tectonic evolution of a part of the tethyside orogenic collage the kargi massif northern turkey the central part of the rhodope pontide fragment one of the major tectonic units in turkey provides critical data for evaluating the cimmeride and alpide evolution of the mediterranean tethysides tectonic events that affected the central part of the rhodope pontide fragment since the end of the paleozoic generated east west trending belts with the event of every episode redeforming and partly obliterating the structures of previous episodes this evolution may be conveniently described in terms of three major episodes 1 two different realms of pre dogger oceanic rocks are present in the area the northern realm coincided with main branch of paleo tethys that was being actively destroyed by south dipping subduction the southern realm the karakaya ocean a back arc basin related to this subduction began opening by rifting of a retroarc carbonate platform during the permo triassic to the west a continental domain with sparse magmatism seperated the two oceanic areas toward the east the two oceans become united by the wedging out of the continental domain these two pre dogger oceans closed during the lias and their remnants were emplaced between the southern margin of laurasia and the fragments of the cimmerian continent 2 the second episode partly overlapped the first with rifting south of the cimmerian continent fragment during the lias this rifting was followed by a transgression which covered the ruins of the cimmeride orogenic belt by the malm this rifting concurrently led to the development of the northern branch of the neo tethys and a south facing atlantic type continental margin a southerly thickening sedimentary prism developed on this margin during the lias to early cretaceous interval 3 the floor of the northern branch of neo tethys began to be consumed along the north dipping subduction zone beneath the previosly constructed continental margin this convergent margin generated a magmatic arc to the north and to the south a subduction accretion complex present width of which approaches 80 km to the south of the subduction accretion complex yet another convergent margin is indicated by the presence of the remnants of an ensimatic arc the northern branch of the neo tethys was totally consumed in the late cretaceous to eocene interval

an example of an accretionary forearc basin from northern central anatolia and its implications for the history of subduction of neo tethys in turkey deformed sedimentary sequences of late cretaceous middle eocene age located between the sakarya continent and the anatolian complex have been interpreted as the fill of a forearc basin the history and structure of this basin are critical for understanding the evolution of the neo tethyan subduction in the middle east i test and elaborate upon this interpretation on the basis of three basic outcrop areas of upper cretaceous lower tertiary sedimentary sequences confined to a northeast southwest trending belt in north west ankara these are the alci kinik and orhaniye areas they expose two different sedimentary sequences called alci and orhaniye in the alci area the sequence starts at the base with the continental red clastic rocks on the erosional surface of an underlying ophiolitic melange and continues upward into the shallow marine reefal buildup of the late maastrichtian age the upper half of the alci sequence is separated from its lower half by a local disconformity and dominated by the continental debris flow deposits composed mostly of volcanic material by contrast both the kinik and orhaniye areas are characterized by a thick continuous and coarsening upward sequence overlying conformably the underlying ophiolitic melange the lower half of the orhaniye sequence is dominated by a deep marine flysch its middle part by continental clastic material and the topmost part by the shallow marine reefal buildup lower contact relationships lithologic composition facies distribution internal structures and the regional tectonic settings of both sequences strongly suggest that the above mentioned three outcrops preserve the remnants of a peripheral accretionary forearc basin forming the north northwestern margin of the haymana polath accretionary forearc basin during middle campanian middle eocene time this peripheral basin is here named orhaniye accretionary forearc basin

subduction zones an introduction to comparative subductology abstract the subduction model for trench arc back arc systems was deduced more or less as a logical consequence of sea floor spreading many features in these systems such as thrust type inter plate earthquakes and deep earthquakes along wadati benioff zones are readily explained by the subduction model but other features such as extensional spreading and high heat flow in back arc regions and arc volcanism are difficult to explain an approach to solve these problems may be to recognize the existence of the two basically different modes of subduction one chilean type causing a compressional stress regime in the arc and back arc regions the other mariana type causing a tensional stress regime implications of the two types of the mode of subduction for some tectonic problems such as vertical movement and sediment accretion at trenches are discussed with special reference to the results of recent dsdp active margin drilling in discussing the possible causes of the two modes it is suggested that the large scale thermal and stress regimes in the back arc areas may not be the direct products of simple subduction but of some additional factors involving much greater energy such as mantle flow associated with the motion of major plates finally the possible great importance of various types of collision accretion and erosion at subduction zones is emphasized

oceanic crust generation in an island arc tectonic setting se anatolian orogenic belt turkey a number of late cretaceous ophiolitic bodies are located between the metamorphic massifs of the southeast anatolian orogenic system one of them the goksun ophiolite northern kahramanmaras which crops out in a tectonic window bounded by the malatya metamorphic units on both the north and south is located in the ew trending nappe zone of the southeast anatolian orogenic belt between goksunand afsin northern kahramanmaras it consists of ultramafic mafic cumulates isotropic gabbro a sheeted dyke complex plagiogranite volcanic rocks and associated volcanosedimentary units the ophiolitic rocks and the tectonically overlying malatya keban metamorphic units were intruded by syn collisional granitoids 85 ma the volcanic units are characterized by a wide spectrum of rocks ranging in composition from basalt to rhyolite the sheeted dykes consist of diabase and microdiorite whereas the isotropic gabbros consist of gabbro diorite and quartzdiorite the magmatic rocks in the goksunophiolite are part of a co magmatic differentiated series of subalkaline tholeiites selective enrichment of some lil elements rb ba k sr and th and depletion of the hfs elements nb ta ti zr relative to n morb are the main features of the upper crustal rocks the presence of negative anomalies for ta nb ti the ratios of selected trace elements nb th th yb ta yb and normalized ree patterns all are indicative of a subduction related environment all the geochemical evidence both from the volcanic rocks and the deeper levels sheeted dykes and isotropic gabbro show that the goksun ophiolite formed during the mature stage of a suprasubduction zone ssz tectonic setting in the southern branch of the neotethyan ocean between the malatya keban platform to the north and the arabian platform to the south during late cretaceous times geological geochronological and petrological data on the goksun ophiolite and the baskil magmatic arc suggest that there were two subduction zones the first one dipping beneath the malatya keban platform generating the baskil magmatic arc and the second one further south within the ocean basin generating the goksun ophiolite in a suprasubduction zone environment

oceanography when glacial giants roll over the energy released by capsizing icebergs can be equal to that of small earthquakes enough to create ocean waves of considerable magnitude should such glacial tsunamis be added to the list of future global warming hazards

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

laboratory investigations of iceberg capsize dynamics energy dissipation and tsunamigenesis 1 we present laboratory experiments designed to quantify the stability and energy budget of buoyancy driven iceberg capsize box shaped icebergs were constructed out of low density plastic hydrostatically placed in an acrylic water tank containing freshwater of uniform density and allowed or forced if necessary to capsize the maximum kinetic energy translational plus rotational of the icebergs was 15 of the total energy released during capsize and radiated surface wave energy was 1 of the total energy released the remaining energy was directly transferred into the water via hydrodynamic coupling viscous drag and turbulence the dependence of iceberg capsize instability on iceberg aspect ratio implied by the tank experiments was found to closely agree with analytical predictions based on a simple hydrostatic treatment of iceberg capsize this analytical treatment along with the high reynolds numbers for the experiments and considerably higher values for capsizing icebergs in nature indicates that turbulence is an important mechanism of energy dissipation during iceberg capsize and can contribute a potentially important source of mixing in the stratified ocean proximal to marine ice margins

tethyan vs cordilleran ophiolites a reappraisal of distinctive tectono magmatic features of supra subduction complexes in relation to the subduction mode abstract supra subduction zone ssz ophiolites deserve special attention because they represent fundamental markers of intraoceanic convergence and generation of new lithosphere above subduction zones moreover owing to their structural characteristics and location in the overriding plate these complexes are far better represented and preserved than mid ocean ridge basalt morb ophiolites in orogenic belts in terms of their structure tectonics and magmatic features ssz ophiolites may be classified in two main types 1 tethyan complexes such as those of the albanide hellenide belt which mostly consist of complete and extensive volcanic dyke plutonic and mantle sections with prevalent island arc tholeiitic iat affinity and the significant presence of boninites obducted as relatively intact lithospheric slabs onto collisional continental margins 2 cordilleran complexes including the circum caribbean ophiolites of guatemala cuba and venezuela mostly represented by dismembered sections of arc volcanic plutonic and subordinate mantle sequences with tholeiitic to calc alkaline iac magmatic affinity and acidic differentiates commonly associated with metamorphic subduction complexes and tectonically emplaced onto or juxtaposed against the continental margin within polygenetic terranes these two types appear to be related to significantly different subduction modes and intraoceanic plate dynamics whereby ssz ophiolites were generated the tethyan complexes can best be compared with west pacific type subduction with accentuated steepening and retreat of the subducted slab accompanied by progressive decoupling of the converging plates intense mantle diapirism and tensional events in the upper plate with generation of large iat sheeted dike complexes in open oceanic spreading systems continuous slab sinking and roll back allow increasing asthenospheric diapirism and interarc spreading from the arc axis to the forearc region with generation of boninites and back arc basin basalts babb with intermediate morb iat composition by contrast the genesis of the cordilleran complexes requires a subduction mode characterized by a steady state regime with moderate and constant dip of the subducted slab and limited extension in the backarc region the magmatic evolution of these ophiolites from iat to iac and the significant presence of rhyodacite and tonalite differentiates coherently indicate a more mature stage of arc magmatism as well as the occurrence of efficient differentiation processes developing under nearly closed system conditions in independent magma chambers tethyan complexes are likely to be obducted as large and relatively intact slabs onto the continental margins through the interposition of metamorphic soles which represent relics of the morb lithosphere underplating the ssz ophiolites on the other hand the common emplacement of cordilleran complexes within polygenetic terranes appears to be controlled by prolonged accretionary mechanisms that trap against the continental margin parts of the arc structure subduction complexes melanges and volcanoclastic products

late palaeozoic marginal basin and subduction accretion the palaeotethyan kure complex central pontides northern turkey the kure complex located in the central pontides of northern turkey is a c 20 km thick pile of thrust imbricated deep sea sediments intercalated with a dismembered ophiolite the ophiolitic rocks include serpentinized harzburgite massive gabbro cumulate and isotropic sheeted dykes and basic volcanic rocks the extrusive rocks are mainly pillow lavas sheet flows and lava breccias geochemical evidence of immobile major and trace elements and pyroxene chemistry indicate mid ocean ridge mor and volcanic arc basalt vab compositions and suggest that the kure ophiolite was generated above a subduction zone chrome spine1 analysis also supports this interpretation in some thrust sheets the extrusives are depositionally overlain by hemi pelagic shales passing up into terrigenous turbidites and shales which are up to several hundred metres thick in intact successions cyprus type massive sulphides interpreted as precipitates from black smokers are located along the lava sediment contact individual intact sediment units up to several kilometres thick within the kure complex are separated by narrow up to 10 m wide zones of intense shearing layer parallel extension and melange formation asymmetrical folds reverse faults thrusts and duplex structures throughout the kure complex indicate mainly northwards emplacement the kure complex is thought to have opened in the late palaeozoic as a marginal basin above a northward dipping palaeotethyan subduction zone located along the southern margin of eurasia the kure marginal basin later closed in response to inferred southward subduction leading to development of an accretionary prism prior to late jurassic time the kure complex is unlikely to represent the main palaeotethyan suture as has been suggested in some earlier tectonic reconstructions regional comparisons with dobrogea crimea and caucasus suggest the kure basin opened then closed along a south eurasia active margin

shyok suture zone n pakistan late mesozoic tertiary evolution of a critical suture separating the oceanic ladakh arc from the asian continental margin abstract the shyok suture zone northern suture of north pakistan is an important cretaceous tertiary suture separating the asian continent karakoram from the cretaceous kohistan ladakh oceanic arc to the south in previously published interpretations the shyok suture zone marks either the site of subduction of a wide tethyan ocean or represents an early cretaceous intra continental marginal basin along the southern margin of asia to shed light on alternative hypotheses a sedimentological structural and igneous geochemical study was made of a well exposed traverse in north pakistan in the skardu area baltistan to the south of the shyok suture zone in this area is the ladakh arc and its late cretaceous mainly volcanogenic sedimentary cover burje la formation the shyok suture zone extends northwards ca 30 km to the late tertiary main karakoram thrust that transported asian mainly high grade metamorphic rocks southwards over the suture zone the shyok suture zone is dominated by four contrasting units separated by thrusts as follows 1 the lowermost askore amphibolite is mainly amphibolite facies meta basites and turbiditic meta sediments interpreted as early marginal basin rift products or trapped tethyan oceanic crust metamorphosed during later arc rifting 2 the overlying pakora formation is a very thick ca 7 km in outcrop succession of greenschist facies volcaniclastic sandstones redeposited limestones and subordinate basaltic andesitic extrusives and flow breccias of at least partly early cretaceous age the pakora formation lacks terrigenous continental detritus and is interpreted as a proximal base of slope apron related to rifting of the oceanic ladakh arc 3 the tectonic melange reconnaissance further east north of the shyok river indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs derived from nearby volcanic centres presumed to lie within the ladakh arc in addition comparison with lower cretaceous clastic sediments maium unit within the northern suture zone west of the nanga parbat syntaxis hunza river reveals notable differences including the presence of terrigenous quartz rich conglomerates serpentinite debris flow deposits and a contrasting structural history the shyok suture zone in the skardu area is interpreted to preserve the remnants of a rifted oceanic back arc basin and components of the asian continental margin in the west hunza river a mixed volcanogenic and terrigenous succession maium unit is interpreted to record syn deformational infilling of a remnant back arc basin foreland basin prior to suturing of the kohistan arc with asia 75 90 ma

the japan trench and its juncture with the kuril trench cruise results of the kaiko project leg 3 this paper presents the results of a detailed survey combining seabeam mapping gravity and geomagnetic measurements as well as single channel seismic reflection observations in the japan trench and the juncture with the kuril trench during the french japanese kaiko project northern sector of the leg 3 on the r v jean charcot the main data acquired during the cruise such as the seabeam maps magnetic anomalies pattern and preliminary interpretations are discussed these new data cover an area of 18 000 km2 and provide for the first time a detailed three dimensional image of the japan trench combined with the previous results the data indicate new structural interpretations a comparative study of seabeam morphology single channel and reprocessed multichannel records lead to the conclusion that along the northern japan trench there is little evidence of accretion but instead a tectonic erosion of the overriding plate the tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the japan trench axis which is a direct consequence of the downward flexure of the pacific plate in addition to these new faults ancient normal faults trending parallel to the n65 oceanic magnetic anomalies and oblique to the japan trench axis are reactivated so that two directions of normal faulting are observed seaward of the japan trench only one direction of faulting is observed seaward of the kuril trench because of the parallelism between the trench axis and the magnetic anomalies the convergent front of the kuril trench is offset left laterally by 20 km relative to those of the japan trench this transform fault and the lower slope of the southernmost kuril trench are represented by very steep scarps more than 2 km high slightly south of the juncture the erimo seamount riding on the pacific plate is now entering the subduction zone it has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches is it due to the collision of an already subducted chain of seamounts or does it correspond to one of the failure lines of the america eurasia plate boundary

superimposed folding and oblique structures in the palaeomargin derived units of the central betics sw spain the subbetic units consist of a deformed wedge of sedimentary rocks deriving from the south iberian palaeomargin in the westernmost segment of the alpine mediterranean orogenic belt in the central betics shortening produced folding thrusting and nappe stacking the structural trend is ne sw to ene wsw and the internal structure of the thrust sheets which shows no preferred vergence is strongly controlled by the rheology of the decollement level a viscous layer of triassic evaporites and of the overlying carbonate rock sequence the relationships of piggyback basin miocene sediments with the main structures show that the latter developed during the aquitanian burdigalian transition superimposed folding is described for the first time in the study area the origin of the interference cannot be determined at present but may be related to initially oblique structures refolded during progressive deformation a revision of previously published palaeomagnetic data in the light of the data presented in this paper in conjunction with a model of the structural evolution of the subbetic units of the western betics permits us to establish milestones of the tectonic evolution of the external zones in the northern branch of the gibraltar arc

the dras arc complex lithofacies and reconstruction of a late cretaceous oceanic volcanic arc in the indus suture zone ladakh himalaya abstract the purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the ladakh himalayas the mainly late cretaceous aptian paleocene dras arc complex in the indus suture zone n india is reconstructed as an oceanic arc passing southwards into a proximal to distal forearc apron the arc complex comprises three structural units from west to east these are the suru unit the naktul unit and the nindam formation the suru unit and the naktul unit are unconformably underlain by dissected late jurassic oceanic crust and mantle the suru unit preserves the interior of the arc and is divided into dras 1 and dras 2 sub units the dras 1 sub unit of mid late cretaceous age was intruded by arc plutonics deformed then unconformably overlain by the poorly dated dras 2 sub unit lower tertiary the dras 1 sub unit comprises arc extrusives volcaniclastic and tuffaceous sedimentary rocks and mainly redeposited shallow water limestones the dras 2 sub unit is dominated by coarse volcaniclastics and lava flows passing up into rhythmically layered acidic extrusives with interbedded turbiditic siltstones and siliceous pelagic limestones further east the naktul unit is mainly clastic with large volumes of massive volcaniclastic talus thick bedded debris flows volcaniclastic turbidites and reworked shallow water carbonates pillowed extrusives and ribbon radiolarites are present mainly low in the succession in some areas while pelagic carbonates are abundant near the top the naktul unit is interpreted as a proximal forearc apron the nindam formation in the east is dominated by deep water volcaniclastic turbidites tuffaceous sediments and pelagic carbonates with subordinate debris flows and is interpreted as a distal deep water forearc succession cyclical alternations of mainly volcaniclastics and pelagic carbonates in the nindam formation are thought to reflect relative sea level changes of tectono magmatic and or global eustatic origin the oceanic dras arc complex formed within neotethys in the mid late cretaceous above an assumed northward dipping subduction zone around 79 ma campanian the oceanic arc underwent collisional deformation possibly related to accretion to the trans himalaya ladakh block and or the southern margin of eurasia to form an andean type active continental margin the suru unit in the west dras 1 sub unit was deformed then overlain by the mainly acidic dras 2 sub unit however there is no direct evidence that the nindam formation in the east was deformed until the early eocene when final collision of india and eurasia took place with southward thrusting of the dras arc complex this was followed by partial erosion during deposition of the indus molasse and then back thrusting and folding related to uplift of the high himalayas in the later tertiary

chemical transects across intra oceanic arcs implications for the tectonic setting of ophiolites systematic spatial variations in ti y and zr are found in volcanic sequences sampled as transects from back arc through arc to trench within the western pacific intra oceanic arc systems these correlations occur regardless of eruption age reflecting the retention of relative positions between individual tectonic units concentrations of these incompatible elements are taken to reflect the nature of the underlying mantle at a particular trench volcano distance during the subduction process volcanics become more depleted trenchwards implying that progressively shallower levels melts were extracted from more refractory or harzburgitic mantle a model is proposed whereby a subduction system is superimposed on a compositionally stratified mantle which is a product of an earlier spreading event on the basis of this evidence the trench distance variation model is applied to the troodos ophiolite complex similar spatial changes in lava chemistry are found across the ophiolite providing evidence for the relative position of the troodos trench and direction of subduction beneath the troodos basin these findings have implications for studies in other orogenic terrains where structure and exposure permit their application

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

backarc basin evolution and cordilleran orogenesis insights from new ocean bottom seismograph refraction profiling in bransfield strait antarctica bransfield strait a backarc basin off the northwestern antarctic peninsula is a modern analog for cretaceous basins inverted in the compressional tectonic regime that initiated the andean cordillera eight new refraction ocean bottom seismograph profiles in the strait demonstrate that crustal thickness in the deep central basin increases from northeast to southwest from 10 km to 14 16 km this confirms multichannel seismic interpretation of upper crustal structures suggesting that the bransfield basin is opening by northeast to southwest rift propagation within arc crust of the antarctic peninsula a process also recorded in the obducted cretaceous rocas verdes basin of the southernmost andes thinning is most prominent along the axis of the strait where the crust is 9 11 km thick in contrast thicknesses beneath the antarctic peninsula margin and the inactive south shetland islands pedestal are 18 km and 24 km respectively seismic velocities and thicknesses suggest that new oceanic crust is not yet being generated extension is focused along the northwest margin imparting the physiographic asymmetry to the strait comparing the bransfield basin with the inverted rocas verdes basin and intraoceanic counterparts in the western pacific suggests that rift propagation and trench side focusing of extension may be fundamental features of young backarc basins resultant asymmetry may facilitate observed obduction of backarc basin floor and arc rocks onto continental margins during compressional orogenesis

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

rapid early holocene ice retreat in west greenland abstract the possible demise of the greenland ice sheet and its effect on global sea level rank among the most serious climate threats to society to improve our knowledge about the future behaviour of the ice margin we studied the ice sheet s response to early holocene warming in west greenland using 47 cosmogenic 10 be exposure ages 26 optically stimulated luminescence ages as well as 15 new and 28 previously published radiocarbon ages paired bedrock and boulder ages show that the entire area was covered by warm based ice during the last glacial maximum lgm although glacial erosion was insufficient to completely remove the upper rock surface containing 10 be inherited from a previous period of exposure in bedrock samples above an elevation of 800 m our compilation of 10 be and 14 c ages demonstrates that the ice sheet retreated from the outer coast to the present ice margin between c 11 4 and 10 4 cal ka bp in the godthabsfjord system and between 10 7 0 6 and 10 1 0 4 ka ago in buksefjord whereas the coast at sermilik became ice free at c 10 5 cal ka bp we find no significant changes in the retreat rates between the deep godthabsfjord system and the buksefjord sermilik region which is characterized by only a few narrow and shallow fjords however deglaciation was initiated c 700 900 years earlier in the godthabsfjord system indicating that the deep fjords probably triggered land based deglaciation by dynamic ice loss leading to an overall rapid early holocene ice retreat and drawdown of the ice sheet in west greenland these results demonstrate that even if there was a topographic control on the onset of deglaciation fast ice retreat is not restricted to deep fjord systems but may occur independently of the topographic setting

nature and significance of late cretaceous ophiolitic rocks and their relation to the baskil granitic intrusions of the elazig region se turkey

iceberg capsize tsunamigenesis calving from the floating termini of outlet glaciers and ice shelves is just the beginning of an interesting chain of events that can subsequently have important impacts on human life and property immediately after calving many icebergs capsize roll over by 90 due to the instability of their initial geometry as icebergs melt and respond to the cumulative effects of ocean swell they can also reorient their mass distribution by further capsize and fragmentation these processes release gravitational potential energy and can produce impulsive large amplitude surface gravity waves known as tsunamis a term derived from the japanese language iceberg capsize tsunamis in greenland fjords can be of sufficient amplitude to threaten human life and cause destruction of property in settlements iceberg capsize tsunamis may also have a role in determining why some ice shelves along the antarctic peninsula disintegrate explosively in response to general environmental warming to quantify iceberg tsunami hazards we investigate iceberg capsize energetics and develop a rule relating tsunami height to iceberg thickness this rule suggests that the open water tsunami height located far from the iceberg and from shorelines where the height can be amplified has an upper limit of 0 01h where h is the initial vertical dimension of the iceberg

lower miocene deformation in the hanging wall of the internal external zone boundary of the betic cordillera deformation at the edges of vertical axis rotation domains in oblique convergent margins

obduction subduction and collision as reflected in the upper cretaceous lower eocene sedimentary record of western turkey late cretaceous early eocene tethyan evolution of western turkey is characterized by ophiolite obduction high pressure low temperature metamorphism subduction arc magmatism and continent continent collision the imprints of these events in the upper cretaceous lower eocene sedimentary record of western anatolia are studied in thirty eight well described stratigraphic sections during the late cretaceous period western turkey consisted of two continents the pontides in the north and the anatolide taurides in the south these continental masses were separated by the izmir ankara neo tethyan ocean during the convergence the pontides formed the upper plate the anatolide taurides the lower plate the arc magmatism in the pontides along the black sea coast is biostratigraphically tightly constrained in time between the late turonian and latest campanian ophiolite obduction over the passive margin of the anatolide tauride block started in the santonian soon after the inception of subduction in the turonian as a result large areas of the anatolide tauride block subsided and became a region of pelagic carbonate sedimentation during the campanian the leading margin of the anatolide tauride block was buried deeply and was deformed and metamorphosed to blueschist facies during campanian times the campanian arc volcanic rocks in the pontides are conformably overlain by shaley limestone of maastrichtian palaeocene age however maastrichtian sedimentary sequences north of the tethyan suture are of fore arc type suggesting that although arc magmatism ceased by the end of the campanian age continent continent collision was delayed until palaeocene time when there was a change from marine to continental sedimentation in the fore arc basins the interval between the end of the arc magmatism and continent continent collision may have been related to a northward jump of the subduction zone at the end of campanian time or to continued obduction during the maastrichtian

tectonic setting origin and obduction of the oman ophiolite the semail ophiolite in the oman mountains is the world9s largest and best preserved thrust sheet of oceanic crust and upper mantle 10 000 km 2 550 km long 150 km wide it was emplaced onto the arabian continental margin during late cretaceous time the ophiolite originated 96 94 ma at a spreading center above a northeast dipping subduction zone associated with initiation of immature island arc tholeiitic lavas lasail arc at the highest levels of the ophiolite simultaneous underthrusting of triassic and jurassic mid oceanic ridge basalt and alkalic volcanic rocks beneath 12 km of upper mantle depleted harzburgites produced garnet clinopyroxene amphibolites formed at temperatures of 850 c dated as 95 93 ma subduction cannot have been initiated at a mid oceanic ridge otherwise the protolith of the amphibolites in the metamorphic sole would be the same age and composition as the ophiolite volcanic rocks above in the northern part of the oman mountains in the bani hamid area united arab emirates 870 m of granulite facies rocks enstatite spinel diopside quartzites garnet diopside wollastonite calc silicate marbles clinopyroxene bearing amphibolites were formed at temperatures similar to those of the garnet diopside amphibolites of the oman sole 800 850 c but at slightly higher pressures as much as 9 kbar they are interpreted as deeper level metamorphosed continental margin sedimentary rocks exhumed by out of sequence thrusting placing granulites over mantle sequence harzburgites during the later stages of obduction subduction of the arabian continental crust beneath the obducting semail ophiolite to 78 90 km depth has been proven by thermobarometry of the as sifah eclogites to 20 23 kbar in the eastern sector in the united arab emirates the subducted continental crust began to partially melt producing unusual biotite muscovite garnet tourmaline cordierite andalusite bearing granites that intrude the uppermost mantle sequence harzburgites and lowermost crustal sequence cumulate gabbros of the ophiolite we suggest that the entire leading northeast edge of the arabian plate was subducted beneath the ophiolite during the final stages of obduction leading to eclogitization of the crustal rocks higher temperatures and pressures in the united arab emirates sector possibly due to a thicker or double thickness ophiolite section led to blueschist amphibolite and granulite facies conditions in the metamorphic sole and crustal melting in the subophiolite basement produced leucocratic granites that intruded up as dikes through the obducted ophiolite a model for ophiolite obduction is presented which accounts for all the structural and metamorphic conditions reported from the oman mountains

glycymeris shell accumulations as indicators of recent sea level changes and high energy events in cadiz bay sw spain abstract recent climatic and sea level changes have significantly modified coastal areas and caused the morphological evolution of littoral environments such is the case in cadiz bay sw spain where important changes have taken place from the late holocene to the present day and which have not yet been sufficiently established in this sense some sedimentary indicators such as the glycymeris shell deposits which can be found interstratified in recent coastal sand banks could shed new light on this issue three questions are addressed in this work firstly the age of these shell deposits secondly what is the depositional mechanism responsible for these shelly accumulations and finally what relationship can be established regarding recent sea level changes sample ages indicate that the shells are older than 1000 years bp while the facies indicate high energy flows as depositional mechanisms tides and waves seem insufficient in order to reach the upper shelly deposits for which a more energetic agent would be necessary such as tsunami waves which is feasible given that the zone is located in a tectonically active area where historical tsunamis have been recorded with respect to the relationship with a possible recent sea level rise this could be a better explanation since marine agents would be able to reach the necessary height

heterogeneous mantle complex crustal processes and obduction kinematics in a unified pindos vourinos ophiolitic slab northern greece

sedimentary geology as a key to understanding the tectonic evolution of the mesozoic early tertiary paikon massif vardar suture zone n greece abstract this paper demonstrates how sedimentary evidence can provide a key to elucidating the regional tectonic and palaeoceanographic significance of a complex partly metamorphic terrane in this case the paikon massif the paikon massif is located centrally within the vardar axios zone of n greece and is critical to the reconstruction of neotethys in the e mediterranean region the massif is here restored as a single tectono stratigraphic unit of jurassic to early tertiary age that originated along the margin of a continental unit known as the serbo macedonian zone in this area a mesozoic oceanic basin the almopias ocean opened in the triassic between the serbo macedonian continent to the ne and another continental unit the pelagonian zone to the sw initial deep water deposition along the northwesterly passive margin of the almopias ocean is represented within the paikon massif by metamorphosed redeposited carbonates and hemipelagic sediments gandatch formation above this the jurassic paikon volcanic group comprises two volcanogenic units of island arc type livadia and kastaneri formations the arc developed along the sw margin of the serbo macedonian continent in response to ne subduction of the almopias ocean the subduction also resulted in the opening of a related back arc basin in mid late jurassic represented by the guevgueli ophiolite now to the ne of the paikon massif the massif underwent ductile deformation and inferred hp lt metamorphism during late jurassic time related to subduction beneath the serbo macedonian active margin exhumation took place rapidly by kimmeridgian time followed by a shallow water transgression khromni limestones subsequent emergence and fluvial deposition ghrammos formation reflect a regional extensional or transtensional event following a marine transgression influenced by eustatic sea level rise and tectonic subsidence aptian albian a carbonate platform developed throughout the paikon massif cretaceous transgressive limestones short lived emergence turonian was followed by deepening in the campanian maastrichtian and pelagic carbonate deposition buff pelagic carbonates overlying terrigenous turbidites tchouka flysch form part of an early tertiary foredeep in a regional contractional setting late stage shortening resulted in bivergent thrusting and folding to form the paikon massif as a large anticlinal pop up structure near the axis of the suture zone localised transpression and neotectonic extension complete the picture

antarctic iceberg distribution and dissolution from ship based observations the australian antarctic program s iceberg dataset from ship based observations including information from the austral summer seasons 1984 85 to 1999 2000 is examined and used to extend earlier studies using snapshots of the iceberg population to provide an idea of the iceberg life cycle the distribution of icebergs between 60 and 1508 e is discussed in terms of calving regions and ocean currents temporal changes are also examined the discussion leads us to the point where we can define an area bounded to the north by the maximum sea ice limit and to the south by the antarctic divergence in which icebergs are confined as they drift eastward this allows estimation of total dissolution in terms of iceberg numbers and volume within 108 longitudinal sectors and with knowledge of drift speeds iceberg movement rates and freshwater input across the sector iceberg dissolution rates are found to be 0 03 0 05 m d 1 and the total mass contribution of fresh water to the ocean as the icebergs traverse our 308 of longitude study sector is 32 gt this amounts to a contribution equivalent to precipitation of 15 5 cm a 1 accounting for 2 of the total iceberg discharge from the antarctic ice sheet

the josephine ophiolite northwestern california the 157 m y old josephine ophiolite is a complete ophiolite consisting of the following units harzburgite tectonite cumulate ultramafics cumulate gabbro interlayered with cumulate ultramafics cumulate gabbro high level gabbro and diorite a 1 5 km thick sheeted dike complex and 0 4 km of pillow lava and breccia the ophiolite is conformably overlain by the galice formation consisting of a thin siliceous pelagic sequence overlain by a thick sequence of turbidites having both volcanic arc and continental margin sources the ophiolite and overlying galice formation were intruded by numerous 150 to 151 m y old calc alkaline dikes and sills followed shortly by deformation and regional metamorphism under conditions of prehnite pumpellyite to lower greenschist facies the josephine peridotite makes up the base of the ophiolite and covers 800 km2 it is an alpine type peridotite that represents upper mantle material and the residue of partial melting ultramafic rocks overlying the josephine peridotite are olivine spinel clinopyroxene cumulates that grade upward into clinopyroxene and orthopyroxene olivine plagioclase cumulates and finally to clinopyroxene plagioclase cumulates high level gabbros and diorites are characterized by highly variable textures complex intrusive relationships strongly zoned plagioclase and abundant mafic dikes plagiogranites occur at this level as dikes small intrusions and screens between mafic dikes but they are rare the sheeted dike complex consists of mafic dikes averaging 0 6 m in thickness chilled margins are locally well preserved and many of the dikes have been split and intruded by younger dikes resulting in half and marginless dikes the dike complex is composed of 100 sheeted dikes near the center but contains gabbro screens near the base and pillow lava and breccia screens in its upper parts the dikes are inclined at 40 to bedding after correcting for folding and are inferred to have been rotated shortly after formation the extrusive sequence consists predominantly of pillow lavas but contains abundant pillow breccias and some massive lavas some of the breccias formed as talus deposits whereas others are graded and matrix supported indicating transport and redeposition possibly in an area of rugged submarine topography the dikes and lavas have geochemical affinities to island arc tholeiites but are in some aspects transitional to mid ocean ridge basalts the dikes and lavas are cogenetic with the underlying plutonic sequence as indicated by similarity in crystallization sequence contradictory intrusive relationships between sheeted dikes and high level plutonic rocks and lack of diabase dikes in the lowermost cumulates and harzburgite the upper portions of the ophiolite were hydrothermally metamorphosed at the spreading center resulting in downward changes in mineralogy texture and 18o in addition metalliferous sediments and massive sulfides that occur overlying and within the pillow lavas probably were formed by precipitation from thermal springs a geothermal gradient of 250 350 c km is inferred from mineral assemblages on the basis primarily of its regional setting the ophiolite is inferred to have formed in a back arc basin in particular it is within a thrust sheet sandwiched between a coeval magmatic arc complex and a slightly older arc complex remnant arc this interpretation is consistent with abundant volcanic arc detritus in graywackes overlying the ophiolite the island arc magmatic affinities of the lavas and dikes may be the result of formation of the ophiolite during the earliest stages of back arc spreading

stratigraphical evidence for the depression of the northern margin of the menderes tauride block turkey during the late cretaceous abstract upper cretaceous units on the menderes tauride block show a transition from a passive continental margin to a pelagic basin this transition is related to the emplacement of ophiolitic nappes the pelagic sediments were studied in the aydincik and arslankoy mersin areas in the central tauride region and in the munzur mountains in eastern tauride region in the aydincik area upper cretaceous units consist of upper campanian carbonate breccias with rudist fragments upper campanian lower maastrichtian slope to basinal sediments overlie these carbonate breccias disconformably in the arslankoy area the upper campanian maastrichtian yavca formation consists of globotruncana bearing biomicrites siliciclastic turbidites calciturbidites and debris flows and overlies jurassic cretaceous platform carbonates disconformably the uppermost levels of the liassic cenomanian platform carbonates in the munzur mountains are composed of cenomanian hippurites orbitolina bearing reefal limestones and then turonian campanian globotruncanidae bearing biomicrites the stratigraphic sequence in the menderes tauride block shows that rifting to form a northern neotethyan basin took place in the triassic and gave rise to the inner tauride ocean from jurassic to cenomanian times the northern part of the menderes tauride platform formed a passive continental margin in the late cretaceous the inner tauride ocean is believed to have commenced intra oceanic northward subduction inner tauride oceanic crust derived nappes were emplaced southward onto the menderes tauride block flexural foreland basins in which pelagic sediments were deposited were formed in the taurus mountains related to southward thrusting and the emplacement of the ophiolite nappes

structure and dynamics of the upper mantle beneath the alpine himalayan orogenic belt from teleseismic tomography abstract the upper mantle structure beneath the alpine himalayan orogenic belt ahb at depths from 100 to 500 km has been studied by its tomographic inversion of p wave travel times from earthquakes that occurred in the region and were recorded by the worldwide seismological network at teleseismic distances from the isc catalogues the resulting maps were obtained as a sum of independent inversions in about 60 overlapping blocks 600 800 km in diameter this approach is similar to high frequency spatial filtration and allows investigation of much subtler structures than in global inversion high velocity linear patterns along the ahb have been interpreted as traces of continental or oceanic lithosphere sinking to the upper mantle under the effect of active regional compression the tomographic maps show well pronounced traces of subduction in the region of cretan arc hindukush and burma also confirmed by independent data as well as other less certain evidence of subduction positive anomalies in the western part of the ahb are attributed to subduction in the area of cyprus and along the caucasus kopet dagh lut plate in the tomographic maps one can see traces of the subducted indian slab under western part of himalayas beneath eastern himalayas the upper mantle is rather hot zones of sinking lithosphere are traceable around the tarim block a strong low velocity anomaly in mongolia is apparently related to the hangai plume whose existence was inferred from geological and geophysical evidence