern east uralian domain they comprise mainly undeformed peraluminous k rich granites whose elemental composition is similar to some late variscan granites of western europe but with much more primitive sr and nd isotope ratios murzinka 254 5 ma is composed of silica rich granites forming two different rock series with a 87sr 86srinit of 0 709 and 0 704 respectively both series have enormous variations in end255 11 9 to 0 1 and 8 9 to 4 1 that reveal derivation from heterogeneous sources dzhabyk 291 4 ma also comprises two coeval magmas which yielded voluminous granites and quartz monzonites respectively with smaller differences in 87sr 86srinit and end290 0 7043 0 8 to 1 6 and 0 7049 0 0 to 0 8 despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle derived parental magma moreover we suggest that dzhabyk granitoids were generated by polybaric partial melting of paleozoic island arc material whereas murzinka granitoids derived from an extremely heterogeneous source consisting mainly of paleozoic and proterozoic metagreywackes this implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the urals since there is neither evidence of significant extension nor a direct link with subduction we suggest that the main cause for late orogenic anatexis was elevated heat production and fertility in the protolith perhaps combined with some additional heat from unexposed mafic intrusions

accretionary complex structure and kinematics during paleozoic arc continent collision in the southern urals abstract the southern urals contain a well preserved accretionary complex that has overthrust the continental margin during arc continent collision between the east european craton eec and the magnitogorsk island arc in the late devonian within the accretionary complex we study three tectonic units that differ in deformation style and each provides a unique geodynamic implication the zilair nappe the largest and best exposed unit consists of 5 6 km of syncollisional arc derived upper devonian to lower carboniferous polymictic and graywacke turbidites that were deposited across the continental margin and incorporated by frontal accretion into the accretionary complex the zilair nappe is a bivergent thrust imbricate where the west vergent thrusts dominate and have associated kilometer scale ramp anticlines with well developed east dipping axial planar cleavage along its eastern contact however the cleavage fans until it dips moderately westward and the folds are east vergent following its emplacement west vergent basement involved thrusting that breached the whole accretionary complex imbricated the zilair nappe the timirovo duplex is structurally beneath the zilair nappe and outcrops for several tens of kilometers along its northwestern margin the duplex forms a west vergent thrust stack composed of a highly deformed and sheared lower and middle devonian reef carbonates of the former eec margin platform these rocks were shallowly underplated at the base of the accretionary complex during emplacement over the margin the suvanyak complex outcrops along the eastern contact of the zilair nappe and consists of polydeformed greenschist facies metasediments of the former eec slope that were offscraped underplated and incorporated at the rear of the accretionary complex

seismic detection of transient changes beneath black rapids glacier alaska u s a ii basal morphology and processes using changes observed in daily seismic reflections we have investigated the basal morphology of black rapids glacier alaska u s a the englacial drainage of ice marginal lakes caused significant changes in the daily reflections as well as dramatic increases in basal motion changes in reflection arrival times and amplitudes indicate that there is a basal till layer at least 5 m thick at some locations beneath this surge type glacier rapid changes in the observed reflection coefficients during the drainage events indicate that changes in till properties must occur throughout the entire 5 m thick layer they must last for several days following the lake drainages and they must be completely reversible over as little as 36 min our seismic analysis shows that changes in effective pressure of the till are unlikely to cause the required changes in the reflection coefficients but that a decrease in till saturation is likely we therefore interpret the cause ofthe seismic anomalies as being a temporary decrease in saturation as water is input to the subglacial hydraulic system and propose that such a change may occur quickly and reversibly by a redistribution ofoverburden pressure higher water pressures within the hydraulic system cause that region to support more of the glacier s weight leaving the remaining areas to support less any till within these areas of decreased normal stress would experience a consequent decrease in pore water pressure causing gas to exolve thus decreasing saturation this decrease in saturation would cause a change in the strength of the basal layer and may affect basal dynamics

the tectono metamorphic evolution of gneiss complexes in the middle urals russia a reappraisal abstract the middle urals are characterized by a major virgation in the linear trend of the urals orogen and represent the most highly contracted part of the late palaeozoic collisional belt this part of the orogen is dominated by metamorphic complexes and major fault and shear zones the main uralian fault zone muf the east dipping suture of the orogen containing low grade metamorphic rocks separates the sysert complex in the east from the ufaley complex in the west the sysert complex in the hanging wall of the muf consists of intensely deformed gneisses granitic intrusions and a metamorphosed melange zone tectonic and isotopic investigations suggest the following stages for the evolution of the sysert complex a pre orogenic rifting and magmatism during ordovician and silurian times b oceanic closure island arc formation related to convergence and subduction during devonian times c major ductile deformation under amphibolite facies conditions related to nw directed thrusting associated with crustal stacking during collision in carboniferous times d exhumation and contractional intracontinental tectonics during permian times and e closing of isotope systems related to cooling and the end of orogenic shortening through triassic times the ufaley complex in the footwall of the muf is interpreted as an east dipping crustal stack that records an amphibolite facies uralian metamorphism lithologically the complex can be divided into pre orogenic european basement west ufaley and intensely deformed palaeozoic metasediments and amphibolites east ufaley high pressure relics in the east ufaley complex are interpreted to be the result of subduction whereas intense ductile deformation is related to overthrusting onto west ufaley the west ufaley complex is composed of gneisses amphibolites migmatites and granitic intrusions and has been thrust onto devonian limestones along a major shear zone in both sysert and ufaley complexes nw trending stretching lineations and top to the nw kinematic indicators suggest an oblique plate convergence with a significant sinistral component the muf is interpreted as a major normal fault that developed congruent with continental subduction and that compensated lithospheric thickening and the rapid exhumation of subducted crust in the footwall

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

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

metamorphism of the central anatolian crystalline complex turkey influence of orogen normal collision vs wrench dominated tectonics on p t t paths the central anatolian crystalline complex cacc is a microcontinent in the alpine himalayan belt it has previously been considered as a coherent structural entity but although the entire cacc is comprised of similar rocks primarily metasedimentary rocks and granitoids it consists of at least four tectonic blocks characterized by different p t t paths these blocks are the kirsehir north west akdag north east nigde south and aksaray west massifs the northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion metamorphic rocks are characterized by clockwise p t paths at moderate p t and local low p high t lp ht overprinting in the highest grade rocks apatite fission track ages are eocene to oligocene 47 32 ma the aksaray block represents the hot shallow mid crust of a late cretaceous early tertiary arc it is dominated by intrusions rare metapelitic rocks record low p 4 kbar regional metamorphism overprinted by lp ht contact metamorphism apatite fission track ages are 50 45 ma the nigde massif is different from the other cacc blocks because it evolved as a core complex in a wrench dominated setting it is characterized by clockwise p t paths at moderate p t followed by widespread lp ht metamorphism apatite fission track ages are miocene 12 9 ma significantly younger than those in the northern massifs nigde rocks resided in the mid crust at a time when the rest of the cacc was at or near the earth s surface variations in p t t and tectonic histories especially timing of exhumation between the northern and southern cacc reflect the difference between head on collision vs mid crustal wrenching

englacial and subglacial water flow at skalafellsjokull iceland derived from ground penetrating radar in situ glacsweb probe and borehole water level measurements we reconstruct englacial and subglacial drainage at skalafellsjokull iceland using ground penetrating radar gpr common offset surveys borehole studies and glacsweb probe data we find that englacial water is not stored within the glacier water content 0 0 3 instead the glacier is mostly impermeable and meltwater is able to pass quickly through the main body of the glacier via crevasses and moulins once at the glacier bed water is stored within a thin 1 m layer of debris rich basal ice 2 water content and the till the hydraulic potential mapped across the survey area indicates that when water pressures are high most of the year water flows parallel to the margin and emerges 3 km down glacier at an outlet tongue gpr data indicates that these flow pathways may have formed a series of braided channels we show that this glacier has a very low water storage capacity but an efficient englacial drainage network for transferring water to the glacier bed and therefore it has the potential to respond rapidly to changes in melt water inputs

gneiss domes metamorphic core complexes and wrench zones thermal and structural evolution of the nigde massif central anatolia 1 the nigde massif a migmatite cored structural dome in south central turkey was metamorphosed deformed intruded and exhumed in an oblique tectonic regime involving a switch from transpression prograde metamorphism to transtension exhumation an 80 ma history of transpression and transtension is recorded in metamorphic rocks of the massif and the last 50 ma are recorded in both basement and overlying basin deposits nigde metamorphic rocks record a high temperature top to north syntranspression ductile fabric that was overprinted by lower grade top to south syntranstension ductile shear zones the 40ar 39ar data for hornblende muscovite and biotite document rapid late cretaceous cooling with the oldest ar hornblende ages 88 79 ma overlapping u pb ages in monazite and zircon 92 78 ma muscovite ar ages are dominantly 81 79 ma suggesting a short time between crystallization of high temperature metamorphic rocks and their cooling biotite ar ages are 79 74 ma with the exception of disturbed samples from the eastern margin of the massif and from eocene granitic stocks in the dome core the eastern margin adjacent to the sinistral central anatolian fault zone records another cycle of burial and exhumation that overprinted earlier fabrics and disturbed isotopic systems these two cycles of burial exhumation took place repeatedly along the same zone this may be characteristic of highly oblique tectonic regimes in the nigde massif burial and exhumation became more localized and of lower amplitude over time suggesting stabilization of the crust

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

active seismic studies in valley glacier settings strategies and limitations subglacial tills play an important role in glacier dynamics but are difficult to characterize in situ amplitude variation with angle ava analysis of seismic reflection data can distinguish between stiff tills and deformable tills however ava analysis in mountain glacier environments can be problematic reflections can be obscured by rayleigh wave energy scattered from crevasses and complex basal topography can impede the location of reflection points in 2 d acquisitions we use a forward model to produce challenging synthetic seismic records in order to test the efficacy of ava in crevassed and geometrically complex environments we find that we can distinguish subglacial till types in moderately crevassed environments where moderate depends on crevasse spacing and orientation the forward model serves as a planning tool as it can predict ava success or failure based on characteristics of the study glacier applying lessons from the forward model we perform ava on a seismic dataset collected from taku glacier in southeast alaska in march 2016 taku glacier is a valley glacier thought to overlay thick sediment deposits a near offset polarity reversal confirms that the tills are deformable

coeval extension and compression in late mesozoic recent thin skinned extensional tectonics in central anatolia turkey abstract the central anatolian crust is composed of high grade metamorphic rocks covered by tertiary shallow marine to continental sedimentary rocks with a middle miocene recent volcanic activity in cappadocia after the late cretaceous closure of the tethyan ocean and following plate collision core complexes formed in nigde and kirsehir regions of central anatolia recent geophysical studies indicate the presence of low seismic velocity zones beneath central anatolia interpreted as regionally thinned and or hot mantle lithosphere or asthenospheric upwelling we present new structural data covering a 300 km wsw nne trending transect between konya and yozgat cities to suggest that central anatolian cenozoic tectonic regime is extensional and the narrow fold thrust zones once taken as evidence of crustal convergence resulted from gravitational movements curie point depths map of central anatolia shows a large scale diameter 140 km upwarping c 15 km of the regional crust we interpret as due to asthenospheric upwelling these considerations suggest that 1 the central anatolian crust deforms by extension transcurrent faults like the central anatolian fault zone accommodate the crustal stretching by transfer faulting 2 post late cretaceous crustal extension favored the placement of hot and low density asthenospheric material in cappadocia by processes that may be explained by rayleigh taylor instability phenomenon 3 in central anatolia large post eocene horizontal crustal displacements we estimate a minimum of 50 km are not achieved by crustal contraction as previously proposed but thin skin extensional tectonics and 4 tethyan suture lines need to be reviewed since their traces may be modified by later extensional displacements

automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls kulessa b a d booth a hobbs and a l hubbard 2008 automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls geophysical research letters 35 24 l24502

extensive storage of basal meltwater in the onset region of a major west antarctic ice stream a major meltwater body exists beneath a tributary of bindschadler ice stream west antarctica in a region where subglacial lakes have not been mapped but near where rapid vertical motion of the ice sheet surface has suggested shifting of a subglacial water body the water is trapped by a local reversal in ice air surface slope arising from ice flow over variable basal topography and from the positive feedback of basal lubrication from the trapped water strong variations in the water content of the sediments upglacier of the water body arise from a similar process these results are revealed by a novel application of the amplitude variation with offset avo seismic technique the existence of such water bodies and of the strong spatial variation in subglacial sediment properties is not captured in current models of subglacial hydrology lubrication of ice stream motion and sediment transport

the ductile shear zone in granitoid of the central anatolian crystalline complex turkey implications for the origins of the tuzgolu basin during the late cretaceous extensional deformation abstract the emizozu shear zone is the west northwest trending ductile shear zone within the agacoren granitoid in central turkey deformation that affected the granitoid along the emizozu shear zone resulted in mylonites with mylonitic foliation and stretching lineation the textural features of the deformed minerals suggest that mylonitization occurred under conditions of upper greenschist facies the shear indicators including asymmetric porphyroclasts oblique foliation and shear bands suggest a down dip top to the southwest displacement the orientation of stretching lineation as well as kinematic indicators indicates the extensional character of the emizozu shear zone although it is not precisely dated the available age constraints suggest that the zone formed at 78 71 ma according to field and micro structural data the agacoren granitoid was most likely emplaced during a regional deformation in central turkey and synchronously or shortly after was overprinted by the extensional emizozu shear zone the zone can also be correlated with the earlier stage development of the tuzgolu basin in central turkey

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

seismic detection of transient changes beneath black rapids glacier alaska u s a i techniques and observations to gain new insight into the mechanisms of basal motion we have demonstrated the feasibility of an active seismic technique to measure temporal changes in basal conditions on sub hourly time scales one region of the bed of black rapids glacier alaska u s a was monitored for a period of 45 days using seismic reflections the majority ofthese reflections were nearly identical however three significant anomalies were recorded several days apart these corresponded with the englacial drainage of two ice marginal lakes and one supraglacial pothole each up glacier of the study site as well as dramatic increases in basal motion two of these seismic anomalies revealed identical changes over 1 km 2 of the bed despite the fact that their drainage events occurred at different locations further these two seismic anomalies were followed by records identical to the non anomalous state showing that the seismic changes were reversible in one of these events two records taken 36 min apart revealed that the transition between the anomalous and normal states occurred completely within this short interval

planktogenic eustatic control on cratonic oceanic carbonate accumulation data on mass age distributions and latitudinal limits of mesozoic cenozoic shelf carbonate on cenozoic deepening of the ccd in all major ocean basins and on the abundance of pelagic chalk in epicontinental carbonate sequences indicate that the primary locus of global limestone deposition has gradually shifted from shallow cratonic to deep oceanic settings since jurassic time this change is generally coincident with progressive emergence of continents during global regression as well as with taxonomic diversification of calcareous plankton and implicates one or both processes as the primary control on carbonate sediment partitioning between shallow and deep marine reservoirs widespread pelagic carbonate does not occur with phanerozoic ophiolite sequences until the late mesozoic and generally corresponds to origins of planktonic foraminifera and diversification of coccolithophorids similarly cratonic chalk is largely re stricted to cretaceous sections correlation of mesozoic cenozoic positions of t

uralian magmatism an overview abstract this paper is an attempt to summarize current knowledge of uralian magmatism focusing on those aspects relevant for understanding its geodynamic evolution the urals consist of three tectonomagmatic domains a suture sector in the west and two n s imbricated island arc continental sectors in the east the suture sector comprises lower palaeozoic mafic ultramafic complexes which show eastward impoverishment in lile thus reflecting the transition of the subcontinental lithospheric mantle of the russian plate to the suboceanic lithospheric mantle of the subducted uralian palaeo ocean the two island arc continental sectors represent the transition from oceanic to continental environments in the middle and south urals collisional magmatism started in the silurian and persisted till the permian migrating progressively eastward and increasing in abundance of lile and 87 sr 86 sr initial magmatic polarity is very similar to that of modern subduction zones and indicates that the subducted slab was dipping eastward during that period the northern and southern island arc continental sectors show many similarities regarding the nature and spatial temporal distribution of magmatism but there are also some important differences which probably indicate somewhat different geodynamic regimes in the northern sector carboniferous tonalite granodiorite batholiths have features compatible with an origin by melting of the oceanic crust in the subducted slab in the southern sector however carboniferous tonalite granodiorite batholiths have features more consistent with a melting event within the lower continental crust above the subduction zone than with melting within the subducted slab upper carboniferous permian granites have high 87 sr 86 sr initial in the north e g 0 7120 in the murzinka batholith but very low 87 sr 86 sr initial in the south e g 0 7045 in the dzhabyk batholith in spite of rocks from both batholiths being equally peraluminous and showing evidence of derivation by anatexis of metasediments the low 87 sr 86 sr initial at dzhabyk might indicate that in the southern sector the accretionary prism grew very rapidly thus allowing involvement in upper palaeozoic melting events

lithosphere scale seismic image of the southern urals from explosion source reflection profiling explosive source deep seismic reflection data from the southern ural mountains of central russia provided a lithosphere scale image of the central eurasian plate that reveals deep reflections 35 to 45 seconds in travel time 130 to 170 kilometers deep from the mantle the data display laterally variable reflectivity at the base of the crust that deepens beneath the central part of the profile documenting a crustal thickness of 55 to 60 kilometers beneath the axis of the orogen these data provide an image of the structure of the crust and underlying mantle lithosphere in a preserved collisional orogen perhaps to the base of the lithosphere

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

palaeostress inversion in a multiphase deformed area kinematic and structural evolution of the cankiri basin central turkey part 1 northern area the kinematic and structural evolution of the major structures affecting the cankiri basin central turkey has been deduced from a palaeostress inversion study four palaeostress tensor configurations indicative of four phase structural evolution have been constructed from the fault slip data collected from the cankiri basin the first two phases indicate the dominant role of thrusting and folding and are attributed to the collision between the pontides and the taurides the proposed interface of which is straddled by the cankiri basin phase 1 occurred in the pre late palaeocene and phase 2 in the late palaeocene pre burdigalian the third phase is dominated by extensional deformation in the middle miocene the latest phase has been active since then and is characterized by regional transcurrent tectonics

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

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

207pb 206pb single zircon evaporation ages of some granitoid rocks reveal continent oceanic island arc collision during the cretaceous geodynamic evolution of the central anatolian crust turkey abstract 207pb 206pb single zircon evaporation age determinations carried out on nine different granitoid units of central anatolia turkey have yielded three distinct granitoid groups with different emplacement ages these are 1 cenomanian turonian granitoids with a weighted mean age wma of 94 9 3 4 ma 2 turonian santonian granitoids with a wma of 85 5 5 5 ma and 3 campanian granitoids with a wma of 74 9 3 8 ma the spatial and temporal relationships between the formation of the metamorphic sole of the supra subduction zone type central anatolian ophiolite ssz type cao crustal metamorphism of the central anatolian crystalline complex cacc and the emplacement of cenomanian turonian to turonian santonian granitoids indicate a geodynamic setting in which all these geological events occurred quasi simultaneously in central anatolia such a geodynamic setting is thought to be related to the cenomanian turonian collision of the tauride anatolide platform tap and an oceanic island arc including the ssz type cao the campanian granitoids appear to be the continuation of this collision related protracted magmatism in central anatolia