on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

melange genesis and ophiolite emplacement related to subduction of the northern margin of the tauride anatolide continent central and western turkey the tauride anatolide continent stretching for c 900 km across western and central turkey is one of the world s best example of a subducted exhumed passive margin within a collisional orogen twelve widely separated areas were studied and correlated to develop a new plate tectonic model a metamorphosed rifted continental margin of triassic lower cretaceous age tauride anatolide platform is overlain by upper cretaceous cenomanian lower maastrichtian pelagic sediments and then by both tectonic melange subduction complexes and sedimentary melange foredeep gravity complexes the melanges are overthrust by unmetamorphosed ophiolitic rocks commonly peridotites with swarms of diabase gabbro dykes and are underlain by metamorphic soles new geochemical evidence from basaltic blocks in the melange indicates predominantly subduction influenced within plate and mid ocean ridge type settings the dykes cutting the ophiolites were probably intruded during early stage intra oceanic arc genesis the metamorphosed continental margin melanges and ophiolites in the north anatolides are correlated with unmetamorphosed equivalents in the taurides further south e g beysehir and lycian nappes oceanic crust of triassic late cretaceous age formed between the gondwana related tauride anatolide continent in the south and the eurasia related sakarya microcontinent in the north following late triassic early cretaceous passive margin subsidence the continental margin was covered by cenomanian turonian pelagic carbonates c 98 90 ma ophiolites formed in an intra oceanic subduction zone setting in response to northward subduction probably within a two stranded ocean with the inner tauride ocean in the se and the izmir ankara erzincan ocean in the north nw metamorphic soles relate to intra oceanic subduction c 95 90 ma oceanic sedimentary igneous rocks accreted to the advancing supra subduction oceanic slab the tauride anatolide continental margin then underwent diachronous collision with the trench c 85 ma deeply subducted and metamorphosed at hp lt c 80 ma accretionary ophiolitic and exhumed hp lt rocks were gravity reworked into a southward migrating flexural foredeep and progressively overridden c 70 63 ma slices of the upper part of the platform and its margin detached and were thrust southwards as the tauride lycian and beysehir nappes together with regional scale ophiolites the continental margin and melange were simultaneously exhumed during maastrichtian early paleocene 70 63 ma and transgressed by shallow water sediments beginning in the late maastrichtian in the east c 64 ma and the mid late paleocene c 60 ma further west remnant oceanic crust was consumed during early cenozoic time followed by mid eocene 45 40 ma diachronous continental collision and a second phase of regional deformation rather than being progressive there were two stages of collision first upper cretaceous ophiolite emplacement driven by continental margin subduction trench collision and secondly eocene collision of the tauride and sakarya eurasian continents

discovery of a natural co2 seep in the german north sea implications for shallow dissolved gas and seep detection a natural carbon dioxide co2 seep was discovered during an expedition to the southern german north sea october 2008 elevated co2 levels of 10 20 times above background were detected in seawater above a natural salt dome 30 km north of the east frisian island juist a single elevated value 53 times higher than background was measured indicating a possible co2 point source from the seafloor measured ph values of around 6 8 support modeled ph values for the observed high co2 concentration these results are presented in the context of co2 seepage detection in light of proposed subsurface co2 sequestering and growing concern of ocean acidification we explore the boundary conditions of co2 bubble and plume seepage and potential flux paths to the atmosphere shallow bubble release experiments conducted in a lake combined with discrete bubble modeling suggest that shallow co2 outgassing will be difficult to detect as bubbles dissolve very rapidly within meters bubble plume modeling further shows that a co2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly co2 enriched water tends to sink toward the seabed results suggest that released co2 will tend to stay near the bottom in shallow systems 200 m and will vent to the atmosphere only during deep water convection water column turnover while isotope signatures point to a biogenic source the exact origin is inconclusive because of dilution this site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor

late permian triassic magmatic evolution in the jinshajiang orogenic belt sw china and implications for orogenic processes following closure of the paleo tethys growth of continental crust involves the complex interplay of subduction zone magmatism to generate the crust followed by stabilization through crustal thickening magmatism and ultimately isolation from the active plate margin the jinshajiang orogenic belt sw china provides an exceptional record of continental development as the result of closure of the paleo tethys seaway and ensuing collision a compilation of u pb age and geochemical data for the plutonic and volcanic rocks within the southern part of the jinshajiang orogenic belt including new high precision ages for the ludian granitoid batholith of 231 to 220 ma enables us to explore the interaction between magmatism and orogeny in the context of the paleo tethys closure and continental amalgamation these age and geochemical constraints in conjunction with other geologic evidence suggest that subduction of the paleo tethys ocean dominated local tectonics prior to the triassic creating a volcano plutonic arc along the eastern margin of the qamdo simao terrane following consumption of the ocean collision zone magmatism dated at 247 to 237 ma was manifested by eruption of voluminous volcanic rocks in a suture parallel zone crustal anatexis was contemporaneous with the earliest phases of collision producing high silica rhyolites of early triassic age ca 247 246 ma between 245 and 237 ma the local tectonic regime switched from compression to extension probably due to strain partitioning caused by oblique convergence which led to the development of rift basins and extensive syn tectonic bimodal volcanism associated with deep water sediments from 234 ma to 214 ma the emplacement of high k calc alkaline granodiorites monzogranites occurred prior to or during isostatic uplift and extension probably caused by breakoff of the subducted slab the resultant exhumation brought deep seated granitoid batholiths to the surface and was contemporaneous with intrusion of ultramafic mafic melts ophiolitic melange ca 362 294 ma and collision related magmatic suites 247 214 ma are unconformably overlain by a late triassic 229 217 ma conglomerate rich sequence that represents an overlap assemblage across the qamdo simao terrane indochina and yangtze block of south china

an experimental investigation into quantifying co2 leakage in aqueous environments using chemical tracers abstract chemical tracers can be an effective means of detecting attributing and quantifying any leaks to the surface from geological co2 stores co2 release experiments have found it difficult to ascertain the fate or quantify the volume of co2 without the application of tracers however a significant proportion of global co2 storage capacity is located offshore and the marine environment poses constraints that could limit the success of using tracers these constraints include uncertainties in the behaviour of tracers in marine sediments and the water column and sampling challenges however to date there have been few experimental investigations to address these uncertainties here we used a benchtop experimental setup to explore how effectively methane a common constituent of captured co2 and of reservoir fluids can aid the quantitation of co2 leakage in aqueous environments the experiment simulated gas leakage into sediments that mimic the seabed and we measured the partitioning of co released gases under different environmental conditions and injection rates we find that the style of seepage and the fate of the co2 are affected by the presence of a sand layer and the injection rate we discuss the implications for leak monitoring approaches including how tracers may be used to quantify the leak rates and fate of co2 in aqueous environments our work contributes to ongoing efforts to develop robust offshore monitoring system that will assure operators regulatory bodies and the public of co2 storage integrity

bimodal magmatism produced by delamination geochemical evidence from late palaeozoic volcanic rocks from the yili block western tianshan northwestern china

nd isotopic mapping of the sri lanka basement update and additional constraints from sr isotopes abstract the high grade crystalline basement of sri lanka can be subdivided into three provinces distinguished by distinct isotopic model ages this confirms the conclusions of milisenda et al 1988 made on the basis of much more limited data high grade ortho and paragneisses from the highland complex in central sri lanka yield palaeoproterozoic to archaean nd model ages from 2 0 to 3 4 ga and reflect an extended premetamorphic crustal history the wanni complex in the western and northwestern part of the island is characterized by meso to neoproterozoic nd model ages ranging from 1 0 to 2 0 ga the vijayan complex in the southeast is occupied by neoproterozoic i type granitoids with nd model ages from 1 0 to 1 8 ga this distinct crustal province appears to fit best a detached continental margin plutonic terrane the isotopic data preclude a common premetamorphic history of the wanni and vijayan complexes with the ancient highland complex the combined nd sr and pb isotope data together with recent geochronological studies strongly suggest that the distinct crustal age provinces are separated by tectonic discontinuities and that they represent terranes that were accreted just prior to the high grade metamorphic event in neoproterozoic time

slab breakoff a critical appraisal of a geological theory as applied in space and time abstract the idea that prominent geological phenomena observed in the crust and at the surface may be caused by the detachment of subducting dense lithosphere has been anticipated by tectonic models in the sixties and seventies and imaged with improved geophysical techniques in the eighties in the mid nineties the model of slab breakoff was defined formally by davies and von blanckenburg initially proposed as a thought provoking working hypothesis the theory rapidly received wide a priori acceptance and was applied to virtually every mountain range around the world and even in orogens as old as paleoproterozoic and archean to explain a range of different phenomena these include magmatic flare ups rapid topographic uplift increasing sediment supply fast exhumation of metamorphic rocks ore mineralizations anomalous distribution of seismicity changes in stress regimes and inversion of subduction polarity even multiple breakoff events were assumed to have occurred at different times in the same orogenic belt or subduction zone in the last 20 years slab breakoff has been invoked in so many settings and time frames that it could have hardly taken place in each and every case in which it was called upon this article does not critically examine the theory but critically examines its use the extensive review of the vast literature presented here on the subject reveals how the model has been often applied to provide ad hoc explanations for a range of poorly understood observations based on incomplete evidence of deep seated processes our aim is to illustrate a paradigmatic example of how earth scientists in the face of evidence that challenges our capacity of understanding often recur to hypotheses based on other hypotheses such an approach may induce researchers to look for confirmation in the absence of compelling constraints or even in the face of conflicting evidence the faith in models should not lead us to confuse speculative theories with axiomatic truths and to build upon them theoretical edifices that are vulnerable and exposed to the risk of circular reasoning

evolution of the mo rich scheelite skarn mineralization at kozbudaklar western anatolia turkey evidence from mineral chemistry and fluid inclusions abstract the kozbudaklar scheelite skarn deposit in the tavsanli zone located approximately 22 km southeast of bursa is hosted by the triassic calcic inonu marble and eocene topuk pluton at least four stages have been recognized through skarn evolution scheelite skarn distributed close to the topuk pluton occurred during the early stage 1 and late stage 2 prograde substages the early prograde endo and exoskarn are composed of hedenbergite hd 96 joh 4 plagioclase an 55 64 and hedenbergite hd 61 94 joh 4 7 accompanied by calcic garnet grs 38 94 sps 1 5 alm 0 and scheelite pow 1 6 the second stage represents a relatively oxidized mineralogy dominated by diopside hd 16 48 joh 0 9 subcalcic garnet grs 24 92 sps 0 11 alm 0 31 and scheelite pow 7 32 the stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing fluid inclusions from skarn rocks are indicative of multiple fluid events 1 low moderate salinity 5 16 wt nacl equiv inclusions homogenized dominantly by a high temperature 308 c to 600 c liquid phase in stage 1 fluid inclusions in an early garnet homogenized over a similar temperature range 440 c and 459 c into both liquid and vapor phases eutectic temperatures ranging from 61 7 c to 35 0 c that indicate the presence of h 2 o nacl mgcl 2 cacl 2 co 2 solutions 2 coexisting daughter mineral bearing high salinity 29 5 70 wt nacl equiv and vapor rich moderate salinity 11 5 16 7 wt nacl equiv inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range 308 c to 600 c in stage 2 eutectic temperatures range from 67 9 c to 51 8 c that shows the presence of h 2 o nacl co 2 ch 4 n 2 solutions 3 low moderate salinity 12 5 7 6 wt nacl equiv and temperature 320 c to 215 c inclusions homogenized by the liquid phase in stage 3 eutectic temperatures range from 59 5 c to 44 2 c indicating the presence of h 2 o nacl mgcl 2 cacl 2 co 2 solutions 4 inclusions of low salinity 9 9 0 9 wt nacl equiv and homogenization temperature 183 c to 101 c in stage 4 these data show that the kozbudaklar skarn deposit was formed in a magmatic hydrothermal system in this model carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 c and 459 c and pressures ranging from 50 mpa to 60 mpa based on hydrostatic considerations early scheelite was precipitated with relatively reduced mineral compositions as a result of depressurization mo rich scheelite with oxidized minerals formed via high salinity and vapor rich inclusions the second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1 5 mpa at shallow depths

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

fracture controlled fluid circulation and dissolutional weathering in sinkhole prone carbonate rocks from central italy abstract fractures karstic cavities and calcite precipitates are analysed on mesozoic carbonate strata from the cornicolani mountains central italy to quantify the relationships between fractures and related karstic cavities and to infer the fracture controlled fluid pathways the study area is characterized by active sinkholes and other karstic caves which are among the deepest ones in the world results show a clear control of fractures on the process of dissolutional weathering and therefore on the fluid circulation a model is proposed in which two different modes of dissolutional weathering coexist i a mode of diffuse weathering consisting in the dissolutional enlargement of closely spaced joints and bedding surfaces this process affects the strata situated at depths of up to 5 m ii a mode of more concentrated weathering active along highly permeable fault damage zones at depths of at least 70 m these processes are mostly connected with the shallow circulation of calcite dissolving meteoric waters and are controlled by the disparity of permeability between the fault damage zones and the surrounding jointed strata some calcite precipitates along the studied fault damage zones may be connected with a dissolutional process operated by waters that interacted with the adjacent quiescent volcanic district such calcite dissolving waters and the presence of high permeable fault damage zones along which the waters may ascent are probably the cause for the development of some of the deep sinkholes along faults in the study area

rhenium enrichment in the muratdere cu mo au re porphyry deposit turkey evidence from stable isotope analyses δ34s δ18o δd and laser ablation inductively coupled plasma mass spectrometry analysis of sulfides the muratdere cu mo au porphyry deposit in western turkey contains elevated levels of rhenium and is hosted within granodioritic intrusions into an ophiolitic melange sequence in the anatolian belt the deposit contains several stages of mineralization early microfracture hosted molybdenite and chalcopyrite followed by a quartz pyrite chalcopyrite vein set associated with cu au grade a quartz chalcopyrite pyrite molybdenite vein set associated with cu mo re grade and a later polymetallic quartz barite sphalerite galena pyrite vein set the rhenium in muratdere is hosted within two generations of molybdenite early microfracture hosted molybdenite and later vein hosted molybdenite in situ laser ablation inductively coupled plasma mass spectrometry analysis of sulfides shows that the later molybdenite has significantly higher concentrations of re average 1 124 ppm 730 ppm n 43 than the early microfracture hosted molybdenite average 566 ppm 423 ppm n 28 pyrite crystals associated with the re rich molybdenite have higher co and as concentrations than those in other vein sets with au associated with as the microfracture hosted sulfides have 34s values between 2 2 and 4 6 consistent with a magmatic source the vein hosted sulfides associated with the high re molybdenite have a 34s signature of 5 6 to 8 8 similar to values found in peridotite lenses in the anatolian belt the later enrichment in re and 34s enriched s may be sourced from the surrounding ophiolitic country rock or may be the result of changing redox conditions during deposit formation

slab breakoff a model for syncollisional magmatism and tectonics in the alps slab breakoff is the buoyancy driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision in a recent paper davies and von blanckenburg 1994 have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts breakoff will lead to heating of the overriding lithospheric mantle by upwelling asthenosphere melting of its enriched layers and thus to bimodal magmatism breakoff will also lead to thermal weakening of the subducted crustal lithosphere thereby allowing buoyant rise of released crustal slices from mantle depths in this paper we present a test of this model in the tertiary evolution of the european alps in the alps both basaltic and granitoid magmatism occur between 42 and 25 ma following the closure of oceanic basins by subduction and continental collision the granitoids are now well established to result from mixing of basalt with assimilated continental crust to identify the tectonically crucial origin of the partial mantle melts we have compiled all published geochemical and isotopic data of numerous mafic dykes occurring throughout the whole alpine arc their trace element and isotopic composition suggests that they have been formed by low degree melting of the mechanically stable lithospheric mantle we see no evidence for melting of asthenospheric mantle it was thus not decompressed to depths shallower than 50 km once initiated rapid lateral migration of slab breakoff will result in a linear trace of magmatism in locally thermal weakened crust this explains why all alpine magmatic rocks intruded almost synchronously along a strike slip fault the periadriatic lineament a compilation of ages from penninic high pressure rocks subducted to depths of up to 100 km shows that subduction took place at circa 55 40 ma followed by uplift at 40 35 ma from the short time interval between their uplift and the onset of magmatism we infer that both processes have been induced by the breakoff the slab breakoff model fulfills its predictions in the case of the alps and therefore supports the assumptions made in the theoretical model on a geological basis we believe that the characteristic association of magmatic activity with the return of high pressure rocks to the surface allows the identification of this process in the earth s mountain belts

petrogenesis and 40ar 39ar geochronology of the volcanic rocks of the usak gure basin western turkiye abstract in spite of much research over the past 30 years the dynamic evolution origin of the volcanism and geometrical stratigraphical relations of the ne sw trending basins in western anatolia are poorly understood the usak gure basin is one of the prominent ne sw trending basins developed on the northern part of the menderes massif core complex three distinct volcanic successions are found in the usak gure basin 1 the beydagi volcanic unit composed of shoshonite latites and rhyolitic lavas followed by dacitic and andesitic pyroclastic deposits 2 the payamtepe volcanic unit composed of potassic intermediate composition lavas latites and trachytes and 3 the karaagac dikes composed of andesite and latite the beydagi volcanic unit occurs in three different ne sw trending volcanic centers beydagi itecektepe and elmadag calderas from southwest to northeast respectively the oldest radiometric ages for the beydagi volcanic unit are from the elmadag volcanic center in the north and range from 17 to 16 ma the data indicate that volcanism was active during the latest early miocene the youngest radiometric age for the beydagi volcanic unit is obtained from the beydagi caldera located 12 ma in the south the data indicate that beydagi volcanism was active in the late middle miocene and migrated from north to south with time 40ar 39ar ages of the payamtepe volcanic unit are restricted to a short period between 16 0 and 15 9 ma volcanic rocks of the usak gure basin are characterized by strong enrichment in lile and lree and depletions of nb ta and ti on morb normalized multi element diagrams geochemical features of the volcanic rocks suggest that they experienced mixing processes between mafic and felsic end members and also fractional crystallization of dominantly plagioclase and pyroxenes from mixed magma compositions crustal contributions to the magma sources may also have occurred during magmatic evolution these processes have resulted in scattered major and trace element variations with respect to increasing silica contents geochemical features of the most mafic samples agree with the results of previous studies from other volcanic areas in western anatolia suggesting that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the african and eurasia plates the volcanic activity in the region which developed synchronously with the formation of the menderes massif core complex is best explained by delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction related processes

geochemistry geochronology and cathodoluminescence imagery of the salihli and turgutlu granites central menderes massif western turkey implications for aegean tectonics abstract the menderes massif western turkey is an important metamorphic core complex located in the aegean region geochemical and geochronological data from this extensional domain facilitates our understanding of large scale extension of the earth s lithosphere s type peraluminous granites salihli and turgutlu that intrude the alasehir detachment which bounds the northern edge of the central menderes massif may have been generated due to subduction of the eastern mediterranean floor along the hellenic trench in situ th pb ion microprobe monazite ages from the granites range from 21 7 4 5 ma to 9 6 1 6 ma 1 higher uncertainty in the ages is attributed to monazite common pb but the range is consistent with cathodoluminescence cl imagery that document complex textures within the samples salihli and turgutlu granites share many similar characteristics including multiple generations of plagioclase some with shocked cores plagioclase replacing k feldspar and the development of myrmekite evidence for fluid interaction and multiple generations of microcracks and microfaults the granites may have evolved from compositionally distinct magma sources as salihli samples in general contain allanite as the major accessory mineral whereas turgutlu granites contain monazite however the cl imagery document similar alteration textures the youngest turgutlu monazite grain 11 5 0 8 ma is located in the rim of a k feldspar grain close to myrmekite and the youngest salihli monazite grain 9 6 1 6 ma is located in the outer edge of an altered plagioclase crystal these ages likely time episodes of deformation as the granites were subjected to exhumation along the alasehir detachment ages reported here are similar to dates constraining extension reported elsewhere in the aegean but indicate a level of complexity when linking movement within the menderes massif to the large scale geodynamic processes that created other metamorphic core complexes in the region difficulties exist in linking the ages obtained from the granites to specific tectonic events due to the presence of secondary alteration textures generations of mineral growth and multiple episodes of deformation

40ar 39ar and rb sr geochronology of high pressure metamorphism and exhumation history of the tavsanli zone nw turkey geochronological investigations in high and ultra high pressure metamorphic rocks are problematic since firstly the low temperatures lead to fine grain size and disequilibrium assemblages and secondly the problem of excess argon affects 40ar 39ar systematics the most commonly used isotopic system the tavsanli zone is a belt of high pressure low temperature hp lt rocks spanning nw turkey and is one such region where previous geochronological studies have produced a range of estimates for the age of hp lt metamorphism raising the question of whether they are geologically significant this study presents new data from the tavsanli zone 40ar 39ar ages are in the range 60 ma to 175 ma whilst rb sr ages are restricted to 79 7 ma to 82 8 ma confirming the presence of excess argon detailed ultra violet laser ablation microprobe uvlamp studies have revealed younger 40ar 39ar ages in the cores of coarser white micas which in conjunction with 40ar 39ar ages from the finest grained lithologies and the rb sr white mica crystallisation ages constrain the post hp lt metamorphism exhumation rates of these rocks petrological and regional constraints suggest that syn subduction exhumation and cooling took place initially by synchronous subduction and exhumation by underplating this is followed by a phase of syn continent continent collision at a rate of approximately 1 5 mma 1 and exhumation to the surface via thrusting the 40ar 39ar hornblende data from a granodiorite intruding the hp lt rocks constrain the later parts of exhumation path this study highlights the importance of a multi system geochronological approach when attempting to determine the history of hp lt rocks

i type plutonism in a continental back arc setting miocene granitoids and monzonites from the central aegean sea greece miocene extension in the aegean sea was accompanied by the intrusion of granitoid and monzonitic magmas at upper crustal levels with increasing distance from the trench the metaluminous to slightly peraluminous i type intrusives show a systematic regional variation in their compositions medium to high k granodiorites in the wsw high k low silica granites in the central region and high k high silica granites monzonites monzogranites and composite lamprophyric monzonitic dikes in the ene the granodioritic and low silica granitic plutons comprise similar ranges of sio2 63 5 71 6 wt and initial nd sr and o isotopic values end i 7 0 to 9 8 87sr 86sr i 0 7092 0 7115 18o 9 7 11 5 but display significant differences in their chemical compositions compared with the granodiorites the low silica granites have higher abundances of large ion lithophile light rare earth and some high field strength elements initial isotopic signatures of the high silica granites in the ene end i 9 0 to 9 6 87sr 86sr i 0 7128 0 7144 18o 10 8 12 0 are slightly more crust like than those of the low silica granites in chemical variation diagrams samples from the high silica granites continue the trends defined by those from the low silica granites it is suggested that all granitoid magmas originated by dehydration melting of metaluminous older crustal sources most probably metagreywackes u pb systematics of zircon populations in conjunction with zr sio2 systematics and zircon saturation temperatures suggest a high proportion of restitic or assimilated crustal material in these magmas monzonitic to monzogranitic rocks show chemical and isotopic characteristics end i 0 8 to 3 6 87sr 86sr i 0 7059 0 7071 18o 9 4 10 6 that are significantly different from those of the granitoids a small portion of an older crustal component in these magmas is indicated by u pb systematics of zircon populations lamprophyric dikes display chemical and isotopic signatures end i 0 5 87sr 86sr i 0 7044 18o 8 9 that are compatible with an origin from either a mantle source previously enriched by slab derived hydrous fluids melts as suggested by negative nb ta anomalies or a new k rich basaltic underplate abundant composite dikes indicate the coexistence of and mingling mixing between lamprophyric melts and monzonitic magmas

geochronology petrogenesis and tectonic significance of huashugou granitoids in north qilian nw china abstract north qilian orogenic belt nqob is a typical early paleozoic orogenic belt in china however the tectonic setting of nqob remains controversial especially the post subduction processes in this study we report whole rock geochemistry zircon u pb ages and hf nd isotopic compositions of huashugou granitoids in the western segment of the nqob nw china la icp ms u pb dating of zircon from huashugou granitoids indicate magmatic crystallization ages of ca 420 ma with late paleoproterozoic captured zircons of ca 1700 ma the huashugou granitoids show enrichment in light rare earth elements and large ion lithophile elements e g rb th and u depletion of heavy rare earth elements and high field strength elements e g nb ta and ti negative eu anomalies and a cnk

collision driven slab breakoff magmatism in northwestern anatolia turkey abstract postcollisional eocene magmatism in northwestern anatolia produced two e w trending linear belts of plutons along and north of the izmir ankara erzincan suture zone iaesz whose geochemical features and age relations support a slab breakoff model for their petrogenetic oinevolution the suture zone granitoids szgs in the southern belt have ages around 54 48 ma are intrusive into blueschist rocks of the iaesz and are composed of diorite quartz diorite granodiorite and syenite the marmara granitoids mgs in the northern belt are slightly younger 48 35 ma intrusive into the paleozoic mesozoic crystalline basement rocks of the sakarya continent and composed of monzogranite granite and granodiorite both szgs and mgs have moderately to highly evolved medium to high k calc alkaline compositions and are predominantly metaluminous i type granitoids nd sr isotope systematics documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepacka

timing aegean extension evidence from in situ u pb geochronology and cathodoluminescence imaging of granitoids from nw turkey abstract the biga peninsula of nw turkey hosts granitoid plutons that record the timing of extension in the aegean region here we focus on three plutons the kozak eybek and kestanbol and apply new methods to obtain a detailed tectonic history of their generation and exhumation in situ in thin section ion microprobe zircon geochronology and color cathodoluminescence cl imaging of zircon grains and whole thin sections show these granites experienced magma mixing brittle deformation and significant fluid rock interactions zircon ages range from the late eocene to late miocene with two ages from a single grain that are permian the late eocene early oligocene ages record the end stages of subduction during the closure of a branch of the neo tethyan ocean whereas late oligocene late miocene ages record the plutons extension and exhumation we present a model in which kozak eybek and kestanbol magmas were initially generated by fluid flux melting from dehydration of the subducting anatolide tauride block as evidenced by the late eocene to early oligocene ages late oligocene ages document the initiation of extension in the biga peninsula region and correlate to ages timing exhumation of the kazdag massif early miocene ages indicate continued aegean extension in the southern biga peninsula region at this time

geochemical and temporal evolution of cenozoic magmatism in western turkey mantle response to collision slab break off and lithospheric tearing in an orogenic belt post collisional magmatism in western anatolia began in the eocene and has occurred in discrete pulses throughout the cenozoic as it propagated from north to south producing volcano plutonic associations with varying chemical compositions this apparent sw migration of magma tism and accompanying extension through time was a result of the thermally induced collapse of the western anatolian orogenic belt which formed during the collision of the sakarya and tauride anatolide continental blocks in the late paleocene the thermal input and melt sources for this prolonged magmatism were provided first by slab break off generated aesthenospheric flow then by lithospheric delamination related aesthenospheric flow followed by tectonic extension driven upward aesthenospheric flow the first magmatic episode is represented by eocene granitoid plutons and their extrusive carapace that are linearly distributed along the izmir ankara suture zone south of the marmara sea these suites show moderately evolved com positions enriched in incompatible elements similar to subduction zone influenced subalkaline magmas widespread oligo miocene volcanic and plutonic rocks with medium to high k calc alkaline compositions represent the next magmatic episode partial melting and assimilation fractional crystallization of enriched subcontinental lithospheric mantle derived magmas were important processes in the genesis and evolution of the parental magmas which experienced decreasing subduction influence and increasing crustal contamination during the evolution of the eocene and oligo miocene volcano plutonic rocks collision induced lithospheric slab break off provided an influx of aesthenospheric heat and melts that resulted in partial melting of the previously subduction metasomatized mantle lithosphere beneath the suture zone producing the eocene and oligo miocene igneous suites the following magmatic phase during the middle miocene 16 14 ma developed mildly alkaline bimodal volcanic rocks that show a decreasing amount of crustal contamination and subduction influence in time both melting of a subduc tion modified lithospheric mantle and aesthenospheric mantle derived melt contribution played a significant role in the generation of the magmas of these rocks this magmatic episode was attended by region wide extension that led to the formation of metamorphic core complexes and graben systems aesthenospheric upwelling caused by partial delamination of the lithospheric root beneath the western anatolian orogenic belt was likely responsible for the melt evolution of these mildly alkaline volcanics lithospheric delamination may have been caused by peeling off during slab rollback the last major phase of magmatism in the region starting c 12 ma is represented by late miocene to quaternary alkaline to super alkaline volcanic rocks that show oib like geochemical features with progressively more potassic compositions increasing toward south in time these rocks are spatially associated with major extensional fault systems that acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface the melt source for this magmatic phase carried little or no subduction component and was pro duced by the decompressional melting of aesthenospheric mantle which flowed in beneath the atte nuated continental lithosphere in the aegean extensional province this time progressive evolution of cenozoic magmatism and extension in western anatolia has been strongly controlled by the interplay between regional plate tectonic events and the mantle dynamics and provides a realistic template for post collisional magmatism and crustal extension in many orogenic belts

post collisional adakite like magmatism in the agvanis massif and implications for the evolution of the eocene magmatism in the eastern pontides ne turkey abstract in the anatolia the caucasus and northwest iran the eocene epoch is characterized by widespread basic to acidic magmatism whose temporal and spatial evolutions and origin are poorly understood in this paper we provide geochronological and geochemical data on a suite of early eocene intrusions from northeast turkey and discuss their origin within a regional tectonic framework post to late collisional moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude permo triassic low grade metamorphic rocks in the southern part of the eastern pontides very close to the neo tethyan izmir ankara erzincan suture in places the intrusives display well developed subsolidus foliations indicating on going penetrative deformation during and shortly after emplacement different emplacement depths were inferred based on the contact metamorphic mineral assemblages al in hornblende barometry and igneous textures quartz diorite 14 16 km vs dacitic porphyries 7 km biotite and hornblende ar ar and zircon u pb data indicate that the compositionally and texturally different intrusives were emplaced at 51 ma ypresian three lines of evidence indicate that the early eocene represents a tectonically active time with high exhumation rates 0 6 cm a 1 i the quartz diorite and dacitic porphyries were emplaced at different crustal depths ii the emplacement ages of these texturally distinct intrusive rocks are geochronologically undistinguishable and iii intrusive rocks locally show a well developed foliation the intrusive rocks display high abundances of al 2 o 3 sr ba lrees and low abundances of y sc and hrees and are similar to high silica adakites from supra subduction zone settings the geochemical features imply a residual and or fractionating assemblage rich in hornblende garnet pyroxene and poor in plagioclase all rock types display similar sr nd isotopic characteristics with initial e nd and 87 sr 86 sr values ranging from 1 0 to 1 1 and from 0 70421 to 0 70494 respectively these three coeval rock groups quartz diorite leucogranodiorite and dacite porphyries were generated from a similar source by variable degrees of partial melting and fractionation these data together with those from the literature clearly reveal that the adakitic signature is common in paleocene to early eocene igneous rocks in northern turkey on both sides of the izmir ankara erzincan suture but disappears towards the middle eocene regional geological constraints indicate that the continental collision between the pontides and the anatolide tauride block occurred in the paleocene and that the middle eocene represents a period of major extension characterized by a marine transgression we therefore suggest that the early eocene adakitic magmatism in northern turkey resulted from the presence of a thickened continental crust following the continental collision along the neo tethyan izmir ankara erzincan suture whereas the voluminous middle eocene magmatism was related to extensional collapse of a thickened orogen

the mount kozak magmatic complex western anatolia abstract the mount kozak igneous complex is located close to the towns of ayvalik bergama and burhaniye in the western anatolia turkey magmatic activity occurred during the late oligocene early miocene beginning with the emplacement of the kozak pluton sheet intrusive rocks formed around it coevally they are surrounded by the volcanic rocks partly contemporaneously with the emplacement of the granitic rocks during the early miocene the upper oligocene lower miocene magmatic rocks of the kozak region are represented by a high k calc alkaline suite of predominantly intermediate and acidic composition their geochemical characteristics suggest that the magmas are hybrid and were formed from a similar source representing mantle derived magmas contaminated by crustal materials the cogenetic plutonic rocks the hypabyssal rocks and the overlying volcanic associations are related to one another in space and time and appear to have been connected to a shallow level granitic intrusion in a caldera collapse setting the calc alkaline magmatic activity waned during the middle miocene when the volcanism was rejuvenated during the late miocene pliocene alkaline basalt lavas were formed as fissure eruptions

the emplacement history of granitic intrusions into the upper crust forceful to passive emplacement of the early miocene solarya pluton nw turkey as a case study abstract post collisional magmatism in western anatolia produced several granitic bodies represented by shallow level intrusions in this study we present field geochronology and geothermo barometry results of the solarya pluton sp nw turkey in order to better understand its emplacement into the different levels of the crust the sp consists of three main plutonic members showing different textural properties the northern part of the plutonic body is represented by k feldspar megacrystalline granodiorite kfmg with distinct porphyritic texture and southern part is made up of microgranite granodiorite mgg displaying microgranular texture whereas haplogranite which displays graphic granophyric textures is represented by a thin aureole between the sp and basement rocks field relations petrography and geothermo barometry studies combined with 40ar 39ar and u pb zircon dating results suggest that different members of the sp were emplaced into different levels of crust with different mechanisms the kfmg 40ar 39ar 23 2 ma u pb 21 8 ma began its emplacement forcefully in the relatively deeper levels in the crust av 1 65 kbar av 797 c 6 1 km depth after this stage mgg 40ar 39ar 22 6 ma u pb 21 2 ma was passively emplaced into the shallow levels av 0 69 kbar av 745 c 2 4 km depth via cauldron subsidence and in the latter stages the sheet intrusive rocks haplogranite 40ar 39ar 21 6 ma and hypabyssal association were emplaced into the ring faults at 1 5 km depth forceful to passive emplacement of the sp into the upper crust occurred under aegean extensional tectonics our study contributes to examination of the granite ascent and emplacement within other extensional provinces worldwide

stratigraphic record of triassic jurassic collisional tectonics in the blue mountains province northeastern oregon sedimentary and volcanic rocks in the blue mountains province bmp of northeastern oregon preserve a well studied record of triassic jurassic magmatism basin evolution and terrane accretion terranes of the bmp represent two magmatic arcs wallowa and olds ferry terranes an intervening oceanic subduction and accretionary complex baker terrane and a complex thick succession of sedimentary rocks commonly known as the izee terrane we divide volcanic and sedimentary rocks into two regionally correlative unconformity bounded megasequences 1 ms 1 late triassic to early jurassic deposits that change up section from 1a older volcanic and volcaniclastic deposits of the wallowa and olds ferry arcs to 1b marine turbidites shale and argillite with chert clast conglomerate and olistostromes derived from the emergent baker terrane and 2 ms 2 early to late jurassic marine deposits that overlap older rocks and structures and record 20 to 40 m y of deep crustal subsidence in a large marine basin many of the known stratigraphic relationships in the blue mountains cannot be explained using the existing model for a middle triassic to late jurassic west facing non collisional volcanic arc and forearc basin we propose a new tectonic model for the bmp based on prior studies and comparison to modern analogues which includes 1 middle triassic magmatism in the wallowa and olds ferry arcs during subduction and progressive closure of an ocean basin 2 late triassic collision between facing accretionary wedges of the wallowa and olds ferry arcs and growth of marine basins on both sides of the emergent baker terrane thrust belt 3 early to middle jurassic terrane continent collision which resulted in closure of a wide back arc basin crustal thickening and loading in nevada and growth of a large marine collisional basin in the bmp and 4 late jurassic thrusting regional shortening and final accretion of the basin and underlying terranes to western north america this analysis suggests that collisional tectonics may have played a significant role in plate interactions that drove triassic jurassic crustal thickening mountain building and basin development in the western north american cordillera

amphibole out phase boundary in partially melted metabasalt its control over liquid fraction and composition and source permeability a number of experimental studies in recent years have demonstrated that partial melting of hydrated basalt at lower crustal to upper mantle pressures is capable of generating up to 40 high sio2 liquids closely comparable in many geochemical respects to tonalitic trondhjemitic granitoids ttg from these studies it is apparent that the initiation of melting coincides with the beginning of amphibole dehydration but that a broad reaction interval over which amphibole coexists with high sio2 liquids is defined by the wet basalt solidus on one side and the amphibole out phase boundary on the other the phase relations of an alkali rich tholeiitic metabasalt have been examined in the outer half of this region up to and beyond the amphibole out phase boundary results indicate that amphibole exerts a strong control over the amount and composition of coexisting liquid over this interval melt fraction increases slowly and gradually from 0 up to 20 30 between the wet basalt solidus and up to amphibole out but increases substantially from 30 to 50 across and immediately beyond it liquids are strongly to moderately peraluminous molar al2o3 cao na2o k2o a cnk 1 0 up to amphibole out neutral at the boundary a cnk 1 0 and increasingly metaluminous a cnk 1 0 beyond it up to amphibole out potassium is strongly partitioned into liquid relative to amphibole i e mineral melt kd 0 2 0 3 whereas titanium is strongly partitioned into liquid kd 2 0 6 0 physical and chemical criteria suggest that efficient melt segregation leading to ttg plutonism requires more than 20 30 batch melting of a garnet bearing basaltic protolith near or beyond the amphibole out phase boundary leaving dry residues of eclogite or garnet granulite and producing metaluminous liquids that are strongly depleted in heavy rare earth elements hrees and yttrium y lower degrees of melting may involve critical melting where melt is squeezed out of the residue by deformation of the crystalline matrix resulting in disequilibrium melt compositions

the diversification of granitoids and plate tectonic implications at the archaean proterozoic boundary in the bundelkhand craton central india

petrogenesis and time progressive evolution of the cenozoic continental volcanism in the biga peninsula nw anatolia turkey abstract the post collisional cenozoic magmatic activity in the biga peninsula nw anatolia started in the middle eocene 45 3 0 9 ma and lasted continuously until the late miocene 8 32 0 19 ma with minor punctuations producing widespread volcanoplutonic complexes these magmatic suites are characterized by calc alkaline high k calc alkaline shoshonitic mildly alkaline and alkaline series the middle eocene to middle miocene lavas have high lile lree lile hfse and 87sr 86sr i 0 7046 0 7087 and low nd i 1 2 to 6 4 values by contrast the late miocene lavas have the lowest 87sr 86sr i 0 7030 0 7033 and the highest nd i 2 6 to 6 7 values geochemical features of these rocks indicate two episodes of enrichment processes during the evolution of the eocene early miocene volcanism in the biga peninsula the first stage source enrichment metasomatism occurred within the continental lithospheric mantle as a result of the previous subduction event s and produced a heterogeneously enriched source the second stage crustal contamination resulted from interaction between the metasomatized mantle derived melts and those magmas derived from the sakarya crustal basement during their ascent to the surface slab breakoff induced asthenospheric upwelling caused the melting of metasomatized mantle lithosphere beneath the sakarya continent and produced the middle eocene calc alkaline lavas geochemical isotopic and age relationships suggest increasing amounts of crustal contamination and a decreasing subduction signature during the evolution of magmas from the eocene through the early miocene crustal input was peaked during the early miocene volcanism coinciding with the exhumation and rapid uplift of the kazdag metamorphic massif asthenospheric upwelling beneath the kazdag core complex contributed to the generation of hybrid magmas formed from mixing of mantle and crustal melts during this stage the middle miocene 15 2 ma mildly alkaline rocks show less pronounced enrichment in lile and lree and display intermediate major and trace element compositions between the early miocene and late miocene lavas the cenozoic volcanism in biga peninsula waned briefly during 15 11 ma and was subsequently rejuvenated late miocene 11 0 0 4 8 32 0 19 ma producing mainly oib type alkaline lavas advanced extensional tectonics throughout nw anatolia in the late miocene led to upwelling of the asthenospheric mantle and its decompressional melting that collectively resulted in the eruption of short lived episodes of mainly oib type alkaline lavas this tectonomagmatic evolution of the cenozoic continental volcanism in western anatolia presents a well documented case study of an idealized post collisional magmatism in most orogenic belts around the world

u pb zircon dating geochemical and sr nd hf isotopic compositions of early indosinian intrusive rocks in west qinling central china petrogenesis and tectonic implications the qinling dabie sulu orogenic belt is the junction between the north and south china blocks which resulted from the final amalgamation of china continents during the indosinian indosinian granitoids are widespread in the qinling orogen and their geneses can thus constrain the evolution of china continent we carried out a combined u pb zircon dating and geochemical study for the shuangpengxi granodiorite pluton and the xiekeng diorite granodiorite pluton in the middle part of the west qinling orogen u pb zircon dating shows that the magma crystallization ages of 242 3 ma for the shuangpengxi pluton and 244 242 ma for the xiekeng pluton geochemical and sr nd hf isotopic compositions reveal that the magma of the shuangpengxi granodiorite was derived from partial melting of crustal materials the xiekeng diorites can be divided into high al diorite and high mg diorite both of them resulted from partial melting of enriched lithospheric mantle but their mantle source had been modified by previous slab derived melt the high al diorite was formed by fractional crystallization of olivine pyroxene and or preferential accumulation of plagioclase and the high mg diorite was formed by fractional crystallization of olivine and or preferential accumulation of pyroxene the xiekeng granodioritic porphyry was formed by mixing of crust derived and mantle derived melts we propose that the early indosinian magmatism resulted from break off of subducted oceanic slab after collision the slab break off model can well explain the linear distribution of the early indosinian plutons and rapid crustal uplift during the middle triassic in the west qinling

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

superposed folding and associated fracturing influence hypogene karst development in neoproterozoic carbonates sao francisco craton brazil abstract porosity and permeability along fractured zones in carbonates could be significantly enhanced by ascending fluid flow resulting in hypogene karst development this work presents a detailed structural analysis of the longest cave system in south america to investigate the relationship between patterns of karst conduits and regional deformation our study area encompasses the toca da boa vista tbv and toca da barriguda tbr caves which are ca 107 km and 34 km long respectively this cave system occurs in neoproterozoic carbonates of the salitre formation in the northern part of the sao francisco craton brazil the fold belts that are around and at the craton edges were deformed in a compressive setting during the brasiliano orogeny between 750 and 540 ma based on the integrated analysis of the folds and brittle deformation in the caves and in outcrops of the surrounding region we show the following 1 the caves occur in a tectonic transpressive corridor along a regional thrust belt 2 major cave passages at the middle storey of the system considering both length and frequency developed laterally along mainly a ne sw to e w and b n to s oriented anticline hinges 3 conduits were formed by dissolutional enlargement of subvertical joints which present a high concentration along anticline hinges due to folding of competent grainstone layers 4 the first folding event f1 was previously documented in the region and corresponds with nw se to n s trending compression whereas the second event f2 documented for the first time in the present study is related to e w compression and 5 both folding events occurred during the brasiliano orogeny we conclude that fluid flow and related dissolution pathways have a close relationship with regional deformation events thus enhancing our ability to predict karst patterns in layered carbonates

regional metallogeny of mo bearing deposits in northeastern china with new re os dates of porphyry mo deposits in the northern xilamulun district with many new discoveries of giant mo deposits in the past decade northeastern china has become the largest molybdenum mineralization region in china the xilamulun district is in the southern part of northeastern china and contains 25 mo deposits and prospects dominantly of porphyry type these deposits are mostly along the e striking xilamulun fault re os dating of hydrothermal molybdenite from four deposits in the northern xilamulun district revealed mineralization ages of 137 to 129 ma 129 4 3 4 ma for aolunhua 135 3 2 6 ma for shabutai 136 4 0 8 ma for haisugou and 136 1 6 6 ma for banlashan in general agreement with the crystallization ages of their host granitoids the compilation of existing data on mo bearing deposits in northeastern china including the new data of this study shows that mesozoic mo deposits in this region have a wide range of ages from 250 to 90 ma we propose that they are linked to three tectonic magmatic events 1 triassic mo deposits 250 220 ma are mainly distributed along the e trending xilamulun fault and are related to postcollisional crustal extension following the final closure of the paleo asian ocean 2 jurassic mo mineralization 200 140 ma displays a clear younging trend from southeast to northwest coincides with the regional magmatism trend and is interpreted to be related to the northwestward flat slab subduction of the paleo pacific plate beneath the eurasian continent that started in the early jurassic ca 200 ma 3 cretaceous mo mineralization 140 90 ma shows a reversed migration trend from northwest to southeast and can be explained by the coastward migration of slab rollback related to lower crust delamination asthenospheric upwelling and lithospheric thinning in eastern china the spatial temporal distribution of mesozoic mo mineralization is important for regional metallogeny and exploration recently numerous epithermal au cu mo deposits have been recognized in the southeast margin of northeastern china according to this study we predict that hidden porphyry skarn systems could be located beneath these epithermal deposits

geochemistry and zircon u pb geochronology of granitoids in the east kunlun orogenic belt northern tibetan plateau origin and tectonic implications abstract the east kunlun orogenic belt ekob in the northern margin of the tibet plateau is characterized by widespread granitic plutons which are keys to understanding the tectonic evolution of the ekob the zhiyu pluton newly recognized in the central part of the ekob mainly consists of monzogranites biotite granites and quartz diorites their la icpms zircon u pb results show formation ages of 447 1 6 ma 448 2 5 ma and 408 1 8 ma the monzogranites and biotite granites are characterized by relatively high sr 208 631 ppm low y 4 28 15 82 ppm and yb 0 44 1 59 ppm contents thus resulting in elevated sr y 30 105 and la yb n 4 79 ratios indicating geochemical features of adakitic rocks these adakitic granites are medium to high k calcic or calc alkaline in composition and display a weak peraluminous character they have low mgo 0 57 1 84 wt average 1 01 wt mg 40 53 average 45 as well as low cr 3 67 17 98 ppm average 7 19 ppm and ni 2 59 9 30 ppm average 4 71 ppm contents these rocks are enriched in lree and show negligible or variable positive eu anomalies eu eu 0 61 3 80 average 1 45 and significant negative nb and ta anomalies majority of the zircon grains from these adakitic granitic rocks have positive ehf t values of 0 09 5 21 with two stage model ages ranging from 1 1 ga to 1 6 ga these features are compatible with those of adakitic rocks derived from a thickened lower crust in the garnet stability field their formation is mainly controlled by the process of crust thickening following the closure of the qimantag ocean the younger quartz diorites belong to medium to high k calc alkalic or alkali calcic and metaluminous series and exhibit a relatively high mgo 2 23 5 18 wt and mg 40 56 average 50 11 with significant lree enrichment and negative eu anomalies as well as depletion of nb ta in addition the quartz diorites have an enriched ehf t values ranging from 5 25 to 3 19 combining the regional tectonic data we infer that the younger quartz diorites were derived from enriched lithospheric mantle sources and contaminated by the crustal materials in a post collision extensional setting

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and its bearing on the evolution of the yinshan yanshan orogenic belt part i structural analyses and geochronological constraints abstract with a cratonic nucleus the north china craton ncc experienced a complex tectonic evolution with multiphase compressional and extensional events during mesozoic times along the northern part of the ncc the yinshan yanshan fold and thrust belt was a typical intraplate orogen jurassic and cretaceous continental sedimentation magmatism widespread intraplate characterize the yinshan yanshan orogenic belt the geodynamic significance of these tectonic events is still in dispute in the western part of the liaoning province the yiwulushan massif crops out at the eastern end of the yinshan yanshan orogenic belt the yiwulushan massif presents an elliptical domal shape with a ne sw striking long axis the structural evolution of this massif brings new insights for the understanding of the mesozoic plutonic tectonic history of the ncc a multidisciplinary study involving structural geology geochronology anisotropy of magnetic susceptibility ams and gravity modeling have been carried out the presentation of the new results splits into two parts part i this paper deals with field and laboratory structural observations and presents the main geochronological results the ams gravity modeling data will be provided in a companion paper part ii the early compressional deformation d1 corresponds to a late jurassic to early cretaceous southward thrusting the subsequent deformation is related to the early cretaceous exhumation of the yiwulushan massif a detailed structural analysis allows us to distinguish several deformation events d2 d3 and d4 the cretaceous extensional structures such as syntectonic plutons bounded by ductile normal faults metamorphic core complexes and half graben basins are recognized in many places in east asia these new data from the yiwulushan massif constitute a link between transbaikalia mongolia north china and south china indicating that nw se extensional mesozoic tectonics occurred throughout the entire region

late cenozoic volcanic evolution of the northeastern aegean region abstract late cenozoic volcanism occurred in an extensional tectonic regime in the northeastern aegean activity commenced in northeastern greece during the early oligocene and in northwestern turkey during the late oligocene early miocene the beginning of activity was characterized by calc alkaline intermediate acid volcanism however alkaline intermediate basic volcanism became dominant from the late miocene until the pleistocene this change in nature of volcanism is not related to a change of regional tectonic regime as previously thought instead we propose that the volcanic evolution reflects an increasing asthenospheric contribution facilitated by a thinned extended lithosphere arising from the regional extensional tectonics

intrusion age of pan african augen gneisses in the southern menderes massif and the age of cooling after alpine ductile extensional deformation

petrology and geochemistry of post collisional middle eocene volcanic units in north central turkey evidence for magma generation by slab breakoff following the closure of the northern neotethys ocean the eocene volcano sedimentary units of northern anatolia are confined into a narrow zone trending parallel to the intra pontide and izmir ankara erzincan sutures along which the northern branch of the neotethys ocean was closed during a period between late maastrichtian and paleocene the middle eocene formations overlie both the imbricated and highly deformed units of the suture zone which are paleocene or older in age as well as the formations of adjacent continental blocks with a regional disconformity therefore they can be regarded to be post collisional these units are composed of subaerial to shallow marine sedimentary beds i e the orencik formation at the base and a subaerial volcanic unit i e the hamamozu formation in the middle and at the top this sudden facies change from marine to subaerial environment in the middle eocene is a common phenomenon across northern turkey implying that a regional uplift event occurred possibly across the suture zone before the initiation of the volcanism during lutetian the middle eocene lavas span the whole compositional range from basalts to rhyolites and display a calc alkaline character except for alkaline to mildly alkaline lavas from the top of the sequence all lavas display a distinct subduction signature our geochemical data indicate that calc alkaline lavas were derived from a subduction modified source whereas alkaline to mildly alkaline lavas of the late stage were possibly sourced by an enriched mantle domain magmas evolved in magma chambers emplaced possibly at two different crustal levels magmas in deeper 13 km and possibly larger chambers fractionated hydrous mafic minerals e g amphibole and biotite two pyroxenes and plagioclase and assimilated a significant amount of crustal material intermediate to acid calc alkaline lavas and pyroclastics were derived from these chambers magmas in the shallower chambers on the other hand 12 km crystallized anhydrous mineral assemblages assimilated little or no crustal material and fed basic to intermediate lavas in the region both deep and shallow chambers were periodically replenished by mafic magmas we argue that a slab breakoff model explains better than any alternative model i why the volcanism during the middle eocene was confined into a rather narrow belt along the suture zone ii why it initiated almost contemporaneous with a regional uplift after the continental collision event iii why it postdated arc volcanism along the pontides in the north by 15 20 my iv why it assimilated significant amount of crustal material and v why alkalinity of lavas increased in time

origin of the early middle devonian magmatism in the sakarya zone nw turkey geochronology geochemistry and isotope systematics abstract a unique example of isotopically dated devonian metagranitoid the camlik metagranite okay et al 1996 crops out in the biga peninsula nw turkey although its contact relationships with the country rocks and geodynamic setting have remained to be enigmatic so far our field work however has shown that a number of metagranitoid bodies similar to the camlik metagranite intruded the country rocks and developed contact metamorphic zones consisting of andalusite and calcsilicate hornfelses garnet epidote and diopsite wollastonite skarns the country rocks of these metagranitoids are made up of regionally metamorphosed metaclastic successions with subordinate metacarbonate metachert metabasites the kalabak formation intercalated with tectonic slices of meta serpentinites the metagranitoids and the kalabak formation are collectively termed here the havran unit which forms a ne sw trending 20 km wide and 80 km long belt in the biga peninsula the havran unit is unconformably overlain by the late triassic shallow marine sediments and is in tectonic contact with the permo triassic karakaya complex interpreted as the palaeotethyan subduction accretion complex u pb shrimp ii and la icp ms dating of the zircons from four individual plutons yielded crystallization ages ranging from 389 1 2 6 to 401 5 4 8 ma i e early to middle devonian based on their geochemical characteristics the metagranitoids are divided into two groups named the camlik and yolindi metagranitoids both granitoids display distinct subduction signature and plot in the volcanic arc granite and post collisional granite fields on tectonic discrimination diagrams 87 sr 86 sr t values of these intrusions vary between 0 707367 and 0 715588 while their 143 nd 144 nd t values range from 0 51166 to 0 51187 very low values of end t from 5 3 to 9 1 imply that the lower to mid devonian metagranitoids in the havran unit might have been generated by partial melting of lower continental crust probably driven by a major magma underplating event delamination and or slab breakoff models are considered to be the most plausible mechanisms for the genesis of these metagranitoids the data obtained in this study has shown for the first time the widespread existence of devonian and older basement in nw turkey regional geological correlations imply that this basement may be an exotic terrane in the sakarya zone emplaced during the late triassic prior to its amalgamation with the palaeotethyan karakaya complex

petrogenesis and tectonic implications of the early paleozoic granites in the western segment of the north qilian orogenic belt china abstract early paleozoic granitic magmatism in the north qilian orogenic belt records a complete wilson cycle and provides critical geological clues for unraveling the regional tectonic history in this study we report the results of zircon u pb ages hf isotopic analysis and systematic whole rock geochemical data for the late ordovician hongliuhe granite and early silurian qingshan monzogranite in the western segment of the north qilian orogenic belt to constrain their emplacement ages petrogenesis and regional evolution history u pb dating reveals that the hongliuhe granite was emplaced around 453 452 ma and the qingshan monzogranite was emplaced about 440 438 ma a geochemical study shows that the two granites belong to the calc alkaline to high k calc alkaline series the hongliuhe granite shows adakitic and peraluminous features while the qingshan monzogranite belongs to metaluminous to weak peraluminous granites zircons in the hongliuhe granite show ehf t values ranging from 15 1 to 11 7 with two stage hf model ages tdm2 of 687 2398 ma whereas zircons in the qingshan monzogranite show ehf t values ranging from 5 7 to 11 0 with two stage hf model ages from 814 to 1057 ma the geochemical characteristics indicate that the hongliuhe granite was a transitional i s type granite and was generated from a thickened lower crust with the addition of minor paleo to mesoproterozoic crustal materials which left a rutile garnet pyroxene plagioclase residue the qingshan monzogranite formed from the partial melting of mafic crust with minor mantle derived materials and the fractionation of ti bearing phases apatite and pyroxene occurred during the magma s evolution which left an amphibole and plagioclase residue we infer that the hongliuhe granite formed during the northward subduction of the north qilian ocean while the qingshan monzogranite was generated during the post collision stage between the qilian and alxa blocks this observation indicates that syn collision stage of the north qilian orogenic belt began before 453 ma and that the extension regime began prior to 444 ma

the evolution from miocene potassic to quaternary sodic magmatism in western turkey implications for enrichment processes in the lithospheric mantle abstract new k ar dating and major and trace element analyses from the usak selendi emet use area constrain the timing of changes in the nature of volcanism in the miocene in western turkey the data reveal a change from dominantly calc alkaline and silicic in the early miocene to largely alkaline and more mafic volcanism in the middle miocene this probably reflects a decreasing amount of crustal contamination with time a result of extensional tectonics high levels of various incompatible elements including k in the more mafic members suggest an enriched subcontinental lithospheric source region for the middle miocene use lavas highly variable nb y ti y and th nb ratios suggest a lithospheric mantle heterogeneously enriched by two processes 1 enrichment by subduction related processes producing high th nb but low nb y and ti y and 2 enrichment by small degree melts of depleted upper mantle producing low th nb but high nb y and ti y both of these enrichment processes have variably contributed to middle miocene k rich lavas in the use area the mechanism which initiated the melting of the enriched lithosphere is considered to be extension which produced decompression melting comparisons with the nearby kula lavas reveals that by the pliocene to quaternary volcanism although still enriched in incompatible elements had become sodic it seems likely that continued extension up to this time thinned the lithosphere to such an extent that asthenospheric melts were produced which ascended and mixed with previously enriched lithosphere

genetic investigation and comparison of kartaldag and madendag epithermal gold deposits in canakkale nw turkey two epithermal gold deposits kartaldag and madendag located in nw turkey have been characterized through the detailed examinations involving geologic mineralogical fluid inclusion stable isotope whole rock geochemistry and geochronology data the kartaldag deposit 0 01 17 65 ppm au hosted by eocene dacite porphyry is associated with four main alteration types with characteristic assemblage of i chlorite smectite illite kaolinite ii quartz kaolinite iii quartz alunite pyrophyllite iv quartz pyrite the last being characterized by three distinct quartz generations comprising massive vuggy early fine medium grained vug lining early and banded colloform comb late textures observed sulfide minerals are pyrite covellite and sphalerite oxygen and sulfur isotope analyses performed on quartz delta o 18 quartz 7 93 to 8 95 parts per thousand and calculated delta o 18 h2o 7 95 to 1 4 parts per thousand and pyrite delta s 34 pyrite 4 8 parts per thousand and calculated delta s 34 h2s 6 08 to 7 20 parts per thousand separates suggest a meteoric water source for water in the hydrothermal fluid and an igneous source for the sulfur dissolved in ore related fluids microthermometric analyses of primary fluid inclusion assemblages performed on quartz late quartz generation yield temperatures th dominantly in the range of 245 285 degrees c and generally low salinity values at 0 to 1 7 wt nacl eq based on the quartz textures and the associated base metal concentrations along with fluid inclusion petrography the early vug lining quartz is considered to have been associated with the mineralization possibly through a boiling and a late mixing process at 285 degrees c the madendag deposit 027 20 60 ppm au hosted by paleozoic mica schists is associated with two main alteration types sericite illite kaolinite and quartz pyrite dominated by two distinct quartz generations i early colloform comb and banded quartz and ii late quartz forming the cement in hydrothermal breccia whereas oxygen isotope analyses of quartz delta o 18 quartz 9 55 to 18 19 parts per thousand and calculated delta o 18 h2o 2 97 to 5 54 parts per thousand suggest varying proportions of meteoric and magmatic sources for the ore bearing fluid sulfur isotope ratios delta s 34 pyrite 2 2 parts per thousand and calculated delta s 34 h2s 3 63 to 3 75 parts per thousand point to an essentially magmatic source for sulfur with or without contribution from sedimentary sources microthermometric analysis carried out on primary fluid inclusion populations of a brecciated sample early quartz give a temperature th range of 235 255 degrees c and 0 0 to 0 7 wt nacl eq salinity based on the textural relationship base metal and high gold contents the ore precipitation stage is associated with late stage quartz formation via a possible boiling process the presence of alunite pyrophyllite and kaolinite vuggy quartz and covellite suggest a high sulfidation type of epithermal deposit for kartaldag on the other hand madendag is identified as an adularia sericite type owing to the presence of significant sericite neutral ph clays mostly illite chlorite smectite and kaolinite low temperature quartz textures e g colloform comb and banded quartz and limited sulfide minerals given the geographical proximity of kartaldag and madendag deposits the similar temperature and salinity ranges obtained from their fluid inclusions and the similar ages of igneous rocks in both deposits kartaldag 40 80 036 to 42 19 0 45 ma madendag 43 34 0 85 ma the mineralizing systems in both deposits are considered to be genetically related c 2013 elsevier b v all rights reserved

evolution of the bayramic magmatic complex northwestern anatolia abstract during the oligocene middle miocene period widespread magmatic activity developed in western anatolia following the continental collision between the sakarya continent and the tauride anatolide platform this produced both intrusive and extrusive rocks which appear to be associated in space and time as exemplified from the bayramic area in the bayramic area the magmatic activity started with the intrusion of the evciler granite and the coeval lower volcanic association this was followed by the development of the upper volcanic association these rock groups form collectively the bayramic magmatic complex which was generated under an on going north south compressional regime the bayramic magmatic complex has a subalkaline composition displaying a calcalkaline trend trace elements and ree contents resemble to island arc and collision related magmas according to the isotope values the bayramic magmatic complex was derived from the magmas of lithospheric mantle origin which were later contaminated while passing through the thick continental crust in a post collisional tectonic setting during the oligocene early miocene period the latest product of the magmatism is the late miocene pliocene basalt lavas their geochemical properties are clearly different from the oligocene early miocene magmatic rocks the basalts were generated when the north south compression gave way to the north south extensional regime

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

mantle unrooting in collisional settings abstract we present a two dimensional numerical model to study the thermo mechanical evolution of the lithosphere under a convergence regime in order to define the conditions that lead to lithospheric mantle break up and consequent unrooting a newtonian rheology with a temperature dependent viscosity is considered the system is not closed and horizontal flow through lateral boundaries is permitted a horizontal velocity is imposed at the top of the model to simulate compression whereas velocity vanishes at the bottom of the model the initial conditions correspond to a homogeneous lithosphere with a constant heat production in the crust the analysis of variations of maximum shear stress strain rate and total kinetic energy allowed us to define four major stages during the mantle unrooting process orogenic growth initiation of gravitational instability until lithospheric failure sinking of the detached lithosphere and relaxation of the system numerical results also show that the conditions for lithospheric unrooting strongly depend on the convergence velocity the wideness of the deformation zone and the imposed rheology

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

exhumation of blueschists along a tethyan suture in northwest turkey a blueschist belt formed during the mid cretaceous 88 ma high pressure metamorphism of a passive continental margin sequence of shale siltstone quartzite and limestone occurs immediately south of the tethyan suture in northwest turkey a transect across the tethyan suture was mapped to constrain the exhumation of blueschist facies assemblages the presence of jadeite glaucophane and lawsonite in the blueschists indicates p t conditions of 20 kbar and 430 c the blueschists are tectonically overlain by a cretaceous oceanic accretionary complex showing an incipient blueschist metamorphism a peridotite slab with subvertical layering lies along a low angle fault contact over the blueschists and the accretionary complex isolated slices of early cretaceous 101 4 ma garnet amphibolites occur at the base of the peridotite the garnet amphibolites which show an incipient blueschist facies overprint have probably formed during the oceanic subduction in the foot wall of the subduction zone and later underplated the hanging wall blueschists and peridotites are abruptly truncated in the north by the steeply dipping suture fault that juxtaposes unmetamorphosed and slightly deformed triassic to jurassic sediments of the northern continent against the peridotite and the accretionary complex tectonic juxtaposition of the lower pressure accretionary complex and peridotites over the higher pressure blueschists implies the removal of a 45 km thick oceanic mantle sequence above the blueschists regional geological and geometric constraints suggest that the exhumation of the blueschists was achieved by a combination of two simultaneously acting mechanisms the first was the detachment of the upper crustal blueschist sequence from its basement in the subduction zone and its incorporation to the hanging wall followed by buoyant ascent the second mechanism is the progressive shallowing of the subducted continental lithosphere resulting in the thinning of the mantle wedge above the subducted slab the blueschists were partly exposed prior to the paleocene continent continent collision post collisional eocene 52 48 ma calc alkaline plutons that were emplaced in the blueschists and the overlying peridotite at 10 km depth are interpreted to have formed by crustal anatexis from advective heating by mantle melts these have probably been generated during the upwelling of the asthenosphere under the shallowing continental lithosphere

experimental high pressure granulites some applications to natural mafic xenolith suites and archean granulite terranes high pressure granulite assemblages have been produced as residues in partial melting experiments on a natural alkalic basalt amphibolite between pressures of 12 and 18 kbar in particular at 18 kbar partial melting of the hornblende plagioclase quartz assemblage under fluid absent conditions produces garnet clinopyroxene new albitic plagioclase melt seismic velocities v p are estimated from the modal data for the experimental assemblages and range from 6 90 km s for hornblende bearing residues to 7 62 for the dominantly garnet clinopyroxene residues these values are typical for rock types in the lowermost crust transitional to mantle the experimental results help place additional pressure temperature a h 2 o constraints on the source region for the natural high pressure granulites the experimental residue assemblage formed at 18 kbar has been described in natural xenolith suites from the delegate pipes in australia where the pipes intrude upper ordovician and lower devonian continental crust and in the bearpaw mountains montana where the xenolith bearing magmas intrude older crust of archean age the combination of these data shows that the xenoliths may indeed represent lowermost continental crust and furthermore helps interpret the nature of the crust mantle boundary in these areas the delegate pipes xenoliths suggest that the crust mantle boundary may be the site for partial melting and assimilation whereas the bearpaw mountains samples indicate that magmatic underplating may have been a major process in generating thick continental archean crust the experimental data and bearpaw mountains xenoliths suggest that the large range of rock types found in archean granulite terranes may not be representative of the lowermost continental crust

paleomagnetic evidence of complex tectonic rotation pattern in the nw anatolian region implications for the tectonic history since the middle eocene abstract the kinematic evolution of the almacik block and the armutlu region which are surrounded by the branches of the north anatolian fault is not completely understood because of incompatible paleomagnetic data a previous paleomagnetic study in the almacik block indicated that there have been large rotations associated with the rotation as a whole coherent block and another study postulated a more complex tectonic evolution the aim of this study was to obtain paleomagnetic directions on middle eocene volcanic volcanoclastic rocks at 25 sites in nw anatolia and to determine the tectonic deformation process along the north anatolian fault zone after rock magnetic measurements and stepwise thermal and alternating field demagnetisation most of the samples taken were characterised by one component of magnetisation after the removal of viscous magnetisation a characteristic remanent magnetisation was obtained at 500 580 c showing evidence of magnetite and titanomagnetite with a small amount of ti however in some cases a high temperature component was isolated between 600 and 650 c indicating a titanohematite composition the mean direction obtained from the istanbul zone d 191 5 i 47 1 95 7 1 indicated no tectonic rotation relative to the reference direction of the stable eurasian plate d 191 0 i 53 2 95 5 0 besse and courtillot 2002 torsvik et al 2008 in the middle eocene the paleomagnetic directions in the almacik block and the armutlu region suggest counterclockwise rotations of 22 3 7 8 and 17 7 14 6 respectively relative to the istanbul zone when integrated together with previous studies our paleomagnetic results indicate that both the armutlu region and the almacik block were emplaced in the same area during the middle eocene the deformation of the northern branch of the north anatolian fault resulted in a bend and an overstep fault offset of 25 km between lake sapanca and lake abant during this process both the almacik block and the armutlu region were separated distinctly from each other with a counter clockwise rotation with respect to the istanbul zone in addition within some parts of the almacik block an internal deformation with large declination anomalies ranging from 160 to 250 was observed in this study and in previous studies these different declinations could be the result of chemical remagnetisation of hydrothermal events stress related magnetisation or small block rotations

diachronous demise of the neotethys ocean as a driver for non cylindrical orogenesis in anatolia continent continent collision drives crustal deformation topographic rise and geodynamic change africa eurasia convergence accommodated in the eastern mediterranean involved subduction of the neotethyan oceanic lithosphere in anatolia subduction was followed by collision of continental crust of greater adria with eurasia to form the izmir ankara erzincan suture zone discerning the effects of this collision from pre collisional ophiolite obduction related orogeny of greater adria is notoriously difficult estimates on the timing of collision in central anatolia are based on a forearc to foreland basin transition along the eurasian margin and suggest a 60 ma age of initial collision here we assess whether this age is also representative for collision in eastern anatolia and across the cenozoic sivas basin that straddles the greater adria europe suture to this end we retro deform regional block rotations in the pontides the kirsehir block and the taurides building a first order regional block circuit around the sivas basin we show that up to 700 km of convergence must have been accommodated across the sivas basin after central anatolian kirsehir pontide collision at 60 ma an order of magnitude more than estimated crustal shortening and that wholesale lithospheric subduction must have occurred throughout much of the cenozoic paleocene collision would require that this subduction consumed continental lithosphere which is unlikely we consequently infer that oceanic subduction continued much longer in eastern anatolia perhaps well into the miocene we postulate that prolonged oceanic subduction and slab pull drew the eastern taurides north relative to the central taurides leading to shortening and oroclinal bending in central anatolia the diachronous demise of the neotethys ocean in anatolia as a function of its paleogeography is thus a likely driver for the strong non cylindricity of the cenozoic anatolian collisional orogen

late paleozoic calc alkaline to shoshonitic magmatism and its geodynamic implications yuximolegai area western tianshan xinjiang article i nfo continuous late paleozoic magmatic activity in the western tianshan xinjiang china temporally overlapped the late carboniferous collision between the tarim and the kazakhstan yili plates isotopic dating whole rock geochemistry and isotopic characteristics of a suite of calc alkaline to shoshonitic rocks from yuximo legai area in the eastern end of the awulale mountains help define the tectonic evolution of this part of the tianshan zircon u pb ages of a quartz diorite and a quartz syenite porphyry are 310 8 2 1 ma and 284 4 3 6 ma respectively the geochemical and isotopic characteristics of late carboniferous igneous rocks including the quartz diorite as well as basaltic andesite and k rich trachyandesite indicate an evolu tion from calc alkaline towards shoshonitic series this was generated by the partial melting of the hydrated mantle wedge induced by changing subduction angles the younger quartz syenite porphyry however was more likely derived from the partial melting of a thickened crust in a post collisional setting or the partial melting of hot juvenile basalt in the lower crust during early permian delamination of the subcontinental lithospheric mantle therefore the generation of the calc alkaline to shoshonitic igneous rocks in yuximole gai area is genetically linked to the geodynamic evolution of the western tianshan from convergent subduc tion to collision during the late paleozoic

relationships between very high pressure subduction complex assemblages and intrusive granitoids in the tavsanli zone sivrihisar massif central anatolia abstract the sivrihisar massif of central anatolia exposes blueschist and eclogite facies metasedimentary and metabasaltic rocks in close association with granitoid plutons the massif is located within the tavsanli zone the subducted and exhumed northern continental margin of the anatolide tauride block the relationship of the very high pressure assemblages to co existing granitoid plutonic bodies kaymaz and sivrihisar is unclear as the region can be considered the type locality for the entrainment of excess argon in k bearing minerals samples from its granitoids and a subduction complex assemblage were collected imaged with cathodoluminescence cl and dated using zircon u pb in situ in thin section ion microprobe methods the granitoids are heterogeneous as evidenced by cl images and geochemical variations finer grained sivrihisar samples are syenite and show plagioclase replacing k feldspar whereas coarser grained rocks are monzonite and show the opposite reaction our samples of the kaymaz granitoids are extremely si rich 82 97 wt sio 2 and have experienced sericitization cl images of both granitoids show evidence for fluid interactions at both the subsolidus and lower temperature stages in their tectonic history subduction along the tavsanli zone was ongoing during the early to late cretaceous and entrained zircons with igneous zonation in cl that crystallized as early as the paleoproterozoic sivrihisar massif granitoids record zircon crystallization from the late cretaceous to early oligocene here we present a model in which the sivrihisar and kaymaz melts source from a subducting slab along the afyon zone further to the south and mix with an igneous component generated during decompression due to break off of the tavsanli slab the model speculates that the tavsanli zone is the northernmost segment of an amalgamation of stacked subduction zones that transition in activity from north to south over time

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature

mantle flow uplift of western anatolia and the aegean interpretations from geophysical analyses and geodynamic modeling 1 the western anatolian and aegean region demonstrates a complex geologic history of horizontal and vertical tectonics active normal faulting and exhumation zones indicate that western anatolia has experienced significant extension since the oligocene early miocene 30 ma our geophysical analyses demonstrate that the region is also uplifted relative to an elevation that would be expected given an isostatic response to the lithosphere structure namely topography residuals indicate a residual uplift of about 1500 m over 200 km sections of western anatolia and the aegean admittance functions between free air gravity and topography indicate that the regional topography is isostatically uncompensated and as it approaches 50 mgal km at the longest wavelengths the uncompensated topography is likely owing to an underlying mantle flow component using forward geodynamic modelling we consider an idealized section of western anatolian lithosphere based on tomographic inversions and examine the magnitude and pattern of surface topography to reconcile with the geophysical observables the models consistently show a plateau type uplift and horizontal extension through western anatolia with an amplitude and wavelength consistent with the residual topography calculations together the geophysical analyses and modelling provide independent quantitative evidence that the thin anatolian aegean lithosphere is being buoyed upwards by underlying mantle flow the mantle flow may be associated with active lithosphere delamination beneath the region a process that would also explain the ongoing crustal extension

tectonostratigraphic evolution of the upper cretaceous cenozoic central anatolian basins an integrated study of diachronous ocean basin closure and continental collision

lithospheric delamination in post collisional setting evidence from intrusive magmatism from the north qilian orogen to southern margin of the alxa block nw china abstract post collisional granitoids are widespread in the north qilian and southern margin of the alxa block and their petrogenesis can provide important insights into the lithospheric processes in a post collisional setting this paper carries out an integrated study of u pb zircon dating geochemical and sr nd hf isotopic compositions for five early paleozoic intrusive plutons from the north qilian to southern margin of the alxa block the geochronological and geochemical results show that their magmatism can be divided into three periods with distinct geochemical features the early period intrusive rocks 440 ma include the lianhuashan lhs and mengjiadawan mjdw granodiorites both of them display high sr y ratios 52 91 coupled with low y and hree contents implying that they were derived from partial melting of thickened lower crust with garnet in the residue the middle period intrusive rocks 430 ma including the mjdw quartz diorites and yangqiandashan yqds granodiorites are high k calc alkaline with low sr y values the geochemical and isotopic data suggest that they are generated from partial melting of lower crust without garnet in the residue the late period intrusive rocks 414 422 ma represented by the shengrongsi srs and xinkaigou xkg plutons are a type or alkali feldspar granites they are possibly derived from partial melting of felsic crustal material under lower pressure condition our data show decreasing magma crystallization ages from mjdw pluton in the north and lhs pluton in the south to the srs and xkg plutons in the central part of the study area we suggest that such spatial and temporal variations of magmatic suites were caused by lithospheric delamination after the collision between the central qilian and the alxa block a more plausible explanation is that the delamination propagated from the margin part of the thickened lithosphere to inward beneath the north qilian and southern margin of the alxa block

evolution of the miocene sedimentary fill of the gediz graben sw turkey abstract the gediz graben is a continental extensional basin filled with miocene to recent sediments the evolution of the graben can be expressed in terms of two phases i miocene half graben phase and ii post miocene graben phase the miocene half graben phase was governed by the southern margin structure evolution of which significantly controlled the stratigraphic variability in the basin alluvial fluvial and lacustrine systems developed in the graben as a function of distance to the southern margin thus alluvial deposits with coarse grained facies dominate the southern margin and grade into finer fractions of fluvial and or lacustrine deposits to the north this depositional architecture repeated three times during the miocene and deposited alasehir caltilik and gediz formations these formations depict distinct thickness and grain size decrease from south to north to emphasize the half graben configuration for the favour of the southern margin the post miocene graben phase started with the faulting of the northern margin this resulted in relatively balanced partitioning of the subsidence between the two margins although the preceding asymmetry was inherited by the graben sediment influx became bipolar and alluvial fan systems developed along the both margins

geology of the ignimbrites and the associated volcano plutonic complex of the ezine area northwestern anatolia abstract the ezine region is located in the northwestern part of anatolia where young granitic and volcanic rocks are widespread and show close spatial and temporal association in this region magmatism began with the kestanbol granite which intruded into metamorphic basement rocks and formed contact metamorphic aureole to the east and southeast the pluton is surrounded by hypabyssal rocks which in turn are surrounded by volcanic associations the volcanic rocks may be divided into two main groups on the basis of their lithological properties lavas and lahar deposits dominate the northern sector while ignimbrites dominate the southern sector the ignimbrite eruptions were formed partly coevally with the plutonic and the associated volcanic rocks during the early miocene they appear to have been associated in a caldera collapse environment geochemical properties of the plutonic and the associated volcanic assemblages indicate that the magmas are hybrid and co genetic and were formed from a similar mantle source under a compressional regime prior to the opening of the present e w trending graben of the aegean western anatolian region

s o and pb isotopic evidence on the origin of the inkaya simav kutahya cu pb zn ag prospect nw turkey abstract the inkaya cu pb zn ag prospect is a typical example of the hydrothermal mineralization occurring in the menderes massif which crop out in western anatolia the prospect located approximately 20 km west of simav kutahya turkey in northern part of the menderes massif have been characterized through the detailed examinations involving geological mineralogical whole rock geochemistry fluid inclusion stable isotope and lead isotope the inkaya cu pb zn ag prospect is located along an e w trending fault in the cambrian simav metamorphics which consist of quartz muscovite schist quartz biotite schist muscovite schist biotite schist and the arikayasi formation which is composed of marbles galena sphalerite chalcopyrite pyrite and fahlore are the main minerals and they are accompanied by small amounts of cerussite anglesite digenite enargite chalcocite covellite bornite and fe oxides with gangue quartz in addition to pb zn cu ag the ore samples contain substantial quantities of as cd and bi and small amount of au average contents of cu pb zn and ag are 77 400 ppm 102 600 ppm 6843 ppm and 203 ppm respectively the 34s values for galena chalcopyrite and pyrite formed in the same stage vary in the range from 1 7 to 2 1 average 2 0 0 1 to 0 3 average 0 2 and 1 5 to 2 6 average 1 5 respectively 34s values for h2s representing the composition of the fluids responsible for the sulfide mineral formations and calculated from the 34s value are between 2 77 and 1 33 it is consistent with the sulfur in sulfide minerals 18oquartz values range from 11 3 to 16 4 and estimated 18ofluid values range from 5 4 to 10 6 pyrite galena and pyrite chalcopyrite pairs calculated to determine equilibrium isotope temperatures based on 34s values are between 254 6 and 277 4 c for pyrite galena and 274 7 c for pyrite chalcopyrite sulfur and oxygen isotope values similar to the values for fluid equilibrated with an felsic magmatic source fluid inclusion studies on quartz of the same silicification stage coexisting with galena sphalerite and chalcopyrite collected from the mineralized vein indicate that the temperature range of the fluids is 235 c to 340 c and that the salinities are 0 7 to 4 49 wt nacl equivalent the wide range of homogenization temperatures and relatively lower salinities of the fluid inclusions indicate that at least two different fluid generations were trapped in the quartz from only one fluid type also lower salinities of fluid inclusion probably indicate mixing of meteoric water and magmatic fluid the galena has 206pb 204pb values of 18 862 18 865 207pb 204pb values of 15 707 15 711 and 208pb 204pb values of 39 033 39 042 the lead isotope values show a similarity with upper crustal values

petrogenesis of the post collisional volcanic rocks from the borcka artvin area implications for the evolution of the eocene magmatism in the eastern pontides ne turkey abstract whole rock geochemistry 40 ar 39 ar data and sr nd isotopes are presented for the eocene borcka volcanic rocks on the eastern corner of the eastern pontide orogenic belt ne turkey borcka artvin volcanic rocks are divided into three suites basic dyke borcka basalt and civankoy suite these rocks contain plagioclase an 49 88 clinopyroxene wo 38 49 en 38 54 fs 8 25 hornblende mg 0 57 0 74 phenocrysts and magnetite titanomagnetite and apatite microphenocrysts 40 ar 39 ar ages on hornblendes ranging from 46 9 0 1 to 39 9 0 5 ma within the middle eocene the volcanic rocks show tholeiitic calc alkaline affinities and have low to medium k contents they are enriched in large ion lithophile lile and light rare earth elements lree with pronounced depleted high field strength elements hfse the chondrite normalized ree patterns la cn lu cn 1 19 show low to medium enrichment indicating similar sources for the rock suite initial 87 sr 86 sr values 87 sr 86 sr 46 ma vary between 0 70423 and 0 70495 while initial 143 nd 144 nd values 143 nd 144 nd 46 ma lie between 0 51263 and 0 51285 the main solidification processes involved in the evolution of the volcanics consist of fractional crystallization with minor amounts of crustal contamination all our evidences support the conclusion that the parental magma of the rocks probably derived from an enriched mantle previously metasomatized by fluids derived from subducted slab in a post collisional extension related geodynamic setting