statistical analysis of irregular wave guide influences on regional seismic discriminants in china additional results for pn sn pn lg and pg sn abstract reducing scatter in measurements of regional phase amplitude ratios is desirable for seismic discrimination applications and also provides insight into crustal structure controls on energy partitioning of regional seismic waves our previous analysis fan and lay 1998 of the regional seismic discriminant pg lg indicated that variations in crustal structure cause path specific fluctuations of those amplitude ratios for earthquakes recorded at broadband station wmq in western china in this study we extend our multivariate regression analysis to pn sn pn lg and pg sn amplitude ratios recorded at wmq in frequency bands of 0 75 to 1 5 hz 1 5 to 3 0 hz and 3 0 to 6 0 hz for the suite of path specific parameters path length mean path elevation variance of topography along the path rms topographic slope variations mean crustal thickness and mean sediment thickness optimal three and four parameter models all achieve reductions in variance of the measurements relative to conventional distance corrections at low frequency the improvements for ratios involving pg can be more than a factor of 2 for all short period amplitude ratios mean path elevation seems to play an important role while crustal thickness and sediment thickness affect ratios involving pg topographic variance and surface slope variations have more influence on ratios involving pn strong crustal variations associated with the structure of the tibetan plateau are responsible for much of the amplitude variations

the berit transect of the tauride thrust belt s turkey late cretaceous early cenozoic accretionary collisional processes related to closure of the southern neotethys abstract we report on an integrated study of a critical segment of the tauride thrust belt in se turkey berit area units related to two sutures are exposed in the northerly and southerly parts of the area studied in the north the upper cretaceous binboga melange reflects the closure of a northerly mesozoic oceanic basin in the south contrasting units document the closure of the southern neotethys in the south the berit or goksun ophiolite formed as an incipient oceanic arc within the southern neotethys during the late cretaceous c 90 ma intercalated amphibolite granulite facies rocks may record a dismembered metamorphic sole an underlying meta sedimentary meta volcanic unit is interpreted as accreted continental rift and oceanic seamount lithologies the berit ophiolite was accreted to the tauride active continental margin to the north around 85 ma and was then intruded by calc alkaline granites c 70 85 ma northerly margin units were exhumed and covered by shelf carbonate sediments during latest cretaceous early cenozoic time northward subduction during the mid cenozoic c 45 ma resulted in back arc extension along the tauride active margin and subduction influenced volcanism possibly controlled by slab roll back during oligocene early miocene time the southern neotethys closed and the tauride active margin was telescoped to create the present south vergent thrust stack this was accompanied by mass wasting of the advancing allochthon to form sub aqueous frontal olistostromes the arabian platform was over ridden by mid miocene time followed by left lateral strike slip along the east anatolian fault zone as anatolia began to escape westwards towards the aegean sea

tectonic development of the eastern mediterranean region the eastern mediterranean region is a classic area for the study of tectonic processes and settings related to the development of the tethyan orogenic belt the present set of research and synthesis papers by earth scientist from countries in this region and others provides an up to date interdisciplinary overview of the tectonic development of the eastern mediterrenean region from precambrian to recent key topics include continental rifting ophiolite genesis and emplacement continental collision extensional tectonics crustal exhumation and intraplate deformation e g active faulting alternative tectonic reconstructions of the tethyan orogen are presented and discussed with important implications for other regions of the world the book will be an essential source of information and interpretation for academic researchers geologists and geophysicists advanced undergraduates and also for industry professionals including those concerned with hydrocarbons minerals and geological hazards e g earthquakes

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

tectonic and petrogenetic implications of major and rare earth element chemistry of troodos glasses cyprus chilled pillow margins dike margins and interpillow hyaloclastites from the extrusive sequences of the troodos ophiolite cyprus reveal two compositional groups of glasses 1 andesites to dacitic andesites containing plagioclase ca rich pyroxene and ca poor pyroxene as phenocrysts occur in a stratigraphically low position and 2 basaltic andesites containing olivine and ca rich pyroxene phenocrysts occur in an upper position in the lava sequence the glasses contain between 52 and 62 wt sio2 and have mg numbers between 65 and 27 the troodos glasses are very similar to basaltic andesite or boninitic glasses from the mariana trench and together these two groups define a trend intermediate between typical calcalkaline and tholeiite evolutions the troodos glasses are inferred by difference to contain 3 4 5 wt h2o which is taken to be of primary origin and to reflect the ocean depth of extrusion and quenching based on normative projections in the basalt phase diagram there are indications that elevated water pressures during formation of the phenocryst assemblages may have shifted the isobaric pseudo quaternary peritectic towards silica quantitative crystal fractionation models fail to explain the observed chemical variation it is suggested that the chemical variation may result from high pressure melts equilibrated to lower pressure 2 and 3 phase cotectic relations some mariana and the troodos glasses have similar ree patterns with relatively low abundances depletion in lree and flattening in the hree region the close similarities between the troodos and the mariana glasses point to an identical tectonic and petrogenetic control on their origin

precise 40ar 39ar ages from the metamorphic sole of the mersin ophiolite southern turkey abstract the mersin ophiolite is located on the southern flank of the e w trending central tauride belt in turkey it is one of the late cretaceous neotethyan oceanic lithospheric remnants the mersin ophiolite formed in a suprasubduction zone tectonic setting in southern turkey at the beginning of the late cretaceous the mersin ophiolite is one of the best examples in turkey in order to study reconstruction of ophiolite emplacement along the alpine himalayan orogenic belt 40ar 39ar incremental heating measurements were performed on seven obduction related subophiolitic metamorphic rocks hornblende separates yielded isochron ages ranging from 96 0 0 7 ma to 91 6 0 3 ma all errors 1 five of the seven hornblende age determinations are indistinguishable at the 95 confidence level and have a weighted mean age of 92 6 0 2 2 ma we interpret these ages as the date of cooling below 500 c intraoceanic thrusting occurred 4 ma soon after formation of oceanic crust the sole was crosscut by microgabbro diabase dikes less than 3 m y later the final obduction onto the tauride platform occurred during the late cretaceous early paleocene our new high precision ages constrain intraoceanic thrusting for a single ophiolite mersin in the tauride belt

age origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the piedmont ligurian ocean basin abstract u pb zircon dating sr nd isotope tracing and major trace re element analyses were performed to constrain the age origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the ligurian alps and the northern apennines in addition a host fe diorite was investigated samples from the ligurian alps were collected from the voltri group and the sestri voltaggio zone whereas the plagiogranites from the northern apennines were taken in the bracco unit all these units have been affected by alpine metamorphism reaching eclogite facies in the voltri group blueschist degree in the sestri voltaggio samples and prehnite pumpellyite facies in the bracco unit which has additionally been affected by rodingitization u pb zircon ages of 150 1 153 1 and 156 ma were obtained respectively for two plagiogranites and the host fe diorite in the ligurian alps and an age of 153 1 ma was determined for the plagiogranite in northern apennines inherited components in zircon and initial pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1 7 2 1 ga old continental crust material ree patterns in both the plagiogranites and the host diorite are characterized by high ree abundance and moderate lree enrichment nd isotopic compositions lie in the range of n morb sources yielding initial epsilon nd values between 8 8 and 9 7 whereas sr is isotopically heterogeneous the geochemical pattern of the plagiogranites and the host fe diorite requires melting of a morb type mantle source that experienced lree enrichment shortly before melting the most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region the basaltic lree enriched parent magmas generated from this enriched domain have probably undergone up to about 72 of low pressure fractional crystallization prior to their emplacement into the gabbro peridotite complex the 156 150 ma magmatism occurred in close relation to normal faulting sedimentation of breccias and detachment of the mantle complex from its overlying continental crust followed by exposure on the ocean floor this tectono magmatic event in the ligurian alps and the northern apennines reflects rifting of the adriatic iberian continental plate segment preceding wider opening of the piedmont ligurian ocean basin and pillow basalt deposition

k ar dating of some infra ophiolitic metamorphic soles from the eastern mediterranean new evidence for oceanic thrustings before obduction abstract k ar dating on separated minerals from the infra peridotitic metamorphic soles outcropping beneath various eastern mediterranean ophiolite complexes pindos nappe in greece lycian antalya beysehir hoyran mersin and pozanti karsanti nappes in the taurides belt turkey baer bassit nappe in syria shows that the main metamorphic recrystallization of those rocks occurred 25 30 m y prior to the tectonic emplacement of the ophiolite complexes onto a continental platform these data support the hypothesis of an early slicing of the oceanic crust before its obduction advocated recently by several authors

origin and emplacement of the late cretaceous baer bassit ophiolite and its metamorphic sole in nw syria abstract the baer bassit ophiolite of inferred late cretaceous age was emplaced from the south tethys ocean onto the leading edge of the arabian continental margin in latest cretaceous maastrichtian time dismembered sequences in different thrust sheets can be correlated to produce a complete ophiolite sequence with a metamorphic sole at the base overlain in turn by upper mantle tectonite rare cumulates massive and layered gabbros localized high level plagiogranites sheeted dykes basic extrusives and minor fe mn sediments umbers the restored ophiolite sequence is similar to that of the more intact troodos and hatay ophiolites but dissimilar to oman the baer bassit extrusives are magnesian and strongly depleted comparable to primitive island arc tholeiites and some boninitic lavas which favours a subduction related origin a well developed metamorphic sole is divisible into high grade amphibolite facies assemblages in the north and lower grade greenschist facies assemblages in the centre of the region but no complete inverted metamorphic gradient is preserved in any one local area the protoliths of both the high grade amphibolites and lower grade rocks greenschists are interpreted as alkali basalts and pelagic sediments including chert similar to the volcanic rocks in an underlying unmetamorphosed melange the metamorphic fabrics progressively evolved from ductile to brittle during tectonic transport towards the southeast most of the metamorphic fabrics evolved during intense shearing but some of the alkaline metabasites apparently were metamorphosed under relatively static strain conditions the apparent absence of preserved inverted metamorphic gradients in baer bassit may reflect a complex deformation history during emplacement alternatively differing p t conditions may be recorded at different depths at the base of the over riding mantle wedge during emplacement the front of the ophiolite was tectonically imbricated and overthrust by the main ultramafic slab bassit massif the thickest massif baer is underlain by a high grade metamorphic sole and was internally shortened but without thrust duplication of the entire ophiolite sequence following covering by late maastrichtian palaeogene marine calcareous sediments the area was subjected to mid tertiary regional folding this was followed by neogene dominantly left lateral strike slip deformation along the african eurasian plate boundary extending from south of cyprus to the dead sea transform fault as a result the originally emplaced thrust sheets were dissected into three main composite units baer bassit and the southeastern units separated by strongly faulted and sheared ophiolitic blocks and unmetamorphosed volcanic sedimentary melange

uranium lead isotopic ages of the samail ophiolite oman with applications to tethyan ocean ridge tectonics plagiogranites are a minor but widespread component of the samail ophiolite plutonic member they crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the tethyan spreading ocean ridge and their ages are thought to mark the time of ocean crust formation isotopic u pb ages of zircons from 13 plagiogranites collected along a 270 km segment of the samail ophiolite subparallel to the regional trend of the sheeted dike complex the former spreading ridge axis direction define a narrow time interval of 93 5 97 9 m y with a pronounced clustering about 95 m y the zircon ages of the plagiogranites agree remarkably well with the early cenomanian to early turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them tippit et al 1981 the agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite u pb ages closely date the time span of ocean crust formation no step changes in age patterns are observed along the ridge axis sheeted dike direction suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse one possible exception occurs at the southeastern end of the sampled interval ibra area where a 3 m y discontinuity might be caused by an unmapped fault assuming that the regional trend of the sheeted dikes n10 25 w marks the direction of the former spreading ridge axis the present array of sample localities spans a distance of 130 to 195 km normal to that axis i e in the spreading direction the data as a whole do not define a clear cut age trend normal to the spreading axis but by eliminating samples that may be aberrant due to faulting the data array suggests a pattern of increasing ages from east to west this would indicate that the samail ophiolite is derived from the western southwestern side of the tethyan spreading system a conclusion reached independently from geological evidence also the gentle age gradient in the spreading direction i e between 130 and 195 km of ocean crust were formed within an age span of no more than 2 m y suggests a very fast spreading rate this conclusion also is supported by independent geologic evidence

kar and 40ar39ar study of metamorphic rocks associated with the oman ophiolite tectonic implications abstract k ar analyses on extracted minerals are reported for a variety of metamorphic rocks associated with the sumail ophiolite amphibolites lying at the sole of the ophiolite yield ages of 95 100 ma which are viewed as reflecting times of crystallization high pressure metamorphics of the saih hatat reveal complex results white micas range in age from 80 to 131 ma whereas blue amphiboles indicate ages that are systematically lower than those of coexisting white micas investigation of a few white micas by the 40 ar 39 ar step heating method yields rather intricate age spectra featuring low apparent ages in the first and the last stages of gas release and high apparent ages in between two explanations can be equally envisaged for these convex upward age spectra the first is the mixing of two generations of micas corresponding to two main metamorphisms the first one m1 is a low to medium temperature high pressure event which conceivably occurred between 130 and 114 m y ago the second m2 overprints m1 and has produced rocks typical of the greenschist facies it took place 80 m y ago and also affected the sole of the ophiolites the second is the presence of excess argon in mica mixtures with complex degassing properties thus the two metamorphic phases identified by microscopic inspection are not significantly different in age they occurred in the 70 80 ma interval moreover k ar dates on amphibole from gabbroic dikes intersecting the peridotites suggest that they are genetically linked to the mafic part of the ophiolites assuming that metamorphism is a tracer of tectonic events we view the infraophiolitic amphibolites as the result of an intraoceanic thrusting which took place near a spreading center nevertheless the uncertainty as to the age of the blueschist metamorphism precludes the possibility of indicating a timetable based on metamorphic ages for the motion shift of africa relative to eurasia during the late cretaceous a tentative model of the obduction of the sumail ophiolite is proposed assuming an age of about 130 ma for m1 we stress differences with respect to earlier reconstructions which advocated an 80 m y old blueschist metamorphism

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

the origin of oceanic plagiogranites from the karmoy ophiolite western norway both field relationships and geochemical characteristics indicate two suites of plagiogranitic and related rocks coexisting in the higher parts of the karmoy ophiolite of western norway the plutonic zone of this ophiolite can be subdivided into three complexes the east karmoy igneous complex the visnes high level complex and the veavagen igneous complex and plagiogranitic rocks are well developed in the first two of these within the east karmoy igneous complex plagiogranites are associated with high temperature pre basic dyke shear zones rare earth element modelling indicates that these plagiogranites were derived by anatexis of amphibolite hydrated diabase assuming a starting material consisting of 40 hornblende and 60 plagioclase and that batch melting occurred within the stability field of hornblende in comparison plagiogranite occurs in a number of bodies in the upper part of the visnes high level complex and forms a sandwich horizon together with biotite diorites and epidosites between a roof assemblage of dykes microgabbros and magnetite gabbros and a floor assemblage of layered and non layered gabbros the r e e modelling of the petrogenesis of this series of plagiogranites indicates that they were derived by filter pressing of a differentiated interstitial liquid to the vari textured gabbros although the distribution of highly hygromagmatophile elements such as k rb ba etc cannot be explained satisfactorily by this model alone depletion in these elements appears to be an autometasomatic effect

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

evidence for upper cretaceous transform fault metamorphism in west cyprus abstract metamorphic rocks of low pressure medium temperature facies occur in west cyprus as blocks and slivers with mafic and ultramafic screens in high angle serpentinite filled fault zones a satisfactory explanation for the origin of the metamorphic rocks has previously remained a subject of controversy the evidence presented here based on a study of their bulk chemistry mineralogy and 40 ar 39 ar geochronology indicates they were produced by greenschist to amphibolite facies dynamothermal metamorphism of alkalic and tholeiitic mafic rocks and associated sediments at between 83 and 90 m y their field relations show similarities with present day oceanic fracture zones suggesting that metamorphism occurred within strike slip faults some of which were probably extensions of the arakapas transform we propose that hot crust generated at an oceanic spreading centre provided the heat for metamorphism when juxtaposed against older cooler rocks during ridge ridge transform movements in addition shear heating may have been facilitated by the strike slip faulting and contributed to the total heat available these interpretations are compatible with many aspects of the broader regional geology of cyprus provide new constraints on the early evolution of the troodos complex and form the basis of a model for transform fault metamorphism

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

metamorphic sole rocks and their mafic dykes in the eastern tauride belt ophiolites southern turkey implications for oib type magma generation following slab break off the metamorphic sole rocks observed between the pozanti karsanti ophiolite and the melange unit are located on the eastern part of the tauride carbonate platform they consist of ortho amphibolites at the top and metasedimentary lithologies at the base amphibolites from the metamorphic sole rocks are represented by oib morb and iat based on their major trace and ree compositions the isolated dolerite dykes intrude both the metamorphic sole rocks and the ophiolitic unit at different structural levels the dolerite dykes cutting the metamorphic sole rocks are enriched in lile and depleted in hfse enrichment in lile such as th relative to hfse is indicative of the presence of a subduction component flat lying ree patterns of the dolerite dykes also confirm an iat source pyroxenite and albitite dykes also cut the metamorphic sole rocks ree patterns of pyroxenite dykes show prominent lree enrichment similar to that observed in within plate alkaline basalts the alkaline isolated pyroxenite dykes were probably the result of late stage magmatism fed by melts that originated from an oib source shortly before the emplacement of the pozanti karsanti ophiolite onto the tauride carbonate platform a hydrothermal alteration stage is characterized by albitite formation in the joints of the metamorphic sole rocks and by secondary mineralization along the contact zones of dolerite dykes mineral parageneses in the metamorphic sole rocks exhibit amphibolite and greenschist facies assemblages geothermobarometric studies based on a newly recognized mineral assemblage e g kyanite and chemical compositions of minerals in the metamorphic sole rocks indicate that the metamorphic temperature during the metamorphism was 570 580 c and the pressure was around 5 6 kbar

u pb and sm nd geochronology of the kizildag hatay turkey ophiolite implications for the timing and duration of suprasubduction zone type oceanic crust formation in the southern neotethys the kizildag hatay ophiolite in turkey represents remnants of the southern neotethyan ocean and is characterized by a complete ocean lithospheric section it formed in a fore arc setting above a n dipping intraoceanic subduction zone and represents the undeformed more northerly part of the same thrust sheet that also forms the baer bassit ophiolite to the south the ophiolite was emplaced southwards from the southerly neotethyan ocean in maastrichtian time u pb and sm nd dates are used to constrain the crystallization age and duration of magmatic activity of the kizildag ophiolite u pb dating yielded ages of 91 7 1 9 ma for a plagiogranite and 91 6 3 8 ma for a cumulate gabbro the cumulate gabbro also yielded a sm nd isochron age of 95 3 6 9 ma the measured ages suggest that the oceanic crust of the kizildag ophiolite formed in a maximum time period of 6 ma and that the plagiogranite may have formed later than the gabbroic section the u pb zircon ages from the kizildag ophiolite and the cooling age of a metamorphic sole beneath the baer bassit ophiolite are indistinguishable within the analytical uncertainties this indicates the presence of young and hot oceanic lithosphere at the time of intraoceanic subduction thrusting in the southern neotethys the u pb zircon ages from the kizildag the troodos and the semail ophiolites overlap within analytical uncertainties suggesting that these ophiolites are contemporaneous and genetically and tectonically related within the same late cretaceous southern neotethyan ocean

rapid emplacement of young oceanic lithosphere argon geochronology of the oman ophiolite 40 ar 39 ar dates of emplacement related metamorphic rocks beneath the samail ophiolite in oman show that cooling to

tectonic history of the hatay ophiolites south turkey and their relation with the dead sea rift abstract the kizildag ophiolite massif lies in the hatay region of s turkey some structural relationships in the area are examined and two geological sections through the ophiolite are presented a sequence of structural events dealing with the emplacement and post emplacement history is established the significance of the events is discussed and it is suggested that the post emplacement structural history was dominated by movements along the dead sea rift

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting