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

clinopyroxene composition of ophiolite basalts as petrogenetic indicator abstract a statistical microprobe study has been carried out on augitic clinopyroxene in high ti to low ti metabasalts from various phanerozoic ophiolites a comparison has been made with clinopyroxenes from mid ocean ridge basalts morb oceanic intraplate basalts island arc tholeiites and boninites leaving aside the effect of cooling rate and of fractional crystallization as major factors influencing pyroxene chemistry their composition appears to be essentially related to the type of host magma both the tio2 and the tio 2 al 2 o 3 in clinopyroxenes are positively correlated with the zr y ratios of the host basalts which is a diagnostic parameter insensitive to alteration increasing regularly from low ti to high ti ophiolitic basalts ti also shows a positive correlation and average d ti cpx rock partition coefficients varying from 0 3 0 6 to 1 from low ti to high ti basalts which compare favorably with those from tongan southwest pacific basaltic andesites 0 3 0 6 and morb 0 75 respectively likewise the average k fe mg calculated for clinopyroxene rock pairs varies from 0 20 in low ti basalts to 0 26 in high ti basalts up to 0 33 in the highest ti rocks suggesting a significant dependence of this parameter on magma composition the compositional correspondence of clinopyroxenes from various ophiolitic basalts with those from oceanic actualistic equivalents is shown in various diagrams concomitantly with increasing tio2 and na2o and decreasing sio2 contents clinopyroxenes from very low ti to high ti ophiolitic basalts are best equated with those from boninites basaltic andesites and tholeiites from island arcs and morb respectively accordingly a parallel increase is shown by the substitutional molecules catial2o6 and natisialo6 within each basalt type fractional crystallization processes are reflected in the natisialo6 and fetial2o6 increase and mgcrsialo6 decrease from early to late crystallized clinopyroxenes

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

amplification of seismic ground motion in the tunis basin numerical bem simulations vs experimental evidences this paper aims at the analysis of seismic wave amplification in a deep alluvial basin in the city of tunis in tunisia this sedimentary basin is 3000m wide and 350m deep since the seismic hazard is significant in this area the depth of the basin and the strong impedance ratio raise the need for an accurate estimation of seismic motion amplification various experimental investigations were performed in previous studies to characterize site effects the boundary element method is considered herein to assess the parameter sensitivity of the amplification process and analyse the prevailing phenomena the various frequencies of maximum amplification are correctly estimated by the bem simulations the maximum amplification level observed in the field is also well retrieved by the numerical simulations but due to the sensitivity of the location of maximum amplification in space the overall maximum amplification has to be considered the influence of the wave field incidence and material damping is also discussed

origin and history of hydrothermal fluids of the reykjanes and krafla geothermal fields iceland the reykjanes and krafla geothermal fields are both examples of active high temperature systems and show similar assemblages of alteration minerals but the fluid at reykjanes is dominantly sea water whereas that at krafla is meteoric oxygen isotope analyses of surface rock and of drill chip samples from different depths are presented together with results for the krafla fluid which is close to local precipitation 18o 11 9 d 86 8

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

subduction complex of pre jurassic age northern anatolia turkey in northern anatolia a zone of pre liassic orogenic deformation is located mainly between the internal anatolian massifs and the north anatolian fault this belt consists of metamorphic rocks in blueschist greenschist and amphibolite facies and an ophiolitic dynamometa morphic melange the metamorphic rocks represent deformed and metamorphosed oceanic crust and upper mantle whereas the melange rocks originated in diverse environments in abyssal plain trench arc trench gap and forearc environments the evolution of these assemblages is interpreted as a product of subduction probably associated with the closure of the tethys subduction related deformation and meta morphism terminated diachronously from pre late triassic in the west to pre late liassic in the east probably as a result of the diachronous closure of the tethys

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

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

a new classification of the turkish terranes and sutures and its implication for the paleotectonic history of the region abstract the turkish part of the tethyan realm is represented by a series of terranes juxtaposed through alpine convergent movements and separated by complex suture zones different terranes can be defined and characterized by their dominant geological background the pontides domain represents a segment of the former active margin of eurasia where back arc basins opened in the triassic and separated the sakarya terrane from neighbouring regions sakarya was re accreted to laurasia through the balkanic mid cretaceous orogenic event that also affected the rhodope and strandja zones the whole region from the balkans to the caucasus was then affected by a reversal of subduction and creation of a late cretaceous arc before collision with the anatolian domain in the eocene if the anatolian terrane underwent an evolution similar to sakarya during the late paleozoic and early triassic times both terranes had a diverging history during and after the eo cimmerian collision north of sakarya the kure back arc was closed during the jurassic whereas north of the anatolian domain the back arc type oceans did not close before the late cretaceous during the cretaceous both domains were affected by ophiolite obduction but in very different ways north directed diachronous middle to late cretaceous melange obduction on the jurassic sakarya passive margin senonian synchronous southward obduction on the triassic passive margin of anatolia from this it appears that the izmir ankara suture currently separating both terranes is composite and that the passive margin of sakarya is not the conjugate margin of anatolia to the south the cimmerian taurus domain together with the beydaglari domain part of the larger greater apulian terrane were detached from north gondwana in the permian during the opening of the neotethys east mediterranean basin the drifting cimmerian blocks entered into a soft collision with the anatolian and related terranes in the eo cimmerian orogenic phase late triassic thus suturing the paleotethys at that time the taurus plate developed foreland type basins filled with flysch molasse deposits that locally overstepped the lower plate taurus terrane and were deposited in the opening neotethys to the south these olistostromal deposits are characterized by pelagic carboniferous and permian material from the paleotethys suture zone found in the mersin melange the latter as well as the antalya and mamonia domains are represented by a series of exotic units now found south of the main taurus range part of the mersin exotic material was clearly derived from the former north anatolian passive margin huglu type series and re displaced during the paleogene this led us to propose a plate tectonic model where the anatolian ophiolitic front is linked up with the samail baer bassit obduction front found along the arabian margin the obduction front was indented by the anatolian promontory whose eastern end was partially subducted continued slab roll back of the neotethys allowed anatolian exotics to continue their course southwestward until their emplacement along the taurus southern margin mersin and up to the beydaglari promontory antaya mamonia in the latest cretaceous paleocene the supra subduction ocean opening at the back of the obduction front troodos type ocean was finally closed by eocene north south shortening between africa and eurasia this brought close to each other cretaceous ophiolites derived from the north of anatolia and those obducted on the arabian promontory the latter were sealed by a maastrichtian platform and locally never affected by alpine tectonism whereas those located on the eastern anatolian plate are strongly deformed and metamorphosed and affected by eocene arc magmatism these observations help to reconstruct the larger frame of the central tethyan realm geodynamic evolution

ridge hotspot interaction the pacific antarctic ridge and the foundation seamounts the study of different magmatic provinces between the resolution fracture zone 33 s 131 w and the pacific antarctic ridge par axis 37 s 111 w suggests that similar processes of interaction between hotspot and spreading axial magmatism occurred 20 25 ma and 0 5 ma ago there is evidence of this process from the changes in composition observed in the lavas erupted near 400 300 km between the present day par axis 37 s 111 w and the eastern tip of the foundation seamount fs hotspot near 36 20 s 114 w where the last alkali enriched volcanics k ti 0 30 zr y 6 and ce yb n 4 have erupted this transitional province between the par and the fs consists of volcanic cones built on several volcanic ridges 20 ma also built on volcanic ridges are identified west 1200 km from the par axis of a failed rift propagator frp forming the eastern boundary of the ancient selkirk microplate some of these seamounts made of alkali basalts were built during the initiation of the fs hotspot 20 23 ma ago the interaction and the influence thermal of mantle plume magmatism with the ancient spreading ridge of the farallon pacific plates was responsible for the eruptions of the t morbs and andesitic lavas this situation is comparable to that presently observed on the par axis where silicic lavas are also erupted in association with t morbs

geochronology of the voisey s bay intrusion labrador canada by precise u pb dating of coexisting baddeleyite zircon and apatite abstract the emplacement history of the voisey s bay troctolite intrusion that hosts the major ni cu co sulfide deposit of the same name has been studied using precise u pb geochronology of baddeleyite zircon and apatite the baddeleyite u pb ages of multiple drill core samples of troctolite and gabbro indicate that all of the mafic rocks studied from different components of the voisey s bay intrusion eastern deeps discovery hill zone and reid brook zone and from the adjacent red dog area were emplaced at 1332 7 1 0 ma on the basis of combined geological and geochronological evidence it is suggested that the voisey s bay ni cu co deposit was formed during the same period the zircons coexisting with the ca 1333 ma baddeleyite show a diversity of ages the zircons from normal troctolite and some of the olivine gabbro samples are coeval with the baddeleyite while zircon from the varied textured troctolite and feeder olivine gabbro are much younger at 1305 0 0 8 ma the identical ages of the younger zircon population and the voisey s bay syenite that cuts the mafic rocks indicate a link between zircon growth in the mafic rocks and contact metamorphism related to the emplacement of the syenite various mechanisms of zircon growth were probably involved including reaction of the 1333 ma baddeleyite with a silica enriched fluid with formation of a secondary polycrystalline zircon and zircon crystallization from syenite micro veins in the mafic rocks the mean 207 pb 206 pb age of 1303 5 2 6 ma of the voisey s bay apatites is similar to the age of the younger zircon population the apatite age may either be a result of resetting the u pb system in response to the syenite intrusion or may reflect the closure of the system during regional cooling and cessation of fluid circulation the presence of xenocrystic zircon in a discovery hill zone feeder olivine gabbro indicates that the voisey s bay magmas were contaminated with 1 90 ga crustal rocks

discrimination of ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts by the al ti ratio in clinopyroxene in mafic igneous suites typical of anorogenic igneous provinces mid ocean ridges back arc basins continental rifts and hotspots clinopyroxenes of tholeiitic and silica undersaturated rocks incorporate al in clinopyroxene chiefly via the charge coupled substitution vimgivsi2 vitiival2 as the catial2o6 molecule this substitution is promoted by high titania activity relative to silica in the melt and hence is particularly characteristic of silica undersaturated mafic rocks mafic igneous suites of convergent plate margins i e arc tholeiites and calc alkalic gabbros and basalts characteristically incorporate al in clinopyroxene largely as the cafe3 alsio6 molecule the vimgivsi vife3 ival substitution is promoted by relatively high fugacities of h2o and o2 a characteristic feature of arc axis magmas recognition of cumulates that are complementary to compositions of eruptive rocks in arcs is crucial to development of valid petrogenetic models for arc magmas plots of tetrahedrally coordinated al vs octahedral ti in augite of gabbroic and ultramafic cumulates show that augite data arrays for arc related cumulates have a trend of substantially higher al ti in clinopyroxene than do those from rift related tholeiites the al ti ratio in clinopyroxene may be utilized to discriminate ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts

interpretation of monazite ages obtained via in situ analysis abstract monazite grains from nepal and vietnam were compositionally analyzed with an electron microprobe and dated th pb with an ion microprobe five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population 1 pb loss due to diffusion 2 dissolution reprecipitation reactions along a retrograde path 3 analytical uncertainties 4 analyses of overlapping age domains and 5 episodic monazite growth the influence of these factors is sample dependent but can be evaluated 1 using peak metamorphic conditions and x ray element maps to assess potential polymetamorphism or retrogression 2 obtaining other geochronologic data including previous work or dating other minerals in the sample 3 evaluating any method related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses and 4 ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element ree oxide or allanite chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms instead of relying on monazite chemical composition major mn fe mg ca and minor y element garnet zoning patterns and peak p t conditions should be used to facilitate age interpretation this thermobarometric data records the sample s thermal history changes in garnet growth rate and mechanisms and accessory mineral breakdown

u pb dating of baddeleyite and zircon from the shizhaigou diorite in the southern margin of north china craton constrains on the timing and tectonic setting of the paleoproterozoic xiong er group abstract the xiong er volcanism marks an important thermal event in the southern margin of the north china craton during the paleoproterozoic precise u pb ages of zircon and baddeleyite from the shizhaigou diorite which intruded the majiahe formation of the upper part of the xiong er group were determined in this study by multi collector sims the mean 207 pb 206 pb ages are 1789 3 5 ma for baddeleyite and 1780 11 ma for zircon from shizhaigou diorite respectively the major and trace elements and sr nd isotopic compositions indicate an em i mantle type signature and crustal contamination features combining with previous chronological data it is proposed that the age of the xiong er volcanism is between 1770 ma and 1800 ma with a peak at 1780 ma our result supports the view that the xiong er volcanic rocks formed in an extensional rift environment

implications of jurassic chert identified in the tokat complex northern turkey the tokat complex is a strongly deformed tectono sedimentary mixture of low grade metamorphic rocks with abundant recrystallized limestone and relatively rare serpentinite and radiolarian chert in blocks of variable size samples from the radiolarian chert blocks found in highly crushed zones each of which corresponds to a thrust sheet within an imbricate thrust zone have yielded a tithonian fossil assemblage they are interpreted as tectonic inclusions emplaced within the tokat complex after its main post early permian pre liassic metamorphism and were derived from the rifting and opening of a neotethyan ocean the presence of tithonian blocks within low grade metamorphic rocks of the tokat complex shows that tethys ocean was in existence in this region by latest jurassic time we also suggest that the presence of ophiolitic slices imbricated with the pontide basement tokat complex explains the swarm of north anatolian fault zone nafz splays in this region where the nafz likely followed a major pre existing crustal weakness

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

formation of the late palaeozoic early mesozoic karakaya complex and related ophiolites in nw turkey by palaeotethyan subduction accretion several pre jurassic tectonic units in nw turkey are crucial to the current debate regarding the timing and direction of subduction of palaeotethys a major ocean that separated eurasia and gondwana in late palaeozoic early mesozoic times the most critical unit is the karakaya complex a deformed low grade assemblage of oceanic origin which comprises a nw verging se dipping stack of tectonostratigraphic units here interpreted as a palaeotethyan accretionary complex the units display lithologies consistent with origins in seamount trench abyssal and rifted carbonate platform settings clastic basin sequences developed on top of the complex other relevant tectonostratigraphic units in the area include ultrabasic rocks of supra subduction zone affinity which tectonically overlie permian carbonate platform units with intervening metamorphic soles and melanges restored structural trends suggest the presence of a southward dipping palaeotethyan subduction zone bordering gondwana related units during the late permian triassic this was probably additional to more important regional northward subduction along the southern margin of eurasia from the eastern mediterranean to the himalayas

age provenance and tectonic setting of paleoproterozoic quartzite successions in the southwestern united states new field studies combined with u pb zircon geochronology constrain the ages of deposition and sedimentary provenance of paleoproterozoic quartzite successions exposed in the southwestern united states orthoquartzites were deposited in short lived basins at two times ca 1 70 and 1 65 ga during crustal assembly of southern laurentia the more voluminous ca 1 70 ga successions occur in southern colorado northern new mexico and central arizona and are interpreted here to be time correlative though not necessarily deposited in the same basins detrital zircon from quartzites and metaconglomerates exposed in southern colorado and northern new mexico is characterized by a single population with a relatively narrow range of ages 1 80 1 70 ga and minimal archean input 5 of grains analyzed peak detrital zircon ages 1 76 1 70 ga vary slightly from location to location and mimic the age of underlying basement unimodal detrital populations suggest local sources and a first cycle origin of the orthoquartzites within a short time interval 1 70 1 68 ga during unroofing of local underlying basement the maximum age of quartzite exposed at blue ridge colorado is constrained by the 1705 1698 ma coarse grained granitoid basement on which quartzite was deposited unconformably the minimum age of ortega formation quartzite new mexico is constrained by ca 1680 1670 ma metamorphic monazite overgrowths these dates agree with direct ages on the lower mazatzal group arizona and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca 1 70 ga yavapai orogeny regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca 1 66 1 60 ga mazatzal orogeny thus making them important time markers separating the yavapai and mazatzal orogenic events our model for syntectonic deposition involves extensional basin development followed by thrust closure possibly due to opening and closing of slab rollback basins related to outboard subduction the first cycle origin of orthoquartzites near the end of the arc collisions of the yavapai orogeny seems to contrast sharply with their extreme compositional maturity this can be explained in terms of protracted extreme diagenesis and or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the proterozoic similarities among quartzites exposed throughout the southwestern united states and along the laurentian margin suggest that they represent a widespread regional and perhaps global episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions a combination that might make these units a signature lithology for paleoproterozoic time

jurassic accretionary complex and ophiolite from northeast turkey no evidence for the cimmerian continental ribbon permian triassic and late cretaceous accretionary complexes ascribed to the consumption of two distinct oceans the paleo and neo tethys are exposed over extensive areas in the eastern mediterranean region however a separating continental ribbon the so called cimmeride continent between the paleo and neo tethys during early mesozoic time cannot be defined here we report a previously unknown early jurassic metamorphic oceanic accretionary complex and ophiolite from northeast turkey bounded by oceanic accretionary complexes of permian triassic and late cretaceous age to the north and the south respectively without a continental domain in between this special tectonic position and widespread coexistence of permian triassic and late cretaceous accretionary complexes alongside the izmir ankara erzincan suture imply that 1 the southern margin of laurasia in the eastern mediterranean region grew by episodic accretionary processes from late paleozoic to end mesozoic time without involvement of a cimmerian continental ribbon and 2 the paleo tethys and northern branch of the neo tethys were not distinct oceans in the eastern mediterranean region

a triassic large igneous province in the pontides northern turkey geochemical data for its tectonic setting abstract a strongly deformed and metamorphosed triassic oceanic seamount s and plateau succession extends as an east west belt for 1100 km along the pontides of northern turkey this succession known widely as the nilufer unit consists mainly of metabasic lava and tuff marble phyllite association including tectonic slices of ultramafic rock and gabbro according to the conodont findings the unit formed during the early to mid triassic and the isotopic age data indicate that it underwent high pressure greenschist facies metamorphism during the latest triassic period the metavolcanic rocks form over 80 of the sequence the nilufer unit covers an area of 120 000 km2 with the volume of mafic lava estimated as 2 105 km3 such a huge volcanic pile has erupted rapidly in a relatively short period during the early to mid triassic approx 10 ma hypotheses for the origin of the nilufer unit include a seamount intra arc and or fore arc basin oceanic plateau and early triassic rift the geochemistry of metabasites and that of relict magmatic clinopyroxenes indicate that there are two main mafic rock groups in the nilufer unit displaying tholeiitic and alkaline affinities no metabasite and clinopyroxene sample display typical orogenic basalt affinity or a subduction signature geochemical data obtained in this study are consistent with the derivation of the metabasites from the topmost extrusive layers of an oceanic plateau lip together with the volcanic rocks of seamount s

variscan amphibolite facies rocks from the kurtoglu metamorphic complex gumushane area eastern pontides turkey the kurtoglu metamorphic complex that forms part of the pre liassic basement of the sakarya zone in northern turkey consists of at least two tectonic units blueschist facies rocks of unknown metamorphic age in the southern part of the complex are tectonically overlain by variscan low pressure high temperature metamorphic rocks the latter comprise mica schists and fine grained gneisses cut by metaleucogranitic dikes as well as migmatitic biotite gneisses and subordinate amphibolite intercalations structural data indicate that metamorphism and penetrative deformation occurred after dyke intrusion peak metamorphic conditions of the mica schists fine grained gneisses and metaleucogranites are estimated to 650 c and 0 4 gpa based on phase relationships in the system nckfmash fe mg partitioning between garnet and biotite as well as garnet aluminosilicate quartz plagioclase gasp and garnet plagioclase biotite quartz gbpq barometry peak temperatures of the migmatitic biotite gneisses and amphibolite intercalations are not well constrained but might have been significantly higher 690 740 c as suggested from hornblende plagioclase thermometry 40ar 39ar incremental dating on muscovite and biotite fractions from the mica schists and fine grained gneisses yielded plateau ages of 323 ma significantly older model ages of 329 and 337 ma were obtained on muscovite fractions from two metaleucogranite samples these fractions contain both relict igneous and newly formed metamorphic muscovite

geochemistry and geochronology of meta igneous rocks from the tokat massif north central turkey implications for tethyan reconstructions located in the eastern pontides of the sakarya zone in north central turkey the tokat massif records the closure of both the paleo tethyan karakaya complex and neo tethyan ocean basins meta igneous samples collected from the region were studied to determine their sources and ages we find significant geochemical differences between metagabbros of the karakaya and neo tethyan units in terms of their trace elements neo tethyan rocks are consistent with generation in an island arc setting whereas karakaya assemblages were likely generated in an oceanic spreading center environment karakaya metagabbros also contain glaucophane consistent with subduction subsequent to formation small 2 50 m zircon and baddeleyite grains from four karakaya metagabbros were dated in thin section using an ion microprobe the results demonstrate the reliability of the method to directly constrain the tectonomagmatic history of these types of assemblages the rocks yield late permian early triassic 238u 206pb crystallization ages of 258 14 ma 1 zircon and 254 8 ma 1 baddeleyite and an early cretaceous minimum metamorphic age of 137 8 ma 1 zircon some zircon grains and baddeleyite grains with zircon overgrowths yield early to middle jurassic ages here we present a model in which metamorphism and deformation in this region occurred during northward subduction and closure of a paleo tethyan ocean basin and accretion of the karakaya units to the laurasian continental margin this was followed by the onset of closure of the neo tethys during the campanian paleocene and accretion of island arc units to the tokat region

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

tectonic evolution of the niksar and tasova erbaa pull apart basins north anatolian fault zone their significance for the motion of the anatolian block abstract the tasova erbaa and niksar basins are two adjacent pull apart basins along the north anatolian fault zone nafz within the tasova erbaa basin sedimentary lithofacies of the upper pontus formation plio pleistocene are asymmetrically distributed with laterally derived alluvial fans coarse braid plain deposits and axial braided stream deposits dominating the northern and western parts of the basin the basin has gently dipping sediments locally affected by pervasive extensional t faulting isolated compressional structures are associated with master faults deformation zone width 500 m pervasive extensional faults t and r and late stage pdz parallel compressional faults are also present an additional set of extensional faults trends perpendicular to the pdz accommodating secondary pull apart stretching within the basin the distribution of sedimentary facies and structural styles is consistent with that predicted by models for pull apart basins the adjacent niksar basin is an active pull apart basin possibly as young as 0 5 1 ma its modern drainage and sedimentary facies are symmetrically arranged adding the lengths of the tasova erbaa and niksar basin suggests 80 km total displacement along the north anatolian fault which is consistent with seymen itu ph d thesis 1975 sengor j geol soc 136 1979 269 282 and armijo et al tectonophysics 243 1999 135 154 who observed about 85 5 km total displacement along the north anatolian fault the change in course of the north anatolian fault marked by the formation of the niksar ezinepazari segment and this new geometry suggest that the anatolian block is rotating anticlockwise by having two separate poles one located near damascus and the other occurring north of the sinai peninsula this change may also mark the transfer of the anatolian triple junction from erzincan to karliova about 1 ma ago furthermore it appears that while the fault shortcuts the older basin a new generation of pull apart basins is formed due to changes of boundary conditions along the fault zone

in situ u pb dating of micro baddeleyite by secondary ion mass spectrometry abstract we introduce a technique for u pb dating of baddeleyite using secondary ion mass spectrometry sims in situ analysis of ng mass crystals that cannot be efficiently extracted by conventional mineral separation techniques average 207 pb 206 pb ages for precambrian baddeleyite crystals are within 206 pb 238 u ratios are corrected for instrumental fractionation calibrated through linear regression in a pb u relative sensitivity vs uo 2 u calibration plot calibration is performed on separated baddeleyite crystals 100 200 m in maximum dimension mounted in random crystallographic orientation 206 pb 238 u ages for baddeleyite from duluth gabbro fc4b and kovdor are accurate within 1 2 when averaging 15 30 individual spot analyses and relative sensitivities calibrated on phalaborwa baddeleyite the relative difference of 206 pb 238 u between large crystals and micro baddeleyite from fc4b is within 1 comparison between silicate glass and baddeleyite as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in pb u sensitivity in baddeleyite due to variable crystal orientations we successfully utilized oxygen flooding and a uo 2 u based calibration to significantly reduce orientation dependent bias